Tomography of inclined scc cracks

Abstract

X-ray microtomography has been used in the past to analyse Stress Corrosion Cracking (SCC) in austenitic stainless steels and aluminium alloys. These studies were carried out to determine the depth of these cracks, where the cracks grew directly into the material at an angle normal to the free surface. In some rare cases, SCC in gas transmission pipelines initially grows normal to the free surface, but then changes direction, growing at an angle up to 60 degrees away from the normal. This can lead to a complex crack interaction problem underneath the pipe surface, resulting in unexpected crack growth rates. This paper presents the feasibility of using X-ray microtomography to determine crack morphology and interaction in cases of inclined SCC cracks in an Australian gas transmission pipeline. Once crack interactions are better understood, existing guidelines and models for SCC crack growth rates could be improved, resulting in recommendations made to International Standards and guidelines. These recommendations would lead to more efficient, safer gas transmission pipeline operations and maintenance.