微小サンプルによる実機配管溶接部のクリープ余寿命評価

抄録

A new method of creep life assessment was developed to consider heat-to-heat variations of welded joints of materials used in power plants. In the method, creep properties of the welded joints are related to those of each base metal because the heat-to-heat variations of welded joints strongly depend on the creep properties of the corresponding base metals. To estimate the creep properties of each base metal of the target pipe, microstructure analyses and small punch creep tests were conducted using small samples cut from the base metals in service, and evaluations were done on the basis of material data base obtained using standard test samples of long-term service exposed pipes. Validity of the assessment method was verified through comparisons of estimation results and experimental ones for welded joints of Grade 91 steel used for long-term at USC plants. Then, the assessment method was applied to piping on site to estimate remaining life of welded joints of the material in service.