Pressure Vessel Design for Sub Zero Design Temperature

There is a "decision tree" for this that is a bit complex. I may be out of date, but the basic idea is like this:

For ASME, low temperature for CS is below -20°F. If you are warmer than that, nothing special is required. In the range of -50°F to -20°F, you can check for the relation of "coincident temperature and pressure." If it can be ensured that as the temperature falls, the pressure also falls, and if you use a suitable low-temperature steel such as 516-70, impact testing may not be needed. The vessel stamping will reflect this with an extra line such as "MDMT -50°F at 60 psi" (MDMT = minimum design metal temperature). For CS below -50°F, impact testing is required.

That is just a brief outline, so you will need to check the Code carefully. Note also that if any other codes apply (such as Coast Guard), the cut-off point for low temperature may differ, and there may be further requirements.

Good answer from me Tornado (not that you need any more )

Codey