vessel inside the vessel

[alexst]

Hello,
Could somebody clarify using the ASME sec.VIII, should the small vessel with atmospheric pressure placed inside larger ASME vessel with internal pressure be treated (design wise) as the ASME vessel as well? For the cryogenic guys- I am talking about ullage vessel.
Thank you all

 

[gr2vessels]

If you are designing a jacketed vessel, then both the outer and inner shell are pressure vessels designed to ASME VIII. The internal vessel will be designed for external pressure equal to the outer shel's internal pressure (minus the atmospheric pressure). By the awy, the cryogenic guys order these vessels from us, the vessel designers.
cheers,
gr2vessels

 

[alexst]

Thank you gr2vessels.
Out typical vessels are jacketed (insulated), but outer jackets are not treated as ASME (probably because the atmospheric, less than 15psi, external pressure). In this case small vessel built inside of the INNER vessel (for ullage) and of course should withstand much higher external pressure (300psi). By this definition it's ASME vessel, on another hand collapsing of this small vessel won't be crytical from the safety point of view.

 

[doct9960]

alexst,

You could use ASME to design the ullage vessel for external pressure, but I don't think it needs to be ASME stamped. That ullage is an internal part of a vessel, right? So it's the bigger vessel that needs ASME stamp. Ullage are usually made of stainless steel or other exotic material so you would want the ullage to be as thin as possible for cost and for faster cooling of the fluid inside the ullage. If the bigger vessel is carbon steel, you'd have to watch out for thermal stress if the ullage is fixed to the CS vessel