Safety Evaluation of Pressure Piping with Weld Flaw after Long Time Service in a Water Power Plant

摘要

Pressure steel pipings in a water power plant have been in service for over fifty years. In order to assess the safety of the piping, whole check and tests for the piping were carried out. The material for some piping is ST3 from former USSR, the other is A3 made in China. The mechanical properties were investigated by tests and were compared with the original material properties. The result shows the yield strength and tensile strength of serviced steels are less than those of original materials. The surfaces of the piping were checked to investigate the corrosion, surface defects. The flaws in the welds and near the welds of the pipings were detected by UT and MT, and several weld flaws were found. Based on the test and NDT investigation results, the strength, fracture and fatigue life of the pipings are assessed according to Chinese standard GB/T19624-2004 and British standard BS7910-2000. The assessment results show that the strength of the piping is enough, and the pipings with these flaws does not fracture. The piping can be safe in service under the normal operating condition for 10~4 to 10~6 cycles.