Underload‐induced crack growth behaviour of minor cycles of pipeline steel in near‐neutral pH environment

Abstract

AbstractDespite decades of research, the mechanisms of near‐neutral pH stress corrosion cracking of pipeline steel are still not fully understood. This investigation was aimed to understand the effect of minor cycles with very high R ratios (minimum stress/maximum stress) on crack growth in air and in near‐neutral pH environments. It has been demonstrated that the minor cycle, even with an R ratio as high as 0.9, could significantly contribute to the crack growth of pipeline steels in the presence of a large underload cycle with a low R ratio of 0.5 in near‐neutral pH environment. Comparing with constant amplitude tests, an increase of crack growth rate by a factor of 3 and 5 was observed when some non‐propagating minor cycles were combined with an underload cycle for tests in air and in near‐neutral pH solution, respectively. Based on the test results, the crack growth mechanisms during minor cycle loading in near‐neutral pH environments were discussed and practical strategies aimed to minimise crack growth during pipeline operation were also proposed.