Prediction and Comparison of Creep Behavior of X20 Steam Plant Piping Network with Different Phenomenological Creep Models

In service, steam pipes are subjected to high temperature close to 0.4 T_m (melting temperature) or higher and pressure; thus, making them prone to failure due to creep. Often, the design methods for these steam pipes usually do not provide their specific in-service life; hence, some type of service fitness tests are performed, and data obtained from the tests are used to inform the routine inspections. Choosing a creep model that favorably describe the creep behavior of components in service is paramount to engineers as well as the plant operators. Reports have shown that there are several creep models available and they all behave differently with different materials, and operating conditions. In this study, the creep behavior of X20 (12Cr-1MoVNi) steam piping network subjected to three phenomenological creep models (conventional hyperbolic sine creep, modified hyperbolic sine creep and constitutive creep model) was investigated. Fortran user subroutine scripts were developed for the three models and implemented in finite element (FE) code, Abaqus to determine the creep stress and strain rate, while the useful creep life and creep damage was determined using fe-safe/TURBOlife software. The results show that the modified hyperbolic sine creep model is more suitable for estimating the creep behavior of X20 steam piping under the specified operating conditions because of its more conservative prediction.