Investigation of the Extent and Nature of the Cracks Found in Segments of Two Cr - 0.5 Mo Pressure Vessels from the Nil Residual Creep Life Program

摘要

A metallographic investigation was carried out on samples taken from two 1 Cr - 0.5 Mo steel headers, operating at 525 C; 81 N/sqmm; 18,000 hr in a controlled test. A nozzle section from each vessel was examined. Both samples show discontinuous surface breaking cracks and microvoids. This damage could be due to reheat cracking which occurred during post weld heat treatment or due to creep. Micrographically it is not possible to distinguish between these two forms of cracking after the vessel is exposed to high temperature. Weld inplant testing may be a way of establishing the sensitivity of this material to reheat cracking and therefore clarify the cause of failure.