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Fracture Toughness and Brittle Failure in Critical Pressure Equipment

Mechanical Integrity: Verifying Fracture Toughness in Critical Pressure Equipment

"Fracture Toughness and Brittle Failure: A Pressure Vessel Case Study" was published by the American Institute of Chemical Engineers (AIChE) in the journal Process Safety Progress. This technical paper was presented at AIChE's 13th Global Congress on Process Safety (GCPS) in San Antonio, Texas, in March 2017.

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, Gas and Chemical industry. In this article, we will review an incident of brittle failure in a pressure vessel used in sour service on an offshore installation, which resulted in an accidental release of gas and condensate. A root cause analysis of the incident identified that a number of performance gaps and root causes related to the vessel's service conditions, manufacture and fabrication combined to cause the brittle failure.

This article examines the performance gaps that led to brittle failure, the effects of the root causes on the vessel's mechanical properties based on the ASME Boiler & Pressure Vessel Code material and fabrication guidelines, and recommendations for correcting these gaps to promote mechanical integrity for safer, more reliable assets.

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