Corrosion Glossary

A         

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  • Abradable Coating  -  It gives wear resistance to highly abrasive material when rubbed against, while leaving the underlying material damage free.
  • Acid  -  A substance that increases the concentration of hydrogen ions (\(H^+\)) in a solution.  Acids are characterized by their sour taste, ability to turn blue litmus paper red, and reaction with bases to form salts and water.
  • Acid Embrittlement  -  A form of hydrogen embrittlement that may be introduced in some metals by acid.
  • Acid Rain  -  Atmospheric precipitation with a pH below 3.6 to 5.7.
  • Acrylic  -  Resin polymerized from acrylic acid, methacrylic acid, eaters of these acids, or acrylonitrite.
  • Alternating Current  -  An electric current that reverses its direction over and over.
  • Annealing  -  A heating and controlled cooling operation to impart specific desirable properties generally concerned with subsequent fabrication of the alloy.
  • Anion  -  A negatively charged ion.
  • Anode  -  The electrons flow away the anode (negative charge) at which corrosion or oxidation occures at the material.
  • Artificial Aging  -  Aging above room temperature.
  • Atmospheric Corrosion  -  A gradual degradation of alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapor, sulfur and chlorine compounds.

B         

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  • Barrier Coating  -  A protective layer of material that prevents the contact of corrosive elements.
  • Base  -  A substance that releases hydroxyl ions when disolved in water.
  • Beach Marks  -  Microscopic progression marks on a figure fracture or stress-corrosion cracking surface that indicate sucessive positions of the advancing crack front.
  • Black Oxide  -  A black finish on a metal produced by immersing it to hot oxidizing salts or salt solutions.
  • Brackish Water  -  Water having salinity values ranging from approximately 500 to 5,000 parts per million.
  • Brine  -  Seawater containing a high concentration of dissolved salt than that of the ordinary ocean.
  • Brittle Fracture  -  Separation of a solid accompanied by little or no microscopic plastic deformation.
  • Buffer  -  A chemical substance which stabilizes pH values in solutions.
  • Buffer Capacity  -  A measure of the capacity of a solution or liquid to neutralize acids or bases.

C         

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  • Camera Pig  -  A configuration pig with a camera and light source recording the inside of the pipeline.
  • Carburization  -  Occurs when carbon bonds with chromium.  This happens often at grain boundaries, causing corrosion to make metal surfaces more brittle.  It also reduces metal’s resistance to oxidation, paving the way for further corrosion.
  • Cathode  -  The electrons flow toward the cathode reducing the corrosion or oxidation of the material.
  • Cathodic Polarisation  -  The electrochemical state changing of an electrode's potential moving in a non-corroding negative direction.
  • Cleaning Pig  -  A utility pig with brushes, cups, and scrapers for cleaning foreign matter from the inside of the pipeline.
  • Corrosion  -  The thinning of a pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
  • Corrosion Allowance  -  The amount of material in a pipe or vessel that is available for corrosion without affecting the pressure containing integrity.
  • Corrosion Coupon  -  Used to monitor the corrosion rate of a material in a process.
  • Corrosion Embrittlement  -  Embrittlement in certain alloys caused by exposure to a corrosive environment.
  • Corrosion Fatigue  -  Combined action of corrosion and fatigue in which local corroded areas act as stress concentrators, causing failure at the point of stress concentration and exposing new metal surfaces to corrosion.
  • Corrosion Inhibitor  -  A substance that slows down the chemical reaction rate of corrosion on metal that is exposed to the environment.  To minimise corrosion, it is very important for heat transfer fluid to be formulated with effective and proven inhibitors.  Specifically, the inhibitor formulation should take into consideration the metals of construction, antifreeze type, susceptibility to air ingress and subsequent bacterial contamination, make-up water quality and effectiveness of pre-commission pipework flushing and conditioning (passivation).
  • Corrosion Mapping  -  An ultrasonic method that identifies and maps corroded areas in a pipelineby yhe varying material thickness.
  • Corrosion Resistance  -  The ability of a material to resist chemical destruction from an environment.
  • Corrosion Types -  A broad term that encompasses various types of deterioration and degradation processes that materials undergo due to chemical or electrochemical reactions with their environment.  Corrosion is nature's wasteful way of returning metals to their ores.  When it loses possession of them by any means whatever, it has experienced corrosion.
  • Crack  -  Cracks can come from fatigue, grith welds, or seam welds.
  • Cracking  -  Surface loss of color and gloss in a coating from degradation of the binder by the UV components in sunlight.  Can be seen as a white deposit on the cured coating surface.
  • Crevice Erosion  -  A type of concentration-cell corrosion; corrosion of a metal that is caused by the concentration of dissolved salts, metal ions, oxygen, or other gases, and such, in crevices or pockets remote from the principal fluid stream, resulting in the build-up of differential cells that ultimately cause deep pitting.
  • Current  -  The rate of flow of electricity in a circuit, measured in amperes.

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  • Decarburization  -  The loss of carbon from the surface of an iron-base alloy as the result of heating in an environment that removes the carbon.  In medium or high carbon steels, decarburization leads to a pronounced lowering of the fatigue limit.
  • Deactivation  -  The process of prior removal of the active corrosive constituents, usually oxygen, from a corrosive liquid by controlled corrosion of expendable metal or by other chemical means.
  • Defective Weld  -  A weld having one or more defects.
  • Dendrite  -  A crystal that has a tree-like branching pattern.  It is most evident in cast metals that are slowly cooled through the solidification range.
  • Diffusion  -  The spread of gases, liquids, or solids from areas of high concentration to areas of low concentration.
  • Diluent  -  A liquid used in coatings to reduce the consistency and make coating flow more easily.
  • Direct Current  -  An electric current that flows in only one direction.
  • Dry Corrosion  -  See gaseous corrosion or hot corrosion.
  • Dye Penetrant Inspection  -  Nondestructive test employing dye or fluorescent chemical and sometimes black light to detect surface defects.
  • Ductility  -  The ability of a material to deform plastically without fracturing, being measured by elongation or reduction of area in a tensile test, by height of cupping in an Erichsen test or by other means.

E        

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  • Elastic Modulus  -  The ratio of the stress applied to a body or substance to the resulting strain within the elastic limits.
  • Electrochemical Corrosion  -  Localized corrosion that results from exposure of an assembly of dissimilar metals in contact with or coupled with one another.
  • Electrode  -  Refered to as the anode or cathode, whichever is approperate.
  • Electrode Potential  -  The potential of an electrode in an electrolyte as a measure against a reference electrode.
  • Electrolyte  -  A chemical substance or mixture, liquid or solid, normally liquid, which conducts electric current.
  • Erosion Corrosion  -  Is where metal and synthetic components are worn down over time, due to one or more of the following causes:  High levels of entrained sediment in the heat transfer fluid, acting as an abrasive inside pumps and bends.  Cavitation is most often observed inside centrifugal pumps.  For example, worn impellers and volutes, but can also be found where there are severe changes in heat transfer fluid direction, or poorly designed pipework etc.
  • Exfoliation  -  A type of corrosion that progresses approximately parallel to the outer surface of the metal, causing layers of the metal to be elevated by the formation of corrosion product.
  • External Corrosion  -  When the outside of a pipe is decayed or eroded by chemical or electrochemical processes or any other environmental conditions.

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  • Faraday's Law of Induction  -  States that whenever a conductor is placed in a varying magnetic field, an electromotive force is introduced.
  • Flux  -  Chemicals used to protect metals from oxidation.
  • Free Corrosion Potential  -  Corrosion potential in the absence of net electric current flowing to or from the metal surface.
  • Fretting Corrosion  -  Takes place where there is friction between two metal surfaces.

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  • Galvanic Corrosion  -  Corrosive action occuring when two dissimilar metals are in contact and are joined by a solution capable of conducting an electric current, a condition which causes a flow of electric current and corrosion of the more anodic of the two metals.  An electric potential difference is generated between the metals and the less noble metal acts as an anode and dissolves, while the more precious metal acts as the cathode.
  • Gaseous Corrosion (Dry Corrosion or Hot Corrosion)  -  Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal.
  • Grinding Cracks  -  Shallow cracks formed in the surface of relatively hard materials because of excessive grinding heat or the high sensitivity of the material.
  • Gouging  -  Mechanical removel of metal from the surface of the pipe.

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  • Halogen  -  Halogen corrosion is when metals react with halogen gas at high temperatures. It can cause volatile metal halides to form on the metal surface.  This can create serious problems for many metals, although stainless steel is especially susceptible to this form of corrosion.
  • Hardness  -  The property of a material that enables it to resist plastic deformation, usually by penetration.
  • Heat Transfer  - The exertion of power that is created by heat, or the increase in temperature.
  • Holiday  -  A discontinuity in painted or coated surfaces.
  • Hot Corrosion  -  See dry corrosion or gaseous corrosion.
  • Huey Test  -  A corrosion test for stainless steels.  The weight loss per unit area is measured after each 48-hour boils in 65% nitric acid.  The test results are calculated to and reported as the average corrosion rate of the five oils in inches per month (ipm) corrosion rates.  The test is used to determine the suitability of a material for nitric acid service.  Since most of the weight loss is due to intergranular attack, the Huey test can be used as an indication of the resistance of a stainless steel to intergranular corrosion.

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  • Incomplete Fusion  -  A weld break where complete fusion did not occur between the weld material and the faces or adjoining weld material.
  • Incomplete Weld  -  A defect in the solder joint that causes cracks or damage to the bond.
  • In-line Inspection  -  When the pipeline is inspected by examining the interior of the pipe.
  • Inhibitor  -  Can reduce the corrosion rate by presenting a protective film.
  • Instrumented Pig  -  A tool with instruments like recorders and sensors to examine the inside of the pipe.
  • Integranular Corrosion  -  Usally of stainless steals or certain nickle-base alloys, that occures as the result of sensitization in the heat affected zone during the welding process.
  • Internal Corrosion  -  The thinning of the interior pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
  • Ion  -  An atom or molecular particle having a net charge.  Positive charged ions are cations and negative charged are anions.
  • Isolation Gasket  -  Used to stop the current flow across metallic pipelines by separating two flanges.

J

K   

L

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  • Lacquer  -  A fast drying, usually clear coating, that is highly flammable and dries by solvent evaporation only.
  • Lamellar Corrosion  -  A form of corrosion in which the expanding corrosion products stack up as layers.
  • Lenz's Law  -  The direction of the current induced in a conductor by changing magnetic field.

M         

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  • Magnetic Flux  -  The number of magnetic field lines passing through a given closed surface.
  • Mapping Pig  -  A configuration pig used to produce an elevation and plan view of the pipeline route with collect data that can be analysed from the inertia sensing or some other technology.
  • Material Hardness  -  The property of a material that enables it to resist plastic deformation, usually by penetration.
  • Mechanical Properties  -  Those properties that reveal the reaction, elastic or plastic, of a material to an applied stress, or that involved the relationship between stress and strain.
  • Molten Metal  -  When liquid metals are used for heat transferring, the contaminant material can come into contact with molten metal and can cause corrosion.  The only real way to prevent this corrosion is an in-depth knowledge of how molten metals react with certain materials in the containment system.
  • Molten Salt  -  Molten salts are often used in heat treatment plants, nuclear energy plants, and sometimes in concentrated solar power plants. When a metal comes in contact with molten salt at high temperatures, it can quickly create corrosion.  Molten salts remove the oxide scale from metal surfaces causing the metal to thin, pit, or experience an intergranular attack.

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  • Natural Gas  -  Gaseous fuel occuring in nature.
  • Neutralizer  -  A common designation for alkaline materials such as calcite or magnesia used in the neutralization of acid waters.
  • Nitridation  -  Metals that are exposed to ammonia or nitrogen filled environments at high temperatures are at increased risk of nitridation.  It caused a hard, brittle metal to form. This corrosion can be prevented by the addition of nickel as an alloyed element in the metal.

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  • Ohm  -  A unit of resistance.
  • Ohm's Law  -  The relationships between power, voltage, current, and resistance.
  • Oxidation  -  The loss of electrons in a chemical reaction in which an element combines with oxygen.  Oxidation and reduction always occur at the same time in equal amounts.
  • Oxidation Corrosion  -  When caused by air and/or dissolved oxygen, will tend to dissolve metals evenly across their surface, and most often affects metals which do not form passive protective layers or are naturally resistant to oxidation corrosion.

P

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  • pH  -  Affects the corrosion rate by affecting the reaction rate of cathodes and anodes.
  • Physical Properties  -  Those properties familiarly discussed in physics, for example, density, electrical conductivity, and thermal expansion coefficient, exclusive of those described under mechanical properties.
  • Pitting  -  A non-uniform corrosion of a metal, not in the form of cracks, whereby a number of cavities, are formed in the surface.
  • Pitting and Crevice Corrosion  -  Is typical in installations where metals protected by a passive coating, such as galvanised or some stainless-steel pipes.  An increased local corrosion rate can occur where there is a flaw in the passive coating, when the potential difference is concentrated.
  • Porosity  -  Happens when a contaminent or gas is absorbed into the weld puddle.

Q

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  • Rupture  -  There are numerous reasons a rupture can happen, depending on the material: age, brittleness, corrosion, internal pressure, movement, etc.
  • Rust  -  A corrosion product consisting primarily of hydrated iron oxide.

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  • Sacrificial Coating  -  A coating that provides corrosion protection wherein the coating material corrodes in preference to the substrate.
  • Salt Fog Test  -  See salt spray test
  • Salt Spray Test   -  An accelerated corrosion test in which the metal specimens are exposed to a fine mist of salt water solution.
  • Saltine Water  -  Water containing an excessive amount of dissolved salts.
  • Silicone  -  A resin used in the binders of coatings.
  • Shear Stress  - Tends to deform the material by breaking rather than stretching without changing the volume by restraining the object.
  • Shinning  -  The formation of a thin, tough film on the surface of a liquid point.
  • Shrinkage  - A decrease in dimensions of a coating during process.
  • Shrinkage Stress  -  The residual stress in a coating caused by shrinkage during processing.
  • Smart Pig  -  Collects information internally about the pipeline with electronic components.
  • Solute  -  A substance which is disolved in and by a solvent.
  • Specific Gravity  -  The density or ratio of any substance to another substance.
  • Gravity  -  The density or ratio of any substance to another substance.
  • Stabilizing Anneal  -  A treatment applied to austenitic stainless steels wherein carbides of various forms are deliberately precipitated.  Sufficient additional time is provided at the elevated temperature to diffuse chromium into areas adjacent to the carbides (usually grin boundaries).  This treatment is intended to lessen the change of intergranular corrosion.
  • Strain  -  The deformation, stretched or compressed, of a material compared to its original length.
  • Strain Rate  -  The time rate of straining for the usual tensial test.
  • Stray Current  -  The flow of electric current into the ground by the leakage on industrial currents.
  • Stress  -  The force per unit area of cross-section.
  • Stress Corrosion Cracking   -  The combined effect of tensile stress and a corrosive environment.  Failure by cracking under combined action or corrosion and stress, either external (applied) or internal (residual).  Cracking may be either intergranular or transgranular depending on metal and corrosive medium.
  • Sulfidation  -  Sulfidation is caused by the presence of sulfur.  Sulfur is often present in impure crude oil, putting pipelines at increased risk.  Sulfidation causes thinning of the pipeline walls and can even lead to breaches in the pipeline, causing spills, leaks, and further ruptures.
  • Surge Pressure  -  See Water Hammer
  • Sweet Corrosion: Carbon Dioxide  -  A weak acidic gas found in condensate, crude oil, natural gas, and produced water and becomes corrosive when dissolved in water.

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  • Tensile Strength  -  The maximum stress a material can resist before it starts to elongate.
  • Tension  -  The force (pulling or stretching) acting on a material.
  • Toughness  -  The ability of a material to absorb considerable energy without fracturing.

U        

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  • Ultrasonic Testing  -  Used to measure the pipe wall thickness perpendicular to the pipe.
  • Utility Pig  -  Used to performing pipeline cleaning of debris and unwanted materials.

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  • Volt  -  A unit of electrical pressure.
  • Voltage  -  One volt is the amount of pressure that will cause one ampere of current in one ohm of resistance.
  • Voltage Coefficient of Resistance  -  The change in resistance with applied voltage.
  • Voltage Drop  -  When the voltage at the end of the cable is less than the beginning of the cable.
  • Voltage Rating  -  The maximum voltage at which a cable or insulated conductor can be safetly maintained during continuous use in a normal manner.      

W

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  • Water Conductivity  -  The ability of water to conduct an electric current.
  • Waterlogged  -  Saturated with water.
  • Water Table  -  The underground boundary between the surface of the soil and the area where groundwater fills the cracks and openings in the rocks and sand.
  • Weld Crack  -  Cracks can appear on the surface, inside the weld or heat effected zone.
  • Weld Decay  -  See integranulat corrosion
  • Welding Defects  -  Blow hole, defect of joint shape, incomplete fusion, overlap, slag inclusion, undercut, weld crack.

X

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  • Yield Strength  -  Yield strength, abbreviated as \(\sigma\) (Greek symbol sigma), also called yield stress, is the minimum stress that leads to permanent deformation of the material.

Z

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