Old ASME vessel, new PSV 1

[foxymophandlpapa]

I have a vessel with a MAWP of 15 psig, stamped as an ASME vessel back in 1973. We're relocating this vessel and a new PSV needs to be provided.

Current ASME Section VIII Div. 1 states that to be a pressure vessel the rating must exceed 15 psig.

How should I approach this relief calculation? Calculate it as ASME which gives me the 21% accumulation? Or do I need to calculate a conservation vent?

 

[dcasto]

For the fire case, yes 21%. For blocked flow, 10%. Use API 520/521.

 

[foxymophandlpapa]

But my vessel is not an ASME vessel, according to ASME section VIII div. 1 because the MAWP does not EXCEED 15 psig. Its MAWP is exactly 15. BUT, it is stamped, back in 1973 as an ASME vessel.

If I put an ASME relief valve on it, I can't have a 15 psi setting. If I put a conservation vent on it, then I have a non-ASME relief device on a stamped ASME vessel, according to its 1973 stamp.

See my problem?

 

[lizking]

Please cite where the code says "exceed 15 psig". I always thought it's 15 AND above.

 

[foxymophandlpapa]

I'm not about to search thru the code, but ASME.org's website says for Section VIII - Pressure vessels Div. 1:

"This Division of Section VIII provides requirements applicable to the design, fabrication, inspection, testing, and certification of pressure vessels operating at either internal or external pressures exceeding 15 psig."

 

[foxymophandlpapa]

Under the Scope U-1(c)(2): Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division....(h)(1)vessels having an internal or external pressure not exceeding 15 psi (100 kPa);

 

[lizking]

I think those paragraphs are referring to operating and/or design pressures. You have a stamped MAWP of 15. Relief must protect against the 10% and 21% overpressures.

 

[foxymophandlpapa]

Actually, I think thats a misinterpretation. It only refers to OPERATING pressure, not design pressure. If my vessel has a stamped MAWP of 15, which doesn't EXCEED 15, then that means I'm OPERATING below 15.

Since ASME states that my operating pressure must exceed 15 to be an ASME vessel (which mine doesn't), then part UG-125(C) does not apply.

Its confusing because ASME says, "must exceed 15 psig" while API 520 says, "...for equipment that has a MAWP of 15 psig or greater."

The scope for API 2000 (low-pressure storage tanks) says its for "operation at pressures from vacuum through 15 psig."

So while my vessel is ASME stamped, it does not meet ASME standards, therefore I don't think Section VIII Div. 1 applies.

 

[pleckner]

The problem as I see it is that the entire paragraph was not quoted. The beginning of this section (section 'h') begins with:

(h) vessels not exceeding the design pressure, at the top of the vessel, (see 3.2) limitations below, with no limitation on size [see UG-28(f), 9-1(c)]:
(h1) vessels having an internal or external pressure
not exceeding 15 psi(100 kPa);
etc.

Part 'h1' refers to paragraph 'h' so the exclusion refers to design pressure NOT operating pressure.

But the document also says:

U-1(c)(2) Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol:
etc.

So even if the vessel would normally not fall within scope, but it gets a stamp, then the vessel now falls within Scope of this division and it must be protected per Section VIII rules. And I believe you can find a certified PSV for a 15 psig set pressure; this being the lowest you can go for an ASME certified PSV.

For regulations, ASME is CODE (if so adopted by your local municipality) but API is only a standard and is not a Code.

 

[foxymophandlpapa]

Pleckner,

Is a vessel that is stamped in 1973 and is unmodified still valid as ASME, though it no longer meets ASME standards?

If this vessel were designed today with its current specs, it would not get a stamp. This vessel's operating or design pressure does not exceed 15 psig. Our municipality has adopted ASME, but this vessel does not meet the requirements.

Also, if we design this PSV according to ASME standards, it will be a less conservative approach because we could allow 21% accumulation for fire scenario.

Otherwise our relieving pressure will be set to the design pressure and therefore our setpoint, and relieving pressure, will be lower creating a larger valve.

 

[pleckner]

If this vessel were designed and constructed to ASME specifications today, then it could be stamped, regardless of the pressure or size. That is what paragraph-h is sayng.

In my years of studying this stuff I have seen nothing that says a vessel designed in the far past would still not need to conform to todays standards if it is still in use today. It is in your best interest to have the vessel inspected and retested, especially if it is going to be used for a different service. I'd be very surprised if the vessel wall thickness has not been reduced after all these years and putting any pressure relief device (including a conservation type) on this vessel set for a value close to 15 psig could be dangerous.

You can have the vessel de-certified by making it a low pressure operation. I've seen this done but I do not know the details of how to go about doing this. Perhaps you should talk to your safety people or contact your insurance company.

 

[lizking]

Two further points:
1. At 15 psig MAWP, this is a 3 psi overpressure limit case (not 10%).
2. Unsubstantiated rumor: the next addendum to the Code will explicitly negate the requirement for a relief device if no credible overpressure scenario can be established. i.e. getting rid of the "courtesy valve" interpretation.

 

[jte]

foxymophandlpapa -
pleckner has stated the case well. A quick search of eng-tips will turn up several other "but its out of scope" arguments with similar "but by putting the stamp on the vessel it as brought into the scope" replies. If your jurisdiction allows (you stated that your municipality has adopted ASME code, so there must be someone in charge...) and your insurance company agrees, you may remove the stamp and deal with the vessel in other ways. I have received jurisdictional approval in the past to remove the U stamp nameplates off of vessels, but it was a struggle.

lizking-
I haven't heard of this change. If you can substantiate the rumor, please follow up...

jt

 

[foxymophandlpapa]

Does ASME have a requirement for testing pressure vessels after a given amount of time? Pleckner does have a point that it has probably eroded with time and has weakened the vessel, but unless there is something that explicitly states we must test the vessel before designing a new PSV for the vessel, it sounds as if we are not obligated to do so.

 

[ggordil]

I have to agree with pleckner.

My understanding is, that if it has an ASME stamp on it, it needs to abide by Section VIII. Currently I am working on safegaurding a unit that was built in the late 60's. All vessels and PSV's are being evaluated using the standards that are in place now. The reason for that is, that OSHA goes by what is on the books now, not when the vessel was built. In addition, I do not believe that ASME requires re-testing after a certain amount of time, but it would be on the conservative side.

If I were you I would use section VIII.

 

[jte]

ASME is a new construction code, and with the exception of the Post Construction Committee documents, will stay out of post construction issues. The Post Construction Committee documents are PCC-1 which deals with bolted flange assembly (substantial changes being worked on), PCC-2 which deals with repair and testing (2008 ed expected in late summer '08), and PCC-3 which will deal with inspectin planning (very similar to API-510, not sure of anticipated publication date).

YES, your vessel needs routine inspection! Hiring an experienced vessel inspector will probably be your most effective way to do this. If you have refineries or chem-plants in your neighborhood you might call them and ask for the Inspection Dept and see if they have or can reccommend anyone who will help you perform the inspection. Chances are that you'll be following the National Board Inspection Code (NB-23, new edition released in December, roughly $150 at

https://www.nationalboard.org/NationalBoard/Products/NBIC_Description.aspx)

or API-510. Any repairs must be made by an "R" stamp holder, not your local structural welder. Another approach would be to get in touch with an Authorized Inspection Agency such as Hartford Steam Boiler Inspection and Insurance at

https://www.hsb.com/products.asp?id=46.

If your jurisdiction provides such a service, that is another option.

It sounds as though you are on the right track. Please follow through! Even a "low" pressure of 15 psi can cause devastating damage.

jt

 

[foxymophandlpapa]

Thanks for the info all, but none of this is in my scope. Sizing the PSV is the part of my scope. For "conservative" reasons, we will size the rupture disk according to API 2000.

 

[CJKruger]

jte, I assume lizking is referring to Code Case 2211-1.

 

[lizking]

For now, you must use Code case 2211; it MIGHT be adopted into the main code with an upcoming addendum along with further clarifications regarding courtesy valves. Again, this has been proposed for quite some time, so it is still in the conjecture mode. Am I being satifactorily vague?