An unexpected failure of 316L Stainless Steel instrument tubing occurred in a high pressure Hydroprocessing unit resulting in a shutdown of the unit. The tubing system consisted of a compression type fitting commonly used in instrument systems and had only been in service for 3 years when the failure occurred. The failed tubing samples were removed for metallurgical analysis and determination of damage mechanism.
Metallurgical analysis and finite element analysis of the tubing identified excessive cold working leading to hydrogen embrittlement as the primary mode of failure. This paper details the investigation into the failure to arrive at the root cause and the preventive measures adopted to assess the installed population of tubing in similar service.