Abstract
We developed a health-monitoring methodology for high-temperature steam pipes that estimated the life prediction of creep–fatigue interaction by directly measuring the displacement of hot parts. Three different methods (boiler code, design stress, and operating stress) were used to estimate the stress of the high-temperature pipe system. As a theoretical approach, the German boiler standard code calculates the stress according to the pipe shape, while design stress, which is also called allowable stress, was determined by a function of the operating temperature. The operating stress was immediately calculated using the surrogate model, with maximum displacement measured using the 3D displacement measurement system. To achieve the surrogate model, the stress was estimated by the pipe-stress analysis under the given displacements, and the surface-response model was developed to relate the stress and displacement. We showed that those methods are efficient methods to predict the stress and are applicable in health-monitoring methodology. Finally, the creep life and the low-cycle fatigue life were investigated using the Larson–Miller parameter equation, as well as the Smith, Hirschberg, and Manson equations. Our proposed monitoring system can be used to predict the fatigue and creep life of high-temperature steam pipes in real time, and we believe that the system can be applied to actual maintenance in thermal power plants.
Highlights
Life prediction of industrial facilities after many years of service is an important issue related to the stability, economy, and replacement of an entire facility
Based on the stress and function of the measured displacements, we developed a surrogate model, correlating stress and displacement and life prediction under the creep–fatigue interaction
Three methods were used to calculate the stress of the high-temperature pipe system in this study: The German boiler standard Technical Rules for Steam Boilers (TRD) code method uses the geometric information of pipes, the yield strength-based method estimates the design stress, and the 3DDMS method obtains the operating stress at maximum displacement through the proposed surrogate model
Summary
Life prediction of industrial facilities after many years of service is an important issue related to the stability, economy, and replacement of an entire facility. In the circumstances of high temperature with cyclic loadings, creep–fatigue interaction, which shows creep cavitation and surface-fatigue damage, may be found within the material and should be considered when evaluating life prediction. Theoretical and experimental studies have been conducted to predict fatigue [15,16,17,18,19,20] and creep [21,22,23,24] life for parts exposed to high temperatures and cyclic loads. Various evaluation methods (i.e., strain energy density, stress-based method, strain range method, linear-damage summation method, and ductility-exhaustion model) were used to evaluate the creep and fatigue life according to the loading conditions and the shape of the specimen. An efficient method for life prediction for a main steam pipe is proposed using the three-dimensional displacement measurement system (3DDMS) and surrogate models developed by a stress-based approach. Our work implemented the stress analysis and life assessment of the piping system for the Manjung power plant in Malaysia, and it shows that the proposed method is quite a reasonable and reliable system for the stress and life assessment of high-temperature steam pipes
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