Nace CP 1, Course Manual

Page: 300 / 535

RP0169-2002
NACE International 29
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Appendix B—Method for Determining Probable Corrosion Rate and Costs of Maintaining Service
Maintenance of a piping system may include repairing
corrosion leaks and reconditioning or replacing all or
portions of the system.
In order to make estimates of the costs involved, it is
necessary to determine the probability of corrosion or the
rate at which corrosion is proceeding. The usual methods
of predicting the probability or rate of corrosion are as
follows:
(a) Study of corrosion history on the piping system in
question or on other systems of the same material in the
same general area or in similar environments. Cumulative
leak-frequency curves are valuable in this respect.
(b) Study of the environment surrounding a piping system:
resistivity, pH, and composition. Redox potential tests may
also be used to a limited extent. Once the nature of the
environment
has been determined, the probable
corrosiveness is estimated by reference to actual corrosion
experience
on similar metallic structures where
environmental conditions are similar. Consideration of
possible environmental changes such as might result from
irrigation, spillage of corrosive substances, pollution, and
seasonal changes in soil moisture content should be
included in such a study.
(c) Investigation for corrosion on a piping system by visual
inspection
of the pipe and/or by instruments that
mechanically or electrically inspect the condition of the pipe.
Condition of the piping system should be carefully
determined and recorded 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,
this may help to determine the existence of corrosion.
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Appendix C—Contingent Costs of Corrosion
In addition to the direct costs that result from corrosion,
contingent costs include:
(a) Public liability claims;
(b) Property damage claims;
(c) Damage to natural facilities, such as municipal or
irrigation water supplies, forests, parks, and scenic areas;
(d) Cleanup of product lost to surroundings;
(e) Plant shutdown and startup costs;
(f) Cost of lost product;
(g) Loss of revenue through interruption of service;
(h) Loss of contract or goodwill through interruption of
service; and
(i) Loss of reclaim or salvage value of piping system.
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Appendix D—Costs of Corrosion Control
The usual costs for protecting buried or submerged metallic
structures are for complete or partial cathodic protection or
for external coatings supplemented with cathodic protection.
Other corrosion control costs include:
(a) Relocation of piping to avoid known corrosive
conditions (this may include installing lines above ground);
(b) Reconditioning and externally coating the piping
system;
(c) Use of corrosion-resistant materials;
(d) Use of selected or inhibited backfill;
(e) Electrical isolation to limit possible galvanic action; and
(f) Correction of conditions in or on the pipe that might
accelerate corrosion.