What is the Sacrificial Anode in Water Heating?

September 24, 2018

Sacrificial anodes, those installed in water heating tanks, have special roles to play. In plain speak, heater anodes are designed to prevent corrosion. The rods live inside sealed water tanks, submerged in hot water. Without it, a vessel would rust and discharge corrosion-brown water. Equipped with a magnesium or aluminium surfaced sacrificial anode, however, the screw-in rods stop that electrochemical process in its tracks.

Deconstructing Sacrificial Anodes 

There’s not a great deal to look at on a standard rod. It’s clearly made of a special material, but that’s the only immediate difference we can find. On reading the device’s installation manual, the material advantages are made clear. It talks of galvanic reactivity, which is measured on a scale. If a more “reactive” metal is introduced into the water heating tank, then it’ll rust while the less reactive metal stays intact. Just like the label says, this anode is sacrificing itself so that the vessel surfaces and its various parts don’t corrode. In this electrochemical reaction, the physically dissimilar materials are generating a tiny electrical current, which means that anode is going to lose electrodes until it breaks down into a decomposing mess of metal.

Maintaining Replaceable Anodes 

A single sacrificial anode is protecting a small residential hot water tank from rust. On a larger commercial model, there could be as many as five rods of material-reactive metal deteriorating slowly inside a high-volume vessel. One thing’s for sure, at some point, perhaps six years down the line, the rod will need replacing. Alternatively, and this is a newer system innovation, there are powered sacrificial anodes on the market. Electrical wires connect powered anodes to a tiny current, which means the rod material doesn’t lose electrons, and it doesn’t disintegrate over time.

Why is This System Asset Important? 

Well, every hot water system and every large or small-scale water containment setting can rust. Primarily, it’s the water that corrodes the metal. Just as importantly, though, there are different types of metals used in water heating technology, including copper, and steel. The “nobler” (less reactive) alloys stay intact, but there’s still that electrochemical process in play, which is accelerated by the presence of thermal energy. Those noble metals will eat away the reactive metals unless there’s a purpose-designed material solution included within the system. Sacrificing their very material bases, these anodes suit their roles very well indeed.

Essentially, this problem occurs in places where water and different metals coexist. In marine ships, inside their ballast tanks, zinc anodes stop rust. In residential and commercial water heating systems, aluminium and magnesium rods give up their materials to subvert the electrochemical process. Galvanic action is inevitable, so the screw-in rods must be replaced every few years. Alternatively, for powered anodes, their electrical supplies must be maintained if they’re to remain intact.

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