Life assessment of weld repairs in 1/2Cr1/2Mo1/4V main steam pipes using the finite element method

Abstract

Weld repair at heavy section weldments is often a natural consequence following inspection of plant under high-temperature conditions. Four typical weld geometries and conditions have been studied: an ‘as new’ weld, a weld taken from plant after long-term service, a ‘full weld repair’ and partial repairs of two forms where repair was associated with either one or both weld interfaces. The parent material was 1/2CrMoV welded with 2CrMo weld metal and was removed from plant after 174 800 h operation. Material properties were obtained at 640 ° C and covered service-aged and new parent materials and weld metals. The heat-affected zone (HAZ) properties, as relevant to the weld models, were measured using indentation creep procedures. Realistic weld models were analysed using the finite element method and Norton's creep law. The expected lifetimes were found using peak representative rupture stresses in each zone, thereby taking account of the multi-axiality effects. For the particular material data used in this investigation, results obtained have shown that the failure lives of fully and partially repaired welds are comparable with those of the service-aged weld and the failure lives of repaired welds are about half that of the new weld. The effects of changing the width of the weld metal region and of changing the axial (system) loading on the failure life and position of the new, aged and fully repaired welds were also considered. Finally, the validity of the finite element predictions of the failure life of weld repairs is discussed.