Power generation plant heat exchangers contain many banks of thin section, small diameter boiler tubes that are usually cold bent to shape (introducing high levels of plastic strain) prior to interconnection by welding. Plastic deformation history has been identified as a key cause for premature creep cracking in boiler tube welds operating at high temperature. The aim of this proposal is to study the effects of plastic strain on macro and micro residual stresses in welded tubes where parent material has been pre-strained by up to 25%.