calcareous coating—a layer consisting of calcium carbonate and other salts deposited on the surface.When the surface is cathodically polarized as in cathodic protection, this layer is the result of the increased pH adjacent to the protected surface.
calcareous deposit—see calcareous coating.
carbon steel—alloy of carbon and iron containing up to 2 mass percent carbon and up to 1.65 mass percent manganese and residual quantities of other elements, except those intentionally added in specific quantities for deoxidation (usually silicon and/or aluminum).
carburizing—the absorption and diffusion of carbon in iron or an iron-based alloy in contact with a suitable carbonaceous environment at elevated temperature.
case hardening—hardening a ferrous alloy so that the outer portion, or case, is made substantially harder than the inner portion, or core. Typical processes are carburizing, cyaniding, carbonitriding, nitriding, induction hardening, and flame hardening.
case in paint—water-thinned paint with vehicle derived from milk.
casting—(1) a component formed at or near its finished shape by the solidification of liquid material in a mold; (2) the creation of such a component.
catalyst—a chemical substance, usually present in small amounts relative to the reactants, that increases the rate at which a chemical reaction (e.g., curing) would otherwise occur, but is not consumed in the reaction.
cathode—the electrode of an electro-chemical cell at which reduction is the principal reaction.(Electrons flow toward the cathode in the external circuit.)
cathodic corrosion—corrosion of a metal when it is a cathode, usually caused by the reaction of anamphoteric metal with the alkaline products of electrolysis.
cathodic disbondment—the destruction of adhesion between a coating and the coated surface caused byproducts of a cathodic reaction.
cathodic inhibitor—a corrosion inhibitor whose primary action is to reduce the rate of the cathodic reaction, producing a negative shift in corrosion potential.
cathodic polarization—(1) the change of electrode potential caused by a cathodic current flowing across the electrode/electrolyte interface. (2) a forced active(negative) shift in electrode potential. [See polarization.]
cathodic protection—a technique to reduce the corrosion rate of a metal surface by making that surface the cathode of an electro-chemical cell.
catholyte—the electrolyte adjacent to the cathode of an electro-chemical cell.
cation—a positively charged ion.
caustic cracking—cracking of a metal or alloy under the combined action of tensile stress and corrosion in the presence of a strongly basic solution (e.g., sodium hydroxide, potassium hydroxide).
caustic embrittlement—an obsolete term referring to caustic cracking.
cavitation—the formation and rapid collapse of cavities or bubbles of vapor or gas within a liquid resulting from mechanical or hydrodynamic forces.
cavitation-corrosion—the conjoint action of cavitation and corrosion.
cavitation damage—the degradation of a solid body resulting from its exposure to cavitation. (This may include loss of material, surface deformation, or changes in properties or appearance.)
cavitation-erosion—the conjoint action of cavitation and erosion.
cell—see electro-chemical cell.
cementation—the introduction of one or more elements into the surface layer of a metal or alloy by diffusion at high temperature. (Examples of cementation include carburizing [introduction of carbon], nitriding [introduction of nitrogen], and chromizing [introduction of chromium].)
cementite—iron carbide(Fe3C) when referred to as a microstructural constituent of steel.
chalking—the development of loose, removable powder (pigment) at the surface of an organic coating, usually caused by weathering.
checking—the development of slight breaks in a coating that do not penetrate to the underlying surface.
chemical conversion coating—an adherent, reaction-product layer on a metal surface formed in situ by reaction with a suitable chemical, used for protective,decorative, or functional purposes. (It is often used to provide greater corrosion resistance or prepare the surface prior to the application of an organic coating.)
chevron pattern—a V-shaped pattern on a fatigue or brittle-fracture surface. The pattern can also be one of straight radial lines on cylindrical specimens.
chipping—(1) removing coating and surface contaminants from a substrate in small pieces by cutting, striking, or applying mechanical force; (2) a failure mechanism in which small pieces orfragments of a material or coating are removed by mechanical damage, loss of adhesion, or both. [contrast with peeling]
chloridestress corrosion cracking—cracking of a metal under the combined action of tensile stress and corrosion in the presence of an electrolyte containing dissolved chlorides.
cleavage fracture—fracture that occurs along planes determined by the crystal structure of the material.(It is typically associated with a brittle fracture.)
coat—one layer of a coating system applied to a surface in a single continuous application to forma uniform film when dry.
coating—(1) a liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film. (2) (in a more general sense) a thin layer of solid material on a surface that provides improved protective, decorative, or functional properties.
coating system—the complete number and types of coats applied to a substrate in a predetermined order. (When used in a broader sense, surface preparation, pretreatments, dry film thickness, and manner of application are included.)
cold cracking—cracking of a weld during or after cooling to ambient temperature, sometimes after a considerable time delay. (It usually occurs at temperatures less than 205 °C[400 °F] for metals, and less than the glass transition temperature for plastics.)
cold lap—a linear discontinuity with rounded edges at exposed surfaces that is caused by solidification of the meniscus of a partially cast metal or alloy (e.g., an anode used for cathodic protection) as a result of interrupted flow of the casting stream or the joining of two casting streams at too low a temperature.
cold shut—horizontal surface discontinuity caused by solidification of a portion of a meniscus during the progressive filling of a mold, which is later covered with more solidifying metal as the molten metal level rises. Cold shuts generally occur at corners remote from the point of pour.
cold working—deforming metal plastically under conditions of temperature and strain rate that induce strain hardening, usually, but not necessarily, performed at room temperature [contrast with hot working]
commercial blast cleaned surface—an abrasive blast cleaned steel surface that is free of all visible contaminants and foreign matter but may have some random staining on no more than 33 percent of the surface area. [See NACE No.3/SSPC-SP 6 for detailed specification.]
compressive strength—the maximum compressive stress a material is capable of withstanding without sustaining permanent deformation.
concentration cell—an electro-chemical cell, the electromotive force of which is caused by a difference in concentration of some component in the electrolyte. (This difference leads to the formation of discrete cathodic and anodic regions.)
concentration polarization—that portion of polarization of an electro-chemical cell produced by concentration changes resulting from current flowing through the electrolyte.
conductive coating—(1) a coating that conducts electricity. (2) an electrically conductive,mastic-like material used as an impressed current anode on reinforced concrete surfaces.
conductive concrete—a highly conductive cement-based mixture containing coarse and fine coke and other material used as an impressed current anode on reinforced concrete surfaces.
conductivity—(1) a measure of the ability of a material to conduct an electric charge. (2)the current transferred across a material (e.g., coating) per unit area per unit potential gradient. (Conductivity is the reciprocal of resistivity.)
contact corrosion—see galvanic corrosion.
continuity bond—a connection, usually metallic, that provides electrical continuity between structures that can conduct electricity.
continuous anode—a single anode with no electrical discontinuities.
conversion coating—see chemical conversion coating.
copper sulfate test— (1) a test method in which a solution of copper sulfate, and possibly other ingredients, in water is swabbed onto the surface of certain metals to determine the presence of metals more active(anodic) than copper. (2) a spot test method in which a 5 to 10 percent solution of copper sulfate in water is swabbed onto a steel surface to determine whether mill scale is present. (The appearance of copper indicates that mill scale is not present.)
corrosion—the deterioration of a material, usually a metal, that results from a chemical or electro-chemical reaction with its environment.
corrosion-inhibitive pigment—a pigment that, when formulated into a liquid coating material, has the property of reducing corrosion of the metal substrate to which the coating is applied.
corrosion fatigue—the process wherein a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required to cause fatigue of that metal in the absence of the corrosive environment.
corrosion fatigue strength—the maximum repeated stress that can be endured by a metal without fracture under definite conditions of corrosion and cyclic loading fora specific number of stress cycles and a specified period of time.
corrosion inhibitor—a chemical substance or combination of substances that, when present in the proper concentration and forms in the environment, reduces the corrosion rate.
corrosion potential—(represented by the symbol Ecorr) the potential of a corroding surface in an electrolyte measured under open-circuit conditions relative to a reference electrode. [also known as electro-chemical corrosion potential, free corrosion potential, open-circuit potential ]
corrosion rate—the time rate of change of corrosion. (It is typically expressed as mass loss per unit area per unit time, penetration per unit time, etc.)
corrosion resistance—ability of a material, usually a metal, to withstand corrosion in a given environment.
corrosiveness—the tendency of an environment to cause corrosion.
counter electrode—the electrode in an electro-chemical cell that is used to transfer current to or from a working electrode.
counter poise—a conductor or system of conductors arranged beneath a power line, located on, above, or most frequently, below the surface of the earth and connected to the footings of the towers or poles supporting the power line.
couple—see galvanic couple.
coupon—a portion of a material or sample, usually flat, but occasionally curved or cylindrical, from which one or more specimens can be taken for testing.
crack—(1) a partial split or break. (2) a split or break in a coating that penetrates to the substrate.
cracking—fracture of a material along a path that produces a linear discontinuity (without complete separation).
crater—(1) a metal surface anomaly consisting of a bowl-shaped cavity with the minimum dimension at the opening greater than the depth. [contrast with pit] (2) a small, rounded dish or bowl-like depression in a wet-applied coating. [contrast with fish eye]
crazing—a network of checks or cracks appearing on the surface of a coating.
creep—time-dependent strain occurring under stress.
creep strength—that stress which, when applied to a material at a specific temperature, will cause a specified amount of elongation in a specified time.
crevice corrosion—localized corrosion of a metal or alloy surface at, or immediately adjacent to, an area that is shielded from full exposure to the environment because of close proximity of the metal or alloy to the surface of another material or an adjacent surface of the same metal or alloy.
critical anodic current density—the maximum anodic current density observed in the active region for a metal or alloy electrode that exhibits active-passive behavior in an environment.
critica lhumidity—the relative humidity above which the atmospheric corrosion rate of a specific metal or alloy increases sharply.
critical pitting potential—(represented by the symbol Ep or Epp)the least noble potential at which pitting corrosion will initiate and propagate in a specific environment. [See breakdown potential.]
curing—chemical process of developing the intended properties of a coating or other material(e.g., resin) over a period of time.
curing agent—a chemical substance used for curing a coating or other material (e.g., resin).[also referred to as hardener]
curing time—the minimum period between application and the time at which the applied material attains its intended physical properties.
current—(1) a flow of electric charge. (2) the amount of electric charge flowing past a specified circuit point per unit time, measured in the direction of net transport of positive charges. (In a metallic conductor, this is the opposite direction of the electron flow.)
current density—the electric current flowing to or from a unit area of an electrode surface.
current efficiency—the ratio of the electro-chemical equivalent current density for a specific reaction to the total applied current density.