Limit load estimation method for pipe with an arbitrary shaped circumferential surface flaw

Li, Y.* ; Hasegawa, Kunio*; Onizawa, Kunio ; Sugino, Hideharu*

When a flaw is detected in a pipe during in-service inspection, the limit load criterion given in the standards such as JSME Rules on Fitness-for-Service for Nuclear Power Plants or ASME Boiler and Pressure Vessel Code Sec. XI is applied to evaluate the integrity of the pipe. However, in the present standards, the limit load criterion is only provided for the case of a flaw with the uniform depth, although many flaws with complicated shape such as stress corrosion cracking have been actually detected in a pipe. In this paper, a limit load estimation method for a circumferential surface flaw with arbitrary shape is proposed, in order to evaluate the integrity of the pipe for the practical case. The plastic collapse moment and stress are obtained by dividing the surface flaw into several segmented sub-flaws. Using this method, good agreement is observed between the numerical solution and reported experimental results. It is shown that the number of the segmented sub-flaws for the semi-elliptical surface flaw is sufficient to be three from engineering judgment.