L51867 Remaining Strength of Pipelines w Coexistent Corrosion and SCC

Abstract

Failures have occurred on gas-transmission pipelines at stress-corrosion cracking (SCC) locations that formed along the bottom of significant metal-loss defects. In one case, axial low pH SCC occurred within a large patch of significant metal loss; in a second case, selective axial metal loss occurred adjacent to the long seam, with coaxial low pH SCC forming at the bottom of this corrosion. While only a few instances of SCC growing in corrosion defects have been identified to date, the fact that initiation of SCC may favor more highly stressed sites, such as metal-loss defects, indicates that these past occurrences can be expected to recur. The increased likelihood of cracking in corrosion highlights the need to develop a failure criterion for SCC lying within metal-loss defects. This report presents the development of a failure criterion for cracks emanating from corrosion defects. The failure criterion is embedded in the suite of PRCI failure criteria for defects in pipelines, which is being delivered as part of the update for the PRCTs failure criterion for sharp defects, known as pipeline axial flaw failure Criterion, PAFFC.