Abstract
Leak before break (LBB) in nuclear piping systems requires determination of leak rate which critically depends on crack opening displacement (COD). Procedures have been developed for accurately estimating the COD resulting from service loads in pipes. However, cracks in nuclear piping and nozzles often occur in and near welds, and the weld residual stresses (WRS) can strongly affect the COD values. Although WRS-influenced COD changes can in some cases close and stop leakage, thus hinder leak detection, the effects have been typically neglected because they could only be evaluated on a case-by-case basis using finite element calculations.
This paper presents a simple estimation scheme that was developed along the lines of classical COD estimation schemes that use influence functions developed from finite element solutions. This estimation scheme has been validated for different WRS fields, a wide range of pipe sizes and for a wide range of crack sizes. The estimation scheme, its development and use, and the validation results are presented here.
