Leakage of gasoil from side cut piping in crude distillation unit of a petroleum refinery

•SS316L elbow has been failed after 3 years of gasoil service in side cut piping.•Material defect existed in the elbow due to poor pre-commissioning inspection.•Middle distillate gasoil produced from sweet crude oil of lower TAN with 26.71 API of 0.21wt% sulfur.•Material defect had magnified the localized stress under actual piping operating condition and lead to brittle fracture. Origin of material defect was discussed. This paper reports failure of elbow from side cut piping after three years of refinery gasoil service and piping metallurgy was SS316L austenitic stainless steel. Systematic investigations including visual inspection coupled with laboratory studies were carried out to determine the cause of failure. The samples from failure location were examined for chemical analysis, hardness, fractography, elemental analysis and metallographic evaluation. Further, crude feedstock was evaluated as well. Various characterization studies concluded that presence of material defect encapsulated in elbow prior to start of initial distillation column (side cut piping) operation was the root cause of failure. Localized stresses induced from internal pressure act on remaining wall thickness have lead to brittle fracture and resulted in gasoil leakage. The existence of material defect in failed elbow prior to initial operation had revealed poor pre-commissioning inspection practice. The origination of detected material defect was discussed and similar leakages shall be avoided by defect free piping components provided with proper support system at critical piping locations. The results in this article intended for petroleum refinery piping/energy pipeline operators for use of qualified piping components at critical locations especially during plant/piping commissioning stage.