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Zinc Anode for Galvanic Corrosion in Marine Heat Exchangers

Time:2024-02-28 15:56:26 Click:12times

<span style="font-family: arial, helvetica, sans-serif; font-size: 16px;">Galvanic Corrosion in Marine Heat Exchangers</span>

Galvanic Corrosion in Marine Heat Exchangers

When two different metals are immersed in seawater, they can form an effective and usable battery due to the surrounding environment. This means that although the electrical currents between the two metals are completely separate, they are connected through the seawater.

As a result, the electrons constituting the current are provided by one of the metals, which actually releases particles into the seawater in the form of metal ions. This process leads to a phenomenon known as "galvanic corrosion" and if ignored, it can damage the metals, eventually leading to failure.

Marine heat exchangers made from materials like naval brass are particularly susceptible to such issues. In most cases, the only way to prevent "dezincification" of naval brass alloy tubes is by installing zinc anodes (also known as "pencil anodes" or "sacrificial anodes").

The principle behind zinc anodes is introducing a third metal into the circuit that either consumes electrons or releases them at a faster rate than the other metals in the heat exchanger. Thus, it essentially "sacrifices" itself to protect the other metals in the heat exchanger.

While zinc anodes are theoretically a practical solution, they pose practical issues as they degrade over time, requiring periodic replacement. The replacement interval depends on several factors, including the required amount of zinc for a given surface area—this varies based on the type of metal being protected and the minerals present in the seawater. To monitor this, it's recommended to periodically check for signs of corrosion on the protected metal, which involves draining, removing, and disassembling the device for inspection of the internal areas.

Additionally, regular checks on the extent of anode consumption are necessary, and zinc anodes should be replaced when they have corroded to about half their original size. This process involves draining the seawater circuit to remove and replace the zinc plugs.

Therefore, while zinc anodes can provide protection for naval brass alloy tubes in heat exchangers, wouldn't it be simpler if heat exchangers didn't require zinc anodes at all?

This conclusion was reached during the development of marine heat exchangers and oil coolers by a certain entity.

As a result, the mentioned heat exchangers are made using standard copper-nickel alloy tubes, eliminating the need for zinc anodes. In fact, installing zinc anodes on these heat exchangers could damage the naturally protective copper oxide film on the tube surfaces!

Furthermore, the mentioned marine heat exchangers are constructed using composite materials, "C" coatings, or DZR brass (dezincification resistant brass). This greatly reduces, or even nearly eliminates, the possibility of galvanic reactions between the end caps and tube bodies.

In fact, hundreds of thousands of these heat exchangers and oil coolers are in service worldwide, proving their reliability and durability, which underscores the excellence of their design and specifications for such applications.

In addition to copper-nickel tubes, alternatives like titanium metal tubes are also offered, boasting the highest corrosion resistance level, with a 10-year warranty on all seawater-contacting titanium materials!