Evaluation of Stress Corrosion Crack Growth in BWR (Boiling Water Reactor) Piping Systems.

摘要

This report presents the results of a study conducted to evaluate the effects of stress intensity factor and environment on the growth behavior of integranular stress corrosion cracks in type 304 stainless steel piping systems. Most of the detected cracks are known to be circumferential in shape, and initially start at the inside surface in the heat affected zone near girth welds. These cracks grow both radially in-depth and circumferentially in length and, in extreme cases, may cause leakage in the installation. The propagation of the crack is essentially due to the influence of the following simultaneous factors: (1) The action of applied and residual stress, (2) Sensitization of the base metal in the heat affected zone adjacent to girth weld and (3) The continuous exposure of the material to an aggressive environment of high temperature water containing dissolved oxygen and some levels of impurities. The report also evaluates the time required for hypothetical cracks in BWR pipes to propagate to their critical size.