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dmi (Mechanical)
20 Jul 10 11:39
I am working on the quench pipe for a liquid helium cooled magnet. (We need 300mm inside diameter and can only have 0.4 bar of back pressure for ~126ft length of pipe.) Right now I am thinking aluminum. Have been searching for a good design reference - ie: which alloys are suitable, connections suitable for these conditions, system contraction, etc.
iainuts (Mechanical)
20 Jul 10 13:49
Hi dmi,
The correct code for this is ASME B31.3 in the US. Don't know what it is in other countries. If US, aluminum alloys are the best material and are rated to the -452 F temperature you need. Stress allowables start on page 182 (ASME B31.3-2006). They also have values for thermal contraction. Designing for thermal contraction is important. 字串2
Another issue you should be aware of is that uninsulated pipe will drip liquid air, so there should be nothing flamable beneath the pipe. It will also drip water, so having electrical equipment beneath the pipe is a no-no. You can insulate the pipe, and it should last a long time since quenches are relatively rare. You might also put drip pans beneath the pipe. Either way, keeping liquid air and water from dripping on things is desireable.
Note that the back pressure MRI manufacturers provide is probably not something you can calculate with any accuracy. They may provide a peak flow rate (flow starts at zero, spikes when the burst disk releases, drops, then increases again before dropping exponentially). Heat transfer during this event is too complicated to calculate with any accuracy, so I'd suggest putting the pipe in they suggest and not worry about doing a pressure drop calculation. If you do want to do the dP calculation, you can be conservative and use a relatively high temperature (say -100 F). 字串3
Another concern is where it is venting. Flow can be very high, and the helium is both extremely cold and an asphixient. Plan on the vent location accordingly.
Why 300 mm though? Most installations I've seen are 4" to 8" pipe. Don't think I've ever seen one at 12".
dmi (Mechanical)
20 Jul 10 15:09
Thanks for the reference and yes I'm in the US.
The pressure(.4bar)is from the manufacturer's rep and he did the calcs to sized the pipe once we had a route. I imagine it's a little larger because we need several elbows before we can get outside.
Are these types of pipes generally welded?
iainuts (Mechanical)
20 Jul 10 18:24
I don't know what's the most common, but I suspect it's welded. My experience with these is one step away from the actual installation. I deal primarily with the manufacturing environment (MRI mfg) and recovery of gas at the plants. 字串5
Just out of curiosity, what is the max flow rate you are designing to? Can you say what magnet and manufacturer? Just curious....
dmi (Mechanical)
21 Jul 10 11:57
The total volume for the unit is 355 liters. Not positive on max flow rate during a quench.
It's a Bruker FTMS.
EdStainless (Materials)
21 Jul 10 15:43
I have seen these in Al, Cu, austenitic stainless steel, Ni alloys (expensive), titanium (including some alloys), and Invar.
Always welded.
Managing stress from expansion/contraction is the real issue.
Don't overlook Ti. It will have fairly low CTE (only Invar will be lower) and this diameter could be fabricated. = = = = = = = = = = = = = = = = = = = =
Plymouth Tube
dmi (Mechanical)
21 Jul 10 16:16
字串2
I'd never heard of Invar. Looks interesting.
Thanks.
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