Glossary

A precipitation-hardening martensitic stainless steel grade with lower copper and higher nickel content than other common grades in the same PH family, valued for a similar combination of high strength and stainless corrosion resistance. It is used for similar applications, such as valve, pump, and fastener components.

A precipitation-hardening martensitic stainless steel grade, valued for combining high strength with good corrosion resistance across a range of heat-treated conditions. It is widely used for components such as valve and pump parts, fasteners, and aerospace hardware that need strength beyond what standard martensitic stainless grades provide.

A precipitation-hardening semi-austenitic stainless steel grade, supplied in an annealed, formable condition and then heat-treated after forming to develop high strength through martensite formation and precipitation hardening. It is used for springs, fasteners, and other components needing high strength combined with stainless corrosion resistance.

A heat-treatable aluminum-magnesium-silicon alloy grade in a specific solution-heat-treated and artificially aged temper, valued for its combination of moderate-to-good strength, corrosion resistance, and weldability. It is one of the most widely used general-purpose structural aluminum alloys.

A pipe welding test position in which the pipe is fixed at a fixed incline, combining aspects of multiple welding positions within a single weld and considered one of the most demanding qualification positions for a welder or a welding procedure.

A nickel-alloyed steel grade formulated to retain adequate toughness at cryogenic temperature, most commonly used for the storage and transport of liquefied natural gas and other refrigerated liquids. Its high nickel content gives it an unusually low ductile-to-brittle transition temperature compared with ordinary carbon or low-alloy steels.

A chromium-molybdenum-vanadium alloy steel grade developed for high-temperature service, such as in power-plant piping and pressure vessels, offering improved creep strength over standard chromium-molybdenum grades at similarly high operating temperature. It is one of a family of creep-resistant alloy steels used in fossil and other thermal power generation.

The prefix for standards and designations issued by the Aluminum Association, an industry body that maintains the widely used numbering system for aluminum alloys.

The AISI designation for a molybdenum-bearing austenitic stainless steel grade, valued for better resistance to pitting and crevice corrosion in chloride environments than more basic austenitic grades.

A ferritic stainless steel grade with a modest chromium content and no nickel, valued for good corrosion resistance in mild environments at low cost, and commonly used in automotive exhaust systems.

An AISI-designated low alloy steel grade containing chromium and molybdenum, valued for a good combination of strength, toughness, and weldability, and widely used in oilfield and aerospace tubular and structural applications.

A chromium-molybdenum low-alloy steel grade with a higher carbon content than other common grades in the same family, valued for good hardenability and a favorable combination of strength and toughness after heat treatment. It is widely used for shafts, gears, and other structural and machine components.

A martensitic stainless steel grade with a higher carbon content than lower-carbon martensitic grades, allowing it to be hardened to a higher hardness by heat treatment, at some cost to corrosion resistance and toughness. It is used for cutlery, molds, and other components needing high hardness and wear resistance.

A common name for a nickel-chromium-molybdenum alloy, widely known by its trade name, valued for outstanding corrosion resistance and high strength across a wide temperature range.

The API specification covering drill pipe used in oil and gas well drilling operations.

A drill-pipe grade within a widely used American Petroleum Institute drill-pipe specification, at the highest of the strength classes that specification defines. Higher-strength grades like this one are selected where drilling loads or depth demand more pipe-body strength than the lower grades in the same specification provide.

The API specification covering seamless and welded steel line pipe used to convey oil, gas, and water in the petroleum and natural gas industries.

A pipeline steel grade within a widely used American Petroleum Institute line-pipe specification's higher-strength series, at a lower strength class than higher-numbered grades in the same series. It is used in the construction of oil and gas transmission pipelines where its strength class is sufficient for the design pressure.

A specific pipeline steel grade within a widely used American Petroleum Institute line-pipe specification, distinguished by a higher minimum strength class than the specification's standard base grade. Such higher-strength grades allow a thinner pipe wall to be used for a given pressure rating in oil and gas transmission pipelines.

A pipeline steel grade within a widely used American Petroleum Institute line-pipe specification's higher-strength series, at a higher strength class than most other grades in the same series. Higher-strength grades like this one allow a thinner pipe wall to be used for a given pressure rating in large-diameter transmission pipelines.

The API specification covering wellhead and christmas tree equipment used in oil and gas drilling and production, specifying design, material, testing, and marking requirements for this pressure-containing equipment.

A commercial abrasion-resistant steel plate grade, through-hardened to a high hardness level, used in mining, earthmoving, and other equipment subject to severe abrasive wear. It trades ductility and weldability for wear resistance compared with structural carbon steel plate.

A US-based professional association, the American Railway Engineering and Maintenance-of-Way Association, that develops recommended practices and standards for railway engineering and infrastructure.

A US-based professional association, the American Society of Mechanical Engineers, that develops widely used codes and standards covering pressure vessels, boilers, piping, and other mechanical engineering equipment.

The prefix used within the ASTM system of standards for specifications covering ferrous metal products, one of several subject-based letter categories ASTM uses alongside its numbered designations.

The ASTM specification covering forged or rolled alloy and stainless steel flanges, fittings, valves, and similar piping components for high-temperature service.

The ASTM specification covering alloy and stainless steel bolting material for high-temperature or high-pressure service.

An ASTM specification covering carbon-silicon steel plate intended for pressure vessels operating primarily at intermediate and higher temperatures.

An ASTM specification covering heat-treated carbon-manganese-silicon steel plate used for pressure vessels requiring improved notch toughness compared with as-rolled plate.

A forged fitting and valve grade within a widely used ASTM forged-fittings specification, made from a superduplex stainless steel and combining that alloy family's high strength and corrosion resistance with the specification's forged product form.

A low-temperature carbon steel pipe grade within a widely used ASTM piping specification, specified for service where the material must retain adequate toughness at low ambient or process temperatures. Different grades within that specification are distinguished mainly by their alloy content and the low-temperature toughness they are qualified for.

A widely used ASTM specification for structural carbon steel plate, shapes, and bar, valued for good weldability and ductility at a low cost, and one of the most common general-purpose structural steel grades.

An ASTM specification covering quenched-and-tempered steel bolts and studs at a higher strength class than ordinary structural bolting, used where a structural connection requires more clamping load or strength than a standard-grade fastener can provide.

The prefix used within the ASTM system of standards for specifications covering non-ferrous metal products, one of several subject-based letter categories ASTM uses alongside its numbered designations.

A standardized rating defined by ASTM that describes the average grain size of a metal's microstructure as seen in a micrograph, with each rating step corresponding to a different average grain size class. It provides a common, comparable way to report grain size across different materials and analyses.

The American Welding Society structural welding code covering the fabrication of aluminum structures, specifying requirements for welding procedures, qualification, and workmanship analogous to the corresponding code for steel structures.

A wear mechanism in which hard particles or a rough counter-surface cut, scratch, or gouge material away from a component's surface through relative sliding motion. It is one of the principal mechanisms grouped under the general term wear, alongside adhesive and erosive wear.

A needle- or plate-like morphology of the alpha phase in titanium alloys, formed when the beta phase transforms rapidly on cooling, as distinguished from a more equiaxed, rounded alpha morphology produced by slower cooling or different processing. Its presence affects the strength, ductility, and fracture behavior of the alloy.

A needle-like form of ferrite that nucleates and grows within austenite grains rather than along their boundaries, commonly found in certain weld metals and associated with a favorable combination of strength and toughness.

A submerged-arc or flux-cored welding flux formulated to add alloying elements to the weld metal through the arc, as distinguished from a neutral flux designed not to change the weld metal's chemistry beyond what the filler metal itself provides. Its effect on weld metal composition needs to be considered particularly when welding thick sections with high dilution or when reusing recovered flux.

A wear mechanism in which material transfers between two sliding surfaces, or is torn away from one, because localized welding or bonding occurs between high points on the two surfaces under contact pressure and is then broken apart by continued relative motion. Galling is a severe, rapidly progressing form of this mechanism.

Carbide particles that have clustered or grown together into larger, coarser groups during prolonged high-temperature exposure, rather than remaining finely and evenly dispersed through the matrix. Their presence is a useful indicator of overheating or extended elevated-temperature service, similar to carbide coalescence.

A form of stress corrosion cracking that occurs in carbon and low-alloy steels exposed to alkaline (caustic) environments under tensile stress, producing intergranular cracks with little general corrosion. It is a recognized failure mechanism in equipment handling caustic solutions, such as certain amine or caustic-treatment systems in oil and gas processing.

A common name for the low-temperature phase in certain metal systems — for example, alpha-iron (ferrite) in steels or the alpha phase in titanium alloys — as distinguished from a higher-temperature beta or gamma phase.

A lightweight, corrosion-resistant metallic element used as a base metal in aluminum alloys and as an alloying addition in some steels and other metals. Its chemical symbol appears throughout the material composition tables in this atlas.

An alloy based on aluminum, valued for its low density combined with useful strength, corrosion resistance, and, in some series, good weldability.

A copper-based alloy containing aluminum as its main alloying element, valued for a combination of good strength, corrosion resistance — particularly in seawater — and resistance to galling and wear, making it common in marine bearings, bushings, and propellers.

A US-based trade association of steel producers, known in materials engineering mainly for the AISI designation system used to identify standard grades of carbon, alloy, and stainless steel.

A US-based trade association for the oil and gas industry that publishes widely used standards and specifications covering equipment, materials, and procedures across exploration, production, and pipeline operations.

An international standards organization that develops and publishes voluntary consensus standards for materials, products, and testing methods across many industries, including a large body of specifications used throughout metallurgy.

A US-based professional association that develops standards, codes, and procedure specifications covering welding processes, qualification, and inspection.

A directional variation in a material's mechanical or physical properties, such that its behavior differs depending on the direction it is tested or loaded relative to its processing history — for example, the rolling direction of a plate. It is an important consideration in the failure analysis of wrought products, where properties in the through-thickness direction are often weaker than in the rolling direction.

A heat treatment in which a metal is heated to a specific temperature and then cooled slowly, used to soften the material, relieve internal stress, improve ductility, or produce a more uniform microstructure before further processing or service. Solution annealing and stress-relief annealing are examples of annealing treatments aimed at a specific microstructural or stress-state outcome rather than general softening.

Straight, mirror-symmetric bands within a grain that form during recrystallization or grain growth on annealing, as distinguished from deformation twins that form by mechanical straining. They are common in annealed austenitic stainless steels, copper alloys, and other low-stacking-fault-energy metals, and are a normal microstructural feature rather than a defect.

A measure of ductility obtained from a tensile test, describing how much a specimen's cross-sectional area narrows at the point of fracture compared with its original size. A larger reduction generally indicates a more ductile material, while an unexpectedly small one can point to embrittlement or a metallurgical defect.

A heat treatment in which a solution-treated, precipitation-hardenable alloy is held at an elevated temperature for a controlled time to promote the controlled precipitation of a strengthening second phase, as distinguished from natural aging, which occurs at room temperature over a longer period. It is the second step of the precipitation-hardening process, following solution treatment.

The condition of a casting as it comes directly out of the mold, before any subsequent heat treatment, machining, or other processing is applied. Properties and microstructure in the as-cast condition are often coarser and less uniform than after a homogenizing or normalizing heat treatment.

An image of a sample surface that has been ground and polished to a smooth, reflective finish but not yet etched, used to examine features such as inclusions, porosity, or coating thickness that etching would otherwise obscure.

An image showing a specimen or component in its as-received condition, before any cutting, polishing, or etching is done to prepare it for microscopic examination. Such images document the failure's overall context before analytical preparation begins.

An image or record produced by a non-destructive testing method, such as ultrasonic, radiographic, magnetic particle, or dye penetrant inspection, used to detect or characterize a discontinuity without damaging the component being examined.

An image focused on a specimen's outer surface, as opposed to a machined or polished cross-section, used to examine surface conditions such as corrosion, coating, or surface-initiated cracking.

A face-centered-cubic phase of iron-based alloys, stable at high temperature in plain carbon steels but retained at room temperature in austenitic stainless steels and certain other alloys through composition and processing.

The characteristic distance between adjacent regions or particles of austenite within a mixed microstructure, such as the spacing between austenite islands in a duplex stainless steel weld. It is a quantitative way to describe how finely or coarsely the phases are distributed, which in turn affects mechanical and corrosion properties.

A family of stainless steels whose microstructure is predominantly austenite at room temperature, achieved through sufficient additions of austenite-stabilizing elements such as nickel. Austenitic grades are generally the most corrosion-resistant and readily weldable stainless steels, though they are not hardenable by heat treatment.

A welding process performed without the addition of filler metal, in which the joint is formed solely by fusing and rejoining the base metal itself. It is commonly used for thin-walled tubing and precision components where added filler material is undesirable.

An application category covering components used in road vehicles, one of the industries represented in this atlas.

A microstructure intermediate between pearlite and martensite, formed when austenite in a steel is cooled at a rate too fast to form pearlite but not fast enough to form martensite, combining a mixture of ferrite and carbide in a characteristic feathery or plate-like arrangement.

A test in which a component or armor material is struck by a projectile at controlled velocity to evaluate its resistance to penetration and its energy-absorbing behavior under high-rate impact loading.

A microstructure in which constituents such as ferrite and pearlite are arranged in alternating, elongated bands aligned with the rolling direction, typically resulting from chemical segregation inherited from the original cast structure and stretched out during hot rolling.

A product category covering long components with a solid cross-section — round, square, hexagonal, or another regular shape — similar to rod but not restricted to a round profile.

The original, unaffected material of a component or joint, as distinguished from weld metal or a heat affected zone in a welded joint, or from an applied coating in other contexts.

Macroscopic, concentric ridge-like markings on a fatigue fracture surface, each corresponding to a pause or change in crack-growth rate, that together outline the successive positions of the advancing crack front. They are one of the classic macroscopic indicators used to identify fatigue as the failure mechanism, visible without magnification.

A machine component that supports and guides a rotating or sliding part while reducing friction between it and a stationary or another moving part, such as a rolling-element bearing using balls or rollers, or a plain sliding bearing. Bearings are common subjects of wear-related failure analysis, given the relative motion and contact stresses they are designed to sustain.

A mechanical test in which a specimen, often taken from a weld, is bent around a former to a specified angle or radius, used to assess ductility and to reveal surface-breaking defects such as cracks or lack of fusion that open up on the outside of the bend.

A condition or deformation mode resulting from a load applied in a way that curves a component, producing tension on one side and compression on the other.

A high-temperature crystal phase found in titanium and certain other alloys, distinct from the lower-temperature alpha phase, whose relative amount and morphology after processing strongly influence the alloy's strength, ductility, and fracture behavior. Alloys are often classified by how much beta phase they retain at room temperature.

The accumulation of marine organisms — such as barnacles, mussels, or algae — on a submerged surface, which can promote localized corrosion beneath the fouling layer by creating stagnant, oxygen-depleted conditions and a habitat for corrosion-influencing microorganisms. It is a common consideration in the inspection and maintenance of marine and subsea equipment.

A microstructure consisting of two distinct phases coexisting within the same matrix — such as ferrite and austenite in duplex stainless steels, or ferrite and pearlite in many carbon steels — as opposed to a fully single-phase structure. The relative amount and distribution of the two phases strongly influence a material's mechanical and corrosion properties.

A surface-preparation process in which abrasive particles are propelled at high velocity against a component's surface to remove scale, rust, old coating, or contamination, or to roughen it before coating or inspection. Excessive or poorly controlled blasting can also introduce surface damage, such as embedded particles or residual stress, that needs to be distinguished from in-service damage.

A stack of valves and sealing devices installed on a wellhead to control or shut in a well and prevent an uncontrolled release of fluids during drilling or production. Its components are subject to demanding material and inspection requirements because their failure can have severe safety consequences.

A product category covering the main, central structural portion of a component — such as a valve, pump, or fitting — that houses its internal parts and connects to the surrounding piping or assembly, distinguished from smaller attached elements such as caps, covers, or stems.

An application category covering equipment used to generate steam or hot water by transferring heat from combustion or another heat source, typically operating under both high temperature and high pressure.

A threaded fastener designed to be used with a mating nut to clamp two or more components together, one of the fastener types covered by this atlas alongside pins and other joining elements.

A hardness test and scale in which a hardened steel or carbide ball is pressed into a material's surface under a fixed load, with hardness calculated from the diameter of the resulting indentation. It is well suited to coarse-grained or heterogeneous materials and to testing over a larger area than more localized hardness methods.

A condition describing a component or material that exhibited little or no plastic deformation before failing, consistent with brittle fracture rather than a ductile failure mode.

Fracture that occurs with little or no prior plastic deformation, typically propagating rapidly and leaving a relatively flat, often crystalline-looking fracture surface. It is associated with low-toughness conditions such as low temperature, high loading rate, or an embrittled microstructure.

A tensile or other mechanical test specimen after it has fractured during testing, examined to relate the specimen's fracture appearance to the properties measured in the test.

A sudden loss of structural stability in which a slender or thin-walled component under compressive load deforms sideways or collapses out of its original shape, rather than failing by simple material overstress. It can occur elastically, at loads well below the material's yield strength, purely as a function of the component's geometry and how it is supported.

The deposition of weld metal onto a worn or undersized surface to restore its original dimensions, as opposed to a weld overlay applied specifically for corrosion or wear resistance rather than for size restoration. It is a common repair technique for worn shafts, rolls, and similar components.

A weld joint in which two members are joined edge to edge in approximately the same plane, typically welded with a groove weld along the joint, as distinguished from a fillet-welded joint where the members meet at an angle. It is a common joint type for joining plates or pipe sections end to end.

A weld overlay of a compatible filler metal applied to one side of a joint before the final weld is made, most often used when welding dissimilar metals, to provide a more compatible transition layer before joining to the second material. It reduces the risk of cracking or embrittlement that can occur when a dissimilar-metal weld is made directly.

A carbon steel whose main strengthening alloying addition is manganese, a common and economical combination used widely in structural and pipeline steels.

An electroplated coating of cadmium applied to steel fasteners and other components to provide corrosion protection and a low-friction, easily lubricated surface, historically common in aerospace and marine hardware. Its use has declined due to the toxicity of cadmium, and it is now restricted or replaced by other coatings in many applications.

The final weld pass in a multi-pass weld, deposited over the underlying fill passes to complete the joint and form the visible weld surface. Its shape, penetration, and any defects are often examined separately from the earlier passes in a weld failure analysis.

The gradual merging and coarsening of fine, dispersed carbide particles into fewer, larger particles during prolonged exposure to elevated temperature, driven by the material's tendency to reduce its total internal interface area. It is a useful indicator, visible under the microscope, of how much high-temperature service or overheating a component has experienced.

The formation of carbide particles from a metal's solid solution, typically triggered by cooling or by exposure to an intermediate temperature range where carbon and carbide-forming elements are no longer fully soluble in the matrix. Where it occurs preferentially at grain boundaries, it can deplete the surrounding matrix of alloying elements and reduce corrosion resistance or toughness.

A thermal cutting and gouging process that uses an electric arc between a carbon electrode and the workpiece, combined with a jet of compressed air, to melt and blow away metal — commonly used to remove a weld root pass before back-welding, or to remove a defect before repair.

A steel whose primary strengthening comes from carbon content, with only incidental amounts of other alloying elements, as distinguished from alloy steels that contain deliberate additions such as chromium, nickel, or molybdenum for specific property improvements.

A condition in which carbon has diffused into the surface of a low-carbon steel component, usually deliberately, to increase surface hardness and wear resistance while retaining a tougher core, though unintended carburization can also occur from certain high-carbon service environments.

A product category covering an outer housing or shell that encloses and protects internal components, such as a bearing case or gearbox case, distinguished from the parts it contains.

A heat-treatment process that hardens only the outer layer, or case, of a steel component — such as by carburizing, nitriding, or induction hardening — while leaving the core softer and tougher. It is used to combine a wear-resistant surface with a core able to absorb impact without becoming brittle.

An iron-carbon alloy with a carbon content high enough to promote the formation of graphite during solidification, giving it good castability and, depending on the form the graphite takes, a range of mechanical properties distinct from steel.

A component or product form produced by pouring molten metal into a mold and allowing it to solidify into the desired shape, as distinguished from a wrought product formed by rolling, forging, or other mechanical deformation.

A corrosion-control technique that makes a metal structure the cathode of an electrochemical cell, either by connecting it to a more easily corroded sacrificial anode or by supplying current from an external power source, so that corrosion is driven to occur elsewhere instead of on the protected structure. It is widely used on buried pipelines, subsea structures, and ship hulls.

A wear and erosion mechanism in which vapor bubbles form in a liquid at a region of locally low pressure, such as near a valve, pump impeller, or propeller, and then collapse violently as they move into a region of higher pressure, generating repeated microscopic shock loading on the adjacent surface. Repeated cavitation collapse can progressively pit and erode a component's surface.

A solidification microstructure intermediate between a fully cellular and a fully dendritic form, in which the growing solid develops short secondary arms off a primary cellular structure. Its appearance reflects the local solidification rate and thermal gradient during casting or welding.

A solidification microstructure in which the solid grows from the liquid as a regular array of rounded or elongated cells, without the branching secondary arms of a dendritic structure, typically forming at a lower solidification rate or shallower thermal gradient than dendritic growth.

A hard, brittle iron carbide phase that forms a major constituent of steel and cast iron microstructures, appearing as lamellae within pearlite, as a network along grain boundaries, or as isolated particles. Its amount, size, and distribution strongly influence a steel's hardness, wear resistance, and toughness.

The concentration of alloying elements or impurities along the central plane or axis of a solidified casting or continuously cast product, occurring where the last liquid to solidify — enriched in rejected solute — collects at the center. It can leave the centerline region weaker or more crack-susceptible than the rest of the cross-section.

A casting process in which molten metal is poured into a rotating mold, using centrifugal force to press the metal against the mold wall and produce a dense, hollow, generally cylindrical product such as a pipe or roll. It typically yields a more uniform, less defect-prone structure than static casting methods.

A standardized mechanical test in which a notched specimen is struck by a swinging pendulum to measure the energy absorbed during fracture, used to assess a material's toughness and its susceptibility to brittle fracture, particularly at low temperature.

An application category covering equipment used in chemical processing, often exposed to a wide range of aggressive process fluids and demanding combinations of temperature and pressure.

V-shaped ridges on a brittle fracture surface that point back toward the origin of fracture, a fractographic feature commonly used to help locate where a crack initiated.

A cast iron in which rapid cooling at the mold surface — often by using a metal chill — suppresses graphite formation and produces a hard, wear-resistant white cast iron layer at the surface, while the slower-cooling interior retains a tougher gray cast iron structure. It combines a hard working surface with a less brittle core.

A form of stress corrosion cracking driven by chloride ions in the environment, particularly affecting austenitic stainless steels under tensile stress in warm, chloride-bearing conditions such as seawater or certain process fluids. It produces branching, often transgranular cracks that can propagate with little visible surface attack.

A thin, chemically formed protective coating produced by treating a metal surface, most often zinc- or aluminum-based, with a chromate solution that reacts with the surface to form a corrosion-resistant conversion layer. It is commonly applied over electroplating to improve corrosion resistance and provide a base for subsequent painting.

A chemical etching solution based on chromic acid, used to reveal specific microstructural features — such as grain boundaries or particular phases — that respond differently to other common etching reagents. The choice of etchant is an important variable in preparing a sample for accurate micrography.

A metallic alloying element that forms a thin, adherent, self-repairing passive oxide film on a metal's surface once present above a threshold amount, which is the basis of stainless steel's corrosion resistance. It also increases hardenability and, at higher levels, high-temperature oxidation resistance.

An electroplated coating of chromium applied to a component's surface to provide a hard, wear-resistant, and corrosion-resistant working surface, or a bright decorative finish, depending on the plating process used. It is commonly applied to piston rods, rolls, and other components subject to sliding wear.

A layer of a corrosion- or wear-resistant alloy metallurgically bonded to the surface of a less expensive or less resistant base metal — typically by roll bonding or explosion welding for plate, or by weld overlay for other product forms — to combine the base metal's structural economy with the cladding alloy's resistance. Clad plate is a common way to obtain a corrosion-resistant surface without fabricating an entire component from the more expensive alloy.

Flat, mirror-like facets on a fracture surface corresponding to fracture along specific crystallographic planes within individual grains, a characteristic fractographic feature of brittle, cleavage-type fracture.

The region of the heat-affected zone nearest the weld fusion line that reaches the highest peak temperature during welding, close to the melting point, causing pronounced grain growth compared with the rest of the heat-affected zone. Its coarse grain structure often gives it lower toughness than other regions of the weld and heat-affected zone, making it a frequent focus of weld toughness testing.

A microstructure with relatively large grains or constituent size, as opposed to a fine structure, often resulting from slow cooling, high-temperature exposure, or grain growth during processing. Coarse structures are generally associated with lower strength and, in some cases, reduced toughness compared with finer structures of the same composition.

A layer of a different material applied to a component’s surface — such as by plating, painting, or thermal spray — to provide protection against corrosion or wear, or another functional property.

A cold-working process in which a metal bar, wire, or tube is pulled through a die to reduce its cross-section and increase its length, increasing strength and hardness through work hardening while producing a smooth surface finish and tight dimensional tolerance.

The plastic deformation of a metal at a temperature low enough that it does not recrystallize during the process, such as by rolling, drawing, or forming at or near room temperature. It increases strength and hardness while reducing ductility, through a mechanism known as work hardening.

Cracking that occurs in or near a weld after it has cooled to near room temperature, commonly associated with hydrogen embrittlement in a hardened heat affected zone microstructure.

The sudden loss of a component's or structure's load-carrying capacity, resulting in a large, often catastrophic change of shape or position, as distinguished from a more localized crack or fracture that may or may not lead to complete failure. It is typically the end result of another underlying mechanism, such as buckling, overload, or advanced corrosion or wear, rather than a mechanism in itself.

Elongated, column-like grains that grow perpendicular to a cooling surface during solidification, a characteristic feature of as-cast metal microstructures, especially near the mold wall.

A reddish, highly conductive metallic element used as a base metal in copper alloys and as an alloying addition in some steels and other metals. Its chemical symbol appears throughout the material composition tables in this atlas.

An alloy based on copper, such as brass or bronze, valued for properties including corrosion resistance, electrical or thermal conductivity, and, in some compositions, resistance to biofouling.

A compositional gradient that develops within individual grains or dendrites as an alloy solidifies, because the first solid to form is depleted in certain alloying elements relative to the last liquid to solidify. It leaves the grain interior and its boundary with different compositions, which can affect local corrosion resistance or mechanical properties until removed by homogenizing heat treatment.

The gradual degradation of a metal through chemical or electrochemical reaction with its environment, one of the most common causes of material failure and a central subject of this atlas.

A form of fatigue in which cyclic loading and a corrosive environment act together, typically producing crack initiation and growth at lower stress levels or after fewer cycles than fatigue in a non-corrosive environment alone.

A localized separation or discontinuity within a material, typically initiated where stress concentrates beyond the material's local strength. It is one of the most common features examined in a failure analysis.

The slow, time-dependent plastic deformation of a material under sustained load, occurring even below the material's yield strength when the service temperature is high enough relative to its melting point. It is a distinct failure mechanism from short-term overload, and the strain it accumulates can eventually lead to rupture in components that operate under load at elevated temperature for long periods.

Small cavities that nucleate and grow within a material during creep deformation, typically forming along grain boundaries and coalescing as deformation continues. Their presence in a micrograph is a diagnostic sign that a component has been subjected to prolonged loading at elevated temperature, often preceding creep rupture.

A localized corrosion mechanism that occurs within a narrow, shielded gap — such as under a gasket or washer, or at a poorly fitted joint — where stagnant conditions let the local chemistry become more aggressive than in the surrounding bulk environment. It is a common cause of unexpected, hard-to-inspect attack in stainless steels and other alloys that rely on a passive surface film.

A copper-based alloy containing nickel as its main alloying addition, valued for excellent resistance to seawater corrosion and biofouling, and widely used for seawater piping, heat exchanger tubing, and marine hardware.

A manufacturing or sample-preparation operation that separates material into pieces or removes material along a defined line, using methods such as sawing, torch or plasma cutting, or machining. Evidence of cutting on a component or a metallographic sample is often simply a normal fabrication or preparation feature rather than a sign of damage, and needs to be distinguished from cracking during examination.

A high-carbon, high-chromium tool steel grade, hardenable to a high hardness while retaining good wear resistance and dimensional stability during heat treatment, widely used for dies, punches, and cutting tools.

The prefix for standards issued by DIN, the German Institute for Standardization (Deutsches Institut fur Normung).

A broad condition category covering components that show some form of degradation or deterioration in service — such as cracking, corrosion, or wear — as opposed to components in sound, as-manufactured condition.

The loss of carbon from the surface of a steel component, typically occurring when it is exposed to a high-temperature oxidizing or otherwise reactive atmosphere during processing or service. It leaves a softer, weaker near-surface layer that can act as a preferential site for cracking, wear, or fatigue initiation.

A near-surface region of a steel component that has lost carbon relative to the bulk composition, typically as a result of exposure to a high-temperature oxidizing or otherwise reactive atmosphere during processing or service. Because the decarburized layer is softer and weaker than the core material, it can act as a preferential site for cracking, wear, or fatigue initiation.

Thin, mirror-symmetric bands within a grain, formed when part of the crystal lattice is sheared into a twin orientation of the surrounding matrix, typically as a mechanism of plastic deformation in certain metals at high strain rate or low temperature. They are visible under the microscope and, in some materials, are a normal deformation feature rather than a sign of damage.

Describes a material or component whose properties have deteriorated from their original state, whether through corrosion, wear, fatigue, or another in-service mechanism.

An intermetallic phase that can form in certain nickel-based superalloys and stainless steels after prolonged high-temperature exposure, distinct from the sigma phase but similarly capable of depleting the surrounding matrix of alloying elements and reducing toughness. Its presence is an important consideration when evaluating components that have seen extended high-temperature service.

A high-temperature form of ferrite retained at room temperature in certain stainless steel weld metals and castings, distinct from the ferrite found in plain carbon and low-alloy steels, and often discussed in terms of its effect on weldability and toughness.

Describes a tree-like, branching microstructure formed during solidification, most commonly seen in as-cast metals before any subsequent hot working breaks up the pattern.

A Norway-based classification society and standards body serving the maritime, energy, and offshore industries, known for its technical rules and certification of vessels, structures, and equipment.

Microstructural phases whose presence, in the amount or form found, is considered harmful to a material's mechanical or corrosion properties, as opposed to a phase that is simply present without adverse effect.

A selective corrosion mechanism in copper-zinc alloys (brasses) in which zinc is preferentially leached from the alloy, leaving behind a porous, weakened, copper-rich layer that retains the original shape of the component. It is a recognized cause of unexpected leaks or fractures in brass fittings and components that otherwise appear visually intact.

A coating process in which a coating element is introduced at the surface and then diffuses into the base metal at elevated temperature, forming a graded layer that is metallurgically bonded to the substrate rather than simply deposited on top of it. Chromizing and aluminizing are common examples, used to improve high-temperature oxidation or corrosion resistance.

The mixing of base metal into the weld metal during welding, which changes the final chemical composition of the weld deposit compared with the filler metal alone. Excessive dilution can alter the weld metal's properties, such as its corrosion resistance or strength, particularly when joining or overlaying dissimilar materials.

Small, cup-like depressions on a fracture surface formed by microvoid coalescence, a characteristic fractographic feature of ductile fracture.

The joining by welding of two base metals with substantially different chemical composition or metallurgical characteristics, such as a carbon steel to a stainless or nickel alloy. Such welds require careful selection of filler metal and procedure to control dilution and to avoid brittle or crack-susceptible microstructures forming at the fusion boundary.

A hollow, threaded pipe used to rotate and convey drilling fluid to a drill bit during the drilling of a well, connected in a string that also transmits weight and torque to the bit.

A microstructure containing two distinct grain size populations within the same material, rather than a single, uniform grain size — for example, a mixture of coarse and fine grains resulting from uneven recrystallization or abnormal grain growth. It can lead to non-uniform mechanical properties compared with a material with a single, consistent grain size.

A condition describing a component or material that exhibited significant plastic deformation before failing, consistent with ductile fracture rather than a brittle failure mode.

A cast iron in which the graphite is present as rounded, nodular particles rather than as flakes, giving it substantially better ductility and toughness than gray cast iron while retaining good castability. It is one of the most widely used cast iron families for components that need to withstand impact or tensile loading, not just compression.

Fracture preceded by significant plastic deformation, typically producing a rougher, more fibrous fracture surface than brittle fracture and often showing microvoid coalescence at higher magnification.

A microstructure containing a mixture of ferrite and austenite in significant proportions, the defining feature of duplex stainless steels, which combines characteristics of both phases.

A nondestructive inspection method in which a liquid dye is applied to a clean surface, allowed to seep into surface-breaking discontinuities such as cracks or porosity, and then drawn back out by a developer to make the flaw visible. It is widely used to detect surface cracks in welds and components that cannot be found by visual inspection alone.

A higher-strength shipbuilding steel grade within a classification-society grading system for hull structural steel, offering greater strength than the base grade for a given steel type while meeting the same toughness requirements for marine service. It is used where a lighter structure or higher load capacity is needed compared with ordinary-strength hull steel.

The prefix for standards issued by CEN, the European Committee for Standardization, and adopted by its national member bodies as European Norms.

A process in which a thin layer of metal is deposited onto a component's surface by passing an electric current through a solution containing dissolved metal ions, which are reduced and deposited onto the part. It is used to provide corrosion protection, wear resistance, or a decorative finish, with cadmium, zinc, chromium, and nickel among the most common plating metals.

A measure of ductility obtained from a tensile test, describing how much a specimen stretches before fracture relative to its original length. It is one of the standard mechanical properties reported alongside strength and hardness to characterize how a material deforms before failing.

An application category covering equipment used in the generation, conversion, or transmission of power — such as in power plants, turbines, and related energy infrastructure — one of the industry sectors represented in this atlas.

An analytical technique, usually paired with a scanning electron microscope, that identifies the chemical elements present in a sample by detecting the characteristic X-rays it emits under electron bombardment. It is commonly used in failure analysis to determine the composition of inclusions, corrosion products, or contaminants observed in a micrograph.

An application category covering components used in internal combustion or other engines, subject to a demanding combination of cyclic mechanical loading and elevated temperature.

The growth of new grains at a solidification front that continue the same crystal orientation as the existing solid grain they grow from, without needing to nucleate a new grain from scratch — the dominant grain growth mechanism at a weld's fusion boundary as it solidifies. It is the reason weld metal grain structure is often continuous with, and oriented similarly to, the adjacent base metal grains at the fusion line.

Grains that are roughly equal in dimension in all directions, as opposed to elongated columnar grains, typically found in the interior of a casting or after recrystallization during hot working or heat treatment.

A wear mechanism in which material is progressively removed from a surface by the impact of a moving fluid, or of solid particles or liquid droplets carried within it, rather than by contact with another solid surface. It is one of the principal mechanisms grouped under the general term wear, and is often accelerated where flow becomes turbulent or changes direction abruptly.

A specific composition at which two or more phases in an alloy system solidify together, simultaneously, from the liquid at a single, minimum melting point lower than that of either phase solidifying on its own. Eutectic structures have a characteristic fine, intergrown microstructure that is often readily recognizable under the microscope.

A specific composition at which a single solid phase transforms into two other solid phases simultaneously on cooling, in a solid-state analogue of a eutectic reaction. In plain carbon steel, the eutectoid reaction produces pearlite from austenite and is the basis for classifying steels as hypoeutectoid, eutectoid, or hypereutectoid according to their carbon content.

An image focused on the outer surface of a component, as opposed to an internal or bore surface, or a cut cross-section.

A condition describing a flaw introduced during a component’s manufacture or fabrication — such as during casting, forging, machining, or welding — as distinguished from damage or degradation that develops later, in service.

A weld made during the original manufacture or fabrication of a component, as distinguished from a weld made later as a repair.

A general product category covering components used to mechanically join or secure two or more parts together, such as bolts, pins, and rivets.

Progressive, localized damage that develops in a material subjected to cyclic loading, eventually leading to crack initiation and growth even at stress levels well below the material's static strength. It is one of the most common mechanical causes of in-service failure.

A crack that initiates and grows under cyclic loading, typically starting at a stress concentration such as a surface flaw, notch, or inclusion, and often recognizable by characteristic features such as beach marks or striations on the fracture surface.

A fine, parallel ridge pattern on a fatigue fracture surface, formed by the incremental advance of a crack with each loading cycle, and one of the clearest fractographic indicators that fatigue was the mechanism of cracking.

A micrograph of a sample etched with a ferric chloride solution, an etchant commonly used on stainless steels and other highly corrosion-resistant alloys that resist more common etchants.

The body-centered-cubic phase of iron, stable at room temperature in plain carbon and low-alloy steels, and one of the basic microstructural constituents from which many other steel microstructures are described.

A weld-metal microstructural constituent consisting of ferrite grains with a second phase — typically carbide or austenite — aligned along the ferrite grain boundaries in a preferred direction, one of the classifications used to describe as-deposited weld metal microstructure. Its presence and amount are assessed when correlating a weld's microstructure with its toughness.

Describes a material or microstructure composed predominantly of ferrite, the body-centered-cubic form of iron, giving it characteristic magnetic and mechanical behavior distinct from an austenitic structure.

Describes a steel microstructure composed of a mixture of ferrite and bainite, an intermediate result between the fully ferritic-pearlitic structures formed at slower cooling rates and fully bainitic or martensitic structures formed at faster ones.

A steel microstructure composed of a mixture of ferrite and pearlite, the equilibrium constituents typically formed in low and medium carbon steels cooled at a moderate rate from an elevated temperature.

A broad material category covering alloys based on iron, including steels and cast irons, as distinguished from non-ferrous alloys such as those based on aluminum, copper, nickel, or titanium.

The consumable material added during welding to help fill the joint and form the weld, such as a welding rod, wire, or electrode core, as distinguished from the weld metal, which is the fused combination of filler metal and any melted base metal after the weld is complete.

A weld of roughly triangular cross-section used to join two surfaces at an angle to each other, typically where one member overlaps or is perpendicular to another, as opposed to a butt weld joining two edges in the same plane. It is one of the most common weld joint geometries in structural and piping fabrication.

A product category covering material or components examined in their completed, in-service or ready-for-service form, as opposed to raw material still awaiting further fabrication.

A component used to connect, adapt, or terminate sections of pipe — such as an elbow, tee, or coupling — as distinguished from a straight run of pipe itself.

A component with a projecting rim, typically bolted to a mating flange to join sections of pipe or equipment, forming a pressure-containing joint that can be disassembled.

A resistance welding process in which the ends of two components are brought together while an electric current arcs across the closing gap, melting the abutting surfaces before they are forced together under pressure to complete the weld. It is commonly used for joining rail, pipe, and other long products end to end in a continuous production line.

A ship-shaped or barge-like offshore vessel that processes and stores produced oil or gas before offloading it to shuttle tankers, used in some offshore fields in place of a fixed platform. Its hull and topside equipment are exposed to a demanding combination of marine and process-related degradation mechanisms.

An arc welding process that uses a continuously fed tubular electrode filled with flux, which shields the weld pool either on its own or together with an auxiliary shielding gas. It is valued for its high deposition rate and is widely used in structural and pipe welding.

In submerged arc welding, the amount of granular flux consumed relative to the amount of wire electrode consumed during welding — a process variable that affects weld bead shape, penetration, and the amount of alloying pickup from an active flux. Keeping this ratio within a qualified range is part of maintaining a consistent, qualified welding procedure.

A component or product form produced by mechanically deforming a heated metal billet under compressive force — by hammering, pressing, or rolling — into the desired shape, as distinguished from a cast product formed by solidifying molten metal in a mold.

The examination of a fracture surface using a scanning electron microscope to characterize how a material failed — for example, distinguishing brittle, ductile, or fatigue fracture features from the morphology of the surface itself.

The separation of a material into two or more pieces under stress, examined in failure analysis to determine how and why the separation occurred — for example, whether it developed suddenly, with little warning, or only after significant deformation.

The microscopic mode by which a crack actually propagated through a material — such as by cleavage, microvoid coalescence, or intergranular separation — determined by examining the fracture surface under a microscope. Identifying the fracture micromechanism is often the key step that links a fracture surface to its underlying failure mechanism.

A steel grade formulated with additions such as sulfur or lead to improve machinability by promoting cleaner chip formation — the steel-specific case of the more general free-machining alloy concept, common in high-volume screw-machine and fastener production.

An alloy formulated with additions — such as lead, sulfur, or bismuth — that make it easier and faster to machine by promoting cleaner chip formation and reducing tool wear, at some cost to other properties such as strength, corrosion resistance, or weldability. Free-machining grades of steel and brass are common in high-volume, machined fastener and fitting production.

A weld in which the weld metal fully fuses through the entire thickness of the joint, leaving no unfused root area, as opposed to a partial penetration weld. It is typically required where the joint must carry the full design load across its cross-section.

The boundary between the weld metal and the base metal in a welded joint, marking where melting occurred during welding. It is a common site for defects and cracking because of the abrupt change in composition and microstructure across it.

The prefix for Chinese national standards (Guobiao), issued under the oversight of China's national standardization administration.

A corrosion mechanism that occurs when two dissimilar metals are in electrical contact within an electrolyte, causing the more active metal to corrode preferentially while the more noble metal is protected — the same electrochemical principle used deliberately in cathodic protection with a sacrificial anode. It is a common cause of accelerated, localized corrosion at bolted or welded connections between dissimilar metals.

The application of a zinc coating to steel, most commonly by hot-dip immersion in molten zinc, to protect the underlying steel from corrosion through both a physical barrier and the sacrificial, cathodic protection the zinc provides once exposed. It is one of the most widely used corrosion-protection methods for structural and outdoor steel.

An arc welding process that feeds a continuous solid wire electrode through a welding gun while an externally supplied shielding gas protects the weld pool from atmospheric contamination. It is a common, highly productive process for both manual and automated welding of steels and other metals.

An arc welding process that uses a non-consumable tungsten electrode to produce the arc, with a separate filler rod added by hand or by machine and an inert shielding gas protecting the weld pool. It produces precise, high-quality welds and is often used where weld appearance and control matter, such as root passes on pipe.

An image showing a broad, low-magnification view of a specimen or feature, used to establish overall context before examining specific details at higher magnification.

The formation of a second phase or particles along the boundaries between grains, rather than dispersed through the grain interior, often during exposure to elevated temperature. Because grain boundaries are already a preferred path for crack growth and corrosion attack, precipitation along them can further weaken the material or its corrosion resistance.

A microstructure with a smaller-than-typical grain size, usually the deliberate result of thermomechanical processing or an alloying addition intended to improve strength and toughness, since finer grains generally improve both properties at once.

A microstructural texture in which grains or constituents appear as discrete, rounded or polygonal units, as opposed to a more elongated, layered, or needle-like arrangement.

Flake-shaped particles of free graphite distributed through the microstructure of gray cast iron, formed as carbon precipitates out of the melt during solidification. Their shape, size, and distribution strongly influence the alloy's strength, machinability, and thermal conductivity, and distinguish gray cast iron from cast irons with nodular or other graphite morphologies.

A cast iron in which most of the carbon is present as flake graphite distributed through a ferritic or pearlitic matrix, giving the fracture surface its characteristic gray color. It offers good machinability, damping, and thermal conductivity, but its flake graphite makes it more brittle and weaker in tension than nodular cast iron.

The region of base metal adjacent to a weld whose microstructure and mechanical properties have been altered by the heat of welding without being melted. Because its properties can differ significantly from both the weld metal and the unaffected base metal, it is a common site of cracking and other weld-related failures.

An application category covering components used to transfer heat between two fluids without mixing them, such as the tubes and shell of a heat exchanger, exposed to a combination of thermal and corrosive service conditions.

A condition describing a component’s state as it relates to a heat-treatment process it received — such as quenching, tempering, annealing, or normalizing — used to achieve a desired combination of strength, hardness, and toughness.

A steel containing a relatively high total content of alloying elements, well beyond that of a low alloy steel, added to achieve properties such as high corrosion resistance, high-temperature strength, or wear resistance — stainless steels are a major example.

A carbon steel with a relatively high carbon content, providing high hardness and strength, particularly after heat treatment, at the expense of ductility and weldability compared with lower carbon grades.

A low alloy steel designed to achieve higher strength than conventional carbon steel primarily through microalloying and controlled processing rather than through heat treatment, while retaining good weldability and toughness.

A condition category covering components exposed to elevated service temperatures, which can promote degradation mechanisms — such as creep, oxidation, or microstructural change — that do not occur, or occur much more slowly, at room temperature.

The shaping or forming of a metal at a temperature high enough to allow easy plastic deformation — and, for steel, typically above the recrystallization temperature — such as by hot rolling or forging, as distinguished from cold working performed near room temperature.

Cracking that occurs in a weld or casting while it is still at an elevated temperature, near or during solidification, typically associated with low-melting-point constituents concentrated at grain boundaries.

A loss of ductility in titanium, zirconium, and certain other reactive metals caused by the formation of brittle hydride phases within the microstructure, most often where hydrogen has been absorbed during processing or service. It is a distinct mechanism from hydrogen embrittlement in steels, since it involves the formation of a new brittle phase rather than dissolved atomic hydrogen alone.

A condition category covering degradation associated with hydrogen absorbed into a metal, encompassing mechanisms such as hydrogen embrittlement and hydrogen-induced or sulfide stress cracking.

A loss of ductility and load-carrying capacity caused by atomic hydrogen dissolved in a metal, which can enter during processes such as welding, pickling, or electroplating, or through exposure to hydrogen-bearing environments in service. It can lead to delayed, often brittle cracking under stresses well below what the material would normally withstand.

A pressure test in which a vessel, pipe, or other pressure-containing component is filled with a liquid, usually water, and pressurized to verify its structural integrity and check for leaks before it is placed in service. It is a common qualification and periodic-inspection method for pressure equipment in the oil and gas and process industries.

The prefix for standards issued by ISO, the International Organization for Standardization, a worldwide federation of national standards bodies.

A diagram or sketch, rather than a photograph, used to identify the location or orientation of a sample or feature within a component.

A mechanical test in which a specimen is struck suddenly, rather than loaded gradually, to evaluate a material's toughness and its tendency toward brittle behavior. The Charpy and Izod tests are the two most common standardized forms.

An image focused on the mid-thickness region of a specimen's cross-section, used to examine features such as segregation, inclusions, or a crack's path through the interior of a component, as distinct from features at or near a surface.

The uneven distribution of alloying elements or impurities that develops between the dendrite arms of a solidifying casting or weld, as the last liquid to solidify becomes enriched in elements rejected by the earlier-forming solid. It can leave the interdendritic regions locally weaker or more susceptible to cracking and corrosion than the rest of the structure.

A localized corrosion mechanism that attacks preferentially along grain boundaries, leaving the grain interiors relatively unattacked, usually because the boundary region has a different composition — often due to precipitation such as chromium carbides — that makes it more susceptible to the environment. Sensitized stainless steels are a classic example of a material susceptible to this mechanism.

Cracking that propagates along the boundaries between a material's grains rather than through the grains themselves. It is often associated with mechanisms that weaken grain boundaries specifically, such as certain forms of stress corrosion cracking, hydrogen embrittlement, or sensitization.

Fracture that propagates along the boundaries between a material's grains, giving the fracture surface a faceted appearance corresponding to the grain structure, as opposed to transgranular fracture, which cuts through the grains themselves.

Stress corrosion cracking that propagates along grain boundaries rather than through the grains themselves, typically where the boundary region has been made more susceptible to the environment by a mechanism such as sensitization. It is distinguished from transgranular stress corrosion cracking by the fracture path it follows relative to the grain structure.

An image focused on the inner surface of a hollow component, such as the bore of a pipe, as opposed to its external or outer surface.

The formation of a second phase or particles within the interior of a grain, rather than along its boundaries, often during aging or prolonged elevated-temperature exposure. Unlike precipitation concentrated at grain boundaries, intragranular precipitation is distributed generally through the grain, affecting bulk properties such as strength and toughness rather than concentrating along a preferential crack or corrosion path.

A metallic element that is the primary constituent of steels and cast irons, forming the base to which carbon and other alloying elements are added to produce the ferrous materials covered in this atlas. Its chemical symbol appears throughout the material composition tables.

A low-magnification photograph of a sample etched with Kalling's reagent, used to reveal larger-scale structure in stainless steels and other highly alloyed materials rather than fine microstructural detail.

A photomicrograph taken by optical microscopy of a sample etched with Kalling's reagent, an etchant commonly used to reveal the microstructure of stainless steels and other highly alloyed materials that nital does not etch well.

A photomicrograph taken by optical microscopy of a sample etched with Keller's reagent, an etchant commonly used to reveal the microstructure of aluminum alloys.

A unit of mass, part of the metric system, used in this atlas mainly when reporting sample or component weight, or as a component of derived units for force and pressure.

A weld discontinuity in which the weld metal fails to fuse completely with the base metal or with a previously deposited weld pass, leaving an unbonded interface within the joint. It behaves as a planar defect that reduces the joint's load-carrying capacity and can act as a site for crack initiation.

A surface defect in a rolled or forged product formed when metal folds over itself without fusing, typically originating from an earlier processing step such as excess material at an edge or a die mismatch.

A dense, soft, corrosion-resistant metallic element occasionally used or found as an alloying or trace element in engineering materials — such as in free-machining alloys, certain bearing and solder alloys, or as an undesirable impurity affecting weldability and toughness.

A condition or observed feature indicating that a pressure-containing component has failed to retain its contained fluid, whether through a crack, a corroded wall, a seal failure, or another loss of containment.

A weld cracking mechanism in which low-melting-point constituents at grain boundaries in the base metal or weld metal are locally melted by the heat of welding and then crack as the surrounding material solidifies and contracts around them. It is associated with segregated or impurity-rich alloys and can occur in the heat-affected zone as well as in the weld metal itself.

Corrosion concentrated in specific areas of a surface rather than distributed evenly across it, encompassing mechanisms such as pitting, crevice corrosion, and corrosion beneath deposits or gaskets, as distinguished from general corrosion.

A pipe formed by rolling plate or strip into a cylinder and welding it along a straight longitudinal seam, as distinguished from a seamless pipe.

A cross-section cut parallel to the long axis or primary direction of a component, such as a pipe or shaft, used to reveal how a feature — a crack or a microstructural gradient — extends along that axis.

A steel containing modest additions of alloying elements — such as chromium, molybdenum, nickel, or vanadium — in amounts too low to be considered a high-alloy steel but sufficient to improve properties such as strength, toughness, or resistance to a specific service condition. It is widely used in structural, pressure-vessel, and piping applications where plain carbon steel does not offer enough performance.

A carbon steel with a relatively low carbon content, giving it good ductility and weldability at the expense of the higher strength and hardenability achievable in medium or high carbon steels.

An image captured at low magnification, showing a broader field of view than a high-magnification micrograph, typically used to establish the overall location and extent of a feature before examining it in more detail.

A component whose final shape and dimensions were produced primarily by machining — such as turning, milling, or drilling — material away from a starting blank, as distinguished from a cast or forged near-final shape.

A low-magnification photograph of a sample etched electrolytically with oxalic acid, a technique commonly used to reveal grain-boundary attack associated with susceptibility to intergranular corrosion in stainless steels.

The visual or low-magnification examination of a metal surface, cross-section, or fracture surface — typically after etching — to reveal large-scale features such as weld profiles, grain flow, segregation, or the path of a fracture, as distinguished from microscopic (micrographic) examination.

A nondestructive inspection method in which a ferromagnetic component is magnetized and then covered with fine iron particles, which gather at surface or near-surface discontinuities where the magnetic field leaks out of the material, making cracks and other flaws visible. It is limited to ferromagnetic materials and is widely used for inspecting welds and forgings.

A metallic element commonly added to steels to improve strength and hardenability and to counter hot shortness by combining preferentially with sulfur. Its chemical symbol appears throughout the material composition tables in this atlas.

A hard, brittle, needle-like microstructure formed when austenite in a steel is cooled rapidly enough to suppress diffusion-controlled transformation, the basis of quench hardening.

A family of stainless steels with a predominantly martensitic microstructure after heat treatment, offering higher hardness and strength than austenitic or ferritic grades but generally lower corrosion resistance and toughness.

A carbon steel with a carbon content between that of low carbon and high carbon grades, offering a balance of strength and ductility, and commonly hardenable by heat treatment such as quenching and tempering.

A unit of pressure or mechanical stress used throughout this atlas to report properties such as tensile strength, yield strength, and hydrostatic test pressure.

Corrosion caused or accelerated by the metabolic activity of microorganisms, such as sulfate-reducing bacteria, that colonize a metal surface and alter the local chemistry beneath biofilms or deposits. It is a recognized cause of localized, often pitting-type attack in pipelines, storage tanks, and other equipment exposed to stagnant or poorly treated water.

Very small cracks, often visible only under microscopic magnification, which can indicate an early stage of a degradation mechanism such as fatigue or stress corrosion cracking before they coalesce into a larger, more obvious crack.

The examination of a polished and typically etched metal surface under a microscope to reveal its microstructure — phases, grain size, inclusions, and similar features too fine to see with the unaided eye. It is one of the most fundamental techniques used throughout this atlas's failure analyses.

A photomicrograph produced using a standardized oxalic acid etch test that reveals grain-boundary attack associated with susceptibility to intergranular corrosion in austenitic stainless steels.

A hardness test performed with a very small indenter and load, used to measure the hardness of small features — such as an individual phase, a thin coating, or a narrow region like a heat-affected zone — rather than the bulk average hardness of a component. Vickers and Knoop are the two most common microhardness scales.

The fine-scale internal structure of a material — its grains, phases, and other constituents — as revealed by preparing and examining a polished and often etched sample. Microstructure is a central subject of failure analysis because it records how a material was processed and how it responded to service conditions.

A ductile fracture mechanism in which small voids nucleate at inclusions or second-phase particles, grow under continued straining, and eventually link together to form the fracture surface — recognized under the microscope by its characteristic dimpled appearance. It is one of the fracture micromechanisms used to distinguish ductile from brittle fracture.

A metallic alloying element added to steels and other alloys to improve strength at elevated temperature, hardenability, and resistance to pitting and crevice corrosion, particularly in stainless steels exposed to chloride environments.

The prefix for European standards (EN) as adopted into the French national standards collection by AFNOR, the French national standards body.

A micrograph of a sample etched electrolytically with a sodium hydroxide solution, a technique commonly used to distinguish ferrite from austenite in duplex and other multiphase stainless steels.

A visual examination method using either direct unaided vision or a stereoscope, a low-magnification binocular microscope, to inspect a specimen at a macroscopic level before more detailed microscopy is performed.

A nickel-based alloy also containing significant chromium and iron, a composition family valued for high-temperature strength and resistance to oxidizing and corrosive environments.

A metallic element added to steels and used as a base metal in nickel alloys to improve toughness, corrosion resistance, and high-temperature performance. Its chemical symbol appears throughout the material composition tables in this atlas.

An alloy based on nickel, valued for exceptional resistance to corrosion and high-temperature strength, commonly used in the most severe corrosive or high-temperature service where stainless steels are insufficient.

A metallic alloying element added in small amounts to steels to refine grain size and increase strength through microalloying, and added to some stainless steels and nickel alloys to stabilize carbon and reduce susceptibility to sensitization during welding.

A low-magnification photograph of a sample etched with nital, used to reveal larger-scale features such as weld profile, heat affected zone extent, or banding across a section, rather than fine microstructural detail.

A photomicrograph taken by optical microscopy of a sample etched with nital, a dilute nitric-acid-in-alcohol solution commonly used to reveal the microstructure of steels and cast irons.

A micrograph of a nital-etched sample captured using a scanning electron microscope rather than an optical microscope, used when higher magnification or resolution is needed to resolve fine microstructural detail.

A commercial name for a nitrogen-strengthened austenitic stainless steel alloyed with silicon and manganese for improved resistance to galling and wear, while retaining good general corrosion resistance. It is commonly used for valve stems, fasteners, and other components subject to sliding or rubbing contact.

Graphite present in a cast iron microstructure as rounded, roughly spherical particles rather than as flakes, produced by adding a nodularizing agent such as magnesium or cerium to the melt before casting. It gives ductile (nodular) cast iron substantially better ductility and toughness than gray cast iron, whose graphite forms as flakes.

A standardized, rounded designation used to describe the size of a pipe or pipe fitting, which does not necessarily match any single physical dimension of the component exactly. It is used together with a wall-thickness designation to fully describe a pipe's dimensions.

A broad material category covering alloys not based on iron — such as those based on aluminum, copper, nickel, or titanium — as distinguished from ferrous alloys.

Particles of oxide, sulfide, or other non-metallic compounds trapped within a metal's microstructure, typically originating from the steelmaking or casting process, which can act as stress concentrators or crack initiation sites, particularly under fatigue loading.

A heat treatment in which steel is heated above its transformation temperature and then air-cooled, producing a more uniform, generally finer-grained microstructure than the as-rolled or as-cast condition. It is commonly used to relieve internal stress and improve the consistency of mechanical properties after hot working.

A fastener with an internal thread, designed to be used with a mating bolt or stud to clamp components together.

An application category covering equipment used in the drilling of oil and gas wells, such as drill string components and related tools.

An application category covering equipment installed and operated at sea, away from shore — such as on platforms or floating production vessels — exposed to a demanding combination of marine corrosion and mechanical loading.

An application category covering equipment and components used in the exploration, production, processing, or transport of oil and gas, one of the primary industries represented in this atlas.

An imaging instrument that uses visible light and lenses to produce magnified images of a material's surface or a prepared cross-section, the instrument behind an optical microscopy examination.

An examination technique that uses visible light and lenses to magnify and inspect a material's surface or a prepared cross-section, commonly used to reveal microstructural features such as grain structure, phases, and inclusions. It is one of the most widely used tools in metallurgical failure analysis, often as a first step before more specialized techniques.

A condition in which a component was subjected to a load exceeding what it was designed to withstand, leading to failure through excessive deformation or fracture rather than through a gradual degradation mechanism.

A layer of metal oxide that forms on a surface exposed to oxygen at elevated temperature or in certain corrosive environments, which can be protective, like a passive film, or detrimental depending on its adherence and growth characteristics.

The formation or restoration of a thin, adherent, protective oxide layer on a metal's surface — most notably on stainless steels — that greatly slows further corrosion. It can occur naturally on exposure to air or a corrosive environment, or be induced deliberately by chemical treatment after fabrication.

A lamellar microstructural constituent consisting of alternating layers of ferrite and cementite, formed during the transformation of austenite in carbon and low-alloy steels on cooling.

Describes a material or microstructure composed predominantly of pearlite, a lamellar mixture of ferrite and cementite formed during the transformation of austenite in carbon and low-alloy steels.

A metalloid element present in steel primarily as an impurity from raw materials, where even small amounts segregate strongly to grain boundaries and can promote embrittlement and reduce toughness. Its content is closely controlled in structural and pressure-critical steel grades.

A small, generally cylindrical component used to connect, align, or act as a pivot between two other parts, such as in a pinned joint or fastening assembly.

A hollow, generally cylindrical product form used to convey fluids or gases, distinguished from tube mainly by the standards and dimensional systems used to specify it rather than by any fundamental difference in shape.

An application category covering the network of pipes, fittings, and related components used to convey fluids or gases within a facility or between locations, as distinguished from a single pipe as a product form.

A localized form of corrosion that produces small, often deep cavities in an otherwise largely unaffected surface, as distinguished from general corrosion, which attacks a surface more uniformly. Because the resulting wall-thickness loss concentrates in a small area, pitting can lead to perforation well before general corrosion would.

Permanent, non-recoverable change in a material's shape caused by stress beyond its elastic limit, as distinguished from elastic deformation, which is recovered once the stress is removed. Evidence of plastic deformation near a fracture is a key clue in distinguishing ductile from brittle failure.

A flat, rolled product form supplied in a range of thicknesses, one of the most common raw material and finished component forms covered in this atlas.

A small cavity within a material, most often associated with trapped gas during solidification in a casting or weld, as distinguished from a larger void or a crack.

Small, rounded voids trapped within a metal as it solidifies, most often formed when dissolved gas is rejected from the melt faster than it can escape before solidification is complete. In welding, porosity is a common defect caused by contamination, moisture, or inadequate shielding of the weld pool, and it reduces the effective load-bearing cross-section of the material.

A controlled heating and cooling cycle applied to a welded joint after welding to relieve residual stresses, temper hard microstructures formed in the heat affected zone, or otherwise restore desired mechanical properties. It is commonly required for thick sections, certain steel grades, or welds intended for demanding service, such as sour or high-pressure environments.

A heat-treatment condition in which fine secondary-phase particles are precipitated within a metal's microstructure to increase its strength and hardness. It is a common strengthening route for certain stainless steels and other alloys that cannot be hardened effectively by quenching alone.

A closed container designed to hold a fluid at a pressure different from the surrounding atmosphere, ranging from small vessels to large process equipment, and subject to specific design and inspection requirements because of the stored energy involved.

Large carbide particles that form directly from the liquid during solidification of a high-carbon or highly alloyed steel or cast iron, as distinguished from finer secondary carbides that precipitate later from the solid matrix. Coarse primary carbides can act as sites of stress concentration and reduce toughness.

The first ferrite to form directly from the liquid during solidification of weld metal, appearing either along the boundaries of the solidification grains or, at slightly lower temperature, within them — two of the classifications used in the standard system for describing as-deposited weld metal microstructure. Its amount and morphology influence the toughness of the finished weld.

The boundary of a grain as it existed in the austenite phase at high temperature, which can remain visible — or influence how a crack propagates — after the steel has transformed to another microstructure on cooling. Its size and any phases or precipitates decorating it are important indicators in the failure analysis of heat-treated and welded steels.

The size of the grains as they existed in the high-temperature beta phase of titanium, zirconium, or certain other alloys, which can remain visible as a boundary network after the material has transformed to a lower-temperature microstructure on cooling. It is analogous to prior austenite grain size in steels and is an important quantity in the metallurgical evaluation of these alloys.

An application category covering components used in pumps, which combine mechanical loading and, in many cases, exposure to the pumped fluid's corrosive or erosive characteristics.

A fracture mode that shares features of both cleavage (flat, faceted regions following crystallographic planes) and ductile fracture (dimpled tearing), commonly seen in tempered or hydrogen-affected martensitic steels. Its mixed appearance under the microscope helps distinguish it from purely brittle cleavage fracture.

A heat-treatment condition produced by rapidly cooling a steel from an elevated temperature to form a hard microstructure, followed by reheating to a lower temperature to reduce brittleness while retaining much of the strength gained from quenching. It is a common route for achieving a favorable balance of strength and toughness in structural and pressure-equipment steels.

A product category covering material examined in its unprocessed or semi-processed form — such as billet, ingot, or plate stock — before being fabricated into a finished component.

The formation of a new set of strain-free grains within a cold-worked metal when it is heated to a sufficiently high temperature, replacing the deformed grain structure and restoring ductility at the expense of the strength gained by cold working. It is the mechanism that limits how much a metal can be cold-worked before it must be annealed to continue forming.

A condition describing a component examined after being taken out of operation, whether due to a planned inspection, a scheduled replacement, or a suspected problem, as distinguished from a component that failed catastrophically while still in service.

A weld made to correct a defect or restore a component after it has entered service or been found deficient during fabrication, as distinguished from an original fabrication weld.

A non-destructive metallographic technique in which a thin film is pressed onto a prepared surface to pick up an impression of the microstructure, allowing examination away from the component itself without removing a sample.

Austenite that remains untransformed within a steel's microstructure after cooling, in a matrix that would otherwise be expected to be fully martensitic or another lower-temperature phase. Its presence affects hardness, dimensional stability, and toughness, making it an important quantity to identify when examining hardened steels.

A product category covering the outer, ring-shaped edge or peripheral portion of a component, such as the rim of a wheel or the flanged edge of a vessel or tank, distinguished from the central body or hub of the part.

A hardness value obtained with the Rockwell testing method using a diamond indenter and a heavy load, commonly used for harder metals such as hardened steels. It is one of several hardness scales referenced in this atlas alongside Vickers hardness.

A product category covering long components with a solid, generally round cross-section, as distinguished from tube or pipe, which are hollow.

A category of image focus covering how and where a sample was taken and examined — such as its location within the component, sectioning direction, and magnification — rather than a specific defect or microstructural feature.

An imaging instrument that uses a focused beam of electrons to produce highly magnified images of a specimen's surface or fracture face, the instrument behind a scanning electron microscopy examination.

An examination technique that uses a focused beam of electrons instead of light to produce highly magnified, detailed images of a sample's surface or fracture face. It is a core tool in failure analysis, often combined with elemental analysis to both image and characterize features such as fracture morphology, corrosion products, or inclusions.

A standardized designation used to describe the wall thickness of a pipe for a given nominal diameter, with different schedule values corresponding to different wall thicknesses of the same nominal size. It is used together with nominal diameter to fully describe a pipe's dimensions.

A linear surface discontinuity in a rolled or drawn product, typically originating from a surface defect present before rolling — such as a crack or fold — that becomes elongated and closed up, but not welded, during subsequent processing.

A pipe produced without a longitudinal weld seam, typically by piercing or extruding a solid billet, as distinguished from welded pipe formed from rolled plate or strip.

Smaller cracks found near a main crack or the primary fracture surface, which can provide additional clues about a failure's cause, such as the general direction of crack growth or a shared underlying degradation mechanism.

Carbide particles that precipitate from a metal’s matrix during cooling or a subsequent heat treatment, as distinguished from primary carbides that form directly during solidification.

Bands of chemical composition variation inherited from the original solidification of a cast metal, which become elongated into parallel bands during subsequent hot working and can produce a corresponding banded microstructure.

A corrosion mechanism in a multi-phase or multi-element alloy in which one constituent is preferentially dissolved away, leaving behind a porous, weakened structure that can retain the original shape of the component even though its mechanical integrity has been lost. Dezincification of brass is one of the most common and well-documented examples of this mechanism.

A microstructural change, most often in austenitic stainless steels, in which chromium carbides precipitate along grain boundaries during welding or other heat exposure, locally depleting the adjacent matrix of the chromium needed to maintain its passive, corrosion-resistant film. Sensitized material becomes susceptible to intergranular corrosion and intergranular stress corrosion cracking in aggressive environments.

A rotating or load-transmitting component with a generally round cross-section along its length, such as in machinery or vehicle drivetrains.

A condition or fracture mode resulting from stress applied parallel to a material's cross-section rather than perpendicular to it, producing sliding-type deformation or failure along that plane.

An arc welding process, often called stick welding, that uses a flux-coated consumable electrode which forms both the weld metal and a protective slag as it melts, without a separately supplied shielding gas. It is valued for its simplicity and portability and remains widely used for field welding and repair.

An application category covering components used in marine vessels, exposed to a combination of seawater corrosion, dynamic loading, and, in some cases, low-temperature service.

Small voids or cavities left within a casting where liquid metal could not flow in to compensate for the volume reduction that occurs as the metal solidifies and cools, typically forming in the last regions to solidify. It is one of the most common internal casting defects and can act as a site of weakness or leakage.

A hard, brittle intermetallic phase that can precipitate at grain boundaries in duplex and austenitic stainless steels and other alloys after prolonged exposure to elevated temperature. Its formation depletes the surrounding matrix of chromium and molybdenum, which lowers both corrosion resistance and toughness, making it an important consideration when analyzing failures in equipment that has seen long high-temperature service.

A metalloid element commonly added to steels as a deoxidizer during steelmaking and as an alloying element to improve strength and resistance to oxidation. Its chemical symbol appears throughout the material composition tables in this atlas.

A US-based professional association, now operating as SAE International, that develops standards for the automotive, aerospace, and commercial vehicle industries, including a widely used numbering system for steel grades.

A heat treatment in which an alloy, most often an austenitic or duplex stainless steel, is heated to a temperature high enough to dissolve precipitated phases back into solid solution and then rapidly cooled to keep them from reforming. It is used to restore corrosion resistance and toughness that secondary-phase precipitation would otherwise degrade.

A condition describing a component examined in its intact, as-manufactured or as-expected state, without the degradation or defects covered by the damage-related condition categories in this atlas.

The absence of internal discontinuities — such as porosity, voids, or inclusions — in a material, most often discussed in the context of castings and welds, where soundness is a key quality attribute.

Service in an environment containing hydrogen sulfide, most often defined by a recognized industry standard for oil and gas equipment, where materials must be selected and qualified to resist sulfide stress cracking and related forms of hydrogen damage. It is a major materials-selection consideration for components in wells, pipelines, and processing equipment handling sour hydrocarbons.

The transformation of lamellar pearlite's carbide plates into rounded, spheroidal particles dispersed through a ferrite matrix, occurring during prolonged exposure to elevated temperature. It softens the steel and improves ductility and machinability, and its presence in a micrograph is also a useful indicator of extended high-temperature service or overheating.

A family of steels containing enough chromium to form a thin, self-repairing passive oxide layer that gives them substantially better corrosion resistance than plain carbon or low-alloy steels. Different stainless steel families — austenitic, ferritic, martensitic, duplex, and precipitation hardened — offer different combinations of strength, toughness, and corrosion resistance.

A broad family of iron-based alloys containing carbon, together with other alloying elements added to achieve specific combinations of strength, ductility, toughness, and other properties.

A product category covering a slender, elongated component that transmits motion or force between an actuator and a moving part — most commonly a valve stem, which connects the handwheel, gear, or actuator to the internal closure element that opens and closes the valve.

A condition in which a metal's strength and hardness have increased, and its ductility decreased, as a result of plastic deformation at room or moderately elevated temperature, rather than through heat treatment.

A local increase in stress at a geometric feature such as a notch, hole, sharp corner, or thread, well above the nominal stress calculated from the applied load and cross-section alone. Stress concentrations are common initiation sites for fatigue cracks and other failures, and are a central consideration in both the design and the failure analysis of loaded components.

A form of cracking that results from the combined action of a sustained tensile stress and a specific corrosive environment, occurring at stress levels well below what the material could otherwise withstand and often with little visible surface corrosion. It is a particularly dangerous failure mode because a component can appear largely intact until sudden, brittle-like cracking occurs.

An application category covering components that provide load-bearing or structural support, as distinguished from piping, pressure vessels, or rotating equipment.

The slow, stable extension of a crack under stresses or repeated loading below the level that would cause sudden, unstable fracture, occurring by mechanisms such as fatigue, stress corrosion cracking, or creep. A component can accumulate subcritical crack growth for a long time before the crack reaches a size at which final, rapid fracture occurs.

An arc welding process in which the arc is formed beneath a blanket of granular flux that shields the weld pool, rather than by a shielding gas or a coated electrode. It produces high deposition rates and clean welds and is widely used for long, straight or gently curved welds such as those in pipe and pressure-vessel fabrication.

An application category covering equipment installed and operated on or below the seabed, such as subsea production and pipeline systems, which combine marine corrosion exposure with high external pressure.

A form of hydrogen-related cracking that occurs in steels exposed to wet hydrogen sulfide environments under tensile stress, in which atomic hydrogen generated by the corrosion reaction embrittles the material. It is a well-known failure mechanism in oil and gas equipment handling sour service and is closely related to hydrogen embrittlement.

A highly alloyed stainless steel with a microstructure containing roughly equal proportions of austenite and ferrite, combined with a higher alloy content than standard duplex grades. It offers a strong combination of high strength and resistance to localized and stress corrosion cracking, and is commonly used in demanding chloride-bearing or sour service.

An image documenting the general visual condition of a surface, typically at low magnification or with the naked eye, before more detailed microscopic examination.

An image documenting a surface's general condition captured with a scanning electron microscope rather than by naked eye or optical means, used when finer detail or higher magnification is needed than optical methods can provide.

Martensite that has been reheated to a lower temperature after quenching to relieve internal stresses and reduce brittleness, producing a more stable microstructure with an improved balance of strength and toughness compared with as-quenched martensite.

A mechanical test in which a specimen is pulled under a controlled, increasing load until it yields and eventually fractures, used to measure properties such as strength, ductility, and elastic behavior. It is one of the most common and fundamental mechanical tests applied to metals in this atlas's failure analyses.

A fatigue mechanism in which repeated heating and cooling cycles generate cyclic stresses — through thermal expansion and contraction, often constrained by the surrounding structure — that eventually initiate and grow cracks, without requiring any externally applied mechanical load. It is a common failure mechanism in components that experience frequent temperature swings in service.

A family of coating processes in which a material, fed as powder or wire, is heated and propelled onto a surface to build up a protective or functional coating. It is commonly used to improve wear or corrosion resistance, or to restore dimensions on a worn component.

A thermal spray coating process in which the sprayed deposit is subsequently heated to fuse it into a dense, metallurgically bonded layer with reduced porosity compared with the as-sprayed coating. It is commonly used to apply hard-facing or corrosion-resistant overlays that require better bonding than a conventional thermal spray coating alone.

A reduction in a component's wall thickness over time, most often caused by corrosion or erosion, which reduces its remaining strength and can eventually lead to leakage or rupture.

A crack that has propagated completely through the wall thickness of a component such as a pipe or vessel, resulting in a loss of containment.

A lightweight metallic element valued for its high strength-to-weight ratio and excellent corrosion resistance, used both as a base metal in titanium alloys and as an alloying addition in some steels. Its chemical symbol appears throughout the material composition tables in this atlas.

An alloy based on titanium, valued for an exceptional strength-to-weight ratio and excellent corrosion resistance, commonly used in aerospace and demanding chemical or marine service.

An application category covering hand-operated or power-driven devices used to perform tasks such as cutting, shaping, drilling, or fastening — spanning both the tools themselves as manufactured products and the broader tooling industry that designs and produces them.

Fracture that propagates through the body of a material’s grains rather than along the boundaries between them, as distinguished from intergranular fracture.

Stress corrosion cracking that propagates through the interior of the grains rather than along their boundaries, typically producing a more branched crack path than intergranular stress corrosion cracking. Chloride-induced stress corrosion cracking of austenitic stainless steels is a well-known example of this crack path.

A cross-section cut perpendicular to the long axis or primary direction of a component, used to reveal features across its thickness or diameter, such as wall thickness, coating layers, or the extent of a defect through the section.

A hollow, generally cylindrical product form, distinguished from pipe mainly by the standards and dimensional systems used to specify it rather than by any fundamental difference in shape.

A condition describing features or characteristics that are typical, expected results of a component’s manufacturing process, rather than a defect or an in-service damage mechanism.

The UNS designation for a nickel-chromium-based superalloy strengthened by precipitation hardening, valued for high strength across a wide temperature range in demanding aerospace and oil and gas applications.

A localized corrosion mechanism that develops beneath a deposit — such as scale, sand, or sludge — settled on a metal surface, where the deposit creates stagnant, oxygen-depleted conditions similar to those in crevice corrosion. It is a common cause of unexpected internal corrosion in pipelines and vessels handling produced fluids that carry solids.

A weld cracking mechanism, most often associated with hydrogen, that occurs in the heat-affected zone beneath the weld bead rather than in the weld metal itself. It is typically found in hardenable steels welded without adequate preheat or with a high-hydrogen welding process, and may not be visible without removing the weld reinforcement or examining a cross-section.

A designation system, jointly maintained by ASTM International and SAE International, that assigns a unique alphanumeric identifier to a specific metal or alloy composition, independent of any single standards body's own numbering scheme. It provides a common cross-reference point when the same alloy is covered by multiple national or industry standards.

A microstructure or surface condition without significant variation in appearance across the field of view, as distinguished from a banded, mixed, or otherwise inhomogeneous structure.

A condition describing a component that has been placed in service and has accumulated some operating history, as distinguished from a new or as-manufactured component, without necessarily implying that damage or a defect is present.

An application category covering components used to control, regulate, or shut off the flow of a fluid, such as valve bodies, seats, and stems.

A fatigue mechanism in which small-amplitude, high-frequency cyclic stresses from mechanical vibration — rather than the primary operating load — accumulate over time and initiate and grow a fatigue crack, often at a resonant frequency of the component or its supporting structure. It can produce fatigue failures at stress levels well below what the component's primary loading would suggest is dangerous.

A hardness value obtained by pressing a small diamond pyramid indenter into a material's surface and measuring the resulting indentation, applicable across a very wide range of material hardness and indentation sizes. It is commonly used in metallurgical failure analysis because it can be applied to small features, such as individual microstructural constituents or narrow zones like the heat affected zone.

A cavity or empty space within a material, which can originate from processes such as casting, welding, or in-service degradation, and which can act as a stress concentrator or a crack initiation site.

Localized removal of material by the erosive or scouring action of a flowing fluid, often occurring preferentially at a weld root, elbow, or other flow-disturbing feature where turbulence is highest. It is a form of erosion damage that can rapidly thin a wall at a specific, predictable location rather than uniformly.

Equipment that captures heat from a hot exhaust or process stream, such as turbine exhaust gas, and transfers it for reuse elsewhere in a facility, improving overall energy efficiency. Its heat-exchanger components can be exposed to high-temperature and corrosive service conditions.

Progressive material loss or damage from the surface of a component caused by relative motion against another surface or a moving substance, encompassing mechanisms such as abrasion, adhesion, and erosion.

The portion of a welded joint that has melted and resolidified, formed from the filler material together with some melted base metal, and metallurgically distinct from both the unaffected base metal and the heat affected zone. Its composition and microstructure are controlled by the welding process and consumables selected for the joint.

A layer of weld metal, often a corrosion- or wear-resistant alloy different from the base metal, deposited over a component's surface to provide a resistant working surface without needing to fabricate the entire component from the more expensive overlay alloy. It differs from cladding in that it is applied by welding rather than by bonding a separate sheet or plate.

A joint where two or more pieces of material have been fused together by welding, encompassing the weld metal, the heat affected zone, and the adjoining base metal as a single region of interest in failure analysis.

The process of permanently joining two or more pieces of material, most often metal, by melting and fusing them together — with or without a filler material — using a heat source such as an electric arc, gas flame, or laser. It underlies most of the joint-related terms in this glossary, and its quality in fabrication is governed by documents such as the Welding Procedure Specification.

A flaw introduced during welding — such as porosity, lack of fusion, undercut, or cracking — that can compromise the integrity of a welded joint.

A written document that specifies the parameters and requirements to be followed when welding a particular joint — such as the process, consumables, preheat, and technique — intended to produce a weld with consistent, qualified properties. It is a central quality-control document in welding fabrication, typically supported by a qualification record demonstrating that the procedure produces acceptable results.

A forged branch-connection fitting welded onto a run pipe to create an outlet for a smaller branch pipe, providing a full-penetration weld joint and reinforcement at the connection without requiring the run pipe's wall to be specially shaped. It is one of a family of forged outlet fittings used in piping systems.

A cast iron in which the carbon is present almost entirely as cementite rather than as free graphite, giving the fracture surface its characteristic light color and the material very high hardness and wear resistance but low ductility and toughness. It contrasts with gray and ductile cast irons, in which most of the carbon is present as graphite.

A product category covering material drawn into a long, thin, generally round cross-section, typically supplied in coils rather than straight lengths.

A yield strength value obtained from a tensile test using a small, defined amount of permanent (plastic) deformation as the criterion for yielding, used because many metals do not show a sharp, easily identified yield point. It is one of the most commonly reported strength properties for structural and pressure-equipment materials.

A yield strength value obtained from a tensile test using a larger, defined amount of permanent (plastic) deformation as the criterion for yielding than the more common offset criterion, applied to certain materials or specifications that call for this alternative basis. It is reported alongside other tensile properties to characterize when a material begins to deform permanently under load.