Corroded Bronze

[shamrock]

So I am in the process of replacing through hull valves that were poorly installed by the PO. Plywood backing plates not glassed in and no bolts, just held in place by the through hull.


Anyway, I get a close look at a bronze T fitting attached to the seacock and see a really significant hole! Wow, I must have been taking water when this valve was opened and it's a good think I shut it when not in use. How did I not notice water gushing out? I don't know but this particular valve is under the head and I can't see it, I just feel around to open and close it.

Could this be electrolysis? or just old bronze. This through hull was not bonded. See photo

Thanks

[SVTatia]

Bronze or brass?

[s/v 'Faith']

Wow! That is crazy, glad you found that.

I bet it is brass, seems plumbing fixtures are more commonly available in brass. Good example of the need to use the right material, and to be diligent about maintenance!

Congrats!

[Teknav]

The blue/green corrosion is usually found in copper/brass metals. Bronze is made of copper and tin. Brass is made of copper and zinc.

Mauritz

[ssanzone]

idk... looks like bronze to me and electrolysis could have weakened the bronze and 'jabbing' the fitting could have resulted in that hole.

the picture isnt very clear but it looked like the hole was banged in as opposed to burst out.

-steve

[Cheechako]

I'd be surprised if that hole was in bronze, but there's always a first time.
I dont think you need the plywood backers to be glassed in... in fact it could be bad; they are then enclosed, not inspectable, and can rot in a trapped environment. Good ply just coated with epoxy or poly resin should be fine.

[barnakiel]

I sometimes see fittings that seem to be bronze, covered with white, frost-like, crystals of salt.

What is this salt, how serious is the issue, and how to counter-act?

Anybody PLS.

b.

[Teknav]

White salt/rust forms on corroded zinc due to high humidity, salty atmosphere and heat. (Aluminum also forms white crystals due to oxidation.) Contact with some acids/vapors will form this rust as well; battery terminals. To retard this corrosion, apply a dab of marine silicone grease to the surface you want to protect.

Mauritz

[zeehag]

electrolysis of bronze is not always only pink in color.
that is electrolysis--look at the color--bronze is not silver.


btw-- try to find any fittings requiring any kind of strength or underwater use in brass... brass too malleable and not strong, is used for decoration and oil and other lamps, light weight and light use trims, etc.
bronze is cast into fittings.

place zinc on new fitting.

[roverhi]

The piece that's corroded looks to be a 'T' fitting. That's something that you can buy at any hardware store and it's almost always going to be Brass not Bronze if bought at a non marine specific business. Bronze and Brass look identical once they are slightly oxidized so it's virtually impossible to tell them apart just by looking. Have to know the supplier to get a guarantee that the golden piece you are getting is the real thing.

The zinc in brass acts just like the sacrificial zinc on your propellor shaft. It corrodes away leaving a porous weak copper substrate behind that may look okay but is honeycombed by corrosion of the zinc.

[psneeld]

Originally Posted by Teknav

The blue/green corrosion is usually found in copper/brass metals. Bronze is made of copper and tin. Brass is made of copper and zinc.

Mauritz

If you don't think bronze turns green...you have never spent much time aboard a boat....

Plus if you don't think bronze wears though if in a highly used system like air conditioning in the tropics...you have never spent much time aboard.