The response from my personal expert (machinist/engineer):
Most, if not all, production expansion chambers aren't "tempered," "hardened," or otherwise heat -treated in any way. They are not made from heat treatable steel - it lacks the carbon content and/or alloy to retain any sort of heat treatment. The high ductility of the material is the very property that allows it to be formed and drawn into such radical contours and shapes so easily without tearing or failing. The only reason it has any rigidity at all is because it has been work hardened by the drawing/forming process by which its shape was created. Even right at the exhaust port, the material there is unlikely to get anywhere near the critical temperature to remove any temper(if it existed) or appreciably relieve any of the work-hardening. And the rest of the pipe is much, much cooler than that even under continuous WOT and high load.
You may be referring to "thermal fatigue," but that is typically only seen in applications with material cross-sections much much thicker than that of any expansion chamber.
Snowmobiles, jet-skis, two stroke street bikes and numerous other two stroke pipes are wrapped as a rule in many applications, and they do it for heat retention and/or to prevent heat transmission from the pipe to inside the shell of the sled/ski or other components on the bike, respectively. I've never seen them mention that wrapping the pipes has any effect on cracking or otherwise undue deterioration of the pipe.
There's a good chance that in whatever application you've seen cracking occur, the pipe was not suspended properly and the extra weight of the wrapping caused the pipe to resonate more radically or at an RPM where the machine was run more frequently/continuously, and the pipe material fatigued much faster than normal simply because it saw drastically higher, high-frequency cyclic stress - much higher than the endurance limit of the likely low-grade material as I mentioned earlier.
Suzuki RMX250s and numerous other enduro 2-stroke bikes used to come with "double-wall" expansion chambers, where there was actually two steel shells -one external one and one internal one perforated with holes, and a layer of fiberglass sandwiched in between them. They were very quiet when new but tended to burn out the fiberglass quickly and then sounded just like a typical thin-walled expansion chamber. My point for mentioning this is that the extra insulation had no effect on fatigue of either layer of steel in the pipe in my experience.
THE END
He talks a lot but he knows his stuff
Now personally I'm worried about the effects of water on the pipe wrap (water crossings, washing the bike etc) but I'm looking into some kind of coating like this:
LINK
Thanks to the wonderful help of Nick at Cycle Pro 775, Elko, NV I am going to get a Q to try out and hopefully test with a sound meter. I've heard of the plastic acerbis s/a but haven't ever seen one.
