We performed failure analysis and subsequent design modifications on a contactor vessel. The vessel failed during startup as a result of excessive internal vacuum due to a process excursion.

The vessel is part of a scrubber process used remove hydrogen sulfide from bio-gas and landfill gas. Fabricated from FRP (Fiber-Reinforced Plastic) the vessel is designed to maximum internal pressure of 10 psig and maximum external pressure of 0.15 psig. 

The Inlet Gas Scrubber is protected from over pressure by a relief valve (PRV). Since it appears that there are no isolation valves between the Inlet Gas Scrubber, Contactor and Outlet Gas Scrubber, all three vessels are somewhat protected by this single PRV. However, it is preferable for each vessel to have its own individual pressure relief valve vented directly to the atmosphere. According to the P&IDs reviewed, there was no vacuum relief device to protect the vessel from excessive external pressure.


We perform failure analysis on vessels, heat exchangers, ductwork and other plant & process equipment.

Give us a call to discuss your engineering challenges.

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Tom O’Donnell, PE
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