Modelling of Creep Property of Base Material for Life Assessment of Mod.9Cr-1Mo Steel Welded Joint

In the Mod.9Cr-1Mo steel pipe used for steam piping of a thermal power plant, Type IV damage originating from the fine grained heat affected zone has been concerned. Although it is necessary to evaluate the remaining life evaluation of the piping based on the simulated results of stress and strain distributions acting on piping system, the appropriate creep strain characteristics of each part should be given to the welded joints (base metal, heat affected zone and weld metal) for the high precision analysis model. Therefore, in this paper, first, the Creep strain equation of the base material part is formulated from creep data of NIMS (National Institute for Materials Science) creep tests and used material collected from steam piping used for about 120,000 hours in actual equipment, and the effectiveness of the model is verified.