And in the more easily understood term: Ya just cooked your headers. ;)
(Yeah...what he said...totally correct.)
- Bernd
At 02:55 PM 08/23/1999 -0400, you wrote:
>Here's my best explanation of why headers fail with header wrap (I'm a
>metallurgist by day). With plain carbon steels, the material itself can
>actually suffer from thermal fatigue, temper embrittlement, and accellerated
>corrosion. Thermal fatigue is just the process of cyclic heating and
>cooling. This is common to all exhaust systems, but the problem is
>exaggerated by the thermal wrap, because the temperature which the header
>material is subjected to is higher than it would be without the header wrap.
>The heat which is normally dissipated throughout the engine compartment is
>held in the headers, causing them to be heated to temperatures where
>corrosion is accellerated, and thermal fatigue is greater due to larger
>gradients in the heating/cooling cycle. Temper embrittlement is caused by
>holding carbon steels in temperature ranges which can be sufficent to cause a
>phase change in the steel. This is often called re-crystallization, and
>causes normally ductile steels to become brittle, and fail in a brittle
>manner.
> The end result is a combination of these phenomena, which results in
>brittle, cracked headers with high levels of corrosion. In short, the header
>wrap will keep the heat out of the engine compartment, but at the cost of
>shortened header life.
>
>SteveM.
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:16:02 EDT