Abstract
Three superheater transition joints, between 2·25Cr–1 Mo and 316 stainless steel, welded with nickel–base weld metal, removed from service after 72337 h, have been examined using optical and scanning electron microscopy. In addition, microhardness measurements have been made and local chemical compositions have been analysed using the energy dispersive X-ray attachment on a scanning electron microscope. Temperature accelerated creep rupture tests have been carried out between 590 and 625°C at stresses of 31–62 MN m−2 on cross–weld tensile specimens machined longitudinally from the walls of the joints. Detailed metallographic examinations showed the same failure mode as that found in long–term service failures. Therefore, the use of post-exposure temperature accelerated testing of uniaxial cross-weld specimens appears to be a viable method of assessing the remanent life of nickel-base transition joints operating at elevated temperatures. The applicability of various multiaxial stress rupture equations to transition joint failures is considered. The present rupture data are compared with previous data generated from initially as-welded specimens to provide upper and lower estimates of the long-term failure lives.
MST/403
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