Nace CP 1, Course Manual

Page: 404 / 535

RP0575-2001
6 NACE International
8.2 Records
8.2.1 Record keeping is vital to effective maintenance
of cathodic protection systems (and thus continued
protection of the vessels).
8.2.2 Monthly records should be kept for all impressed
current anode installations. The records should show
DC voltage and amperage readings for each anode.
8.2.3 Quarterly records should be kept for galvanic
anode installations. The records should show current
readings on galvanic anodes.
8.3 Maintenance
8.3.1 Malfunctions should be repaired promptly to
ensure desired performance. Corrosion damage can
occur whenever the potentials are less negative than
the values indicated in Paragraph 7.1.2.
8.3.2 Anodes must be replaced periodically as they
are consumed. Zero current readings usually indicate
deteriorated
anodes, broken anode cables,
malfunctioning rheostats, or loose connections in the
circuit. Low current readings in galvanic systems may
indicate similar problems.
8.3.3 Zero reported voltage or current readings may
occur because of various malfunctions.
A rectifier
troubleshooting guide should be consulted when such
malfunctions occur.
8.3.4 During maintenance of the vessel, visual
examination of the vessel surfaces should be
conducted to verify the effectiveness of the cathodic
protection system. Deterioration of the surface of the
vessel and/or interior welds indicates the need for
relocation of the anodes, increasing quantity of anodes,
or an appraisal of the cathodic protection system.
________________________________________________________________________
Section 9: Safety
9.1 Precautions must be taken to avoid sparks in the
presence of flammable substances and explosive gas
mixtures that may be present around oil-treating vessels.
9.2 The 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 performing maintenance on cathodic
protection systems in vessels containing H
2
S. If the anodes
in such vessels are to be removed for replacement or
inspection, a mask approved for use in H
2
S environments
must be worn. Additional information on the toxicity of H
2
S
can be obtained from the Manufacturing Chemists’
Association’s
(2)
“Chemical Safety Data Sheet SD-36,”
2
and
from Dangerous Properties of Industrial Materials.
3
9.5 The rectifier case, external AC disconnect switch box,
and any related metallic equipment must be grounded.
9.6 Depending on the area classification, explosion-proof
rectifiers and electrical devices may be required.
9.7 Special gaskets capable of withstanding high
temperatures should be used to mount anodes in fired
vessels, particularly if the gaskets are located near the fire
tubes.
9.8 Equipment, wiring, enclosures, and installation of
cathodic protection systems must comply with all applicable
codes, including OSHA regulations.
________________________________________________________________________
References
1. NACE Publication 35201 (latest revision), “Report on the
Application and Interpretation of Data from External
Coupons Used in the Evaluation of Cathodically Protected
Metallic Structures” (Houston, TX: NACE).
2. “Chemical Data Safety Sheet SD-36” (latest revision)
(Washington, DC: Manufacturing Chemists’ Association).
3. N. Irving Sax, Dangerous Properties of Industrial
Materials (New York, NY: Reinhold Book Corp., 1984).
___________________________
(2)
Manufacturing Chemists’ Association, 1825 Connecticut Ave. NW, Washington, DC 20009.