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How can you prevent Galvanic Corrosion? Answered

My parents bought a new green heater they've had repaired by 2 different guys in the past 2 months. The last one was a guy my brother knew; he said that it needed to be sanded, which I thought was a bit strange. It's beginning to act a bit funny again, kicking on, then going off. So I opened it up today, thinking that it was probably Galvanic corrosion from the way he talked. It seems as if a few companies are getting a bit careless in there designs. :-) So I opened it up and there was still corrosion laying on the bottom of the case from the first fix. He didn't even know what I was talking about.

I read the Wikipedia article: Galvanic Corrosion.

They mostly advise electroplating, which could get a bit labor intensive in this case. From what I understand, the idea is to separate the base metals, the anode and the cathode, from the electrolyte. In this case, it's the water vapor in the air. Wouldn't it just require some type of heat resistant coating to act as a barrier against water? Like some kind of spray on coating?

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orksecurityBest Answer (author)2010-12-06

Most modern water heaters already contain a sacrificial anode, which gets eroded so the rest of the heater doesn't (as quickly). The rust in the bottom could be from that anode; you should still plan on flushing out that corrosion periodically. And the anode will need to be replaced periodically, since it does get eaten away.

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orksecurity (author)orksecurity2010-12-08

BTW, a standard reminder: Sacrificial anodes work ONLY when they and the metal being protected are immersed in the same body of electrolyte. They work for boats. The ones sold for cars, however, are a scam unless you plan on sinking your car in the East River.

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Vorenus (author)orksecurity2010-12-15

Is that the same as cathodic protection? A buddy of mine was just talking about how they used it in the navy on their hulls. But he said it was for keeping sea life from growing on the hull.

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orksecurity (author)Vorenus2010-12-15

Basically the same process. "Cathodic protection" usually refers to deliberately putting voltage on the metal; the sacrificial anode approach usually refers to letting the dissimilar metals work as a battery and provide their own voltage.

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Kiteman (author)caarntedd2010-12-07
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lemonie (author)2010-12-07

Galvanic corrosion I can look-up easily, but I don't know what your heater is.
Can you link me to that?

L

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Vorenus (author)lemonie2010-12-09

Model #C8MPN075B12A1 

It's the right model number; but that exploded parts view doesn't look quite right.

So if it's a sacrificial anode, then we found two bungling repairmen? It definitely sounds more plausible then the corrosion happening twice. The time frame didn't make sense to me either; even with my EE background. Or maybe he didn't replace the anode, just dusted it off so the heater would work temporarily?

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lemonie (author)Vorenus2010-12-10


OK, I don't like this: "My parents bought a new green heater"- if it was defective it should have been repaired/replaced FOC under warranty.

But as far as corrosion goes - I think it got wet.
Steel doesn't rust without water, that's your problem - where did t'water come from?

L

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Vorenus (author)lemonie2010-12-13

We just talked to a friend of ours who does his own maintenance for his rental properties. He's going to show me how to fix it.

I'm still fairly certain it's Galvanic Corrosion. From what I've read; the aluminum and the copper or steel and  copper essentially form the anode and the cathode of a battery as current passes through. So that when it comes in contact with water, which acts as the electrolyte being charged, galvanic corrosion forms. So the galvanic corrosion is the acid of the battery electrolyte and the water vapor in the air is the water?  I just want to make sure I understand this correctly. So why can't we just separate the anode and the cathode from the electrolyte? I would have thought even a layer of latex paint would work.

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lemonie (author)Vorenus2010-12-13


Air is a very-poor electrolyte - try to keep it dry first.
But if it's badly-built do consider arguing that it is either defective or unfit-for-purpose. Money was paid after all.

L

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steveastrouk (author)2010-12-07

There is active galvanic protection which applies an equal but opposite voltage to the galvanic potential.

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