Conditions from which the cryogenic design is required

[Fran67]

Hello everybody,

I just wonder if there is good practices (standards...etc) to determine the need of cryogenic design on gate/globe/ball manual valves, especially when the "cryogenic" conditions appears only during transient or accidental cases?

My project is a piping system with a electrical heating device with manual valves upstream the heater:
- In normal operation, the temperature upstream the heater is +0°C -> cryogenic design is not required for valves for this case
- During transient cases (heater start-up), temperature of fluid upstream the heater can decrease under -70°C during a very short duration (30sec - 1min)

Piping design codes say generally that only long-period (en 13480) or normal operation cases (b31.3) have to be considered for the rating of the valves selection. If I follow this recommendation I don't need cryogenic design on the valves.

Do you have an experience or a standard to share to help me for this subject?

Thank You
F67

 

[gerhardl]

Risk assesment?
In cases where something can go wrong you should always ask yourself following questions:
What are the worst possible consequences?
What is the cost of the consequences in money / health / life ?
Who bears the responsibillity and the cost?

For mechanical systems 'just a tiny bit of overexposure ' will usually require an upgrade to correct level of construction class. As an example only a small portion of a pressure/temperature curve above allowed level will require use of the higher, correct pressure class.

 

[bcd]

MSS SP-134 defines cryogenic temperature as -73 C. MSS SP-134 defines requirements for valves for cryogenic service, including requirements for body/bonnet extensions. ASME b16.34 and API valve standards refer to MSS SP-134 for requirements for cryogenic valves. Per your explanation, you are just outside the limit of SP-134 so cryogenic valve design and test requirements should not apply.