Erosion-corrosion failure analysis of the elbow pipe of steam distribution manifold

This work discusses a case study of the failure of rice condition plant boiler pipe fittings. The failure analysis was performed on the 45 degrees and 90 degrees API 5L X65 steel pipe elbows connected to a steam manifold in a boiler of a rice conditioning plant. Failure analysis was performed by visual observation, microscopic analysis, hardness measurements, and numerically by Computational Fluid Dynamics (CFD). It was confirmed that the mechanism of failure was due to erosioncorrosion. The results showed also that, erosion -corrosion at the outlet of the 90 degrees and 45 degrees elbows due to the maximum particle impact in the high pressure and high turbulence intensity region. Microscopic analysis of the 90 degrees and 45 degrees elbows showed that large pits and cuts were the main reason for leakage perforation. Erosion at the inner bend of the 90 degrees and 45 degrees elbows is lower than at the outer bend, which is related to the higher particle-wall impaction, pressure, and turbulence intensity. The main cause of leakage and wall thinning in both elbows is the development of limescale which leads to pitting corrosion and the formation of leaks at higher oxygen concentrations. The simulation results show that the maximum material removal rate in the 45 degrees elbow is 42 % lower than in the 90 degrees elbow, the erodent impaction and higher wall shear are liable for the development of the perforation near the exit of 90 degrees and 45 degrees elbows.