A degraded condition as defined in NRC Inspection Manual 0326 Paragraph 03.02: “A degraded condition is one in which the qualification of an SSC or its functional capability is reduced. Examples of degraded conditions are failures, malfunctions, deficiencies, deviations, and defective material and equipment. Examples of conditions that can reduce the capability of a system are aging, erosion, corrosion, improper operation, and maintenance.”
A nonconforming condition as defined in US NRC Inspection Manual 0326 Paragraph 03.06: “A nonconforming condition is a condition of an SSC that involves a failure to meet the CLB or a situation in which quality has been reduced because of factors such as improper design, testing, construction, or modification. The following are examples of nonconforming conditions:
Degradation by wall thinning can be the result of corrosion (including microbial-influenced corrosion MIC), erosion (or wear), or the combination of corrosion and erosion such as in flow-accelerated corrosion (FAC).
The various levels of evaluation are illustrated in Figure 1, and are as follows:
Note: When applying FEA to wall-thinning it is recommended to impose a minimum acceptable projected wall thickness, regardless of stresses, in the order of 1/16 in. to prevent pinhole leak.
Degradation by cracking can be the result of a fabrication weld flaw, corrosion (including stress corrosion cracking), fatigue, or a combination of any of these three causes, for example environmental fatigue.
The various levels of evaluation are illustrated in Figure 2, and are as follows:
A thermal expansion over-stress is one of several types of actual or postulated overloads that are non-conformances. A thermal over-stress is a nonconformance which can be the result of an accidental interference, a damaged support or snubber, excessive pipe-to-support friction, the discovery of a design calculation error, or other causes by which the B31.1, B31.7, or ASME III design flexibility (expansion and contraction) stress equation limits are exceeded.
The various levels of evaluation are illustrated in Figure 3 and are as follows:
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George Antaki, Fellow ASME, has over 40 years of experience in nuclear power plants and process facilities, in the areas of design, safety analysis, startup, operation support, inspection, fitness for services and integrity analysis, retrofits and repairs. George has held engineering and management positions at Westinghouse and Washington Group International, where he has performed work at power and process plants, and consulted for the Department of Energy (DOE), the Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI).
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