A process called galvanic corrosion is a common form of rusting that occurs in salt water. Do not confuse this with electrolysis. They are not the same process. It occurs when two or more different metals make electrical contact with one another in seawater. When this type of connection forms, they have formed a battery and some current will flow between the metals. One of the metals in the pair acts as an anode. This causes it to oxidize faster than it would if left by itself. Alternatively, the other metal behaves as the cathode and corrodes more slowly than it would alone. Whether either metal in the couple corrodes on its own in seawater is not the issue. The problem is that when there is contact with a different metal, the rates of corrosion will change. decay of the anode will speed up and decay of the cathode will slow down or stop entirely. Fortunately, the use of a sacrificial zinc anode helps to alleviate this ever present|pervasive) problem.

This type of corrosion is of special concern especially for the shipping and fishing industries where metal equipment is always in immersed in salt water. Employing the use of zinc anodes will keep things like steel tanks, rails and ship hulls from rusting. Because the zinc rusts far easier than iron, it corrodes first. To greatly increase the life of their metal crab traps, crab fishermen depend on attaching a zinc anode. The crab trap becomes the cathode and remains protected while the anode disintegrates over time. A replacement anode should be attached after the previous one has rusted away to about half of its original size.

Most boaters are extremely cognizant that the most common victim of galvanic corrosion is boat propeller and shaft. The corrosion is counteracted by adding a third metal. As mentioned before, zinc is the metal of choice because it oxidizes more quickly than the other metals. This piece of metal is called a sacrificial anode, because it is sacrificed in order to save the other metal parts from rusting away. Its very important that zinc anodes are kept tabs on because if one waits too long, the metal parts they were meant to protect will definitely disappear.

Although utilizing zinc anodes is a smart step in protecting metal equipment immersed in sea water, knowing how much zinc to add is even more important. The amount of protection provided by the zinc anode is dependent upon its surface area. Other variables include the type of metal that needs protecting as well as the specific chemistry of the water. The anode should be checked frequently to look for any corrosion. If any rust is detected, then zinc with a greater surface area is needed. If the zinc anode must be replaced in less than a year, then one with more weight should be used instead.

Attaching the anode is another critical step in protecting metal components. Mounting the zinc just anywhere is not going to provide any protection at all. There must be metal-to-metal contact to ensure that electrons will flow. Two options exist: direct physical contact or connected by a wire. This also means that paint cannot cover any of the metal surfaces or sufficient contact will not be made.

When utilizing zinc anodes, there are crucial steps that cannot be overlooked if the anode is to be effective. Use an anode with enough surface area and weight, attach it so it makes physical contact and be sure there arent any coatings on either metal that will impede the electrical contact.

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