A process called galvanic corrosion is a common form of deterioration that takes place in aquatic environments. Do not confuse this with electrolysis. They are not the same process. It happens because two or more different metals make electrical contact with one another in seawater. In this electrochemical process, they have formed a battery and some current will flow between the metals. One of the metals in the couple behaves 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 orrodes on its own in seawater is not the issue. The problem is that when there is contact between dissimilar metals, the rates of corrosion will change. Corrosion of the anode will speed up and corrosion of the cathode will slow down or stop entirely. Fortunately, the use of a sacrificial zinc anode helps to take care of 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 prevent like steel tanks, rails and ship hulls from rusting. Because the zinc is more reactive than iron, it corrodes first. To greatly increase the life of their metal crab traps, crab fishermen have long practiced 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 dissolved 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 can be avoided 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 maintained regularly 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 in contact with 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. Additional factors 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 needs replacing 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 benefits whatsoever. There must be metal-to-metal contact to allow that electrons will flow. The metals can be either in direct physical contact or connected by a wire. This also means that there cannot be paint on 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 mass, attach it so it makes physical contact and make certain that there aren’t any coatings on either metal that will impede the electrical contact.