Application of Modern Weld Modelling Techniques in the Design of a Ring Weld Reheat Cracking Test Specimen

Abstract

New test specimens to study initiation of reheat cracking in stainless steels have been developed using modern finite element (FE) weld modelling techniques. Residual stress simulations of two theoretical ring weld test specimens were conducted in order to optimise the specimen designs so that large zones of creep damage are predicted when subject to elevated temperatures. Each design was optimised to predict damage in the heat affected zone (HAZ) or weld metal region respectively. Fabrication of test components is proceeding on the basis of these studies. The general design is based on a thick disc of parent material with a multi-pass manual metal arc (MMA) ring weld on one surface. The overall objective was to design a specimen that produces macro cracks when soaked at temperatures of 600°C–650°C within several thousand hours. However, consideration was also given to the ease at which automated NDT procedures could be applied to monitor the development of creep damage, as well as the ability to measure residual stress levels by neutron diffraction and the contour method. The design analysis followed a pragmatic approach whereby an ‘appropriate’ geometry for the ring weld test specimen was analysed based upon a ‘baseline’ set of welding parameters, namely, heat input, lay-up sequence and inter-pass temperature. This ‘baseline’ design was then subject to a number of sensitivity studies to ascertain the performance of the specimen where key parameter’s were varied; these being lay-up sequence, number of capping passes, specimen thickness, radial weld position and weld fill. Also investigated was the introduction of an offset weld in order to control the location at which initiation occurred, either HAZ or weld metal. Residual stresses in this multi-pass MMA weld were predicted using a 2D axisymmetric model, simulating both the welding procedure, subsequent machining and furnace heat soak. The coupled thermal-mechanical analysis was performed using the FE code ABAQUS. A heat source modelling tool was employed to calculate welding fluxes, which were read into ABAQUS via a user subroutine. Fusion boundaries were assessed a correlation for total fused area.