SCAT tubing and corrosion

[Jamie]

I mentioned in another thread that I'm stuck at KCGI until at least Monday due to mechanical problems. The A&P that was in on Saturday took me on a brief tour of the stuff they're currently working on.

 

-Three- different Cessnas of various type had severe corrosion apparently induced by rotting SCAT tubing for the air ducts. The scenario painted was that the condensation coupled with rotting tubing eventually causes dissimilar metal corrosion. The aluminum parts I saw were swelling / layered where they touched the rusting steel rings in the tubing. Major corrosion and mostly hidden from sight. In at least two of the cases, the problem was only spotted because they were after something else.

 

Other than the big SB's for the leaking windows / insulation, do we have anything like this?

 

 

 

[FloridaMan]

I would bet it's more likely CAT tubing and not SCAT, and I'd double-down on that tubing being above the headliner of those Cessnas. CAT is black and is some sort of fabric that absorbs moisture and accelerates corrosion. SCAT is silicon and is orange. Black hoses, especially in areas that aren't open for easy inspection or are close to other stuff accelerate corrosion and should be replaced (think SB208B for Mooneys). 

 

SCAT (orange) and CAT (black) tubing:

 

[Jamie]

Ah. Yup. That must be it. The A&P probably said something like "similar to the SCAT tubing on the engine" and I didn't understand.

 

The 182 was the scariest. The wing root vent for the cabin air had caused -major- corrosion of the wing spar attach point. The airplane was otherwise perfect and well maintained. If they hadn't replaced the windshield they probably wouldn't have caught it until the wing came off.