Failure Stresses for Pipes With Multiple Circumferential Flaws

Abstract

Flaw evaluation for fully-plastic fracture uses the limit load criterion. As stainless steels are high toughness ductile materials, limit load criterion is applicable to stainless steel pipes. When a single circumferential flaw is detected in a stainless steel pipe during in-service inspection, the single flaw is evaluated in accordance with Article EB-4000 in the JSME Code or Appendix C in the ASME Code, Section XI. However, multiple flaws such as stress corrosion cracking are sometimes detected in the same circumferential cress-section in a pipe. If the distance between adjacent flaws is short, the multiple flaws are considered as a single flaw in compliance with combination rules. Failure stress is easily calculated by the equations given by Article EB-4000 or Appendix C. If the two flaws are separated by a large distance, it is not required to combine the two flaws. Each flaw is treated as independent. However, there are no equations for evaluating collapse stress for a pipe containing multiple independent flaws in Article EB-4000 and Appendix C. The present paper focus on a proposal of simple equations for evaluating collapse stresses for pipes containing multiple circumferential part-through wall flaws.