Reliability Analysis for the Feeder Subject to Wall Loss

Wall thinning is one of the most common degradation mechanisms experienced in piping system. Gradual wall thinning can cause the pipe to leak or in the worst scenario, to rupture. Wall thinning due to FAC of feeder pipe in CANDU^® reactors has been identified as an active degradation mechanism, and local thinning has been observed in various locations such as elbows/bends and Grayloc. The assessment of structural integrity is important for the fitness-for-service of those feeders whose wall thickness is predicted to be lower than the required minimum wall thickness before their design life and therefore subject to costly repair or replacement. Among various probabilistic methods, the first-order reliability method (FORM) is adopted in this paper to evaluate the structural reliability of feeders subject to wall thinning, while the wall thickness, one of the key parameters in the reliability analysis, is modeled by three methods based on the wall thickness measurements. They are linear regression analysis, random thinning rate analysis and gamma process modeling. The difference and limitation of the methods for reliability analysis are addressed.