A Root Cause Analysis of Catastrophic Failure of Industrial Discharge Hopper Pipe

Several failures of the industrial pipes have been reported in the past and most of them are due to Stress Corrosion Cracking (SCC), sensitization and hydrogen embrittlement. Stress Corrosion Cracking is a delayed failure where corrosion environments such as condensed water, ammonia solutions, moist air, and solutions containing chlorides and nitrides play a major role. This work presents a detailed investigation and root cause analysis of the catastrophic failure of an industrial discharge hopper pipe. The hopper pipe investigated in the present work is made of austenitic stainless steel, 316 grade, a commonly used grade for valves, pipes and heat exchanger tubes. The pipe fractured in the transverse direction, leading to the failure of the discharge pipe. Visual inspection, dye penetrant test, chemical analysis, microstructural analysis, and fractography analysis were carried out on the failed part and it was concluded that stress corrosion cracking led to the failure of the hopper pipe. The pipe constantly being under exposure to industrial water and the presence of chlorine content in it made it susceptible to stress corrosion cracking. Transgranular fracture was clearly observed in the microstructure of the failed sample and spot EDX at the fracture location confirmed the presence of chlorine content. This indicates that the pipe has been subjected to corrosion because of service conditions/environment and any of those minor cracks would have opened up with the continued service operation, had the major transverse fracture not taken place. Further, fractography showed striations indicating fatigue loading. The work concluded that stress corrosion cracking was the root cause of failure. Cathodic protection or suitable polymer coating should be considered as the preventive measures to avoid stress corrosion cracking in future.