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# [img http://res.cloudinary.com/engi

## [img http://res.cloudinary.com/engi

(OP)

I have seen one of the datasheet for cryogenic vessel which specifying the vessel shall be designed for Allowable temperatures of -196 Deg C as the minimum and -20 deg C as the maximum.
I beleive that this implies the vessel can withstand with a lowest temperatue of -196 deg.C and maximum temperature of -20 deg.C.. please suggest me whether my understanding is correct or not If my understanding is correct , then it means that the vessel can not withstand a temperature which is higher than -20 Deg.C.. then how we can do the fabrication and keeping of the vessel before commissioning at ambient temperatures which is for sure higher than this -29 Deg C.
once we are filling the vessel with cryogen the vessel temp will reduces to very low values say -196 Deg C.. but still doest it make sense to consider the maximum allowable temperature as -20 deg c for the design ??.. please clarify my doubt ..

### RE: [img http://res.cloudinary.com/engi

It is rated across the range of service pressures for that temp range.
After all, how would you load it and pressurize the inner vessel unless it was cold?

As a practical mater most of the materials used for this application would have similar properties at 50C and -50C, that is why they are used for such tanks.

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P.E. Metallurgy, Plymouth Tube

### RE: [img http://res.cloudinary.com/engi

Sruthish,
It seems that you are suggesting that the Vessel cannot be fabricated or tested which is rather silly!!!

### RE: [img http://res.cloudinary.com/engi

From a process engineer's point of view, it does look strange why the max permissible operating temp is -20degC. Would the vessel then mechanically fail at 20degC at atmospheric pressure, which would occur during routine vessel internal maintenance?? I'd check with the plant owner / process design team.

### RE: [img http://res.cloudinary.com/engi

So this may have no relation to your scenario but it reminded me of something I've seen. Say there's two pipe specs, one for carbon steel with a MDMT of -20°F and another with low temp carbon steel with a MDMT of -50°F. Instead of having pressure/temperature ratings over the entire range of the two specs, you'll just find low temp carbon steel with a range of -50°F to -21°F and the carbon steel spec -20°F to say 600°F. They were simply temperature ranges for which material to use.

Your scenario is likely that the design info was stated with a max temperature of -20°C so they never bothered finding out the actual upper limit for the vessel.

Thanks,
Ehzin

### RE: [img http://res.cloudinary.com/engi

Or, worse yet, some beancounter saw a lower limit and insisted that there be an upper limit. We had a cryo system once specified to cool below 77K, and someone insisted there needed to be a lower limit, meaning that it wasn't allowed to cool below 50K, even though that meant that the system was performing exceeding well. So, yeah, we figured out how to get to consistently cool below 50K, but because it "failed" its low limit, our solution was tossed out.

TTFN (ta ta for now)
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