Creep behaviour and stress analysis of a seventeen-year service-exposed primary super heater tube in a thermal power plant

Abstract

The elastic, inelastic deformation and stress distribution pattern of a seventeen year service-exposed primary super heater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element Computer code ANSYS (R) was used for stress analysis. The methodology is a valuable design tool for development of new boiler tubes as well as for considering the effects of numerous operating variables on creep life. The health of the tube was also assessed based on microstructure, hardness and a few conventional creep tests carried out at 500 degrees C at various stress levels (40 to 177 MPa). Results revealed that there was not much variation in the microstructure and hardness of the service-exposed tubes compared to the virgin material. Creep deformation behaviour of the service-exposed and virgin tubes of the same material at 40 MPa revealed that deterioration of the creep properties fell within the 20% scatter band, which is well within the specified limits of ASTM standard. The service-exposed primary super heater tube is thus in a good state of health.