AMPP CP4 Specialist 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 so that oxidation of the metal is suppressed.

A metal, such as zinc, aluminum, or magnesium, that is more active than the protected structure and corrodes preferentially to supply protective current. It requires no external power source and is consumed over time.

A cathodic protection arrangement in which an external DC power source forces current from an inert or semi-inert anode through the electrolyte to the protected structure, allowing high current output and adjustable control.

The structure-to-electrolyte potential at which corrosion is effectively arrested. Common criteria include -850 mV versus a copper-copper sulfate reference electrode with the current applied, or a 100 mV polarization shift.

A stable half-cell, such as copper-copper sulfate, silver-silver chloride, or a high-purity zinc electrode, used to measure structure-to-electrolyte potentials against a known and reproducible electrochemical standard.

The voltage lost as current flows through the electrolyte and any coating between the reference electrode and the structure surface, which can cause measured potentials to appear more protective than the true polarized potential.

The shift of a metal's potential away from its open-circuit value caused by net current flow at its surface. Cathodic polarization is the change that indicates protective current is actually reaching the metal.

The change in potential observed after protective current is interrupted, as the structure depolarizes. A decay of at least 100 mV is a widely used criterion confirming adequate cathodic protection.

A testing method that momentarily switches off all protective current sources so that potentials can be read without IR drop, revealing the true polarized potential of the structure.

The natural, unpolarized potential a metal exhibits in an electrolyte when no protective current is applied, serving as the baseline against which polarization and protection criteria are judged.

The difference between the open-circuit potential of a galvanic anode and the protection potential of the structure. It determines the current a galvanic anode can deliver through a given circuit resistance.

The total opposition to current flow in a cathodic protection circuit, including anode-to-electrolyte resistance, structure-to-electrolyte resistance, cable resistance, and any backfill or coating effects.

The resistance between an anode and the surrounding electrolyte, dominated by the anode's size, shape, and electrolyte resistivity. It is often the largest single term in a galvanic circuit.

A measure of how strongly a soil or water resists the passage of electric current, usually expressed in ohm-centimeters or ohm-meters. Low resistivity means easier current flow and more effective protection.

Field testing, commonly using the Wenner four-pin method, that maps resistivity variations with depth and location to guide anode placement, estimate current requirements, and predict corrosion risk.

The total protective current needed to polarize a structure to its protection criterion, estimated from bare surface area, coating condition, environment aggressiveness, and historical operating data.

Protective current per unit of exposed metal surface area, typically expressed in milliamperes per square foot or per square meter. It is a key input for sizing both galvanic and impressed current systems.

The fraction of a structure's surface effectively shielded from electrolyte by its coating. It is used to estimate the bare area that must be protected when calculating current demand.

A small defect, pinhole, or discontinuation in a protective coating where bare metal is exposed to the electrolyte and where corrosion and cathodic protection current concentrate.

The arrangement of impressed current anodes and surrounding backfill installed in the earth or water to distribute protective current. Its design controls resistance, current distribution, and anode life.

A conductive carbonaceous or gypsum-bentonite material packed around an anode to lower anode resistance, improve current distribution, retain moisture, and extend anode life by controlling consumption.

A device that converts AC power to the adjustable DC output used by an impressed current system, allowing current and voltage to be set and monitored for changing protection needs.

The rate at which an anode material is lost per unit of current output over time, expressed as mass per ampere-year. It determines anode life and replacement intervals.

The fraction of an anode's theoretical electrochemical output actually delivered as useful protective current rather than lost to self-consumption or unwanted reactions.

The reduction of protective current and potential along a structure, such as a pipeline or well casing, caused by the electrical resistance of the metal and the current leaking to the electrolyte.

A plot of structure-to-electrolyte potential versus distance along a structure, used to identify areas of inadequate protection, locate anodes, and evaluate attenuation and coating quality.

The ability of a coating to allow current to leak from the structure to the electrolyte, expressed per unit area. Higher conductance increases attenuation and current demand along a structure.

Current flowing through the electrolyte along paths other than the intended cathodic protection circuit, often from foreign sources, which can cause accelerated corrosion where it discharges from a structure.

Metal loss that occurs at locations where stray current leaves a structure to return to its source, causing anodic dissolution that cathodic protection must be designed or bonded to control.

A deliberate electrical connection between structures or between a structure and a grounding system, used to drain stray current, equalize potentials, or share cathodic protection current.

A high-resistance barrier coating applied to a structure to isolate it electrically from the electrolyte, reducing current demand and improving current distribution while limiting galvanic corrosion.

A field access point, typically with a test lead connected to the structure and a reference electrode, used to measure potentials and verify that protection criteria are met along a structure.

The loss of coating adhesion around a defect caused by the alkaline environment and hydrogen generated at a cathodically protected surface, which can enlarge holidays and raise current demand.

Applying more cathodic protection current than needed, which wastes energy, accelerates coating disbondment, and can cause hydrogen embrittlement or dangerous gas generation on some structures.

The stable, unpolarized potential a structure exhibits in its environment before any cathodic protection current is applied, often recorded as a baseline for later comparison.

A design application in which anodes or an impressed current system protect the external surface of a well casing, where current distribution and attenuation along the deep casing must be evaluated.

A design application protecting the soil side of an aboveground storage tank bottom, often using shallow or deep anodes, closely spaced anodes, or a liner to control current distribution.

The expected service duration of a galvanic anode, calculated from its mass, consumption rate, efficiency, and average current output, and used to plan replacement schedules.