PROBABILISTIC MECHANICS ANALYSIS OF THE IMPACT OF STRESS CORROSION CRACKING ON PIPELINE LEAK BEFORE BREAK

摘要

Stress corrosion cracking has developed into a serious concern among nuclear and gas pipeline operators as well as in the aircraft and aerospace industries. One of the risk mitigation strategies employed in the pipeline industry is the Leak Before Break (LBB) concept. In this situation one must be able to demonstrate that a defect will grow in such a manner as to break through the wall and leak in a stable fashion for a long enough period of time that it can be detected before it causes a catastrophic failure of the piping system. There are many uncertainties associated with these analyses including the material properties, the weld, the weld stresses, the location of the defect, and so forth. This requires that a probabilistic analysis of the piping system be performed in order to demonstrate the LBB characteristics with confidence. Historically the damage in the pipe was assumed to be due to fatigue crack growth. Recently it has been found that there is a significant impact to the LBB concept from Stress Corrosion Cracking (SCC). While fatigue damage will only increase with load cycles, SCC is time dependent and will continue to grow even when there is no, or minimal, loading. This paper presents the results of a model development effort which combines fatigue crack growth and SCC damage over the service life of a pipeline system. The various leak rates are calculated and compared to the probability of detection.