Designing Cryogenic Manifolds

You didn't say anything about joint design. I would suggest a lap joint/socket where the depth of the socket is roughly equal to at least 1/2 the diameter of the cap. Furnace brazing with 56% silver in a hydrogen atmosphere.

The information provided is too sketchy. What is "TE" copper? Was the brazed joint leak tight before the liquid nitrogen began flowing? How leak tight? We do this type of work every day and the key beyond correct design is correct implementation. Torch brazing using easy flo 45, a 45% silver alloy silver solder and a good white paste flux (Handy & Harmon Brand) will give a suitable joint but the leak tightness of the joint is a function of the braze joint design & quality, not the method of brazing. The alloy you used for furnace brazing is fine but if the joint leaked, it leaked before the liquid nitrogen hit or flowed through it. Copper brazed or silver soldered will not fail because it is maleable enough not to be affected by thermal shock. Work on getting your brazing correct and leak tight and the use at cryogenic temperatures will follow. Why not go to stainless steel and GTAW welding? This is all we use now and my company does about 20,000 welds a year all mass spectrometer tight and flowing liquid helium, hydrogen or nitrogen in vacuum. ability@ameritech.net

Thank you for replying back, Still I am at a lose. You ask what te copper is which I was confused to hear. The few Cryo companys I have talked to have either said use 56% silver furnace braze or a 430 solder to jion the parts together. Alittle more detail on the parts. I have a main body of TE copper that is 1.25 wide by 3 inch long, has 5 2MM holes drilled thru it in the long direction and a .375 C'bore on each end, Paralell to the c'bores are 2 .20 dia holes drilled thru to the c'bores,with a .250 x .188 c'bore as well from the outside. this is where sst tubing is brazed in so I can flow LN2 thru. Each end is wide open and i need to close the ends up so the LN2 does not leak out so I made two flat pieces of .25 thk te copper to have furnace brazed on to seal the holes. When I recieved these parts I pressure tested them at room temp with 60 psi for 10 mins and there where no leaks (cheaking with snoop), when I put the assy into teh vacuum chamber, we where able to if the chamber down to 5 x10-5, once we started to flow LN2 thru the system the pressure when to about 1 x 10-3, we ruled out any leaks from the swagelok fitting we used to attach the sst tubes to the chamber. This left us with the sldered joints and becuase it in the vauum chamber there is no way for us to find the leak. so we think its the brazing. We had made a part out of OFCopper but its had to machine and TE Copper is not, also the Thermo Coff. are not that far from each other. If you have any more ideas please call me on Monday from 7:30 to 3:30 thank you

Ken 781-275-9535 x621

You still didn't say what TE copper is! Do you mean Tellurium Copper Alloy?

morning, yes this is TE Copper that we care using. 781-275-9535 x-621

Ken

yes that is what re copper is.