Cryogenic temperature allowables

[JDmagnet]

I work in the field of superconducting magnet design. I am now designing a liquid helium vessel that carries 100 psi fluid pressure max. at -269 deg C. in addition to applied loads from magnetic coils creating as much as 800 psi mechanical loads on varying areas of the vessel. It is a flat plate welded structure trying to be designed to intent of Sec VIII, div 2., even though it is not to be a code vessel. It has many space constraints as these devices usually have. Current von Mises from FEA peaks around 70 ksi. An elastic-plastic analysis criteria will be applied to the vessel if possible. The magnetic loads are limiting in the fact that a disturbance creates a quench which dumps the stored energy of the magnet as heat within a couple seconds, the lorentz force load being gone accordingly. The heat goes into the helium which then vaporizes and uses the 100 psi overpressure protection. It is important to note here that the lorentz forces require a temp of -267 C or lower (superconductivity), otherwise only the 100 psi pressure applies to the vessel between room temp and that value, no added pressure from the coils. Stainless steels 304 and 316 have significantly increased strength at these temperatures, especially 304N and 316N but the Sec II tables, Part D, Table 5A list allowables below 100F only. Is there any provision for increased allowables at low temperature in the code for these materials?

 

[SnTMan]

JDmagnet, Sec VIII, Div 1 specifically prohibits this, see for example UHA-23. Div 2 may have a similar prohibition, I can't confirm.

Regards,

Mike

 

[JDmagnet]

Section 3.2.1 of Div. II basically says this unless in 3.2.1.5 data are submitted and approved by the BPVC committee. This type of equipment may fall more into the category of outside the scope of this division under 1.2.4.2 C)pressure containers that are integral parts where the primary design consideration and/or stresses are derived from the functional requirements of the device, in this case the magnetic coils. It may however overlap into the pressure vessel category in terms of the 100 psi fluid pressure which this design can easily satisfy (coils not energized). The problem is that some funding agencies seem to think that the BPVC has provisions in the code for all this stuff when they actually do not. It should be noted also that the helium vessel is contained within another vessel under vacuum for heat insulating purposes whose pressure protection is any positive pressure in the vessel and sized for flow according to a worst case of a rupture in the helium vessel. All of these questions were brought up at an initial review of this device and I want to be sure I haven't missed something somewhere. This is a great forum and feel fortunate to have found it.

 

[unclesyd]

Here I go with me trying to remember things from long ago.

This was before Div II

If your were going to build a vessel for cryogenic service at LHe temperatures you could use the code RT values for Aust SS and not use the enhanced values unless given permission. If you use the RT code values for this construction you could stamp the vessel for service at this temperature.

If the vessel was for something like military or space or your case you could use the enhanced values up to 100F from there you had to use the code values.

My list of enhanced values for Aust SS cuts off at RT (78F)