Catastrophic Failure of a Dissimilar Metal Weld in a High Pressure Steam Venturi

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In mid-2009 at the BASF FINA Petrochemical L.P. Steam Cracker in Port Arthur, Texas, a venturi-type flow meter in super-high-pressure steam service ruptured catastrophically, resulting in a major release of pressure and trip of the plant. Initially a steam leak was observed at the flow meter, and shortly thereafter the rupture occurred, completely separating the pipe and releasing 1,500-psi, 900oF steam. Fortunately no one was injured in the incident, but significant physical damage occurred from the concussion blast as well as from the loss of steam and subsequent plant-wide trip. The flow meter had been in service for over nine years with no prior indication of leakage or damage.

The 16” venturi body was basically a three-piece component constructed of 9-Chrome (A335-P91) pipe sections on each end with a 316 stainless steel throat in the center. The P91 pipe was buttered with a deposit of ¼” Inconel 182, and then welded to the 316 throat. The fracture occurred at the edge of the P91 pipe weld, at the interface with the buttering layer, with cracking in the heat affected zone identified as the failure mechanism.

The purpose of this paper is to describe the nature of the failure, the analyses undertaken and their results, the causes and contributing factors, corrective actions taken, and recommendations for preventing such failures in the future. This information is presented with the intent to heighten awareness in the industry about the potential hazards associated with welding dissimilar metals, in particular chrome alloys to stainless steels, and to encourage undertaking preventive measures to identify areas of concern before catastrophic failures can occur.
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