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Posted by Randal O'Brian on May 14, 2008, 2:03 pm
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> Will urine ie human waste corrode 316L valves and pipe? The question is
> asked because waste tanks are typically plastic, but Lloyds A1
> certification requires all through hull valves to be fire proof. Fireproof
> valves are typically 316L. I have purchased all my valves from the
> chemical industry. I have been told that urine will corrode 316 over time.
> I don't believe it. If 316 is good enough for corrosives in industry, why
> would it not stand up to human waste? If anybody knows for sure, please
> let me know.
> Steve
IIRC 316 is susceptible to chloride stress corrosion cracking. However,
316L is much better in that regard. I'm not sure if this relates to your
problem, but thought you should know.
Randal
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Posted by on May 14, 2008, 3:52 pm
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On Wed, 14 May 2008 17:47:45 +0200, "Steve Lusardi"
>Will urine ie human waste corrode 316L valves and pipe? The question is
>asked because waste tanks are typically plastic, but Lloyds A1 certification
>requires all through hull valves to be fire proof. Fireproof valves are
>typically 316L. I have purchased all my valves from the chemical industry. I
>have been told that urine will corrode 316 over time. I don't believe it. If
>316 is good enough for corrosives in industry, why would it not stand up to
>human waste? If anybody knows for sure, please let me know.
>Steve
>
>
Greetings Steve,
Stainless steels will corrode faster if not exposed to free oxygen.
Stainless that is constantly submerged in salt water will corrode when
the same piece above water will not. This corrosion can also be from
biological processes. Science News had an article several years ago
about stainless piping that had to be replaced in some nuclear power
plants because of corrosion induced largely by bacteria. I have
machined many stainless prop shafts that were replacements for shafts
that had what appeared to be worm holes in them that ran roughly
parallel with the shaft axis and were anywhere from 3 to 18 inches
deep. Washington State had to have a bunch of stainless pipe replaced
on some ferries because the boat builder used it in a salt water
system where the inside of the pipes were always flooded.
ERS
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Posted by Steve Lusardi on May 15, 2008, 4:01 am
Please log in for more thread options ERS,
You are correct. I am aware of the rules of use of 316 and that the
corrosion protection is the oxygen layer on its surface. The corrosion you
described is called crevice corrosion and can occur even in fresh water, not
just salt water, but it is caused by oxygen deprivation where all the free
oxygen has been consumed in the water. Crevice corrosion will not occur if
the corrosive medium is continually flushed with new fluid. It is when the
corrosive medium becomes stagnant and its oxygen content is not refreshed is
when crevice corrosion occurs. It is the other aspect you mentioned that
concerns me, the bacteria thing, that I do not understand. Through proper
use and period flushing, I should be able to reduce the risk of crevice
corrosion.
Steve
> On Wed, 14 May 2008 17:47:45 +0200, "Steve Lusardi"
>
>>Will urine ie human waste corrode 316L valves and pipe? The question is
>>asked because waste tanks are typically plastic, but Lloyds A1
>>certification
>>requires all through hull valves to be fire proof. Fireproof valves are
>>typically 316L. I have purchased all my valves from the chemical industry.
>>I
>>have been told that urine will corrode 316 over time. I don't believe it.
>>If
>>316 is good enough for corrosives in industry, why would it not stand up
>>to
>>human waste? If anybody knows for sure, please let me know.
>>Steve
>>
>>
> Greetings Steve,
> Stainless steels will corrode faster if not exposed to free oxygen.
> Stainless that is constantly submerged in salt water will corrode when
> the same piece above water will not. This corrosion can also be from
> biological processes. Science News had an article several years ago
> about stainless piping that had to be replaced in some nuclear power
> plants because of corrosion induced largely by bacteria. I have
> machined many stainless prop shafts that were replacements for shafts
> that had what appeared to be worm holes in them that ran roughly
> parallel with the shaft axis and were anywhere from 3 to 18 inches
> deep. Washington State had to have a bunch of stainless pipe replaced
> on some ferries because the boat builder used it in a salt water
> system where the inside of the pipes were always flooded.
> ERS
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Posted by Bruce in Bangkok on May 14, 2008, 9:12 pm
Please log in for more thread options On Wed, 14 May 2008 17:47:45 +0200, "Steve Lusardi"
>Will urine ie human waste corrode 316L valves and pipe? The question is
>asked because waste tanks are typically plastic, but Lloyds A1 certification
>requires all through hull valves to be fire proof. Fireproof valves are
>typically 316L. I have purchased all my valves from the chemical industry. I
>have been told that urine will corrode 316 over time. I don't believe it. If
>316 is good enough for corrosives in industry, why would it not stand up to
>human waste? If anybody knows for sure, please let me know.
>Steve
>
There was a thread on rec.boats.cruising today in which a lady named
Peggie Hall states:
----------------------------------------------------------------------------------------------------------
SS fittings in the sanitation system plumbing??? Not a good choice,
'cuz urine will corrode 'em. At least one trawler mfr who puts all
fittings on the top of the tank, with a pickup tube inside the tank on
the discharge (a great idea) used stainless fittings and pickup
tubes--a
VERY bad idea, 'cuz the tubes are corroding, even falling off in
pieces
inside the tank, in just a few years.
--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems
and
Other Sources of Aggravation and Odor"
http://shop.sailboatowners.com/boat_odors/
---------------------------------------------------------------------------------------------------------
Peggie has been posting on rbc for some years now and her posts have
always been logical and informative.
You might try contacting her for additional information.
Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)
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Posted by Steve Lusardi on May 15, 2008, 4:40 am
Please log in for more thread options Bruce,
It is precisely Peggie's response that generated this query. I have spoken
to her on the phone about this issue in February. Peggie does not know one
stainless alloy from another and could not give me the precise circumstances
that created this condition, nor could she identify the alloy used. I
respect her knowledge immensely and do not doubt for a second that this
occurred and is true, but I am faced with a dilemma and need to understand
the corrosion risks better in order to mitigate those as well as possible,
hence this query. Please note Spehro's response above. It verifies my
initial response to Peggie's statement. There was something else going on.
It could be this bacteria thing, but my best guess at the moment is
stagnation, free oxygen deprivation and the resultant crevice corrosion was
the culprit. In addition to this query, I sent a similar one to the valve
manufacturer, but I have not yet received the response. Right now it looks
like my solution to the dilemma is to double valve the holding tank exit
line, first with plastic and secondly with 316L at the hull.
Steve
> On Wed, 14 May 2008 17:47:45 +0200, "Steve Lusardi"
>
>>Will urine ie human waste corrode 316L valves and pipe? The question is
>>asked because waste tanks are typically plastic, but Lloyds A1
>>certification
>>requires all through hull valves to be fire proof. Fireproof valves are
>>typically 316L. I have purchased all my valves from the chemical industry.
>>I
>>have been told that urine will corrode 316 over time. I don't believe it.
>>If
>>316 is good enough for corrosives in industry, why would it not stand up
>>to
>>human waste? If anybody knows for sure, please let me know.
>>Steve
>>
> There was a thread on rec.boats.cruising today in which a lady named
> Peggie Hall states:
>
>
>
----------------------------------------------------------------------------------------------------------
> SS fittings in the sanitation system plumbing??? Not a good choice,
> 'cuz urine will corrode 'em. At least one trawler mfr who puts all
> fittings on the top of the tank, with a pickup tube inside the tank on
> the discharge (a great idea) used stainless fittings and pickup
> tubes--a
> VERY bad idea, 'cuz the tubes are corroding, even falling off in
> pieces
> inside the tank, in just a few years.
>
> --
> Peggie
> ----------
> Peggie Hall
> Specializing in marine sanitation since 1987
> Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems
> and
> Other Sources of Aggravation and Odor"
> http://shop.sailboatowners.com/boat_odors/
>
---------------------------------------------------------------------------------------------------------
>
> Peggie has been posting on rbc for some years now and her posts have
> always been logical and informative.
>
> You might try contacting her for additional information.
>
> Bruce-in-Bangkok
> (correct Address is bpaige125atgmaildotcom)
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> asked because waste tanks are typically plastic, but Lloyds A1
> certification requires all through hull valves to be fire proof. Fireproof
> valves are typically 316L. I have purchased all my valves from the
> chemical industry. I have been told that urine will corrode 316 over time.
> I don't believe it. If 316 is good enough for corrosives in industry, why
> would it not stand up to human waste? If anybody knows for sure, please
> let me know.
> Steve