AMPP Corrosion Technologist key terms

A technique that reduces corrosion of a metal surface by making it the cathode of an electrochemical cell, typically by supplying electrons from an external source or a sacrificial metal.

A metal, such as zinc, aluminum, or magnesium, that corrodes preferentially to protect a more noble structure because it has a more negative electrochemical potential.

A cathodic protection method in which an external DC power source drives current through an inert anode into the electrolyte to protect a buried or submerged structure.

A stable half-cell, such as copper/copper sulfate or silver/silver chloride, used to measure the potential of a structure relative to a known standard.

The voltage difference measured between a buried or submerged metal structure and a reference electrode placed in contact with the surrounding electrolyte.

The minimum negative potential, measured against a specified reference electrode, at which a metal is considered adequately protected from corrosion.

A condition in which excessive cathodic protection current produces high pH at the metal surface, risking coating disbondment or hydrogen embrittlement on susceptible steels.

An arrangement of anodes installed in soil or water to discharge protective current into the electrolyte for an impressed current cathodic protection system.

The amount of protective or corrosion current per unit area of metal surface, usually expressed in milliamperes or amperes per square meter.

Current flowing through paths other than the intended circuit, often from DC transit systems or welding equipment, which can cause accelerated corrosion where it leaves a structure.

Metal loss caused when stray current discharges from a metallic structure into the electrolyte, acting as an unintended anode.

A potential survey in which structure-to-electrolyte readings are taken at closely spaced intervals along a pipeline to detect areas of inadequate cathodic protection.

A ranking of metals and alloys by their corrosion potential in a specific electrolyte, used to predict which metal will act as anode when two are coupled.

Accelerated corrosion of one metal in a couple between dissimilar metals in an electrolyte, where the less noble metal becomes the anode and dissolves.

A metal with a relatively positive electrochemical potential that tends to resist corrosion and acts as the cathode when coupled with a less noble metal.

A condition in which a metal forms a thin, stable surface oxide film that greatly reduces further corrosion, as seen with stainless steels and aluminum.

Localized corrosion that produces small, deep cavities in a metal surface, often penetrating rapidly while most of the surface remains unaffected.

Localized attack occurring in narrow gaps or shielded areas where stagnant electrolyte becomes depleted of oxygen, creating an oxygen concentration cell.

Cracking of a susceptible alloy, commonly austenitic stainless steel, caused by the combined action of tensile stress and chloride-containing environment.

Loss of ductility and cracking of a metal caused by absorption of atomic hydrogen, often associated with high-strength steels or excessive cathodic protection.

An electrochemical cell created by differences in electrolyte composition or oxygen content across a metal surface, driving localized corrosion.

A type of concentration cell in which areas shielded from oxygen become anodic and corrode relative to oxygen-rich areas of the same metal.

A barrier layer applied to a metal surface to isolate it from the environment and reduce corrosion, often the primary defense supplemented by cathodic protection.

Cleaning and profiling of a substrate before coating application to remove contaminants and create the anchor pattern needed for adhesion.

The roughness pattern produced on a metal surface by abrasive blasting, which improves mechanical adhesion of the applied coating.

A small discontinuity, pinhole, or skip in a protective coating that exposes the underlying metal and can be located with a high-voltage or low-voltage detector.

Loss of adhesion between a coating and the substrate, allowing electrolyte to spread beneath the film and corrosion to initiate.

Coating adhesion loss that spreads from a deliberate defect when cathodic protection current generates alkaline conditions at the exposed metal surface.

Deterioration of the inside surfaces of pipes, tanks, or vessels caused by contact with the contained fluid or gas.

A chemical added in small concentrations to a process stream to slow corrosion by forming a protective film, altering the environment, or blocking anodic or cathodic reactions.

A chemical, such as sodium sulfite or hydrazine, that removes dissolved oxygen from water to prevent oxygen-driven corrosion in boilers and closed systems.

A chemical agent used to control or kill microorganisms in water systems, thereby limiting microbiologically influenced corrosion and biofilm formation.

Corrosion accelerated by the metabolic activity of microorganisms, often producing localized pitting and sulfide deposits in pipelines and tanks.

A small, pre-weighed specimen of metal installed in a process system to measure corrosion rate by weight loss over a known exposure period.

The speed at which a metal deteriorates, commonly reported as mass loss per unit area per time or as penetration depth per year.

Application of cathodic protection to the wetted interior surfaces of tanks, vessels, or pipelines, typically using anodes immersed in the contained electrolyte.

The fraction of a sacrificial anode's theoretical current capacity that is actually delivered, reduced by self-corrosion and reaction byproducts.