Complete Dictionary of Corrosion Engineering Terms

Understanding the terminology of corrosion and its associated damage mechanisms is vital for professionals in industries such as refining, petrochemicals, and materials science. This glossary offers precise, technical definitions of key terms related to corrosion processes, metallurgical phenomena, and damage mechanisms commonly encountered in industrial applications.

885 °F (475 °C) Embrittlement A metallurgical change causing loss of ductility and fracture toughness in stainless steels with ferrite phases. It occurs during exposure to temperatures between 600 °F and 1000 °F (315 °C to 540 °C), leading to cracking failures, particularly during plant shutdowns or start-ups.

Abrasion The removal of surface material from a solid caused by the frictional interaction with another solid, liquid, gas, or a combination thereof.

Absorption A process in which molecules are absorbed into and distributed throughout the body of a liquid or solid material.

Acceleration Corrosion Test A testing methodology designed to replicate, within a short timeframe, the corrosive effects typically experienced under long-term service conditions.

Acicular Ferrite A highly substructured, non-equiaxed ferrite that forms during continuous cooling through a mixed diffusion and shear transformation. This process initiates at a temperature slightly above the transformation range for upper bainite. Unlike bainite, acicular ferrite contains minimal carbon, resulting in only trace amounts of carbide.

Acid A substance that releases hydrogen ions (H⁺) when dissolved in water. Acids typically dissolve common metals and react with bases to form neutral salts and water.

Acid Embrittlement A specific form of hydrogen embrittlement that can occur in certain metals exposed to acidic environments.

Acid Rain Atmospheric precipitation with a pH ranging between 3.6 and 5.7, primarily caused by the combustion of fossil fuels. This generates oxides of nitrogen and sulfur, which are subsequently converted into nitric and sulfuric acids, leading to precipitation that accelerates atmospheric corrosion.

Acrylic A resin polymerized from acrylic acid, methacrylic acid, or their esters, as well as acrylonitrile. It is commonly used in coatings and adhesives.

Activation The process of converting a passive metal surface into a chemically active state. This is the opposite of passivation, where a surface becomes more resistant to chemical reactions.

Active A condition where a metal is corroding or is prone to corrode, as opposed to being in a passive, non-corroding state.

Active Metal A metal that readily corrodes or is in the process of corroding.

Active Potential The electrochemical potential of a corroding material, representing its tendency to undergo corrosion.

Activity A measure of the effective concentration of a substance in a reaction, accounting for non-ideal behavior.

Activity (Ion) The ion concentration corrected for deviations from ideal behavior, calculated as concentration multiplied by the activity coefficient.

Activity Coefficient A numerical value expressing the deviation of a solution from ideal thermodynamic behavior, often used for electrolytes.

Addition Agent A substance added to a solution to control or modify a process, such as inhibitors in corrosion protection.

Additive A small quantity of a substance introduced to a fluid for a specific purpose, such as reducing friction or preventing corrosion.

Aerated A solution containing more than 10 parts per billion (ppb) of dissolved oxygen.

Aeration The process of introducing air into a solution, substrate, or medium to improve oxygen levels or chemical reactions.

Aeration Cell An electrolytic cell formed due to differences in dissolved oxygen concentrations at different points, leading to localized corrosion.

Age Hardening The process of hardening a metal by aging, often following rapid cooling or cold working.

Aging Changes in the properties of metals or alloys over time at ambient or elevated temperatures, often due to phase transformations or stress relief.

Alclad A composite aluminum product with a corrosion-resistant alloy layer bonded to the surface to protect the core material.

Alkali Metal A group of highly reactive metals from group IA of the periodic table, including lithium, sodium, and potassium, which form strongly alkaline compounds.

Alkaline Having the properties of a base, typically with a pH greater than 7.

Alkaline Cleaner A mixture of alkaline hydroxides and salts used for cleaning metal surfaces, often with added surfactants for enhanced performance.

Alkyd A type of resin made from polyhydric alcohols and polybasic acids, commonly used in coatings and paints.

Alkylation A chemical reaction introducing an alkyl group into an organic compound, often used in refinery processes to improve fuel quality.

Alligatoring A wide cracking pattern on coatings resembling alligator hide or the longitudinal splitting of flat materials parallel to the surface.

Alloy Plating The deposition of a coating composed of two or more metallic elements to enhance surface properties.

Alloy Steel Steel that contains significant amounts of alloying elements (such as chromium, nickel, molybdenum) to enhance properties like strength, toughness, or corrosion resistance.

Alpha Iron The body-centered cubic form of pure iron, stable at temperatures below 910°C (1670°F).

Alternate Immersion Test A corrosion test where specimens are periodically exposed to a liquid medium and then to air, simulating real-world environmental conditions.

Aluminizing A process of coating a metal surface with aluminum to enhance its resistance to oxidation and corrosion.

Amalgam An alloy formed by mercury combining with one or more other metals.

Amine Corrosion Localized corrosion of carbon steel in amine treatment systems caused by contaminants like dissolved CO2, H2S, heat-stable amine salts, and degradation products. This damage is influenced by operating conditions, contaminants, and equipment design, rather than by the amines themselves.

Amine Stress Corrosion Cracking A type of SCC (stress corrosion cracking) affecting carbon steel in specific amine environments under tensile stress. This phenomenon often arises due to poor process control or the presence of system contaminants.

Ammeter An instrument used to measure the electric current in a circuit.

Ammonia Stress Corrosion Cracking SCC caused by ammonia exposure, typically seen in carbon and low-alloy steels under tensile stress. This form of cracking is prevalent in systems handling ammoniated water, particularly in water-cooling or processing environments.

Ammonium Bisulfide Corrosion Corrosion caused by ammonium bisulfide in alkaline sour water systems, commonly affecting carbon steel components such as piping and vessels. This occurs in units processing sour water, especially in the presence of H2S and ammonia.

Ammonium Chloride Corrosion Highly localized corrosion that occurs when ammonium chloride or amine hydrochloride deposits form on equipment surfaces. This is commonly seen in overhead systems of hydroprocessing units, especially under conditions conducive to salt deposition.

Amorphous Solid A rigid material lacking a regular crystalline structure, with constituent atoms or molecules not repeating in three-dimensional patterns. Examples include glass and metallic glass.

Amphoteric A substance, such as certain oxides or hydroxides, that can act as both an acid and a base depending on the chemical environment.

Anaerobic A condition or environment that exists in the absence of air or free oxygen.

Anchor Pattern/Surface Profile The shape and amplitude of the surface profile created by methods like blasting, which influences the adhesion of coatings or metallic layers to the substrate.

Anchorite A type of zinc-iron phosphate coating applied to steel for enhanced corrosion resistance.

Anion A negatively charged ion that migrates toward the anode during electrolysis.

Annealing A heat treatment process that involves heating a material to a specific temperature, holding it there, and then cooling it slowly to improve softness, machinability, and internal stress relief.

Anode An electrode at which oxidation occurs during electrochemical reactions, often resulting in material loss due to corrosion.

Anode Corrosion The degradation or dissolution of a metal surface serving as an anode in an electrochemical system.

Anode Corrosion Efficiency The ratio of the actual corrosion experienced by the anode to the theoretical corrosion expected based on the total current flow.

Anode Effect A phenomenon in electrolysis where the anode becomes polarized due to a gas film, resulting in an increase in voltage and a decrease in current.

Anode Efficiency A measure of the effectiveness of an anode, calculated as the actual current used for the desired reaction divided by the total current passed through the system.

Anode Film The thin layer of electrolyte or material directly adjacent to the anode surface, where concentration gradients are steep.

Anodic Cleaning An electrolytic cleaning process where the workpiece is made the anode to remove surface impurities or contaminants. Also known as reverse-current cleaning.

Anodic Coating A protective layer formed on a metal surface through an electrolytic process where the surface acts as the anode.

Anodic Inhibitor A chemical substance that reduces or prevents the rate of anodic (oxidation) reactions in a corrosion process.

Anodic Metallic Coating A coating composed of a metal that is anodic (electrochemically positive) relative to the substrate, providing sacrificial protection to the base material.

Anodic Polarization The increase in the electrode potential of an anode due to current flow, moving it to a more noble (positive) state.

Anodic Potential The potential required to maintain an anode in a highly polarized state, reducing its tendency to corrode.

Anodic Protection A technique to reduce corrosion by applying sufficient current to maintain a metal surface in its passive region.

Anodic Reaction An electrochemical reaction at the anode, involving the oxidation of a substance and the transfer of electrons to the external circuit.

Anodizing A surface treatment process that forms an oxide layer on a metal surface through anodic oxidation, typically applied to aluminum for enhanced corrosion resistance.

Anolyte The electrolyte adjacent to the anode in an electrochemical cell, where oxidation reactions occur.

Anti-fouling A property or treatment designed to prevent the attachment or growth of marine organisms on submerged surfaces, often through toxic or chemical-resistant coatings.

Anti-pitting Agent A chemical additive used in electroplating solutions to prevent the formation of pits or pores in the deposited coating.

Aqueous Refers to solutions or systems in which water is the solvent or primary component.

Aqueous Organic Acid Corrosion Corrosion caused by the presence of dissolved organic acids in water. It affects carbon steel and stainless steel equipment, commonly in environments where crude oil or process streams contain organic acids.

Artificial Aging A process of accelerating the aging of a material by exposing it to elevated temperatures to achieve desired mechanical properties more quickly.

Atmospheric Corrosion The gradual degradation of a material caused by exposure to environmental factors such as oxygen, water vapor, and pollutants in the atmosphere.

Austenite A solid solution of one or more elements in face-centered cubic iron, typically formed at high temperatures in ferrous alloys.

Austenitic Refers to materials or alloys, such as stainless steel, that maintain the face-centered cubic (FCC) crystal structure at room temperature.

Austenitic Stainless Steel A class of stainless steel alloys containing sufficient chromium and nickel to retain austenitic structure at ambient temperatures.

Austenitic Stainless Steels A group of stainless steels including 300 series types such as 304, 304L, 316, 316L, 321, and 347. The "L" suffix indicates low carbon content, while "H" denotes high carbon content. These alloys are characterized by an austenitic microstructure.

Austenitizing The process of heating a ferrous material to a temperature where it transforms into austenite, followed by controlled cooling to achieve specific mechanical properties.

Automatic Welding A welding process where the variables and execution of the weld are fully controlled by a machine or automated system.

Auxiliary Anode A supplementary anode used in electroplating or corrosion protection to achieve better current distribution and coating uniformity.

Auxiliary Electrode An electrode in an electrochemical cell used to transfer current to or from a working electrode, often made of a non-corroding material.

Backfill Material used to fill spaces around buried anodes, vent pipes, or other components in a cathodic protection system to improve electrical conductivity.

Bactericide A chemical agent used to kill bacteria and prevent microbial-induced corrosion or contamination.

Bainite A microstructure in steel consisting of ferrite and cementite, formed during the transformation of austenite at temperatures below the pearlite range but above martensite formation.

Banded Structure A metallurgical feature where alternating bands of different compositions or phases are aligned, often resulting from hot working.

Bandwidth (Ultrasonics) The range of frequencies around a central frequency used in ultrasonic testing or inspection.

Base A chemical substance that yields hydroxide ions (OH⁻) in aqueous solutions, often used to neutralize acids.

Base Metal The primary metal or material to be welded, soldered, or joined, which may also refer to a less noble metal in an alloy.

Beach Marks Macroscopic progression marks on a fracture surface, indicating successive positions of an advancing crack front, commonly seen in fatigue or stress-corrosion failures.

Bead A single run or pass of deposited weld metal on a surface.

Bimetallic Corrosion (Galvanic Corrosion) Corrosion that occurs when two dissimilar metals are in electrical contact in a conductive environment, leading to accelerated corrosion of the less noble metal.

Biocide A chemical substance used to kill living organisms, including bacteria, that can contribute to corrosion in various environments.

Biological Corrosion Deterioration of a material due to the activity of living organisms, such as bacteria or algae, often in environments like soil, water, or petroleum products.

Biostat A chemical agent that inhibits the growth of living organisms, such as bacteria, to reduce the risk of biological corrosion.

Bipolar Electrode An electrode in an electrochemical cell not directly connected to the power supply, but with one part anodic and the other cathodic, depending on its position in the electrolyte.

Bituminous Coating A protective layer made from coal tar or asphalt, used to prevent corrosion on submerged or buried metal structures.

Black Liquor A byproduct of the pulpwood cooking process in paper production, which can cause corrosion in associated equipment.

Black Oxide A black finish on metal achieved by immersing it in oxidizing salts or solutions, often to improve corrosion resistance or aesthetic appeal.

Blast Cleaning The process of cleaning and roughening a surface using metallic or non-metallic grit projected at high velocity by air, water, or centrifugal force.

Blast Peening A treatment process where rounded abrasive particles impact a surface to induce compressive stresses, relieving tensile stress and improving fatigue resistance.

Blister A raised area on a surface caused by loss of adhesion between a coating and the base material, or due to gas trapped beneath the surface layer.

Blowdown The removal of accumulated impurities from systems like boilers or cooling towers to maintain efficiency and prevent corrosion.

Blue Brittleness A condition in some steels where they become brittle when heated to a specific temperature range, typically between 200°C and 370°C.

Blushing A whitening or loss of gloss in organic coatings caused by moisture absorption, also referred to as blooming.

Boiler Water and Steam Condensate Corrosion Corrosion caused by dissolved oxygen, carbon dioxide, and impurities in boiler water and steam condensate systems. This is seen in piping and equipment exposed to improperly treated boiler water or condensate return.

Bonderizing A proprietary phosphatizing process used to prepare steel surfaces for painting or corrosion protection.

Brackish Water Water with salinity levels between freshwater and seawater, often challenging for corrosion resistance due to its variable composition.

Braze Welding A joining process similar to fusion welding, using a filler metal with a lower melting point than the base metal, but without capillary action.

Brazing A metal joining technique where molten filler metal is drawn into the gap between closely fitted surfaces by capillary action, typically at temperatures above 500°C.

Brazing Alloy The filler metal used in brazing processes, specifically formulated to flow and bond without melting the base metals.

Breakaway Corrosion A sudden and significant increase in corrosion rate, often seen in high-temperature environments such as dry oxidation.

Breakdown Potential The minimum potential at which localized corrosion, such as pitting or crevice corrosion, initiates and propagates.

Brightener An additive in electroplating baths used to produce a smooth and lustrous metallic deposit.

Brine A highly concentrated saltwater solution, often used in industrial processes but posing significant corrosion challenges.

Brine Corrosion Corrosion of materials in brine solutions, particularly those containing high concentrations of salts like sodium chloride. This is common in desalination plants, brine treatment facilities, or other equipment handling saline or seawater solutions.

Brittle Fracture A type of fracture that occurs with minimal plastic deformation, typically due to rapid crack propagation under low-energy conditions.

Burning Damage to metals caused by overheating, leading to incipient melting or oxidation, or discoloration during grinding operations.

Butt Joint A weld joint configuration where two parts meet edge-to-edge or end-to-end at angles between 135° and 180°.

CO2 Corrosion Corrosion of carbon steel caused by carbonic acid formed from dissolved CO2 in aqueous environments. It is common in oil and gas production systems, pipelines, and other equipment handling CO2-saturated water or hydrocarbons.

CUI (Corrosion Under Insulation) A form of corrosion that occurs on metal surfaces beneath thermal insulation, often exacerbated by moisture and contaminants.

Calcareous Coating or Deposit A layer of calcium carbonate and magnesium hydroxide that forms on cathodically protected surfaces due to increased pH.

Calomel Electrode A reference electrode commonly used in corrosion studies and pH measurements, based on mercury and mercurous chloride.

Calorizing A process where aluminum is diffused into a metal surface at high temperatures to improve resistance to oxidation and corrosion.

Carbon Dioxide Welding A welding process where carbon dioxide gas is used to shield the arc and molten pool during metal arc welding.

Carbon Steel An alloy primarily composed of iron (Fe) with small amounts of carbon (C). It contains no deliberate alloying elements but may have trace amounts of manganese, chromium, and silicon, which can influence corrosion resistance, hardness, and toughness.

Carbonate Stress Corrosion Cracking Stress corrosion cracking caused by the presence of carbonate species, typically in caustic environments. This type of damage affects carbon and low-alloy steels in environments with high carbonate ion concentrations, especially at elevated temperatures.

Carbonitriding A case-hardening process that involves the simultaneous diffusion of carbon and nitrogen into the surface of a ferrous material at elevated temperatures.

Carburization The process of introducing carbon into the surface layer of a metal to enhance hardness and wear resistance, often through high-temperature exposure to a carbonaceous material.

Carburizing A heat treatment process where carbon atoms are diffused into the surface of a ferrous material, creating a hardened outer layer with a softer core.

Case Hardening A generic term for heat treatment processes that modify the surface layer of a metal, such as carburizing or nitriding, to increase hardness while retaining a softer core.

Cathode The electrode in an electrochemical cell where reduction reactions occur, typically resulting in a gain of electrons.

Cathode Film The layer of solution or deposit immediately adjacent to the cathode surface in an electrochemical reaction.

Cathodic Corrosion Corrosion that occurs at the cathodic site of a structure, often involving amphoteric metals reacting with alkaline electrolytic products.

Cathodic Disbondment The loss of adhesion between a protective coating and its substrate due to cathodic reactions at the coating interface.

Cathodic Inhibitor A chemical substance that reduces the rate of cathodic reactions, thereby decreasing the overall corrosion rate.

Cathodic Pickling An electrolytic cleaning process in which the workpiece serves as the cathode to remove scale, oxides, or other contaminants.

Cathodic Polarization A shift in the cathodic potential of a metal surface due to current flow, making the surface more negative relative to its equilibrium potential.

Cathodic Protection A corrosion control technique where the metal is made the cathode in an electrochemical cell, either through sacrificial anodes or impressed current systems.

Cathodic Reaction An electrochemical reaction occurring at the cathode, typically involving the reduction of cations or oxygen.

Catholyte The portion of electrolyte that is in immediate contact with the cathode in an electrochemical cell.

Cation A positively charged ion that migrates toward the cathode in an electrochemical cell.

Caustic A substance, such as sodium hydroxide or potassium hydroxide, that is strongly alkaline and capable of causing severe corrosion or chemical burns.

Caustic Corrosion Severe localized corrosion resulting from exposure to caustic (alkaline) environments, such as sodium hydroxide. It typically affects carbon steel in heat exchangers, boilers, and other equipment with concentrated caustic solutions at elevated temperatures.

Caustic Dip A strongly alkaline solution used to clean or etch metal surfaces, neutralize acids, or remove organic contaminants.

Caustic Embrittlement A form of stress-corrosion cracking in carbon steels or alloys exposed to concentrated alkaline solutions at elevated temperatures.

Caustic Stress Corrosion Cracking A type of stress corrosion cracking that occurs in carbon and low-alloy steels exposed to caustic environments under tensile stress. Commonly referred to as caustic embrittlement, it typically occurs in boilers and piping systems operating in concentrated alkaline solutions.

Cavitation Erosion damage caused by the formation and collapse of vapor bubbles in liquid systems, leading to high-pressure impacts on material surfaces. It is commonly seen in pump impellers, piping elbows, and other high-velocity flow areas.

Cavitation (Erosion) Damage caused by the formation and collapse of vapor bubbles in a liquid, generating high-energy shock waves that degrade the material surface.

Cavitation Damage The material degradation resulting from cavitation, often appearing as pitting, surface deformation, or material loss.

Cell An electrochemical circuit consisting of an anode and cathode in electrical contact, where corrosion typically occurs at the anodic areas.

Cementation Coating A protective surface layer produced by diffusing elements like aluminum or chromium into a base metal at high temperatures.

Cementite A compound of iron and carbon (Fe₃C) present in steel, characterized by its hard and brittle nature.

Chalking The formation of a loose, powdery surface on organic coatings due to weathering and degradation.

Chamfering The process of beveling the edge or corner of a material to improve fit, appearance, or reduce stress concentration.

Checking The development of small cracks or breaks in a coating that do not penetrate through to the substrate.

Checks Fine cracks or fissures that appear on a surface due to processing or service conditions, often associated with thermal cycling or mechanical stress.

Chelate A chemical complex formed when a metal ion bonds with multiple coordinating atoms in a single molecule, creating a ring-like structure.

Chelating Agent A substance that forms chelate compounds by bonding with a metal ion, often used to control metallic ions in solutions.

Chelation A chemical process where a chelating agent forms a stable, ring-like complex with a metal ion.

Chemical Cleaning A method of surface preparation that uses chemicals to remove rust, scale, sediments, or coatings, either during operation or offline.

Chemical Conversion Coating A protective or decorative surface layer formed by a chemical reaction between a metal surface and a chosen environment.

Chemical Potential The change in Gibbs free energy of a system with respect to the addition or removal of a substance at constant temperature and pressure.

Chemical Vapor Deposition A process where gaseous reactants decompose on a heated substrate, depositing a solid material on the surface.

Chemisorption The adsorption of a substance onto a surface through chemical bonding, resulting in a stronger interaction compared to physical adsorption.

Chevron Pattern A fracture surface pattern resembling nested 'V' shapes, often indicative of brittle fracture and used to trace fracture origins.

Chloride Stress Corrosion Cracking A form of SCC that occurs in austenitic stainless steels exposed to chloride-containing environments under tensile stress. It is a major concern in heat exchangers, piping, and other equipment operating at elevated temperatures or in marine or coastal conditions.

Chromadizing A surface treatment for aluminum alloys, primarily for aircraft, to enhance paint adhesion through exposure to chromic acid.

Chromate Treatment A corrosion protection process that involves immersing metals in a solution of hexavalent chromium compounds to form a protective layer.

Chromating The process of applying a chromate treatment to improve corrosion resistance and enhance paint adhesion on metal surfaces.

Chrome Pickle A solution used to produce a temporary chromate coating on magnesium surfaces, offering protection and a paintable base.

Chromizing A surface diffusion process where chromium is introduced into a metal at high temperatures to improve corrosion and wear resistance.

Clad Metal A composite material composed of two or more metals bonded together, often to combine strength and corrosion resistance.

Clad Metals Sheets or plates made by bonding a base metal to a more expensive, corrosion-resistant metal layer.

Cleavage A type of fracture occurring along crystallographic planes, commonly observed in brittle materials.

Cleavage Fracture A brittle fracture mechanism where cracks propagate along specific crystallographic planes, resulting in shiny, flat facets.

Co-ordination Compound A complex chemical structure where a central atom is surrounded by ligands bonded through coordinate covalent bonds.

Cold Cracking A type of weld cracking that occurs at low temperatures, often due to hydrogen, stress, and a susceptible microstructure.

Cold Working The plastic deformation of metals at temperatures below the recrystallization point, improving strength and hardness through strain hardening.

Combined Carbon Carbon in steel or cast iron that exists in a combined state, typically as carbides, rather than as free graphite.

Compatibility The ability of a material to coexist without degradation in a specific environment or when in contact with another material.

Complexation The formation of complex chemical species through the coordination of ligands to a central metal ion.

Compressive Relating to forces that tend to reduce the volume or shorten the dimensions of a material.

Compressive Strength The maximum stress a material can withstand under compression without failure or permanent deformation.

Compressive Stress The internal stress within a material subjected to compressive forces, causing it to shorten or deform.

Concentration Cell An electrochemical cell where a potential difference arises due to differences in ion concentration at different locations.

Concentration Cell Corrosion Localized corrosion caused by differences in ion concentration between areas on a metal surface. This occurs in crevices, under deposits, or in regions with varying oxygen concentration, leading to anodic and cathodic areas.

Concentration Polarization The reduction in reaction rate in an electrochemical cell caused by the accumulation or depletion of reactants near the electrode surface.

Conductivity A measure of a material's ability to conduct electric current, commonly expressed in Siemens per meter (S/m).

Contact Corrosion A form of galvanic corrosion occurring at the interface of two dissimilar metals in electrical contact.

Contact Plating A metal plating process where the plating current is generated by galvanic action between the workpiece and another metal, without an external power source.

Contact Potential The potential difference that arises at the junction of two dissimilar substances due to differences in their electron affinities or work functions.

Continuity Bond A metallic connection installed to provide electrical continuity between two metal structures, ensuring uniform cathodic protection.

Controlled Galvanic System A cathodic protection system where sacrificial anodes are controlled using fixed or variable resistors to optimize protection efficiency.

Conversion Coating A coating formed by the chemical or electrochemical reaction of a metal surface with its environment, providing corrosion protection or a paintable surface.

Cooling Water Corrosion Corrosion in systems handling cooling water, caused by dissolved oxygen, salts, and microorganisms. It typically affects heat exchangers, piping, and other components exposed to untreated or poorly managed cooling water systems.

Copper Ferrule A copper ring or cap used to reinforce slender shafts, such as tool handles, and prevent splitting or damage.

Copper-Accelerated Salt Spray (CASS) Test An accelerated corrosion test designed to evaluate the performance of certain electrodeposits and anodic coatings on aluminum.

Corrodkote Test A specific accelerated corrosion test used to evaluate the resistance of electrodeposits to corrosion under controlled conditions.

Corrosion The chemical or electrochemical reaction between a material, typically a metal, and its environment, leading to material degradation and functional impairment.

Corrosion Damage Any degradation caused by corrosion that negatively affects the functionality of the material or system.

Corrosion Effect The result of corrosion on a system, including material loss, structural weakening, or aesthetic changes.

Corrosion Embrittlement A severe reduction in ductility caused by corrosive attack, often not visually apparent, and typically occurring intergranularly.

Corrosion Engineer A professional responsible for monitoring, interpreting, and mitigating corrosion in structures or systems.

Corrosion Fatigue The premature fracturing of a material due to the combined effects of cyclic stress and corrosive environmental exposure.

Corrosion Fatigue Limit The maximum cyclic stress a material can endure in a given corrosive environment without failure after a specified number of cycles.

Corrosion Fatigue Strength The highest cyclic stress that a material can sustain without failure under specific conditions of corrosion and repeated loading.

Corrosion Inhibitor A substance added to an environment to significantly reduce the rate of corrosion on a metal surface.

Corrosion Potential The electrochemical potential of a corroding surface in an electrolyte, measured relative to a reference electrode.

Corrosion Product Substances formed as a result of corrosion, such as rust or oxide layers on metals.

Corrosion Protection Measures taken to prevent or reduce corrosion damage, including coatings, inhibitors, or cathodic protection systems.

Corrosion Rate The speed at which a material deteriorates due to corrosion, commonly expressed in mils per year or microns per year.

Corrosion Resistance The ability of a material to withstand corrosion in a specific environment without significant degradation.

Corrosion System A system comprising the metal, environment, and all interactions that contribute to the corrosion process.

Corrosion Under Insulation (CUI) Localized corrosion of materials beneath insulation due to trapped moisture or water ingress. It commonly affects carbon and stainless steels in insulated piping and equipment, particularly in environments with temperature cycling or humidity.

Corrosive Agent A substance that promotes or accelerates corrosion when in contact with a susceptible material.

Corrosive Environment An environment containing corrosive agents that can cause material degradation.

Corrosivity The tendency of an environment to cause corrosion in a given system or material.

Couple A galvanic cell formed between two dissimilar metals in contact within a conductive environment, leading to corrosion of the anodic metal.

Coupons Material samples used in testing or monitoring environments to evaluate the effects of corrosion.

Covered Filler Rod A welding filler rod with a protective flux coating to shield the weld area from contamination during the process.

Covering Power The ability of an electroplating solution to deposit metal uniformly over a surface, including low-current-density areas.

Cracking The development of fractures or separations in a material, often caused by stress, environmental factors, or inherent defects.

Cracking (of Coating) Breaks or fissures in a protective coating that extend to the substrate, reducing its protective effectiveness.

Crazing A network of fine cracks appearing on the surface of a material, often caused by thermal cycling or stress.

Creep The time-dependent deformation of a material under constant stress, often occurring at high temperatures.

Creep and Stress Rupture Material deformation and failure due to prolonged exposure to high stress and temperature. It is commonly seen in high-temperature equipment such as reformers, furnaces, and turbines, where the material gradually deforms until rupture occurs.

Creep-Rupture Embrittlement A loss of ductility in materials subjected to prolonged high-temperature stress, often due to impurities or microstructural changes.

Creep-Rupture Strength The maximum stress a material can sustain before fracturing under high-temperature creep conditions over a specified time period.

Crevice Corrosion Localized corrosion occurring in confined spaces or crevices where a stagnant environment promotes aggressive attack.

Critical Anodic Current Density The highest anodic current density observed in the active region for a metal or alloy before passivation begins.

Critical Flaw Size The maximum size of a defect in a structure that can be tolerated without leading to failure under specific stress conditions.

Critical Humidity The relative humidity above which the corrosion rate of a material increases significantly.

Critical Pitting Potential (Ecp, Ep, Epp) The minimum potential required to initiate and sustain pitting corrosion in a given environment.

Current The flow of electric charge through a conductor or electrolyte, measured in amperes.

Current Density The electric current flowing per unit area of an electrode surface, typically expressed in amperes per square meter or centimeter.

Current Efficiency The ratio of the actual current used for a specific electrochemical reaction to the total applied current, expressed as a percentage.

De-Alloying The selective removal of one or more components from an alloy, typically leaving a porous or weakened structure.

Deactivation The process of reducing or eliminating the reactivity of corrosive constituents in a liquid or gas, often by chemical means.

Dealloying The selective corrosion of one or more alloying elements from a material, leaving behind a weakened structure. Examples include dezincification in brass and graphitic corrosion in cast iron.

Dealuminization The selective leaching of aluminum from an alloy, often resulting in a brittle or porous structure.

Decarburization The loss of carbon from the surface of a carbon-containing alloy, typically due to high-temperature exposure to oxidizing environments.

Decobaltification The selective removal of cobalt from a cobalt-based alloy, often leading to material degradation.

Decomposition Potential The minimum potential required to decompose an electrolyte or its components during electrolysis.

Deep Ground Bed A cathodic protection installation where anodes are buried at significant depths to provide uniform protection to a structure.

Demineralization The removal of dissolved mineral content from water, often to prevent scaling or corrosion in industrial systems.

Dendrite A tree-like crystal structure formed during the solidification of metals, often affecting mechanical properties.

Denickelification The selective leaching of nickel from nickel-containing alloys, particularly in corrosive environments like seawater.

Density (of Gases) The mass per unit volume of a gas at a specified temperature and pressure.

Density (of Solids and Liquids) The mass per unit volume of a solid or liquid at a specified temperature, typically expressed in g/cm³ or kg/m³.

Deoxidizing The removal of oxygen from a material, often to improve properties or reduce corrosion risks.

Depolarization The reduction or elimination of polarization effects in an electrochemical cell, often improving reaction rates.

Depolarizer A substance or process used to minimize polarization effects in electrochemical systems, enhancing efficiency.

Deposit A foreign substance that accumulates on a material's surface from its environment, potentially causing localized corrosion or other effects.

Deposit Attack Corrosion localized under deposits, often due to differences in oxygen concentration or other chemical imbalances.

Deposit Corrosion A type of localized corrosion occurring beneath or around deposits on a metallic surface, also referred to as poultice corrosion.

Deposited Metal Filler metal added during a welding process that solidifies to form part of the welded joint.

Descaling The process of removing scale, oxide layers, or similar residues from a metal surface, often through chemical or mechanical methods.

Dezincification The selective removal of zinc from brass or other zinc-containing alloys, leading to a porous, weakened structure.

Dichromate Treatment A chromate conversion coating process for magnesium alloys, offering temporary protection and a paintable surface.

Dielectric Strength The maximum electrical field a material can withstand without breakdown or electrical discharge.

Diethanolamine (DEA) A chemical used in amine treating processes to remove hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from hydrocarbon streams.

Differential Aeration Cell An electrochemical cell caused by variations in oxygen concentration, often leading to localized corrosion.

Diffusion The process by which atoms or molecules move from areas of high concentration to low concentration within a material.

Diffusion Coating A surface treatment where materials diffuse into a substrate at high temperatures, enhancing surface properties like corrosion resistance.

Diffusion-Controlled Process A chemical or electrochemical reaction whose rate is limited by the diffusion of reactants to the reaction site.

Diglycolamine (DGA) A chemical compound used in amine treatment for the removal of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from hydrocarbon streams.

Dimensional Stability The ability of a material to maintain its original dimensions under mechanical, thermal, or environmental stress.

Discontinuity An interruption in the physical or structural continuity of a material, which may act as a site for stress concentration or corrosion.

Dislocation A defect within a crystal lattice where atoms are misaligned, affecting a material's mechanical properties.

Dissimilar Metal Corrosion Corrosion that occurs when two different metals are electrically connected in a conductive environment, also known as galvanic corrosion.

Dissimilar Metal Weld Cracking Cracking in weldments joining dissimilar metals due to differences in thermal expansion, metallurgical incompatibility, or residual stresses. It is commonly seen in welds between carbon steels and stainless steels or nickel-based alloys.

Dissociation The separation of a compound into two or more components, such as the ionization of a salt in water.

Double-Layer Capacitance The capacitance that arises at the interface between a conductive electrode and an electrolyte due to charge separation.

Drainage Cell An electrochemical cell that forms due to improper drainage or accumulation of water on a metallic surface.

Dry Corrosion Oxidation or chemical reaction of a material with its environment at high temperatures in the absence of water or moisture.

Ductility The ability of a material to undergo significant plastic deformation before rupture, often characterized by elongation or reduction of area.

Duplex Alloy An alloy with a two-phase microstructure, often combining properties like strength and corrosion resistance.

Duplex Stainless Steel A type of stainless steel with a microstructure of both austenite and ferrite, offering high strength and excellent corrosion resistance.

E-Coating An electrocoating process where a charged coating material is deposited onto a conductive surface via electrodeposition.

Edge Effect Localized differences in current density or corrosion rates at the edges of a material or structure.

Edge Preparation The process of preparing the edges of a material for joining or coating, often through grinding or machining.

Efflorescence The formation of crystalline deposits on a material's surface as a result of moisture evaporation and solute crystallization.

Elastic Deformation Reversible deformation of a material under stress, where the material returns to its original shape upon unloading.

Elastic Limit The maximum stress a material can withstand without experiencing permanent deformation.

Electrical Conductivity A measure of a material's ability to conduct an electric current, typically expressed in Siemens per meter (S/m).

Electrical Isolation The condition in which a metallic structure is electrically separated from other structures or the environment, typically to prevent stray currents or galvanic corrosion.

Electrical Resistivity The resistance of a material to the flow of electric current, expressed as the resistance multiplied by the cross-sectional area and divided by the length of the current path. It is the reciprocal of electrical conductivity.

Electrochemical Admittance The reciprocal of electrochemical impedance, representing the ease with which an electrochemical system allows the flow of current.

Electrochemical Cell A system comprising an anode, cathode, and electrolyte, where electrochemical reactions occur. The anode and cathode may be different metals or different areas on the same metal surface.

Electrochemical Corrosion Corrosion that involves electron flow between anodic and cathodic areas on a metallic surface, typically facilitated by an electrolyte.

Electrochemical Equivalent The mass of a substance oxidized or reduced at 100% efficiency by the passage of a unit quantity of electricity, usually expressed in grams per coulomb.

Electrochemical Impedance A complex proportionality factor that represents the total opposition of an electrochemical system to current flow, including resistance and reactance. It is determined by applying a small alternating current and measuring the response.

Electrochemical Impedance Spectroscopy (AC Impedance) A technique to evaluate the electrochemical properties of a metal-fluid interface by applying a sinusoidal voltage across a range of frequencies to measure impedance.

Electrochemical Potential The combined chemical and electrical contribution to the free energy of a system. It is the reversible work required to move a unit charge within the system, relative to a reference electrode under open-circuit conditions.

Electrochemical Series A list of elements arranged according to their standard electrode potentials, predicting their tendency to oxidize or reduce when immersed in an electrolyte.

Electrode A conductor that facilitates the transfer of electrons to or from an electrolyte, serving as an anode or cathode in an electrochemical system.

Electrode Polarization The change in electrode potential caused by current flow, relative to a reference potential. It occurs due to factors such as concentration changes or applied currents.

Electrode Potential The potential of an electrode in an electrolyte relative to a reference electrode, measured under equilibrium conditions without resistance losses in the solution or external circuit.

Electrode Reaction A reaction at the interface between an electronic conductor (electrode) and an ionic conductor (electrolyte), involving charge transfer. Examples include anodic oxidation and cathodic reduction reactions.

Electrodeposition The process of depositing a substance on an electrode by passing an electric current through an electrolyte.

Electrogalvanizing A process of coating steel or other metals with zinc by electroplating to enhance corrosion resistance.

Electrokinetic Potential (Zeta Potential) The potential difference across a double layer in a solution, caused by an unbalanced charge distribution near a charged surface. It is distinct from electrode potential and is important in colloidal stability.

Electroless Plating A process of chemically depositing a metal layer onto a substrate without applying external current, using an autocatalytic reduction reaction.

Electrolysis A process that induces chemical changes in an electrolyte through the application of an external electrical current.

Electrolyte A substance, typically a liquid, that contains ions capable of conducting electricity. Electrolytes are crucial in electrochemical reactions.

Electrolytic Cell A setup consisting of electrodes, an electrolyte, and a power source, designed to carry out electrolysis.

Electrolytic Cleaning A method of removing contaminants, scale, or corrosion products from a metal surface by making it an electrode in an electrolytic bath and applying a current.

Electrolytic Protection A form of cathodic protection achieved by using an impressed current system to prevent corrosion.

Electromotive Force (EMF) The voltage generated by an electrochemical cell when no current flows, representing the cell's ability to drive a reaction.

Electromotive Force Series (EMF Series) A list of elements arranged by their standard electrode potentials, showing their relative reactivity. More noble elements have higher potentials, while more active elements have lower potentials.

Electron Flow The movement of electrons in an external circuit connecting the anode and cathode of an electrochemical system. The conventional current flow is in the opposite direction.

Electron-Beam Welding A fusion welding technique where a focused beam of high-energy electrons melts the materials to be joined.

Electroplating The electrochemical deposition of a metal or alloy onto a surface to improve properties such as corrosion resistance or aesthetics.

Electropolishing A process of smoothing and brightening a metal surface by making it the anode in an electrolytic cell, where high points dissolve faster than low points.

Electroslag Welding A high-efficiency welding process where a molten flux electrically melts the joint faces and filler material, forming a continuous weld.

Electrotinning The process of electroplating a layer of tin onto a metal substrate to improve corrosion resistance and solderability.

Embrittlement A severe loss of ductility or toughness in a material, often caused by environmental or thermal factors. Forms include hydrogen embrittlement, thermal embrittlement, and stress-corrosion cracking.

Encapsulation A protective process where an assembly is sealed using inhibited organic sealants, plastic caps, or casting compounds to isolate it from the environment.

Endurance Limit The maximum stress that a material can withstand indefinitely under cyclic loading without experiencing fatigue failure.

Environment The surrounding conditions, including physical, chemical, and mechanical factors, in which a material exists and interacts.

Environmental Cracking Brittle failure of a normally ductile material caused by the combined effects of stress and a corrosive environment. It includes stress-corrosion cracking, hydrogen embrittlement, and corrosion fatigue.

Environmentally Assisted Embrittlement A reduction in toughness or ductility caused by environmental factors such as corrosion or chemical exposure, often leading to brittle failure.

Epoxy A class of resins formed by the reaction of bisphenol and epichlorohydrin, commonly used in coatings and adhesives for their durability and chemical resistance.

Equilibrium (Reversible) Potential The potential of an electrode at which the forward and reverse rates of an electrochemical reaction are balanced, creating a state of dynamic equilibrium.

Erosion The mechanical removal of material from a surface due to the abrasive action of moving fluids, often accelerated by solid particles in suspension.

Erosion and Erosion-Corrosion Erosion involves purely mechanical wear, while erosion-corrosion is a combined effect of mechanical wear and chemical or electrochemical reactions. It often produces directional grooves, gullies, or pitted patterns on metal surfaces.

Erosion-Corrosion The accelerated removal of material caused by the combined effects of mechanical abrasion and chemical or electrochemical corrosion, often observed in fluid systems.

Erosion/Erosion-Corrosion Material loss caused by mechanical wear from solids, liquids, or gases in motion, sometimes combined with corrosion. Erosion-corrosion accelerates damage by removing protective films or scales, typically in areas like elbows, impellers, and nozzles exposed to high-velocity flow.

Etch The controlled corrosion of a metal surface to reveal its composition and microstructure.

Ethanol Stress Corrosion Cracking Stress corrosion cracking that occurs in carbon steel equipment exposed to ethanol-containing environments under tensile stress. This is a common concern in pipelines and tanks used in ethanol fuel storage and transportation.

Eutectic A reversible isothermal reaction where a liquid transforms into two or more solid phases simultaneously, producing an intermixed structure of the resulting solids.

Eutectoid A reversible isothermal reaction where a solid transforms into two or more intimately mixed solid phases, commonly seen in steels as the transformation of austenite into ferrite and cementite.

Exchange Current The rate at which anodic and cathodic reactions occur at an electrode in equilibrium, where the net current is zero.

Exchange Current Density The rate of charge transfer per unit area at an electrode when it is in equilibrium, expressed as a measure of the electrode's reaction activity.

Exfoliation A type of localized corrosion where metal layers parallel to the surface separate, creating a laminated or flaky appearance, commonly seen in aluminum alloys.

External Circuit The external components, such as wires, connectors, and current sources, that enable the flow of electrons in an electrochemical cell.

Failure The condition where a material or component becomes inoperable, unreliable, or unsafe due to structural degradation or fracture.

Faraday's Law A principle stating that the amount of material dissolved or deposited during electrolysis is proportional to the total electric charge passed. Additionally, different substances react proportionally to their equivalent weights under the same charge.

Fatigue The progressive cracking or fracture of a material under repeated cyclic loading, often resulting in characteristic features like beach marks on fracture surfaces.

Fatigue Crack Growth Rate The rate at which a crack extends under cyclic loading, typically expressed as crack extension per load cycle.

Fatigue Life The number of stress cycles a material can endure before failure under specified test conditions.

Fatigue Limit The maximum cyclic stress level that a material can withstand indefinitely without experiencing fatigue failure.

Fatigue Strength The maximum stress a material can endure for a specified number of cycles without failure, often under completely reversed stress conditions.

Ferrite A solid solution of one or more elements in body-centered cubic iron (BCC). In steels, ferrite is generally low in carbon content and forms a soft, ductile phase.

Ferritic Relating to materials with a body-centered cubic (BCC) crystal structure, commonly found in certain stainless steels and low-carbon steels.

Ferritic Stainless Steels A class of stainless steels including Types 405, 409, 410S, 430, 442, and 446, characterized by their ferritic microstructure, high resistance to oxidation, and magnetic properties.

Filiform Corrosion A localized corrosion phenomenon that occurs under thin coatings, forming fine, thread-like corrosion patterns.

Filler Metal A metal added during welding, brazing, or surfacing to fill the joint or build up the surface.

Filler Rod A filler metal in the form of a rod used in welding or brazing processe

Film A thin layer of material, not necessarily visible, that forms on a surface, often as a result of oxidation or other chemical reactions.

Fish Eyes Circular areas with a characteristic white crystalline appearance on a steel fracture surface, often indicating brittle fracture or inclusions.

Flakes Short, discontinuous internal fissures in wrought metals, typically caused by stresses from cooling after hot working. On etched surfaces, they appear as short cracks; also known as shatter cracks or snowflakes.

Flame Hardening A surface-hardening process using an oxyacetylene torch to rapidly heat the surface of metal, followed by rapid cooling to increase surface hardness.

Flame Spraying A thermal spraying process in which a coating material is melted in an oxyfuel gas flame and then sprayed onto a substrate, often using compressed gas for atomization and propulsion.

Flue Gas Dew Point Corrosion Corrosion caused by the condensation of acidic gases (e.g., SO2, HCl) in flue gas when temperatures drop below the acid dew point. This damage typically occurs in chimneys, economizers, and other equipment in contact with flue gas streams.

Flux A material used during welding, brazing, or soldering to clean the joint, prevent oxidation, and aid in fusion by reducing impurities.

Fogged Metal A metal surface whose luster is reduced by a surface film, usually composed of corrosion products or environmental deposits.

Foreign Structure Any metallic structure not intended to be part of a cathodic protection system but that could interact electrically or environmentally with the system.

Fouling The accumulation of unwanted deposits, including marine organisms on underwater surfaces or inorganic deposits in heat exchangers.

Fouling Organism An aquatic organism that attaches to submerged structures, such as ships, during its sessile adult stage, contributing to fouling.

Fractography The study and characterization of fracture surfaces, often using photographs at low (macrofractography) or high magnifications (microfractography), to determine the causes and mechanisms of failure.

Fracture Mechanics A field of study focusing on the relationship between material properties, applied stresses, crack geometry, and structural behavior to predict failure.

Fracture Toughness A measure of a material's resistance to the propagation of cracks, determined using specific fracture mechanics tests.

Free Carbon Carbon present in steel or cast iron in elemental form, such as graphite, as opposed to being chemically combined in carbides.

Free Corrosion Potential The naturally occurring electrochemical potential of a metal surface in an electrolyte, without any external electrical current.

Free Ferrite Ferrite that forms directly from the cooling of hypoeutectoid austenite, without simultaneous formation of cementite. Also called proeutectoid ferrite.

Free Machining A characteristic of alloys that allows easy machining with small, broken chips, lower power consumption, and longer tool life, often achieved by adding elements like sulfur, lead, or bismuth.

Fretting A type of wear caused by cyclic, small-amplitude motion between tightly fitted surfaces. Often accompanied by corrosion, it leads to material degradation and can cause significant damage over time.

Fretting Corrosion A form of erosion-corrosion caused by repeated small-amplitude motion between contacting surfaces, resulting in wear and accelerated oxidation.

Fuel Ash Corrosion A type of high-temperature corrosion caused by the deposition and melting of ash constituents, such as vanadium, sodium, or sulfur compounds, on metal surfaces. This damage occurs in boilers, furnaces, and other high-temperature equipment where ash from burning fuels accumulates.

Furan A type of resin derived from reactions involving furfuryl alcohol, often used in industrial applications for its chemical resistance.

Fusion Penetration The depth to which the base metal has been melted and fused during a welding process.

Fusion Welding A welding process where the weld is formed by melting the base metals, often without applying external pressure.

Fusion Zone The part of the base metal that has melted and fused with the weld material.

Galvanic Pertaining to the electrochemical interaction resulting from the coupling of dissimilar electrodes in an electrolyte, which produces an electric current.

Galvanic Anode A sacrificial metal that corrodes preferentially to protect a more noble metal in a galvanic couple, often used in cathodic protection systems.

Galvanic Cell An electrochemical cell where a chemical reaction generates electrical energy, often involving two dissimilar conductors in contact with each other and an electrolyte.

Galvanic Corrosion Corrosion that occurs when two dissimilar metals are electrically connected in a conductive environment, causing the less noble metal to corrode preferentially.

Galvanic Corrosion Corrosion that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte. The more anodic metal corrodes preferentially, while the cathodic metal is protected. This is common in marine environments and piping systems with dissimilar metal connections.

Galvanic Couple A pair of dissimilar metals in electrical contact, often leading to galvanic corrosion due to potential differences.

Galvanic Couple Potential See mixed potential.

Galvanic Current The electrical current that flows between two metals or conductive materials in a galvanic couple, driven by their potential difference.

Galvanic Series A list of metals and alloys arranged according to their relative corrosion potentials in a specific environment, often seawater, showing their tendency to act as anodes or cathodes in galvanic corrosion.

Galvanize The process of coating a metal, typically steel or iron, with a layer of zinc to protect it from corrosion, commonly done using methods like hot-dip galvanizing or electroplating.

Galvanizing The process of applying a zinc coating to steel or iron to prevent rusting, often performed by immersing the metal in molten zinc (hot-dip galvanizing).

Galvanneal A process that produces a zinc-iron alloy coating on steel or iron by allowing the molten zinc coating to fully alloy with the base metal during hot-dip galvanizing.

Galvanometer An instrument used to measure or detect small electric currents through mechanical deflection caused by electromagnetic forces.

Galvanostatic An experimental technique where an electrode is maintained at a constant current in an electrolyte to study corrosion, electrochemical behavior, or surface reactions.

Gamma Iron The face-centered cubic form of pure iron, stable between 910°C and 1400°C (1670°F to 2550°F).

Gaseous Corrosion Corrosion that occurs in the absence of a liquid phase, involving gases as the corrosive agent, often at elevated temperatures; also referred to as dry corrosion.

Gaseous Oxygen-enhanced Ignition and Combustion A failure mechanism caused by the sudden and violent reaction of oxygen-enriched gas streams with combustible materials, resulting in severe damage. This can occur in oxygen-handling systems, particularly if contaminants or hydrocarbons are present.

General Corrosion A form of corrosion that occurs uniformly over an exposed surface, leading to even thinning of the material.

Gibbs Free Energy A thermodynamic property defined as ΔG = ΔH − TΔS, where H is enthalpy, T is temperature, and S is entropy. It determines the spontaneity of chemical reactions.

Glass Electrode A specialized electrode with a glass membrane, commonly used to measure pH by detecting hydrogen-ion activity in a solution.

Grain An individual crystal in a polycrystalline metal or alloy, characterized by an orderly atomic arrangement within its boundaries.

Grain Boundary The interface or transition zone between two adjacent grains in a polycrystalline metal, where the atomic arrangements are misaligned.

Grain-Boundary Corrosion Also known as intergranular corrosion, this occurs along grain boundaries in a material, often due to segregation of impurities or depletion of protective elements like chromium.

Graphitic Corrosion The selective leaching of metallic constituents from gray cast iron, leaving behind a weakened structure of intact graphite.

Graphitic Corrosion of Cast Irons Selective leaching of iron in cast iron, leaving behind a weakened structure of graphite. Commonly found in buried pipelines and components exposed to groundwater or other aqueous environments, this form of damage is also referred to as "graphitization."

Graphitization A metallurgical phenomenon in which carbide phases in certain steels, particularly at high temperatures, decompose into graphite and ferrite. This reduces the strength and toughness of the material, leading to potential failure. It typically occurs in equipment exposed to long-term high temperatures.

Graphitization A metallurgical process where iron carbide decomposes to form graphite at elevated temperatures; not to be confused with graphitic corrosion.

Green Liquor A solution of sodium carbonate and sodium sulfide formed by dissolving smelt in water, commonly used in the kraft process for pulping wood.

Green Rot A form of high-temperature corrosion in chromium-containing alloys, where chromium oxide (Cr₂O₃) forms alongside remaining metallic constituents.

Ground Bed A buried assembly, often made of graphite or scrap metal, that serves as an anode in cathodic protection systems for pipelines or other underground structures.

Half Cell A system consisting of a pure metal in contact with a solution of its ions, developing a reproducible potential, often used to measure the potential of other systems when paired in an electrochemical cell.

Halogen Any element from the halogen group, including fluorine, chlorine, bromine, iodine, and astatine, known for their high reactivity.

Hard Chromium A thick layer of electroplated chromium, applied for engineering purposes to enhance wear resistance or reduce friction rather than decorative use.

Hard Water Water containing dissolved minerals like calcium or magnesium salts, which can form scale deposits in boilers or interfere with soap's cleaning action.

Hardenability A material's ability to form martensite throughout its structure during quenching, typically measured by hardness depth from the surface.

Hardfacing A process of depositing a wear-resistant material onto a surface by welding, brazing, or spraying, to improve resistance to abrasion, erosion, or impact.

Heat Check A network of surface cracks caused by repeated rapid heating and cooling, often seen on tools and dies subjected to thermal cycling.

Heat-Affected Zone (HAZ) The portion of the base metal adjacent to a weld, brazed, or cut area where microstructural changes have occurred due to thermal cycling, affecting properties like corrosion resistance.

Hematite A naturally occurring iron oxide (Fe₂O₃) and an important iron ore, known for its reddish-brown color and high iron content (around 70%).

Hermetic Seal A gas- or moisture-tight seal, typically made by fusing metals or ceramics, used to protect sensitive components from environmental exposure.

High-Strength Low-Alloy Steel (HSLA) A family of carbon steels with enhanced strength achieved through the addition of small amounts of alloying elements like titanium, vanadium, and niobium. HSLA steels are more prone to hydrogen embrittlement during fabrication.

High-Temperature Hydrogen Attack A form of damage in steels caused by high-temperature hydrogen reacting with carbides to form methane, leading to decarburization, internal fissures, and loss of strength and ductility.

High-temperature H2/H2S Corrosion Corrosion caused by high-temperature hydrogen sulfide (H2S) environments, where sulfide scale formation provides limited protection to underlying metal. Carbon steels and low-alloy steels are most commonly affected, particularly in process units handling high-pressure hydrogen and sulfur compounds.

High-temperature Hydrogen Attack A damage mechanism in steels exposed to high-temperature hydrogen environments, where hydrogen reacts with carbon in the steel to form methane. This results in decarburization, internal fissuring, and strength reduction, commonly seen in reformers and hydrogen service equipment.

Holidays Discontinuities in a coating, such as porosity or cracks, that expose the base material to the environment, leading to potential corrosion.

Hot Corrosion Accelerated metal deterioration caused by the combined effects of oxidation and reactions with contaminants, such as sulfates or chlorides, forming molten salts that disrupt protective oxide layers.

Hot Cracking Also called solidification cracking, this occurs in weldments when low-melting-point constituents segregate along grain boundaries, causing tearing under thermal contraction stresses during cooling.

Hot Dip Coating A protective metallic coating applied by immersing the base material into molten metal, such as zinc, aluminum, or tin.

Hot Shortness The tendency of some alloys to crack along grain boundaries when stressed or deformed at temperatures near their melting points due to the presence of low-melting-point constituents.

Hot Working Deformation of metals at temperatures high enough to allow recrystallization to occur simultaneously with the deformation, preventing strain hardening.

Huey Test A corrosion test performed by boiling stainless steel in nitric acid to assess its susceptibility to intergranular corrosion.

Humidity Test A controlled corrosion test where specimens are exposed to specific levels of humidity and temperature to evaluate their resistance to moisture-related degradation.

Hydrochloric Acid Corrosion Corrosion of metallic materials caused by exposure to hydrochloric acid (HCl) in liquid or vapor phases. Carbon steel and low-alloy steels are particularly vulnerable, especially in environments with high acidity and chloride concentrations, such as in overhead systems of crude distillation units.

Hydrofluoric Acid Corrosion Corrosion caused by exposure to hydrofluoric acid (HF), a highly aggressive chemical. HF can corrode carbon steel and many alloys, depending on its concentration, temperature, and water content, often used in alkylation units.

Hydrofluoric Acid Stress Corrosion Cracking of Nickel Alloys Stress corrosion cracking of nickel-based alloys exposed to hydrofluoric acid, typically occurring under high tensile stress. This damage is a concern in equipment handling concentrated HF, such as in alkylation units.

Hydrogen Blistering The formation of blisters on or beneath a metal surface due to excessive internal pressure caused by hydrogen gas accumulation, often originating from corrosion or plating processes.

Hydrogen Damage A general term for deterioration in metals caused by hydrogen, including embrittlement, blistering, or decarburization, often exacerbated by high temperature or pressure.

Hydrogen Disintegration Formation of deep internal cracks within a metal due to the accumulation of hydrogen under high pressures, leading to severe structural damage.

Hydrogen Embrittlement Reduction in ductility and toughness of a metal due to the presence of atomic hydrogen. It occurs through internal or environmental hydrogen absorption, often resulting in cracking under stress.

Hydrogen Embrittlement A degradation process where atomic hydrogen diffuses into metals, reducing ductility and toughness. This can result in cracking or failure under tensile stress. High-strength steels and some alloys are particularly vulnerable, especially in environments with hydrogen gas or cathodic protection systems.

Hydrogen Overvoltage The extra voltage required to liberate hydrogen gas during an electrochemical reaction, beyond the theoretical electrode potential.

Hydrogen Probes Devices designed to measure the rate of hydrogen permeation through a material, often used to detect and assess hydrogen-induced cracking.

Hydrogen Stress Cracking (HSC) Cracking caused by hydrogen embrittlement under tensile stress.

Hydrogen Stress Cracking in Hydrofluoric Acid Cracking caused by the absorption of hydrogen in metals exposed to hydrofluoric acid environments under stress. This mechanism is a significant concern for carbon steels and low-alloy steels in HF service.

Hydrogen Sulfide (H₂S) A toxic and corrosive gas whose concentration affects material behavior. Classified as "low H₂S" (3–6 ppm), "high H₂S" (>6 ppm), or environments containing more than 1 ppm of H₂S.

Hydrogen-Assisted Cracking (HAC) Cracking induced by hydrogen embrittlement.

Hydrogen-Assisted Stress-Corrosion Cracking (HSCC) Stress-corrosion cracking influenced by the presence of hydrogen.

Hydrogen-Controlled Electrode A welding electrode designed to minimize hydrogen in the weld deposit, reducing the risk of hydrogen-induced cracking.

Hydrogen-Induced Cracking (HIC) Formation of internal cracks within metals caused by hydrogen embrittlement, often resulting from hydrogen diffusion into the material.

Hydrolysis A chemical reaction in which water decomposes a compound, producing a weak acid or base in aqueous solutions of electrolytes.

Hydrophilic A material or surface that attracts and absorbs water. Opposite of hydrophobic.

Hydrophobic A material or surface that repels water, preventing wetting or absorption. Opposite of hydrophilic.

Hygroscopic A substance that readily absorbs moisture from the atmosphere, altering its physical properties.

Immersion Plating A process of depositing a metallic coating onto a material by immersing it in a solution, without using an external electric current.

Immunity The condition where a metal resists corrosion due to its thermodynamic stability in a specific environment.

Impingement Corrosion Localized erosion-corrosion caused by high-velocity fluid impinging on a solid surface, often leading to accelerated material loss.

Impressed Current An externally supplied direct current used to provide cathodic protection for a metal structure, making it the cathode in a corrosion cell.

Impressed Current Protection A method of cathodic protection where external current is used to polarize a metal surface cathodically, reducing its corrosion rate.

Inclusions Foreign particles, such as oxides or sulfides, trapped within a metal matrix during solidification, affecting its mechanical and corrosion properties.

Incubation Period The time period during which no detectable corrosion occurs after a metal is first exposed to a corrosive environment.

Industrial Atmosphere An environment characterized by pollutants like soot, fly ash, and sulfur compounds, often accelerating corrosion.

Inert Anode An anode that remains insoluble in the electrolyte during electrolysis, ensuring minimal material loss.

Inhibitor A chemical substance that reduces or prevents corrosion when added to an environment in the proper concentration.

Inorganic Substances not based on hydrocarbons or their derivatives, including minerals and metals. Contrast with organic.

Inorganic Zinc-Rich Paint A coating composed of zinc powder pigment in an inorganic binder, offering sacrificial corrosion protection.

Intensiostatic Synonymous with galvanostatic, referring to maintaining a constant current in an electrochemical cell.

Intercrystalline Corrosion Corrosion that occurs along grain boundaries of metals, often caused by compositional differences or impurities.

Intercrystalline Cracking Cracking along the grain boundaries of a polycrystalline material, often caused by stress or environmental factors.

Interdendritic Corrosion Corrosion progressing preferentially along the spaces between dendrites in cast alloys, often due to compositional variations or impurities.

Intergranular Refers to areas located between grains or crystals in a polycrystalline material. Also known as intercrystalline. Contrast with transgranular.

Intergranular Corrosion Selective attack along the grain boundaries of a material, often due to compositional differences or impurities. Commonly observed in sensitized austenitic stainless steels near weld zones.

Intergranular Cracking Fracturing or cracking along the grain boundaries of a polycrystalline material. Also called intercrystalline cracking. Contrast with transgranular cracking.

Intergranular Fracture A brittle fracture that occurs along the grain boundaries of a metal, leaving the grains intact. Contrast with transgranular fracture.

Intergranular Stress-Corrosion Cracking (IGSCC) Stress-corrosion cracking localized along the grain boundaries of a material, often leading to brittle fracture.

Intermediate Electrode A bipolar electrode located between the anode and cathode in an electrochemical system, functioning as both a cathode and an anode simultaneously.

Internal Oxidation The formation of corrosion products beneath the surface of a metal, caused by the inward diffusion of reactive elements like oxygen or sulfur.

Intumescence The swelling or bubbling of a coating, often due to exposure to heat. Commonly used in fire protection applications.

Ion An atom or group of atoms that has gained or lost electrons, resulting in an electric charge. Positively charged ions are cations, and negatively charged ions are anions.

Ion Erosion Material loss caused by the impact of high-energy ions on a surface.

Ion Exchange A reversible process where ions in a liquid are exchanged with ions on a solid substrate without altering the solid's structure.

Iron Rot Degradation of wood in contact with iron or iron alloys due to chemical interactions.

Isocorrosion Diagram A chart depicting constant corrosion rates under varying environmental conditions, such as solution composition and temperature.

KISCC The critical value of the plane strain stress-intensity factor that causes stress-corrosion cracking in a specific material under given environmental conditions.

Killed Steel Steel that has been fully deoxidized by adding elements like aluminum or silicon, preventing gas evolution during solidification and resulting in a cleaner microstructure.

Knifeline Attack A form of intergranular corrosion that occurs in stabilized stainless steels near weld zones when exposed to sensitization temperatures, typically resulting in sharp, narrow attack along the weld line.

Kraft Process A wood-pulping method using sodium sulfate in the digestion liquor to produce strong paper products. Also known as sulfate pulping.

Lamellar Tearing A step-like cracking near welds in the base metal caused by through-thickness strains from weld metal shrinkage. Often occurs in highly restrained joints and can be mitigated with proper design.

Laminar Scale Rust formation in the form of thick, layered deposits.

Langelier Saturation Index A calculated index that indicates the tendency of water to precipitate or dissolve calcium carbonate, based on factors like pH, temperature, and dissolved solids.

Ledeburite A eutectic microstructure in iron-carbon alloys consisting of austenite and cementite. Upon cooling, austenite transforms into ferrite and cementite.

Ligand A molecule, ion, or group that binds to a central atom in a coordination compound or chelate.

Limiting Current Density The maximum current density that can be achieved for a desired electrode reaction before polarization or other effects interfere.

Linear Elastic Fracture Mechanics (LEFM) A fracture analysis method to determine the stress required to propagate a crack in a material, based on the crack size and geometry.

Linear Polarization Resistance (LPR) A method to measure the corrosion rate by determining the resistance to polarization at small applied potentials near the corrosion potential.

Lipophilic A material with an affinity for oils or nonpolar substances. Contrast with hydrophilic and hydrophobic.

Liquid Metal Embrittlement A catastrophic failure mechanism in which ductile metals become brittle when in contact with certain liquid metals, such as molten zinc or cadmium. This typically occurs under tensile stress and is observed in brazing, galvanizing, or high-temperature applications.

Liquid Metal Embrittlement (LME) Catastrophic failure of a normally ductile material caused by exposure to a liquid metal while under tensile stress.

Local Action Corrosion caused by localized galvanic cells that develop due to inhomogeneities on a metal surface in contact with an electrolyte.

Local Cell A galvanic cell formed by physical or chemical differences between adjacent areas on a metal surface in an electrolyte.

Localized Corrosion Corrosion that occurs at specific, discrete areas on a metal surface, such as pitting or stress-corrosion cracking.

Long-line Current Current flowing through the earth from an anodic area to a cathodic area on a continuous metallic structure, typically caused by concentration-cell action and spanning significant distances.

Low-Alloy Steel A category of steels containing up to 9% chromium and other alloying elements, designed for high-temperature strength and resistance to creep. Common grades include 1Cr-0.5Mo, 2.25Cr-1Mo, and 9Cr-1Mo. These are typically ferritic in structure.

Luggin Probe (Luggin–Haber Capillary) A capillary tube filled with electrolyte that provides an ionic conducting path without significant diffusion, positioned near a surface under study to improve accuracy in potential measurements.

MIG Welding (Metal Inert Gas Welding) A type of arc welding that uses a consumable electrode and an inert shielding gas to protect the weld from atmospheric contamination.

Macroscopic Pertains to features of a material visible at magnifications of 25× or less.

Macrostructure The structure of a metal as observed on a polished and etched surface at low magnification, revealing features such as grain size, segregation, and porosity.

Magnetite A naturally occurring iron oxide (Fe₃O₄) with magnetic properties, commonly found in corrosion products of iron and steel.

Manual Welding A welding process where the welder manually controls both the welding device and the application of the weld, often involving a hand-held torch or electrode holder.

Martensite A hard, brittle microstructure formed in steels and other alloys through diffusionless phase transformation, characterized by acicular patterns and high strength.

Martensitic Refers to a hard microstructure (martensite) formed through rapid cooling (quenching) after heat treatment or welding. Martensite often requires tempering to reduce brittleness for industrial use.

Martensitic Stainless Steel A group of stainless steels including grades such as 410, 416, 420, and 440C. These steels are characterized by their martensitic structure, offering hardness and moderate corrosion resistance.

Mechanical Fatigue (Including Vibration-induced Fatigue) Failure caused by cyclic or fluctuating stresses that lead to crack initiation and propagation. This includes vibration-induced fatigue, which occurs in piping and rotating equipment subjected to repeated dynamic loading.

Mechanical Plating A method of coating metals by tumbling them with fine metal powders and impact media to produce an adherent layer without the use of electricity or heat.

Metal Arc Welding An arc welding process that uses a consumable electrode to create the weld. The electrode serves as both the heat source and the filler material.

Metal Dusting A form of accelerated corrosion in high-temperature carbonaceous environments, where metal surfaces are converted to metal dust. This damage is often seen in equipment handling synthesis gas or reducing atmospheres at temperatures between 900 °F and 1500 °F (482 °C and 815 °C).

Metal Dusting A high-temperature corrosion process in which carbonaceous gases degrade metals, forming a dust-like corrosion product and sometimes pitting. Often accompanied by simultaneous carburization.

Metal Ion Concentration Cell A galvanic cell caused by variations in the concentration of metal ions at different locations on the same metal surface, leading to localized corrosion.

Metallic Glass An amorphous alloy with a glass-like structure, lacking the regular crystalline arrangement of atoms typically found in metals.

Metallizing The application of metallic coatings to a surface by methods such as thermal spraying, vapor deposition, or electrodeposition, often to enhance corrosion resistance or conductivity.

Meteor Perforation Damage to materials in outer space caused by impacts from meteors or other space debris.

Methyl Diethanolamine (MDEA) A chemical used in amine treating processes to remove hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from hydrocarbon streams, often favored for its lower corrosion potential compared to other amines.

Microbiologically Influenced Corrosion (MIC) Corrosion significantly accelerated by the activity of microorganisms such as sulfate-reducing or acid-producing bacteria.

Microbiologically Influenced Corrosion (MIC) Corrosion that is accelerated or influenced by microbial activity. Sulfate-reducing bacteria, acid-producing bacteria, and other microorganisms create localized conditions that lead to pitting or under-deposit corrosion in aqueous systems such as cooling water, pipelines, or storage tanks.

Microscopic Pertains to features of a material observable only at magnifications above 25×, typically using a microscope.

Microstructure The arrangement and features of a material as observed under a microscope, including grain boundaries, phases, and defects at high magnification.

Mill Scale An oxide layer formed on the surface of metals during processes like hot rolling, welding, or heat treatment, commonly removed to improve surface finish or coating adhesion.

Mixed Potential The potential of a metal surface in an electrolyte where multiple electrochemical reactions occur simultaneously, such as anodic and cathodic processes.

Molal Solution A solution with a concentration expressed as moles of solute per 1000 grams of solvent.

Molar Solution A solution containing 1 mole of solute per liter of solution, commonly used as a standard concentration in chemistry.

Mole A unit representing the amount of substance containing 6.022×10236.022 \times 10^{23}6.022×1023 elementary entities (e.g., atoms, molecules, or ions), equivalent to the molecular weight expressed in grams.

Monoethanolamine (MEA) A chemical compound commonly used in amine gas treating to remove hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from gas streams.

Monomer A small molecule capable of reacting with identical or different molecules to form a polymer through a chemical bonding process.

Naphthenic Acid Corrosion Corrosion caused by naphthenic acids in crude oils, occurring at elevated temperatures in atmospheric and vacuum distillation units. This type of corrosion primarily affects carbon and low-alloy steels and is influenced by factors such as acid concentration, temperature, and velocity.

Neutralization A chemical reaction in which an acid and a base react to form a salt and water, typically resulting in a neutral pH.

Nickel Plating The process of applying a thin layer of nickel to a substrate by electroplating or electroless methods for corrosion resistance or decorative purposes.

Nickel-Based Alloys A class of alloys with nickel as the primary element (>30%), including grades such as Alloy 625, C276, and 718, known for exceptional corrosion resistance, especially in high-temperature environments.

Nitriding A form of surface hardening caused by nitrogen diffusion into the metal, leading to brittle nitride phases. It occurs in high-temperature environments with nitrogen-rich gases, such as in furnaces, resulting in embrittlement and cracking of components.

Nitriding A surface-hardening process in which nitrogen is diffused into the surface of steel at elevated temperatures to form hard nitrides, improving wear and corrosion resistance.

Node A point in a galvanic cell or system where current enters the electrode surface, often referred to as the anode.

Non-Ferrous Metal Metals or alloys that do not contain significant amounts of iron, such as aluminum, copper, and nickel, often valued for their corrosion resistance and low density.

Normalizing A heat treatment process for steel that involves heating to a temperature above its critical range, followed by air cooling, to refine the grain structure and improve mechanical properties.

Notch Sensitivity The tendency of a material to exhibit lower mechanical performance, such as reduced fracture toughness or fatigue strength, due to the presence of notches or other geometric discontinuities.

Nucleation The initial stage in the formation of a new phase or structure, where atoms or molecules arrange themselves into a stable configuration, often preceding the growth of grains or crystals.

Open Circuit Potential The potential of an electrode measured relative to a reference electrode when no current is flowing in the system, representing the equilibrium state of the metal in a given environment.

Organic Coating A protective or decorative layer made from organic compounds such as polymers, resins, or paints, applied to a surface to prevent corrosion or enhance appearance.

Orthorhombic Crystal Structure A crystal system characterized by three unequal axes, all perpendicular to one another, commonly observed in some minerals and metals.

Overaging A condition in age-hardenable alloys where prolonged exposure to elevated temperatures results in coarsening of precipitates, reducing hardness and strength but increasing ductility.

Overpotential The difference between the actual potential of an electrode under current flow and the equilibrium potential, caused by polarization effects during electrochemical reactions.

Oxidation A chemical reaction where a material, typically a metal, reacts with oxygen to form an oxide, often resulting in corrosion or the formation of a protective layer.

Oxidation The reaction of a metal with oxygen to form an oxide layer on the surface. At high temperatures, oxidation can result in the formation of non-protective or scaling oxide layers, leading to material loss and failure, commonly observed in furnace tubes and high-temperature components.

Oxide A compound formed by the reaction of oxygen with another element, often appearing as a thin film on metals that can either protect against or contribute to corrosion.

Oxide Film A thin layer of oxide that forms on the surface of a metal due to oxidation, which can provide corrosion resistance or degrade the material’s properties depending on its composition and environment.

Oxygen Concentration Cell A type of electrochemical cell that forms due to differences in oxygen concentration between two locations on a metal surface, causing localized corrosion at the anode.

Oxygenated Process Water Corrosion Corrosion that occurs in water systems containing dissolved oxygen, which accelerates general corrosion or pitting. This is especially significant in low-temperature systems like cooling water and boiler feedwater systems where oxygen removal is insufficient or ineffective.

Passivation The process by which a metal becomes less chemically reactive, often by forming a protective oxide layer that prevents further corrosion.

Passive Film A thin, stable, and protective oxide layer that forms naturally or through treatment on a metal surface, significantly reducing the rate of corrosion.

Passive State A condition where a metal resists corrosion due to the presence of a protective oxide layer, contrasting with an active state where corrosion occurs readily.

Pearlite A two-phase microstructure found in steels and cast irons, consisting of alternating layers of ferrite and cementite, formed during slow cooling from austenite.

Pencil Electrode A small-diameter electrode used in electrochemical studies to measure localized corrosion or other electrochemical phenomena in confined areas.

Permeation The process by which a substance, such as a gas or liquid, passes through a solid material, often studied in the context of hydrogen diffusion through metals.

pH A measure of the acidity or alkalinity of a solution, defined as the negative logarithm of the hydrogen ion concentration, where a pH below 7 indicates acidity and above 7 indicates alkalinity.

Phenol (Carbolic Acid) Corrosion Corrosion caused by exposure to phenol or carbolic acid, particularly in carbon steel equipment. The damage typically involves general thinning or localized attack, influenced by factors such as phenol concentration, impurities, and temperature.

Phosphate Coating A conversion coating applied to metals using phosphoric acid solutions, providing corrosion resistance and a base for further coating or painting.

Phosphating The process of forming a phosphate coating on a metal surface to enhance corrosion resistance and adhesion of subsequent coatings.

Phosphoric Acid Corrosion Corrosion of metals in environments containing phosphoric acid (H3PO4). Carbon steel and stainless steels are commonly used, but the corrosion rate depends on the acid concentration, temperature, and presence of impurities such as chlorides or fluorides.

Photomicrograph A photograph taken through a microscope, used to document the microstructure of materials for analysis and characterization.

Pilling-Bedworth Ratio A ratio that describes the protective nature of an oxide film formed on a metal, comparing the volume of the oxide to the volume of the metal consumed. Ratios close to 1 indicate better protection against oxidation.

Pit Growth Rate The rate at which localized corrosion, or pitting, deepens into a metal surface, often influenced by environmental factors like chloride concentration.

Pitting Corrosion A localized form of corrosion characterized by small, often deep holes or cavities in a metal surface, commonly caused by chlorides and other aggressive ions.

Plain Carbon Steel Steel containing up to 1.5% carbon, with low levels of silicon (≤ 0.5%) and manganese (≤ 1.5%), and trace amounts of other elements.

Plasma Spray Coating A thermal spraying process that uses a plasma torch to melt and project coating material onto a substrate, forming a dense and wear-resistant layer.

Plastic Deformation The permanent change in shape of a material under stress beyond its elastic limit, where the material does not return to its original dimensions after the load is removed.

Polarization The deviation of an electrode's potential from its equilibrium value caused by the passage of current, often classified as either activation, concentration, or resistance polarization.

Polarization Curve A graph showing the relationship between the current density and the potential of an electrode in an electrochemical system, used to study corrosion and electrochemical reactions.

Polarization Resistance The resistance to changes in current density as an electrode's potential is shifted from equilibrium, often used to estimate corrosion rates in metals.

Polished Specimen A material sample that has been polished to produce a smooth, reflective surface, typically for metallographic or microscopic examination.

Polyester A resin formed by the condensation of polybasic and monobasic acids with polyhydric alcohols.

Polymer A long chain of organic molecules produced by the joining of smaller primary units called monomers.

Polythionic Acid Stress Corrosion Cracking Cracking that occurs in austenitic stainless steels exposed to polythionic acids (formed from sulfide scales and oxygen in wet environments). Typically occurs after shutdowns or cleaning procedures, especially in sulfur-containing refinery units like hydroprocessing or FCC units.

Potential A measure of the driving force behind an electrochemical reaction. It represents various states of intensity in a field, such as corrosion potential, open-circuit potential, or electrode potential.

Potential Surveys The measurement of a structure or pipeline's potential relative to a reference electrode to monitor corrosion activity or cathodic protection.

Potentiodynamic A technique involving the continuous variation of an electrode's potential at a preset rate to study corrosion or electrochemical behavior.

Potentiostat An electronic device used to maintain a constant potential of an electrode, often used in anodic protection systems.

Poultice Corrosion Corrosion caused by the accumulation of road salts, debris, and moisture in automotive parts, typically in pockets or crevices.

Pourbaix Diagram A graph plotting redox potential against pH, showing the thermodynamic stability regions of a metal and its compounds in a specific environment, based on the Nernst equation.

Powder Metallurgy The process of producing metal powders and shaping them into solid materials or objects through compaction and sintering.

Precious Metal Rare and valuable metals such as gold, silver, and platinum-group metals, also referred to as noble metals due to their resistance to corrosion.

Precipitation Hardening Hardening of a material caused by the formation of precipitates from a supersaturated solution, typically achieved through aging.

Precipitation Heat Treatment A heat treatment process used to precipitate a constituent from a supersaturated solid solution, improving material strength.

Precracked Specimen A test specimen that has been intentionally notched and pre-stressed to create a crack for use in fracture mechanics or stress-corrosion testing.

Pressure Welding A welding process where sufficient pressure, with or without heat, is applied to surfaces to achieve plastic flow and join the materials.

Primary Current Distribution The current distribution in an electrolytic cell unaffected by electrode polarization.

Primary Passive Potential The potential at which a metal transitions from an active to a passive state during corrosion, typically corresponding to a maximum active current density.

Primer The initial coating applied to a surface to promote adhesion of subsequent layers, enhance corrosion protection, or improve surface bonding.

Principal Stress The maximum or minimum normal stress at a point on mutually perpendicular planes, with no shear stress present on these planes.

Profile The anchor pattern or texture of a surface, often created by abrasive blasting or acid etching, to enhance coating adhesion.

Protective Potential The corrosion potential threshold required to achieve cathodic protection, reducing or halting corrosion.

Protective Potential Range The range of corrosion potentials within which acceptable corrosion resistance is achieved for specific applications.

Pulse Width (Ultrasonics) The duration of a single transmitted pulse in ultrasonic testing.

Quench Age Embrittlement Embrittlement caused by rapid cooling of low-carbon steels, leading to carbon precipitation and increased hardness, often mitigated by controlled quenching.

Quench Aging Aging caused by rapid cooling of a material after solution heat treatment, leading to the precipitation of secondary phases.

Quench Cracking Cracking that occurs during quenching, typically in hardened steels, due to high internal stresses caused by rapid cooling and transformation to martensite.

Quench Hardening Hardening achieved by austenitizing a material and rapidly cooling it to form martensite or other hard microstructures.

Quenching The rapid cooling of metals from an elevated temperature to achieve desired mechanical properties, often involving immersion in water, oil, or forced air.

Radiation Damage Alteration of material properties due to exposure to ionizing radiation, such as X-rays, gamma rays, or neutron radiation.

Radiography (X-Ray) A non-destructive testing method that uses X-rays to detect internal imperfections or measure material thickness.

Rare Earth Metal A group of 15 chemically similar metals with atomic numbers 57 through 71, known as the lanthanides, often used in high-tech applications due to their unique magnetic, optical, and catalytic properties.

Reactive Metal Metals such as titanium, zirconium, and beryllium that combine readily with oxygen at elevated temperatures to form stable oxides; they may also become embrittled by interstitial absorption of gases.

Recrystallization Formation of a new, strain-free grain structure in cold-worked metal by heating; also refers to structural changes from one crystal form to another during heating or cooling.

Redox Potential The potential of a reversible oxidation-reduction electrode, measured relative to a reference electrode and adjusted to a standard hydrogen electrode scale.

Reducing Agent A chemical compound that donates electrons to another substance, causing its reduction and becoming oxidized in the process.

Reduction A chemical reaction involving a gain of electrons and a decrease in valence; the opposite of oxidation.

Reference Electrode A stable, non-polarizable electrode with a known potential used to measure the electrode potential of another system in electrochemical analyses.

Refractory Degradation Damage to refractory linings due to chemical attack, thermal cycling, mechanical stresses, or erosion in high-temperature environments such as furnaces, reactors, and boilers. Common factors include slagging, spalling, and reactions with alkalis or acids.

Refractory Metal Metals with extremely high melting points, such as tungsten, molybdenum, and tantalum, used in high-temperature applications due to their resistance to heat and wear.

Relative Humidity The ratio, expressed as a percentage, of the water vapor present in the air to the maximum amount of water vapor the air can hold at the same temperature.

Residual Stress Internal stresses remaining in a material after it has been subjected to mechanical deformation or thermal treatment, which can influence its structural performance.

Resistance The opposition offered by a material to the flow of electrical current, calculated as the voltage drop across it divided by the current.

Resistance Welding A welding process in which heat generated by electrical resistance at the joint is combined with applied pressure to join materials.

Resistivity The property of a material that quantifies its opposition to electric current flow, expressed as resistance times the cross-sectional area per unit length.

Resolution (Ultrasonics) The ability of an ultrasonic system to distinguish between two closely spaced defects in depth or lateral position.

Rest Potential The potential of a metal in an electrolyte in the absence of any net current flow; also called the corrosion or open-circuit potential.

Ringworm Corrosion A localized form of corrosion observed in oil-well tubing, characterized by circumferential attack near regions of mechanical upset.

Riser (1) A vertical section of pipeline extending from the ocean floor to a platform. (2) A reservoir of molten metal in casting that compensates for shrinkage during solidification.

Run A single pass of deposited metal or weld bead during a welding operation.

Rust A reddish-brown corrosion product primarily consisting of hydrated ferric oxide, formed on iron or steel when exposed to moisture and oxygen.

Rusting The corrosion of iron or iron-based alloys leading to the formation of rust as the primary product.

S-N Diagram A graph showing the relationship between applied stress (S) and the number of cycles (N) a material can endure before fatigue failure.

Sacrificial Anode A metal electrode deliberately made anodic to protect a more noble metal structure from corrosion by undergoing galvanic corrosion itself.

Sacrificial Protection The protection of a metal by coupling it with a more active metal that preferentially corrodes in its place.

Salt Fog Test An accelerated corrosion test where specimens are exposed to a fine mist of a salt solution to evaluate their resistance to corrosion.

Salt Spray Test A synonym for the salt fog test, commonly used for testing corrosion resistance of coatings and materials.

Saturated Calomel Electrode A reference electrode consisting of mercury, mercurous chloride (calomel), and a saturated aqueous chloride solution.

Scaling (1) Formation of thick corrosion products on a metal surface at high temperatures. (2) Deposition of water-insoluble materials, such as calcium carbonate, on metal surfaces in contact with water.

Season Cracking An outdated term describing stress-corrosion cracking of brass under corrosive conditions.

Selective Corrosion Preferential removal of specific alloying elements from a metal, such as dezincification of brass or dealloying of aluminum bronzes.

Selective Leaching A corrosion process where specific elements in an alloy are removed, often in stagnant or deposit-covered areas, potentially weakening the material without significantly changing its overall dimensions.

Semi-Automatic Welding Welding where certain variables, like wire feed, are controlled automatically, but manual guidance is required to direct the weld.

Sensitization The precipitation of chromium carbides at grain boundaries in austenitic stainless steels when exposed to temperatures between 550°C and 850°C, making them more susceptible to intergranular corrosion.

Sensitization Heat Treatment A heat treatment process, intentional or incidental, that causes precipitation of constituents at grain boundaries, often leading to susceptibility to intergranular corrosion or cracking.

Shear A force that causes parts of a material to slide relative to each other along parallel planes.

Shear Strength The stress required to fracture a material in a plane of cross-section under shear loading, calculated as the maximum load divided by the cross-sectional area.

Sherardising A zinc-coating process where the steel or iron is heated in zinc powder at temperatures below zinc's melting point, forming a diffusion coating.

Short-term Overheating-Stress Rupture (Including Steam Blanketing) Failure resulting from localized overheating, often caused by steam blanketing or insufficient cooling. This leads to rupture in materials like carbon steel or low-alloy steel, typically seen in boiler tubes or other heat exchanger components exposed to thermal stress.

Sigma Phase A brittle, hard intermetallic phase that forms in certain alloys during prolonged exposure to high temperatures, often causing reduced ductility and toughness.

Sigma Phase Embrittlement A brittle condition resulting from the precipitation of sigma phase (a hard intermetallic compound) in stainless steels during long-term exposure to elevated temperatures (1000–1600 °F or 540–870 °C). This results in reduced toughness, ductility, and susceptibility to intergranular cracking.

Sigma-Phase Embrittlement A type of embrittlement caused by the precipitation of sigma phase in iron-chromium alloys, such as stainless steel, during long exposure to temperatures between 560°C and 980°C, leading to brittleness and corrosion susceptibility.

Slip Plastic deformation in crystalline materials caused by shear displacement along specific crystallographic planes and directions.

Slow Strain Rate Technique A test method for stress-corrosion cracking susceptibility that involves pulling a specimen to failure at a controlled slow strain rate in a corrosive environment.

Slushing Compound An outdated term for oil or grease coatings applied to provide temporary protection against atmospheric corrosion.

Smelt A molten mixture of inorganic materials, commonly used in the pulp and paper industry to recover cooking chemicals.

Soft Water Water that is free of hardness-causing salts, such as magnesium or calcium, often used to prevent scale formation.

Soil Corrosion Corrosion caused by environmental factors in buried or partially buried structures such as pipelines or storage tanks. The rate of attack depends on soil resistivity, moisture content, pH, and presence of chlorides or sulfates, often leading to localized pitting or general thinning.

Soil Resistivity The electrical resistivity of soil, which influences current distribution and potential levels in cathodic protection systems for buried structures.

Solder Embrittlement A reduction in mechanical properties caused by solder penetration along grain boundaries.

Solid Solution A homogeneous crystalline phase containing two or more elements, with the solute atoms dispersed uniformly within the solvent crystal lattice.

Solid-Metal Embrittlement Embrittlement occurring below the melting point of an embrittling metal species, distinct from liquid-metal embrittlement.

Solution A homogeneous mixture of two or more components, which may be gases, liquids, or solids, forming a single phase.

Solution Heat Treatment Heating an alloy to a suitable temperature to dissolve constituents into a solid solution, followed by rapid cooling to retain the dissolved phase.

Solution Potential The electrode potential in a system where the reaction involves only the metal electrode and its ions.

Solvent The primary component of a solution that dissolves the solute.

Sour Gas A hydrocarbon gas containing significant amounts of hydrogen sulfide (H₂S) or carbon dioxide (CO₂), which can cause material degradation in exposed equipment.

Sour Water Wastewater containing sulfur compounds, often with a strong odor, typically from industrial processes.

Sour Water Corrosion (Acidic) Corrosion caused by acidic sour water containing hydrogen sulfide (H2S) and low pH. This is commonly observed in refinery sour water systems and affects carbon steel, particularly in deaerated or high-temperature conditions, leading to pitting or thinning.

Spalling The breaking or chipping off of surface layers due to stresses, often caused by thermal cycling, mechanical forces, or corrosion.

Spatter Globules of molten material expelled during welding, which adhere to the workpiece surface and surrounding areas.

Spelter A brazing alloy composed of approximately 50% copper and 50% zinc, commonly used for joining ferrous metals.

Spheroidite A microstructure of spherical iron or alloy carbides distributed in a ferritic matrix, produced by heat treatment for improved machinability and toughness.

Spheroidization (Softening) A metallurgical phenomenon where carbide particles in steel form spheroidal shapes after prolonged exposure to elevated temperatures, reducing hardness and strength. This is typically seen in heat-affected zones or during improper heat treatment of steels.

Sputtering A coating process where ions are accelerated toward a target material, causing its atoms to dislodge and deposit as a coating on the substrate.

Stabilizing Treatment Heat treatments performed to ensure dimensional stability or to transform retained phases, such as austenite, in metals before final finishing.

Stainless Steel An iron-based alloy containing at least 10.5% chromium, providing corrosion resistance. Stainless steels are categorized into four main groups based on microstructure: austenitic, ferritic, martensitic, and duplex.

Standard Electrode Potential The reversible potential of an electrode under standard conditions, relative to the standard hydrogen electrode.

Steel - Austenite The face-centered cubic (FCC) phase of iron or its solid solutions, stabilized by certain alloying elements, commonly present in stainless steels.

Steel - Bainite A microstructure in steel formed at intermediate cooling rates between martensite and pearlite, consisting of ferrite and cementite in a non-lamellar structure.

Steel - Cementite The iron carbide (Fe₃C) phase, a hard and brittle compound found in steel and cast iron, contributing to their hardness and strength.

Steel - Ferrite The body-centered cubic (BCC) phase of pure iron or solid solutions in iron, often found in low-carbon steels.

Steel - Martensite A hard, brittle microstructure formed in steels by rapid cooling (quenching) of austenite, characterized by its high carbon content in supersaturated solid solution.

Steel - Pearlite A lamellar mixture of ferrite and cementite formed during the cooling of austenite in steels, giving rise to increased strength and hardness.

Steel - Sorbite and Troostite Microstructures formed when martensite or bainite undergo tempering to reduce brittleness and hardness, often improving ductility and toughness.

Strain The deformation per unit length caused by applied stress, expressed as a dimensionless ratio or percentage.

Strain Age Embrittlement The reduction in ductility of steel caused by the precipitation of carbon or nitrogen at dislocations after plastic deformation, often occurring during low-temperature aging.

Strain Aging A phenomenon where carbon and nitrogen atoms in low-carbon steels lock dislocations after plastic deformation, increasing strength but reducing ductility. Strain aging may result in embrittlement, commonly observed in rimmed or capped steels after deformation and subsequent aging.

Strain Aging The process in which properties of metals, such as strength and hardness, change due to the effects of aging following plastic deformation.

Strain Hardening The increase in a material's strength and hardness due to plastic deformation at temperatures below the material's recrystallization point.

Strain Rate The rate at which strain (deformation) occurs in a material over time, typically measured during tensile testing.

Stray Current Electrical current that flows through unintended paths, potentially causing corrosion in buried or submerged metal structures.

Stray Current Corrosion Corrosion caused by stray electrical current, typically in direct current (DC) systems, which creates localized anodic areas on metal surfaces.

Stress The internal resistance or force within a material per unit area when subjected to an external load, expressed in terms of force per unit area (e.g., N/m² or psi).

Stress Concentration Factor (Kt) A multiplier for stress at a structural discontinuity (e.g., notch, hole), defined as the ratio of maximum localized stress to the nominal stress.

Stress Corrosion Cracking The formation of branched cracks in a material due to the combined effects of tensile stress and a corrosive environment, often leading to sudden failure.

Stress Intensity Factor (K) A parameter in fracture mechanics used to predict the stress distribution at the tip of a crack, influencing crack growth under loading.

Stress Raisers Structural discontinuities, such as notches, sharp corners, or holes, that locally increase stress and may lead to material failure under loading.

Stress Ratio (R) The ratio of minimum to maximum stress in a cyclic loading cycle, expressed as R=Smin/SmaxR = S_{\text{min}} / S_{\text{max}}R=Smin​/Smax​.

Stress Relaxation Cracking (Reheat Cracking) Intergranular cracking caused by relaxation of residual or applied stresses at elevated temperatures, particularly in materials like low-alloy steels. It typically occurs during post-weld heat treatment or long-term exposure to high temperatures in creep-prone materials.

Stress-Intensity Factor Range (ΔK\Delta KΔK) The difference between maximum and minimum stress-intensity factors during a fatigue cycle, critical for predicting crack growth.

Stress-Relief Cracking Cracking that occurs in heat-treated metals due to the relief of residual stresses during post-weld or high-temperature processing, often intergranular in nature.

Striation Microscopic fatigue features on a fracture surface, indicating the incremental advance of a crack front under cyclic loading.

Submerged Arc Welding An arc welding process where the arc is shielded by a blanket of granular flux, which protects the weld and forms slag on the weld surface.

Substrate The underlying material or surface to which a coating or treatment is applied.

Subsurface Corrosion Corrosion that occurs beneath the surface of a material, typically involving the preferential oxidation of specific alloy components.

Sulfidation A high-temperature chemical reaction between a metal or alloy and sulfur compounds, resulting in the formation of sulfide scales on the surface.

Sulfidation A high-temperature corrosion process caused by the reaction of sulfur compounds with metal surfaces, forming metal sulfides. It primarily affects carbon steel and low-alloy steels in environments containing H2S or sulfur vapors, such as heaters, boilers, and hydroprocessing units.

Sulfide Stress Cracking A form of environmental cracking caused by the combined effects of hydrogen sulfide, water, and tensile stress on susceptible materials, typically high-strength steels.

Sulfuric Acid Corrosion Corrosion caused by exposure to sulfuric acid (H2SO4), commonly found in process units such as alkylation, wet gas scrubbers, or acid storage tanks. The rate of attack depends on acid concentration, temperature, and impurities. Carbon steel and stainless steel are commonly affected.

Surface Treatment Processes used to clean, modify, or prepare a surface to achieve desired properties such as improved adhesion, corrosion resistance, or surface profile.

Surfactant A surface-active agent that reduces the surface tension of liquids, allowing them to spread more easily on solid surfaces.

TIG-Welding Tungsten inert gas welding, a precise arc welding process using a non-consumable tungsten electrode and inert shielding gas to protect the weld area.

Tafel Diagram A semi-logarithmic plot of electrode potential versus current density, used to study corrosion behavior and electrochemical reactions.

Tafel Line A graphical representation of the relationship between electrode potential and logarithmic current density in a corrosion system, used to analyze corrosion rates and reaction kinetics.

Tafel Slope The slope of the Tafel line, representing the rate of change of electrode potential with respect to current density, used to calculate corrosion rates.

Tarnish The formation of a thin, non-protective corrosion layer, often discoloring the surface of metals such as silver or copper.

Temper A heat treatment process to adjust the hardness, toughness, and ductility of a material, typically applied to hardened steels by reheating below the critical temperature.

Temper Color A thin oxide film that forms on steel during tempering, causing characteristic colors (e.g., straw, blue) that correspond to specific tempering temperatures.

Temper Embrittlement A loss of toughness in alloy steels due to the segregation of impurities at grain boundaries during slow cooling or holding within a specific temperature range, typically between 550–650°C.

Temper Embrittlement A loss of toughness in low-alloy steels due to exposure to the temperature range of 850–1100 °F (450–600 °C). It is caused by the segregation of impurities like phosphorus, tin, and antimony at grain boundaries, leading to a shift in the ductile-to-brittle transition temperature.

Tempered Martensite Embrittlement Embrittlement of high-strength steels caused by tempering within the temperature range of 205–400°C (400–750°F), often resulting from carbide precipitation and impurity segregation at grain boundaries.

Tempering Reheating a hardened material below its critical temperature to reduce brittleness and increase toughness, commonly used for steels.

Tensile Strength The maximum stress a material can withstand while being stretched or pulled before breaking, calculated as the maximum load divided by the original cross-sectional area.

Tensile Stress A type of stress that acts to elongate a material by pulling it apart, opposite to compressive stress.

Tension The force exerted on a material causing elongation or stretching.

Terne An alloy of lead and tin, typically containing 3–15% tin, used as a corrosion-resistant coating for steel sheets.

Terne Plate Steel sheets coated with a lead-tin alloy (terne) to improve corrosion resistance, formability, and paintability.

Thermal Cutting A cutting process where heat is used to melt or burn through materials, often involving oxygen or plasma as a cutting medium.

Thermal Electromotive Force The voltage generated in a circuit of two dissimilar metals with junctions at different temperatures, commonly used in thermocouples.

Thermal Embrittlement A reduction in toughness of maraging steels due to precipitation of carbides or intermetallic phases during slow cooling or exposure to elevated temperatures.

Thermal Fatigue Cracking caused by cyclic thermal stresses in components exposed to fluctuating temperatures. This occurs due to repeated expansion and contraction, commonly found in boilers, heat exchangers, and fired heater tubes.

Thermal Shock Sudden failure caused by rapid temperature changes that induce high thermal gradients in materials. This leads to cracking or spalling, particularly in brittle materials like refractories or metals subjected to quenching or rapid heating.

Thermal Spraying A coating process in which molten or semi-molten materials are sprayed onto a surface to form a protective layer, commonly used for corrosion resistance or wear protection.

Thermocouple A device for measuring temperature based on the voltage generated at the junction of two dissimilar metals when subjected to a temperature gradient.

Thermogalvanic Corrosion Corrosion caused by a thermally induced potential difference in a system, typically resulting from a temperature gradient across a metal surface.

Threshold Stress The minimum stress level required to initiate stress-corrosion cracking or other stress-related failure mechanisms under specified conditions.

Throwing Power The ability of an electroplating solution to deposit metal uniformly on irregularly shaped surfaces or in recessed areas.

Tinning The process of coating a metal surface with a thin layer of tin, often to prevent corrosion or facilitate soldering.

Titanium Hydriding A damage mechanism in titanium alloys caused by the absorption of hydrogen, leading to the formation of brittle hydrides. This can result in embrittlement and cracking, typically occurring in acidic or high-temperature environments.

Torsion A twisting deformation of a material caused by an applied torque, often resulting in shear stresses within the material.

Torsional Stress The shear stress induced in a material when subjected to a twisting force or torque.

Total Carbon The total amount of carbon present in a ferrous alloy, including both free carbon (graphite) and combined carbon (in carbide form).

Toughness The ability of a material to absorb energy and undergo plastic deformation before fracturing, often measured as the area under a stress-strain curve.

Transcrystalline A term synonymous with "transgranular," referring to events occurring through or across individual grains in a material.

Transcrystalline Cracking Cracking or fracturing that propagates through or across individual crystals or grains in a polycrystalline material, also referred to as transgranular cracking.

Transcrystalline Fracture A fracture that occurs through the grains or crystals of a material, rather than along grain boundaries, also known as transgranular fracture.

Transition Metal A group of metals characterized by partially filled d-orbitals, including iron, cobalt, nickel, tungsten, and others, known for their catalytic properties and high melting points.

Transition Temperature The temperature range in which a material undergoes a rapid change in fracture behavior, such as from ductile to brittle failure, or a change in microstructure during heating or cooling.

Transpassive Region The region on an anodic polarization curve beyond the passive potential range, where increased current density indicates significant metal dissolution or oxygen evolution.

Transpassive State The condition of a passivated metal when a further increase in potential causes metal dissolution at higher rates or other reactions, such as oxygen evolution.

Triaxial Stress A stress state in which three mutually perpendicular normal stresses are present, with none being zero.

Tuberculation The formation of localized corrosion products that appear as knob-like mounds (tubercles) on a metal surface, often associated with iron corrosion in water systems.

U-Bend Specimen A test sample bent into a U-shape to evaluate susceptibility to stress-corrosion cracking under tensile stress.

Ultimate Strength The maximum stress a material can sustain before fracture, often synonymous with tensile strength.

Ultrasonic Measurement A non-destructive testing method using high-frequency sound waves to measure material thickness, detect flaws, or characterize materials.

Underfilm Corrosion Corrosion that occurs beneath protective coatings, often taking the form of thread-like filaments or isolated spots.

Uniaxial Stress A stress condition where force is applied in a single direction, causing elongation or compression along one axis.

Uniform Corrosion A type of corrosion that occurs evenly across a metal surface, leading to a consistent loss of material thickness.

Vacuum Deposition A coating process where materials are deposited onto a substrate in a vacuum environment through vaporization or sputtering.

Valence The measure of an element's ability to combine with other atoms, represented by the number of bonds it can form.

Vapor Deposition A method of applying thin films or coatings to a substrate through the condensation of vaporized materials, often in a vacuum.

Vapor Plating A deposition process involving the reduction or decomposition of volatile compounds to coat a surface, sometimes performed under vacuum conditions.

Voids Cavities or gaps in a material, often referring to defects in coatings, welds, or films that compromise structural integrity or protection.

Vulcanizing A chemical process for strengthening rubber by adding sulfur or other cross-linking agents to improve elasticity, durability, and heat resistance.

Wash Primer A thin primer coating, often chromate-based, used to improve adhesion and corrosion resistance of subsequent paint layers.

Weather Resistance The ability of a material to withstand exposure to environmental conditions, such as UV light, temperature changes, moisture, and pollutants, without significant degradation.

Weld The union of two or more metal pieces joined by applying heat, pressure, or both, with or without filler material.

Weld Cracking Cracking that occurs in or near a weld due to stresses, material defects, or improper welding procedures. Examples include hot cracking, cold cracking, and lamellar tearing.

Weld Decay Intergranular corrosion occurring in the heat-affected zone of a weld, often in stainless steel due to chromium carbide precipitation.

Weld Metal The portion of a weld joint composed of filler material or melted base material that has solidified to form the weld.

Weld Zone The area comprising the weld metal and the adjacent heat-affected zone, which experiences thermal and microstructural changes during welding.

Welding The process of joining materials, typically metals, by applying heat, pressure, or both, often using filler materials to form a strong, cohesive bond.

Wet H2S Damage A family of damage mechanisms caused by exposure to wet hydrogen sulfide environments, including hydrogen blistering, hydrogen-induced cracking (HIC), stress-oriented hydrogen-induced cracking (SOHIC), and sulfide stress cracking (SSC). Carbon steel is particularly susceptible in sour water environments.

Wetting The ability of a liquid to maintain contact with a solid surface, influenced by the surface tension of the liquid and the surface energy of the solid.

Wetting Agent A chemical compound that lowers the surface tension of a liquid, improving its ability to spread over or penetrate a solid surface.

White Liquor A caustic solution used in the kraft pulping process, typically produced by recausticizing green liquor with lime, primarily containing sodium hydroxide and sodium sulfide.

White Rust A powdery corrosion product primarily composed of zinc oxide and zinc hydroxide, forming on the surface of zinc or galvanized coatings when exposed to moisture.

Work Hardening The process of increasing the hardness and strength of a metal through plastic deformation below its recrystallization temperature, also called strain hardening.

Working Electrode The test or specimen electrode in an electrochemical cell, where the primary electrochemical reactions of interest occur.

Yield The permanent plastic deformation in a material when subjected to stress, marking the onset of failure under load.

Yield Point The first point in a stress-strain curve at which a material shows a significant increase in strain without an increase in stress, marking the start of plastic deformation.

Yield Strength The stress level at which a material begins to exhibit permanent deformation, typically defined at a 0.2% offset in strain.

Yield Stress The stress value between the yield strength and ultimate strength where the material transitions into plastic deformation.

Zeta Potential The electrokinetic potential of a particle in a solution, representing the potential difference between the dispersion medium and the stationary layer of fluid attached to the particle.

References:

• American Petroleum Institute. API 571: Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, 3rd ed., API, 2020.

• Bahadori, Alireza. Corrosion and Materials Selection: A Guide for the Chemical and Petroleum Industries. 1st ed., John Wiley & Sons, 2014.