Mechanical Response Of An Industrial Piping System Under Strong Cyclic Loading

Abstract The paper presents a combined experimental and numerical investigation of cyclic loading response of an internally pressurized 8-inch-diameter steel piping system. The piping system comprises three elbows and is subjected to quasi-static end-displacement excitation. Global deformation and local strain measurements are obtained, indicating significant strain ratcheting at critical locations of the elbows. The piping system failed under low-cycle fatigue undergoing through-thickness cracking at the flank of the most strained elbow, after 129 loading cycles with measured strain range of approximately 3%. Postfatigue metallographic examination of the elbows indicated that fatigue cracking initiates from the inner surface of the pipe elbow. In all elbows, several microcracks develop along the inner surface of elbow flanks, whereas the outer surface remained practically intact before through-thickness cracking occurred. Finite element simulations, with a cyclic-plasticity model calibrated properly in terms of small-scale material tests, provide very good predictions in terms of local strain evolution at critical locations. Numerical results at the intrados and the extrados of the critical elbow of the piping system verify strain ratcheting and the location of crack initiation observed in the experiments. This paper can be used as a reference for future experiments on cyclic loading of piping components, and for benchmarking constitutive modeling for simulating ratcheting.