Corrosion engineering is a branch of engineering that focuses on preventing and controlling the deterioration of materials due to chemical reactions with their environment. Corrosion is a major problem in many industries, including oil and gas, chemical processing, and transportation, as it can lead to equipment failure, safety hazards, and environmental damage. The work of a corrosion engineer typically involves identifying the causes and mechanisms of corrosion, selecting appropriate materials and coatings to prevent corrosion, and developing strategies to control and mitigate the effects of corrosion. They use a variety of tools and techniques to analyze the properties and behavior of materials in different environments, such as electrochemical testing, material characterization, and computational modeling.
Corrosion engineers work in a variety of industries and settings, including research and development, design and construction, and maintenance and repair. They may work on projects related to pipeline integrity, oil rig maintenance, or material selection for chemical processing equipment. In addition to preventing and controlling corrosion, corrosion engineers may also work on projects related to material testing and certification, environmental monitoring and remediation, and safety and risk assessment. They often collaborate with other engineers, scientists, and technicians to develop and implement effective corrosion management strategies.
These engineering is a critical field that plays an important role in many industries. By preventing and controlling the effects of corrosion, corrosion engineers help to ensure that industrial processes operate safely and efficiently, while also minimizing environmental impact and protecting public health and safety.
Nomenclature & Symbols
- Cavitation - Corrosion gas bubble formation & immediate collapse. The erosion is caused by the relative movement between a corrosive fluid and a metal surface. Localized cavities of vapor form on the low pressure side of the pump (suction) and collapse on themselves as energy is added to the fluid.
- Corrosion Erosion - Velocity aggravated corrosion. Caused by the rapid flow of any turbulent liquid through the piping. The rate of corrosion is dependent on the level of turbulance.
- Corrosion Fatigue - Corrosion on cyclic loads. Stress corrosion cracks occur due to the effecte of static stress. The applied stresses are cyclic as a result of mechanical or thermal effects.
- Crevice - Portion of the surface is isolated from the environment. The presence of small volumes of stagnant solution beneath deposits and seals, or in crevices, at nuts and rivet heads. Deposits of sand, dust, scale and corrosion products can all create zones where the liquid can only be renewed with great difficulty.
- Galvanic Corrosion - Caused by dissimilar metals. An electrochemical process whereby one metal corrodes when in contact with another metal through an electrolyte. During this process, one metal can experience severe corrosion, while the other remains relatively unaffected.
- Intergranular - Corrosion at the grain boundaries. It happens along the crystal boundary of the metal when exposed to certain corrosive medium. The corrosion starts from the surface, develops into the inside of the metal along the crystal boundary until it collapses devoid of all the metal strength. It happens even when the surface looks fine but actually the grains inside the metal have lost the binding force and the metal sound.
- Pitting - Localized on metal surface. A localized form of corrosion which is characterized by small holes forming in materials, most often metal piping. While these pits may be small on the surface, they can be larger underneath, potentially being more damaging than they appear.
- Selective Leaching - Only one metal in an alloy is attacked. in some solid solution alloys, when in suitable conditions a component of the alloys is preferentially leached from the material. The less noble metal is removed from the alloy by a microscopic-scale galvanic corrosion mechanism. The most susceptible alloys are the ones containing metals with high distance between each other in the galvanic series.
- Stress Corrosion Cracking - When a susceptible material is exposed to a contaminant that concentrates in an area affected by tensile stresses in excess of its threshold.
Corrosion Engineering GlossaRy
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- Abradable Coating - It gives wear resistance to highly abrasive material when rubbed against, while leaving the underlying material damage free.
- Acid - A chemical substance that yields hydrogen ions (\(H^+\)) when dissolved in water.
- Acid Embrittlement - A form of hydrogen embrittlement that may be introduced in some metals by acid.
- Acid Rain - Atmospheric precipitation with a pH below 3.6 to 5.7.
- Acrylic - Resin polymerized from acrylic acid, methacrylic acid, eaters of these acids, or acrylonitrite.
- Alternating Current - An electric current that reverses its direction over and over.
- Annealing - A heating and controlled cooling operation to impart specific desirable properties generally concerned with subsequent fabrication of the alloy.
- Anion - A negatively charged ion.
- Anode - The electrons flow away the anode (negative charge) at which corrosion or oxidation occures at the material.
- Artificial Aging - Aging above room temperature.
- Atmospheric Corrosion - A gradual degradation of alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapor, sulfur and chlorine compounds.
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- Barrier Coating - A protective layer of material that prevents the contact of corrosive elements.
- Base - A substance that releases hydroxyl ions when disolved in water.
- Beach Marks - Microscopic progression marks on a figure fracture or stress-corrosion cracking surface that indicate sucessive positions of the advancing crack front.
- Black Oxide - A black finish on a metal produced by immersing it to hot oxidizing salts or salt solutions.
- Brackish Water - Water having salinity values ranging from approximately 500 to 5,000 parts per million.
- Brine - Seawater containing a high concentration of dissolved salt than that of the ordinary ocean.
- Brittle Fracture - Separation of a solid accompanied by little or no microscopic plastic deformation.
- Buffer - A chemical substance which stabilizes pH values in solutions.
- Buffer Capacity - A measure of the capacity of a solution or liquid to neutralize acids or bases.
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- Camera Pig - A configuration pig with a camera and light source recording the inside of the pipeline.
- Carburization - Occurs when carbon bonds with chromium. This happens often at grain boundaries, causing corrosion to make metal surfaces more brittle. It also reduces metal’s resistance to oxidation, paving the way for further corrosion.
- Cathode - The electrons flow toward the cathode reducing the corrosion or oxidation of the material.
- Cathodic Polarisation - The electrochemical state changing of an electrode's potential moving in a non-corroding negative direction.
- Cleaning Pig - A utility pig with brushes, cups, and scrapers for cleaning foreign matter from the inside of the pipeline.
- Corrosion - The thinning of a pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
- Corrosion Allowance - The amount of material in a pipe or vessel that is available for corrosion without affecting the pressure containing integrity.
- Corrosion Coupon - Used to monitor the corrosion rate of a material in a process.
- Corrosion Embrittlement - Embrittlement in certain alloys caused by exposure to a corrosive environment.
- Corrosion Fatigue - Combined action of corrosion and fatigue in which local corroded areas act as stress concentrators, causing failure at the point of stress concentration and exposing new metal surfaces to corrosion.
- Corrosion Inhibitor - A substance that slows down the chemical reaction rate of corrosion on metal that is exposed to the environment. To minimise corrosion, it is very important for heat transfer fluid to be formulated with effective and proven inhibitors. Specifically, the inhibitor formulation should take into consideration the metals of construction, antifreeze type, susceptibility to air ingress and subsequent bacterial contamination, make-up water quality and effectiveness of pre-commission pipework flushing and conditioning (passivation).
- Corrosion Mapping - An ultrasonic method that identifies and maps corroded areas in a pipelineby yhe varying material thickness.
- Corrosion Resistance - The ability of a material to resist chemical destruction from an environment.
- Crack - Cracks can come from fatigue, grith welds, or seam welds.
- Cracking - Surface loss of color and gloss in a coating from degradation of the binder by the UV components in sunlight. Can be seen as a white deposit on the cured coating surface.
- Current - The rate of flow of electricity in a circuit, measured in amperes.
- Deactivation - The process of prior removal of the active corrosive constituents, usually oxygen, from a corrosive liquid by controlled corrosion of expendable metal or by other chemical means.
- Defective Weld - A weld having one or more defects.
- Diffusion - The spread of gases, liquids, or solids from areas of high concentration to areas of low concentration.
- Diluent - A liquid used in coatings to reduce the consistency and make coating flow more easily.
- Direct Current - An electric current that flows in only one direction.
- Dry Corrosion - See gaseous corrosion or hot corrosion
- Elastic Modulus - The ratio of the stress applied to a body or substance to the resulting strain within the elastic limits.
- Electrochemical Corrosion - Localized corrosion that results from exposure of an assembly of dissimilar metals in contact with or coupled with one another.
- Electrode - Refered to as the anode or cathode, whichever is approperate.
- Electrode Potential - The potential of an electrode in an electrolyte as a measure against a reference electrode.
- Electrolyte - A chemical substance or mixture, liquid or solid, normally liquid, which conducts electric current.
- Erosion Corrosion - Is where metal and synthetic components are worn down over time, due to one or more of the following causes: High levels of entrained sediment in the heat transfer fluid, acting as an abrasive inside pumps and bends. Cavitation is most often observed inside centrifugal pumps. For example, worn impellers and volutes, but can also be found where there are severe changes in heat transfer fluid direction, or poorly designed pipework etc.
- External Corrosion - When the outside of a pipe is decayed or eroded by chemical or electrochemical processes or any other environmental conditions.
- Faraday's Law of Induction - States that whenever a conductor is placed in a varying magnetic field, an electromotive force is introduced.
- Flux - Chemicals used to protect metals from oxidation.
- Free Corrosion Potential - Corrosion potential in the absence of net electric current flowing to or from the metal surface.
- Fretting Corrosion - Takes place where there is friction between two metal surfaces.
- Galvanic Corrosion - Corrosive action occuring when two dissimilar metals are in contact and are joined by a solution capable of conducting an electric current, a condition which causes a flow of electric current and corrosion of the more anodic of the two metals. An electric potential difference is generated between the metals and the less noble metal acts as an anode and dissolves, while the more precious metal acts as the cathode.
- Gaseous Corrosion (Dry Corrosion or Hot Corrosion) - Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal.
- Gouging - Mechanical removel of metal from the surface of the pipe.
- Halogen - Halogen corrosion is when metals react with halogen gas at high temperatures. It can cause volatile metal halides to form on the metal surface. This can create serious problems for many metals, although stainless steel is especially susceptible to this form of corrosion.
- Hardness - The property of a material that enables it to resist plastic deformation, usually by penetration.
- Holiday - A discontinuity in painted or coated surfaces.
- Hot Corrosion - See dry corrosion or gaseous corrosion
- Incomplete Fusion - A weld break where complete fusion did not occur between the weld material and the faces or adjoining weld material.
- Incomplete Weld - A defect in the solder joint that causes cracks or damage to the bond.
- In-line Inspection - When the pipeline is inspected by examining the interior of the pipe.
- Inhibitor - Can reduce the corrosion rate by presenting a protective film.
- Instrumented Pig - A tool with instruments like recorders and sensors to examine the inside of the pipe.
- Integranular Corrosion - Usally of stainless steals or certain nickle-base alloys, that occures as the result of sensitization in the heat affected zone during the welding process.
- Internal Corrosion - The thinning of the interior pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
- Ion - An atom or molecular particle having a net charge. Positive charged ions are cations and negative charged are anions.
- Isolation Gasket - Used to stop the current flow across metallic pipelines by separating two flanges.
- Lacquer - A fast drying, usually clear coating, that is highly flammable and dries by solvent evaporation only.
- Lamellar Corrosion - A form of corrosion in which the expanding corrosion products stack up as layers.
- Lenz's Law - the direction of the current induced in a conductor by changing magnetic field.
- Magnetic Flux - The number of magnetic field lines passing through a given closed surface.
- Mapping Pig - A configuration pig used to produce an elevation and plan view of the pipeline route with collect data that can be analysed from the inertia sensing or some other technology.
- Material Hardness - The property of a material that enables it to resist plastic deformation, usually by penetration.
- Mechanical Properties - Those properties that reveal the reaction, elastic or plastic, of a material to an applied stress, or that involved the relationship between stress and strain.
- Molten Metal - When liquid metals are used for heat transferring, the contaminant material can come into contact with molten metal and can cause corrosion. The only real way to prevent this corrosion is an in-depth knowledge of how molten metals react with certain materials in the containment system.
- Molten Salt - Molten salts are often used in heat treatment plants, nuclear energy plants, and sometimes in concentrated solar power plants. When a metal comes in contact with molten salt at high temperatures, it can quickly create corrosion. Molten salts remove the oxide scale from metal surfaces causing the metal to thin, pit, or experience an intergranular attack.
- Natural Gas - Gaseous fuel occuring in nature.
- Neutralizer - A common designation for alkaline materials such as calcite or magnesia used in the neutralization of acid waters.
- Nitridation - Metals that are exposed to ammonia or nitrogen filled environments at high temperatures are at increased risk of nitridation. It caused a hard, brittle metal to form. This corrosion can be prevented by the addition of nickel as an alloyed element in the metal.
- Ohm - A unit of resistance.
- Ohm's Law - The relationships between power, voltage, current, and resistance.
- Oxidation - The loss of electrons in a chemical reaction in which an element combines with oxygen. Oxidation and reduction always occur at the same time in equal amounts.
- Oxidation Corrosion - When caused by air and/or dissolved oxygen, will tend to dissolve metals evenly across their surface, and most often affects metals which do not form passive protective layers or are naturally resistant to oxidation corrosion.
- pH - Affects the corrosion rate by affecting the reaction rate of cathodes and anodes.
- Physical Properties - Those properties familiarly discussed in physics, for example, density, electrical conductivity, and thermal expansion coefficient, exclusive of those described under mechanical properties.
- Pitting - A non-uniform corrosion of a metal, not in the form of cracks, whereby a number of cavities, are formed in the surface.
- Pitting and Crevice Corrosion - Is typical in installations where metals protected by a passive coating, such as galvanised or some stainless-steel pipes. An increased local corrosion rate can occur where there is a flaw in the passive coating, when the potential difference is concentrated.
- Porosity - Happens when a contaminent or gas is absorbed into the weld puddle.
- Rupture - There are numerous reasons a rupture can happen, depending on the material: age, brittleness, corrosion, internal pressure, movement, etc.
- Rust - A corrosion product consisting primarily of hydrated iron oxide.
- Sacrificial Coating - A coating that provides corrosion protection wherein the coating material corrodes in preference to the substrate.
- Salt Fog Test - See salt spray test
- Salt Spray Test - An accelerated corrosion test in which the metal specimens are exposed to a fine mist of salt water solution.
- Saltine Water - Water containing an excessive amount of dissolved salts.
- Silicone - A resin used in the binders of coatings.
- Shear Stress - Tends to deform the material by breaking rather than stretching without changing the volume by restraining the object.
- Shinning - The formation of a thin, tough film on the surface of a liquid point.
- Shrinkage - A decrease in dimensions of a coating during process.
- Shrinkage Stress - The residual stress in a coating caused by shrinkage during processing.
- Smart Pig - Collects information internally about the pipeline with electronic components.
- Solute - A substance which is disolved in and by a solvent.
- Specific Gravity - The density or ratio of any substance to another substance.
- Gravity - The density or ratio of any substance to another substance.
- Strain - The deformation, stretched or compressed, of a material compared to its original length.
- Strain Rate - The time rate of straining for the usual tensial test.
- Stray Current - The flow of electric current into the ground by the leakage on industrial currents.
- Stress - The force per unit area of cross-section.
- Stress Corrosion Cracking - The combined effect of tensile stress and a corrosive environment.
- Sulfidation - Sulfidation is caused by the presence of sulfur. Sulfur is often present in impure crude oil, putting pipelines at increased risk. Sulfidation causes thinning of the pipeline walls and can even lead to breaches in the pipeline, causing spills, leaks, and further ruptures.
- Surge Pressure - See Water Hammer
- Sweet Corrosion: Carbon Dioxide - A weak acidic gas found in condensate, crude oil, natural gas, and produced water and becomes corrosive when dissolved in water.
- Tensile Strength - The maximum stress a material can resist before it starts to elongate.
- Tension - The force (pulling or stretching) acting on a material.
- Toughness - The ability of a material to absorb considerable energy without fracturing.
- Ultrasonic Testing - Used to measure the pipe wall thickness perpendicular to the pipe.
- Utility Pig - Used to performing pipeline cleaning of debris and unwanted materials.
- Volt - A unit of electrical pressure.
- Voltage - One volt is the amount of pressure that will cause one ampere of current in one ohm of resistance.
- Voltage Coefficient of Resistance - The change in resistance with applied voltage.
- Voltage Drop - When the voltage at the end of the cable is less than the beginning of the cable.
- Voltage Rating - The maximum voltage at which a cable or insulated conductor can be safetly maintained during continuous use in a normal manner.
- Water Conductivity - The ability of water to conduct an electric current.
- Waterlogged - Saturated with water.
- Water Table - The underground boundary between the surface of the soil and the area where groundwater fills the cracks and openings in the rocks and sand.
- Weld Crack - Cracks can appear on the surface, inside the weld or heat effected zone.
- Weld Decay - See integranulat corrosion
- Welding Defects - Blow hole, defect of joint shape, incomplete fusion, overlap, slag inclusion, undercut, weld crack.
- Well Integrity - An operation of technical, operational, and organizational solutions to reduce fisk of controlled release of formation fluids throught the life cycle of a well.
- Yield Strength - Yield strength, abbreviated as \(\sigma\) (Greek symbol sigma), also called yield stress, is the minimum stress that leads to permanent deformation of the material.