Stress Analysis and Creep Behavior of Service Exposed Primary Superheater Tube in a Thermal Power Plant Ashok Kumar Ray , Kumar Diwakar*, Jitendra Kumar Sahu, Hemant Kumar Das , Nilima Roy, and Rabindra Nath Ghosh National Metallurgical Laboratory (CSIR), Jamshedpur-831007, India * Department of Mechanical Engineering, National Institute of Technology Jamshedpur- 831014, India (Received April 8, 2008; final form April 15, 2008) ABSTRACT The elastic, inelastic deformation and stress distribution pattern of a seventeen years service exposed primary superheater 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 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°C at various stress levels (40- 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 behavior of the service exposed and virgin tubes of the same material at 40 MPa reveal that deterioration of the creep properties fall within the 20% scatter band, which is well within the specified limits of ASTM standard. The service exposed primary superheater tube is thus in a good state of health. Key words: Elastic, inelastic deformation, stress, creep deformation, boiler tubes, finite element analysis, incremental solution technique 1. INTRODUCTION The consequences of power plant failure can be tragic and expensive. There are many cases of engineering disasters resulting in loss of life and property. For boiler components utmost attention is a must to ensure that such incidents should not take place. These components have finite life because of prolonged exposure to high temperatures, stresses and aggressive environments. Remaining life assessment (RLA) of aged power plant components in the present highly competitive industrial scene has become very popular both for economy and safety reasons. Most of the power plants are over 25 years old and RLA has become an imperative task for evaluating their lives. In real life situation both premature retirement and life extension (in relation to design life) can be encountered. The decision for retiring a component is not purely technical but also one of economy and safety. In view of the increasing cost of setting up a new plant, there is now considerable interest in life extension of the existing units. In order to arrive at a quantitative estimate of the remaining life of such ageing components, it is necessary to have creep data. Non-destructive test results cannot predict the future creep life and creep deformation behavior of the service exposed tubes. Creep involves time dependent deformation and fracture of materials l\l. The creep and stress rupture properties of boiler steels at low temperature is of very 79 Brought to you by | University of California Authenticated Download Date | 6/10/15 4:14 PM