Thermal Degradation Analysis of Platen Super Heater Tubes in Thermal Power Plants using a Nonlinear Ultrasonic Technique

Standard supercritical pressure coal-fired power plants are operated in high-temperature environments typically under a steam temperature of 540 degrees C. In general, the design life of standard coal-fired power plants is 30 years, and life diagnosis and management are performed periodically by evaluating the degradation of boiler tubes through visual inspection, thickness and hardness measurements, etc. In this study, samples of boiler tubes operated in thermal power plants for approximately 20 years (approximately 160,000 h) were obtained from different locations, and various degrees of degradation based on the locations of the boiler tubes were evaluated using the surface nonlinear ultrasonic technique. These results were then compared with tensile test results. Variations in the ultrasonic nonlinearity parameter, tensile strength, and yield strength were highly correlated depending on the locations of the sample boiler tubes. The results confirmed that the nonlinear ultrasonic technique could be used to evaluate changes in mechanical characteristics caused by boiler tube degradation.