Fracture Toughness and Brittle Failure: A Pressure Vessel Case Study

That the manufacturing and fabrication process can introduce low fracture toughness and cause brittle failure in steel has been documented in well-known studies. These include failure of Liberty ships during World War II and, more recently, weld failures in steel moment frames during the 1994 Northridge earthquake. In both of these cases, the manufacturing and fabrication process introduced stress states that reduced fracture toughness and caused brittle failures. Control of the manufacturing and fabrication process to maintain sufficient fracture toughness remains a challenge for the Oil and Gas Industry. In this article, we will review an incident of a brittle failure of a pressure vessel. The head of the pressure vessel, which was operating as a low-pressure separator, detached about its circumference at a pressure much less than the vessel's maximum operating pressure. A root cause analysis of the incident identified the performance gaps and root causes from the vessel's service conditions, manufacture, and fabrication that combined to cause the brittle failure. This article examines the performance gaps that lead to the failure and their root causes. The effect of the root causes on the vessel's mechanical properties is discussed. Further, the performance gaps are related to material and fabrication guidelines in the ASME Boiler & Pressure Vessel Code. Finally, recommendations for correcting the performance gaps are offered. (C) 2017 American Institute of Chemical Engineers