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