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Vacuum Pressure Rating

Vacuum Pressure Rating

Vacuum Pressure Rating

(OP)
Hi All,

We make vessels to Section VIII Div 1.  The MAWP for internal pressure was established by burst testing as per UG-101(m) because there are no applicable rules for our design.  We are now looking to add a vacuum rating to the vessel.  How can we go about this?  The rules for external pressure are not applicable.  It wouldn't be practical to build a pressurized enclosure around our vessel to do an external pressure hydro-test.  The only thing I can think of is FEA using the Div 1 stresses.  However, since we don't have properly trained FEA experts in house I was hoping to avoid this route.  Any help would be greatly appreciated!

Best,
Steris

RE: Vacuum Pressure Rating

It is common practice to sweep that underneath U-1(c)(2)(h)(1). But then I don't think you could stamp the vacuum rating on the nameplate.

We had a similar case last year, and in the end we built a custom pressurized enclosure for the specific part that needed an external pressure test.

If you want to use FEA, that's Div. 2, not Div. 1.

RE: Vacuum Pressure Rating

(OP)
Hi Trottiey,

Thanks for the information.  It is my understanding that you can use FEA for Div 1 as long as you maintain the same safety factors as Div 1 ie. use the same allowable stresses.  I know of more than a few different manufacturers that do this for unusual designs and claim U-2(g) for acceptance.

I agree with you that U-1(c)(2)(h)(1) could apply but wouldn't be justification for stamping vacuum on the name plate.

Thanks again,
Steris

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