Vessel Operating Below MDMT

[garfio]

I have a propane vessel with an MDMT of -20F. Due to autorefrigeration effect, temperature could get below this level. Reference books mention that vessels could be operated at lower temperatures than MDMT if they are at lower pressure. As pressure will reduce with temperature for propane, I believe this is a case in which this could be applicable.

I would like to know where in the code is the basis to allow this and how could I determine the pressure at which the vessel could operate at the lower pressure than MDMT.

Thanks

 

[doct9960]

See UCS-160

 

[carthago]

..Yes , First determine what is the ratio of =
( pressure at depressurization ) : design pressure.

with ratio this you might have a sort of bonus and make your MDMT warmer...Providind your client accept this and is convinced.
In ASME VIII div 1 , there is an example in appendix L.

API 579 gives also the same tip and some others too...
such as fracture mechanics..