jmedclay
Mechanical
- Apr 6, 2010
- 6
A client wishes (to their credit only if totally acceptable from H&S perspectives) to re-purpose a 6000 gallon, U-Stamped pressure vessel for use in a process which will generate about 4 lbs/min of H2S in the head space. IDLH is 100 ppm; a small leak would have serious H&S consequences. We have been asked to help navigate the issue. In searching for guidance, and in spite of the lethal service language in the code, it appears that some industries don’t, by default, consider vessels containing substantial concentrations/quantities/pressures of H2S as constituting lethal service while others do. Quantitative breakpoints are not apparent to me. Neither I nor my firm are pressure vessel experts or are calibrated to this part of the CPI world, hence my kicking this around, here.
Steam jacket pressure will be approximately 40 psig, process liquor pressure about 4 psig. The process area is within a building and neighborhoods aren’t far away. My interpretation is that this is indeed a pressure vessel as defined by B31.3 and that a lethal service verdict must be formally made wrt H2S release. The client would like to avoid that classification and use the existing vessel. Are there methods whereby that be done in good conciseness? Are there engineering and administrative approaches which are professionally sound and well protective of human health in which this service could be considered non-lethal? Say, H2S gas monitors at all flanges, manways, seals etc. with alarms in the op-area and CR, SCBA + radio for all in the op-area, vacuum conditions in the transport of headspace gas as soon as possible in the line, burst disks ducted to the scrubber (or flare), immediate feed SD on alarm (which quickly stops the reaction), induced building ventilation, and so on. I assume many of those safety items would be used regardless but, again, I am not calibrated to the CPI world; I do not know what is considered reasonable & customary in this context. If the answer to the question is NO, that it’s absolutely contrary to accepted practice, there is no way around it, then so be it. If the answer is “maybe, sometimes one can reasonably do that sort of thing” then a next question seems to be: Is this U-Stamped vessel close enough in the details that matter to be reliably used for this process? Because time is short (surprise!) I requested the U-1, any R-1s and 4s, all inspection reports, mfg fab drawings & materials used, and anything else in the vessel file, with the suggestion that we put them in front of a U, R & L-Stamp shop for an opinion as to how close it is to complying with L-Stamp requirements. I also suggested consulting the client’s insurer straight away.
Any reactions? I’d greatly value experienced feedback.
Thanks much,
John
Steam jacket pressure will be approximately 40 psig, process liquor pressure about 4 psig. The process area is within a building and neighborhoods aren’t far away. My interpretation is that this is indeed a pressure vessel as defined by B31.3 and that a lethal service verdict must be formally made wrt H2S release. The client would like to avoid that classification and use the existing vessel. Are there methods whereby that be done in good conciseness? Are there engineering and administrative approaches which are professionally sound and well protective of human health in which this service could be considered non-lethal? Say, H2S gas monitors at all flanges, manways, seals etc. with alarms in the op-area and CR, SCBA + radio for all in the op-area, vacuum conditions in the transport of headspace gas as soon as possible in the line, burst disks ducted to the scrubber (or flare), immediate feed SD on alarm (which quickly stops the reaction), induced building ventilation, and so on. I assume many of those safety items would be used regardless but, again, I am not calibrated to the CPI world; I do not know what is considered reasonable & customary in this context. If the answer to the question is NO, that it’s absolutely contrary to accepted practice, there is no way around it, then so be it. If the answer is “maybe, sometimes one can reasonably do that sort of thing” then a next question seems to be: Is this U-Stamped vessel close enough in the details that matter to be reliably used for this process? Because time is short (surprise!) I requested the U-1, any R-1s and 4s, all inspection reports, mfg fab drawings & materials used, and anything else in the vessel file, with the suggestion that we put them in front of a U, R & L-Stamp shop for an opinion as to how close it is to complying with L-Stamp requirements. I also suggested consulting the client’s insurer straight away.
Any reactions? I’d greatly value experienced feedback.
Thanks much,
John