Carbon absorbent by S.S.

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)
Reply to
Bruce in Bangkok
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Bruce:
David Deuchar already has told you briefly that your choice of stainless steel type 316L will not work in seawater.
For more information, see the Sandvik paper by Esterberger on Duplex Stainless steel:
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at the page 8 for stress corrosion resistance and page 9 for crevice corrosion resistance. Seawater has about 19,000 ppm or 1.9 wt % of chloride.
See the older Nickel Institute publication on Nickel stainless steels for marine environments, natural waters, and brines:
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see High performance stainless steels:
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Go look on the Nickel Institute web site for lots more information.
Pittsburgh Pete
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Reply to
metalengr
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Yes, I took his message to heart and another that said "google chloride corrosion" which I did. Horrifying.
Of course this is exactly what Usenet was originally designed for -- and it still does work.
Thanks all for the advice. (Even though it wasn't what I wanted to hear =:{
Bruce-in-Bangkok (Note:remove underscores from address for reply)
Reply to
Bruce in Bangkok
Word of caution for others. While duplex grades will be OK for moderate temperature, they are not good at high temperatures and are not for example suitable for uncooled exhausts.
Reply to
David Deuchar

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