Long Seam Welds in Gas and Liquids Pipelines and Near-Neutral pH Stress Corrosion Cracking and Corrosion Fatigue

Near-neutral pH SCC and corrosion fatigue at the toe of the longitudinal weld has been responsible for several pipeline failures in Canada. In this paper examples of such failures and other in-service toe cracks are discussed. The results of an investigation into several factors affecting near-neutral pH SCC at the toe of the longitudinal weld are discussed and summarized. Four different pipes were evaluated including both double submerged arc welded (DSAW) pipe and electrical resistance welded (ERW) pipe. The properties considered were 1) residual stresses near the toe of the weld as determined by hole drilling and slitting, 2) stress-raising characteristics of the weld shape as determined by elastic finite element analysis and 3) electrochemical properties near the toe of the weld as determined by the scanning reference electrode technique. For one line pipe we also evaluated the room-temperature creep characteristics near the weld with and without cyclic loading. The implications of these results for near-neutral pH SCC and corrosion fatigue are discussed. It is concluded that high stresses originating from the stress-multiplying effects of the weld crown contributed significantly to the failures.