Early Generation Pipeline Girth Welding Practices and Their Implications for Integrity Management of North American Pipelines

Abstract

The characteristics of early generation pipelines (i.e., “vintage pipelines”) reflect the rapid evolution of pipeline materials, welding, and inspection practices that occurred during the first half of the twentieth century. The diverse range of welding and inspection practices and the unique characteristics of early generation pipeline welds can influence pipeline segment risk ranking and integrity assessment. This paper summarizes some of the key findings regarding girth weld fabrication, performance and integrity assessment determined during the course of a literature review performed as part of a recently completed PRCI project. Some of the key findings include: 1. The failure rate of early generation girth welds is low, particularly for welds made by arc welding and for welds made after 1930. This is especially true when considering the rate of catastrophic failures (ruptures or nearly full circumference breaks). Welds are typically reported to be responsible for no more than about 6% of significant pipeline failures. 2. Pipeline girth welds are unlikely to fail unless subjected to axial strains that far exceed the strains related to internal pressure alone. Girth welds containing significant workmanship flaws are likely to be resistant to failure at stresses less than the pipe yield strength unless the welds are undermatched and/or are susceptible to brittle fracture initiation. Common mechanical tests, such as Charpy impact testing or CTOD tests may result in grossly conservative indications of the likelihood of brittle fracture occurring in vintage girth welds. 3. A diverse range of early generation girth weld joint designs exist, some of which hamper effective inspection using ILI or represent challenges to effective assessment using conventional fitness-for-service or engineering critical assessment methods (ECA). Effective probabilistic ECA is further hampered by wide variations in workmanship and difficulty in determining mechanical property distributions. 4. Pipeline vintage is a poor indicator of girth weld integrity. Pipeline girth weld integrity is more likely related to project-specific inspection and testing practices than to pipeline age. Welding and inspection practices evolved very quickly in the 1920s through the 1940s and a wide range of practices were used on different pipelines that were constructed in the same time period. Girth weld integrity is typically highest for post 1930s pipelines that were subjected to radiographic inspection.