Surface protection products and corrosion protection products are used to protect metal surfaces in marine, transportation, chemical processing, papermaking, and petroleum applications. Surface and corrosion protection products are applied to ships, water tanks, oil pipelines, buried vessels, and transmission line towers in order to prevent corrosion. Corrosion is the electrochemical degradation of metal due to reaction with the environment. It can result from gradual chemical action such as rusting or a rapid chemical action such as pickling. Corrosion can also be caused by a reduction in electrical efficiency between a metal and a contiguous substance. Electrolytic corrosion is caused by the disintegrating effects of strong electrical current or ground return currents in electrical systems.
Types of Corrosion Inhibitors
Surface protection products and corrosion protection products use two basic types of corrosion inhibitors: anode inhibitors and cathode inhibitors. During electrical discharge, an anode emits electrons and becomes an electron-deficient. By contrast, a cathode accepts electrons as part of the corrosion process. The half-reaction at the cathode is called reduction, and the cathodic metal is said to be reduced. Consequently, the cathodic metal is said to be reduced. Common results from reduction at the cathode include the production of hydrogen gas or pure metal from metal ions. Surface protection products and corrosion protection products that use anode inhibitors form a soluble compound with the newly-produced metal ion. Typically, the protected surface is connected to a more anodic metal with a wire. This concentrates corrosion at the more anodic metal, which is sometimes called the sacrificial anode. As sacrificial anodes corrode, the parent metal remains protected. Surface and corrosion protection products that use cathodic inhibitors produce hydrogen through a chemical reaction in an acidic solution. Both anode inhibitors and cathode inhibitors are added in small quantities to metals exposed to aqueous environments.
Some surface protection products and corrosion protection products may also use a process called cathodic rectification. Cathodic rectifiers apply an impressed current in the opposite direction to nullify the corrosion current. Consequently, a cathodic rectifier affects the corroding metals from anode to cathode. Cathodic rectifiers are used mainly in large structures (such as ships) for long-term operations (such as naval deployments). Other surface and corrosion protection products are also available.