AMPP Senior Corrosion Technologist key terms

The oxidation half-reaction in which a metal loses electrons and enters solution as ions, producing the corrosion current at the anode surface.

The reduction half-reaction that consumes the electrons released by metal dissolution, commonly reducing oxygen or hydrogen ions depending on the environment's pH and oxygen content.

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

A relatively positive corrosion potential that makes a metal less likely to dissolve and more likely to act as the cathode in a galvanic couple.

A relatively negative corrosion potential that makes a metal prone to dissolution and likely to behave as the anode when coupled to a nobler material.

A corrosion cell created when one area of metal sees lower dissolved oxygen than another, making the oxygen-starved region anodic and the oxygen-rich region cathodic.

Localized attack that develops in narrow gaps where solution stagnates, oxygen becomes depleted, and the shielded metal becomes anodic to the surrounding open surface.

Highly localized breakdown of a passive film that produces deep, narrow cavities, often initiated by chloride ions and difficult to detect because metal loss is small overall.

Formation of a thin, adherent oxide or similar film that greatly reduces corrosion rate by separating the metal from the environment, as with stainless steel in air.

Selective attack along grain boundaries, often caused by sensitization such as chromium carbide precipitation in austenitic stainless steel, which depletes chromium adjacent to the boundaries.

Microstructural change in which alloying elements such as chromium precipitate at grain boundaries during heating, leaving adjacent zones depleted and susceptible to intergranular attack.

Accelerated metal loss caused by the combined action of flowing or impinging fluid and corrosion, where the flow continually removes protective films or corrosion products.

A chemical added in small concentration to an environment to reduce corrosion rate, typically by adsorbing on the metal surface, forming a film, or altering the local chemistry.

A long-chain organic molecule with a polar head that adsorbs on metal and a hydrocarbon tail that repels water, forming a barrier film in closed-loop and wet systems.

A chemical such as sulfite or hydrazine dosed into water to remove dissolved oxygen, preventing oxygen-driven cathodic reactions and pitting in boilers and closed loops.

A chemical, often a phosphonate or polymer, that interferes with crystal nucleation or growth so mineral salts stay dispersed rather than depositing on equipment surfaces.

A chemical dosed to kill or control microorganisms in a water system, limiting microbiologically influenced corrosion and biofilm formation on surfaces.

Corrosion accelerated by the metabolic activity of microorganisms, often through production of corrosive species or creation of localized oxygen and pH differences under biofilms.

Localized corrosion beneath a buildup of scale, sediment, or debris, where the deposit shields the surface and creates a differential aeration cell.

The bond strength between a coating film and the substrate, which governs resistance to undercutting, blistering, and disbondment when the coating is damaged or exposed.

A small discontinuity, pinhole, or skip in a coating film that exposes the substrate and is typically located with high-voltage or low-voltage detection equipment.

Loss of coating adhesion around a defect caused by the alkaline environment and hydrogen generated when cathodic protection current flows to the exposed steel.

Cleaning and profiling of a substrate before coating application, typically by abrasive blast cleaning to a specified standard, to achieve the anchor pattern and cleanliness needed for adhesion.

The roughness pattern produced on a substrate by abrasive blasting, which provides mechanical keying for the coating and is measured in mils or micrometres.

The temperature at which air becomes saturated with moisture; coating application requires the substrate to remain a set margin above dew point to avoid condensation and poor adhesion.

Deterioration of the inner surface of pipe, tubing, or vessels caused by contact with transported or contained fluids, often concentrated at low spots, welds, and water-wet areas.

A weighed specimen of known metallurgy installed in a pipeline or vessel to be exposed to the process stream, then removed and assessed to determine corrosion rate and mechanism.

An instrument that measures loss of metal thickness through the increase in electrical resistance of an exposed element, allowing near-real-time corrosion rate monitoring.

Running a device through a pipeline to clean debris, remove liquids, or inspect the wall, and often to apply batch chemical treatments to the internal surface.

A cathodic protection method in which a metal with a more active potential, such as zinc or magnesium, is coupled to the protected structure and corrodes in its place.

A cathodic protection method that uses an external DC power source and inert anodes to drive protective current to the structure, allowing high current output and voltage adjustment.

The structure-to-electrolyte potential at which cathodic protection current is sufficient to suppress corrosion, typically a specified negative value measured against a reference electrode.

A stable half-cell, such as copper-copper sulfate or silver-silver chloride, used with a voltmeter to measure structure potential and assess cathodic protection effectiveness.

The voltage lost as current flows through the electrolyte and soil between the reference electrode and the structure, which must be accounted for when interpreting potential readings.

Metal loss caused by current from an outside source, such as a DC transit system or foreign cathodic protection system, discharging from a structure into the electrolyte.

A planned procedure for entering a space with limited access and hazardous atmosphere potential, requiring atmospheric testing, ventilation, attendant standby, and rescue provisions before entry.

A formal authorization required before welding, cutting, grinding, or other ignition-source activity, documenting fire watch, area preparation, and gas testing to control ignition hazards.

An energy isolation procedure in which hazardous energy sources are de-energized, locked, and tagged so equipment cannot be started or released while work is in progress.

A structured review that breaks a task into steps, identifies hazards at each step, and defines controls before work begins, often used to plan corrosion control and inspection activities.