Weld materials at high temperature
Reliable maintenance of thermoelectric power generation plants would be impossible without the advanced design of complex pipe systems. Novel materials that can withstand high temperature have contributed to their enhanced thermal efficiency. However, the performance of pressurised high temperature components is governed by creep related failure of local connections. Improving the current understanding of welded components' behaviour under creep conditions was one of the main objectives of the WELDON project. Experimental testing methods were employed to demonstrate the effects of weld's geometry and materials' properties and to generate essential data for the validation of life estimation techniques. Actual high temperature components or realistic models were, for this purpose, tested under conditions identical to those in service. With the use of finite element (FE) methods, complex models were generated to predict the rupture strength of cross-weld specimens and assess the impact of creep deformation on end-loaded pipes. The in-house code, developed at the University of Nottingham, is an extension of commercial finite element analysis codes with user-defined subroutines that incorporate appropriate constitutive laws for continuum damage mechanics. Continuum damage mechanics has been proven to be a valuable tool for the determination of material deterioration and creep processes' influence on the tolerance of pre-existing defects. These models of the creep response can provide a better intuitive insight into weld weakening and possible failure modes, and importantly, give a quantitative description of possible solutions. Enhancing current knowledge of welds' behaviour, they may ultimately promote the harmonisation of design and assessment procedures.
