----- Original Message -----
Sent: Monday, March 08, 2004 7:44
PM
Subject: Re: [PSUBS-MAILIST] Interior
paint (was: Scuttle valve)
To add to my last e-mail. I would like to talk a little about
corrosion and corrosion control. Which is usually the primary purpose of a
coating system (corrosion control). It takes 4 things to make corrosion: An
Anode, a Cathode, a metal path, and an electrolyte. Oxygen is the primary
electrolyte. Oxygen is contained in water, and of course a normal atmosphere.
The salt in sea air (not only sea water) is a strong electrolyte.
The easiest and most common method of corrosion control is to put a
barricade on the metal surfaces to prevent the electrolyte from contacting the
metals (anode and cathode). Since any structural metal is an alloy ie: steel
is an alloy of Iron and Carbon you alread have an anode and cathode in contact
with each other. We can't prevent this.
There are charts available in corrosion control manuals, or
corrosion engineer manuals that list how far apart metals are from being the
cathode or the anode. The anode gives up electrons or is the one to rust away
(if you don't mind these terms "rust") We put zinc anodes on steel ships to
save the steel. The zinc anode is eaten away instead of the steel, then as a
rule of thumb, the zinc anode is replace when it is half gone.
Anytime you put a metal fastener thru metal, you again create a
corrosion problem. As the fastener is seldom the same alloy as the material it
is holding together.
I'll try to keep this short, and simple !!!
When you add electricity to the system, you have more electron
flow, and increase you potential for a corrosion problem. It's very difficult
to keep electricity out of a modern boat!
Once all the metal is welded it is probably (possibly
depending on the situation and design) the best time to clean the surface.
Apply a chemical conversion if you are going to, prime the surface and apply a
top coat. Then add the systems. It is very important to coat all metals used
in the marine industry. There are few exceptions, one being that when you use
an anode (such as zinc on steel) that the contact surface be bare. As it
wouldn't do much good to put the zinc on a painted (or coated) steel surface.
Corrosion control is an ongoing war in the marine
industry.
Bob
Bob Duncan <katsurencho@yahoo.com>
wrote:
Hello,
I would think that if it is an ambient pressure submarine, that
you should be able to use the same kind of coating that is used in
hyperbaric chambers.
For a 1ATM submarine, i would use epoxy or polyurethane primer
and topcoat. We dont' use the word paint, because paint is a decorative, and
these are a coating system. I'm sure you will have a fair amount of
condensation, on the inside of the boat.
bob
Michael B Holt <tlohm@juno.com>
wrote:
On
Mon, 8 Mar 2004 15:05:26 -0800 Steven Mills writes:
>
>I had
not thought of water-proofing the interior, but it makes
sense.
>Paint or plastic? Would there be residual out-gassing over
time from
>the plastic if one used spray-on vinyl like used in beds
of pick-up
>trucks?
>What would be the curing time of paint
versus plastic?
Hey, let's talk about this. What sort of paint can
be used
safely on the interior of any sealed cabin? Some paints
have
an odor that lasts for a long
time.
Mike
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