Transgranular crack growth in the pipeline steels exposed to near-neutral pH soil aqueous solutions: The role of hydrogen

The aim of this investigation was to understand why some transgranular cracks developed in the pipeline steels exposed to near-neutral pH environments, typically 5% of total crack population, can propagate repeatedly and cause pipeline rupture. Crack growth in the current condition is related to two competitive processes at the crack tip: the intrinsic blunting and the extrinsic sharpening. Balance of both determines whether cracks will be dormant or actively grow. For a given pipeline, the presence of near-neutral pH environments and high residual stresses on the pipe surface determines whether a crack colony can develop, while the presence of high concentration of diffusible hydrogen is thought to determine whether repeated crack growth can occur. This is believed to be a key reason why a small fraction of cracks, typically 5% of total population, can grow repeatedly and cause pipeline rupture.