For certain standards pertaining to control valves used in hydrogen services, why is it recommended that installation of a bypass (and blockvalve) be avoided?
Answers
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06/06/2008
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A:
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Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
The simple answer is whether or not the control valve can be safely isolated and maintained without taking oil feed out and depressurizing and inverting the atmosphere at ~ 1 psig to nitrogen. In many instances, manual operation of a bypass valve raises major risk management issues with respect to the hydroprocessing unit.
In some instances, the control valve can be twinned with one CV operated until "failure or excess wear" and then operations switched to the twin CV.
Single isolation valves with thin blind installation flanges may be provided so that the "failed or worn" CV can be serviced when the high-pressure reactor loop is undergoing unscheduled short outage and has been depressurized to ~ 1 psig under "sweet hydrogen" atmosphere.
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