On Tue, 04 Dec 2007 23:53:43 -0500, Ned Simmons
wrote:

On Wed, 05 Dec 2007 10:42:34 +0700, Bruce in Bangkok
wrote:


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?


Have you got a source other than "prevailing knowledge" that describes
that corrosion mechanism? I spent about 10 years in the marine
hardware fabricating business and realize that SS is subject to some
surprising corrosion processes, but that's a new one to me. Perhaps
it's a muddled explanation of carbide precipitation, which does
involve carbon and elevated temperatures, but the source of the carbon
is the metal itself. It also only occurs at higher temperatures than
what you're describing. Minimizing carbide precipitation is the the
reason for the L (extra low carbon) grades.
http://www.burnsstainless.com/TechAr...s_article.html

I built many SS exhaust risers with water injection (but no manifolds)
from 1-1/2" sch5 T316L, and never had complaints of corrosion
failures, but it's possible I got away before the failures began.

No source and that is what prompted this post. "Everybody says" is the
usual reference. I built two all stainless systems for two boats that
I have owned and had no problems with either. These are built
basically from Schedule 40 pipe and about 4 mm plate. No crack,
corrosion or other problems in ten years. But still "Everybody says"
so I have usually gone along with the owners and built them out of
mild steel.

However if I could cite some reference for using stainless I could
build nice shiny stainless manifolds (that were OBVIOUSLY more
valuable) and charge more money for them.

Thanks all for the answers.

Bruce-in-Bangkok
(Note:remove underscores
from address for reply)