location:
Do you really mean to "regulate" the flow of Liquid Nitrogen (LIN)? At 150 psig (approx. storage pressure), LIN will have a temperature of approximately -270 oF and will be saturated - that means it will only require its latent heat of vaporization to convert to the vapor phase at that same temperature. Any throttling -such as would be experienced with a regulator valve - would lead to immediate flashing and you would be creating a 2-phase flow downstream. Is this what you want to do? Do you intend to regulate your LIN down to 25 psig? What would be the conditions of your inlet LIN?
The materials of construction for a LIN valve should be no problem; stainless steel should do well. However, I would worry more about the results. What will you do with the flash vapor? You need to fully explain what it all is that you're going to do, complete with basic data.
Art Montemayor
Spring, TX