Should the Jacket of a Cryogenic Vessel be considered as pressure vessel?

[kremenco]

Cryogenic pressure vessels are double walled with outer jcakets fully enveloping the inner vessel. The annular space between the inner and outer vessels is fully vaccumized and filled with expanded perlite. In a normal case the external pressure on the jecket is 15 psig or less. As per Appendix- 9-1(c) of ASME Sec VIII Div-1, the jacket does not come within the scope of Appendix 9 even when the expernal pressure on the jacket more than 15 psi. Also, as per U-1(c)(2)(-h)(-1), vessels having an internal or external pressure not exceeding 15 psig are not included in the scope of the code. The question is when the external pressure on the jecket is more than 15 psi, should the jacket be considered as a pressure vessel and designed, constructed and code stamped as per ASME Sec VIII Div-1. The vessel will be installed in the hull of a ship where the nitrogen purge pressure is maintained as 3 psig. Accordingly the external pressure on the vacuum jacket is going to be 18psig.

 

[DriveMeNuts]

It does appear to come within the scope of ASME VIII.
Perhaps design the annulus to take a one-off internal pressure test.
But, oh for all the additional costs associated with inspections and testing.

 

[EdStainless]

If the internal vessel fails, then then the outer one will see full internal pressure.
What provisions are there for pressure relief?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[DriveMeNuts]

A big hole in the jacket with a thick steel plate sitting loosely on top of it. This flat plate is held in place by vacuum.
Internal pressure will cause the plate to simply fall off.

 

[EdStainless]

And a loose plate will seal at <10 microns?
I have seen engineered blow out panels.
But I have also seen small tanks where the outer shell was rated for full pressure.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[DriveMeNuts]

Yes, an ordinary loose plate with an O-Ring seal. The vacuum maintains the seal.
The loose plate has a chain attached to it so that it doesn't launch onto a person's head.

 

[kremenco]

@DriveMeNuts
Yes, we are mainly concerned about the costs related addional inspection and tests.
Will it be acceptable to conduct a leak test for the vacuum jacket in line with UG-99 (f)(2) in lieu of a hydrostatic test?
@EdStainless
There are safety heads on the vacuum jacket sized as per CGA-341.
Kind Regards

 

[LittleInch]

It's not easy and you can get wrapped up in all sorts of complications. Language is crucial in terms of how you describe this "jacket". Any mention of "double wall" or "secondary containment" and setting the positive pressure rating at anything more than "atmospheric" leads you down all sorts of strange paths.

I've done something similar with pipe with a vacuum jacket plus insulation and it gets very complex to understand what is required in terms of testing and pressure testing in particular.

With the added pressure on the outside I think you've crossed over into PV status. It will make it a bit easier to explain to th whoever is authorising this what you've done if you're able to show it has been designed, built and tested as a PV.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.