Thanks, for reply, this is in a Pegasus HP powered Cermark Viper II, that has flown for 10+ years and has even taken a Best Civilian Jet at Route66 as well as IRON MAN at Kentucky Jets so it has many flights proven on tailpipe at Eagle Tree Pitot speeds routine of 199.99MPH
As an engineer I am well versed on heat expansion/contraction, thus my question/confusion with tailpipes "BY DESIGN". So my take away is the corrugated standoff ring that "is" spot welded to "inner pipe" is just an "OD" dimensional friction fit to outer wall cooling pipe and mine has now lost some of its friction fit tolerance between the two.
The inner Pipe has two straps holding it to the kevlar full bypass, so I was thinking a security strap attached on the front end in like manner attached to wooden bulkead would not inhibit any dimensional expand/contract in diameter/length only acting a as piece of mind since it now will freely fall off if stood on end on the bench out of the model. This is something in never did before and no other pipe I own exhibit.
Tam uses 2 "Z" folded strips of metal to space out his inner and outer pipes. I know that the strips are spot welded to the inner pipe on at least one end and I thought that they were also spot welded to the outer pipe as well. I'll have to take a look at one when I get home to see.
The CARF pipes typically have tabs welded to the inner pipe that come up through slots in the other pipe and are bent over to retain it.
Either way, I've never had or seen a 2-walled pipe where the inner and outer walls are not mechanically connected together. I know your's was and then came apart, and my suggestion is to connect them back together using some of the above advice. I suppose you could secure the outer pipe to the airframe somehow to retain it, but I've never seen it done myself.
Bob