I build water cooled exhaust manifold systems for small 2 - 4 cyl sail boat engines. The prevailing practice is to not build exhaust systems from stainless steel. However, I believe that stainless would both last longer and look better, the latter IS important, and am in doubt as to the prevailing practice.
The operating conditions are as follows:
The actual manifold consists of the necessary exhaust passages welded up from stainless pipe and encased inside a water jacket with engine cooling water circulated through it. A short "mixing elbow" is attached to the outlet of the water cooled manifold and sea water is injected at this point to cool the exhaust gasses for passage through a rubber hose to the hull outlet. Water and exhaust gas exiting the hull outlet are relatively cool.
Estimated temperatures are: exhaust gas within the water cooled manifold approximately 3-400 degrees F.
Gasses entering the mixing elbow - probably a little lower due to the water cooled manifold.
Gasses and water exiting the elbow - warm to touch but can hold hand on elbow below water injection point indefinitely. Gas and water exiting outlet warm but not too hot to hold hand in exhaust stream.
Now my question. Since I believe that the prevailing "knowledge" is based on the fact that stainless will absorb carbon at high temperatures and become hard and consequently be inclined to crack or break with vibration, at what temperature will stainless, say 316L, start to absorb carbon from the exhaust gasses. In short, would a stainless exhaust system absorb sufficient carbon over say, a 10 year period to become brittle?
Your comments, or a pointer to existing data, will be highly appreciated.
Bruce-in-Bangkok (Note:remove underscores from address for reply)