Lifetime Predictions For High-Temperature Low-Alloy Ferritic Steel Weldments

Abstract

The paper reports the finite element creep continuum damage mechanics (CDM) analysis of the creep rupture behaviour of thin-section butt-welded, internally pressurized pipes, and of uniaxial cross-welded tension testpieces made of Cr-Mo-V steels. The CDM analyses are shown to predict accurately lifetimes and failure mechanisms observed from metallographic analyses of sectioned components. The paper then addresses the lifetime prediction of components by comparing predictions made using British Standards BSi PD 5500 with the results of the experiments. Predictions have been based on uniaxial plain bar data for both parent and Type IV materials; both of these have been obtained by integration of constitutive equations. Comparison of predicted and experimental weldment lifetimes has been made using a weld strength reduction factor. It is found that the required factors are very dependent on temperature and the ratio of axial to hoop pipe stresses. Finally, the paper examines the British Energy Generation Limited R5 assessment procedure and compares lifetime predictions with those made using the British Standards BSi PD 5500 approach. It is noted that the stresses in both approaches are in good agreement for the external/internal radius ratio of 1.25 considered in the butt-welded pipe experiments.