Creep-fatigue Crack Growth Assessments of Elbow end Welds

Elbows are highly stressed components and are critical to the integrity of the pipework systems and important to the safety of plants. In this paper, a local collapse solution for elbow end welds has been developed and subsequently used in defect assessments. A creep-fatigue crack growth assessment of the elbow end weld has been carried out assuming a defect initiated in the weld under the loading conditions of internal pressure, system moment, high temperature and welding residual stress. For the elbow end weld, the limiting defect calculation has been conducted using R6 procedures and the creep-fatigue crack growth assessments have been performed using R5.Furthermore, appropriate combinations of creep deformation and creep crack growth used for the R5 assessment are detailed in the paper. A surface breaking circumferential semi-elliptical defect postulated on the external surface has been assessed. After presenting the detailed assessment result, conclusions are drawn.