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CHAPTER 6

Stray Current Interference

CP 1 – Cathodic Protection Tester Course Manual

©

NACE International, 2000

02/01/05

Definitions

Interference

is any electrical disturbance on a metallic

structure caused by a

stray current

. Stray current

may be defined as current flowing on a structure

that is not part of the intended electrical circuit. For corrosion to occur as the
result of stray currents there must be an exchange of current between a
metallic structure and an electrolytic environment.

Effects

Direct stray currents, as opposed to alternating stray currents, have the most
pronounced effect on corrosion. Direct current (DC) flows continuously in
one direction. Alternating current (AC60H

z

commercial power) reverses

direction 120 times per second. Although there are exceptions, alternating
currents do not cause significant corrosion of common structural materials.
AC current can be a significant safety hazard.

In accordance with Faraday's law, the weight of metal corroded is
proportional to the amount of current being discharged from it into the
electrolyte. Stray current corrosion is of serious concern because a large
amount of current is usually involved. Whereas natural corrosion may
generate milliamperes worth of current, stray current can involve hundreds of
amperes. A current of 100 amperes (entirely reasonable with some rail transit
systems) would destroy 910 kg (2,000 lbs.) of steel in one year.
Consequently, when stray current is found, it is necessary to find the source
and implement a solution.

Sources

Stray currents can be produced by any system conducting an electric
current that has two or more points of contact with an electrolyte. These
points of contact must have a voltage between them.

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Содержание CP 1

Страница 1: ...CP 1 Cathodic Protection Tester Course Manual February 2005 NACE International 2000 ...

Страница 2: ...rry Garleiser Exxon Co USA Houston Texas Kevin Garrity CC Technologies Dublin Ohio Robert Gummow CorrEng Consulting Service Inc Downsview Ontario Brad J Lewis Kinder Morgan Energy Partners L P Tucson Arizona Thomas H Lewis LORESCO Inc Hattiesburg MS Ed Ondak EJ Ondak Associates Inc Littleton Colorado Larry Rankin Corrpro Companies Inc Houston Texas John Schmidt CC Technologies Houston Texas David ...

Страница 3: ...ization is implied concerning the use of patented or copyrighted material The information is advisory only and the use of the materials and methods is solely at the risk of the user Printed in the United States All rights reserved Reproduction of contents in whole or part or transfer into electronic or photographic storage without permission of copyright owner is expressly forbidden ...

Страница 4: ...asic Electricity Introduction 1 1 Electrical Terms 1 1 Electrons 1 1 Voltage 1 1 Current 1 2 Resistance and Resistivity 1 3 Electrical Schematic Diagram Symbols 1 6 Electric Circuit 1 7 Electrical Laws 1 7 Ohm s Law 1 7 Power 1 9 Kirchhoff s Laws 1 10 Series Circuit 1 11 Parallel Circuit 1 13 Series Parallel Circuit 1 15 Direct Current DC 1 18 Alternating Current AC 1 18 Meter Operation 1 21 Gener...

Страница 5: ...Circuits 2 8 Corrosion Cell 2 9 Anode Reactions 2 9 Cathode Reactions 2 10 Use of Voltmeters 2 12 Reference Electrodes Half Cells 2 15 Driving Force for Corrosion 2 18 Corrosion Rate 2 19 Faraday s Law 2 19 Polarization 2 20 Anode Cathode Ratio 2 21 Influence of the Environment 2 21 Causes of Corrosion 2 23 General 2 23 Naturally Occurring Corrosion 2 23 Experiment 2 1 Metal Electrode Potentials i...

Страница 6: ... Systems 3 11 Anodes 3 11 Specifications of Galvanic Anode Systems 3 13 Impressed Current Systems 3 14 Power Sources 3 15 Limitations of Impressed Current Systems 3 16 Component Parts of Impressed Current Systems 3 16 Backfill 3 18 Power Supply 3 18 Factors Influencing Operation of Cathodic Protection 3 22 Moisture Content of Soil 3 22 Coating 3 22 Soil Texture 3 22 Temperature 3 23 Oxygen Content...

Страница 7: ... 5 Field Measurements Other Portable Reference Electrodes 5 1 Typical Applications 5 3 Measuring Current 5 8 Use of an Ammeter 5 8 Shunts 5 10 Typical Applications 5 15 Measuring Resistance 5 22 Typical Measurements 5 22 Using Ohm s Law 5 22 Using an Ohmmeter 5 23 Electrical Continuity 5 24 Electrical Isolation 5 24 Purpose and Usage 5 24 Isolation Insulating Joints 5 25 Accidental Contacts 5 25 T...

Страница 8: ...ate Stray Current 6 2 Identification of Stray Current 6 3 Dynamic Stray Current 6 3 Steady State Stray Current 6 4 Stray Current Corrosion Control 6 6 Mitigation Bonds 6 6 Mitigation with Cathodic Protection 6 8 Experiment 6 1 Demonstration of Cathodic Interference 6 9 Section 7 Chapter 7 Monitoring Cathodic Protection Effectiveness and Recordkeeping Introduction 7 1 Reasons for Monitoring 7 1 Mon...

Страница 9: ... Galvanic Sacrificial Anodes 8 14 General 8 14 Prepackaged Anodes 8 15 Non Packaged Anodes 8 17 Ribbon or Strip Anodes 8 17 Bracelet Anodes 8 17 Offshore Anodes 8 18 Impressed Current Groundbeds 8 19 General 8 19 Handling and Inspection of Anodes and Cable 8 20 Surface Groundbed Configurations 8 22 Deep Anode Groundbed Configuration 8 26 Negative Circuit 8 28 Installation of Rectifiers or Other Po...

Страница 10: ...sion Control of Underground Storage Tank Systems by Cathodic Protection RP0176 Corrosion Control of Steel Fixed Offshore Platforms Associated with Petroleum Production RP0388 Impressed Current Cathodic Protection of Internal Submerged Surfaces of Steel Water Storage Tanks RP0177 Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems RP0575 Inte...

Страница 11: ...es TM0497 Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Piping Systems TM0101 Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Storage Tanks Section 11 Worksheets CP Tester Practical Exam Reference Sheet ...

Страница 12: ...mailed the report will show a mail date in the status column Just go to http nace org NACE Content Education Courses GradeStatus asp or visit the NACE Website at www nace org and click on Education Certification then click on Grade Status All you need to find your course information is the following Course Name Course Location Course Date If you have not received your grade letter within two weeks...

Страница 13: ...t to participate please insert your student ID AND a 4 digit password on your examination ParScore sheet see example Your student ID is listed on your registration confirmation notice Create your own 4 digit password the password you choose should be written in the phone number box If you do not provide both your student ID and your Password then you will not be able to access your grades on the I...

Страница 14: ...question Just ask Got the answer Share it The discussions sometimes will be one time questions and sometimes there will be debates The topics will range from questions and answers about cathodic protection to materials and chemical inhibitors and tons more What do you need to join An E mail address That s all Then 1 Send a blank email message to Join nace nacecorrosionnetwork com 2 To Unsubscribe ...

Страница 15: ...pter 5 Field Measurements DAY THREE Chapter 5 Field Measurements continued Chapter 6 Stray Current Interference Chapter 7 Monitoring Cathodic Protection Effectiveness and Recordkeeping Introduction to Indoor Field Measurement Test Stations Indoor Field Measurement Test Station Practice DAY FOUR Outdoor Field Program weather permitting DAY FIVE Chapter 8 Installing CP Components Chapter 9 Troublesh...

Страница 16: ...cus on the control of metallic corrosion by applying cathodic protection This course was developed for cathodic protection field technicians although this knowledge is also needed by corrosion engineering personnel Corrosion prevention can be better understood after acquiring a good understanding of corrosion itself Corrosion is defined as the deterioration of a substance or its properties as a re...

Страница 17: ...gin on Sunday at 1 00 pm and concludes on Friday afternoon Reference Books The primary reference for this course is Peabody s Control of Pipeline Corrosion by A W Peabody and will be furnished to each student EXPERIMENTS Throughout the week there will be experiments to help illustrate and reinforce principles discussed in the lecture sections CAUTION Students should realize that these experiments ...

Страница 18: ...m the concepts discussed in this training manual Non communicating battery operated silent non printing calculators including calculators with alphanumeric keypads are permitted for use during the examination Calculating and computing devices having a QWERTY keypad arrangement similar to a typewriter or keyboard are not permitted Such devices include but are not limited to palmtop laptop handheld ...

Страница 19: ... Program Step Successfully Completed Category Name CP 1 Cathodic Protection Tester CP 2 Cathodic Protection Technician CP 3 Cathodic Protection Technologist CP 4 Cathodic Protection Specialist 4 I understand that the registration number and or category title may be used only by Certified Cathodic Protection persons persons who have successfully completed CP 1 CP 2 CP 3 or CP 4 I understand that th...

Страница 20: ...x 409 111 1234 Address 987 Gage Avenue City Millspec State Province TX Zip Postal Code 77987 Country USA Please summarize below the information on each copy of Form 2 Individual Job Documentation List your experience beginning with the most recent followed by less recent experience From Month Year To Month Year Number of Months in this job Job Title Company Name 1 92 1 95 36 CP pipeline readings Z...

Страница 21: ...ion Name Phone Company Fax Address City State Province Zip Postal Code Country Please summarize below the information on each copy of Form 2 Individual Job Documentation List your experience beginning with the most recent followed by less recent experience From Month Year To Month Year Number of months in this job Job Title Company Name Applicant Affidavit I understand that if I knowingly provide ...

Страница 22: ...PERIENCE Page ___ of ___ Describe in detail what are were your cathodic protection related duties in this job Do not write on the back of this form You may attach additional single sided sheets THIS SECTION MUST BE COMPLETED Your application will be returned if this space is left blank _______________________________________________________________________________________ _________________________...

Страница 23: ...tion work to public safety and welfare and to protection of the environment 2 Agree to apply myself with diligence and responsibility to the cathodic protection work that lies within my area of competence 3 Agree to pursue my work with fairness honesty integrity and courtesy ever mindful of the best interests of the public my employer and of fellow workers 4 Agree to not represent myself to be pro...

Страница 24: ...re important concepts are discussed in this chapter Electrical Terms Electrons Electrons are particles that carry a negative charge They also help hold matter together a bit like the mortar in a brick wall Voltage Voltage joule coulomb or potential is an electromotive force or a difference in potential expressed in Volts Voltage is the energy that puts charges in motion This force is measured in v...

Страница 25: ...urrent Current is the flow of charges along a conducting path and is measured in amperes Current is frequently abbreviated as amps milliamps or microamps In corrosion work we use all three units The following shows their relationship Ampere the common unit of current a flow rate of charge of 1 coulomb per second One coulomb is the unit of charge carried by 6 24 x 1018 electron charges 1 000 ampere...

Страница 26: ...ek letter omega Resistance is important in such matters as cathodic protection groundbeds resistance of a structure to the electrolyte and the linear resistance of a long structure such as a pipe or cable Resistivity is the resistance of a conductor of unit length and unit cross sectional area The symbol used for resistivity is ρ Greek letter rho Resistivity is constant for a given material and is...

Страница 27: ...quation Resistance to current flow is lowest for Low resistivity high conductivity media Short length for current flow Large area of current flow Resistance will be greatest for High resistivity low conductivity media Long path length for current flow Small cross sectional area of current flow Crossectional Area A cm2 h x w where h height cm w width cm A cm2 πr2 where r radius cm ...

Страница 28: ...0 1 x 10 2 1 x 1 x 1 01 The common unit of resistivity measurement for an electrolyte is ohm centimeter Electrolytes dealt with in corrosion and cathodic protection includes soils and liquids water Since electrolytes do not usually have fixed dimensions the earth or a body of water for example resistivity is usually defined as the resistance between two parallel faces of a cube one cm on each side...

Страница 29: ...Basic Electricity 1 6 CP 1 Cathodic Protection Tester Course Manual NACE International 2000 02 01 05 Electrical Schematic Diagram Symbols Resistor Ground Battery Connection Rectifier Switch Diode T R ...

Страница 30: ...re 1 2 Basic DC Electrical Circuit Electrical Laws Electrical laws govern the relationships in electric circuits Ohm s Law Ohm s Law is a relationship between the ratio of voltage and current to the resistance of a circuit The law states that a voltage of 1 volt will create a current of 1 ampere in a circuit having a resistance of 1 Ohm Ohm s Law can be expressed as follows where E or V Voltage el...

Страница 31: ...resistance An easy way to use the Ohm s Law triangle is to place your thumb over the quantity you are looking for If you want to find resistance as in the above example place your thumb over the R and you can see that R E I If you want voltage placing the thumb over the E shows you that E I x R Note that the units used must be consistent amperes volts and Ohms Amperes and millivolts or volts and m...

Страница 32: ... is in volts not millivolts Ohm s Law plays an important role in your work and you need to be thoroughly familiar with it Turn now to Group Exercise 1 1 at the end of this chapter and work through the calculations in the exercise Power Power is the energy used by an electrical device It is necessary to know the power required by a cathodic protection rectifier for example in order to size the alte...

Страница 33: ...his circuit is a 24 volt battery The voltage I x R or IR drop across each resistor is 8 volts In this example the three resistors are the same size If the resistors were of different sizes the sum of the voltage drops across them would still equal 24 volts Voltage drops in an electrical circuit are like pressure drops along a length of pipeline If the various pressure drops are added up they will ...

Страница 34: ...me everywhere The voltage drops may all be different depending on the value of each resistance but the sum of the voltage drops ET must add up to the voltage of the source an example of Kirchhoff s Voltage Law The total resistance RT of a series circuit equals the sum of the individual resistances In cathodic protection work we are concerned with series circuits for example in the length of cables...

Страница 35: ...it RT Total Resistance in the Circuit IT Total Current in the Circuit E1 E2 R1 R2 R3 I E2 E1 R3 R2 R1 Figure 1 6 Series Circuit Given E1 5 V E2 5 V R1 5 Ω R2 3 Ω R3 2 Ω Ω Ω Ω Ω 10 2 3 5 R T A 1 10 V 10 R E IT Ω I1 1 A ITR1 1 A x 5 Ω 5 V I2 1 A ITR2 1 A x 3 Ω 3 V I3 1 A ITR3 1 A x 2 Ω 2 V Total IR Drop 10 V OR IRT 1 A x 10 Ω 10 V ET 10 V Note that Kirchhoff s Voltage Law is fulfilled ...

Страница 36: ...t to flow through the circuit you have a parallel circuit Galvanic anodes attached to a structure represent a parallel circuit The same is true for impressed current anodes the more anodes you add the lower the resistance to the electrolyte and the more current you get For a parallel circuit Voltage drop across each branch is the same and is equal to source voltage Total current flowing into and o...

Страница 37: ...r the following circuit E I I1 I2 I3 I R1 R2 R3 Figure 1 7 Parallel Circuit IT I1 I2 I3 ET I1R1 I2R2 I3R3 3 2 1 T R 1 R 1 R 1 1 R 1 T R E I1 2 T 2 R E I 3 T 3 R E I Given E 20 V R1 5 Ω R2 4 Ω R3 2 Ω IR1 ET 20 V I1 ET R1 20 V 5 Ω 4 A IR2 ET 20 V I2 ET R2 20 V 4 Ω 5 A IR3 ET 20 V I3 ET R3 20 V 2 Ω 10 A IT 4 A 5 A 10 A 19 A ...

Страница 38: ...al to one of the resistances divided by the number of resistors N R RT where RT Total resistance R Resistance of each resistor N Number of resistors Turn now to Group Exercise 1 3 for further practice with parallel circuits Series Parallel Circuit A series parallel circuit Figure 1 8 combines the elements of both a series circuit and a parallel circuit Very complex circuits can be reduced to a cir...

Страница 39: ...8 Series and Parallel Circuits Combined Given E 20 V R1 5 Ω R2 4 Ω R3 2 Ω R4 0 95 Ω First reduce the parallel part of the circuit to a single resistance using the same formula as shown for Figure 1 7 Ω Ω Ω Ω 05 1 95 0 1 2 1 4 1 5 1 1 RT We now have an equivalent series circuit of two resistors 1 05 Ω and 0 95 Ω for a total resistance of 2 00 Ω ...

Страница 40: ...tage across the parallel part of the circuit This is equal to the total voltage less the voltage drop across R4 or 20 V 10 A x 0 95 Ω 10 5 V Calculating the currents through R1 R2 and R3 is simply a matter of applying Ohm s Law I1 10 5 V 5 Ω 2 10 A I2 10 5 V 4 Ω 2 63 A I3 10 5 V 2 Ω 5 25 A IT 9 98 A Note that Kirchhoff s Current Law is fulfilled also The currents entering Points A B and C equal th...

Страница 41: ...nt 0 Figure 1 10 Pure Direct Current Alternating Current AC Alternating current such as that which we have in our homes and buildings reverses direction on a cyclic basis most commonly 100 or 120 times a second A full cycle is completed in a 50th or 60th of a second The word hertz hz is used to represent a cycle so AC is known as 50 hz or 60 hz current Figure 1 11 shows a typical alternating curre...

Страница 42: ...urrent is important in understanding cathodic protection rectifiers Some of the more important factors follow Transformers Transformers may be used to increase or decrease voltage or to isolate an incoming voltage source from the outgoing voltage The transformer has a laminated iron core as illustrated in Figure 1 13 that shows a transformer as part of a cathodic protection rectifier There are two...

Страница 43: ...the secondary voltage to the primary voltage is directly proportional to the ratio of the secondary turns to the primary turns This ratio can be expressed as follows This exact relationship holds true under no load conditions Losses in the core and laminations reduce the output voltage when under load In cathodic protection rectifiers taps are located in the secondary wiring so that several voltag...

Страница 44: ...r digital Earlier instruments were constructed using an electromechanical movement with an analog display and are referred to as analog meters These instruments have a needle that rotates across the meter face and indicates the reading on a scale Today most instruments are electronic with digital displays and are referred to as digital meters Hybrid meters that are electronic with analog displays ...

Страница 45: ...rent is converted into a mechanical force as indicated in the following steps 1 Current from the external circuit flows through the coil and creates a magnetic field 2 The coil rotates due to the reaction of its magnetic field with the magnetic field of the permanent magnet 3 As the coil rotates it works against a mechanical spring causing tension in the spring 4 The pointer comes to rest along th...

Страница 46: ...troyed easily if large currents flow through it therefore resistors are placed either in series or parallel to the meter movement to control the maximum current flow through the meter coil Whether an analog meter is used to measure voltage current or resistance each of these measurements depend on the measurement of current flow The meter measures current directly and by knowing one of the other v...

Страница 47: ...ed as an ammeter resistors are placed parallel to the moving coil to shunt a significant portion of the total current around the moving coil The position of the range switch determines the value of the shunt resistance The higher the current to be measured the smaller the shunt resistor must be to allow greater portions of the current to bypass the coil Ohmmeters If the current is measured and the...

Страница 48: ...to DC volts prior to the analog to digital conversion The displayed value is not continuous but a sample of the input value measurements However the measurement is taken several times per second The measured value is displayed as discrete digits the digits do not require operator interpretation as the analog display does If a voltage is changing the numbers are also changing and it may be difficul...

Страница 49: ... P V x I _______________ Given A corrosion circuit produces 2 A of current at a driving voltage of 1 6 V What is the resistance of this circuit __________________ Given A structure requires 100 mA for adequate cathodic protection and the total resistance is 1 5 Ω What is the required voltage for this circuit ____________ Given The driving voltage between the anodes and the structure of a cathodic ...

Страница 50: ...3 1 Ω Calculate total resistance __________________________ Calculate current ________________________________ Calculate voltage drop across R1 ____________________ Calculate voltage drop across R2 ____________________ Calculate voltage drop across R3 ____________________ Calculate the sum of the voltage drops _____________________ Does the voltage drop sum total power voltage Y N Is Kirchhoff s V...

Страница 51: ... current through R1 ____________________ What is the voltage drop across R2 ___________________ Calculate current through R2 ____________________ What is the voltage drop across R3 ___________________ Calculate the resistance of R3 _______________________ Calculate total current ____________________________ Calculate total resistance using Ohm s Law ________________________ Calculate total resista...

Страница 52: ...nctions of a digital multimeter can be used to determine the characteristics and operating parameters of DC electrical circuits The circuit board and digital multimeter contained in the experimental kits will be used for the following experiments The circuit board layout is shown in below Battery Posts 9 V 10 kΩ 100 Ω 10 Ω Diode 1 000 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω ...

Страница 53: ... in series and measure the total resistance RT with the ohmmeter DO NOT CONNECT BATTERY Does your measurement equal your calculation If not why Step5 Using Ohm s Law and your measured values of ET and RT calculate total current IT Step 6 With resistors still connected in series connect the battery and the ammeter in series CAUTION Make certain that the meter is set to mA scale before connecting ba...

Страница 54: ...__________ V STEP 2 RESISTANCE MEASUREMENTS Nominal Measured R1 10 000 Ω ______________ R2 1 000 Ω ______________ R3 100 Ω ______________ R4 10 Ω ______________ SERIES CIRCUIT STEP 3 Calculated Total Resistance RT R2 R3 R4 ______ Ω STEP 4 Measured Total Resistance RT R2 R3 R4 ____________ Ω STEP 5 Calculated Current IT ET RT __________________ A STEP 6 Measured Current IT __________________ A ...

Страница 55: ..._________ V Across 1000 Ω resistor V2 ______________ V Across 100 Ω resistor V3 ______________ V Across 10 Ω resistor Calculated Total VT ______________ V Measured Source Voltage ET ______________ Volts DIODE CHECK FORWARD READING REVERSE READING Good ____________ _____________ Bad ____________ ____________ Shorted ____________ ____________ ...

Страница 56: ...oad OL or 3 When reading current milliamps or amperes direct and an amperage reading is not displayed or the amperage reading fluctuates To check fuses perform the following 1 Remove screws and remove back cover On some meters the fuses can be found in the battery compartment 2 Remove each fuse and test using another multi meter using the ohm resistance scale A good fuse will read a small resistan...

Страница 57: ...t Figure Values Band A Band B Band C Band D Black 0 Black 0 Black 1 Silver 10 Brown 1 Brown 1 Brown 10 Gold 5 Red 2 Red 2 Red 100 Orange 3 Orange 3 Orange 1 000 Yellow 4 Yellow 4 Yellow 10 000 Green 5 Green 5 Green 100 000 Blue 6 Blue 6 Blue 1 000 000 Violet 7 Violet 7 Gray 8 Gray 8 Silver 0 01 White 9 White 9 Gold 0 1 Example A Red 2 C Orange 1 000 B Blue 6 D Silver 10 Resistance Value 26 000 Ω 1...

Страница 58: ...ss in which a chemical reaction that produces an electric current Pertinent terms and descriptions are given in this chapter Elements All matter is made up of chemical elements These elements are the building blocks of the physical world and are composed of atoms As of 1998 there were 109 recognized elements some of which have been found only as products of nuclear reactions and last for only very...

Страница 59: ...ne an electron is transferred from sodium to chlorine creating a positively charged sodium ion and a negatively charged chloride ion The two ions now of opposite charge are electrostatically attracted to each other forming a molecule Ions allow for transfer of electrical charge in liquids Compounds Molecules Molecules are composed of two or more atoms A molecule is the smallest unit of a substance...

Страница 60: ...eous solution and is classified according to the pH scale The definition of pH is the negative logarithm to the base 10 of the hydrogen ion concentration or pH log H When an alkali dissociates the anion produced is a hydroxyl ion OH A medium is said to be alkaline when an excess OH hydroxyl ions are present This concept is better understood if we look at pure water H2O Pure water will ionize into ...

Страница 61: ... pH An understanding of pH is important in corrosion and cathodic protection work For many metals the rate of corrosion increases appreciably below a pH of about 4 Between 4 and 8 corrosion rate is fairly independent of pH Above 8 the environment becomes passive and corrosion rates tend to decrease This is shown in Figure 2 4 which is typical of the behavior of steel The corrosion rate of aluminum...

Страница 62: ...droxyl ions or removal of hydrogen ions This is important when working with amphoteric metals as the corrosion of these metals can actually be accelerated under excessive cathodic protection due to the rise in pH around the structure Basic Electrochemistry Electrochemistry is the division of chemistry that deals with the transfer of electric charge in chemical reactions These chemical reactions ar...

Страница 63: ...egative charge For example when a neutral iron atom Fe oxidizes it may lose two or three electrons producing positively charged iron ions Fe or Fe as shown in Figure 2 5 Fe Fe 2e Fe Fe 3e Fe Fe Fe Fe Fe Fe Fe Fe Fe e e e e e e e e e e e e e e e e e e ANODE ELECTROLYTE Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe e e e e e e e e e e e e e e e e e e ANODE ELECTROLYTE Fe Fe Fe Fe Fe Fe Fe Fe Fe e e e e e e e e e e ...

Страница 64: ... A reduction reaction occurs any time that electrons are gained by an atom or molecule The atom or molecule increases in negative charge For example when a hydrogen ion H is reduced it gains one electron producing a neutral hydrogen atom H H e H The electrode or metallic site where reduction occurs is called a cathode The process appears in Figure 2 6 H2 e e e e e e e e e e e e e e e e e CATHODE H...

Страница 65: ... e Metallic Path ions ions Electrolytic Path Conventional Current Flow Figure 2 7 Basic Corrosion Cell An Electrochemical Circuit Electrolyte The electrolyte is an ionized solution capable of conducting electricity Ionization In addition to ions that may be produced in oxidation and reduction reactions ions may be present in the electrolyte due to dissociation of ionized molecules Cations are posi...

Страница 66: ...ectrolyte interfaces Corrosion occurs within a corrosion cell A corrosion cell consists of four parts as illustrated in Figure 2 8 Anode Cathode Electrolyte Metallic Path Anode e Metallic Path ions ions Electrolyte Cathode Anode e Metallic Path ions ions Electrolyte Cathode Figure 2 8 Corrosion Cell Anode Reactions The chemical reaction that occurs at the anode the anodic reaction is an oxidation ...

Страница 67: ...thodic reaction that occurs will depend on the electrolyte The following reactions are the two most common reduction reactions that occur at the surface of the cathode Oxygen Reduction more common in neutral environments 2H2O O2 4e 4OH Hydrogen Ion Reduction more common in acidic environments H e Ho Corrosion never occurs at the cathode of a corrosion cell The anode and the cathode can be on diffe...

Страница 68: ...e e e Direction of Electron Flow e e e e e e e e ELECTROLYTE e e e e e e e e e e e e e e e Direction of Electron Flow ELECTROLYTE ELECTROLYTE CATHODE ANODE e e e e e e e e e e e e e Direction of Electron Flow e e e e e e e e Figure 2 10 Electron and Ion Flow Charge Transfer in the Electrolyte Movement of charged ions is the mechanism for charge transfer through an electrolyte as opposed to the flo...

Страница 69: ... analysis of meter polarity connection and sign displayed allows the determination of the direction of conventional current flow Voltmeter Hook Up When measuring voltage across an element of a circuit the voltmeter is connected in parallel across the element A parallel connection is made when the external circuit is not broken For example the voltmeter in Figure 2 11 is connected in parallel to Re...

Страница 70: ...mistakes in meter connections misreading the meter or overlooking problems with the system Polarity Sign Most digital meters will display a negative sign for a negative reading and no sign for a positive reading When a voltmeter is connected across a metallic element such as a wire or pipeline with external current flow the voltage display is positive when the positive terminal of the voltmeter is...

Страница 71: ...sitive terminal is connected to the more noble metal and the negative terminal to the more active metal then the reading is positive Current will flow from the active to the noble metal through the electrolyte and from the noble to the active metal through the metallic path Therefore the reading is positive because conventional current is flowing into the positive terminal of the voltmeter Structu...

Страница 72: ... several potential benchmarks in common use but all of them are related to a basic standard In this standard one half of the cell generating the potential to be measured is represented by a platinized electrode over which hydrogen gas is bubbled while immersed in a solution having a definite concentration of hydrogen ions If it is arbitrarily agreed that the potential of the platinized electrode c...

Страница 73: ...and 2 15 The copper ions in the saturated solution prevent corrosion of the copper rod and stabilize the reference electrode This electrode is portable Copper Rod Saturated Copper Sulfate Solution Copper Sulfate Crystals Porous Plug Clear Window Connection for Test Lead Figure 2 14 Copper Copper Sulfate Reference Electrode in Contact with Earth Figure 2 15 Portable Copper Copper Sulfate Reference ...

Страница 74: ...water Chloride contamination changes the chemical reactions and the reference potential becomes a lower composite with the error being 20 mV at concentrations of 5 ppt and 95 mV at concentrations of 10 ppt Keep a few spares on hand Electrodes do get lost now and then and you need to have extras to continue your work Keep one fresh electrode in the office or shop to be used to calibrate your field ...

Страница 75: ...ent flow is similar to water flow Water will flow if there is a difference in elevation between the starting and ending flow points See Figure 2 16 Elevation Difference Direction of W a t e r F l o w Figure 2 16 Elevation Difference Causes Water to Flow Likewise current will flow from one point to another if there is a voltage difference between the two points This voltage difference may be genera...

Страница 76: ...me and current flow The law is expressed in the following formula Wt KIT kg where Wt weight loss kg K electrochemical equivalent kg A yr I Amps T years The value of K in kg A yr and lb A yr for some common metals is shown in Table 2 1 Table 2 1 Consumption Rate K for Various Metals 1 Metal Kg A yr Lb A yr Carbon 1 3 2 86 Aluminum 3 0 6 5 Magnesium 4 0 8 8 Iron Steel 9 1 20 1 High Silicon Chromium ...

Страница 77: ... protection anodes Knowing the anode material and expected output of an anode you can calculate the life expectancy These calculations are beyond the scope of this course but are covered in advanced cathodic protection courses Polarization Polarization is the deviation from the open circuit potential of an electrode resulting from the passage of current There are two major types of polarization Th...

Страница 78: ...l cathode is connected to a large anode copper rivet in a steel plate for example the corrosion current density on the anode steel is much less than in the opposite case discussed above and the anode corrodes more slowly Polarization may play an important role here too The small cathode may polarize rapidly reducing the rate of corrosion current flow Influence of the Environment Moisture Content E...

Страница 79: ...trolyte that provides the Redox Oxidation Reduction reactions necessary to drive a corrosion cell Some of the chemical species present in an electrolyte may assist in retarding or slowing chemical action by aiding the production of protective films Carbonates for example may lead to the formation of a passive film on zinc in such environments galvanized structures may undergo virtually no corrosio...

Страница 80: ...tural energy levels of different metals or composition variations formed during alloying Metals occur in nature in the form of various chemical compounds referred to as ores After ore is mined the metallic compound is removed from the rock like ore and refined to produce a nearly pure state of the metal Various processes mechanical chemical and electrical are employed to transform ores into useful...

Страница 81: ...End When two different metals are connected a voltage is generated between them The more active metal toward the anodic end becomes the anode of the cell A classic example of a galvanic cell is the flashlight battery shown in Figure 2 17 This consists of a zinc case enclosing an electrolyte and a carbon rod From Table 2 2 you can see that the voltage difference between the two metals is about 1 4V...

Страница 82: ...o dissimilar metals the grain boundary may be more active or more noble than the adjacent metal causing a voltage difference Also the more active metal used to make an alloy may corrode leaving behind the more noble metal This is usually referred to as the active metal leaching from the alloy such as zinc from brass dezincification Mechanical Stresses When a metal experiences mechanical stress the...

Страница 83: ...jacent metal the more the noble the metal becomes For metal ions that are different from the adjacent metal the effect may be difficult to determine When a simple salt is present that does not contain a metal ion the area of the metal in the higher concentration of salt is usually the anode Microbiological Influences Microbiologically induced corrosion MIC is common Various bacteria enter into red...

Страница 84: ...nesium into the tray making sure they do not touch each other 2 Add 1 1 2 inch of tap water to the tray 3 Set the meter to the V DC scale 4 Connect the meter s negative lead to the reference electrode 5 Connect the meter s positive lead to the metal being tested 6 Place the reference electrode near the copper and record the copper s potential 7 Place the reference electrode near the steel and reco...

Страница 85: ... Results Metal Reference Electrode Position Anticipated Potential mV CSE Actual Potential Copper Near Copper 100 Steel Near Steel 500 Zinc Near Zinc 1000 Magnesium Near Magnesium 1700 Conclusions 1 Magnesium is more electronegative than copper steel or zinc 2 Zinc is more electronegative than steel or copper 3 Steel is more electronegative than copper 4 Copper is more electropositive than steel zi...

Страница 86: ...Tap Water in Tray Steel Sheet 1 Place the copper and steel pieces at opposite ends of the tray 2 Add 1 1 2 inch of tap water to the tray 3 Set the meter to the V DC scale as shown on the next page 4 Connect the meter to the metal samples as indicated below Results Meter Positive Lead Meter Negative Lead Anticipated Potential mV Actual Potential Copper Steel 400 Steel Copper 400 ...

Страница 87: ... of the two cells is the cathode The corrosion cell potential can be estimated using the following expression cell potential potentialcathode potentialanode Step B Potential Measurement Copper Sheet Steel Sheet Tap water in tray V V Copper Sheet Steel Sheet Tap water in tray V V 1 Connect voltmeter positive lead to copper and connect negative lead to a copper copper sulfate reference electrode 2 P...

Страница 88: ...ential Copper Steel Conclusion 1 Steel is more electronegative than copper 2 The difference in potential between the steel and the copper is the same as measured in Step A Step C Polarized Potential Measurement Copper Sheet Steel Sheet 10 Ω V V Reference Electrodes 1 Connect the steel to the copper through the 10 Ω resistor 2 Repeat steps B1 B2 and B4 ...

Страница 89: ...ential is unchanged or less electronegative Step D Current Direction in the External Circuit in a Corrosion Cell 10 Ω V _ Metal Sample No 2 Tap Water in Tray Metal Sample No 1 1 Connect the meter as indicated across a 10 Ω resistor between the two metals See the figure on the next page 2 Record the voltage drop across the resistor and note polarity 3 Evaluate the direction of the current 4 Repeat ...

Страница 90: ...r Positive Lead Meter Negative Lead Measured Voltage Drop mV Copper Steel Steel Copper Zinc Steel Steel Zinc Copper Zinc Zinc Copper Meter Positive Lead Meter Negative Lead Direction of Conventional Current in External Circuit Which metal is the anode Copper Steel to Steel Copper to Zinc Steel to Steel Zinc to Copper Zinc to Zinc Copper to ...

Страница 91: ...ternal circuit is from the cathode to the anode 2 The direction of current in the resistor emphasizes that the direction of conventional current is from the least electronegative cathode to the most electronegative active electrode in the external circuit Thus an Fe Fe electrode can be either an anode or a cathode depending on the other electrode to which it is connected ...

Страница 92: ...OCEDURE 1 Place the zinc and copper at the sides of the tray 2 Add 1 1 2 inch of tap water to the tray 3 Set the meter to the V DC scale 4 Connect the meter to the zinc and to the reference electrode as indicated in the figure 5 Record the electrode potential with the reference electrode in the two positions indicated in the figure 6 Evaluate the direction of current V Reference electrode Position...

Страница 93: ...Measured Potential mV CSE Zinc Reference Position 1 Zinc Reference Position 2 Conventional current will pass from the locations in the electrolyte that are more negative to the locations that are less negative as indicated by potential readings at the reference electrode positions Conclusion 1 Conventional current in the electrolytic circuit is from the anode to the cathode ...

Страница 94: ...y or 3 Copper sulfate crystals are not visible or 4 When compared to a standard cell there is significant difference potential Contaminated Cells To restore reference electrodes for proper operation perform the following steps 1 Remove the reference cell tip rod and end cap and properly dispose of the fluid contained in the cell 2 With non metallic abrasive material sandpaper clean copper rod to a...

Страница 95: ...r copper sulfate solution approved for reference cell use to a point just below the manufactured threads in the cell body 6 Assemble and screw in a reference cell tip that has been presoaked in distilled water 7 Shake cell several times to mix cell solution with copper sulfate crystals 8 Maintain fluid so that 95 of the cell is fluid filled 9 Maintain cell so that copper sulfate crystals are alway...

Страница 96: ...000 volts 1 megavolt 1 000 volts 1 kilovolt 1 0 volt 1000 millivolts 0 100 volt 100 millivolts 0 010 volt 10 millivolts 0 001 volt 1 millivolt 0 000001 volt 1 microvolt 1 000 000 amperes 1 mega ampere 1 000 amperes 1 kiloampere 1 0 ampere 1000 milliamperes 0 100 ampere 100 milliamperes 0 010 ampere 10 milliamperes 0 001 ampere 1 milliampere 0 000001 ampere 1 microampere 1 000 000 ohms 1 mega ohm 1...

Страница 97: ...n Ω cm R Resistance in Ω A Cross Sectional Area in cm2 L Length in cm Using the Wenner method the soil resistivity is determined by ρ 2πaR Whereρ resistivity in ohm cm a the spacing of the pins cm R the resistance measured Ω ρ resistivity Ω cm OR ρ 191 5aR Whereρ resistivity in Ω cm a the spacing of the pins feet R the resistance measured Ω ρ resistivity Ω cm Ohm s Law E IR I E R R E I ...

Страница 98: ...CP 1 Cathodic Protection Tester Course Manual NACE International 2000 07 01 04 Chapter 2 Appendix 3 U S Customary Metric Conversions ...

Страница 99: ... corrosion control However nonmetallic materials will not be discussed in this course except for their use in electrical isolating devices Protective Coatings Underground or Submerged Structures General Coatings are the first line of defense in many corrosion control programs Unfortunately coatings are not perfect and accelerated corrosion occurs at breaks holidays in a coating Cathodic protection...

Страница 100: ...fin and Polyethylene These coating systems consist of polyolefin or polyethylene extruded over a butyl or asphalt mastic adhesive The coatings have high impact resistance and resist the development of holidays over time Tape Coatings Most tape systems are cold applied The system consists of a primer a corrosion sealant inner layer with a mechanical protective outer layer backing usually polyethyle...

Страница 101: ... Surface Preparation Proper surface preparation is essential if the coating is to bond properly to the metal Each type of field coating will have a specific surface preparation requirement that must be followed For all coatings the surface must be clean and dry Often this is accomplished with power tools but in some cases abrasive blasting and solvents is required Some coatings require a primer on...

Страница 102: ...ing is found it may be necessary to excavate more of the pipe to see how far the deterioration exists Electrical Isolation Electrical isolation devices may be used to separate different metals or other anodic and cathodic components of a corrosion cell Insertion of dielectric material interrupts the electronic portion of the corrosion cell thereby isolating the anode from the cathode Electrical is...

Страница 103: ...s an important role in the corrosion reaction may be controlled by the addition of oxygen scavengers This is especially important in the treatment of boiler water Adjustment of pH The pH of water affects its ability to precipitate out a protective scale Control of pH is used to create a water that will not be aggressive to the metal piping and vessels it contacts Maintenance of Environmental Contr...

Страница 104: ...Corrosion Cell on the Surface of a Pipeline Figure 3 1 Microscopic Corrosion Cell The concept of cathodic protection involves reducing the potential difference between local anodic and cathodic sites on a metal surface to zero resulting in zero corrosion current flow This can be accomplished by causing a current to flow onto the structure from an external anode which current polarizes the cathodic...

Страница 105: ...lyte to the metal surface At the point this current leaves the cathodic protection anode an anodic reaction occurs Where it is picked up on the protected surface a cathodic reaction occurs The current then flows to the metallic connection and returns to the anode Note that in this discussion we are utilizing the concept of conventional current flow see Chapter 2 Definition Cathodic protection is t...

Страница 106: ... interiors ship hulls ballast tanks docks sheet piling foundation piles on land and in the water bridge decks and substructures hot water storage tank interiors heat exchanger water boxes and tube sheets internal surfaces of oil heater treaters reinforcing steel in concrete lead or steel sheathed telephone and electrical cables Cautionary Note It is possible to overprotect some materials such as p...

Страница 107: ...potential difference or driving voltage between a galvanic anode and the structure to be protected The galvanic anode is connected to the structure it is protecting either directly or through a test station so it can be monitored A typical galvanic cathodic protection system is shown in Figure 3 3 ANODE STRUCTURE CURRENT CURRENT Figure 3 3 Typical Galvanic Anode Cathodic Protection Anodes There ar...

Страница 108: ...all impressed current cathodic protection systems may have isolated points where additional current in relatively small amounts is needed These requirements can be met with galvanic anodes Typical applications include Poorly or incompletely coated buried valve installations Shorted casings that cannot be cleared Isolated sections where the coating has been badly damaged Areas where electrical shie...

Страница 109: ...e Easy to install Easy to add anodes in most cases Provide uniform distribution of current Minimum right of way easement costs Limitations of Galvanic Anodes Low driving voltage current output Many anodes may be required for poorly coated structures May be ineffective in high resistivity environments Higher cost per unit ampere than impressed current due to lower efficiency self consumption May be...

Страница 110: ...awater applications because it has a much lower consumption rate than magnesium or zinc Aluminum anodes are not used in fresh water except as impressed current anodes They are not used underground An alloy of aluminum zinc and indium is used as a sacrificial anode on reinforced concrete structures Aluminum anodes are commonly used in process vessels containing brine At temperatures above 120 F 49 ...

Страница 111: ...ed for galvanic anodes consists of 75 gypsum CaSO4 20 bentonite clay and 5 sodium sulfate The chemical backfill surrounding magnesium and zinc anodes provides a uniform environment that reduces self consumption of the anode The chemical composition of the backfill is such that the anode functions more efficiently because the backfill reduces polarization of the anode Also the backfill swells upon ...

Страница 112: ...tructure Impressed Current Systems An impressed current system consists of an external power source and anodes The external power source forces current to flow from the anode to the structure through the electrolyte The anodes used in an impressed current system are usually constructed of a relatively inert material A typical installation is shown in Figure 3 4 ANODE STRUCTURE CURRENT CURRENT Powe...

Страница 113: ...advantages over other impressed current power sources Applications of Impressed Current Cathodic Protection Typical uses of impressed current are for large current requirements particularly for bare or poorly coated structures in all electrolyte resistivities as an economical way of protecting structures having dissipated galvanic anodes to overcome stray current or cathodic interference problems ...

Страница 114: ...nt interference May cause overprotection resulting in coating damage hydrogen embrittlement Component Parts of Impressed Current Systems Anodes GRAPHITE CARBON Graphite anodes installed underground with carbonaceous backfill function well Graphite also exhibits excellent performance in chloride environments such as seawater Where oxygen evolution takes place on the surface of a graphite anode the ...

Страница 115: ... ions particularly in process applications Platinized anodes are economical only when operated at high current densities such as in seawater where there can be rapid migration of chlorides to the anode and products away from the anode Where the predominant anodic reaction is the evolution of oxygen higher driving voltages are needed In terms of both the costs of the anode and the power required it...

Страница 116: ...d steel piling and sections of old pipe have been used as impressed current anodes LEAD SILVER This material is used only in chloride environments The most common application is seawater Backfill For underground applications impressed current anodes are almost always backfilled in a carbonaceous material The backfill serves three purposes reduces the anode to ground resistance increases the curren...

Страница 117: ... Constant current the current output remains constant over a wide range of circuit resistances up to the maximum rated output voltage 3 Constant potential the current and voltage output vary to maintain a pre selected structure potential Where AC power is economically available rectifiers have clear economic and operating advantages over other power sources SOLAR PANELS Solar panels generate DC by...

Страница 118: ...ng Oil Rectifier Gas Powered Engine Insulated Flange Regulator Alternator Control Center AC SupplyLine to Rectifier Groundbed AC Generator Structure Figure 3 6 Engine Generator Unit WIND POWERED GENERATORS Wind powered generators may be used in areas with prevailing winds of sufficient velocity The generators also charge storage batteries so as to provide constant cathodic protection current Groun...

Страница 119: ...rate voltage by heating a junction of two dissimilar metals They generate small currents so are used in places having low current requirements Electrical Connections All electrical connections used in impressed current cathodic protection systems except the active anode surfaces must be completely sealed with dielectric insulating materials EXPERIMENT 3 2 ...

Страница 120: ... structure requires sufficient current to protect all the metal exposed to the electrolyte On a coated structure it is necessary to protect only the metal exposed at breaks or holidays in the coating A well coated structure may well have less than 1 of its surface exposed at holidays As the coating ages however some deterioration may occur Also when protecting older coated structures tests need to...

Страница 121: ...ements will be higher than in cooler ones Heat exchanger water boxes and oil heater treater vessels are good examples of higher temperature environments Gas pipelines downstream of a compressor station normally require a high current density for the increase in temperature caused by the compressed gas Increasing temperature acts to reduce polarization This also increases current requirements As me...

Страница 122: ... especially sulfate reducing bacteria have a depolarizing effect on the protected structures It may be necessary to increase the level of cathodic protection in such electrolytes The fluid chemistry in oil heater treaters affects anode performance Carbon dioxide and hydrogen sulfide for example have a passivating effect on zinc Electrical Shielding Metal Metal components connected to a protected s...

Страница 123: ...rosion potentials the initial measurements are most likely to be an average of corrosion potentials for several corrosion cells Therefore several surrogate criteria have been developed to assist meeting the true criterion Various criteria are recommended by NACE International and other international standards organizations NACE International Recommended Criteria General There are several criteria ...

Страница 124: ...yte Electrolyte Polarization Structure Contact Test Lead Structure Test Lead Contact Test Measuring Lead Measuring Lead Internal Meter 900 v Polarization Film Structure Electrolyte Reference Cell Voltmeter Measurement C P current across electrolyte 900 v Polarization Film Structure Electrolyte Reference Cell Voltmeter Measurement C P current across electrolyte Figure 3 9 Voltage Drops in a Measuri...

Страница 125: ...xcept for the one through the electrolyte The IR drop through the electrolyte can be reduced to nearly zero however by placing the reference electrode near the structure it can be reduced to zero by interrupting the current flow In addition to attempting to make the IR drop negligible another approach is to determine the magnitude of the IR drop either through measurement or calculations and adjus...

Страница 126: ...urated copper copper sulfate reference electrode CSE and one is a polarization shift of 100 mV The three criteria defined are A negative cathodic potential of at least 850 millivolts with the cathodic protection applied This potential is measured with respect to a saturated copper copper sulfate reference electrode contacting the electrolyte Voltage drops other than those across the structure to e...

Страница 127: ... or by shutting off the current On a bare structure if the potential is measured at the structure to electrolyte boundary then the electrolyte is no longer in the measuring circuit and its resistance is nearly zero If cathodic protection current is interrupted then current is zero Remember that polarization will dissipate when current is interrupted and polarization is the measurement of interest ...

Страница 128: ...ese metals are covered in RP0169 The 100 mV cathodic polarization criterion is used for both materials Aluminum is an amphoteric metal and can be damaged by excessive cathodic protection A polarized potential more negative than 1200 mV should not be exceeded Dissimilar Metal Situations RP0169 gives a criterion of a negative voltage to a stable reference electrode equal to that required for protect...

Страница 129: ...torage Tanks specifies 0850 to 1050 mV polarized to CSE Oil Heater Treaters RP0575 Internal Cathodic Protection Systems in Oil Treating Vessels A minimum of 850 mV vs CSE 800 mV vs a silver silver chloride electrode Ag AgCl If however the fluid contains sulfides or hydrogen sulfide a minimum potential of 950 mV 900 vs Ag AgCl can be required Above Ground Storage Tanks RP0193 External Cathodic Prot...

Страница 130: ...rtation Systems Part 1 On land pipelines Metal to electrolyte potential chosen for a corrosion rate less than 0 01 mm yr 0 39 mils yr Polarized potential more negative than 850 mVCSE Limiting critical potential not more negative than 1 200 mVCSE Anaerobic soils or sulfate reducing bacteria SRB more negative than 950 mVCSE High soil resistivity 750 mVCSE for 100 ρ 1 000 Ω m 650 mVCSE for ρ 1 000 Ω ...

Страница 131: ...Japan Corrosion Protection and Repair Manual for Port and Harbor Steel Structures Japanese Port Authority Association Part 1 Harbor Facility Technology Criteria and Discussion Japanese Water Piping Association WSP 050 Cathodic Protection Manual for Coated Steel Water Pipe Australia Australian Standards Institute Standard No 2832 covers cathodic protection It has three parts Part 1 Pipe Cables and ...

Страница 132: ...n NOTE Instructor will demonstrate this experiment PROCEDURE A V Corrosion Current V Reference Electrode V Rm Magnesium Anode Tray with Tap Water Cathodic Protection Current Closed Circuit Steel Copper Experiment to Demonstrate Mitigation of Local Action Cell Corrosion with Cathodic Protection Part A 1 Insert steel and copper sheet in side of tray and 1 1 2 inches of fresh tap water 2 Follow the d...

Страница 133: ...tial of steel and copper 4 Connect ammeter between copper and steel sheet and measure corrosion current Icorr A second meter from another kit can be used to obtain current flow amperes or a single meter can be relocated to obtain the information as shown 14 mA Conventional Current Corrosion Current 14 mA Conventional Current Corrosion Current 5 Measure polarized potentials of steel and copper ...

Страница 134: ...ium anode in tray and connect to the copper sheet through a 10 000 ohm resistor 2 Measure corrosion current Icorr 3 Determine the cathodic protection current Ic p by calculating it from the voltage drop across the variable resistance 4 Measure polarized potentials of steel and copper 10 mV 0 31 V 0 29 V 5 mA 10 000 O 1 000 O 100 O 10 O Same Meter 10 mV 10 mV 0 31 V 0 29 V 5 mA 10 000 O 1 000 O 100...

Страница 135: ...r Corrosion Current Icorr mA CP Voltage Drop Vr Resistor Calculated Icp Native OC open circuit N A N A N A Polarized Cu Fe connected N A N A 10 000 ohms 1 000 ohms 100 ohms 10 ohms CONCLUSIONS 1 Corrosion current decreases as cathodic protection current increases 2 Corrosion current decreases as polarized potential of cathode is made more electronegative ...

Страница 136: ...e Part A 1 Place copper sheet in one end of tray and magnesium anode in opposite end 2 Add 1 1 2 inches of tap water to the tray 3 Connect anode to copper sheet as shown and measure initial cathodic protection current and polarized potential of the structure A second meter from another kit can be used to obtain current flow amperes or a single meter can be relocated to obtain the information Part ...

Страница 137: ...pper Cathodic Protection mV Current mA Instant of connection ______________ ______________ ______________ ______________ ______________ ______________ ______________ ______________ ______________ CONCLUSIONS 1 Polarized potential of the structure shifts electronegatively with time 2 Cathodic protection current decreases with time ...

Страница 138: ... that are encountered in cathodic protection testing or inspection are listed below After a specific hazard assessment is completed for a particular job the appropriate preventative measures must be determined to reduce higher risk and hazard exposure This can be addressed by completing a Job Safety Analysis JSA that identifies each hazard and the preventative measures for each step of the project...

Страница 139: ...a project This is not intended to cover a complete safety program The following safety hazards are those specifically related to cathodic protection and are not always in a standard safety program Electrical Cathodic protection testers and technicians can become complacent with electricity as in many cases the voltage being measured is very low with a low source of energy This is not the case when...

Страница 140: ... Law I E R the current through the body is 120 mA likely enough to be fatal Note that rectifiers may be serviced with 240 VAC 480 VAC or up to 600 VoltsAC thus the body current would increase proportionally Cathodic Protection CP Rectifiers CP rectifiers have exposed electrical AC and DC terminals on the panel of the rectifier The voltage exposure varies with the rectifier rating and design Do not...

Страница 141: ...hen working on or removing rectifier components No one else can then inadvertently turn the AC on before it is safe Lock Out Tag Out A lock out tag out LOTO is intended to ensure that the power can not be turned on inadvertently while people are still working on the equipment In addition it instills a safe work habit As an example seat belts in vehicles were felt a nuisance at first but now one fe...

Страница 142: ...pment is exposed in a hazardous area it must be turned off locked out and tagged out to avoid the exposure of an arc that may act as a source of ignition Explosions or Ignitions In addition to hazardous areas many structures containing potentially explosive or combustible substances are cathodically protected Under certain circumstances a cathodic protection system may have sufficient energy to ig...

Страница 143: ...ectifier s until the vessel is securely bonded to the dock Finally any cathodic protection component that might generate an ignition spark should not be allowed within specific areas where explosive atmospheres may exist Examples are within dikes around tanks containing combustible materials facilities housing or encompassing propane natural gas or combustible product pipeline components gas or oi...

Страница 144: ...ure and a copper copper sulfate reference electrode in contact with the earth or other low resistance ground If an AC voltage in excess of 15 V is measured the structure is considered hazardous and steps must be undertaken to reduce the hazardous voltage level If the potentials are determined to be less than 15 Vac no specific action is necessary however caution should be maintained as this voltag...

Страница 145: ...l the work comes out No worker is required to work in conditions unsafe and can refuse to enter Be aware that a person need not be completely buried to suffocate or have the heart receive a fatal shock Hazardous Material During your work you may encounter hazardous materials such as those listed below Do not handle these materials unless you have the proper training or certification These material...

Страница 146: ... either at the anode surface or at the cathode surface Among possible gases that may be encountered are oxygen chlorine carbon dioxide carbon monoxide and hydrogen Some gases are potentially explosive Asphyxiation can occur due to the displacement of oxygen by some of the other gases listed Some gases are toxic when inhaled Low pH acid environments can exist around anodes in deep groundbeds Due to...

Страница 147: ...anual NACE International 2000 12 01 04 Know the handling storage procedures for chemicals or other hazardous materials or equipment Working at heights Animals reptiles and insects Vehicles Drive defensively and be aware of hazard situations that could occur ...

Страница 148: ... hydrogen reference electrode SHE is a laboratory reference electrode and is used to determine the potential of other reference electrodes that are better suited for field use Zinc Reference Electrode Zinc is sometimes used as a reference electrode since the potential of zinc is relatively stable Zinc is actually a pseudo reference electrode since the potential of zinc can change as the environmen...

Страница 149: ...es to Copper Copper Sulfate Reference Electrode Electrode Half Cell Potential Volt Copper Copper Sulfate 0 000 Silver Silver Chloride saturated Saturated Calomel 0 050 0 070 Hydrogen SHE 0 320 Zinc 1 100 Electrode used under standard conditions from RP0169 Stationary reference electrodes A stationary copper copper sulfate reference electrode is used for installation underground These electrodes ar...

Страница 150: ...al Basis of Measurement A structure to electrolyte potential commonly is referred to as a structure to electrolyte or structure to soil potential The definition of a structure to electrolyte potential is The potential difference between the metallic surface of the structure and electrolyte that is measured with reference to an electrode in contact with the electrolyte A structure to soil potential...

Страница 151: ...ery of the tank This may not yield accurate data about the potentials under the tank bottom particularly if the anodes are in a ring around the tank Permanent reference electrodes under the tank bottom yield the best data Close Interval Potential Survey A series of structure to electrolyte potentials measured over the top of a pipeline may be helpful in determining variations in cathodic protectio...

Страница 152: ...d often printed in graph form The survey is made over the line so other personnel are assigned to locate and stake the line and provide other assistance When testing multiple pipelines that are bonded together the survey data may represent an average of all the pipelines Reading _ Cu Cu SO4 Ref Cell Voltmeter Pipe Electrolyte Potential Profile Figure 5 2 Pipe to Soil Potential Profile ...

Страница 153: ...tential Measurement Between Two Reference Electrodes Voltage IR Drop in Potential Data Accuracy of data is one of your most important responsibilities Without accurate data those responsible for your company s corrosion control program will not know how well the structures are protected Knowledge of voltage drops in the potential measuring in the potential circuit is critical to obtaining accurate...

Страница 154: ...ded The computer can also create graphs of data Figure 5 4 shows a photo of a data logger Datalogger Figure 5 4 Data Logger X Y Plotters These instruments have two pens that record data on the X horizontal axis and the Y vertical axis They are very useful in stray current areas where voltages are constantly varying They are often used to make correlation curves between rail to pipe voltage and pip...

Страница 155: ...s is its internal resistance The internal resistance of an ammeter should be low to prevent adding resistance to the external circuit thus reducing the current of the external circuit Caution because of this low internal resistance it is important not to set your multimeter on the ammeter when attempting to measure voltage This can blow a fuse or damage the meter In practice even the low internal ...

Страница 156: ...nal Since the direction of current flow in cathodic protection work is as important as the magnitude you should anticipate the direction of the current before connecting the meter into the circuit Figure 5 6 depicts direction of current flow in an ammeter measurement Current is flowing from the anode through the soil to the pipe and then through the meter back to the anode Note that the current is...

Страница 157: ...e of the high cost for large clamps and the meter associated with those clamps Clamp on DC ammeters are available for pipes using special sensing hoops Figure 5 7 Clamp On Ammeter Shunts This is the third method of measuring current In using a shunt you measure a voltage drop across a known resistance and calculate the current General In practice even the low internal resistance of an ammeter will...

Страница 158: ...e circuit Voltmeter is connected in parallel across the current shunt _ _ VOLTS RA RB RC E I Current Shunt with known resistance value is in series with the circuit Voltmeter is connected in parallel across the current shunt _ _ VOLTS RA RB RC E I Current Shunt with known resistance value is in series with the circuit Voltmeter is connected in parallel across the current shunt Figure 5 8 Shunt Mea...

Страница 159: ...he millivolt drop by the amps millivolt rating This will give you the current flow through the shunt in amps For example Given Shunt data 15 A 50 mV Measured voltage drop 28 mV Determine shunt rating Rating 15A 50 mV 0 3 A mV Calculate current Current 0 3 A mV x 28 mV 8 4 A For shunts that you test regularly writing the amps millivolt rating on the shunt will speed up your work considerably when t...

Страница 160: ...e needle has swung to the right from the left hand zero position This indicates that current flow is from left to right through the shunt Note also the battery and the direction of current flow around the circuit Current is leaving the positive terminal of the battery and proceeding counter clockwise around the circuit Consequently the current is flowing from left to right through the shunt Variou...

Страница 161: ...01 1 SS 25 25 001 1 SO 50 50 001 1 SW or CP 1 50 05 02 SW or CP 2 50 025 04 SW or CP 3 50 017 06 SW or CP 4 50 0125 08 SW or CP 5 50 01 1 SW or CP 10 50 005 2 SW 15 50 0033 3 SW 20 50 0025 4 SW 25 50 002 5 SW 30 50 0017 6 SW 50 50 001 1 SW 60 50 0008 1 2 SW 75 50 0 00067 1 5 SW 100 50 0005 2 J B Type Agra Mesa 5 50 01 1 Cott or MCM Red MCM 2 200 1 01 Red Cott 5 50 1 01 Yellow MCM 8 80 01 1 Orange ...

Страница 162: ...ected by a shorting strap In many test stations however the connection is made with a split bolt connector and then taped Opening this connection takes time and after testing the connection must be made again As mentioned earlier even the low resistance of the ammeter can cause the instrument to read a current lower than the actual anode output Consequently a shunt in the circuit is the preferred ...

Страница 163: ...asked to assist in making current requirement tests In these tests a current is impressed on a structure to be protected and the potential changes brought about by that current are measured From the data the amount of current required for protection can be determined The current in the test circuit can be determined by inserting an ammeter into the circuit or by the use of a shunt Here again if an...

Страница 164: ... coded 0 17 mV _ Pipe size and wall thickness or weight per foot must be known Pipeline N Pipe Span in Feet Wires must be color coded 0 17 mV _ Pipe size and wall thickness or weight per foot must be known Pipeline Pipe Span in Feet Wires must be color coded 0 17 mV _ Pipe size and wall thickness or weight per foot must be known Pipeline N West East Figure 5 9 2 wire Line Current Test Because the ...

Страница 165: ... to Figure 5 9 Note the meter is showing a positive indication This means the current is entering the meter on the positive terminal The positive terminal is connected to the west end of the span Since the meter is in parallel with the span current flow on the pipe is from west to east The accuracy of this test method depends greatly on accurate knowledge of the dimensions of the pipe Should there...

Страница 166: ...6 81 26 5 29 17 36 16 16 00 40 64 0 375 0 95 62 6 93 16 4 61 15 12 18 18 00 45 72 0 375 0 95 70 6 105 07 4 09 13 42 20 20 00 50 80 0 375 0 95 78 6 116 97 3 68 12 07 22 22 00 55 88 0 375 0 95 86 6 128 88 3 34 10 96 24 24 00 60 96 0 375 0 95 94 6 140 78 3 06 10 04 26 26 00 66 04 0 375 0 95 102 6 152 69 2 82 6 25 28 28 00 71 12 0 375 0 95 110 6 164 59 2 62 8 60 30 30 00 76 20 0 375 0 95 118 7 176 65 ...

Страница 167: ...he change in voltage drop across the span E using the inside leads Divide the current flow in amperes I by the change in voltage drop in millivolts to express the calibration factor K in amperes per millivolt The calibration factor is calculated as follows K I E I E with current applied E with no current applied Normally if the pipeline operating temperature is stable this can be done only once as...

Страница 168: ... outside leads resulting in voltage drop change E of On 5 08 mV Off 0 17 mV E 4 91 mV Then the calibration factor will be mV A 04 2 mV 17 0 08 5 A 10 or m 91 4 A 10 K Without test current applied the voltage drop across the span between the inner leads is 0 17 mV Therefore current flow is mA 347 A 347 0 mV mV 17 x A 04 2 drop mV x K I Referring again to Figure 5 10 note that the positive lead of t...

Страница 169: ... fittings casing to pipe structure continuity structure to structure structure to anode structure to earth anode to earth In this course we will cover testing resistance across an isolating fitting and between a casing and a pipe We will also cover measuring structure continuity and diode bias Measurements are made using Ohm s Law and sometimes by using an ohmmeter These two methods are discussed ...

Страница 170: ...ctrochemical paths because the DC voltage causes polarization and a change in resistance Using an ohmmeter to check effectiveness of an isolation joint in service is not reliable because of the parallel resistance paths through the soil as illustrated in Figure 5 11 320 _ Parallel resistance path may display low resistance indicate shorted insulator Soil Figure 5 11 Isolation Joint Test Using an O...

Страница 171: ...inges and bolts It is important that electrical continuity between the water box and the shell be maintained in order to protect the tube sheet Electrical Isolation Purpose and Usage The purpose of electrical isolation is to confine the protective current to the structure being protected If for example a production well casing is being protected and it is electrically connected to unprotected stru...

Страница 172: ...nt companies usually all running in the same right of way In cases like this the pipelines can be connected together and protected by a series of rectifiers with each company assuming responsibility for a portion of the system Isolation Insulating Joints Commercial fittings available for providing electrical isolation include flanges couplings unions monolithic isolating pipe joints nonmetallic pi...

Страница 173: ...nary position If the difference in potential is approximately 100mV or greater the isolation fitting is effective If less than 100mV further testing may be necessary If the cathodic protection current can be interrupted on and off pipe to soil potentials can be recorded on each side of the isolation fitting with the reference cell in the same location Similar on and off potentials on opposite side...

Страница 174: ...so be tested by using a pipe or cable locator These instruments are discussed later in this chapter Diode Bias This is a multimeter operated in the diode bias mode A functioning diode will typically display a meter value from 0 3 V to 0 9 V in the forward bias positive lead to anode negative lead to cathode In the reverse bias condition positive lead to cathode and negative lead to anode a functio...

Страница 175: ...current flowing between the two outside pins After resistance is measured at a given spacing then the spacing can be changed and resistance measured at the new spacing a ρ 2 π a R a a P1 P2 C1 C2 Resistivity Test Instrument Figure 5 12 Four Pin Wenner Method of Measuring Soil Resistivity It is important that the pins are placed in a straight line and that they are equally spaced Nearby metallic un...

Страница 176: ...hows a typical layer situation ρ1 avg ρ2 avg ρ3 avg S1 S2 ρ1 layer ρ2 layer ρ3 layer S3 ρ1 avg ρ2 avg ρ3 avg S1 S2 ρ1 layer ρ2 layer ρ3 layer S3 Figure 5 13 Average and Layer Resistivity This measurement is done by taking a series of measurements at ever widening pin spacings It is important that the pin spacing be centered on a fixed point between the center two pins This means moving all four pi...

Страница 177: ...y from in situ soil resistivity measurements A soil box consists of two plates at the end of the box for current flow and two pins in the center for voltage measurement as illustrated in Figure 5 14 The linear and cross sectional areas between the voltage pins are equal resulting in a box calibration factor of 1 Therefore the measured resistance equals resistivity of the sample in ohm cm The soil ...

Страница 178: ...d contacting soil at a depth of desired soil resistivity measurement Insulated wire inside of rod from tip to terminal Hollow bare metal probe rod Terminals One to rod One to tip Soil Resistivity Instrument Figure 5 15 Single Probe Soil Resistivity Measurement Measuring pH Electrolyte pH can be measured in several ways For liquids pH litmus paper or a pH meter may be used For soils a pH meter may ...

Страница 179: ... the pH can be determined from the scale Use of Pipe Locating Devices During corrosion testing it is often necessary to accurately determine the location of such buried items as a pipeline conduit or storage tank Also it is important to determine points of electrical continuity and discontinuity A pipe and cable locator can be a great time saver for making such determinations Most locators include...

Страница 180: ...red volts peak This AC voltage is connected between ground and the structure to be traced The AC signal will then flow through the earth to the structure and finally to the structure connection to complete the circuit When the receiver is near the structure the AC field around the structure induces a voltage in the pickup coil This voltage is amplified and produced as an audible signal heard by th...

Страница 181: ...the location of underground metallic structures where it is not feasible to attach a wire directly to the structure as in the case of the conductive locator This is accomplished by a coil in the transmitter that establishes a strong magnetic field that induces an AC current in the structure The AC field surrounding the structure can then be detected in a manner similar to that described for the co...

Страница 182: ...Figure 5 19 Current Interrupter Coupon Measurements Coupons are often used to check the effectiveness of cathodic protection These are made of the same metal as the structure and are electrically connected to it They are weighed prior to installation and then weighed periodically to determine if any weight loss has occurred Corrosion is evidenced by weight loss Some test stations are equipped with...

Страница 183: ...ctric resistance probes are also used to monitor the effectiveness of cathodic protection These can be placed underground inside water storage tanks or other vessels or on marine structures An instrument is used to measure corrosion rate electrically If the protection is effective the corrosion rate is zero ...

Страница 184: ...ugh there are exceptions alternating currents do not cause significant corrosion of common structural materials AC current can be a significant safety hazard In accordance with Faraday s law the weight of metal corroded is proportional to the amount of current being discharged from it into the electrolyte Stray current corrosion is of serious concern because a large amount of current is usually in...

Страница 185: ...icked up the structure is protected corrosion occurs where the current leaves the metal and re enters the electrolyte Types of Stray Current Dynamic Stray Current Dynamic stray currents vary in magnitude and often in direction These currents can be manmade or natural in origin Manmade dynamic stray currents come from such sources as electrically powered rail transit systems or mine railroads and a...

Страница 186: ...d the source of the stray current To determine the extent of the fluctuations you need a recording instrument such as a strip chart recorder or datalogger These instruments store or display the measurements over the test period so that the stray current activity can be evaluated Figure 6 1 shows a typical recording of potentials produced by dynamic stray current POTENTIAL TEST POINT Figure 6 1 Rec...

Страница 187: ... Steady State Stray Current Measurement Indications Interference current can be recognized in several ways Structure to electrolyte potential changes Changes in current flow on a pipeline Localized pitting near or immediately adjacent to a foreign structure Coating breakdown in a localized area near an anode bed or other source or stray current If you are making a routine survey and you find an ar...

Страница 188: ...ample you will want to determine who the owner is and whether the structures have impressed current cathodic protection Galvanic anodes seldom cause interference As you drive about your territory be alert for cathodic protection rectifiers If you find one you haven t seen before or find a new one replacing an old unit the new rectifier may be a source of interference current When you are talking w...

Страница 189: ...ed through the cable back to the source rather than leaving the structure through an earth path A resistor may be incorporated in a bond to control the amount of stray current being drained If dynamic currents are involved a diode or reverse current switch may be needed to prevent reversal of current flow Mitigation bonds need to be maintained If not kept in good working order the affected structu...

Страница 190: ...Bond across High Resistance Joints Figure 6 3 Mitigation Bond Used to Control Stray Current from a Rail Transit System Cathodic Protection Current Protective Current Protected Line Foreign or Affected Line Protective Current Picked Up by Foreign Line MITIGATION BOND Interference Corrosive Current Flowing Through the Earth to Return to Protected Line p Figure 6 4 Mitigation Bond Used to Solve a Cat...

Страница 191: ...urrent is not so large that it cannot be overcome with the cathodic protection current An advantage of using cathodic protection is that it avoids the use of bonds and the installation and maintenance problems that may accompany them Galvanic anodes may be used to overcome cathodic interference problems Anodes are placed in the area of current discharge The testing and design of such systems are h...

Страница 192: ...p the experiment as shown above without the steel rod foreign structure 2 Measure and record potentials on cathodically protected structure the steel sheet at positions A B and C 3 Disconnect cathodic protection system 4 Place the steel rod foreign structure in the water in the tray as shown 5 Measure and record potentials on the foreign structure at reference electrode positions D E and F 6 Conne...

Страница 193: ...mV A B C D E F Step 2 Step 5 Step 7 8 CONCLUSIONS 1 Stray current pickup and a negative potential shift on the foreign structure occurs at position F 2 Stray current discharge and a positive potential shift on the foreign structure occurs at position D 3 The potentials on the cathodically protected structure are altered by the presence of the foreign structure because the current distribution has ...

Страница 194: ...g properly when they may not be This could lead to failures leakage fires explosions and other hazardous situations You must know how instruments work and what errors are possible This means having a thorough understanding of the instruments you use and a knowledge of how the data should appear It means taking the time in the field to review your data and make certain they are correct Remember if ...

Страница 195: ...dic protection In the United States a majority of facilities containing hazardous materials are regulated by agencies enforcing the Code of Federal Regulations CFR Corrosion control requirements can be found in these parts of the code Natural Gas Pipelines 49 CFR Part 192 Subpart I Liquefied Natural Gas 49 CFR Part 193 Subpart G Hazardous Liquids 49 CFR Part 195 Subpart D Underground Storage Tanks...

Страница 196: ...ed to some large bare structure would measuring 10 amps at the rectifier still represent adequate protection on the structure of interest The answer is probably no The only way current output can be used as a measure of cathodic protection is if the system has remained unchanged since the potential survey was conducted Therefore all other measurements and tests that are done between potential surv...

Страница 197: ...t of an accident or lawsuit good records are essential to legal defense Data Sheets Data sheets are extremely important Data must be entered accurately and neatly Obviously it isn t always possible to keep neat data sheets particularly when working in inclement weather or in adverse or dirty conditions It may be necessary to copy the data onto fresh sheets after returning from the field Data sheet...

Страница 198: ...he latest data are then entered into the database Spreadsheets can also be generated showing test points that do not meet criteria These can be taken into the field for trouble shooting If you have been collecting data on a computer data logger the data can be entered directly into a computer Graphs and spreadsheets of data can be generated or the data can be downloaded into the company computer s...

Страница 199: ...essential Those responsible for updating facility maps will depend on your information to keep the maps current or to generate new maps Consequently as built drawings of corrosion control installations must be accurate Likewise if you are involved with repairs of structures or corrosion control components accurate information must be turned in Accuracy in your work documentation is just as importa...

Страница 200: ...ation crossings with foreign structures measurement of current flow on a pipe or a cable system Location Selection of locations for test stations is at the discretion of the design engineer It is preferable to err on the side of more test stations rather than fewer test stations When in doubt install a test station All major buried isolating fittings should be provided with suitable test stations ...

Страница 201: ...uld be clean dry and free of foreign materials at points of connection when the connections are made Test lead wire connections to a structure must be installed to remain mechanically secure and electrically conductive All test lead wire attachments and all test lead wires should be coated with electrically insulating material If the structure is coated the insulating material should be compatible...

Страница 202: ...ction check for stray current effects and on unprotected or partially protected pipelines to locate areas of active corrosion These test stations consist typically of two No 12 AWG insulated wires thermite welded to the pipe The test station head may be mounted on a post as shown in Figure 8 1 or it may be flush mounted as illustrated in Figure 8 2 Test Box Structure Test Wires Figure 8 1 Typical ...

Страница 203: ...are used it is good practice to cast a concrete collar around the top of the station to minimize loss of the test point IR Millivolt Drop Current Span These test stations are used to measure the magnitude and direction of current flow on a pipeline This information is useful in monitoring the spread of cathodic protection locating areas of bad coating on a pipeline and for finding areas where shor...

Страница 204: ... and also for measuring the current flow If the wires are not installed as designed erroneous reading will be obtained Should one or more wires be installed differently from the designed color scheme be certain the actual location of the wires is shown on as built sketches Pipe Casing The original intent of encased piping was for the casing to support dynamic loads caused by road traffic or trains...

Страница 205: ... may serve as one of the connections to the casing The two connections to the casing and carrier pipe are necessary to make casing to pipe resistance tests Foreign Line Crossing Underground structures such as pipelines or cables frequently cross each other or are in proximity to other facilities Where one or both structures have cathodic protection there may be an interaction between the two This ...

Страница 206: ...installed where an explosive or combustible environment is present Select locations where an electrical spark or discharge across the dielectric materials of the isolation device cannot produce ignition If an isolating joint must be installed in a area where the atmosphere or leakage of product could cause ignition if a spark occurred a grounding cell or surge protector must be installed across th...

Страница 207: ...Cathodic Protection Tester Course Manual NACE International 2000 07 01 04 ISOLATING UNION INSULATING GASKET PIPE END SEPARATOR ARMORED GASKET Figure 8 6 Isolating Coupling DI ELECTRIC GASKET DI ELECTRIC SPACER Figure 8 7 Isolating Union ...

Страница 208: ...tions structural members are isolated from supports using sheet type dielectric material and insulating sleeves and washers A properly isolated casing is shown in Figure 8 9 Vent Pipe Casing Insulating Spacers Insulating End Seal Secured to Pipe and Casing Dynamic Load Figure 8 9 Properly Isolated Casing Service conditions can vary greatly on different systems In selecting an electrical isolating ...

Страница 209: ...th other test stations containing wires of different colors it is important that the wires are placed as shown on the design drawings Pipeline Isolating Joint Test Station Typically No 12 AWG Test Wires No 8 AWG Wire for Bonding if Needed Figure 8 10 Isolation Joint Test Station Mitigation Bond Coupons Coupon test stations may contain one or both of two types of coupons polarization coupons and el...

Страница 210: ...l be zero Coupon test stations are used mainly on pipelines They should be installed so that the foot of the test station containing the coupons is within the pipeline backfill and at the depth of the bottom of the pipe The tube of the test station should be about 6 inches 15 cm from the side of the pipe to prevent shielding of cathodic protection current from the pipe Backfill around the pipe car...

Страница 211: ...e made Connections to the structure must remain mechanically secure and electrically conductive Wire should be installed with slack Damage to insulation should be avoided and repairs should be made if damage occurs Test leads should not be exposed to excessive heat or sunlight Thermite Exothermic Welding The most common method of attaching wires and cables to a structure is by exothermic welding a...

Страница 212: ...dards for the proper size charge The heat affected zone around the weld can be hardened and thus serve as a site for failure initiation This is particularly true for high yield point steels After the weld has partially cooled remove the welder and clean welding slag from the weld with a chipping hammer and wire brush Check the security of the weld by tapping with a hammer If the weld is not secure...

Страница 213: ...y made with a clamp and conductive epoxy Above ground connections may be made using lugs attached to the end of the wire or cable The lugs can then be bolted to the structure Coating All wire and cable attachments should be coated with electrically insulating material If the structure is coated the insulating material must be compatible with the coating on the structure It is especially important ...

Страница 214: ...ll material should be intact If the packaging container is torn or broken the anode should not be used Prepackaged anodes are supplied in waterproof containers the container must be removed before installation Prepackaged anodes should be kept dry during storage also they should not be pre wetted or soaked prior to installation The lead wire must be securely connected to the anode and should be in...

Страница 215: ...0 07 01 04 Structure Packaged Anode with Attached Insulated Lead Coated Powder Weld Connection Anode Lead Wire Figure 8 13 Single Prepackaged Vertical Anode Structure Anode Spacing Header Cable Insulated Connections Hole Depth Based on Soil Resistivity Figure 8 14 Multiple Prepackaged Vertical Anodes ...

Страница 216: ...r to backfilling with native soil Ribbon or Strip Anodes Ribbon type anodes can be trenched or plowed in with or without special backfill as specified These types of anodes are usually placed parallel to the section of pipeline to be protected See Figure 8 15 Strip Anode Protected Structure Insulated Wire Connection to Structure Special Galvanic Anode Backfill Earth Backfill Figure 8 15 Ribbon or ...

Страница 217: ...forcing mesh and pipe Figure 8 16 shows a typical bracelet anode installation Isolation Joint Sea Water Bracelet Anode Land Isolation Joint Typical Bracelet Anode Pipe Anode Metal Figure 8 16 Bracelet Anode Installation for Underwater Piping Offshore Anodes Offshore anodes for use in salt water are usually made of an aluminum alloy and may weigh up to about 1 400 pounds each The anodes are cast on...

Страница 218: ...ow The anodes may be cast on steel mounting strips or provided with a drilled hole for mounting on a stud bolt Impressed Current Groundbeds General Impressed current cathodic protection systems provide protection in a manner similar to galvanic anodes The difference is that in an impressed current system the current is supplied by an external source rather than by the galvanic action between the a...

Страница 219: ... anode must be rejected Anode backfill material should conform to specifications The backfill used around impressed current anodes is a carbonaceous material called coke breeze It serves two purposes First it enlarges the size of the anode thus reducing the anode to ground resistance Second it provides a uniform environment around the anode this greatly increases anode life since most of the curre...

Страница 220: ...d should be kept to a minimum Connections between header cable and conductors from anodes should be mechanically secure and electrically conductive If buried or submerged these connections must be sealed to prevent moisture penetration such that electrical isolation from the environment is ensured Care must be taken when installing direct burial cable to the anodes positive lead wire to avoid dama...

Страница 221: ...the plans This is important as the design is based on the resistivity of the soil and the depth of the water table If you are installing bare anodes place and thoroughly tamp the designed amount of coke breeze in the bottom of the hole Lower in the anode using support ropes do not lower the anode by the lead wire Center the anode in the hole and thoroughly tamp layers of coke breeze backfill to th...

Страница 222: ...one in a manner similar to that for a vertical anode installation The anode installation depends on the spacing of the anodes If the spacing is more than 10 feet it is usually best to excavate a separate hole for each anode With closer spacing it is usually more economical to dig one long trench for both the header cable and the anodes Bare or prepackaged anodes may be used They are installed usin...

Страница 223: ...ed in When plowing in cable be very careful not to damage the insulation Splice each anode lead wire to the header cable and carefully insulate the splice The splice is the most critical part of the installation and must be done properly Complete the installation by backfilling the header cable trench The cable should be laid on about three inches of sand or select backfill and after all splicing ...

Страница 224: ...he current A typical surface point installation is illustrated in Figure 8 21 _ Pipeline Power Source Distance between the structure and the anodes is a remote distance Negative Header Cable Impressed Current Anodes Positive Header Cable Figure 8 21 Surface Remote Groundbed Configuration Distributed Anode Configuration The distributed configuration is frequently used in complex areas to provide go...

Страница 225: ... Deep Anode Groundbed Configuration Deep anode installations are those where the anodes are installed in the bottom of a drilled hole The general layout is shown in Figure 8 24 The installation is begun by drilling a hole of the specified depth and diameter An electrical log is frequently made of the hole to determine areas of lowest resistivity This is done by measuring the resistance between a m...

Страница 226: ...h a fine coke breeze backfill The backfill and anodes constitute what is known as the active column or anode area The hole above the coke breeze may be filled with native soil gravel or simply left open The installation is completed by a length of surface casing which may have been installed at the beginning of the drilling with a cap on it The vent pipe terminates in a screened cap The anode lead...

Страница 227: ...the current flowing to each structure negative cables may be run to a junction box in which resistors can be placed Follow wiring diagrams carefully to ensure the negative circuits are connected to the correct terminals in the junction box Be careful not to damage the insulation on the negative cable Damage to the insulation is not as critical as it is on the positive cable because the negative ca...

Страница 228: ...rent Rating of the direct current power source should comply with construction specifications Care should be exercised in handling and installing Rectifiers or other power sources should be installed so that the possibility of being damaged or vandalized is minimized Wiring to rectifiers must comply with local and national electrical codes and the requirements of the utility supplying power An ext...

Страница 229: ...ed in detail previously in the sections on various types of groundbeds At the rectifier the anode cable is connected to the POSITIVE terminal and the structure is connected to the NEGATIVE terminal Be certain that this connection is made to the proper terminal Connecting a rectifier backward with the structure cable connected to the rectifier positive terminal will lead to rapid corrosion of the s...

Страница 230: ...tial measurements indicate inadequate protection or when some other malfunction occurs Electrical Isolation General A single metallic contact called a short circuit or short can destroy the effectiveness of an entire cathodic protection system The entire structure that is accidentally shorted to the protected facility becomes part of the system to be protected The severity of the problem depends o...

Страница 231: ...e system it may be possible to locate a short by tracing current flow In a distribution system where metallic service lines are electrically continuous with the mains a failed isolating fitting at the meter will cause a short circuit Cathodic protection current lost to other structures through this short will return to the main on the service line Using a clamp on ammeter service lines in the affe...

Страница 232: ...lly continuous paths Use caution when connecting and disconnecting this type of locators as high voltages may be involved Also do not use this type locator in an explosive atmosphere as a spark might cause ignition The transmitter is connected between the pipeline and a suitable ground such as a steel post probe bar etc If a service line is shorted the signal will travel up the line and across the...

Страница 233: ...side the casing A simple way of testing for a short is to measure the pipe to soil potential of both the casing and the pipeline This requires wires on both the pipeline and the casing If there are no wires on the casing the vent can be used instead There should be difference of anywhere from about 0 250 volt to 1 000 volt or more between the pipe to soil potentials of the casing and the pipeline ...

Страница 234: ...al pipe to soil potential should lead you to suspect a shorted casing If a metallic short exists the potential to a copper copper sulfate electrode will be essentially the same from the pipe and the casing test wires When a low resistance medium such as salt water brine or some other very low resistivity material gets into the annular space between the casing and the carrier pipe the manifestation...

Страница 235: ...ating joints flanges couplings monolithic joints etc should have test wires attached on either side of them to facilitate testing the effectiveness of the joint If no test wires are in place testing can be conducted if contact can be made to the pipe on either side of the joint Testing is similar to that for casings If the joint is effective the pipe to soil potential on either side of it should d...

Страница 236: ...d and AC is present a hum will be heard in the earphone If no AC is present and there is a DC potential difference across the fitting a scratching noise will be heard in the earphone when contact is made across a good fitting The earphone must be used with caution as high levels of AC may create excessively loud noises in the earphone Also if the structure to electrolyte potential happens to be th...

Страница 237: ...on of the anode itself will be accelerated This will lead to increased anode to earth resistance and decreased anode life Cable Breaks Cable breaks may be caused by third party damage from excavation or from discharge of current from positive cables If a splice has been poorly insulated or if the wire is exposed at breaks in the insulation rapid deterioration of the wire will ensue Such cable brea...

Страница 238: ...e to maintain protection therefore with less current during dry periods than otherwise Rectifiers Routine Maintenance Many problems with rectifiers can be prevented by regular maintenance The primary objective of a good rectifier maintenance program is the prevention of failures and prompt repair when failures do occur For energy pipelines regular monitoring is required by code If certain basic ob...

Страница 239: ...fore an actual outage Even with the best of maintenance programs however failures do occur Often basic step by step troubleshooting techniques can determine the cause of the outage For the following discussions only standard single phase manual adjustment type rectifiers are considered When checking rectifier outputs on a routine basis there are four basic cases of symptoms requiring investigation...

Страница 240: ...nent at a time to the circuit until the circuit breaker trips The short circuit must be the last component connected when the circuit breaker trips For example the transformer can be connected to the input circuit breaker with the tap adjustment bars removed The sequence of short circuit location is shown in Figure 9 9 Isolate shorted component by adding one component at a time AC Input Voltage Pr...

Страница 241: ...wer circuit resistance is indicated This could be due to system additions shorts to other underground structures or major coating damage If the current output significantly decreased a higher circuit resistance is indicated Some of the possible causes might include installation of inline isolators groundbed deterioration discontinuity due to disconnection of system component or gas blockage Season...

Страница 242: ...ociated with Petroleum Production RP0388 Impressed Current Cathodic Protection of Internal Submerged Surfaces of Steel Water Storage Tanks RP0177 Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems RP0575 Internal Cathodic Protection Systems in Oil Treating Vessels RP0193 External Cathodic Protection of On Grade Metallic Storage Tank Bottoms...

Страница 243: ... App 2 CP 1 Cathodic Protection Tester Course Manual NACE International 2000 07 01 04 TM0101 Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Storage Tanks ...

Страница 244: ...r further study and information Parker M Peattie E Pipeline Corrosion and Cathodic Protection Third Edition Gulf Publishing 1984 Romanoff M Underground Corrosion NACE International Reprint 1989 Cathodic Protection of Steel in Concrete P M Chase Editor NACE International Houston 1998 Practical Corrosion Control Methods for Gas Utility Piping Second Edition NACE International Houston 1995 Other Stan...

Страница 245: ...ards Association Standard Z662 Oil and gas Pipeline Systems Standard Z169 Cathodic Protection of Aluminum Canadian Gas Association Recommended Practice OCC 1 For the Control of Corrosion on Buried or Submerged Metallic Piping Systems Germany Standard DIN 30676 Cathodic Protection Japan The Overseas Coastal Area development Institute of Japan Corrosion Protection and Repair Manual for Port and Harb...

Страница 246: ...r Works Association AWWA Standard D104 Automatically Controlled Impressed Current Cathodic Protection for the Interior of Steel Water Tanks American Petroleum Institute API Recommended Practice 651 Cathodic Protection of Above Ground Petroleum Storage Tanks Recommended Practice 1632 Cathodic Protection of Underground Petroleum Storage Tanks and Piping Systems U S Government Code of Federal Regulat...

Страница 247: ...ze ALKYD Type of resin formed by the reaction of polyhydric alcohols and polybasic acids part of which is derived from saturated or unsaturated oils or fats ALLIGATORING Pronounced wide cracking over the surface of a coating which has the appearance of alligator hide AMPHOTERIC METAL A metal that is susceptible to corrosion in both acid and alkaline environments ANAEROBIC Free of air or uncombined...

Страница 248: ... a protective coating for a surface BLAST ANGLE 1 The angle of the blast nozzle with reference to the surface during abrasive blast cleaning 2 The angle of the abrasive particles propelled from a centrifugal blasting wheel with reference to the surface being abrasive blast cleaned BLOWDOWN 1 Injection of air or water under high pressure through a tube to the anode area for the purpose of purging t...

Страница 249: ...ode of an electrochemical cell CATION A positively charged ion that migrates through the electrolyte toward the cathode under the influence of a potential gradient CAVITATION The formation and rapid collapse of cavities or bubbles within a liquid which often results in damage to a material at the solid liquid interface under conditions of severe turbulent flow CELL See Electrochemical Cell CEMENTA...

Страница 250: ...tive force of which is caused by a difference in concentration of some component in the electrolyte This difference leads to the formation of discrete cathodic and anodic regions CONCENTRATION POLARIZATION That portion of polarization of a cell produced by concentration changes resulting from passage of current though the electrolyte CONDUCTIVE COATING 1 A coating that conducts electricity 2 An el...

Страница 251: ...g the intended properties of a coating or other material e g resin over a period of time CURING AGENT A chemical substance used for curing a coating or other material e g resin Also referred to as Hardener CURRENT 1 A flow of electric charge 2 The amount of electric charge flowing past a specified circuit point per unit time measured in the direction of net transport of positive charges In a metal...

Страница 252: ...n additional plate or thickness of steel used to provide extra strength at the point of anode attachment to an offshore platform DRAINAGE Conduction of electric current from an underground or submerged metallic structure by means of a metallic conductor DRIVING POTENTIAL Difference in potential between the anode and the steel structure DRYING OIL An oil capable of conversion from a liquid to a sol...

Страница 253: ... scale or corrosion products from a metal surface by subjecting the metal as an electrode to an electric current in an electrolytic bath ELECTROMOTIVE FORCE SERIES A list of elements arranged according to their standard electrode potentials the sign being positive for elements whose potentials are cathodic to hydrogen and negative for those anodic to hydrogen ELLIPSOMETRY An optical analytical tec...

Страница 254: ...cture of a material under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material FATIGUE STRENGTH The maximum stress that can be sustained for a specified number of cycles without failure FAULT CURRENT A current that flows from one conductor to ground or to another conductor due to an abnormal connection including an arc between the two A fault curre...

Страница 255: ...TION The formation of graphite in iron or steel usually from decomposition of iron carbide at elevated temperatures Should not be used as a term to describe graphitic corrosion GRIT Small particles of hard material e g iron steel or mineral with irregular shapes that are commonly used as an abrasive in abrasive blast cleaning GRIT BLASTING Abrasive blast cleaning using grit as the abrasive GROUNDB...

Страница 256: ...g fluid against a solid surface IMPRESSED CURRENT An electric current supplied by a device employing a power source that is external to the electrode system An example is direct current for cathodic protection IMPRESSED CURRENT ANODE An electrode suitable for use as an anode when connected to a source of impressed current which is generally composed of a substantially inert material that conducts ...

Страница 257: ...with the interior surface of a container used to protect the container against corrosion by its contents and or to protect the contents of the container from contamination by the container material LIQUID METAL CRACKING Cracking of a metal caused by contact with a liquid metal LONG LINE CURRENT Current though the earth between an anodic and a cathodic area that returns along an underground metalli...

Страница 258: ...a chemical species is assumed to vary linearly from the value in the bulk solution to the value at the electrode surface NOBLE The positive direction of electrode potential thus resembling noble metals such as gold and platinum NOBLE METAL 1 A metal that occurs commonly in nature in the free state 2 A metal or alloy whose corrosion products are formed with a small negative or a positive free energ...

Страница 259: ...sed for pickling PIGMENT A solid substance generally in fine powder form that is insoluble in the vehicle of a formulated coating material It is used to impart color or other specific physical or chemical properties to the coating PIPE TO ELECTROLYTE POTENTIAL See Structure to Electrolyte Potential PIPE TO SOIL POTENTIAL See Structure to Electrolyte Potential PITTING Localized corrosion of a metal...

Страница 260: ...ial pH Diagram POWER TOOL CLEANING Removal of loose rust loose mill scale and loose paint to degree specified by power tool chipping descaling sanding wire brushing and grinding See SSPC SP 3 PRECIPITATION HARDENING Hardening caused by the precipitation of a constituent from a supersaturated solid solution PRIMARY PASSIVE POTENTIAL The potential corresponding to the maximum active current density ...

Страница 261: ...SCOPE An electron optical device that images topographical details with maximum contrast and depth of field by the detection amplification and display of secondary electrons SENSITIZING HEAT TREATMENT A heat treatment whether accidental intentional or incidental as during welding that causes precipitation of constituents usually carbides at grain boundaries often causing the alloy to become suscep...

Страница 262: ...of one human step which is defined as one meter determined in the direction of maximum potential gradient STEPWISE CRACKING See Hydrogen Induced Cracking STRAY CURRENT Current through paths other than the intended circuit STRAY CURRENT CORROSION Corrosion resulting from current through paths other than the intended circuit e g by any extraneous current in the earth STRESS CORROSION CRACKING Cracki...

Страница 263: ...at of a coating system Also referred to as Finish Coat TOUCH POTENTIAL The potential difference between a metallic structure and a point on the earth s surface separated by a distance equal to the normal maximum horizontal reach of a human approximately 1 0 m 3 3 ft TRANSPASSIVE The noble region of potential where an electrode exhibits a higher than passive current density TUBERCULATION The format...

Страница 264: ...id condition that is formed to a desired shape by working rolling extruding forging etc usually at an elevated temperature X Y Z YIELD POINT The stress on a material at which the first significant permanent or plastic deformation occurs without an increase in stress In some materials particularly annealed low carbon steels there is a well defined yield point from the straight line defining the mod...

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Страница 269: ...ual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of material...

Страница 270: ... used in its entirety Using or citing only specific paragraphs or sections can lead to misinterpretation and misapplication of the recommendations and practices contained in this standard This standard does not designate practices for every specific situation because of the complexity of conditions to which buried or submerged piping systems are exposed This standard was originally published in 19...

Страница 271: ...r Cathodic Protection 12 Bibliography for Section 6 15 7 Design of Cathodic Protection Systems 17 Bibliography for Section 7 20 8 Installation of Cathodic Protection Systems 21 9 Control of Interference Currents 22 10 Operation and Maintenance of Cathodic Protection Systems 24 11 External Corrosion Control Records 25 References 27 Appendix A Interference Testing 28 Appendix B Method for Determinin...

Страница 272: ...ive or only partially effective sometimes exist Such conditions may include elevated temperatures disbonded coatings thermal insulating coatings shielding bacterial attack and unusual contaminants in the electrolyte Deviation from this standard may be warranted in specific situations provided that corrosion control personnel in responsible charge are able to demonstrate that the objectives express...

Страница 273: ...from an electrolyte Electroosmotic Effect Passage of a charged particle through a membrane under the influence of a voltage Soil or coatings may act as the membrane Electrolyte A chemical substance containing ions that migrate in an electric field For the purpose of this standard electrolyte refers to the soil or liquid adjacent to and in contact with a buried or submerged metallic piping system i...

Страница 274: ...etermination of Need for External Corrosion Control 3 1 Introduction 3 1 1 This section recommends practices for determining when an underground or submerged metallic piping system requires external corrosion control 3 1 2 Metallic structures buried or submerged are subject to corrosion Adequate corrosion control procedures should be adopted to ensure metal integrity for safe and economical operat...

Страница 275: ...hering or distribution system laterals 4 3 1 3 Inlet and outlet piping of in line measuring and or pressure regulating stations 4 3 1 4 Compressor or pumping stations either in the suction and discharge piping or in the main line immediately upstream and downstream from the station 4 3 1 5 Stray current areas 4 3 1 6 The junction of dissimilar metals 4 3 1 7 The termination of service line connect...

Страница 276: ...ng installations 4 5 1 2 Metallic structure crossings 4 5 1 3 Isolating joints 4 5 1 4 Waterway crossings 4 5 1 5 Bridge crossings 4 5 1 6 Valve stations 4 5 1 7 Galvanic anode installations 4 5 1 8 Road crossings 4 5 1 9 Stray current areas and 4 5 1 10 Rectifier installations 4 5 2 The span of pipe used for line current test stations should exclude 4 5 2 1 Foreign metallic structure crossings 4 ...

Страница 277: ...x may be required or self produced when brazing with some filler metals or soldering with some low melting point soft solders Because flux residues may cause corrosion they should be removed ________________________________________________________________________ Section 5 External Coatings 5 1 Introduction 5 1 1 This section recommends practices for selecting testing and evaluating handling stori...

Страница 278: ...ion is primarily by reference to other documents It is important that the latest revision of the pertinent reference be used 5 1 3 1 Table 1 is a listing of types of external coating systems showing the appropriate references for material specifications and recommended practices for application 5 1 3 2 Table 2 is a grouping of references for general use during installation and inspection regardles...

Страница 279: ...m may be due to unavailability of reference standards or lack of data B American National Standards Institute ANSI 1819 L Street NW Washington DC 20036 C American Water Works Association AWWA 6666 West Quincy Ave Denver CO 80235 D American Petroleum Institute API 1220 L St NW Washington DC 20005 E CSA International 178 Rexdale Blvd Toronto Ontario Canada M9W 1R3 F Deutsches Institut fur Normung DI...

Страница 280: ...stress Underground Corrosion34 ASTM D 427 35 Resistance to specific liquid not normally encountered in virgin soil ASTM D 543 36 Federal Test Standard C No 406A Method 7011 37 ASTM G 20 38 Resistance to thermal effects ASTM D 2304 39 ASTM D 2454 40 ASTM D 2485 41 Suitability of supplementary materials for joint coating and field repairs ASTM G 8 25 ASTM G 19 26 ASTM G 42 27 ASTM G 95 28 ASTM G 9 2...

Страница 281: ...NSI AWWA C 20 40 NACE Standard RP0375 11 NACE Standard MR0274 12 ANSI AWWA C 214 13 ANSI AWWA C 209 14 Peabody s Control of Pipeline Corrosion15 ANSI AWWA C 213 16 API RP 5L7 17 CSA Z245 20M 18 NACE Standard RP0190 19 NACE Standard RP0185 20 DIN 30 670 21 ANSI AWWA C 215 22 Special Requirements for Application of Coating Over the Ditch ANSI AWWA C 20 40 NACE Standard RP0375 11 NACE Standard MR0274...

Страница 282: ...data 5 2 2 Inspection 5 2 2 1 Qualified personnel should keep every phase of the coating operation and piping installation under surveillance 5 2 2 2 Surface preparation primer application coating thickness temperature bonding and other specific requirements should be checked periodically using suitable test procedures for conformance to specifications 5 2 2 3 The use of holiday detectors is recom...

Страница 283: ...performance tests are made to confirm the success of the previous steps The steps of the method are 1 laboratory tests 2 application under recommended practices 3 installation under recommended practices and 4 in service field performance tests If good results are obtained after five years only Steps 2 and 3 are required thereafter 5 3 3 1 1 Applicable sections of Tables 3 and 4 are recommended fo...

Страница 284: ...red for valid interpretation of this voltage measurement NOTE Consideration is understood to mean the application of sound engineering practice in determining the significance of voltage drops by methods such as 6 2 2 1 1 1 Measuring or calculating the voltage drop s 6 2 2 1 1 2 Reviewing the historical performance of the cathodic protection system 6 2 2 1 1 3 Evaluating the physical and electrica...

Страница 285: ...al to that required for the protection of the most anodic metal should be maintained 6 2 5 2 PRECAUTIONARY NOTE 6 2 5 2 1 Amphoteric materials that could be damaged by high alkalinity created by cathodic protection should be electrically isolated and separately protected 6 3 Other Considerations 6 3 1 Methods for determining voltage drop s shall be selected and applied using sound engineering prac...

Страница 286: ...Materials Protection 6 9 1967 p 33 Ewing S P Potential Measurements for Determination of Cathodic Protection Requirements CORROSION 7 12 1951 p 410 Haycock E W Current Requirements for Cathodic Protection of Oil Well Casing CORROSION 13 11 1957 p 767 Kuhn R C Cathodic Protection of Underground Pipelines Against Soil Corrosion American Petroleum Institute Proceedings IV 14 1953 p 153 McCollum B and...

Страница 287: ...n Dilute Aqueous Solutions CORROSION 7 5 1951 pp 156 160 Koybayaski T Effect of Environmental Factors on the Protective Potential of Steel Proceedings of the Fifth International Congress on Metallic Corrosion Houston TX NACE 1980 Krivian L Application of the Theory of Cathodic Protection to Practical Corrosion Systems British Corrosion Journal 19 1 1984 Kuhn R J Cathodic Protection on Texas Gas Sy...

Страница 288: ...roject PR 3 129 1983 Barlo T J et al Controlling Stress Corrosion Cracking by Cathodic Protection AGA Annual Report Project 3 164 1984 Parkins R N et al Hydrogen Gas Evolution From Cathodically Protected Surfaces CORROSION 41 1985 pp 389 397 Parkins R N and R R Fessler Stress Corrosion Cracking of High Pressure Gas Transmission Pipelines Materials in Engineering Applications 1 pp 80 96 Parkins R N...

Страница 289: ...urate with the required life of the protected structure or to provide for periodic rehabilitation of the anode system 7 2 4 To provide adequate allowance for anticipated changes in current requirements with time 7 2 5 To install anodes where the possibility of disturbance or damage is minimal and 7 2 6 To provide adequate monitoring facilities to test and evaluate the system performance 7 3 Inform...

Страница 290: ... a given current density from the anode surface in a specific environment Therefore for a given current output the anode life depends on the environment and anode material as well as the anode weight and the number of anodes in the cathodic protection system Established anode performance data may be used to calculate the probable deterioration rate 7 6 2 Data on the dimensions depth and configurat...

Страница 291: ...d K Kawate Design of Platinum Clad Wire Anodes for Impressed Current Protection Materials Performance 23 9 1984 pp 31 35 Collected Papers on Cathodic Protection Current Distribution Houston TX NACE 1989 Doremus G and J G Davis Marine Anodes The Old and New Materials Performance 6 1 1967 p 30 Dwight H B Calculations for Resistance to Ground Electrical Engineering 55 1936 p 1319 George P F J J Newpo...

Страница 292: ...n bands and the inner side of bracelet anode segments it should be inspected and if damaged repaired before the anodes are installed 8 4 2 Installing Anodes 8 4 2 1 Anodes should be installed according to construction specifications 8 4 2 2 Packaged galvanic anodes should be backfilled with appropriately compacted material When anodes and special chemical backfill are provided separately anodes sh...

Страница 293: ...ack should be left to avoid strain on all cables Backfill material around the cable should be free of rocks and foreign matter that might cause damage to the insulation when the cable is installed in a trench Cable can be installed by plowing if proper precautions are taken 8 5 2 8 If insulation integrity on the buried or submerged header cable including splices is not maintained this cable may fa...

Страница 294: ...om a foreign source such as the following 9 3 1 1 Pipe electrolyte potential changes on the affected structure caused by the foreign DC source 9 3 1 2 Changes in the line current magnitude or direction caused by the foreign DC source 9 3 1 3 Localized pitting in areas near or immediately adjacent to a foreign structure and 9 3 1 4 Damage to external coatings in a localized area near an anode bed o...

Страница 295: ...ent operation of cathodic protection systems 10 1 1 1 Electrical measurements and inspection are necessary to determine that protection has been established according to applicable criteria and that each part of the cathodic protection system is operating properly Conditions that affect protection are subject to change Correspondingly changes may be required in the cathodic protection system to ma...

Страница 296: ...ices 10 8 An electrical short circuit between a casing and carrier pipe can result in inadequate cathodic protection of the pipeline outside the casing due to reduction of protective current to the pipeline 10 8 1 When a short results in inadequate cathodic protection of the pipeline outside the casing steps must be taken to restore cathodic protection to a level required to meet the cathodic prot...

Страница 297: ...nent information and 11 5 2 1 3 Magnitude and polarity of drainage current 11 5 2 2 Details of reverse current switch 11 5 2 2 1 Location and name of companies 11 5 2 2 2 Type of switch or equivalent device and 11 5 2 2 3 Data showing effective operating adjustment 11 5 2 3 Details of other remedial measures 11 6 Records of surveys inspections and tests should be maintained to demonstrate that app...

Страница 298: ...Tape Coating Systems for the Exterior of Steel Water Pipelines Washington DC ANSI and Denver CO AWWA 14 ANSI AWWA C 209 latest revision Cold Applied Tape Coatings for the Exterior of Special Sections Connections and Fittings for Steel Water Pipelines Washington DC ANSI and Denver CO AWWA 15 Ronald Bianchetti ed Peabody s Control of Pipeline Corrosion 2 nd ed Houston TX NACE 2000 16 ANSI AWWA C 213...

Страница 299: ...st Method for Joints Fittings and Patches in Coated Pipelines West Conshohocken PA ASTM 43 ASTM G 55 latest revision Standard Test Method for Evaluating Pipeline Coating Patch Materials West Conshohocken PA ASTM 44 ASTM G 21 latest revision Standard Practice for Determining Resistance of Synthetic Polymetric Materials To Fungi West Conshohocken PA ASTM 45 Federal Test Standard No 406A Method 6091 ...

Страница 300: ...ecorded each time a portion of the line is excavated for any reason d Maintenance records detailing leak locations soil studies structure to electrolyte potential surveys surface potential surveys line current studies and wall thickness surveys used as a guide for locating areas of maximum corrosion e Statistical treatment of available data f Results of pressure testing Under certain conditions th...

Страница 301: ...RP0169 2002 32 NACE International ISBN 1 57590 035 1 ...

Страница 302: ...al volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials...

Страница 303: ...up T 10A 14 as Control of External Corrosion on Metallic Buried Partially Buried or Submerged Liquid Storage Systems The standard was revised in 1995 by Task Group T 10A 14 on Corrosion Control of Underground Storage Tank Systems a component of Unit Committee T 10A on Cathodic Protection It was revised in 2001 by TG 011 on Corrosion Control of Underground Storage Tank Systems by Cathodic Protectio...

Страница 304: ...ection Contents 1 General 1 2 Definitions 1 3 Cathodic Protection of New UST Systems 2 4 Cathodic Protection of Existing UST Systems 5 5 Criteria for Cathodic Protection 7 6 Cathodic Protection Design 8 7 Installation of Cathodic Protection Systems 11 8 Operation and Maintenance 13 9 References 15 Table 1 Conversion of Voltage Measurements to CSE Equivalents 8 _____________________________________...

Страница 305: ...mical cell at which oxidation occurs Electrons flow away from the anode in the external circuit Corrosion usually occurs and metal ions enter the solution at the anode Cathode The electrode of an electrochemical cell at which reduction is the principal reaction Electrons flow toward the cathode in the external circuit Cathodic Disbondment The destruction of adhesion between a coating and the coate...

Страница 306: ... a metal surface resulting from the passage of current directly to or from an electrode Polarized Potential The potential across the structure electrolyte interface that is the sum of the corrosion potential and the cathodic polarization Potential Gradient A change in the potential with respect to distance expressed in millivolts per unit of distance Reference Electrode An electrode whose open cir...

Страница 307: ...in lieu of CP 3 3 3 Several design parameters to be considered in selecting materials include a compatibility with the environment b compatibility with the product to be contained and c pressure and temperature 3 3 4 Metallic Piping 3 3 4 1 Metallic piping in contact with an electrolyte shall be protected from external corrosion through the application of coatings and CP 3 3 4 2 When available fac...

Страница 308: ...tank Isolation devices are normally installed at the manufacturing plant to eliminate installation errors and to be compatible with the product being stored The device used to ensure isolation is dependent on the type of connection being made to the tank Electrical isolation devices should only be used within their temperature and pressure limitations 3 5 1 1 Dielectric bushings are used for threa...

Страница 309: ...ng or electrical isolation of underground metallic structures should be considered Unnecessary electrical grounds should be considered for removal The method of electrical joining of piping tanks and associated underground structures including conduits may affect the CP design 4 2 4 Other Underground Structures The presence of additional underground structures unrelated to the tank system can affe...

Страница 310: ...centrated electrolytic corrosion can cause rapid deterioration of UST systems The presence of stray current is detected through the use of structure to soil potential current flow and potential gradient measurements 4 4 4 4 Current requirement Tests simulating the effects of a permanently installed CP system can be evaluated to determine the DC requirements for protection Temporary CP anodes are i...

Страница 311: ...tion 4 6 4 All UST systems may not be good candidates for a CP system If tests reveal critically damaged components consideration should be given to UST system replacement or removal from service ______________________________________________________________________________ Section 5 Criteria for Cathodic Protection 5 1 General 5 1 1 This section lists criteria for cathodic protection which when c...

Страница 312: ...peratures disbonded coatings shielding bacterial attack and unusual contaminants in the electrolyte 5 4 3 When structures that have dissimilar metals are protected a negative structure to soil potential voltage equal to that for protection of the most anodic metal should be maintained ______________________________________________________________________ Section 6 Cathodic Protection Design 6 1 Ge...

Страница 313: ...ture of 50 gypsum and 50 bentonite can be used with zinc anodes 6 2 4 6 The anodes should be supplied with adequate lead wire attached Lead wire shall be at least 4 mm 2 12 AWG 6 solid wire with TW thermoplastic insulated wire or equivalent oil and water resistant insulation 6 2 5 Galvanic Anode Installation 6 2 5 1 The CP anodes shall be installed around the tank in a manner that allows optimal c...

Страница 314: ...ent for achieving a given protection criterion can be determined by preliminary testing on existing structures through the use of temporary or simulated CP systems The current requirement can be estimated by calculating surface areas and applying a minimum protective current density based on experience and sound engineering judgment 6 3 3 7 Although there are many sources of DC for impressed curre...

Страница 315: ...easures and electrical grounding or internal linings should be considered in the design of the CP system for the UST system ______________________________________________________________________________ Section 7 Installation of Cathodic Protection Systems 7 1 General 7 1 1 All work shall be performed in accordance with all applicable health and safety regulations 7 1 2 Notifications 7 1 2 1 Coord...

Страница 316: ...l material around the cable shall be free of rocks and foreign matter that might damage the wire insulation when the wire is installed in a trench 7 3 6 2 Underground splices of header cable to the groundbed should be avoided Connections between header cable and conductors from anodes shall be mechanically secure and electrically conductive If buried or submerged all splices and connections must b...

Страница 317: ...unicipal or utility structures serving the facility at which the tank s is are located 7 4 7 Testing 7 4 7 1 The final operating levels of CP systems shall be established to achieve the appropriate CP criterion see Section 5 7 4 7 2 Documentation of all operating para meters such as initial base line data as built drawings operating currents locations of test facilities key monitoring locations eq...

Страница 318: ...tance The effectiveness of isolating devices and continuity bonds should be evaluated during the periodic surveys This can be accomplished by on site inspection or by evaluating corrosion test data 8 2 4 Test equipment used for obtaining each electrical value shall be of an appropriate type See Paragraph 4 4 4 Instruments and related equipment shall be maintained in good operating condition and ch...

Страница 319: ... Method West Conshohocken PA ASTM 10 ASTM G 51 latest revision Standard Test Method for Measuring pH of Soil for Use in Corrosion Testing West Conshohocken PA ASTM 11 ASTM D 512 latest revision Standard Test Methods for Chloride Ion in Water West Conshohocken PA ASTM 12 Method 4500 Standard Test Method for the Examination of Water and Waste Water in Water Quality Criteria 1972 A Report of the Comm...

Страница 320: ...l volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials ...

Страница 321: ...ive corrosion protection of structures by the presentation of reliable information Corrosion on offshore structures can be divided into three major areas the submerged zone the splash zone and the atmospheric zone The submerged zone also includes that portion of the structure below the mudline This standard does not include procedures for the control of internal corrosion of wells piping and assoc...

Страница 322: ...Bibliography 33 Appendix A Typical Design Parameters for Offshore Petroleum Production 35 Appendix B Energy Capabilities and Consumption Rates of Various Commercial Galvanic Anodes Available for Cathodic Protection of Offshore Structures 37 Appendix C Consumption Rates in Seawater of Various Commercial Types of Impressed Current Anodes Available for Cathodic Protection of Offshore Structures 38 Ap...

Страница 323: ...orrosion Related Terms 3 Anchor Pattern The irregular peak and valley pattern cre ated on the surface of steel by the effect of blasting media hitting the steel at high velocity Anode The electrode of an electrochemical cell at which oxidation occurs Electrons flow away from the anode in the external circuit Corrosion usually occurs and metal ions en ter the solution at the anode Atmospheric Zone ...

Страница 324: ...icle J Tube A curved tubular conduit designed and installed on a structure to support and guide one or more pipeline risers or cables Mill Scale The oxide layer formed during hot fabrication or heat treatment of metals Mudline The ocean floor at the location of interest Padeye A lifting or connection point that is shaped like an eye and is used to accommodate hooks tackle or slings Pipeline A cond...

Страница 325: ...cture in the splash zone to protect it from anticipated corrosion and or erosion caused by ice and or high velocity silt laden water ________________________________________________________________________ Section 3 Structural Design for Corrosion Control 3 1 Introduction 3 1 1 This section recommends design features that simplify corrosion control of structural steel in the at mospheric splash an...

Страница 326: ...ructures in which fatigue or corro sion fatigue is a critical factor welds may be stress relieved to reduce the likelihood of fatigue or corro sion fatigue failures in the heat affected zone HAZ This may be important in cold water envi ronments where polarization tends to develop slowly or in partially shielded areas on a structure See API 1 RP 2A WSD 4 and RP 2A LRFD 5 3 4 1 3 All weld joints sho...

Страница 327: ...stalled in pull tubes or J tubes To restrict contact with seawater and at mospheric oxygen the pull tube annulus should be sealed at the above water end with a suitable nonwick ing packing after the lines have been pulled into posi tion 3 5 5 Floating production units have mooring systems intended for long term service Special considerations are required for the corrosion protection of these moor ...

Страница 328: ... it includes the voltage drop across the steel water interface but does not include the voltage drop in the water see Paragraphs 4 5 1 1 and 4 6 1 4 3 1 3 The potential at which corrosion is con trolled is a function of the temperature and the environment In waters exposed to the air and at typical ambient temperatures the criteria listed in Paragraphs 4 3 1 1 and 4 3 1 2 have proved to be satisfa...

Страница 329: ...o the members of the structure 4 5 1 5 A number of permanent reference elec trodes may be mounted on a structure While the exact electrode locations are known the informa tion obtained from these electrodes is limited to the adjacent structure surfaces Although this limitation holds true for any potential measurement this method can provide a repro ducible basis for comparing potentials at differe...

Страница 330: ... tected steel and increase the current required to pro duce protective potentials Depolarization is less likely to be a problem for well polarized structures with well formed calcareous deposits or for coated steel struc tures 4 6 3 Marine growth may mask the true condition of the steel surface during a visual inspection it must be removed from the areas being inspected All potential measurements ...

Страница 331: ...deration should be given to the following 5 1 2 1 Selection and specification of materials equipment and installation practices that ensure the safe installation and operation of the CP sys tem 5 1 2 2 Specification of materials and installation practices in conformance with applicable codes regulations and standards that may be issued by the following a Structure operator b NACE International c A...

Страница 332: ... oper ating experience a Protective current requirements to meet appli cable criterion or criteria see Paragraph 5 6 b Water resistivity considering possible strati fication of water properties c Changes in construction specifications d Electrical isolation and or continuity e Interference currents see Section 7 f Performance history of previous or existing CP systems in the same general environme...

Страница 333: ...ction with galvanic anodes and selection of anode material can be established by consideration of the fol lowing see Appendixes a Resistivity of the electrolyte b Anode to structure potential when structure is at protected level c Freedom from mechanical damage in installation launching and operation d Useful life expectancy of anode material and e Structure weight and structural limitations 5 5 5...

Страница 334: ... waters with higher current density requirements in shield ed areas such as large conductor bundles and or on structures with extended design lives 5 6 3 2 The current demand of a coated structure increases with time as the coating deteriorates Enough CP capacity should be provided to main tain protection as the coating deteriorates Current demand may increase more or less rapidly than a visual in...

Страница 335: ...from 0 75 to almost 1 0 For standoff type anodes utilization factors of 0 90 to 0 95 are common For bracelet anodes val ues of 0 75 to 0 90 may be used 5 8 Special Mechanical and Electrical Considerations 5 8 1 The performance of a CP system is dependent on the ability of the various components to withstand the physical stresses to which they are subjected The type of system the various components...

Страница 336: ...t repeating members below water The anodes should be lowered through the casings which protect the anode lead wires and should be allowed to extend below a termination fitting at the bottom of each casing This method provides a means of anode retrieval or replacement using the anode cable without diver assistance Marine growth or corrosion scale may make anode retrieval difficult b Anodes with ess...

Страница 337: ...g hazard of insulating de vices should be recognized and considered in the de sign and location of such devices ________________________________________________________________________ Section 6 Installation of Cathodic Protection Systems 6 1 Introduction 6 1 1 This section recommends procedures for instal ling CP systems in accordance with design consider ations outlined in Section 5 6 2 Construc...

Страница 338: ...ifiers shall comply with any applicable regulatory codes and with the oper ator s specifications An external disconnect switch in the AC wiring to the rectifier should be provided The rectifier case shall be properly grounded Connecting the negative to the case prevents in advertent reversal of polarity 6 5 2 3 On thermoelectric generators a reverse current device should be installed to prevent ga...

Страница 339: ...us damage to structures with complete penetration of the submerged member as a result of welding current interference The following measures should be implemented to prevent interfer ence current during welding operations from a barge moored alongside during construction a All welding machines should be electrically isolated from the barge and b the grounding cable from each machine should be conn...

Страница 340: ...c sheets plastic pipe sleeves and coated standoffs or supports for im pressed current anodes 8 5 Design Considerations 8 5 1 Electrochemical reactions at the anode and cathode produce corrosives and gases that may attack the dielectric shield or cause disbonding by gas forma tion under the dielectric shield Materials selected should be suitable for the intended service 8 5 2 For proper performance...

Страница 341: ...ing life of the anode system should be reassessed based on a survey of potentials and remaining anode mass and the need for a retrofit assessed If the original CP design was conservative the actual remaining anode life may be well in excess of two years This actual remaining anode life can be used in scheduling future CP surveys on the same five year two year basis Local regulatory requirements th...

Страница 342: ...orrosion and wear during the life of the struc ture Wear plates are usually 13 to 19 mm 0 50 to 0 75 in thick 10 3 2 Wear plates are needed because damage can occur to coatings or sheathings used in the splash zone 10 3 3 In addition to providing a corrosion allowance wear plates add stiffness and strength thereby provid ing greater impact resistance 10 3 4 Wear plates are usually coated or sheath...

Страница 343: ...ied to 200 µm 8 mils and sealed with a silicone sealer have been used in the splash zone Good surface preparation and cleanliness are essential The coating should be applied in a minimum of two passes The sealer seals the por osity of the coating and enhances service life and appearance U S Military Specification MIL STD 2138 12 offers guidelines for application and quality control 10 4 6 2 Coatin...

Страница 344: ...pheric zone of fixed offshore structures 12 2 General 12 2 1 The objectives of surface preparation for steel in the atmospheric zone are to provide the necessary degree of cleanliness and the specified anchor pattern required for the designed coating system 12 2 2 Automated blast cleaning machines are econo mically desirable as a means of preparing plate beams and tubular members prior to fabricat...

Страница 345: ... 4 SSPC SP 7 18 states that a brush off blast cleaned surface when viewed with out magnification shall be free of all visible oil grease dirt dust loose mill scale loose rust and loose coating Tightly adherent mill scale rust and coating may remain on the surface Mill scale rust and coating are considered tightly adherent if they cannot be removed by lifting with a dull putty knife 12 3 1 5 A cros...

Страница 346: ...gh only high performance protective coating systems should be specified Proper application and performance require ments of these systems demand rigorous surface prep aration see Section 12 and skilled craftsmanship in coating application and inspection see Section 14 This can be achieved only through the enforcement of detailed and complete job specifications 13 2 2 Proper application of high per...

Страница 347: ...resistant films 13 3 3 2 Solvent Deposited or Thermoplastic Type Coatings These materials include vinyl acrylics vinyls or chlorinated rubbers These coatings dry by the evaporation of solvents which distinguishes them from epoxies polyesters and other chemically cured coatings The change from a liquid to a solid state is not accompanied by any chemical change This mode of drying permits coating ap...

Страница 348: ...terials should comply with the coating manufacturer s recommendation or if independently purchased they should be of compositions approved by the coating manufacturer 13 5 1 2 Single supplier responsibility should be maintained by using primers intermediates and finish coatings from the same supplier 13 5 1 3 All coating materials should be thorough ly agitated prior to application If there is set...

Страница 349: ... to be performed depends on many vari ables including the following items a Extent and location of corrosion damage on the structure b Stress or loading of the affected structure members c Danger of spills and leaks from production piping and vessels d Cost of recoating work including set up charge e Cost of deferred production and any equipment downtime during coating operations f Safety of perso...

Страница 350: ...topcoats for better chem ical and salt water exposure 13 10 5 All galvanizing shall be applied in accordance with ASTM A 123 33 and A 153 34 ________________________________________________________________________ Section 14 Coatings Inspection 14 1 Introduction 14 1 1 This section provides inspection procedures to verify compliance with the governing coating specific ations 14 1 2 The inspection ...

Страница 351: ...ssure gauge is required to mea sure actual pressure at the nozzle 14 4 3 A surface profile comparator can be used to determine surface profile or anchor pattern Replica tapes as described in NACE Standard RP0287 35 can also be used to measure the anchor pattern 14 4 4 A set of NACE surface preparation standards for comparing surface preparation is recommended see Paragraph 12 3 14 4 5 A humidity g...

Страница 352: ...1 1 Design criteria used design life assumed anode output and consumption rate and current density requirements 15 2 1 2 Number size composition and if known the manufacturer cost and supplier of the anodes 15 2 1 3 Location of each anode the method of attachment and date of installation If anodes are installed during structure construction the date of actual setting of the structure offshore shou...

Страница 353: ... 3 5 Maintenance The following should be re corded 15 3 5 1 Date of each touch up and recoating job and the reason for the job such as post erection post drilling routine maintenance etc 15 3 5 2 Total area recoated the surface prepara tion and coating system used and the inspection procedure 15 3 5 3 Name of the coating contractor labor materials and equipment used and the total cost of the job _...

Страница 354: ...pparatus for UV Exposure of Nonmetallic Materials West Conshohocken PA ASTM 26 ASTM G 155 latest revision Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non Metallic Materials West Conshohocken PA ASTM 27 ASTM D 2247 latest revision Standard Practice for Testing Water Resistance of Coatings in 100 Relative Humidity West Conshohocken PA ASTM 28 ASTM D 522 latest revision ...

Страница 355: ...heeler Zinc Anodes in Sea water Journal of Applied Chemistry 6 10 1956 p 415 Davis J G G L Doremus and F W Graham The Influ ence of Environment on Corrosion and Cathodic Pro tection Journal of Petroleum Technology 3 1972 pp 323 328 Designing Impressed Current Cathodic Protection Systems With Durco Anodes 2nd ed Dayton Ohio The Duriron Company Inc 1970 Doremus G L and J G Davis Marine Anodes The Ol...

Страница 356: ...e Structures MP 26 11 1987 pp 22 27 Townley D W Unified Design Equation for Offshore Cath odic Protection CORROSION 97 paper no 473 Houston TX NACE 1997 Uhlig H H Corrosion Handbook New York NY John Wiley and Sons Inc 1948 Vennett R M and R R Matthews Stratification of Water Properties Along the Louisiana Coast and Its Influence on Cathodic Protection Systems MP 14 7 1975 pp 31 39 Wang W and W H H...

Страница 357: ... result in similar long term current densities The rela tionship between design slope and maintenance current density can be established by on site experiments or by re view of experience at that location Current density is strongly dependent on water temperature For deep water structures different design values should be used for different temperature zones To optimize the de sign the structure s...

Страница 358: ... values and ratings based on average conditions remote from river discharge B Water resistivities are a function of both chlorinity and temperature In the Corrosion Handbook37 by H H Uhlig the following resistivities are given for chlorinities of 19 and 20 parts per thousand ppt C In ordinary seawater a current density less than the design value suffices to hold the structure at protective potenti...

Страница 359: ...onsider that anode capacity may be less than is predicted from short term testing Segregation of some minor alloys and or impurities during cooling can alter the galvanic properties of the anode mat erial Any potential segregation is more pronounced on the interior portions of larger anodes because of slower cooling after casting Any anode material must be capable of a sufficient driving voltage t...

Страница 360: ...his figure can increase when current density is extremely high and or in low salinity waters ________________________________________________________________________ Appendix D Typical Method for Calculation of Galvanic Anode Current Output Using Initial Maintenance and Final Current Densities This method has been commonly employed in the past for CP design so practitioners tend to be familiar wit...

Страница 361: ...ce mA m 110 Density Current Initial N 2 2 D3 The initial current density 110 mA m2 is obtained from Table A1 In order to meet the second current density requirement for the structure which determines the number of kg lb of anode material required to protect the structure over the 20 year design life use Equation D4 anodes 99 mA A 1 000 kg anode 330 hr kg A 2 750 hr yr 8 760 yr 20 Life m 9 300 Area...

Страница 362: ... ohms ρ resistivity of water in ohm cm A area of exposed anode in cm 2 ________________________________________________________________________ Appendix E Typical Method for Calculation of Galvanic Anode Current Output Using Design Slope and Maintenance Current Density This method is proposed as an alternative to calculation of the initial mean and final current densities Appendix D It affords the...

Страница 363: ...odes needed as shown in Equation E4 1 total A A N E4 where N total number of anodes 9 Determine whether the design slope based on final conditions 90 anode consumption is acceptable but using the value of Ra for an expended anode Ra of an ex pended anode can be calculated using the same procedure described to determine the current output of an expended anode in Equations D5 and D6 The long term po...

Страница 364: ...retations by individual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with...

Страница 365: ...is intended for use by engineers water utilities tank erectors and other contractors and owner operators of steel water storage tanks This standard was originally prepared in 1988 by Task Group T 7L 1 a component of Unit Committee T 7L on Cathodic Protection The task group was composed of corrosion engineers and others experienced in the design installation and maintenance of impressed current cat...

Страница 366: ...age Tanks Contents 1 General 1 2 Definitions 1 3 Determination of the Need for Cathodic Protection 2 4 Design of Impressed Current Cathodic Protection Systems 3 5 Installation of Impressed Current Cathodic Protection Systems 5 6 Criteria for Cathodic Protection and Measurement Procedures 6 7 Automatic Impressed Current Systems 7 8 Operation and Maintenance 8 References 9 __________________________...

Страница 367: ...tion Any applicable regulations such as those from the U S Environmental Protection Agency EPA 1 and ANSI 2 NSF 3 612 should be checked In the United States all materials in contact with potable water or exposed to the interior of potable water tanks must be classified in accordance with ANSI NSF 61 1 8 The provisions of this standard should be applied under the direction of a competent corrosion ...

Страница 368: ...nt IR Drop The voltage across a resistance in accordance with Ohm s Law Polarization The change from the open circuit potential as a result of current across the electrode electrolyte interface Reference Electrode An electrode whose open circuit potential is constant under similar conditions of measurement which is used for measuring the relative potentials of other electrodes Resistivity A measur...

Страница 369: ...sed current system the following items must be considered a Design of the tank accessibility crevices shielded areas b Present and future condition of the coating and the generic type of coating employed c Voltage and current capacity of the power source d Impressed current anode material and configuration e Impressed current anode life and ease of replacement f Type of power source control g Hard...

Страница 370: ... uncoated surface under the same conditions 4 3 2 3 Current capacity for a coated tank should be selected so that there is sufficient capacity available even after considerable coating deterioration typically 10 to 20 for a 20 year system design life 4 3 3 Output Voltage Capacity 4 3 3 1 The output voltage capacity is governed by the current requirement and the circuit resistance The voltage capac...

Страница 371: ...d installed with applicable codes The use of conduit for insulated impressed current anode wiring inside the tank is not necessary 4 5 5 Permanent reference electrodes lead wire should be brought to the rectifier location to facilitate readings Reference cell wiring shall not be routed through the same conduit used for system DC wiring ______________________________________________________________...

Страница 372: ...ductive These connections must be sealed to prevent moisture penetration ________________________________________________________________________ Section 6 Criteria for Cathodic Protection and Measurement Procedures 6 1 Introduction 6 1 1 This section describes the criteria for impressed current cathodic protection along with measurement techniques which when followed provide virtually complete co...

Страница 373: ... 7 1 2 The use of manually controlled cathodic protection systems is acceptable and may be desirable depending on specific structure conditions as determined by the design corrosion engineer 7 2 General 7 2 1 Cathodic protection current requirements for protection in accordance with the criteria in Paragraph 6 2 can vary with coating deterioration accumulation of polarization films temperature wat...

Страница 374: ...critically corrosive situations when the tank has previously suffered extensive metal loss as a result of corrosion or when there are highly variable conditions 8 3 1 5 Remote monitoring equipment can aid in the collection of the data reduce monitoring costs and allow for more frequent real time data collection during a variety of tank operations such as filling and sudden drops in water level 8 3...

Страница 375: ...tment 8 4 2 2 Operational information about frequency of draining cleaning and filling should be recorded 8 4 3 Cathodic Protection System 8 4 3 1 Complete information about the installation and design should be recorded including a Power source capacity both AC and DC b Number and configuration of impressed current anodes c Impressed current anode material and design life d Wiring and anode suspe...

Страница 376: ...dividual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of mat...

Страница 377: ...ween 600 ohms and 10 000 ohms 1 A reasonable safe value for the purpose of estimating body currents is 1 500 ohms hand to hand or hand to foot In other work by K S Gelges and C F Dalziel on muscular contraction the inability to release contact would occur in the range of 6 to 20 milliamperes for adult males 2 Ten milliamperes hand to hand or hand to foot is generally established as the absolute ma...

Страница 378: ...ems Contents 1 General 1 2 Definitions 1 3 Exposures and Effects of Alternating Current and Lightning 3 4 Design Considerations for Protective Devices 4 5 Personnel Protection 10 6 AC and Corrosion Control Considerations 13 7 Special Considerations in Operation and Maintenance of Cathodic Protection and Safety Systems 15 References 16 Bibliography 17 Appendix A Wire Gauge Conversions 17 __________...

Страница 379: ... systems AC Power System The components associated with the generation transmission and distribution of alternating current Affected Structure Pipes cables conduits or other metallic structures exposed to the effects of alternating current and or lightning Bond A low impedance connection usually metallic provided for electrical continuity Breakdown Potential A voltage potential in excess of the ra...

Страница 380: ...tance Reclosing Procedure A procedure which normally takes place automatically whereby the circuit breaker system protecting a transmission line generator etc recloses one or more times after it has tripped because of abnormal conditions such as surges faults lightning strikes etc Reference Electrode An electrode whose open circuit potential is constant under similar conditions of measurement whic...

Страница 381: ...many factors including the overall geometric configuration of the structures involved the magnitude of the current in the power circuit and any current imbalance If the currents in a three phase power system are equal balanced and the affected structure is equidistant from each of the conductors the total induced voltage is zero This however is seldom the case and induced AC voltage is usually pre...

Страница 382: ...ermanent grounding mats bonded to the structure may be used at valves metallic vents cathodic protection test stations and other aboveground metallic and nonmetallic appurtenances where electrical contact with the affected structure is possible 4 3 2 Grounding mats should be large enough to extend through and beyond the entire area on which people may be standing when contacting the affected struc...

Страница 383: ...stributed grounding system and the structure the test lead connection should be made in an accessible dead front test box When galvanic anodes are used as part of a grounding system the useful life of the electrode material should be considered Dissipation of the anode material increases the grounding system resistance 4 7 Casings 4 7 1 Bare or poorly coated casings may be deliberately connected t...

Страница 384: ...10 1 The coordinated selection and installation of electrolytic grounding cells polarization cells 2 5 V DC maximum threshold or other devices between the affected structure and suitable grounds should be considered where arcing and induced AC potentials could develop These devices may eliminate or greatly reduce the induced potentials resulting during normal operation or surge conditions and also...

Страница 385: ...RP0177 2000 NACE International 7 Figure 1 Approximate current required to raise the temperature of stranded annealed soft drawn copper cable 684ºC 1 232ºF above an ambient temperature of 20ºC 68ºF ...

Страница 386: ... ICEA Publication P 32 382 copyright 1994 7 ____________________________ A To calculate this formula using metric units change A to metric values as indicated in Table A1 Appendix A I Short circuit current in amperes A Conductor area in circular mils t Time of short circuit in seconds T1 Maximum operating temperature of 75q qC T2 Maximum short circuit temperature of 150q qC ...

Страница 387: ...n ICEA Publication P 32 382 copyright 1994 ____________________________ A To calculate this formula using metric units change A to metric values as indicated in Table A1 Appendix A I Short circuit current in amperes A Conductor area in circular mils t Time of short circuit in seconds T1 Maximum operating temperature of 90q qC T2 Maximum short circuit temperature of 250q qC ...

Страница 388: ...ection 5 Personnel Protection 5 1 Introduction 5 1 1 This section recommends practices that contribute to the safety of people who during construction system operation corrosion survey or cathodic protection maintenance of metallic structures may be exposed to the hazards of AC potentials on those structures The possibility of hazards to personnel during construction and system operation because o...

Страница 389: ...nful shock Muscular control lost cannot let go 20 to 50 mA Painful shock Severe muscular contractions breathing difficult 50 to 100 mA possible Ventricular fibrillation Death will result if prompt cardiac massage not administered 100 to 200 mA certain Defibrillator shock must be applied to restore normal heartbeat Breathing probably stopped 200 mA and over Severe burns Severe muscular contractions...

Страница 390: ... used for bonding or for connections to grounding facilities shall have good mechanical strength and adequate conductivity As a minimum copper conductor 35 mm 2 0 054 in 2 No 2 AWG stranded welding cable or equivalent is recommended See Table 1 and Figures 1 2 and 3 for cable sizes adequate to conduct the anticipated fault current safely 5 3 6 Temporary cable connections to the affected structure ...

Страница 391: ...ablished prior to removing the unit for service 5 4 3 Testing of cathodic protection systems under the influence of AC potentials must be performed by or under the supervision of a qualified person In all cases tests to detect AC potentials shall be performed first and the structure shall be treated as a live electrical conductor until proven otherwise Cathodic protection records should include th...

Страница 392: ...vides only an indication of current flow and cannot be readily converted to amperes because of the AC impedance characteristics of ferromagnetic materials A clamp on AC ammeter may be used to measure current in temporary or permanent bond connections 6 2 3 3 Indications of AC power levels on affected structures may be obtained by temporarily bonding the structure to an adequate ground and measurin...

Страница 393: ...1 Cathodic protection rectifiers that are subject to damage by adjacent electric utility systems should be checked for proper operation at more frequent intervals than rectifiers not subject to electric system influence 7 2 2 Cathodic protection testing or work of similar nature must not be performed on a structure subject to influence by an adjacent electric utility system during a period of thun...

Страница 394: ...la Societé Francaise Des Electriciens October 1947 2 C F Dalziel The Effects of Electrical Shock on Man Transactions on Medical Electronics PGME 5 Institute of Radio Engineers 7 1956 Available from IEEE 3 IEEE Standard 80 latest revision Guide for Safety in AC Substation Grounding New York NY Institute of Electrical and Electronics Engineers Inc 4 NFPA 8 Standard 70 latest revision National Electr...

Страница 395: ...isual Presentation Prepared by Work Group T 10B 5a Houston TX NACE 1983 Wakelin R G R A Gummow and S M Segall AC Corrosion Case Histories Field Testing and Mitigation CORROSION 98 paper no 565 Houston TX NACE 1998 Westinghouse Transmission and Distribution Handbook Newark NJ Westinghouse Electric Corp Relay Instrument Div 1950 _______________________________________________________________________...

Страница 396: ...eers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials equipmen...

Страница 397: ...with applicable codes including OSHA 1 regulations This standard was originally prepared in 1975 by Task Group T 1E 6 a component of Unit Committee T 1E on Cathodic Protection of Oilfield Equipment and revised in 1995 by Task Group T 1E 11 It was reaffirmed in 2001 by Specific Technology Group STG 35 on Pipelines Tanks and Well Casings This STG is composed of corrosion consultants corrosion engine...

Страница 398: ...tems in Oil Treating Vessels Contents 1 General 1 2 Definitions 1 3 Determination of Need for Cathodic Protection 2 4 Design and Selection of Cathodic Protection System 2 5 Anode Installation 4 6 Reference Electrode Entrance 5 7 Criteria for Protection 5 8 Monitoring Records and Maintenance 5 9 Safety 6 References 6 ________________________________________________________________________ ...

Страница 399: ... material usually a metal that results from a reaction with its environment Corrosion Engineer A person who by reason of knowledge of the physical sciences and the principles of engineering and mathematics acquired by professional education and related practical experience is qualified to engage in the practice of corrosion control Current Density The current to or from a unit area of an electrode...

Страница 400: ...gn Criteria 4 1 1 The design of a vessel s cathodic protection system depends on the internal configuration of the vessel Selection of the appropriate system depends on factors such as initial cost maintenance type and condition of coatings if any power availability and cost and system life 4 1 2 Vertical cylindrical vessels containing no baffles compartments firetubes etc are usually protected wi...

Страница 401: ...r composition and temperature and selective electrochemical attack 4 2 2 Impressed current systems have greater flexibility if high current demand is anticipated 4 2 2 1 Impressed current systems can be used in any water but are usually the most practical in high resistivity waters where an appreciable amount of current is required to achieve protection 4 2 2 2 Impressed current systems typically ...

Страница 402: ...ed to distribute current uniformly to the vessel walls and bottom and at a depth that assures that some anodes are submerged regardless of water level Either type of anode galvanic or impressed current can be installed in this manner 5 1 2 Impressed current anodes must be suspended from a suitable hanger deck mount properly isolated to prevent grounding of the lead wire to the vessel 5 1 3 Galvani...

Страница 403: ...of cathodic protection Coupons must be electrically connected to the vessel wall Coupon weight loss measurements are used to determine the effectiveness of protection ________________________________________________________________________ Section 8 Monitoring Records and Maintenance 8 1 Monitoring 8 1 1 Operating personnel should visually inspect surfaces under cathodic protection whenever vessel...

Страница 404: ...he cable to anode connections in impressed current systems shall never be disconnected nor shall the anode be removed while the rectifier is in operation 9 3 Usual precautions to prevent fire or explosion must be taken before a cathodic protection system can be installed or repaired in a vessel handling water mixed with oil or gas 9 4 CAUTION Usual precautions must be taken when monitoring or perf...

Страница 405: ... individual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of ...

Страница 406: ...new on grade carbon steel storage tanks upgrade cathodic protection on existing storage tanks or install new cathodic protection on existing storage tanks This NACE standard was originally prepared by Task Group T 10A 20 a component of NACE Unit Committee T 10A on Cathodic Protection in 1993 It was technically revised by Task Group 013 in 2001 Task Group 013 is administered by Specific Technology ...

Страница 407: ...arriers 12 9 Installation Considerations 15 10 Energizing and Testing 17 11 Operation and Maintenance of Cathodic Protection Systems 18 12 Recordkeeping 19 References 19 Bibliography 20 Figures Figure 1 Soil Resistivity Testing Four Pin Method 3 Figure 2 Temporary Groundbed for Current Requirement Testing 5 Figure 3 Stray Current Corrosion 6 Figure 4 Vertically Drilled Anode CP System 9 Figure 5 A...

Страница 408: ...ical cell Cell See Electrochemical Cell Current Density The current to or from a unit area of an electrode surface Deep Groundbed One or more anodes installed vertically at a nominal depth of 15 m 50 ft or more below the earth s surface in a drilled hole for the purpose of supplying cathodic protection Differential Aeration Cell An electrochemical cell the electromotive force of which is due to a ...

Страница 409: ...her the tank has been jacked up leveled etc k Unusual environmental conditions l Operating history of the tank including leak information internal and external m Maintenance history of the tank n Containment membranes impervious linings o Secondary bottoms p Water table and site drainage information q Liquid levels maintained in the tank r Nearby foreign structures s Type of liquid stored t Operat...

Страница 410: ... include a Tank to earth resistance tests b Tank to grounding system resistance and potential tests c Tank to electrolyte potential tests d Electrical continuity tests for mechanical joints in interconnecting piping systems e Electrical leakage tests for isolating fittings installed in interconnecting piping and between the tanks and safety ground conductors 3 3 3 Cathodic Protection Type Current ...

Страница 411: ...ter than those required under natural conditions Possible sources of stray current include DC operated rail systems and mining operations other cathodic protection systems welding equipment and high voltage direct current HVDC transmission systems 3 3 4 1 1 Field tests to determine whether stray currents are a concern include those that provide tank to electrolyte and structure to electrolyte pote...

Страница 412: ...trol the corrosion of an on grade carbon steel storage tank bottom in contact with an electrolyte The selection of a particular criterion for achieving this objective depends in part on prior experience with similar tank bottoms and environments in which the criterion has been successfully used 4 2 2 The criteria in Paragraph 4 3 were developed through laboratory experiments or were determined emp...

Страница 413: ...emonstrate that cathodic protection has been achieved one or more of the following must apply to the system 4 3 1 1 A negative cathodic potential of at least 850 mV with the cathodic protection current applied This potential shall be measured with respect to a saturated copper copper sulfate reference electrode CSE contacting the electrolyte Consideration must be given to voltage drops other than ...

Страница 414: ...el storage tanks 5 2 Cathodic Protection Objectives and System Characteristics 5 2 1 The major objectives for the design of a cathodic protection system are a To protect the tank bottom from soil side corrosion b To provide sufficient and uniformly distributed current c To provide a design life commensurate with the design life of the tank bottom or to provide for periodic anode replacement d To m...

Страница 415: ...tem Alternately a current density can be used for design purposes based on a current density successfully used at the same facility or at a facility with similar characteristics 5 4 2 For design purposes current requirements on new or proposed tank bottoms may be established by calculating surface areas and applying a protective current density based on the size of the tank the electrochemical cha...

Страница 416: ...________ Section 6 Design Considerations for Impressed Current Cathodic Protection 6 1 This section recommends procedures and considerations that specifically apply to the design of impressed current cathodic protection systems for on grade carbon steel storage tank bottoms 6 2 Impressed Current Anode Systems 6 2 1 Impressed current anodes shall be connected with an insulated cable either singular...

Страница 417: ...ance with NACE Standard RP0572 4 6 2 4 Anode materials have varying rates of deterioration when discharging current Therefore for a given output the anode life depends on the environment anode material anode weight and the number of anodes in the cathodic protection system Established anode performance data should be used to calculate the probable life of the system Sand Sand Deep Groundbed Anodes...

Страница 418: ...ns Bonding cables must be used when parting piping joints ________________________________________________________________________ Section 7 Design Considerations for Galvanic Anode Cathodic Protection 7 1 This section describes the factors that should be considered in the design of external corrosion protection of on grade carbon steel storage tank bottoms without secondary containment that are p...

Страница 419: ...arrier can prevent the flow of cathodic protection current from anodes located outside the barrier envelope Anodes must be placed between the barrier and the carbon steel tank bottom so that current flows to the surfaces requiring protection If release prevention barriers made of conductive material are used with a cathodic protection system with anodes outside the space contained by the barrier t...

Страница 420: ...pical new tank or double bottom impressed current anode design 8 4 1 3 Due to the depolarizing effect of oxidation by products typically chlorine oxygen or carbon dioxide migrating from the anode to the steel cathode the current density for protection with an impressed current system may be higher than that required for a galvanic anode system 8 4 2 Adequate space must be provided between the two ...

Страница 421: ...RP0193 2001 14 NACE International Figure 9 Typical Double Bottom Galvanic Anode Design Figure 10 Typical New Tank or Double Bottom Impressed Current Anode Design Tank Shell Tank Shell Wire Anode ...

Страница 422: ...ced in the soil under the tank bottom or positioned inside the perforated reference electrode access piping Reference electrodes placed inside access piping should be surrounded with a backfill material designed to provide contact between the electrode and the electrolyte outside the pipe If practical provisions should be made for future verification of all stationary reference electrode potential...

Страница 423: ...ation or junction box in a galvanic system may be equipped with calibrated resistors shunts in connections between the anodes and the tank to measure the anode current output and thus the estimated anode life Shunts are typically rated between 0 001 and 0 1 ohm 9 5 6 The test station or junction box should be clearly marked and accessible for future monitoring of the tank bottom and if possible sh...

Страница 424: ...als measured are representative of the entire tank bottom The potential measured at the perimeter of a large diameter tank does not represent the potential at the center of the tank 10 4 Current Adjustment 10 4 1 The desired operating level of a cathodic protection system must often be determined by a series of trial tests at various operating levels The specific operating level depends on the cri...

Страница 425: ... Making more frequent surveys of the system may be desirable in critically corrosive environments or where highly variable conditions are present The accuracy of stationary reference electrodes should be evaluated during these surveys The effectiveness of isolating fittings and continuity bonds should also be evaluated during the periodic surveys 11 2 3 All sources of impressed current should be c...

Страница 426: ...ection systems should be kept including the following information a Tabulations of bimonthly readings of impressed current power source b Reports of periodic or annual inspections c All adjustments repairs and additions d Costs of maintenance e Test equipment calibration records ________________________________________________________________________ References 1 ASTM G 57 latest revision Standard...

Страница 427: ... Metallic Piping Systems Houston TX NACE Pearson J M Electrical Instruments and Measurements in Cathodic Protection Corrosion 3 11 1947 p 549 Underground Corrosion National Institute for Standards and Technology 3 Circular 579 April 1957 pp 180 186 Available from the U S Dept of Commerce Clearinghouse 4 ___________________________ 3 National Institute for Standards and Technology NIST Gaithersburg...

Страница 428: ...reclude the issuance of interpretations by individual volunteers Users of this NACE standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE standard may not necessarily address all potential health and safety problems or environmental hazards associated wi...

Страница 429: ...not be practical for relatively large tanks This standard was originally prepared in 1996 by NACE Task Group TG T 7L 1 a component of Unit Committee T 7L on Cathodic Protection It was revised in 2004 by TG 284 on Cathodic Protection Galvanic Anode for Internal Submerged Surfaces of Steel Water Storage Tanks Review of NACE Standard RP0196 Galvanic Anode Cathodic Protection of Internal Submerged Sur...

Страница 430: ...l Submerged Surfaces of Steel Water Storage Tanks Contents 1 General 1 2 Definitions 1 3 Determination of Need for CP 2 4 Design of Galvanic Anode CP System 3 5 Installation of Galvanic Anode CP Systems 5 6 Criteria for CP 6 7 Operation and Maintenance 7 References 9 Table 1 Typical Galvanic Anode Materials and Characteristics 5 _____________________________________________________________________...

Страница 431: ...onal education and related practical experience is qualified to practice corrosion control including CP for water storage tanks Such persons may be Registered Professional Engineers or persons recognized as being qualified or certified as Corrosion Specialists or CP Specialists by NACE if their professional activities include suitable experience in corrosion control and CP 1 9 This standard may no...

Страница 432: ... length of a substance with uniform cross section 2 A measure of the ability of an electrolyte e g soil to resist the flow of electric charge e g CP current Resistivity data are used to design a groundbed for a CP system For the purpose of this standard resistivity is a measure of the ability of the water to resist the flow of current Water resistivity is used in the design of the galvanic anode C...

Страница 433: ...de CP systems for steel water storage tanks are outlined in this section 4 1 2 In the design of a galvanic anode system the following items must be considered a Health and safety b Compliance with local and national regulations 3 c Design of the tank accessibility crevices shielded areas baffles and compartments d Present and future condition of the coating and the generic type of coating employed...

Страница 434: ...he galvanic anode and on which the anode can be supported either vertically or horizontally 4 3 3 Galvanic Anode Arrangement 4 3 3 1 Galvanic anodes shall be arranged to provide as close to uniform current density as is practical When uniform current density cannot be achieved the total system current output must be increased to compensate by adding anodes or adjusting the system current output th...

Страница 435: ...y high strength compression connector or welding 4 3 6 4 All cables located inside the tank shall be rated for use in submerged conditions 4 3 6 5 For bolted and riveted tanks electrical continuity of all joining components must be achieved if these components are to receive CP ________________________________________________________________________ Section 5 Installation of Galvanic Anode CP Syst...

Страница 436: ..._____ Section 6 Criteria for CP 6 1 Introduction 6 1 1 The purpose of this section is to list the criteria for CP which when complied with either separately or collectively indicate that adequate CP of submerged portions of steel water tank interiors has been achieved 6 2 General 6 2 1 The objective of using galvanic anode CP is to control the corrosion of submerged portions of steel water tank in...

Страница 437: ...eration 7 2 1 After the system has been allowed to reach a stable polarization level the system shall be tested and adjusted to obtain the potentials indicated in Paragraph 6 3 7 2 2 For a galvanic anode CP system to control corrosion effectively it must be kept in continuous operation and provide the desired tank to water potential 7 3 Maintenance 7 3 1 Maintenance should be conducted under the d...

Страница 438: ... be examined to determine consumption When galvanic anode remaining life is less than the time to the next inspection anodes should be scheduled for replacement 7 5 Records 7 5 1 Tank Information 7 5 1 1 Complete information and the history of the tank itself should be recorded including a Dimensions and capacity b Tank erection and CP contractor c Date of erection d Coupon type configuration and ...

Страница 439: ...__ References 1 NACE Standard RP0388 latest revision Impressed Current Cathodic Protection of Internal Submerged Surfaces of Carbon Steel Water Storage Tanks Houston TX NACE 2 J B Bushman D H Kroon Cathodic Protection of Water Storage Tanks AWWA 1 Journal 76 1 1984 3 ANSI 2 NSF 3 61 Drinking Water System Components Health Effects Ann Arbor MI NSF International 4 R L Benedict ed Anode Resistance Fu...

Страница 440: ...ce of interpretations by individual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards ass...

Страница 441: ...by Task Group T 11 1d 4 This standard was originally prepared in 1990 by NACE Task Group T 3K 2 a component of Unit Committee T 3K on Corrosion and Other Deterioration Phenomena Associated with Concrete It was revised by Work Group T 11 1a formerly T 3K 2 in 2000 and is published by NACE International under the auspices of Group Committee T 11 on Corrosion and Deterioration of the Infrastructure T...

Страница 442: ...ontents 1 General 1 2 Criteria 1 3 Design of Impressed Current Cathodic Protection Systems 4 4 Installation Practices 6 5 Energizing and System Adjustment 6 6 Operation and Maintenance of Impressed Current Cathodic Protection Systems 7 7 Records 8 References 9 Bibliography 10 Appendix A Glossary of Terms 10 Appendix B Additional Information Useful for Design 11 Appendix C Test Equipment 12 _______...

Страница 443: ...dic protection NOTE For further information see a glossary of terms in Appendix A 1 3 Scope and Limitations 1 3 1 The provisions of this standard should be applied under the direction of a registered Professional Engineer or a person certified by NACE International as a Corrosion Specialist or certified as a Cathodic Protection Specialist The person s professional experience should include suitabl...

Страница 444: ...ons responsible for corrosion control be limited to these criteria if it can be demonstrated by other means that corrosion control has been achieved A combination of criteria may be used for a single structure 2 3 1 100 mV Polarization Development Decay 2 3 1 1 A minimum of 100 mV of polarization should be achieved at the most anodic location in each 50 m 2 500 ft 2 area or zone or at artificially...

Страница 445: ...st period to ensure that these conditions have not affected the readings The period for potential decay or polarization development is largely determined by oxygen availability at the reinforcement surface and is not a reflection of the efficiency of the cathodic protection system Longer periods of decay or polarization development are required for FIGURE 1 Typical Polarization Decay Curve POTENTI...

Страница 446: ...aterials such as platinum clad or electroplated on niobium or titanium conductive polymers carbon based or metallic coatings mixed metal oxide coated titanium conductive grouts and conductive asphaltic concrete 3 3 Information useful for selecting and designing an impressed current cathodic protection system includes 3 3 1 As built drawings of the concrete structure 3 3 2 Condition survey in accor...

Страница 447: ...ode system length anode spacing and size and conductor size in order to achieve the criteria set forth in Section 2 3 5 4 The proximity of anodes to other metallic embedments such as form ties chairs tie wire embedment plates and electrical conduit shall be determined Minimum depth of cover over the reinforcement must be maintained in accordance with the manufacturer s recommendations If the minim...

Страница 448: ...m Adjustment 5 1 This section presents recommended procedures for the energizing and adjustment of an impressed current cathodic protection system 5 2 Component Installation Inspection 5 2 1 Prior to energizing the AC service to the cathodic protection system shall be inspected for compliance with the National Electrical Code and such local codes and ordinances that may be applicable or in force I...

Страница 449: ...ect protection are subject to change with time Corresponding changes may be required in the cathodic protection system to maintain protection Periodic measurements and inspections are necessary to detect changes in the cathodic protection system Conditions in which operating experience indicates that testing and inspections need to be made more frequently than recommended herein can exist 6 1 2 Ad...

Страница 450: ...l the physical design and test data accumulated on the installation 7 2 The following information if collected during the design survey should be made an integral part of the record 7 2 1 Results of chloride in concrete tests and other chemical and physical analyses 7 2 2 Delamination survey data 7 2 3 Depth of cover data 7 2 4 Reinforcement and permanent reference electrode potential data 7 2 5 E...

Страница 451: ...rogress by NACE Task Group T 11 1d Criteria for Cathodic Protection of Prestressed Concrete Structures Houston TX NACE 5 ASTM E 105 latest revision Standard Practice for Probability Sampling of Materials West Conshohocken PA ASTM 6 ANSI ASQC Z1 4 latest revision Sampling Procedures and Tables for Inspection by Attributes Milwaukee WI ASQC 7 ASTM C 876 latest revision Test Method for Half Cell Pote...

Страница 452: ...cations for Advances in the Field of Cathodic Protection Corrosion Science 36 12 1994 pp 2193 2209 SHRP S 337 Cathodic Protection of Reinforced Concrete Bridge Elements A State of the Art Report Wachington DC National Research Council 1993 Solving Rebar Corrosion Problems in Concrete Houston TX NACE 1983 SP 1 latest revision Concrete Primer F McMillian L Tuthill eds Farmington Hills MI ACI Interna...

Страница 453: ...unteracted to a desired degree in reinforced concrete the prestress is commonly introduced by tensioning the tendons Rectifier An electrical device for converting alternating current to direct current Reference Electrode An electrode whose open circuit potential is constant under similar conditions of measurement which is used for measuring the relative potentials of other electrodes Step and Touc...

Страница 454: ...________________________________________________________________ Appendix C Test Equipment Equipment used for evaluating corrosion and corrosion control of reinforced concrete can include the following 1 pH testing equipment 2 Resistivity meter AC type 3 Sulfate and chloride test equipment 4 DC voltmeter with variable input impedance 5 Multimeter AC DC volts ohms amps 10 megohm minimum 6 Portable ...

Страница 455: ...dividual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of mat...

Страница 456: ... of its use External loading of the carrier pipe has now been eliminated by the installation of heavy wall casing pipe and isolating spacers are used to prevent electrical contact between the casing and the carrier pipe End seals are used to keep mud and water out of the annular space between the carrier pipe and casing This standard was prepared by NACE Task Group T 10A 18 a component of Unit Com...

Страница 457: ...oring 5 References 6 Bibliography 6 Appendix A Typical Casing Filling Procedures 7 Appendix B Monitoring Techniques 8 Figures Figure B1 Potential Survey Measurement 8 Figure B2 Internal Resistance Test 9 Figure B3 Four Wire IR Drop Test Calibrating the Inside Terminals 12 Figure B4 Establishing a Circuit for a Four Wire IR Drop Test U S End 12 Figure B5 Four Wire IR Drop Test Establishing the Circ...

Страница 458: ... s leg Electrolytic Contact Ionic contact between two metallic structures via an electrolyte Holiday Testing Electrical testing of a coating to locate imperfections holidays Isolator or Spacer A dielectric device specifically designed to electrically isolate a carrier pipe from a casing and provide support for the carrier pipe Metallic Short Direct or indirect metallic contact between two metallic...

Страница 459: ... be handled and stored in a manner that minimizes coating and end damage Lifting shall be accomplished utilizing approved slings wide belts or appropriate end hooks If skids are utilized to support the pipe or casing padding material shall be used to prevent coating damage In addition the skids shall be removed upon completion of the installation 4 3 New Casing Installation 4 3 1 Cased crossings a...

Страница 460: ...rrier pipe during installation if not installed properly if the casing is bent or if the installation is out of line Inadequate support of the pipe allows the pipe to sag and make metallic contact with the casing The inspector should be aware of this potential problem during the installation 4 4 5 The cased crossing shall be tested in accordance with Section 5 to confirm that the casing and carrie...

Страница 461: ...erial shall be used to protect seam areas on the carrier pipe while the split casing halves are being properly supported The installation of new vent piping test leads and backfilling shall be performed in accordance with Paragraphs 4 3 3 4 5 and 4 6 respectively _______________________________________________________________________ Section 5 Maintenance And Repair 5 1 Actions necessary in the co...

Страница 462: ...One or more of the following basic electrical test methods should be used to monitor pipelines and casings on an annual basis Procedures are provided in Appendix B 6 2 1 Potential Survey This method is the initial test conducted to identify a shorted casing A voltmeter and a reference electrode are used to conduct the test 6 2 2 Internal Resistance This method indicates whether direct metal to met...

Страница 463: ... surveys should be done at the frequency required by the applicable code or in accordance with the operating company s practice _______________________________________________________________________ References 1 NACE Standard RP0169 latest revision Control of External Corrosion on Underground or Submerged Metallic Piping Systems Houston TX NACE 2 NACE Standard RP0286 latest revision The Electrica...

Страница 464: ...mastic pump with inductor plate is required An environmentally acceptable corrosion inhibitor may be poured down the fill vent pipe just prior to the installation of the casing filler Hoses shall be connected to the fill vent pipe The filler material shall be pumped into the casing until it is full If the casing contains water the casing filler shall be installed through the vent pipe at the high ...

Страница 465: ...ectly over the pipeline and near the end of the casing see Figure B1 2 Measuring casing potential One lead of the voltmeter shall be connected to the casing by way of the vent test lead or probe bar The other lead of the voltmeter shall be connected to the reference electrode which shall be placed at the same location as where the pipeline potential was taken see Figure B1 VOLT METER CARRIER PIPE ...

Страница 466: ...g vent T1 may be used The other lead shall be connected in series with the ammeter to the carrier pipe at T4 3 A constant current shall be applied between terminals T3 and T4 The current I shall be measured in amperes 4 The pipe to casing potential shall be measured between terminals T1 and T2 with the current applied VOLT METER CARRIER PIPE CASING GROUND LEVEL T1 T2 T3 T4 VENT PIPE BATTERY AM MET...

Страница 467: ...esistance the presence of an electrical short is indicated Example 2 A pipe to casing potential of 0 100 V is measured between terminals T1 and T2 After 1 70 A of current is applied between terminals T3 and T4 a pipe to casing potential of 0 302 V is measured between terminals T1 and T2 Pipe to Casing Potential Before Current is Applied 0 100 V Pipe to Casing Potential After Current is Applied 0 3...

Страница 468: ...d until factors are within 5 Note Equation B5 can be used to convert ohms to amperes mV resistance to conductance 1 000 A mV m Ω µ m 1 B5 2 Establishing the Circuit Upstream U S End a The circuit shall be established by connecting the negative terminal of the battery to T2 pipe lead and connecting T1 upstream vent to the positive terminal of the battery See Figure B4 b The inside terminals T3 and ...

Страница 469: ... VARIABLE RESISTOR TEST LEAD TEST LEAD VENT PIPE VENT PIPE b FIGURE B3 Four Wire IR Drop Test Calibrating the Inside Terminals VOLT METER CARRIER PIPE CASING GROUND LEVEL T1 T3 T4 BATTERY AM METER T2 PIPE LEAD a D S End U S End b VENT PIPE VARIABLE RESISTOR TEST LEAD FIGURE B4 Establishing a Circuit for a Four Wire IR Drop Test U S End ...

Страница 470: ...of the insulated probe bar and test leads is required to obtain contact for measurement of the IR drop on T3 and T4 or erroneous readings may result If more than one metal to metal contact exists this test may not accurately identify the location of the shorts All safety precautions shall be implemented when lead acid batteries are used Example 1 A pipe casing is 76 2 cm 30 0 in in diameter 12 2 m...

Страница 471: ...e B1 Determine the length from the positive inside terminal to the short The resulting equation is a modified version of Equation B5 ohms m 10 6 x 9 48 A x 9 00 10 3 mV x 1 035 Length Length 12 1 m B5 Because the length from the positive inside terminal to the short is equal to the entire length of the pipe this test indicates that the short is at the downstream end Step 3 Measure the voltage with...

Страница 472: ... pipeline The same potential measurement if taken while the cathodic protection rectifier is being cycled may provide additional information for evaluation of casing isolation conditions Procedure This technique may be applied to a pipeline survey using an interrupter in the most influential cathodic protection rectifier unit The location of the cycling rectifier selected shall be sufficiently rem...

Страница 473: ...oil potential also shifts in a positive direction usually by about the same magnitude as the casing As subsequent steps are taken the pipe to soil potential largely tracks the positively shifting potentials of the casing B Casing Clear If there is no short the pipe to soil potential may shift in a positive direction by only a few millivolts whereas there will be a dramatic shift in the casing to s...

Страница 474: ...2 00 Amps 0 1350 0 1000 0 035 Conclusion Casing is shorted NOTE During this test current is being discharged from the casing and this could result in creating an interference condition with other structures 6 Use of Pipe Cable Locator The presence and location of a pipe to casing metallic contact may also be approximated by following a low power audio or radio signal pipe locator trace set between...

Страница 475: ...95 0 313 33 84 22 74 31 1 9 49 32 120 105 38 0 6882 2 258 6 8822 119 22 21 91 8 625 8 18 0 322 42 49 28 55 24 8 7 56 40 33 132 3 0 6882 2 258 6 8822 119 22 21 91 8 625 9 53 0 375 49 17 33 04 21 4 6 53 46 66 153 1 0 6882 2 258 6 8822 119 22 27 31 10 75 6 4 0 25 41 73 28 04 25 7 7 39 606 129 94 0 8577 2 814 8 578 148 6 27 31 10 75 9 27 0 365 60 24 40 48 17 5 5 33 57 174 187 58 0 8577 2 814 8 578 148...

Страница 476: ...1 780 202 69 1 756 5 760 17 560 304 11 59 373 23 375 9 53 0 375 137 2 92 19 10 2 3 11 98 079 321 78 1 865 6 120 18 650 323 11 59 373 23 375 11 9 0 469 170 7 114 7 8 20 2 50 122 07 400 49 1 865 6 120 18 650 323 11 61 24 7 14 0 281 106 0 71 25 13 2 4 02 75 801 248 69 1 915 6 283 19 150 331 75 61 24 7 92 0 312 117 7 79 06 11 9 3 62 84 110 275 95 1 915 6 283 19 150 331 75 61 24 8 74 0 344 129 2 86 85 ...

Страница 477: ...43 6 10 1 86 164 29 539 02 2 873 9 425 28 727 497 63 91 36 11 9 0 469 264 72 177 88 5 28 1 61 189 24 620 87 2 873 9 425 28 727 497 63 91 36 10 0 50 282 12 189 57 4 95 1 51 201 68 661 68 2 873 9 425 28 727 497 63 91 36 14 3 0 562 316 82 212 89 4 43 1 35 226 49 743 07 2 873 9 425 28 727 497 63 91 36 15 9 0 625 351 41 236 13 3 97 1 21 251 21 824 19 2 873 9 425 28 727 497 63 91 36 17 4 0 687 385 86 25...

Страница 478: ...erpretations by individual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated w...

Страница 479: ...s provided in this standard were compiled from information submitted by committee members and others with expertise on the subject Variations or other techniques not included may be equally effective The complexity and diversity of environmental conditions may require the use of other techniques Appendix A contains information on the common types use and maintenance of reference electrodes Appendi...

Страница 480: ...eel and Cast Iron Piping With Cathodic Protection Applied 10 9 Test Method 2 Negative 850 mV Polarized Pipe to Electrolyte Potential of Steel and Cast Iron Piping 11 10 Test Method 3 100 mV Cathodic Polarization of Steel Cast Iron Aluminum and Copper Piping 13 References 17 Bibliography 17 Appendix A Reference Electrodes 18 Appendix B Net Protective Current 19 Appendix C Using Coupons to Determine...

Страница 481: ...thodic protection testing and having a chemical composition approximating that of the pipe The coupon size should be small to avoid excessive current drain on the cathodic protection system Coating A liquid liquefiable or mastic composition that after application to a surface is converted into a solid protective decorative or functional adherent film Conductor A bare or insulated material suitable...

Страница 482: ...e An electrode whose open circuit potential is constant under similar conditions of measurement which is used for measuring the relative potentials of other electrodes Resistance to Electrolyte The resistance of a structure to the surrounding electrolyte Reverse Current Switch A device that prevents the reversal of direct current through a metallic conductor Shielding Preventing or diverting the c...

Страница 483: ..._________________________________________________________ Section 4 Instrumentation and Measurement Guidelines 4 1 Cathodic protection electrical measurements require proper selection and use of instruments Pipe to electrolyte potential voltage drop potential difference and similar measurements require instruments that have appropriate voltage ranges The user should know the capabilities and limit...

Страница 484: ...ative terminal One instrument test lead is usually black in color and the other red The black test lead is connected to the negative terminal of the instrument and the red lead to the positive terminal 5 2 Voltage measurements should be made using the lowest practicable range on the instrument A voltage measurement is more accurate when it is measured in the upper two thirds of a range selected fo...

Страница 485: ...ferent potentials e Shielding f Effects of other structures on the measurements g History of corrosion leaks and repairs h Location of impressed current anodes i Unknown inaccessible or direct connected galvanic anodes j Location of isolation devices including high resistance pipe connections and compression couplings k Presence of electrolytes such as unusual corrosives chemical spills extreme so...

Страница 486: ...e potential does not vary Pipe potential is the variable Pipe 0 1 Figure 1a Instrument Connection Pipe Test Lead Voltmeter Direction of meter current Reference Electrode C L Electrode potential does not vary Pipe potential is the variable Pipe DC VOLT COM 0 850 Figure 1b Alternative Instrument Connection FIGURE 1 Instrument Connections ...

Страница 487: ...tions of insufficient quantity or saturation only laboratory grade chemicals and distilled water if water is required should be used in a reference electrode b Reference electrode plug not sufficiently porous to provide a conductive contact to the electrolyte c Porous plug contaminated by asphalt oil or other foreign materials d High resistance contact between reference electrode and dry or frozen...

Страница 488: ...gital meter internal impedance is not several orders of magnitude higher than the sum of the other resistances in the measurement circuit 7 1 2 Pipe Current flowing within the pipe wall creates a voltage drop This voltage drop and the direction of the current shall be considered when the reference electrode is not near the pipe connection and significant current is conducted by the pipe Considerat...

Страница 489: ... TO ELECTROLYTE MEASUREMENT WHEN CURRENT IS TOWARD PIPE CONTACT Figure 2a Correction When Pipeline Current Flows Toward Pipe Test Connection _ PIPE METAL VOLTAGE DROP PIPELINE CURRENT PIPE TEST CONNECTION REFERENCE ELECTRODE VOLTMETER SUBTRACT PIPE METAL VOLTAGE DROP FROM PIPE TO ELECTROLYTE MEASUREMENT WHEN CURRENT IS AWAY FROM PIPE CONTACT Figure 2b Correction When Pipeline Current Flows Away fr...

Страница 490: ...included in this measurement these drops shall be considered as discussed in Paragraph 8 6 8 3 Comparison with Other Methods 8 3 1 Advantages a Minimal equipment personnel and vehicles are required and b Less time is required to make measurements 8 3 2 Disadvantages a Potential measured includes voltage drops other than those across the pipe metal electrolyte interface and b Meeting the requiremen...

Страница 491: ...Method 2 describes the most commonly used test method to satisfy this criterion see Paragraph 9 2 This method uses current interruption to determine whether cathodic protection is adequate at the test site according to the criterion 9 2 Scope This method uses an interrupter s to eliminate the cathodic protection system voltage drop from the pipe to electrolyte potential measurement for comparison ...

Страница 492: ...l significant DC sources protecting the pipe at the test site and place in operation with a synchronized and or known off and on cycle The off cycle should be kept as short as possible but still long enough to read a polarized pipe to electrolyte potential after any spike as shown in Figure 3a has collapsed 9 6 3 Determine the location of the site to be tested Selection of a site may be based on a...

Страница 493: ...g equipment h Parallel coated pipelines electrically connected and polarized to different potentials i Uninterrupted current sources j Unintentional connections to other structures or bonds to mitigate interference and k Long line currents 10 2 2 3 The magnitude and duration of a voltage spike caused by current interruption can vary but the duration is typically within 0 5 second After the current...

Страница 494: ...arization Decay Figure 3a Polarization Decay Normal Operation On Potential Current Interruption Instant Off Potential Polarization Cathodic Protection Applied Corrosion Potential Polarizing Line Figure 3b Polarization Formation FIGURE 3 Cathodic Polarization Curves 1 200 1 100 1 000 900 800 700 600 500 1 100 1 000 900 800 700 600 500 400 ...

Страница 495: ...ff potentials and their polarities with respect to the reference electrode 10 2 5 6 1 The instant off pipe to electrolyte potential is the baseline potential from which the polarization decay is calculated 10 2 5 7 Turn off sufficient cathodic protection current sources that influence the pipe at the test site until at least 100 mV cathodic polarization decay has been attained 10 2 5 7 1 Continue ...

Страница 496: ...hms An analog instrument with an internal resistance of 100 000 ohms per volt may be adequate in certain circumstances in which the circuit resistance is low A potentiometer circuit may be necessary in other instances 10 3 4 2 Two color coded meter leads with clips for connection to the pipeline and reference electrode 10 3 4 3 Sufficient current interrupters to interrupt influential cathodic prot...

Страница 497: ...ctures and Corrosion Control Systems Houston TX NACE 3 F J Ansuini J R Dimond Factors Affecting the Accuracy of Reference Electrodes MP 33 11 1994 p 14 4 NACE Publication 35201 latest revision Technical Report on the Application and Interpretation of Data from External Coupons Used in the Evaluation of Cathodically Protected Metallic Structures Houston TX NACE _____________________________________...

Страница 498: ...k because they are generally less rugged unless specially constructed than the other two reference electrodes A2 1 The voltage equivalents at 25 C 77 F to negative 850 mV referred to a CSE are A2 1 1 Ag AgCl seawater reference electrode used in 25 ohm cm seawater 800 mV 3 and A2 1 2 Saturated KCl calomel reference electrode 780 mV A2 2 A CSE is composed of a pure copper rod immersed in a saturated...

Страница 499: ...th s surface Measurements should be made at 3 m 10 ft intervals directly over the centerline of the pipe The instrument positive terminal is connected to the lead front reference electrode in the direction of survey travel A suspected anodic condition is indicated by a change of the instrument polarity indication Suspected anodic conditions and their magnitudes can be confirmed by making two refer...

Страница 500: ...condition is indicated See Figure B1 B3 8 The severity and extent of an anodic condition may be further determined by making two reference electrode surface measurements lateral to the direction of the pipe This is accomplished by relocating the rear reference electrode to the side of the pipe A positive value measured from this side reference electrode indicates current flowing from the pipe into...

Страница 501: ...ments It is also useful to provide space for a sketch of the area surveyed B4 Data Interpretation B4 1 Interpretation of survey data is complex but should consider the following a Polarity change of a measured value b Magnitude of the value measured c Magnitude of the lateral two reference electrode value d Soil resistivity e Unknown pipe resistances f Physical location of the pipe with respect to...

Страница 502: ... area s B6 2 It is necessary to wait until polarization has stabilized before making a detailed evaluation of the net current protective level Polarization of bare pipe may require a relatively long time ranging up to several months B6 3 When an impressed current source is used the side drain potential potential gradient lateral to the pipe longitudinal direction should be measured at the predeter...

Страница 503: ... CATHODIC AREA Electrolyte Current Electrolyte Current UNPROTECTED PIPELINE v v v v NOTE Actual readings are usually 50 mV or less As the anodic condition in the center of the figure is passed traveling left to right the indicated polarity switches from positive to negative This polarity reversal indicates an anodic condition FIGURE B1 Surface Potential Survey ...

Страница 504: ...RE REEL _ Figure B2b Reference Electrode Intervals for Potential Survey Using Moving Meter and Wire Reel 0 100 200 300 400 500 600 700 800 400 500 600 Pipe to Electrolyte Potential mV AREAS EXPERIENCING CORROSION 700 CATHODIC PROTECTION NOT APPLIED Linear Distance Figure B2c Variation of Pipe to Electrolyte Potential with Survey Distance FIGURE B2 Pipe to Electrolyte Potential Survey of a Noncatho...

Страница 505: ...time the connection is open to measure the coupon s off potential should be minimized to avoid significant depolarization of the coupon The off period is typically less than 3 seconds When possible coupon current direction and magnitude should be verified using a current clip gauge or resistor permanently placed in series with the coupon lead Measurements showing discharge of current from the coup...

Страница 506: ...ization on the pipe at the test site The causes of these variations include the pipe surface condition soil strata variations oxygen differentials and length of time the pipe has been polarized Making precise comparisons may not be possible C2 7 Monitoring When the polarized coupon to electrolyte potential has been determined to equal or to exceed a negative 850 mV the pipeline on potential may be...

Страница 507: ...al resistance of 100 000 ohms per volt may be adequate in certain circumstances where the circuit resistance is low A potentiometer circuit may be necessary in other instances C3 4 2 Two color coded meter leads with clips for connection to the coupon and reference electrode C3 4 3 Reference electrode C3 4 3 1 CSE C3 4 3 2 Other standard reference electrodes may be substituted for the CSE These ref...

Страница 508: ...ds on the coupon surface condition the soil in which the coupon is placed its level of polarization and its time polarized Therefore the depolarized potential of the coupon may not be the same as that of the pipe and may not accurately reflect the polarization on the pipe at the coupon location It must also be understood that the polarization measured on the pipeline is a resultant of the variatio...

Страница 509: ...uance of interpretations by individual volunteers Users of this NACE International standard are responsible for reviewing appropriate health safety environmental and regulatory documents and for determining their applicability in relation to this standard prior to its use This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards ...

Страница 510: ...f buried underground or submerged tank systems or similar structures including those used to contain oil gas and water It was prepared by Task Group 209 formerly Work Group T 10A 14b a subcommittee of Task Group T 10A 14 on Test Methods and Measurement Techniques Related to Cathodic Protection Criteria Task Group 209 is administered by Specific Technology Group STG 35 on Pipelines Tanks and Well C...

Страница 511: ...er Than Across the Tank to Electrolyte Interface 9 8 Test Method 1 Negative 850 mV Tank to Electrolyte Potential of Steel Tanks with Cathodic Protection Applied 9 9 Test Method 2 Negative 850 mV Polarized Tank to Electrolyte Potential of Steel Tanks 11 10 Test Method 3 100 mV Cathodic Polarization of Steel Tanks 12 11 Test Methods for Continuity Testing of Steel Tank Systems 17 12 Piping and Appur...

Страница 512: ...lectrons flow toward the cathode in the external circuit Cathodic Disbondment The destruction of adhesion between a coating and the coated surface caused by products of a cathodic reaction Cathodic Polarization The change of electrode potential in the active negative direction caused by current across the electrode electrolyte interface See also Polarization Cathodic Protection A technique to redu...

Страница 513: ...trolyte interface Polarized Potential The potential across the structure electrolyte interface that is the sum of the corrosion potential and the cathodic polarization Potential Gradient A change in the potential with respect to distance expressed in mV per unit of distance Potentiometer A device for the measurement of an electromotive force by comparison with a known potential difference Protecti...

Страница 514: ...nt use appropriate barricades flagging and or flag persons 3 1 6 Before entering excavations and confined spaces inspect these areas to determine whether they are safe Inspections may include shoring requirements for excavations and testing for hazardous atmospheres in confined spaces 3 1 7 Observe appropriate electrical codes and applicable safety regulations _____________________________________...

Страница 515: ...ssed current waveform and calculate a tank to electrolyte potential free of voltage drop is available This equipment may minimize problems resulting from spiking effects drifting of interrupters and current from other direct current DC sources 4 4 Instrument Accuracy 4 4 1 Instruments must be scheduled for periodic calibration to a certified standard Instruments shall be checked for accuracy befor...

Страница 516: ...ons may be necessary to increase their contact area with the environment 5 6 Meter Polarity 5 6 1 Tank to electrolyte potentials are often measured by connecting the negative terminal of the measuring instrument to the tank and the positive terminal to the reference electrode placed in the electrolyte which is in contact with the tank With this connection the instrument indicates that the referenc...

Страница 517: ...e 1a Conventional Instrument Connection Pipe Test Lead Voltmeter Direction of meter current Reference Electrode C L Electrode potential does not vary Pipe potential is the variable Pipe DC VOLT COM 0 850 Figure 1b Alternative Instrument Connection Figure 1 Instrument Connections Tank Test Lead Tank potential is the variable Tank Tank Test Lead Tank potential is the variable Tank does not vary does...

Страница 518: ...yte potential measurements 5 12 The effect of voltage drops on a tank to electrolyte potential measurement can be determined by interrupting all significant current sources before taking the potential measurement This measurement must be taken without delay after the interruption of current to avoid loss of polarization This measurement is referred to as an instant off potential and is considered ...

Страница 519: ...bonded tubing or pipe systems can cause the tank to be electrically discontinuous between the test connection and the reference electrode location Section 11 provides guidance on methods of troubleshooting that identify continuity or discontinuity 6 1 4 Parallel paths can be inadvertently established by test personnel contacting instrument terminals or metallic parts of the test lead circuit such ...

Страница 520: ... b A voltage drop caused by large voltage gradients in the electrolyte that occur near operating anodes sometimes called raised earth effect 7 1 2 3 Testing to locate anodes by moving the reference electrode along the tank may be necessary when the locations are not known 7 1 3 Coatings 7 1 3 1 Most coatings provide protection to the tank by reducing contact between the tank surface and the enviro...

Страница 521: ...trode Color coded meter leads are suggested to avoid confusion of polarity for the measured value 8 4 3 A CSE or other standard reference electrode may be used Reference electrodes that may be used in place of a CSE are described in Paragraph 5 5 8 5 The following procedure shall be followed when this test is conducted 8 5 1 Before the test verify that cathodic protection equipment has been instal...

Страница 522: ...2 2 Current sources that can affect the accuracy of this test method include the following a Unknown inaccessible or direct connected galvanic anodes b Other cathodic protection systems on associated piping or foreign structures c Electric railway systems d Galvanic or bimetallic cells e DC mining equipment f Adjacent tanks electrically connected and polarized to different potentials and g Uninten...

Страница 523: ...rcuit resistance on the tank to electrolyte potential as indicated in Paragraph 5 7 9 5 6 Record the tank to electrolyte on and instant off potentials and their polarities with respect to the reference electrode 9 5 7 Record a sufficient number of measurements to determine the level of cathodic protection over the entire structure 9 6 Evaluation of Data 9 6 1 Cathodic protection shall be judged ad...

Страница 524: ... recording polarization decay 10 2 4 2 Meter leads with insulated wire and terminal connections suitable for making reliable electrical contact with the tank and reference electrode Color coded meter leads are suggested to avoid confusion of polarity of the measured value 10 2 4 3 Sufficient and adequate means to interrupt cathodic protection current sources such as sacrificial anodes rectifiers a...

Страница 525: ...nded polarization decay time periods are anticipated it may be desirable to use recording voltmeters to determine when adequate polarization decay or a corrosion potential has been attained 10 2 5 9 Record a sufficient number of measurements to determine the level of cathodic protection over the entire structure 10 2 6 Evaluation of Data 10 2 6 1 Cathodic protection shall be judged adequate at the...

Страница 526: ... Interruption Instant Off Potential Polarization Cathodic Protection Applied Corrosion Potential Polarizing Line Figure 2b Polarization Formation FIGURE 2 Cathodic Polarization Curves Time Period May be seconds minutes hours or days Pipe to Electrolyte Potential mV Pipe to Electrolyte Potential mV Time Period May be seconds minutes hours or days 1 100 1 000 900 800 700 600 500 400 1 200 1 100 1 00...

Страница 527: ...nsulated wire and terminal connections suitable for making reliable electrical contact with the tank and reference electrode Color coded meter leads are suggested to avoid confusion of polarity of the measured value 10 3 4 3 Sufficient and adequate means to interrupt cathodic protection current sources such as sacrificial anodes rectifiers and electrical bonds that are influencing the tank simulta...

Страница 528: ... equipment may be used to test for electrical continuity or discontinuity 11 2 Underground storage tank UST systems may have been designed to be electrically isolated from other metallic structures such as piping conduit grounded electrical equipment and hold down devices A lack of electrical isolation from these structures can result in lowered levels of cathodic protection or a reduction in the ...

Страница 529: ...rotection test equipment to determine electrical continuity This test can also be used to confirm the fixed cell moving ground and potential difference technique test results 11 5 2 The following procedure shall be followed when testing using the applied current technique 11 5 2 1 Make electrical contact between the reference electrode and the electrolyte at a location remote from the system to be...

Страница 530: ...Underground Storage Tank Systems by Cathodic Protection Houston TX NACE 2 NACE Standard RP0177 latest revision Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems Houston TX NACE 3 NACE Standard RP0169 latest revision Control of External Corrosion on Underground or Submerged Metallic Piping Systems Houston TX NACE 4 NACE Publication 10A190 w...

Страница 531: ... TX NACE 1954 NACE Publication 2C157 Some Observations on Cathodic Protection Criteria Houston TX NACE 1957 NACE CEA Report Cathodic Protection Monitoring for Buried Pipelines Houston TX NACE 1990 Peabody A W Control of Pipeline Corrosion Houston TX NACE 2001 Parker M E Pipeline Corrosion and Cathodic Protection 2nd ed Houston TX Gulf Publishing 1962 Stephens R W Surface Potential Survey Procedure...

Страница 532: ...magnitude should be verified using a current clip gauge or resistor permanently placed in series with the coupon lead Measurements showing discharge of current from the coupon should be reason to question the validity of using a coupon at the test site A 5 The basic test equipment for both of these tests is the same A 5 1 Voltmeter with adequate input impedance Commonly used digital instruments ha...

Страница 533: ... may not accurately reflect the polarization on the tank at the coupon location A 6 4 3 The polarization measured on the tank is a resultant of the variations of polarization on the tank at the test site The causes of these variations include the tank surface condition soil strata variations oxygen differentials and length of time the tank has been polarized Making precise comparisons between the ...

Страница 534: ... until it either a Has become at least 100 mV less negative than the instant off potential or b Has reached a stable depolarized level A 7 3 10 Reconnect the coupon test lead to the tank test lead for normal operations A 7 3 11 The use of polarization formation as stated in the criterion can also be used to assess the adequacy of cathodic protection The procedure is different in that a base line v...

Страница 535: ...TM0101 2001 24 NACE International ISBN 1 57590 137 4 ...

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