Pressure relief requirements for non-code vessels

[JohnyO]

My company is designing a water treatment system that will use several pressure vessels (ambient temp water, approx 300 gallons capy) that are not ASME code stamped and a few questions come to my mind:
1) If it's not an ASME code vessel, what regulations govern it?
2) Is over pressure protection required, and by whom?

If it were an ASME code vessel my extremely limited knowledge based on excerpts I've found of the code suggest to me that they would need OP protection from the feed pump as well as OP protection from thermal events and blocked-in conditions. Is that accurate? But what if it's not an ASME vessel. What then?

Thanks much,
John

 

[gr2vessels]

John, it's hard to answer your question;- I can't imagine a company to design and fabricate pressure vessel without following a recognized design code. I assume from your post that the vessel is correctly qualified as pressure vessel, not atmospheric storage tank. It is against your local regulations which prohibit the use of pressure vessel without proper certification for safety and conformance to a recognized standard. Please note that the vessel can be designed in accordance with ASME VIII-1, without U-stamp. Also, you may get some proprietary certified design calculations, but in overall the equipment cannot be sold and operated without a 'safety certification', issued by the fabricator and endorsed by a qualified inspector. The vessel must be protected against over pressure by means of a suitable sized nozzle fitted with a PRV. If the vessel is custom designed for a particular service, the pressure relief valve might be placed on the connecting piping to protect the entire system. That is, the vessel sold as generic vessel, it has to be fitted with its own PRV. Please note also the ASME VIII BPVC does not specify which process conditions are the most onerous for the relief valve sizing, irrespective of the vessel designed mechanically to ASME VIII or other standard. You might need to review and apply the API 2000 standard.

 

[SnTMan]

JohnyO, how much overpressure? You could just design the vessel to that, nothing additional required.

Regards,

Mike

 

[gr2vessels]

A quick clarification;- you are designing a water treatment system, not pressure vessels, right? Do you buy the suitable pressure vessels for your service? Do you write the specification for those pressure vessels?
Cheers,
gr2vessels

 

[JohnyO]

All – Thank you for your time and assistance.

Correctly qualified as pressure vessels? To my way of thinking they must be – they aren’t atm tanks, but perhaps there is some framework in which they don’t qualify as PVs (not a smart alec comment, maybe there is some language or exception for water treatment or something). I don’t see how they could fail to be classified as PVs but I have been wrong before. These are one of the types being used:

http://www.yardneyfilters.com/sand_media_filters_indst.aspx

The state in which these vessels will be operated is MD and based on what I read last night at this URL, all new pressure vessels must be ASME stamped:

http://www.dllr.state.md.us/labor/safety/boil.shtml

I did not investigate beyond that page as it seemed pretty clear.

My belief is that OP protection is required for two scenarios: 1) OP due to the feed pump which is capable of generating pressure that exceeds the MWP of these vessels by 30% and 2) OP protection for a completely filled vessel (water), blocked in during a system shutdown during freezing weather. Relief for fire, internal reactions and such aren’t possible with this process.

Some in my company believe that the MD building code, which I haven’t read (don't yet know if they have), has jurisdiction. I’ll look at it on Monday, but given the language in the MD link above, the bldg code would have to come up with some exemption based on size, intended usage, or some such. Further my people state, and I don’t know on what basis yet, that “Boiler codes, or any codes related to the handling of steam and condensate systems are not applicable to our treatment system”. The problem I see with that is this phrase from the MD code: “The Law also requires that any Boiler or Pressure Vessel that will be installed in Maryland be built to American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and be registered with the National Board of Boilers and Pressure Vessel Inspectors.”

We didn’t really write a specification for the vessels, just said “those ones”! Pretty hot shot engineering, eh?

You guys are going to be laughing at me…but at least I'm swinging the bat in the right ballpark.

Thanks a lot to you all!

 

[SnTMan]

JohnyO, Sec VIII, Div 1 exempts PV's containing water to 300 F / 210 psig. However, the driver is going to be your jurisdiction. You will have to carefully read all the relevant rules thereof to figure it out, I'm afraid.

Regards,

Mike

 

[SnTMan]

Sorry, 300 psig, 210 F, just call me Dick Lexia

 

[JohnyO]

Thank you SnTMan!

So OP protection devices are not required for ASME code compliance on water pressure vessels operating up to 300 psig and 210F. I wonder if there are any vessel size limits that apply to that. I know of a couple of 20,000 gallon ASME vessels that operate at 120 psi and ambient temps, and have OP protection; it's counter intuitive to me that the code wouldn't require OP protection on such a large vessel. Then again, maybe it would just fracture, relieve and not really cause damage, though 120 psig jets could put a hurt on a person, never mind a 299 psig jet!

I'll do some more reading.

Thanks again.

 

[SnTMan]

JohnyO, what I meant to convey is that vessels meeting those criteria are completely exempted from meeting Sec VIII, Div 1, which would of course include overpressure protection requirements as well. There do not appear to be any size limitations on vessels meeting those criteria.

Again, your jurisiction may dictate differently.

Good luck,

Mike

 

[JohnyO]

Thanks Mike,

I found that the ASME code has been adopted by the state and I see the citation you noted. I wonder: Is there some other division of the ASME code that addresses the requirements for water vessels at 300psig & 210F or less? It just doesn't seem reasonable to me that pressure relief devices (and headspace air control) aren't required on vessels, of apparently unlimited size, containing, say, 290psig/200F water. Am I missing something?

I'm trying to find a local copy of the code but no luck so far.

John

 

[JohnyO]

BTW: For anyone in the same circumstances, I just discovered this thread. It has some helpful info:

http://www.eng-tips.com/viewthread.cfm?qid=221218

It sure looks like there are no requrements for pressure relief. Now if gas can accumulate in the headspace (they are downflow vessels) from entrained air (pretty unlikely) or biological activity (not out of the realm of reasonable possibility) then things would seem to change. I need to see where the code quantifies the amount of headspace gas that is acceptable, and the amount that makes this a pressure vessel or something requireing gas release.

 

[JStephen]

The purpose of having pressure relief isn't to comply with the random whims of some code writers, but to make a vessel safe to operate. If operating the vessel without pressure relief presents some sort of hazard, then it should have it, whether it's a code requirement or not.

For example, if I remember right, vessels less than 6" diameter are exempted from the ASME Section VIII. That doesn't mean if a 7" vessel blows up, it's dangerous, but if a 5" vessel blows up, it's perfectly safe. It just means one is addressed by the code, the other isn't.

There are a lot of items designed that do not fall under a specific code of construction, and non-code vessels are one of those. They may be covered to some extent by building codes or by tank standards or pipe standards, etc. Where not covered by a standard of some kind, good engineering practice would be to make it as safe as similar items furnished under other circumstances.

 

[JohnyO]

Your are preaching to the choir JStephen; I couldn't agree more. I am in the position of having to justify the rationale for the two relief scenarios that in my opinion require engineering controls and am running into "well, the code doesn't require it so we don't think it's necessary". My task would be more assured of success if I could point to a code and say "there - we have to do it". Translation - the budget is in trouble.

 

[GenB]

Certifications of non ASME vessels are to ANSI UL standards. In order to legally sell your products you should certify them as so. I do not think your local codes get involved in cold water vessels of any size. Prv's are required to protect the system and lawsuits if a vessel causes damages to life and property. Genblr.