NACE Glossary of Corrosion Related

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NACE Glossary of Corrosion Related

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The following corrosion and materials terms have been selected from the
NACE Glossary of Corrosion Related Terms:'

Active (1) The negative direction of electrode potential. (2) A state of a metal
that is corroding without significant influence of reaction product.
Amphoteric A metal that is susceptible to corrosion in both acid and alkaline
Anion A negatively charged ion that migrates through the electrolyte.
Anode The electrode of an electrochemical cell at which oxidation occurs.
Electrons flow away from the anode in the external circuit. Corrosion usually
occurs and metal ions enter the solution at the anode.
Anodizing Oxide coating formed on a metal surface (generally aluminum)
by an electrolytic process.
Austenite The face-centered cubic structure of iron-based alloys.
Austenitic A steel in which the predominant structure at room temperature
is austenite.
Brittle fracture Fracture with little or no plastic deformation.
Casting (cast component) Metal obtained at or near its finished shape by
the solidification of molten metal in a mould.
Carbon steel Alloy of carbon and iron containing up to 1% carbon and up
to 1.65% manganese and residual quantities of other elements except those
intentionally added in specific quantities for deoxidation (usually silicon,
aluminum or both.)
Cast iron Iron-carbon alloy containing approximately 2 to 4 % carbon.
Cathode The electrode of an electrochemical cell at which reduction is the
principal reaction. Electrons flow toward the cathode in the external circuit.

Cathodic corrosion Corrosion resulting from a cathodic condition of a structure
that is usually caused by the reaction of an amphoteric metal with the
alkaline products of electrolysis.
Cathodic protection A technique to reduce the corrosion of a metal surface
by making that surface the cathode of an electrochemical cell.
Cation A positively charged ion that migrates through the electrolyte toward
the cathode under the influence of a potential gradient.
Cavitation The formation and rapid collapse of cavities or bubbles within a
liquid that often results in damage to a material at the solid-liquid interface
under conditions of severe turbulent flow.
Corrosion The deterioration of a material, usually a metal, that results from
a reaction with its environment.
Corrosion fatigue Fatigue-type cracking of metal caused by repeated or
fluctuating stresses in a corrosive environment characterized by shorter life
than would be encountered as a result of either the repeated or fluctuating
stress alone or the corrosive environment alone.
Corrosion inhibitor A chemical substance or combination of substances
that, when present in the environment, prevents or reduces corrosion.
Corrosion potential (Ecom) The potential of a corroding surface in an electrolyte
relative to a reference electrode under open-circuit conditions (also
known as rest potential, open-circuit potential, or freely corroding potential).
Corrosion rate The rate at which corrosion proceeds.
Corrosion resistance Ability of a material, usually a metal, to withstand
corrosion in a given system.
Corrosion-resistant alloy (CRA) Alloy intended to be resistant to general
and localized corrosion of oilfield environments that are corrosive to carbon
Corrosiveness The tendency of an environment to cause corrosion.
Creep Time-dependent strain occurring under stress.
Crevice corrosion Localized attack of a metal at or near an area that is
shielded from the bulk environment.
Dealloying The selective corrosion of one or more components of a solidsolution
alloy (also known as parting or selective dissolution).
Dezincification A corrosion phenomenon resulting in the selective removal
of zinc from copper-zinc alloys. (This phenomenon is one of the more common
forms of dealloying.)
Ductile (nodular) cast iron Cast iron that has been treated while molten with
an element (usually magnesium or cerium) that spheroidizes the graphite.

Electrochemical cell A system consisting of an anode and a cathode immersed
in an electrolyte so as to create an electrical circuit. The anode
and cathode may be different metals or dissimilar areas on the same metal
Electrolyte A chemical substance containing ions that migrate in an electric
Embrittlement Loss of a material's ductility resulting from a chemical or
physical change.
Environment The surroundings or conditions (physical, chemical, mechanical)
in which a material exists.
Environmental cracking Brittle fracture of a normally ductile material in
which the corrosive effect of the environment is a causative factor. Environmental
cracking is a general term that includes corrosion fatigue, hydrogen
embrittlement, hydrogen-induced cracking (stepwise cracking), hydrogen
stress cracking, liquid metal cracking, stress corrosion cracking, and sulfide
stress cracking.
Erosion The progressive loss of material from a solid surface due to mechanical
interaction between that surface and a fluid, a multicomponent fluid, or
solid particles carried with the fluid.
Erosion-corrosion A conjoint action involving corrosion and erosion in the
presence of a moving corrosive fluid or a material moving through the fluid,
leading to accelerated loss of material.
Femte Body-centered cubic crystalline phase of iron-based alloys.
Femtic steel Steel whose microstructure at room temperature consists predominantly
of ferrite.
Fretting corrosion Deterioration at the interface of two contacting surfaces
under load that is accelerated by their relative motion.
Galvanic corrosion Accelerated corrosion of a metal because of an electrical
contact with a more noble metal or nonmetallic conductor in a corrosive
Graphitic corrosion Deterioration of gray cast iron in which the metallic
constituents are selectively leached or converted to corrosion products, leaving
the graphite intact.
Graphitization The formation of graphite in iron or steel-usually from
decomposition of iron carbide at elevated temperatures. This term should
not be used as to describe graphitic corrosion.
Heat-affected zone (HAZ) That portion of the base metal that is not melted
during brazing, cutting, or welding but whose microstructure and properties
are altered by the heat of these processes.
Heat treatment Heating and cooling a solid metal or alloy in such a way as
to obtain desired properties. Heating for the sole purpose of hot working is
not considered heat treatment.
Hydrogen blistering The formation of subsurface planar cavities called hydrogen
blisters in a metal resulting from excessive internal hydrogen pressure.
Growth of near-surface blisters in low-strength metals usually results in
surface bulges.
Hydrogen embrittlement A loss of ductility of a metal resulting from absorption
of hydrogen.
Hydrogen-induced cracking (HIC) Stepwise internal cracks that connect
adjacent hydrogen blisters on different planes in the metal or to the metal
surface (also known as stepwise cracking).
Inhibition Retarding or slowing the rate of corrosion-usually by the addition
of other chemicals to the system.
Intergranular corrosion (IGC) Preferential corrosion at or near the grain
boundaries of a metal.
Low-alloy steel Steel with a total alloying element content of less than about
5%, but more than specified for carbon steel.
Metallizing The coating of a surface with a thin metal layer by spraying,
hot dipping, or vacuum deposition.
Oxidation (I) Loss of electrons by a constituent of a chemical reaction.
(2) Corrosion of a metal that is exposed to an oxidizing gas at elevated
Passivation A reduction in the anodic reaction rate of an electrode involved
in a corrosion process.
Passive (1) The positive direction of electrode potential. (2) A state of a metal
in which a surface reaction product causes a marked decrease in the corrosion
rate relative to that in the absence of the product.
pH The negative logarithm of the hydrogen ion activity written as pH
= -loglo(aH+), where aH+ = hydrogen ion activity = the molar concentration
of hydrogen ions multiplied by the mean ion-activity coefficient.
Pitting Localized corrosion of a metal surface confined to a small area and
that takes the form of cavities called pits.
Pitting factor The ratio of the depth of the deepest pit resulting from corrosion
divided by the average penetration as calculated from mass loss.
Riser (1) That section of pipeline extending from the ocean floor up to an
offshore platform. (2) The vertical tube in a steam generator convection bank
that circulates water and steam upward.
Rust Corrosion product consisting of various iron oxides and hydrated iron
oxides. (This term properly applies only to iron and ferrous alloys).
Sensitization Precipitation of constituents (usually carbides) in a structure
as a result of heating and cooling through a certain temperature range. Can
lead to intergranular corrosion.
Stress corrosion cracking (SCC) Cracking of metal involving anodic processes
of localized corrosion and tensile stress (residual, applied, or both).
Sulfidation The reaction of a metal or alloy with a sulfur-containing species
to produce a sulfur compound that forms on or beneath the surface of the
metal or alloy.
Sulfide stress cracking (SSC) Cracking of a metal under the combined action
of tensile stress and corrosion in the presence of water and hydrogen
sulfide (a form of hydrogen stress cracking).
Transpassive The noble region of potential where an electrode exhibits a
higher-than-passive current density.
Weld (verb) To join two or more pieces of metal by applying heat, pressure,
or both with or without filler metal to produce a union through localized
fusion of the substrates and solidification across the interfaces.
Weld decay Intergranular corrosion associated with sensitization due to
Weldment That portion of a component on which welding has been performed,
including the weld metal, the heat-affected zone (HAZ), and the base
Weld metal That portion of a weldment that has been molten during
Wrought metal Metal in the solid condition that is formed to a desired
shape by working (rolling, extruding, forging, etc.)-usually at an elevated
Yield strength Stress at which a material exhibits a specified deviation from
the proportionality of stress to strain.
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