anode rods

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Doug Lassiter

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Joined
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Location
New York, NY
Let's talk anode rods. I am aware that anode rods prevent corrosion to the water heater tank. 'Nuff said. But WHAT corrosion? My water is high pH (9.0 or so) and a low-middling mineral (carbonate, from limestone) content. That's why they raise the pH, to precipitate out a lot of the minerals. Is anode-rod servicing of importance in this case? What specific properties of water produce the corrosion that anode rods are supposed to deflect? I just got a new water heater, but my old one was going strong after almost 20 years with no anode rod replacement.
 
Porcelain glass is what keeps steel water heaters from rusting.
They develop microcracks quite readily during heating cycling.
The anode rod sacrifices off to rust and protects the steel from perforating.
I've seen tanks fail at 5 years and I've seen over 26 years.
I pulled an anode on one of mine at the 5 year mark and there was no sacrificial depletion, just whitish minerals built up on the surface of the anode.
 
That doesn't really answer my question. What exactly is it in the water that the sacrificial anode protects the tank from? But maybe you're saying that ANY water produces the rust that the sacrificial anode protects against? That doesn't make a lot of sense. The anode attracts something in the water.
 
Anodes are made of less noble metals, like magnesium, zinc, and aluminum, than the tank, which in turn causes the electrons in the water to attack the anode first oxidizing it before the steel of the tank preventing the tank from rusting as quickly as it otherwise would.
 
Doug Lassiter said:
But maybe you're saying that ANY water produces the rust that the sacrificial anode protects against? That doesn't make a lot of sense.
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Apparently, you think that there is some water that does not rust carbon steel. That is what doesn't make sense. Here's an article that may help explain water corrosion.
https://twon.tamu.edu/wp-content/uploads/sites/3/2021/06/drinking-water-problems-corrosion.pdf

As breplum and GReynolds929 said, the sacrificial anode rod corrodes rather than the steel shell of the water heater when cracks or holes develop in the glass lining. The rate of corrosion is affected by many factors as pointed out in the article. From the article, "The rate of corrosion triples or quadruples as water temperature rises from 60°F to 140°F."
 
OK, so this is not about acidity or alkalinity. (My water is HIGHLY alkaline, which is why I ask.) This is just about RUST, as in oxidation by dissolved oxygen in water, and the anode gives up electrons that the oxygen in the water accepts? That's interesting. Thank you. But my understanding is that dissolved minerals can speed up that electrogalvanic process.
 
Doug Lassiter said:
OK, so this is not about acidity or alkalinity. (My water is HIGHLY alkaline, which is why I ask.) This is just about RUST, as in oxidation by dissolved oxygen in water, and the anode gives up electrons that the oxygen in the water accepts? That's interesting. Thank you. But my understanding is that dissolved minerals can speed up that electrogalvanic process.
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Simply put, rust results when water and oxygen meets iron.
 
Of course, if that were the case, an anode wouldn't do much good, because water and oxygen meets the iron in the tank whether or not there is an anode there. So it's a little more complicated than that.
 
Thanks, those are somewhat useful. But the issue here isn't then just water, it's electrolytes, which is water that is electrically conductive, like seawater. In principle, distilled water is just a weak electrolyte in that water molecules largely do not dissociate into ions, but it will absorb minerals and make it slightly more conductive. As a result, you get more corrosion with tap water than with distilled water, and LOTS more with seawater. This would suggest that in a tank, water with high mineral content requires a sacrificial anode more than it would with less mineral laden water. That's what I'm asking about. What KINDS of water are more requisite of a sacrificial anode. I vaguely gather, looking at other sources, that the optimal material for a sacrificial anode depends somewhat on whether the water is acidic or alkaline. As noted, my water is highly alkaline.
 
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Not understanding what you don’t understand, or why, or why you want to do a deep dive into well understood science. There’s probably a few phd theses on the subject. You could probably find them if you searched. All water is conductive. All water has oxygen. It causes rust and corrosion. You deal with it with a sacrificial anode. Doesn’t matter if it’s a domestic hot water tank, a navy ship or even a high tension power line tower. The answer is the same. Sacrificial anode. It really doesn’t matter what kind of potable water you have in your tank. You need the anode rod. If you remove it, your warranty is over.
 
There are powered anode rods out there that use a small power supply plugged into the AC line. The advertised 20-year warranty seems attractive even though the initial cost outlay of the device is upwards of $175.

Has anyone tried one of these and, if so, do they really work for ~20 years?
 
Mitchell-DIY-Guy said:
Not understanding what you don’t understand, or why, or why you want to do a deep dive into well understood science. There’s probably a few phd theses on the subject. You could probably find them if you searched. All water is conductive. All water has oxygen. It causes rust and corrosion. You deal with it with a sacrificial anode. Doesn’t matter if it’s a domestic hot water tank, a navy ship or even a high tension power line tower. The answer is the same. Sacrificial anode. It really doesn’t matter what kind of potable water you have in your tank. You need the anode rod. If you remove it, your warranty is over.
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Why I want to do a deep dive into well understood science? Um, it's because I don't quite understand it, and the questions I asked are not addressed in any of the materials you posted. Feel free to post links to all those PhD theses. All water is NOT conductive. Distilled water is VASTLY less conductive than salt water.
 
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