Inclined stress corrosion cracks in steel pipelines

Stress corrosion cracking (SCC) in steel gas pipelines has been experienced in many regions of the world and have been known to cause ruptures. A typical description of a high pH SCC crack is a hoop aligned crack that grows directly into the pipe wall, perpendicular to the direction of applied stress. Many studies have been carried out to understand the crack growth rates of such cracks, and SCC management models have been developed to aid asset owners to manage SCC. However, a few cases have been found in Canada and Australia where high pH SCC cracks grow at an angle away from the perpendicular, causing the cracks to travel in the hoop direction subsurface. There is little knowledge as to how common this phenomenon occurs in the world, what causes it and whether current SCC management models can still be used for these inclined cracks. This paper presents the results of some studies carried out in order to better understand the occurrence and characteristics of this phenomenon.