Abstract
Cracks were found in high temperature steam pipes which had been used for 100 000 hours. The mechanical properties of pipe material were tested, and the causes of cracks were analyzed by metallographic and scanning electron microscopy. The fracture parts of the tensile specimens were all in the weld fusion line. The metallographic photos of the weld section showed that there were a large number of precipitates on the fusion line. The energy spectrum analysis showed that the main alloying elements of the precipitates were chromium and molybdenum. The location of a large number of precipitates was consistent with the location of surface cracks. Combined with the working parameters of the pipeline, it was judged that the crack was a creep crack. The existence of precipitates led to micro-local stress concentration and provided conditions for the initiation of cracks, resulting in the weld fusion line becoming the primary part of the creep crack. The stress rupture test showed that the fracture time of the weld sample was shorter under larger load. The residual life of the pipeline was analyzed by using the mechanical properties obtained from the test. The conservative calculation results showed that the residual life of some stress concentration parts was 139.68 hours.
