Would you consider this an ASME Code vessel?
Would you consider this an ASME Code vessel?
(OP)
There is a customer that has a "design pressure" of 5 PSI, but then they are also asking to design for an 'extreme overpressure event' of 150 PSI in the event of a damaging event that is possible with this vessels service, they say they are adding this to the design so that the vessel would not become shrapnel as it fails, they say that if this event were to occur that would be the end of the vessel and it would be removed from service.
If you were given this job would you consider the 150PSI a design pressure (ie a stamped Code vessel)?
If you were given this job would you consider the 150PSI a design pressure (ie a stamped Code vessel)?





RE: Would you consider this an ASME Code vessel?
If the client and/or the jurisdiction requires, it would also be a Code vessel.
Regards
Regards,
Mike
RE: Would you consider this an ASME Code vessel?
A few questions and opinions.....
- What is the diameter, volume and desired material for this device ?
If the diameter is modest, say less than 36 inches, it may cost very little to upgrade the pressure rating for the item and go with an ASME vessel design ( with or without a code stamp. I would never design to 5 psig.... the calculated wall thickness becomes too small. For a while power plant deaerators were designed to too small of a pressure for the transient events that were commonly encountered. Failure resulted. This sounds like a similar situation.
- Have relief devices been considered..... tell us more about the system ?
Tinman is correct insofar as it is the responsibility of the client to specify design pressure of the system. However, it seems that you may want to consider the savings in capital costs from the addition of a relief device versus an expensive but thick relief vessel.
An ASME vessel designed for a design pressure 150 psig does not become schrapnel when pressurized above this number. Failure commonly will occur when pressurized to 2.5 to 3.0 times this limit. A lot depends on the specific design.
My opinions only....
MJCronin
Sr. Process Engineer
RE: Would you consider this an ASME Code vessel?
RE: Would you consider this an ASME Code vessel?
RE: Would you consider this an ASME Code vessel?
RE: Would you consider this an ASME Code vessel?
Either design for 150psi (you might be able to justify 135 + 10% accumulation) or design a relief system which prevents overpressure (bursting discs, bent pin valves etc)
Start form the basis that this extreme event makes it a code vessel and then work the options from there.
Loads and loads of questions about normal operation and this extreme event need to be asked and understood to make an informed judgement and provide for a safe and efficient design.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Would you consider this an ASME Code vessel?
If the device is designed for 15 psig, relief set at 5 psig and the accumulated overpressure during relief is below 16.5 psig, then it isn't a pressure vessel either- and you have a hope in hell of designing a relief device- but if the flow chokes anywhere in the relief line, you're done- accumulation will increase beyond the safe limit.
If the device is designed for 150 psi and the relief set at 5 psi, what's your safe maximum accumulation? If it's above 16.5 psig, it walks and talks like a pressure vessel in my book and probably should be one. You need the code rules for design and fabrication and inspections (and AI involvement) required of a code vessel to justify that the design will safely withstand the higher accumulated overpressure. Design pressure doesn't matter per se- relief pressure is what matters, and relief pressure determines the hazard of a resulting failure.
Now if the relief consists of nothing but a properly sized pipe open to the atmosphere, that's a different story...
RE: Would you consider this an ASME Code vessel?
I guess my question stems from the definition of design pressure in the BPVC which is the "most severe condition of coincident pressure and temperature expected in normal operation", and according to the Agent this is not in normal operation but an unlikely event (that would result in the vessel being taken out of service if it were to occur).
Since we will not be building this vessel and the Agent is responsible for telling the designer/fabricator the design conditions I wasn't sure if I was interpreting the rules of the Code correctly. If in fact the design pressure is meant to cover the pressures in 'normal operation', and it is the owners responsibility to inform us of the design conditions it seems to me that this vessel could be considered non-Code.
Also, the vessel is designed at the 5PSI with the appropriate SF, but the explosion condition they want designed to SF=1.5 at UTS.
I told them that I thought it should be Code Stamped (which if it is the SF for the 150PSI would be 3.5), but ultimately they are the ones signing off on the design so I'm not sure if I've covered my bases or if I should be doing something else, which I guess would be declining to do these calcs if they insist on it being non-Code and not introducing a burst plate or other means of dealing with the overpressure condition. What do you think?
RE: Would you consider this an ASME Code vessel?
PipingEquipment, it seems that if designed for the overpresssure per the clients requirements, and if normal design condition is 5 psi, it could be justified as a non-Code vessel w/o overpressure protection. Big however, however.
If not a Code vessel, to what standards / methods is it designed in the first place? What IS the appropriate SF? What does the jurisdiction say? If designed as Code vessel at 5 psi, how shall UG-22(i) be considered? What's YOUR exposure in the whole thing?
Can o' worms. My preference would be to design to Code at 150.
Regards,
Mike
RE: Would you consider this an ASME Code vessel?
I think my point remains which is how on earth do you actually design this given these wildly different criteria. The SF of 1.5 over UTS ( I assume this means the max stress levels are 66% of UTS?) will imply a much higher design pressure than 5 psi and result in a significantly thicker vessel.
I think you need to design it twice - one at 5 psi with suitable bursting discs / protection devices and cost that and one able to withstand the 150 psi without breaking apart (code vessel in all likelihood) and cost that, plus weight on the skid etc. Then you have done your job and they can decide based on rational designs.
So in essence you use the 150psi figure as your ultimate occasional short duration pressure and after allowing for the maximum percent over DP or MAWP you can, back calculate the DP to use in the code design (probably somewhere about 120-130 psig).
My other difficulty as a designer is that you cannot rely on the owners word that in the event of an overpressure event he would actually remove and replace this vessel. What happens if the overpressure only reached 100 or 125 psi - would he still replace it? Too many ifs and not enough answers...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Would you consider this an ASME Code vessel?
The BPVC does not have the allowance for exceeding the DP the way the B31 codes.
I would design this as a non-code vessel with overpressure protection set at less than 15 psi. The 150 psi pressure buildup sounds akin to an external fire causing an overpressurization of the vessel. Since it would be a sudden increase in pressure, a very reactive pressure relief device is necessary. A rupture disc works.
RE: Would you consider this an ASME Code vessel?
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Would you consider this an ASME Code vessel?