An investigation of a recent pre-1970 ERW Pipe Seam Weld Failure incident is presented. The investigation uses an interdisciplinary approach that combines metallurgical and fractographic analysis, fracture mechanics testing, as well as failure analysis diagram to determine the origin and nature of the failure, the initial and final size of the flaw that causes the failure, the fracture toughness of the basemetal, HAZ, and seam weld, and the critical conditions for the failure. The paper summarizes the findings of the investigation and compares the analysis with the observed failure. In addition, fatigue analysis is performed based on the pressure cyclic data for understanding the reasons of the sub-critical crack growth observed. The findings of the study suggest that future ILI inspections should have a capability of detecting small defects with appropriate excavation and mitigation plans to account for tool uncertainty and ensure future integrity of the pipeline.
Key words: ERW seam failure, failure analysis, crack initiation, subcritical crack growth, fatigue, cleavage, FAD analysis, life estimate.