Factors in the fail safe approach to pressure vessel assessment

The 'leak before break' concept is described in the context of pressure vessel assessment. The factors which determine whether a pipe containing an axial flaw will leak or break under pressure loading are discussed using a post-yield fracture mechanics method. A model is used in which it is assumed that initially the ligament beneath the flaw fails to form a full thickness defect in the pipe. The stability of the full thickness defect at the pressure causing ligament failure is then examined to ascertain whether it would remain at the snap through length or would propagate by fast fracture, to form a leak or a break. The method is used to analyse the results of a series of pipe rupture tests, and it is found that a distinction between leaks and breaks is achieved. (author)