Metallurgical Analyses of 26 EMAT Anomalies on a 1949 Vintage Electric Flash Welded Pipeline

Abstract There are more than 2.6 million miles of oil and gas pipelines in the United States, all of which can be characterized as either seamless or longitudinally seamed. The majority of longitudinally seamed pipelines constructed between 1940 and 1970 involved submerged arc welded (SAW) or either electric resistance welded (ERW) or electric flash welded (EFW) seams. While SAW line pipe is formed with filler metal, ERW and EFW line pipe are autogenous and require no filler. Both ERW and EFW pipes are formed with pressure and electrical current and are both prone to similar manufacturing flaws including hook cracks and lack-of-fusion (LOF) flaws. Hook cracks and LOF flaws can grow pre-service or in-service but are less likely to fail at pressures below the mill and commissioning hydrostatic burst testing (hydrotest). Thus, these flaws are typically considered stable in gas transmission pipelines. This paper summarizes the findings of metallurgical and hydrotesting performed on multiple manufacturing seam weld flaws from an EFW natural gas pipeline.