Testing a Vessel

The accident investigation found that the leak test should have been conducted with a hydraulic procedure and not air and that the vessel should have been protected with a relief device. In addition, the fitters should have taken more time to check out the gauge to ensure that it was correct for this application. 

Two maintenance workers were replacing part of a ribbon in a large ribbon mixer. The main switch was left energized the mixer was stopped with one of three start-stop buttons. 

As one mechanic was completing his work inside the mixer, another operator on an adjoining floor pushed, by mistake, one of the other start-stop buttons. The mixer started, killing the mechanic between the ribbon flight and the shell of the vessel. 

Lock-tag-and-try procedures were developed to prevent accidents of this kind. A padlocked switch at the starter box disconnect, with the key in the mechanics pocket, prevents this type of accident. After the switch gear lockout, the mechanic should also verify the dead circuit by testing the push-button at all switches this is the try part of the lock-tag-and-try procedure. 

Two vinyl chloride polymerization reactors were being operated by the same team of operators. Reactor 3 was in the cool down and dump phase of the process, and reactor 4 was nearly full of monomer and in the polymerization phase. The foreman and three employees set to work 

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In order to confirm the capability of acoustic emission to detect the evolution of a defect during a pneumatic test, a vessel with a lack of thickness due to the action of corrosion was pressurized pneumatically until burst. 

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