Performance And Residual Lifetime Evaluation On P22 Steel For Pipe Material After Long Term Operation

2.25Cr-1Mo steel has good processability,welding property and plasticity.It was widely used in main steam line,superheater and reheater pipe system of thermal power plants and nuclear power plants in the 1980s.This paper has carried out the room temperature tensile test of P22 steel non welds sample and welded sample of 350MW unit of a power plant for about 200 thousand hours.During the temperature range of 510? to 600? and the stress range of 60MPa to 175MPa,the high temperature endurance test of the P22 steel non welds and welded samples were carried out.The interruption test of the non welds specimen is carried out at 540? and 100MPa.The experimental materials were analyzed by metallographic analysis,scanning electron microscopy,energy spectrum analysis and hardness measurement.The results show that the crystals grow obviously after long term operation,and the microstructure is ferrite and bainite,the spheroidization of carbides is close to 4 degree.The precipitation and the aggregation on the carbide of the alloy elements Mo and Cr lead to the decrease of the properties.The properties of P22 steel decreased after long term service.Compared to the new P22 steel,the isotherm extrapolation method shows that the residual life of the main steam pipe material is about 10%to 20%.The L-M parameter methord showed that the corresponding residual life is about 19%?21%.The residual life of the material was estimated to be about 9%?10%according to the damage factor.The material residual life assessment based on the degree of spheroidization shows that the main steam pipe material residual life is about 24%.It is concluded that the residual life of the material is about 9%?24%.