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

When a flaw is detected in a stainless steel pipe during in-service inspection, the limit load criterion given in the codes such as JSME Rules on Fitness-for-Service for Nuclear Power Plants or ASME Boiler and Pressure Vessel Code Section XI can be applied to evaluate the integrity of the pipe. However, in the present codes, 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 is proposed considering a circumferential flaw with arbitrary shape, in order to make it possible to evaluate the integrity of the pipe for general 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. Several numerical examples are also given to show the validity of this method. Finally, it can be seen that the number of the segmented sub-flaws for the semi-elliptical surface flaw is sufficient to be three from engineering judgment. (author)