CDM prediction of creep failure modes in thin and thick section Cr-Mo-V Butt-welded pipes under combined internal pressure and end loads at temperatures in the range 540-620 C

摘要

The paper examines the dependence of creep failure modes of butt-welded pipes upon: temperatures in the range 540-620 °C; the ratio of axial to pressure loadings (loading condition); and, load levels which result in failure times in the region 2000-250000 h. Continuum damage mechanics (CDM) analyses have been used to analyse two extreme geometries: thin section pipes (4.52 mm) and thick section steam pipes (46 mm) of the type found in power generation plant. The thick pipes have been selected to allow through-thickness constraint to be developed. Two predominant modes of failure have been predicted: Fusion Boundary failure and Type IV failure. For the thin section pipes the modes of failure are not strongly dependent on applied loading levels, and loading condition, but are dependent on temperature: at 540 °C failure is in the Fusion Boundary and at 620 °C it is in the Type IV region. Failure mode in the thick pipes is dependent on temperature, and applied loading levels, but is essentially independent of loading condition. At 540 and 565 °C failure is in the Fusion Boundary; whereas at 575 °C, failure is in the Type IV region at higher applied stress levels, and in the Fusion Boundary at lower applied stress levels.