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If metallic materials come into contact with water and oxygen, sooner or later there will be corrosion. The oxygen in the air reacts with the metallic material so that it gradually decomposes. A sacrificial anode is intended to protect hot water storage tanks from this harmful reaction. But how does the protective anode work and when is it used?

Sacrificial anode of the heater: functional principle explained in an understandable way

The sacrificial anode is a metallic workpiece that is intended to protect hot water storage tanks from corrosion damage. It usually consists of rod-shaped magnesium that is placed directly in the drinking water storage tank. It is important to know that the magnesium anode is below the steel of the storage tank walls in the electrochemical series. So it is less noble and is therefore first attacked by rust. That means: Experts sacrifice the metal to protect the memory. For this reason, the component bears the name “sacrificial anode”.

A galvanic element forms in the storage tank with the protective anode

If metals come into contact with water and oxygen, a so-called galvanic cell (also galvanic element) is formed. The oxygen reacts with the material. The iron oxidizes and releases electrons. Rust forms and the materials gradually decompose. This does not happen with a sacrificial anode. Because here the less noble magnesium anode dissolves instead of the hot water tank. The free metal particles then migrate via the water (the electrolyte) to the storage walls, which no longer degrade with this arrangement.

Use and service life of the protective anode in the hot water storage tank

The sacrificial anode is used in the heating system - more precisely in enamelled steel storage tanks for drinking water. Because until today it is not possible to apply the protective enamel layer without errors. There are always small gaps or cracks where the metal comes into direct contact with the oxygen-containing drinking water.

In addition to use in hot water storage tanks, there are numerous other areas of application for the protective anodes. For example in shipping. Here, the less noble metal rods protect, for example, the screws or oars of ships that sail through electrochemically aggressive salt water. In addition, the sacrificial anode also protects tank systems, underground pipelines or oil drilling rigs from oxygen corrosion.

Oxygen decomposes the magnesium sacrificial anode

It is important to know that the electrochemical reaction consumes the magnesium sacrificial anode. The rod-shaped or chain-shaped components must be replaced at regular intervals and ensure higher maintenance costs. A protective anode in the hot water tank usually lasts for at least two years. If the metal is used up faster, this is a sign of very oxygenated water. In addition, the problem could indicate that the memory is too small. More water flows through it, which means that corrosion takes place more quickly.

Cost of a magnesium anode for corrosion protection

A sacrificial anode for hot water storage tanks can be installed yourself with a little manual skill. The magnesium rods cost 30 to 80 euros and can be changed if necessary. Tradespeople usually recognize when this exists during heating maintenance. If the experts take over the exchange of the protective anode, there are additional labor costs of 40 to 80 euros. To do this, they carry out the work professionally and take over the guarantee in the event of damage.

Overview of advantages and disadvantages of the sacrificial anode

The magnesium anodes are cheap. They are comparatively easy to change and reliably protect enamelled drinking water storage tanks against rust. However, they have a limited lifespan and must be replaced at regular intervals. This leads to higher maintenance and repair costs for the heating system. The following table shows the advantages and disadvantages in comparison.

Alternative: the impressed current anode to protect against corrosion

In addition to the sacrificial anode for heating, there are now alternative solutions for corrosion protection. The so-called impressed current anode, which also consists of a rod-shaped metal, is widespread. As the name suggests, impressed current anodes are connected to an external power source. They thus supply an excess of electrons, which effectively protects the storage walls from corrosion. The special thing about it: Neither the protective anode nor the storage tank are consumed with this variant. This lowers the maintenance costs, but causes higher costs for the electricity used. As a rule, however, these are no more than ten euros a year.

Conclusion by Alexander Rosenkranz

The sacrificial anode is a mostly rod-shaped workpiece made of magnesium. It is used in enamelled drinking water storage tanks and reliably protects them from oxygen corrosion. Since the magnesium anodes dissolve over time, they must be replaced at regular intervals. So-called impressed current anodes, which do not consume, offer a maintenance-free alternative.

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