Creep of service-aged welds
The creep behaviour of welds in service-aged pipes are studied. The aims of the research have been achieved using analytical, numerical and experimental approaches to the relevant subjects. Several features of the work are presented: (i) a systematic parametric study of the creep of two-material test specimens including a stress singularity analysis, (ii) an impression creep testing method using a rectangular indenter, which can be applied to study the creep properties in welds, and (iii) methods used for damage constitutive equation generation involving FE-damage modelling of the rupture tests of cross-weld specimens. General observations on the creep of two-material structures have been made using analytical solutions derived from four simple structures. The effects of geometries and relative creep properties on the creep stress or strain-rate distributions have been investigated using the finite element approach with idealised, two-material, axisymmetric models. The stress variations have been extensively studied on the centre-line and in the singularity regions of the models. An impression creep testing technique with a "long" rectangular indenter has been developed for the study of the creep properties in the narrow zones within weldments. The effect of varying the geometric test parameters has been fully analysed. The application and the possible advantages of the technique for determining the creep properties in welded components have been highlighted. Experimental testing has been performed for the purpose of verifying the impression creep testing technique and to provide the creep and rupture information required for the generation of creep and damage parameters for the exposed materials. The results obtained have further validated the applicability of the impression creep testing technique. Creep continuum damage investigations have been performed in order to generate the material parameters in a continuum damage constitutive equation and to model practical weldments. The methods used for material data generation have been established. The failure analysis and prediction for the service-aged welded pipes using steady-state analysis, damage modelling and extrapolation technique have been addressed.