A PROCEDURE FOR ANALYSIS OF LEAK BEFORE BREAK IN PIPES SUBJECTED TO FATIGUE OR IGSCC ACCOUNTING FOR COMPLEX CRACK SHAPES

A procedure is described which predicts the growth of an initial circumferential surface crack through a pipe wall and further on to final failure of the pipe. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes, since especially the last growth mechanism often results in a substantially longer crack length on the inside of the pipe than on the outside for the initial leaking crack due to the distribution of weld residual stresses. The procedure has been implemented in a computer program that in an integrated Fashion calculates crack sizes and mass leak rates as a function of time and also predicts when leakage and final failure occur. The information obtained makes it possible to judge if the concept of leak before break is fulfilled.