Analysis of the Type IV creep failures of three welded ferritic pressure vessels

Creep rupture and creep crack growth assessments are performed on three 0.5Cr–0.5Mo–0.25V welded pressure vessels using reference stress methods. Each test vessel failed by steam leakage through the Type IV location of a weld. Estimated rupture times and failure locations are compared with the experimental results. The location of failure is shown to be correctly predicted and the calculated time to failure to be conservative with respect to the test results in each case. Estimates of creep crack growth from a pre-existing defect in the Type IV region of one vessel weld are also described. Conservative predictions of growth close to vessel failure are obtained.