Generic and Profile Specific Feeder Stress Analysis

Abstract

Generic and Profile Specific Feeder Stress Analysis Thinning of feeder wall has been observed on CANDU feeder pipes. Thinning mainly occurs in outlet feeders at the the first two bends immediately downstream of the Grayloc fitting. In fitness for service analysis, the inspected or predicted minimum thicknesses are often used in the stress analysis. However, the determination of the exact location of the thinnest spot, axially and circumferentially, is dose intensive during inspection. Two types of stress analysis approaches are developed. Type A analysis is conducted using general piping analysis software using "Average-Minimum-Average" approach. The Type A analysis provides a set of required minimum wall thickness and average wall thickness. The required minimum wall thickness is not location specific and the thin spot can reside anywhere in the first two bends. It provides great flexibility to disposition feeders with either general or local thinning. On the other hand, type B analysis conducted with the exact thickness profile. Type B analysis has been performed on feeders which did not pass Type A. The two approaches have been demonstrated in Darlington feeders, the majority (413 out of 480) of feeders have Type A requirements, while 67 out of 480 have Type B requirements. Type A requirements provide a greater flexibility to mitigate impact of local thinning problem.