Creep–fatigue damage assessment in high-temperature piping system under bending and torsional moments using wireless MEMS-type gyro sensor

Piping systems in thermal power plants are generally subjected to creep–fatigue loading caused by internal pressure, bending moment, and torsional moment in a high-temperature environment. These loadings cause Type IV cracks to form in the heat-affected zone in the weldment of the piping. In this study, we attempt to predict the creep–fatigue Type IV crack initiation life using a wireless micro-electromechanical system-type gyro sensor to understand the damage progress in plant components for the establishment of digital twin technology, which has recently attracted attention. The strategy for developing the system is as follows: i) remotely and sequentially import signals from a sensor attached to the actual component to a personal computer and ii) identify mechanical conditions such as bending and torsional moments in the piping component even in a high-temperature environment. This study first shows how to identify both moments in a piping system based on the rotation angles (deflection and torsion angles) measured using a gyro sensor. Next, a creep–fatigue life diagram is constructed based on the equivalent bending moment, which can combine the two independent parameters of bending and torsional moments into a single parameter. Finally, creep–fatigue tests were performed on a P91 steel piping weldment specimen using the high-temperature bending–torsional creep–fatigue testing machine developed by our group, and it was shown that the equivalent bending moment identified from the gyro sensor attached to the piping specimen can predict the Type IV creep–fatigue crack initiation life at the weldment.