Allowable External Flaws and Acceptance Standards for High Toughness Ductile Pipes Subjected to Bending Moment and Internal Pressure

Abstract

Abstract Failure stresses for ductile high toughness pipes are predicted by Limit Load Criteria based on a net section stress concept. Allowable flaws of the Acceptance Standards provided by the Article IWB-3514 in the ASME B&PV Code Section XI were determined by the Limit Load Criteria. The allowable flaws are applicable for ductile high toughness pipes with circumferential internal and external flaws. Authors have developed more precise equations using the Limit Load Criteria, which is called Modified Limit Load Criteria, hereafter. As the results of the Modified Limit Load Criteria, failure stresses for external flawed pipes are always smaller than the failure stresses obtained by the Limit Load Criteria provided by the ASME Code Section XI. It seems that the allowable flaw sizes of the Acceptance Standards provided by the ASME Code Section XI are less conservative for external flaws. The objective of this paper is to demonstrate difference of failure stresses by the Limit Load Criteria and Modified Limit Load Criteria for external flawed pipes. In addition, the allowable flaws of the Acceptance Standards are examined by large and small diameter pipes with external flaws using the Modified Limit Load Criteria.