COOLING WATER CORROSION CONTROL

Corrosion, in the simplest terms, is nothing more than the return of refined metals, such as steel, copper or brass, back into their original states as found in nature. Corrosion is an electrochemical process in which a difference in electrical potential develops between two metals, or between different parts of a single metal. This difference in potential allows current to pass through the metal causing reactions to occur at both the Anodic and Cathodic sites. Anodic and Cathodic sites together form corrosion cell, and it acts exactly the same as a battery. The anode is the area of lower potential, while the cathode is the region of higher potential.

In a typical corrosion cell, an electrochemical reaction occurs. At the anode, the metal (iron in most cases) oxidizes from a metallic state to an oxide form. The corrosion product formed when iron corrodes is Ferric Oxide, or rust. At the cathode, the opposite reaction takes place, and electrons flow from one part of the cell to another.

Corrosion inhibitors commonly work by inhibiting either the cathodic or anodic reaction. All advanced corrosion inhibitors are blends that have materials that inhibit both the anodic and cathodic reactions.

Corrosion can take many forms in a cooling water system, but it can be divided into two general types of corrosion, according to how it attacks the metals in the systems.

GENERAL CORROSION or UNIFORM CORROSION is where large areas of a system are corroded relatively evenly. This is the least damaging type of corrosion, since it attacks the system at a slow rate and does not cause sudden failure leaving opportunities to control it.

PITTING CORROSION exists in various systems. Pitting corrosion happens when the corrosion is localized to a small area. Such as in hot areas of a system, at an interface between two different types of metal, or when a corrosion protection program is improperly administered. Pitting corrosion results in small, deep pits in a metal's surface, often very rapidly. Pitting corrosion can cause system failure very quickly and must be thoroughly addressed to properly protect the system.

Corrosion often proceeds at widely varying rates. In some systems, corrosion is a slow process, whereas in other systems it is rapid and deadly.

Listed below are number of factors affecting corrosion rates :

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