Research on the residual life of the superheating system steam header for a 220MW ultra-high pressure thermal power plant during extended service period

Abstract The superheating system steam header is one of the most important components of the thermal power unit which is related closely with the safe and stable operation for the power plant during the life extended period. The deterioration of material properties caused by the aging of microstructure is the primary cause for the early failure of high-temperature bearing components and their welding parts. In this paper, the residual service life of a 220MW boiler's steam header is comprehensively analyzed based on nondestructive test, hardness test, metallographic structure and creep-fatigue damage analysis after 30-years-service. To calculate the creep-fatigue damage, both the modified elastic based method according to ASME-III-NH and the FEM simulation according to the Bailey-Norton constitutive are implied to assess the high temperature fatigue-creep life of the steam header. To calculate the fatigue strain range, the elastic strain range is modified by introducing the multi-axial stress factor and the Poisson's ratio adjustment factor, and the creep strain modified by the creep adjustment factor is added into the fatigue strain range. The results show that there still is 8.2 years' residual life for the steam header, if the thermal power unit continues to operate on the same conditions as the past 29 years.