Re: Carbon absorbent by S.S.
- From: "David Deuchar" <d.deuchar@xxxxxxxxxxxx>
- Date: Fri, 07 Dec 2007 20:47:38 GMT
"Bruce in Bangkok" <b_paige_125@xxxxxxxxx> wrote in message
news:1mnfl39p0agg7r4not7nd9ga9rvl0u0gje@xxxxxxxxxx
On Wed, 5 Dec 2007 17:34:00 -0800 (PST), metalengr@xxxxxxxxxxx wrote:Word of caution for others.
On Dec 4, 8:30 pm, Bruce in Bangkok <b_paige_...@xxxxxxxxx> wrote:
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)
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:
http://www.the-eic.com/meetings/presentations/DuplexStainlessSteel.pdf
Look 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:
http://www.stainless-steel-world.net/pdf/11003.pdf
Also see High performance stainless steels:
http://www.stainless-steel-world.net/pdf/11021.pdf
Go look on the Nickel Institute web site for lots more information.
Pittsburgh Pete
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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)
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.
.
- References:
- Carbon absorbent by S.S.
- From: Bruce in Bangkok
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