I know I've answered a few posts about folks wanting to put header wrap on their headers, and I'm against it in most cases due to fire if oil drips on it. There are times when its warranted to keep things from melting and only if there's no chance of oil getting on it.
Steel is always a bad idea to wrap because it just can't stand the heat that wrapping will introduce to the metal and here is a good example.
There is a 2 inch section I had wrapped to keep my heater hose from melting where it goes into the firewall on my LT4 truck.
They are about 7 years old, and the wrap has been on there about 4 years...now I'm tasked with trying to temporarily patch it up until I can get some new ones, which will be stainless this time and they are backordered...

 

hmmmmn, better go get the razor blade. I have some wrap to cut off lol.

 

Just cut out the damage and weld in a new piece.

That is a good example of why it is a bad idea (plus the fire hazard reason).

 

tada....all done Hopefully this will hold for a few weeks. Guess it was my calling to switch to long tubes anyway.

 

Well played sir!

 

I'd of just put a new piece of header wrap on it and call it a day.

 

 

+1 for coated longtubes

 

 

i have seen several sets of wrapped headers rust out in less than 1 1/2 years, go for coated if you can

 

These were coated but most of it had came off or burned off. When these were on a TPI motor, when it was fired up for the first time the timing was off and heated them up real good and they were never shiney after that.
The coated headers are all steel as I would think the heat being kept in would still cause premature failure. Going with a set of stainless long tubes this time and hopefully it will last 10 years.

This is a pic of the headers when they were new:


And then with about 20k miles on them with new motor


And now they have about another 60k miles on them with the LT4....so I think its time for LTs anyway

 

...so is it the heat, or moisture retention?

 

You'd think there would be other areas of the primaries with about the same kind of damage if it were from moisture. Good question though. I've always been told it was a bad idea on street cars that see any kind of weather. Hell even those with coated headers shouldn't drive them on roads with salt, wet or dry.

 

How can moipsture collect on a surface that approaches 1,000*F? The problem is the mild steel reaching an even higher temperature, approaching the exhaust gas temperature, due to the insulating properties of the header wrap. The iron particles are so hot that they are basically "burning" (combining with oxygen), and being eaten away.

This is not a problem with coated headers, because the primaries are coated on the inside as well, reflecting the heat back into the exhaust gas, and lowering the tube metal temperatures. And, even without the coating, there is no oxidation taking place on the inside surfaces, because there is very little oxygen in the exhaust gasses.

 

This was the only portion that was wrapped to keep the heater hose from melting, it was wrapped from the 90* turn just out of the heads down to about 2 inches before it combines with the other primary, only a few inches. You can barely see where the back band clamp was imprinted in the coating where its still light gray colored.