Normal Operating Pressure under 15psi considering UG-22 (i)

[tanksauce]

If I have a piece of equipment that functions like a gravity-fed silo normally operating at atmospheric but may experience an internal dust explosion, is this equipment considered a pressure vessel? In the previous versions of ASME VIII-1, UG-22 did not have a paragraph (i), while the newer version does. Paragraph (i) lists abnormal pressures, such as deflagration as a loading that must be considered. However, again, the "normal" operating pressure is atmospheric, which would be outside the scope per U-2.

 

[nuche1973]

It has been my understanding that the operating pressure had to exceed 15psi to be considered a pressure vessel. However, your question may be more related to NFPA. You would have to research what the increase in pressure would be at a deflagration and compare that to the 15psi requirement.

"I drank what?!" Socrates?

 

[tanksauce]

The abnormal pressure is calculated to be well over 15psi. Has anyone seen an interpretation for this?

 

[StoneCold]

Wouldn't you install blowout panels to handle the deflagration case, keepign the blowout panel set pressure below 15 psig so you don't have an ASME vessel? Maybe check out NFPA 68 and 69.

Regards
Stonecold

 

[tanksauce]

This is a pre-existing vessel. Apparently, the site has calculations to show that the vessel can withstand the deflagration pressure... but we are trying to determine if the site is required to register it with the local jurisdiction.

 

[moltenmetal]

In my opinion, neither operating pressure nor design pressure matter. What matters is RELIEF pressure. Relief above 15 psig, or no relief? Then it's a code vessel.

 

[psafety]

If you intend to contain the deflagration you are in a ASME Section VIII Stamped pressure vessel. NFPA 69 gives guidance. A rule of thumb most organic dusts will have a Pmax value around 100-psig. You don't have to have 100-psi design as you are allowed to go up around the yield.

If this a non stamped vessel 15-psi is as high as you can go during venting (Pred). The 2007 NFPA 68 is then the guide, there are many factors involved in explosion venting.

I'd be real cautious of a silo or bin with values as high as you state, but you can't use that anyway you have a 15-psi vessel -and- I'd verify that design pressure.

You could also consider a chemical (sodium bicarb) deluge, if this equipment isn't too large. If a explosion condition exist you now have to isolate this equipment from other equipment, this can be done chemically or mechanically.

psafety

 

[Duwe6]

To add to moltenmetal's post, the correlary is:

If adequately protected by a PRV set below 15 psig, it does not meet the ASME Sect. VIII definition of a "Pressure Vessel", so there is no need to list your non-vessel with the state Boiler & Pressure Vessel board.