Mechanical Response of an Industrial Piping System Under Strong Cyclic Loading

The paper presents a combined experimental and numerical investigation of cyclic loading response of an internally pressurized 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 the 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. Post-fatigue metallographic examination of the elbows indicated that fatigue cracking initiates from the inner surface of the pipe elbow. In all elbows, several micro-cracks develop along the inner surface of elbow flanks, whereas the outer surface remained practically intact before through-thickness cracking. Finite element simulations, with a properly calibrated 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.