Rust won't hurt anything. Rust is iron oxide. There are
other metals in stainless steel, but I would not think
that they would stay in solution any longer than iron.

As far as stainless steal holding up in salt water, that
depends on the grade of stainless steal.

Low oxygen does not cause rust. In fact keep iron in an
oxygen free environment, and it will never rust.

But yes the chlorine in the salt can dissolve it by
creating metal chlorides. I would not worry about it
unless it was creating a structural problem.

Where screws corrode fast is where they are in contact
with a different metal in salt water.

Wayne Sallee
Wayne's Pets



Tidepool Geek wrote on 11/3/2006 2:26 PM:
MartyPowerJazz wrote:
I'm going to avoid my usual overdoing and try not to
order the plastic ones...

Hello again,

Before you decide that replacing the screws is "overdoing" read this:
http://tinyurl.com/y9jqz7

The article describes why stainless steel is stainless and also why
stainless steel often isn't stainless in certain environments.
Specifically, two situations that can overcome the chemistry of SS are
as follows:

1. An oxygen poor environment - This is what you get on SS surfaces
that are in tight contact with another surface such as in the case of
SS screws. It's sometimes referred to as "crevice corrosion" and is a
well known problem in the marine trades (ships, boats, offshore oil
rigs, etc.)

2. Galvanic corrosion - This one comes from the chloride ions in
sal****er attacking the protective film that SS produces on its
surface; basically, seawater is capable of breaking down this film
faster than the SS can regenerate it.

Read through the thread I linked in my earlier post and you'll see that
some of the participants had rusting of the SS screws in their Mag 5's.
One guy claimed that it caused some mortality in his tank but I'm a bit
suspicious of that claim. OTOH: At the very least, corroded screws
would make pump maintenance more difficult.

Caveat: I have never owned a Mag 5 but I have seen many instances of
crevice corrosion in sal****er environments.


Stainlessly yours,

Alex