L52310 Criteria for Evaluating Failure Susceptibility Due to Crack Defects Phase II

Seam cracks can pose a serious threat to the integrity of electric resistance welded (ERW) liquid and gas pipelines. Of concern to the industry is not just the assessment of cracks under service conditions, but also ways that may be used to establish the remaining lives of pipelines based on the results of a hydrostatic pressure test. An accurate crack assessment procedure is required. The main objective of Phase II is to validate the J-based crack assessment method developed in Phase I by using it to predict the results of full-scale burst tests on seam-welded pressurized pipes containing axial surface flaws. The comparisons between measured and predicted burst test conditions demonstrated that the Level 3C (J-based) assessment resulted in conservatively calculated critical burst conditions when fracture toughness values measured using highly constrained bend specimens were used in the analysis. This initial validation exercise highlighted some of the difficulties that may be encountered when attempting to validate the accuracy of advanced flaw assessment methodologies using vintage thin-walled pipe sections containing axial cracks. A second set of validation calculations were performed using modified material properties chosen to compensate for the effects of (a) extraneous plastic strains on stress-strain curves measured on flattened tensile specimens and (b) plastic constraint effects, and the J-based Level 3C assessment methodology developed in Phase I predicted accurate critical flaw sizes and critical pressures for the burst test pipe samples.