Overpressure caused by Fire 4

[Idontknowit]

Hi Guys

I couple months ago I had some conversation with my lead engineer regarding the maximum relieving pressure for fire sizing. In my relief calcluations for fire case I used 21% of overpressure,which was crossed and replaced by 10% by my lead. So when I asked him why it was changed to 10%,he told me the reason is because this vessel is not ASME vessel.I did not argue any more as he was experienced englishman engineer with more than 20 years in oil and gas industry.

Now I am again delaing with PSV and still wondering whether it should be 10 or 21% of overpressure?

I appreciate any comments

 

[JimCasey]

Last time I remember searching thru Section VIII, any vessel of greater than (as I recall) 15 ft3 exposed to greater than 15 psi was governed by the code. The vessel in question may not have carried a code certification, but I would not suggest having a reportable incident with that vessel if it should be code-stamped and it is not.

Sizing for 10% accumulation is certainly more prudent and thus hard to criticise.

 

[MortenA]

It may "not be an ASME vessel" because its a "PED vessel"?

There are some confusion with regards to what the relieving pressure should be in the fire case - but the PED guideline section 5/2 clearly states that "The 1,1 PS restriction does not apply to fire".

This means that the practise recommended by ASME could be used - but 10% may also be used - engineering judgement.

Best regards

Morten

 

[Idontknowit]

Hi guys,

Many thanks for your comments. I really needed some back up from experienced engineers like you to be sure.

Idontknowit

 

[JoeWong88]

You may confirm with your englishman lead engineer if the vessel designed to BS code. If so, then probably this is the reason. BS probably allow 10% overpressure for fire case.

 

[gr2vessels]

idontknowit,
Check out the "Instrument Engineer's Handbook" by the hungarian Bela G. Liptak, it has extensive work on the fire relieving issue, for vessels, tanks and other pressurized equipment. Very comprehensive and documented, including calculations.
cheers,
gr2vessels

 

[kranthi1]

idontknowit,

First look at the Technical Bid Evaluation done by mechanical)
You can identify in the codes and standards section whether the vessel is designed as per BS /PD5500 OR ASME.


If the Vessel is desgined as per PD 5500 (British standard Page no:275)it states as follows

The total capacity of the pressure relief device or devices fitted to any vessel or system of vessels shall be
sufficient to discharge the maximum quantity of fluid, liquid or gaseous, that can be generated or supplied
without occurrence of a rise in vessel pressure of more than 10 % above the design pressure.

NOTE 1 The safety valve standards only cover liquid or gaseous fluids. For applications where the valve(s) may be required to
discharge a two-phase mixture, the type and capacity of proposed safety valves should be discussed with the valve manufacturer.

NOTE 2 Any requirements for additional safety valve capacity to prevent excessive pressure in the event of fire should be specified
by the purchaser in the purchase specification after due consideration of potential fire risks and resulting hazards.


If the Vessel is ASME then Refer to API 520 Part 1(Page no 50)it is stated as follows:

In accordance with the requirements of the
ASME Code, Section VIII, Division 1, accumulated pressure
shall be limited to 121% of the maximum allowable
working pressure, MAWP, in vessels that are protected by
pressure relief devices sized for fire contingencies. This
applies to single-, multiple-, and supplemental-device installations.

I hope it helps.

Cheers
omkranthi1

 

[Idontknowit]

JoeWong88,

You probably right about BS standard,however I can not check it with eng.lead engineer since I changed my job.

Thanks for your comments guys.

Now I know I am on safe side of design.

Idontknowit

 

[mechsarah]

BS5500 allows a maximum accumulation of 10% only and as such this is the limiting factor when sizing to API for firecase. It should be noted that this also restricts the overpressure allowance for multiple SRV's (116%)as well.

Sarah

 

[MortenA]

BS5500 dosnt exists anymore - but PD5500 (i think its called) does and the same.

Howvere PED is the law (also in Britan allthough its implemented by a British law not called PED - same as here in Denmark)In the PED the fire case is not covered because its not an operational case (c.f. the reference to the guidelines i gave).

But you can freely state that the vessel shall be designed to PD5500 of course because then the PED will also be met.

Best regards

Morten