MIL-HDBK-1004/10
Criteria for lead shall be as follows:
3.3.2.1
Criteria for Lead.
a) -750 mV or more negative with respect to a copper/copper
sulfate reference cell. This potential is measured with the protective
current applied.
b) 100 mV or greater negative polarization shift measured between
the pipe surface and a stable reference electrode contacting the electrolyte.
NOTE: With the same precautions regarding potentials over
1.2 V and contact with alkaline soils as those for
aluminum.
NACE RP-02-85. Criteria for the interpretation of structure-to-
3.3.2.2
electrolyte potentials on storage tanks are given in NACE RP-02-85 Control of
External Corrosion on Metallic Buried, Partially Buried, or Submerged Liquid
Storage Systems. The criteria in this recommended practice refer to the
protection of steel structures and are essentially the same as in NACE
RP-01-69.
Failure Rate Analysis. Corrosion damage, as measured by frequency
3.4
of system failure, usually increases logarithmically with time after the first
occurrence of corrosion failure. When effective cathodic protection is
applied to a structure which has experienced corrosion damage, the frequency
of failures will be significantly reduced. However, due to the presence of
existing corrosion damage, the failure rate will not immediately be reduced to
zero. Mechanical damage and previously undetected corrosion related damage
may still result in failure, but if effective cathodic protection is achieved,
corrosion failures should cease after a period of 1 or 2 years. Accurate
failure records should be kept for both protected and unprotected systems in
order to determine the need for cathodic protection and the effectiveness of
installed systems. A typical failure rate analysis is shown in Figure 7.
Nondestructive Testing of Facility. Periodic evaluation of the
3.5
condition of the protected system can also be used to determine the adequacy
of the cathodic protection system installed on the structure, or to establish
the need for protection.
Visual Analysis. If the surface of a structure is accessible or is
3.5.1
exposed for repairs, alterations, or specifically for the purposes of
inspection, visual inspection may be used to evaluate the need for protection
of the effectiveness of cathodic protection applied to the structure. Signs of
corrosion such as the presence of corrosion products, pitting, cracking,
reduction in physical size, or other evidence of deterioration should be
noted.
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