Two MAWP for Div-1 Vessel

[ting123]

Dear's,

I would like to know if it is possible to mark 2 MAWP @ 2 Temp on a same ASME Nameplate. The Vessel is single chamber and not multi chamber. I want to certify the vessel as per 2013 Div-1. I am aware that a range of MAWP is not acceptable as per Interpretation.

Need your support.

Thanks in advance...

 

[marty007]

Yes, you can have multiple MAWP markings on a pressure vessel.

Per 2011a edition of the code, see UG-116 footnote 37.

Per 2013 edition of the code, I can't seem to find the footnotes in the digital version of the code that I have... have they reorganized the code?

 

[marty007]

Heh, hit submit too fast...

They have reorganized the footnotes, they are now located just after the non-mandatory appendices. See Endnote #10:

"When a pressure vessel is expected to operate at more than one pressure and temperature condition, other values of maximum allowable working pressure with the coincident permissible temperature may be added as required. Sss UG-20(b)"

Cheers,

 

[fegenbush]

I have done it previously by specifying the pressure rating of individual areas of the vessel. In my case, it was the temperature that varied across the vessel, but the procedure would be the same for pressure. Hydro testing would be interesting, as it was for me, but it can be done.

 

[steris]

This is very interesting - I didn't know that this was allowable. It makes sense though. This is slightly off topic, but how do you configure safety relief valves for this arrangement? The higher temperatures would have a lower MAWP. If you install a safety relief valve for the lower value, you essentially negate the availability of the higher MAWP under lower temperatures. Are there safety valves available that have temperature and pressure set points?

 

[marty007]

steris,

To be honest, I know of this rule with respect to MAWP, but have yet to actually apply it to a vessel design. A similar situation however where I have used multiple design conditions was for the MDMT of vessels containing pure fluids.

In this case, since the saturation curve is well defined, you are able to specify multiple MDMT temperatures at different pressures. When the vessel is at its coldest temperature, the pressure is also at the lowest pressure so you can take advantage of reduction curves such as UCS-66.1. As things warm up, the pressure increases, but you also don't need as much of a reduction. I think we analysed three different MDMT conditions.

Otherwise, I could imagine all sorts of crazy control systems involving three-way valves with two relief valves etc... But until I've suffered through a HAZOP looking at this issue, I don't know what would fly.

Cheers,
Marty