Consider carefully where you place this device ..... they ROAR !!!

Consider the possible need for a sound enclosure ...

MJCronin
Sr. Process Engineer

The first thing to understand whether this requires a PRV, is to what code/design standard are you working to?

You also state a (maximum?) pressure of 300 PSIG and that the upstream pressure is 'limited to under 300 PSIG' - but how much under? What is the maximum pressure that can be generated against all possible causes?

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

Obturator, to clarify the design pressure (MAWP) of the heater is 300 psig, and normal 250 psig steam will be fed to the heater. The upstream steam pressure could never exceed 300 psig, so that the heater cannot be overpressured (a fire case was taken off the table, plus I am not sure it is relevant regardless). Likely, it is built to ASME but I will be checking with the vendor to confirm.

You may want to review ASME VIII Division 1 UG-140 "Overpressure by System Design", where it states that that a PRV is not required "...if the pressure is self limiting".

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

Just guessing, I'd say that this heater is built to pipe code (ASME B31.3), but it's possible that they designed it according to ASME Sec VIII. Either way, the answer is the same. If you have any potential causes for overpressure, then a PRV is needed. If not, then a PRV isn't required.

If it's designed per ASME Sec VIII, why isn't relief protection required for this item? It's true that we can't ordinarily choose to forego relief protection for Sec VIII equipment - Sec VIII design/construction means that the item must be protected from overpressure according to the requirement in that code. However, the opening section in ASME Sec VIII (U-1 Scope) explains specific cases which are exempted from the scope of Sec VIII. Refer to U-1(c). The item we're discussing is one such case which can be exempted from Sec VIII scope (exempted from Sec VIII requirements). U-1(c)(2)(e) states that piping components (e.g strainers, mixers) which are generally recognized as a piping component or accessory, can be exempted. It's reasonable to say that this steam/water mixer fits that exemption. And, BTW, this is separate from UG-140. UG-140 only applies when omitting PRDs from vessels that are not exempted in U-1(c).

Bill3752, pardon me for piling on, but don1980 said something that is very much on topic with something I have to struggle with once in a while.

don1980, a bag filter is basically a coarse strainer with a nylon sock (filter bag) in it. The standard single and double length basket filters are fabricated from 8" pipe; therefore it does not qualify for the 6" ID exemption, U-1(c)(2)(i). We view these bag filters as more "pipe-ular" than "vessel-ular", but this gets challenged once in a while. Does this specific case seem reasonable for exemption under U-1(c)(2)(e) to you?

Obturator, ditto?

A fact that is favorable for not having a PSV on these bag filters, is our products are white, sticky stuff that dries readily, thus any relief device will become plugged and useless in short order without a superhuman effort to keep it clean.

Good Luck,
Latexman

If something is built to pipe code, but is registered as a pressure vessel, it will have to comply with ASME 8 and an RV will be required.

Latexman (If I read your query as separate to the OP) Exemption against U-1(c)(2)(e)? I say Yes. The description to me suggests this piece of equipment is not 'end of line' system pressure containing. Use of Bursting Disc otherwise.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

Yes, it is not 'end of line'. We are transferring a batch from one vessel/tank at atmospheric pressure, and it passes thru the filter en-route to another vessel/tank/tanker truck at atmospheric pressure.

Oh, we almost always put the filter in the suction side of an AOD pump to limit the dP across the bag, because in some soft particle (low Tg) products the large particles can be extruded through the filter media at high dP.


Good Luck,
Latexman

Latexman, subjective user interpretation is required in order to decide what is a "piping item" and what is a "vessel". One of the examples of piping items listed in U-1(c)(2)(e) is "strainers". One can certainly interpret this to include bag and cartridge filters. Possibly an auditor would agree, or possibly they wouldn't. i can't say. But personally I'd say that bag/cartridge filters are not included in this exemption - i don't think such filters are what ASME had in mind when they used the word "strainers". I think they are referring to things like Y-strainers, which we can all agree are better described as a "piping item" rather than a vessel.

If a relief device is omitted from a bag filter, then I think you should apply UG140, and generate the documentation for that.

Latexman/don1980/Obturator,

Often the filter housings are provided and stamped with a UM stamp. To me, that seems a clear indication that the filter housings are NOT piping items. In that case, it is generally a good idea to prevent any over-pressure from occurring per UG-140, especially when considering, as you noted, neither a rupture disc nor relief valve work particularly well in such an application.

Bill3752,

If your steam pressure is truly limited by an upstream PSV, then you won't have to size for an over-pressure event. This may, or may not, mean you can eliminate any PSV on the heater - you likely will still have a "blocked inlet/outlet" thermal expansion case. It does mean, however, you can likely reduce the PSV size.

If you truly have no over-pressure case, I would not install a "courtesy" valve. It would be additional time, expense, and PMs. If you do not install a pressure relieving device, make darn sure you are thorough and document all scenarios evaluated.

Thanks, don1980. Your insights into the ASME Code language, history, etc. is very valuable.

Good Luck,
Latexman