The Effect of Induction Heating Stress Remedies on piping reliability

Abstract

To address the effect of Intergranular stress corrosion cracking (IGSCC) on the probability of a leak in BWR piping, we have introduced some changes to the model of IGSCC for the Probabilistic fracture mechanics PRAISE code. This semi-empirical model is based on experimental and field data compiled from several sources. Using probabilistic techniques, the model addresses various stress corrosion phenomena, including crack growth, crack initiation, and linking of multiple cracks. The model also considers the effect of residual stresses in addition to cyclic stresses resulting from normal plant operation. Residual stresses which are an inherent result of conventional welding processes have long been known to play an important role in the failure of structural components. Such stresses can have a beneficial or detrimental influence, depending primarily on whether they are tensile or compressive at the inside surface of the pipe. Residual stresses undoubtedly are influential in both the initiation and propagation of cracks. The purpose of this paper is to review the influence of residual stresses on the reliability of piping under IGSCC. A procedure such as induction heating stress improvement (IHSI) is a means of altering the residual stress pattern in a pipe. Examples of the use of this technique to the initiation and growth of stress corrosion cracks in pipes are presented for various pipe sizes and residual stress distributions. The effectiveness of IHSI as an eternal countermeasure for IGSCC depends upon the level of service stress as well as the crack size and its large benefit is immediately apparent.