Let me apologize if this is too off topic for this group but I do read
you guys talking about carbon content, etc.

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 a 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)

I have a SS exhaust on my Lycoming powered helicopter. The exhaust has been
on for 12 years and only cracked initially at the edge of a weld.
Subsequent cross beading at the welds has stopped the cracking.
I had a non SS exhaust on a dinghy engine when I had a sail boat and that
exhaust didn't last long in the salty environment.

"Bruce in Bangkok" wrote in message
...
Let me apologize if this is too off topic for this group but I do read
you guys talking about carbon content, etc.

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 a 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)

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.

--
Ned Simmons

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)

On Dec 4, 11:36�pm, Bruce in Bangkok wrote:
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?

Having been in the marine fab business for over 30 years now, I know
about the prevailing knowledge and have followed it. SS for a gas
engine isn't too bad but a disaster for a Diesel as the sulfur forms
sulfuric acid that consumes 300 series SS. A second problem with SS
is crevice corrosion. SS must have oxygen to continuously protect
itself. If it has trapped stagnant water it will corrode very rapidly
and this situation occurs on the lower side of the jacketed manifold
when it sits idle. Leigh at MarMachine formerly known as Marine
Machine & Mfg,

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

Let me apologize if this is too off topic for this group but I do read
you guys talking about carbon content, etc.

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 a 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
aircraft use stainless exhausts.
the flanges are typically quarter inch 321 stainless.
the sheet components are inconel.(some dialect of stainless suitable
for extended high temp operation)
all tig welded together.

for corrosion you could use an inhibitor in the engine cooling water
and a heat exchanger rather than neat sea water..

just a data point.
Stealth Pilot

"Bruce in Bangkok" wrote in message
...
snip
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.

If you want some PhD authorities, go to Google Scholar and search on
{stainless steel marine exhaust corrosion). After you get through the
patents there are 2,000 references, quite a few of which address the
corrosion mechanisms.

--
Ed Huntress

In article ,
"Ed Huntress" wrote:

"Bruce in Bangkok" wrote in message
...
snip
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.

If you want some PhD authorities, go to Google Scholar and search on
{stainless steel marine exhaust corrosion). After you get through the
patents there are 2,000 references, quite a few of which address the
corrosion mechanisms.

I would be tempted to call the material application experts at some
steel manufacturers. This cannot be a new issue.

Joe Gwinn

"Joseph Gwinn" wrote in message
...
In article ,
"Ed Huntress" wrote:

"Bruce in Bangkok" wrote in message
...
snip
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.

If you want some PhD authorities, go to Google Scholar and search on
{stainless steel marine exhaust corrosion). After you get through the
patents there are 2,000 references, quite a few of which address the
corrosion mechanisms.

I would be tempted to call the material application experts at some
steel manufacturers. This cannot be a new issue.

Joe Gwinn

I'm sure you're right, but it would have to be someone who was expert
specifically on marine applications. Stress corrosion and so on is well
known, but the acid and related things probably are particular to this
situation.

--
Ed Huntress