Addressing the coatings-I reckon most paint finishes and coatings(if cured) will mess up because when the pipe expands/contracts due to heat, The coatings may not expand or contract quite as readily. Simple physics.
Chrome and aluminium coatings are the exceptions as they are a type of steel and will expand and contract. Plus, they are good indicators of how the motor is running, Just look at the color of the downpipe... Ever wondered why most bike buidlers use chrome or ali. coated exhausts? Not just 'cause it looks nice
.Powder coating warms up and stretches when it get's hot, but it has to be applied correctly or it won't adhere properly and even then, if the coating is baked on hard(as the coaters do, it's what the ovens are set for) it will be a hard surface trying to stick to a surface that changes in dimensions. Tough job for a coating of any kind.
May be why good pipes are sold uncoated. It then gives the buyer a choice of what to do...
Painting or coating so that the finish is not cured might be the answer to the problem 'cause it will still be sticky and strecthy. That may be why cheap paint works if not cured properly. Good chrome or ali. coatings, if applied correctly, never fall off, they simply change color according to the heat going through it.
I heard that all down the pub, so take it with a grain of salt
