vacuum insulated pipe

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Has anyone had experience fabing vacuum insulated pipe, and be willing to discuss details?Peter
Reply:Used to machine a lot of it, friend did the welding. It was triple wall. inner wall for liquid helium or nitrogen, middle heat sheild, outer vacuum jacket. spaced with coils of stainless spring wire.  Most was .005" to .015" 304 stainless. 1/8" to 1' id, 5/16" to 1 1/2 " od.  I've done some larger to 4" by .020 corugated, weld and fabbed. some feedthroughs on the small stuff would have bundles of a dozen tubes 1/8" apart all individually welded. mostly autogenous welding, no filler, melt the socket back.  A sheilding bag with gloves helps, couldn't use a gas cup for a lot of those, he would heat the tungsten and bend it hot. as little as 8 amps current. mirrors and magnifiers for the close stuff. Microscope  and rotator when he could. DC motor, hollow right angle drive and a lathe chuck. Each  connection was a machined socket and spigot joint, for hard vacuum the inner line  would be butt welded. Each liquid transfer line would have a few hundred parts, would take a couple of weeks at the monarch EE lathe to machine and a couple of weeks of work for him with the cybertig or  the syncro to weld  up. Now you would probably use a  Dynasty dx. The older machines have a softer arc, but the pulsing may be nice. each segment was helium leak checked before it was covered with the next layer. Lots of money, lots of work. the lines had  built in ball valves welded in to each layer for the pumping ports and main lines, I machined those on a MAHO CNC mill, milled the threads as well, od and id. Spent a lot of hours running those machines. . Some valves were vacuum jacket insulated.  Aluminum to stainless joints were purchased bybraze assemblies, delicate. I've had some success tigging aluminum to steel, but not that I would trust for vacuum.    We sent some to nasa to weld, they cam back junk. costly mistake. Tried e-beam welding, too hard to set up, couldn't turn the long tubes and assemblies.    What size, layout?past work toys; lathes,mills, drills, saws,  robots, lasers ironworker, shears, brake, press, grinders, tensile tester,  torches, tigs, migs, sticks, platten table, positioner,  plasmas , gleeble and spot. Retired June 30, 2009.
Reply:wesdavidsonI saw on some websites that a bellows is used for liquid inner pipe, used for expansion and contraction. Is this necessary for short runs? Or could a slip be made with a o-ring setup? The pipe that I an thinking of fabing is short about 1 foot, to be used with liquid argon. Inner- 1 inch with 3 inch outter. Probably 304, inner tube pressure 250 psi. What kind of wall thickness needed for outer (vacuum)? What type of fittings are used for vacuum port?. You seem to have quite a bit of  experiance with this.ThanksPeter