Using header wrap? Check your exhaust

[walkman]

I just took my -8 down for MX to do a warranty replacement on my Skytec starter and replace my whining ND alternator. As I always do whenever I have the cowl off, I checked the exhaust (among other things).

The builder or prior owner had wrapped the crossover pipe between 1 and 2 down to the join, presumably to help protect the cowl from radiant heat. I noticed soot on the inside of the cowl and some degradation of the header wrap. Upon removal I found this. It appears that the reduced ability to shed heat might have caused the weld to fail.

https://www.dropbox.com/s/39txj250igq97tq/2014-05-29%2020.20.38.jpg
https://www.dropbox.com/s/ed15c8sg69...2020.20.55.jpg
https://www.dropbox.com/s/5hydoutkwr...2020.21.15.jpg

[Paul K]

Glad you found that! Very significant!

[BCP Boys]

Wow, good thing you found it when you did.

[Clint B]

HI Everyone, I thought that I would take a minute to mention that as you can see, header wrap is a BAD DEAL. This particular model of exhaust in the picture above has been very, very trouble free. The only time we have ever gotten them back is when an airplane is involved in a hard/gear up landing, and damages the exhaust that way, header wrap, or ceramic coating.
If your exhaust has ever had header wrap on it, it NEEDS to be inspected as they usually go less then 50 hours after the wrap has been installed before a major failure occurs.
Ceramic coatings are somewhat of a mixed bag, because there have been many,many exhausts out there that are going strong with it on. That being said, when we get an exhaust back in the shop for repair, it more then likely has been ceramic coated, as ceramic coated exhausts account for a majority of our repairs. Also keep in mind that a ceramic coated exhaust with a break is usually not repairable and must be replaced, as we usually can't get the stuff off well enough to weld.
Clint Busenitz /Vetterman Exhaust

[Gisnar]

I guess I am being dumb or unobservant, but why would a exhaust wrap cause that kind of crack? I understand how it could increase corrosion. I would also think (incorrectly) that it may decreases cracking by acting as insulation and thus decreasing thermal shock.
I am not debating that the stuff if bad.
Please help me out and explain how and why.
Thanks

[Clint B]

Stainless steel starts to degrade very rapidly when the surface temperature exceeds 1200 degrees. Since most EGT's are 1300 plus that means the the stainless is going to deteriorate very rapidly. That is the main reason why it is so bad. The pipes need to have air flow going by them so that they don't over heat. This is why a heat muff always needs to have air flowing through it weather or not it is being used in the cockpit.
Several years ago, we got an exhaust back that had been wrapped and in the branch area, it looked like someone had been beating on it with a ball peen hammer from the inside. I have always wished that I would have saved them to show to people.

[ColoRv]

Wrap also acts like an oil sponge if you ever develope a leak...which then performs a really nice imitation of a lit oil lamp wick. I've had two such fires on race cars....I hate exhaust wrap now. Not worth it.

[aerhed]

Exhaust wrap makes about as much sense as a 4bbl Holley.