Corrosion problems in fresh water
 

This might be just a little off topic, but who better to know about
corrosion than the regulars on wreck.boats.

I have a water intake for my cabin in a fresh water lake. The pump sits
up on shore and the end in the lake is as follows: A 1.25" PVC water
line from the pump out to a point about 20' deep in the lake. This is
attached to a PVC elbow, a 6" section of 1.25" galvanized iron pipe and
a brass check valve and screen.

The check valve is held off the lake bottom with a concrete anchor
(about 50 pounds) cast with a 2' section of galvanized threaded rod
sticking up, to which the 6" pipe section is clamped so the intake
points up.

At the top of the threaded rod, I had attached an eye and a length of
galvanized iron chain leading to a shallow spot where I could use it to
recover the intake if necessary. This contraption has been in the lake
for about 10 years.

The other day, in order to do some maintenance, I located the chain. It
has rusted solid and weakened to the point that I broke it when pulling
on it by hand. This chain was the same stuff I have used with an 8000 lb
winch, so that is pretty seriously degraded.

Does the brass/galvanized iron interface cause this kind of corrosion?
Would the galvanized components survive if I isolate the brass check
valve from the galvanized components with a short PVC section. If not,
what materials are suitable for this kind of environment?

--
Paul Hovnanian
------------------------------------------------------------------
A physicist is an atom's way of knowing about atoms.
-- George Wald

"Paul Hovnanian P.E." wrote
Does the brass/galvanized iron interface cause this kind of corrosion?

Probably contributes to it, brass and zinc/galvanized-steel being at
opposite ends of the galvanic scale. Maybe a stainless steel chain would
fare better. Taking the brass out of direct contact with with the steel
would reduce but probably not totally eliminate galvanic current. Painting
the brass might help. Simplest thing might be to pull it up every 2-3 years
for maintenance.

Paul Hovnanian P.E. wrote:

This might be just a little off topic, but who better to know about
corrosion than the regulars on wreck.boats.

I have a water intake for my cabin in a fresh water lake. The pump sits
up on shore and the end in the lake is as follows: A 1.25" PVC water
line from the pump out to a point about 20' deep in the lake. This is
attached to a PVC elbow, a 6" section of 1.25" galvanized iron pipe and
a brass check valve and screen.

The check valve is held off the lake bottom with a concrete anchor
(about 50 pounds) cast with a 2' section of galvanized threaded rod
sticking up, to which the 6" pipe section is clamped so the intake
points up.

At the top of the threaded rod, I had attached an eye and a length of
galvanized iron chain leading to a shallow spot where I could use it to
recover the intake if necessary. This contraption has been in the lake
for about 10 years.

The other day, in order to do some maintenance, I located the chain. It
has rusted solid and weakened to the point that I broke it when pulling
on it by hand. This chain was the same stuff I have used with an 8000 lb
winch, so that is pretty seriously degraded.

Does the brass/galvanized iron interface cause this kind of corrosion?
Would the galvanized components survive if I isolate the brass check
valve from the galvanized components with a short PVC section. If not,
what materials are suitable for this kind of environment?


Even in the absence of electrogalvanism, iron will rust naturally in
fresh water. Paint will protect it, but not at the rubbing places.
The remedy is a refit, new chain every few years. It's cheaper than
prevention.

Try nylon rope? It won't rust and will go 10 years in water.

Terry K

Joe Blizzard wrote:

"Paul Hovnanian P.E." wrote
Does the brass/galvanized iron interface cause this kind of corrosion?

Probably contributes to it, brass and zinc/galvanized-steel being at
opposite ends of the galvanic scale. Maybe a stainless steel chain would
fare better. Taking the brass out of direct contact with with the steel
would reduce but probably not totally eliminate galvanic current. Painting
the brass might help. Simplest thing might be to pull it up every 2-3 years
for maintenance.

I can isolate the brass check valve from the plumbing pretty easily with
a PVC fitting. Painting the brass probably won't work since it has
internal surfaces such as valve seats that won't take paint.

I'm wondering about the rest of the structure. The supporting post cast
into the concrete is galvanized, as are some nuts, bolts and clamps.
Stainless steel will get quite espensive. The chain is a no-brainer. A
piece of nylon rope will suffice.

Thanks to everyone for the advice.

--
Paul Hovnanian
------------------------------------------------------------------
The opinions stated herein are the sole property of the author. All
rights
reserved. Void where prohibited. For external use only. Standard
disclaimers
apply. If irritation, rash or swelling occurs, discontinue use
immediately
and consult a physician.

"Paul Hovnanian P.E." wrote in message
...
Joe Blizzard wrote:

"Paul Hovnanian P.E." wrote
Does the brass/galvanized iron interface cause this kind of corrosion?

Probably contributes to it, brass and zinc/galvanized-steel being at
opposite ends of the galvanic scale. Maybe a stainless steel chain would
fare better. Taking the brass out of direct contact with with the steel
would reduce but probably not totally eliminate galvanic current.
Painting
the brass might help. Simplest thing might be to pull it up every 2-3
years
for maintenance.

I can isolate the brass check valve from the plumbing pretty easily with
a PVC fitting. Painting the brass probably won't work since it has
internal surfaces such as valve seats that won't take paint.

I'm wondering about the rest of the structure. The supporting post cast
into the concrete is galvanized, as are some nuts, bolts and clamps.
Stainless steel will get quite espensive. The chain is a no-brainer. A
piece of nylon rope will suffice.

Thanks to everyone for the advice.

--
Paul Hovnanian
------------------------------------------------------------------
The opinions stated herein are the sole property of the author. All
rights
reserved. Void where prohibited. For external use only. Standard
disclaimers
apply. If irritation, rash or swelling occurs, discontinue use
immediately
and consult a physician.


Stainless is a waste. Submerged, stainless is not stainless. Takes air to
cause the oxides that make it stainless. Monel, would work, but you could
probably put in a lift and a newer boat for the cost of a chain.

"Bill McKee" wrote
Submerged, stainless is not stainless. Takes air to cause the oxides that
make it stainless.

I thought it took oxygen?

"Joe Blizzard" wrote in message
...
"Bill McKee" wrote
Submerged, stainless is not stainless. Takes air to cause the oxides
that make it stainless.

I thought it took oxygen?


Enough free O2.