At 05:42 PM 6/25/2011, Robert Stevens wrote...

>Except for the fact that exhaust pipes ALWAYS rust from the inside out

No, they don't. Mufflers often do, especially if the vehicle is mostly
used for around town driving, where the temperature doesn't get hot
enough to prevent condensation of water in the exhaust gases. For much
of the length of the exhaust (pre-resonator/muffler), this isn't an
issue.

>That's one reason (aside for performance and function) why ceramic
>coating is done both inside and out, and now different coatings are
>used inside.

It's more common to find stainless exhausts, presumably because it's
cheaper than ceramic coating, and you don't have to worry about the
integrity of the coating on a substrate which undergoes frequent
thermal expansion cycles. Ceramic coatings are popular on turbocharged
vehicles, pre-turbo, as an insulator to retain exhaust heat.