Nace CP 1, Руководство по эксплуатации

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RP0285-2002
NACE International 5
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Section 4: Cathodic Protection of Existing UST Systems
4.1 Prior to initiation of the field testing necessary for
design of CP, it is advisable to assemble information
concerning the history of the tank(s) to be protected. This
information generally falls
into two groups: physical
description and operating history. Although all information
may not be available for every tank, it is important to obtain
as much as possible.
This information can save field
investigation time, resulting in a more cost-effective system,
and can help to avoid an ineffective design.
4.2 Physical Description
4.2.1 Size, Configuration, and Condition: The type of
CP system and the amount of cathodic current required
to protect the tanks and piping depends on the surface
area, coating quality of the structures, and the
properties of the electrolyte. The configuration of the
tanks and piping and their location with respect to other
structures at the site may also affect the type of system
selected.
4.2.2 Materials of Construction: Knowledge of the
materials and construction of the tanks, piping, and
related facilities is required to assess the probable
corrosion mechanisms affecting the facilities and to
determine which structures will require CP.
The
materials of construction include any buried portion of
the tank system (e.g., valves, fittings, tank pads, straps,
anchors, foundations, ground rods, cables, monitoring
devices, the tank, and the piping). The use of different
metals for the various components can accelerate
corrosion on an unprotected UST system and can
affect the current required for CP. The existence and
condition of coatings on the metallic components also
have a significant influence on the design of the CP
system.
4.2.3 Electrical Continuity: The design and operation
of CP systems are dependent on the extent of electrical
continuity of the underground metallic structures. The
existence
of intentional bonding, grounding, 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 affect the feasibility, type, and capacity of
the proposed CP system.
4.2.5 Pavement: The presence and thickness of
pavement at the site can affect both the operation of
the CP system and the cost of installation.
The
location, type, age, and probable repaving schedule
are of interest to the designer. The presence of other
significant site improvements must be considered.
4.3 Integrity Assurance
4.3.1 The operating history of the UST system,
including the date of installation and as-built drawings,
provides important information for evaluation.
4.3.2 The results of tightness testing, internal
inspection, or other industry recognized methods of
integrity assurance should be analyzed (see API
(3)
RP
1631
8
for additional information).
4.3.3 The leak history of the UST may influence the
feasibility of the retrofit CP system. The date, location,
and type of each leak should be assessed.
4.3.4 Repairs or replacements of UST system
components should be analyzed as to their effect on
the system’s probability for corrosion or on the
operation and effectiveness of the retrofit CP system.
The reason for repairs, replacements, or system
modifications, as well as the materials and methods
used, should be analyzed.
4.3.5 Operating data of any previous CP system for
the UST, including the type of CP system (galvanic or
impressed current), the date of installation, the type,
size, and placement of anodes, and the level of
protection, should be reviewed.
4.4 On-Site Testing
4.4.1 All test methods shall be in accordance with
applicable engineering standards.
4.4.2 Soil borings may be performed. The following
measurements should be recorded as each test hole
boring progresses:
(a) tank-to-soil potential profile; and
(b) soil resistivity profile.
___________________________
(3)
American Petroleum Institute (API), 1220 L Street NW, Washington, DC 20005.