Crack Growth Behavior of Pipeline Steel in Near-Neutral pH Soil Environments

This article reports the crack growth behavior of X-65 pipeline steel in near-neutral pH environments. Although it is often referred to as stress corrosion cracking (SCC), the crack growth behavior of pipeline steels in near-neutral pH environments has been found to be consistent with that of true corrosion fatigue, and the crack growth rate da/dN can be correlated with $$ {\Delta K² K_{{\max }} } \mathord{\left/ {\vphantom {{\Delta K² K_{{\max }} } {f^{{0.1}} }}} \right. \kern-\nulldelimiterspace} {f^{{0.1}} } $$ . This correlation enables the determination of threshold $$ {\Delta K² K_{{\max }} } \mathord{\left/ {\vphantom {{\Delta K² K_{{\max }} } {f^{{0.1}} }}} \right. \kern-\nulldelimiterspace} {f^{{0.1}} } $$ values that demarcate the boundary between active growth and dormancy. Crack tip blunting was observed when a loading condition gave a $$ {\Delta K² K_{{\max }} } \mathord{\left/ {\vphantom {{\Delta K² K_{{\max }} } {f^{{0.1}} }}} \right. \kern-\nulldelimiterspace} {f^{{0.1}} } $$ value below the threshold. The threshold is found to be environmentally sensitive, and possibly also material dependent, but the details are yet to be determined.