Cooldown rate of 304 SS piping in LNG system

[bstover]

Hello,

During a recent inspection my facility was questioned on our cooldown procedure for our LNG vaporization piping system, specifically the temperature target and rate of cooldown/warmup we monitor. We've never had concrete numbers in our procedures but always aimed for under 50 degF/hour and began recirculation of LNG when piping temperatures reached -50degF to -100 degF. In recent years, I've observed the piping system warming quicker than in the past and have resorted to running our cooldown/recirculation pump once a day.

Thank you.

 

[LittleInch]

The issue that exists is really differential cooling, either one part is still warm and the one part starts to contract or one half has cold liquid in the bottom but warmer gas above it so starts to bend like a banana.

When I look at this there is no real reason or calculation you can do, only do something which doesn't "frighten the horses".

Anything faster will make all sorts of strange banging and creaking as the pipes contract and slide over their supports or tension up bits of pipe.

30 C/hour sounds really quite slow to me, but depends o the complexity of the system.

Was there a question here?

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[bstover]

Thank you. I guess the question is what is the desired rate of cooldown and at what temperature should a pump be started to re-initiate cooldown.

 

[LittleInch]

How long is a piece of string?

Don't think there is anything other than general "guidance" or ROT which seem to vary company by company.

Not easy to do this in any meaningful way as where is the limit?

You are currently at 30C/hour.

If the system is small enough this could easily be 300C/hr.

It's usually based on how much cooling or BOG the cooling down creates and hence is process driven.

For an existing system maybe just try going a bit faster?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.