Omitting PSV on pressure vessel 6

[dennisr]

It is well known that a PSV does not provide any protection against failure due to fire on an unwetted vessel. Many recognised companies practice not to install PSVs on unwetted vessel if fire is the only contingency.

Does anyone know of any officel reference, ASME clause or other codes that support the above practice?

 

[JoeWong88]

If the pressure vessel if designed to ASME, then a PSV is required...

JoeWong
Chemical & Process Technology

 

[gr2vessels]

Check out this tread...

http://www.eng-tips.com/viewthread.cfm?qid=17298&page=5

gr2vessels

 

[moltenmetal]

When ASME says that you need a PSV as protection on every vessel, I'm quite certain that they don't mean you need to install a PSV- they mean you need secure overpressure protection that does not rely on operator intervention to function.

It's in areas like this where ASME and many other such codes sometimes fall down- they should contain design philosophy and guidance for professionals to use rather than making a prescriptive edict to apply one particular solution which may, as in this case, offer an unskilled person a false sense of security.

While it may be the right tool to protect against operational overpressure, a re-seating device such as a PSV is the wrong type of protection against overpressure due to fire for a vessel containing gas or other non-vaporizing contents. A rupture disc, passive automatic depressurization valve (ie. with fusible link) or thermal relief (fusible plug) combined with fire suppression etc. are the right tools for the job.

 

[Latexman]

Take a look at ASME Code Case 2211. It lists conditions where a relief device would not be required. The basis is overpressure protection is provided by system design.

Good luck,
Latexman

 

[CJKruger]

Latexman, I seriously doubt you can use Code Case 2211 to eliminate a fire case relief valve, and I base this on Interpretation VIII-1-04-38 below:

Question (6): Is it required by the rules of Section VIII, Division 1 that overpressure protection be
provided for an unexpected source of external heat if engineering analysis shows that the vessel will fail
due to excessive temperature before the pressure relief device(s) would be activated?

Reply (6): Yes.

 

[dennisr]

Thanks a lot for all your valuable inputs. Unfortunately the conclusion is not as clear as I hoped for.

It seems that ASME require a PSV til be installed even though fire is not real source of overpressure.

I dont have a problem with installing a depressuring valve. However it really hurst my technical pride to install a PSV when everyone knows that it does no good.

Any new input on this thread is appreciated.

 

[BenThayer]

"If the pressure vessel if designed to ASME, then a PSV is required..."

i think to say a PSV is required is not accurate. if the intent is a relief device is required, i would not argue.

"....A rupture disc, passive automatic depressurization valve (ie. with fusible link) or thermal relief (fusible plug) combined with fire suppression etc. are the right tools for the job. "

i think that moltenmetal gave some sound advice here but it appears to have been over-looked.

what is wrong with a rupture disc or fusible plug for this application?

 

[lizking]

The 2008 addendum to ASME Section VIII incorporated Code case 2211 as paragraph UG-140. This essentially eliminates the need for a "courtesy" RV provided you have adequate documentation.

 

[Latexman]

I like that phrase "courtesy RV". I've done that several times to avoid the onerous Code case 2211 documentation.

Good luck,
Latexman

 

[psafety]

It was my understanding, if Code Case 2211 is declared it must be prior to building the vessel.

Although, I will admit I have not reviewed the 2008 revision.

 

[Latexman]

psafety,

That's the way it was prior to the 2008 addendum. Not sure now, but it probably still must be declared prior to building the vessel.


Good luck,
Latexman

 

[JoeWong88]

@BenThayer & moltenmetal
Thanks for knocking my head...I agree with you. It should be relief device i.e PSV, RD, etc instead of PSV only.

As for code case 2211, i believe it can be applied for process contingency. However, i doubt it can be applied for fire contingency.

@Latexman
When you said "I've done that several times to avoid the onerous Code case 2211 documentation.". Is this applicable to fire contingency as well ? I have seen application HIPS for process contingency plus a relief device and depressruring valve for fire contingency. Do you mean High Integrity Protection system (HIPS) is also initiate the depressuring valve ?

For fire contingency, we always experience same argument in every projects. Everyone aware that relief device will not able to protect the vesssel under fire contingency, it only "buy" time for operator to take early action. However, everytime we can not avoid to put a relief device for vessel designed to ASME VIII (code requirement), like the answer given in CJKruger's response. Having a "courtesy RV", we focus on other protection measures i.e. depressusring, RD instead of PSV, external cooling, fire proofing, etc.

@dennisr,
"It seems that ASME require a PSV til be installed even though fire is not real source of overpressure."

Well... it is not easy to eliminate fire contingency. I really have no one experience that i can eliminate fire contingency. Anybody has ? How this is eliminated ?

JoeWong
Chemical & Process Technology

 

[CJKruger]

JoeWong88, the only way (I know of) to avoid a fire case is to elevate the vessel to above 25ft or 35ft.

However, I am trying to get hold of WRC Bulletin 498 to see if it allows us to use UG-140 (old Code Case 2211, thanks Lizking) to eliminate a PSV for a fire case.

 

[JoeWong88]

CJKruger,

Thanks for your idea. Beside, i am looking for this document also.

Elevate the vessel to above 25ft per API Std 521(why 35ft ?) is one the "measures" as it considered only pool fire. For some applications in gas plant, LNG plant, petrochemical plant, etc which possibly has jet fire scenarios, elevate vessel may becoming impractical.




JoeWong
Chemical & Process Technology

 

[Latexman]

JoeWong,

Not applicable to a credible fire case. The cases I recall used a vessel with enough MAWP to contain all credible scenarios; fire was not credible. They also did not use HIPS.

Good luck,
Latexman

 

[chemicalengineerthai]

1) PSV is not PRV
2) Jet fire can sometime 30-80 meter from the source) but can be diluted by PFP ( paasive fire protection coated/lining at vessel surface) use CFD study, then you can save a lot of money.
3) Vessel can happen under fire pool is for liquid vessel contains C4 and heavier, which normally not so high design pressure vessel.
6) Mechanical protection was normally by vessel thickness + PSV,BDV, while instrumntation by PSHH, HIPPS , it depend you use philosophy 2 barrier or 3 barrier( PSHH+BDV+HIPPS or PSV/Flare), to save flare sizing people will use HIPPS but need regular maintenance and redundant valve
7)All vessel if use need ASME stamp- you must has over pressure protection ( PRV or PSV), when design pressure>3.5 barg/ Diameter >6",etc.

 

[don1980]

Guys.....let me set the record straight.

Code Case 2211 [or now UG-140(a)] can indeed be used even if the vessel is exposed to the risk of fire. CC2211 originated from just such a case.....a vapor-filled pressure vessel that would fail before the vapor expanded enough to lift the PSV.

UG-140 has two parts, 140(a) and 140(b). Part 140(a) is essentially the same as the old CC2211. 140(b) is new, going a little beyond the old CC2211.

 

[dennisr]

don1080,

Very interesting! Where do you have this information from. I would really like to know if UG-140 have been used to exclude fire case on a vapour filled vessel.

 

[JoeWong88]

Latexman,
Thanks for your information.

Your case "Not applicable to a credible fire case." still maintain my understanding...

JoeWong
Chemical & Process Technology