LHe Transfer Line Handling Tips
Liquid helium transfer lines are used to transfer liquid helium from a storage dewar to the magnet system dewar.
These lines are usually constructed of all-welded stainless steel. To aid in handling the line, the center section is vacuum-jacketed flexible piping. This piping is connected on either end to smaller diameter non-flexible vacuum-jacketed tubing. These smaller diameter tubes are inserted into the storage dewar and the magnet dewar.
Although LHe transfer lines are rugged and can give years of service, they must be handled correctly in order to maximize their lifetime.
It is very important that the non-flexible tubes are inserted into the storage and magnet dewars in a straight up and down motion. Bending the non-flexible tubing while it is supercooled will apply too much stress to the welds and will eventually cause failure.
Transferring liquid helium is a minimum two-person operation. One person needs to guide the tube into the storage dewar and the other person needs to guide the tube into the magnet dewar. Each person should be positioned so they may grasp the large curved tubing between the flexible and small outside diameter tubing. Additional personnel may be positioned at the tube ends to help guide the tube into the dewars.
Stable platforms should be provided to stand on if the storage or magnet dewar is too tall for personnel to refill while standing on the floor.
Do not allow the weight of the transfer line to be supported by the small outside diameter tubing!
Using proper equipment to protect the operators from frostbite, have the personnel on the storage dewar leg carefully guide the tube into the storage dewar until it is slightly submerged in liquid helium.
Allow the transfer tube to cool until a plume is noticed on the magnet dewar side leg of the transfer tube. The personnel operating the magnet dewar leg should then carefully guide the tube into place. It is very important that all personnel handle the tube assembly by the large curved tubing and the flexible tubing – not the small outside diameter tubing!
After refilling the magnet dewar, carefully remove the transfer tube by pulling straight up using the large curved tubing. Use extreme care not to bend the small outside diameter tubing of the assembly.
SEALING PROCEDURE TO BE FOLLOWED AT THE COMPLETION OF EACH HELIUM TRANSFER:
1. Minimize the time the system is open to the atmosphere during liquid helium transfer
This is the most likely time for air and water to be drawn into the system.
2. Immediately following helium transfer, seal all valves and fittings
Carefully check all hoses, pop-off valves, etc. for leaks by wiping soapy water over all connections and watching for bubbles to appear.
3. Monitor off-gas from the system using an appropriate gas flow meter
Helium flow should begin within 24 hours after sealing the system. If gas flow through the flow meter is not detected within 24 hours, recheck all seals carefully and determine whether a High Pressure Atmospheric System has moved through your area during the past 24 hours. If one has, monitor the flow for another 24 hours.
4. Periodically check the flow meter on the system to see that helium gas is flowing out of the system
If gas flow is not detected for more than 24 hours, recheck all fittings as described above. If no off gas is generated within another 24 hours, CONTACT THE FACTORY IMMEDIATELY!
