Life assessment of weld repairs in (1)/Cr-2(1)/Mo-2(1)/V-4 main steam pipes using the finite element method

Weld repair at heavy section weldments is often a natural consequence follo wing inspection of plant under high-temperature conditions. Four typical we ld geometries and conditions have been studied: an 'as new' weld, a weld ta ken from plant after long-tenn service, a 'full weld repair' and partial re pairs 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 174800 h operation. Material properties we re obtained at 640 degreesC and covered service-aged and new parent materia ls and weld metals. The heat-affected zone (HAZ) properties, as relevant to the weld models, were measured using indentation creep procedures. Realist ic weld models were analysed using the finite element method and Norton's c reep law. The expected lifetimes were found using peak representative ruptu re stresses in each zone, thereby taking account of the multi-axiality effe cts. For the particular material data used in this investigation, results obtain ed 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 changin g the width of the weld metal region and of changing the axial (system) loa ding on the failure life and position of the new, aged and fully repaired w elds were also considered. Finally, the validity of the finite element pred ictions of the failure life of weld repairs is discussed.