Failure analysis of an oil refinery sour water stripper overhead piping loop: Assessment and mitigation of erosion problems

This study investigated the integrity of the outlet nozzle and elbow of the piping system downstream the finfan cooler in sour water stripping unit. The piping system in these locations experienced severe thinning and occasional leaks. The unit was modelled using process simulation software with the use of the appropriate thermodynamic methods for electrolyte models to accurately estimate the flow rates, properties in vapour and liquid phases in the piping system. The results from the process simulation were subsequently used in the Computational Fluid Dynamics (CFD) simulation. The CFD simulation results matched the erosion pattern that caused the loss of wall thickness. The eroded nozzles were also visually and optically examined using scanning electron microscopy (SEM) and Energy Dispersion X-ray (EDX). The results have indicated that the erosion is inevitable regardless of the fluctuation in the throughputs to the unit. Iron sulfide, indicative of the synergy between erosion and corrosion, was observed in the pipes elbows. For mitigation, an option has been recommended to change the operating mode of the finfan cooler so as to alleviate alloy change.