Here's my question. I have a physical example, but no idea how it was made.

There is a stainless steel pipe in a spiral shape, like in a condensor, with 8 levels or 360 degree turns.
The inner diameter of the pipe is 1/2".
In the middle of the tube is another pipe made of copper. The inner copper pipe maintains center all the way through and never touches.

How could both pipes be made to be concentric?

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Perhaps with a hard parafin liner that kept it appart during the manuafaturing but was easily gotten rid of later.

Sort of like lost foam casting processes when engines are made......

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if both pipes shared the same geometry; i.e. the same radius to their centers and pitch, the smaller would thread into the larger.

don

Like a double walled tube? I turned down the job that would have given me that info. Could tell you how a single wall tube is made in intimate detail though. I would guess that the copper strip is fed on top of the stainless but the softness of the copper would make it difficult to breakdown the stainless strip properly. Both metals are best welded together with TIG so trhat makes it possible. The other possibility is that they are two seamless tubes redrawn to take out the air gap between them. This would work well but I'm guessing very expensive.

Mark