Visual Testing Glossary

13 C HAPTER Visual Testing Glossary

Introduction Definitions

Purpose A Standards writing bodies take great pains acceptable quality level (AQL): to ensure that their standards are Maximum percent defective (or the definitive in wording and technical maximum percentage of units with accuracy. People working to written rejectable discontinuities) that, for the contracts or procedures should consult purposes of sampling tests, can be definitions referenced in standards when considered satisfactory as a process appropriate. For example, persons who average. work in accordance with standards acceptance criterion: Benchmark against published by ASTM International are which test results are to be compared encouraged to refer to definitions in the 1 for purposes of establishing the ASTM standards. functional acceptability of a part or The definitions in this Nondestructive system being examined.4 Testing Handbook volume should not be acceptance level: Measured value or referenced for tests performed according values above or below which test to standards or specifications or in objects are acceptable, in contrast to fulfillment of contracts. This glossary is rejection level.4 provided for instructional purposes. No acceptance standard: (1) Specimen, other use is intended. similar to the product to be tested, containing natural or artificial On References discontinuities that are well defined and similar in size or extent to the Many definitions in this glossary are 4 adapted from other volumes of the maximum acceptable in the product. Nondestructive Testing Handbook series, (2) Document defining acceptable especially from the second edition’s Visual discontinuity size limits. See also and Optical Testing (1993).2 standard. Some terms apply generally to accommodation: Of the eye, adjustment nondestructive testing and are not specific of the lens’ focusing power by to visual testing — terms on subjects such changing the thickness and curvature as metallurgy, quality control and of the lens through its movement by personnel qualification. Many of these tiny muscles. definitions come from the second edition ACGIH: American Conference of volume Nondestructive Testing Overview Governmental Industrial Hygienists. (1996)3; some are rephrased in the third acuity: See neural acuity, vision acuity. edition’s most recent volume, Magnetic adaptive thresholding: Threshold value Testing (2008).4 varying with inconstant background Entries from other volumes in the gray level. Nondestructive Testing Handbook series are adhesive wear: See wear, adhesive. reprinted but generally not referenced alpha ferrite: Form of pure iron that has below. a body centered cubic structure stable below 910 °C (1670 °F). Also called alpha iron. alpha iron: See alpha ferrite. ambient light: Light in the environment as opposed to illumination provided by a visual testing system. ampere (A): SI unit of electric current.4 angle: See field angle. angstrom (Å): Disused unit of length. 1 Å = 0.1 nm.

304 Visual Testing anomaly: (1) In nondestructive testing, a blue light hazard: Danger posed to the nonrelevant indication. (2) In eye by long term exposure to high nondestructive testing, an frequency visible light at intensities unintentional or undesired material and durations that may damage the condition that may qualify as a defect. retina. Compare defect; discontinuity. Some borescope: Industrial endoscope; a anomalies, such as inadequate case periscope or telescope using mirrors, hardening or rough surface finish, prisms, lenses, optic fibers or may be defects but, because there is no television wiring to transmit images interruption in the material structure, from inaccessible interiors for visual are not discontinuities. testing. Borescopes are so called ASNT Recommended Practice because they were originally used in No. SNT-TC-1A: See Recommended machined apertures and holes such as Practice No. SNT-TC-1A. gun bores. There are both flexible and ASNT: American Society for rigid borescopes. Nondestructive Testing. borescope, angulated: Borescope bent for automated system: Acting mechanism viewing at forward oblique, right angle that performs required tasks at a or retrospective angles for visual determined time and in a fixed testing of surfaces not accessible with sequence in response to certain conventional borescopes. conditions or commands. borescope, calibrated: Borescope with axial: Of or pertaining to a direction gage on external tube to indicate the along the length of an oblong object depth of insertion during a test. and perpendicular to its radius — for Borescopes with calibrated reticles are example, down the length of a used to determine angles or sizes of cylinder. Compare radial. objects in the field when held at a predetermined working distance. borescope, cave: Multiangulated, B periscopic borescope used for remote observation of otherwise inaccessible background cylinder and difference areas. cylinder: Two devices used to borescope, fiber optic: Industrial calculate illuminance by using the endoscope, or fiber optic borescope, equivalent sphere illumination 2,5 that uses glass or quartz fibers to technique. transmit light and the optical path to binary system: In metallurgy, a and from the test object. two-element alloy system. See also borescope, indexing: Borescope that can isomorphous binary system. be bent 90 degrees by rotation of a birefringence: Splitting of a light beam knob after the instrument has been into two parts through a translucent inserted through an aperture. A knob material. at the eyepiece can rotate the objective black body: Theoretical object that head through 360 degrees for radiates more total power and more scanning a circumferential weld seam. power at any wavelength than any borescope, micro-: Borescope with an other source operating at the same 2,5 outside diameter generally from 1 to temperature. 5 mm (0.04 to 0.2 in.), typically using blackbody: See black body. quartz filaments. Compare miniature black light: Term sometimes used for borescope. ultraviolet radiation, particularly in borescope, miniature: Borescope with an the near ultraviolet range of about outside diameter generally less than 320 to 400 nm. 13 mm (0.5 in.). Sometimes called blacklight: See black light. miniborescope. See also microborescope. blind spot: Portion of the retina where borescope, panoramic: Borescope with a the optic nerve enters, without rods scanning mirror mounted in front of and cones and hence insensitive to 2,6 the objective lens system. Rotation of light. the mirror is adjusted at the ocular blister: Discontinuity in metal, on or near end of the instrument to scan in the surface, resulting from the forward oblique, right angle and expansion of gas in a subsurface zone. retrospective directions. Very small blisters are called pinheads 4 borescope, retrospective: Borescope that or pepper blisters. looks backward more than 90 degrees blotch: (1) An irregularly spaced area of from the distal line of interrogation color change on a surface. (2) The normal to the plane of a conventional nonuniform condition of a surface objective lens. characterized by such blotches. borescope, rigid: Borescope that does not blowhole: Hole in a casting or a weld bend, typically in order to keep the caused by gas entrapped during 4 geometrical optics in alignment solidification. through a light train system.

Visual Testing Glossary 305 borescope, ultraviolet: Borescope channels: In biology, mechanisms equipped with ultraviolet lamps, filters functioning as band pass filters in the and special transformers to transmit visual cortex of mammals, causing radiation of ultraviolet wavelengths. sensitivity to visual stimuli in borescope, video: Borescope transmitting particular frequencies and ranges. image electronically. charge coupled device (CCD): Solid state borescope, waterproof/vaporproof: image sensor. Charge coupled devices Borescope completely sealed and are widely used in inspection systems impervious to water or other types of because of their accuracy, high speed fluid, used for internal tests of liquid, scanning and long service life. gas or vapor environments. check cracking: Surface crack caused by borescope, wide field: Borescope with overheating and having cross hatched rotating objective prism to provide pattern. See grinding crack. fields of view up to 120 degrees. closing: In image processing, dilation borescopy: Viewing or inspection with a followed by erosion. A single pixel by borescope. closing connects a broken feature brinelling: Repeated stripe indentations separated by one pixel. See also made by a spherical object. False opening. brinelling refers to a type of surface closure: Process by which a person wear. cognitively completes patterns or burr: Raised or turned over edge occurring shapes that are incompletely on a machined part and resulting from perceived. cutting, punching or grinding.2,5 cocoa: Debris (usually oxides of the burst: In metal, external or internal contacting metals) of fretting wear, rupture caused by entrapped gas. retained at or near the site of its butt weld: Weld that joins the edges of formation — a condition easily two work pieces in the same plane. identified during visual tests. With ferrous metals, the debris is brown, red or black, depending on the type of C iron oxide formed. For this reason, ferrous debris is called cocoa or, when calibration: (1) Ratio of the output from a mixed with oil or grease, red mud. device to a reference input. Knowledge code: Standard enacted or enforced as a of this ratio helps to infer a device’s law. input from its output. (2) Act of coefficients of the filter: Values in a returning an instrument to the mask that serves as a filter in image parameters and settings of the original processing. equipment manufacturer. cold light: Disused word for fluorescence. (3) Statement of the scale of a device. color: Visual sensation by means of which candela (cd): Base SI unit of luminous humans distinguish light of differing intensity, in a given direction, of a hue (predominant wavelengths), monochromatic radiation source that saturation (degree to which those × 14 has a frequency of 5.4 10 Hz and radiations predominate over others) that has a radiant intensity in that –1 4 and lightness. direction of 1.464 mW·sr . color blindness: Deficiency in ability to candle: Former name for candela. perceive or distinguish hues. cavitation fatigue: Form of pitting, color discrimination: Perception of caused by erosion from vibration and differences between two or more hues. movement in liquid environments. color temperature: Rating of a light CCD: See charge coupled device. source for color vision. cementite: Iron carbide (Fe3C), a hard compound microscope: See microscope, and brittle substance present in steels. compound. certification: With respect to cone: Part of the eye; color sensitive nondestructive test personnel, the photoreceptor at the inner region of process of providing written testimony the retina. Cones assist with mesopic that an individual has met the vision and are responsible for qualification requirements of a specific photopic vision. Compare rod. practice or standard. See also certified confidence level: Level of assurance for and qualified. detecting a specified discontinuity size certified: With respect to nondestructive with a specified probability. See also test personnel, having written probability of detection. testimony of qualification. See also constitution diagram: See phase diagram. certification and qualification. contrast: (1) Difference in color or CGS system: Obsolete system of brightness between a test indication measurement units based on the and background. (2) Difference centimeter, gram and second. between the amount of light reflected Compare SI. or transmitted by an object and by the chafing: See wear, fretting. background in the field of view.

306 Visual Testing control: See in control, process control and deformation: Change of shape under quality control. load. See also creep and elastic corrosion: Loss or degradation of metal deformation. because of chemical reaction. delta ferrite: Solid solution with body corrosion, crevice: Corrosion found in centered cubic structure and iron as tight crevices or pores (pits) and solvent. Also called delta iron. accelerated by galvanic activity from delta iron: See delta ferrite. high ion concentrations. depth of field: In photography, the range corrosion-erosion: Simultaneous of distance over which an imaging occurrence of erosion and corrosion. system gives satisfactory definition corrosion, fretting: Corrosion facilitated when its lens is in the best focus for a by fretting, particularly where a specific distance. protective surface has been chafed in a dewetting: In soldering, the flow and corrosive environment. retraction of solder, caused by corrosion, poultice: Corrosion occurring contaminated surfaces, dissolved under a layer of foreign material (for surface coatings or overheating before example, under mud in automobile soldering. rocker panels). difference cylinder: See background cosine law: Physical law stating that the cylinder. illumination of a surface varies as the dilation: In image processing, the cosine of the incidence angle. condition of a binary image where the Maximum illumination is obtained pixel in the output image is a 1 if any where the cosine equals one and when of its eight closest neighbors is a 1 in the source is perpendicular to the the input image. See also closing, surface. erosion and opening. crack: (1) Stress induced break, fissure or diopter: Unit used to express the rupture, sometimes V shaped in cross resolving power of lenses, equal to the section and relatively narrow. By inverse of the length (in meters) of the convention, a crack is called linear if it optical axis. is at least three times longer than it is directional lighting: Lighting provided wide. (2) Propagating discontinuity on the work plane or object caused by fatigue, corrosion or stresses predominantly from a preferred such as heat treating or grinding. May direction.2,6 be difficult to detect unaided because direct photometry: Simultaneous of fineness of line and pattern (may comparison of a standard lamp and an have a radial or latticed appearance). unknown light source.2,6 creep: Gradual and permanent change of direct substitution alloy: Alloy in which shape in a metal under constant load, the atoms of the alloying element can usually at elevated temperature. occupy the crystal lattice spaces Occurs in three stages: primary creep, normally occupied by the atoms of the secondary creep and tertiary creep. See parent metal. also deformation. direct viewing: (1) Viewing of a test crevice corrosion: See corrosion, crevice. object in the viewer’s immediate presence. The term direct viewing is used in the fields of robotics and D surveillance to distinguish conventional from remote viewing. dark adaptation: Process by which the (2) Viewing of a test object during retina becomes adapted to a which the light image is not mediated luminance less than about –2 2,6 through a system of two or more 0.034 cd·m . In dark adaptation, lenses (as in a borescope) or the pupils dilate and the two types of transduced through an electronic photoreceptors in the retina change signal (as with a charge coupled chemical balance. After a finite camera). The term direct viewing is used amount of time, possibly 10 min, in some specifications to mean vision will change from photopic viewing possibly with a mirror or vision to mesopic or scotopic low 4 magnifier but not with a borescope. illumination vision. Compare indirect viewing; remote dark adapted vision: See accommodation, viewing. visual; scotopic vision. direct vision instrument: Device offering defect: Discontinuity whose size, shape, a view directly forward. A typical orientation or location (1) makes it scene is about 20 mm (0.75 in.) wide detrimental to the useful service of its at 25 mm (1 in.) from the objective host object or (2) exceeds an lens. accept/reject criterion of an applicable specification. Some discontinuities do not exceed an accept/reject criterion and are therefore not defects. Compare crack; discontinuity; indication. From Nondestructive Testing Handbook, Third Edition: Volume 9, Visual Testing © 2010. Reprinted with permission of The American Society for Nondestructive Testing Inc.

Visual Testing Glossary 307 discontinuity: Interruption in the equivalent 20/20 near vision acuity: physical structure or configuration of a Vision acuity with remote viewing or test object. After nondestructive other indirect viewing that testing, a discontinuity indication can approximates 20/20 direct viewing be interpreted to be a defect.4,7 closely enough to be considered the Compare defect; indication. same for visual testing purposes. discontinuity, artificial: Reference equivalent sphere illumination: Level of discontinuity such as hole, perfectly diffuse (spherical) indentation, crack, groove or notch illuminance that makes the visual task introduced into a reference standard as photometrically visible within a to provide accurately reproducible comparison test sphere as it is in the indications for determining test real lighting environment. sensitivity levels.4 erosion: (1) Loss of material or discontinuity, inherent: Material degradation of surface quality through anomaly originating from friction or abrasion from moving solidification of cast metal. Pipe and fluids, made worse by solid particles in nonmetallic inclusions are the most those fluids or by cavitation in the common inherent discontinuity and moving fluid. See wear. (2) In image can lead to other types of processing, condition of a binary discontinuities in fabrication.2,5 image where the pixel in the output discontinuity, primary processing: image becomes a 1 if each of its eight Discontinuity produced from the hot neighbors is a 1 in the input image. or cold working of an ingot into See also closing, dilation and opening. forgings, rods, bars and other erosion-corrosion: Simultaneous shapes.2,5 occurrence of erosion and corrosion. discontinuity, secondary processing: etch crack: Shallow crack in hardened Discontinuity produced during steel containing high residual surface machining, grinding, heat treating, stresses, produced in an embrittling plating or other finishing acid environment.2,5 operations.2,5 eutectic liquid: Liquid metal having a discontinuity, service induced: proportion of metals such that two or Discontinuity caused by the intended more solid phases form at the same use of the part. temperature during cooling. distal: In a manipulative or interrogating eutectic point: Temperature and system, of or pertaining to the end proportion of metals at which two or opposite from the eyepiece and more phases of a eutectic liquid form. farthest from the person using the Compare eutectoid. system. Objective; tip. eutectoid: Similar to eutectic but in a solid system during cooling. evaluation: Process of deciding the E severity of a condition after an indication has been interpreted, to elastic deformation: Temporary change determine whether it meets in shape under a load. The material acceptance criteria. returns to its original size and shape eye sensitivity curve: Graphic expression after the load is removed. Elastic of vision sensitivity characteristics of deformation is the state in which most the human eye. In the case of a metal components are used in service. physical photometer, the curve should elasticity: Ability of a material to resume be equivalent to the standard observer. its former shape after deformation. The required match is typically electric arc welding: Joining of metals by achieved by adding filters between the heating with electric arc. Also called sensitive elements of the meter and arc welding. the light source. See photopic vision. endoscope: Device for viewing the interior of objects. From the Greek words for inside view, the term F endoscope is used mainly for medical instruments. Nearly every medical false brinelling: Fretting wear endoscope has an integral light source; indentations. Compare brinelling. many incorporate surgical tweezers or false indication: Test indication that other devices. See borescope. could be interpreted as originating equilibrium diagram: Phase diagram from a discontinuity but that actually showing the phases present at originates where no discontinuity equilibrium in a material system. exists in the test object. Compare indication, nonrelevant; defect.4

308 Visual Testing farsightedness: Vision acuity functionally flakes: Short discontinuous internal adequate for viewing objects at a fissures in ferrous metals attributed to distance, generally farther than arm’s stresses produced by localized length. Also called hyperopia. Compare transformation and/or decreased nearsightedness. solubility of hydrogen during cooling far vision: Vision of objects at a distance, usually after hot working. On a generally beyond arm’s length. fractured surface, flakes appear as Compare near vision. bright silvery areas; on an etched feature extraction: From an enhanced surface, flakes appear as short, image, derivation of some feature discontinuous cracks.2,5 values, usually parameters for flaw: Rejectable anomaly.4 See also defect. distinguishing objects in the image. fluorescence: Phenomenon of absorption ferrite: Solid solution of one or more of electromagnetic radiation and its other elements in alpha iron. reemission at a lower energy (longer fiber optic borescope: See borescope, fiber wavelength). In visual testing, optic. fluorescence is typically a response to fiber optics: Technology of efficient ultraviolet radiation. transmission of light through focus: Position of a viewed object and a transparent fibers such as glass, quartz lens system relative to one another to and plastic by means of total internal offer a distinct image of the object as reflection. seen through the lens system. See fiberscope: Jargon for fiber optic accommodation and depth of field. borescope. focus, principal plane of: Single plane in field: In video technology, one of two focus in a photographic scene. video picture components that focusing, automatic: (1) Feature of a together make a frame. Each picture is camera whereby the lens system divided into two parts called fields adjusts to focus on an object in the because a frame at the rate of thirty field of view. (2) Metaphorical frames per second in a standard video attribute of a borescopic instrument’s output would otherwise produce a depth of field (the range of distance in flicker discernible to the eye. Each focus). The depth of field is so great in field contains one half of the total the case of video borescopes that picture elements. Two fields, then, are focusing is unnecessary for most required to produce one complete applications. Despite the name, no picture or frame so the field frequency mechanism is actively adjusted. The is sixty fields per second and the frame large depth of field is due both to the frequency is thirty frames per second. small diameter of the lens aperture field angle: Included angle between those and to the proximity of the lens to the points on opposite sides of a beam charge coupled device. axis at which the luminous intensity is focusing, primary: Focusing by the lens 10 percent of the maximum value. of the image onto a fiber optic bundle This angle may be determined from an at the tip of a probe. illuminance curve or may be focusing, secondary: Focusing at the approximated by use of an incident eyepiece of a borescope or other light meter.2,6 optical instrument, specifically the field of view: Range or area where things manual refocusing needed when the can be seen through an imaging viewing distance changes. system, lens or aperture. Compare footcandle (ftc): Disfavored unit of depth of field. illuminance, where field of vision: Range or area where 1 ftc =1lm·ft–2 = 10.76 lx. things can be perceived by eyesight at footlambert (ftl): Disfavored unit of a point in time, assuming the eye to luminance, where 1 ftl = 3.426 cd·m–2. be immobile. forging crack: Stress induced fillet weld: Weld of approximately discontinuity formed during triangular cross section joining two mechanical shaping of metal; see surfaces approximately at a right angle crack. to each other. fovea centralis: Region of sharpest vision filter: Processing component or function in the retina, where the layer of blood that excludes a selected kind of signal vessels, nerve fibers and cells above or part of a signal. the rods and cones is far thinner than filtering: See low pass filtering. in peripheral regions. fit up: To secure one or more joint foveal vision: See photopic vision. members with special external fracture mechanics: Field of solid fixturing in order to prevent mechanics that deals with behavior of movement during welding.2,5 cracked bodies subjected to stress and strain.

Visual Testing Glossary 309 frame: Complete raster scan projected on general examination: In personnel a video screen. There are thirty frames qualification, a test or examination of per second in a standard video output. a person’s knowledge, typically (in the A frame may be comprised of two case of nondestructive testing fields, each displaying part of the total personnel qualification) a written test frame. See also field. on the basic principles of a frequency: Number of times per second nondestructive test method and that a cyclical waveform repeats. The general knowledge of basic equipment unit of frequency is hertz (Hz). used in the method. (According to fretting corrosion: See corrosion, fretting. ASNT’s guidelines, the general fretting wear: See wear, fretting. examination should not address friction oxidation: See wear, fretting. knowledge of specific equipment, codes, standards and procedures pertaining to a particular application.) G Compare practical examination and specific examination. galling: Type of surface damage caused by geometrical optics: Mathematical study friction. of how light rays are reflected and galvanic series: List of metals, alloys and refracted and practical techniques graphite (a nonmetal) in sequence based on such understanding, with the most anodic (easily corroded) including the transmission of images in liquids at one end of the list and by lenses and mirrors. Also called lens the most cathodic (least easily optics. corroded) at the other end. For glare: Excessive brightness (or brightness practical reasons, this sequence is varying by more than 10:1 within the compiled using seawater as the field of view) that interferes with electrolyte — 3 to 5 percent sodium observation or interpretation of a test chloride and other salts dissolved in response. Glare may be caused by water. reflection, whether specular (smooth gamma iron: Iron with face centered surface) or diffuse (rough surface), of cubic structure formed by slow cooling light or radiation sources. of delta ferrite. This characteristic glare, blinding: Glare so intense that for lattice structure is stable between an appreciable length of time after it 906 °C (1663 °F) and 1391 °C has been removed, no object can be (2535 °F). Also called austenite. seen.2,6 gas metal arc welding (GMAW): Inert glare, direct: Glare resulting from high gas shielded metal joining process that luminances or insufficiently shielded uses a continuous and consumable light sources in the field of view. wire electrode. Also called MIG (metal Direct glare is usually associated with inert gas) welding. Compare gas bright areas, such as luminaires, tungsten arc welding and shielded metal ceilings and windows which are arc welding. outside the visual task or region being gas tungsten arc welding (GTAW): Inert viewed.2,6 gas shielded metal joining process that glare, reflected: Glare resulting from uses a nonconsumable tungsten specular reflections of high electrode. Filler material, when luminances in polished or glossy needed, is manually fed into the surfaces in the field of view. It usually molten weld puddle. Also called is associated with reflections from tungsten inert gas (TIG) welding. within a visual task or nearby areas.2,6 Compare gas metal arc welding; shielded gloss meter: Reflectometer used to metal arc welding. measure specular reflectance.2,6 gasket seal: Resilient ring, usually virgin gnomon: Artifact intended to cast a polytetrafluoroethylene (PTFE), in a shadow. The shadow may be used to piping or tubing connection. Compare measure time or distance. interference sealing thread. gouge: Surface indentation caused by forceful abrasion or impact or flame cutting. Also called nick. Compare tool mark. grain: Solid particle or crystal of metal. As molten metal solidifies grains grow and lattices intersect, forming irregular grain boundaries. grain boundary: Interface that forms between grains of solidifying metal as the random oriented crystal lattices meet. See grain.

310 Visual Testing gray body: Radiator whose spectral I emissivity is uniform for all wavelengths. illuminance: Intensity of radiant energy gray level: Integer number representing (density of luminous flux) on a the brightness or darkness of a pixel surface, in the visible light spectrum. or, as a composite value, of an image Illuminance is measured in lux. comprised of pixels. illuminate: Cast light on (something). green rot: Form of attack due to illumination: Act of illuminating or state simultaneous carburization and of being illuminated. See also oxidation of stainless heating elements illuminate. Compare illuminance.2,6 common to nickel chromium and image: Visual representation of an object nickel chromium iron alloys, or scene. especially in furnace environments. image enhancement: Any of a variety of grinding crack: Shallow crack formed in image processing steps, used singly or the surface of relatively hard materials in combination to improve the because of excessive grinding heat or detectability of objects in an image. the brittleness of the material. image guide: Fiber bundle that carries the Grinding cracks typically are oriented picture formed by the objective lens at 90 degrees to the direction of the distal end of a fiber optic grinding.4 borescope back to the eyepiece. image orthicon: Television tube that uses the photoemission method. Compare H vidicon tube. image processing: Actions applied singly Hadfield’s steel: Austenitic manganese or in combination to an image, in specialty steel, easily work hardened. particular the measurement and halitation: Rings of light visible around a alteration of image features by spot on a video screen where an computer. Also called picture processing. electron scanning beam is held. image segmentation: Process in which heading: Upsetting wire, rod or bar stock the image is partitioned into regions, in dies to form parts having some of each homogeneous. the cross sectional area larger than the in control: Within prescribed limits of original. Examples are bolts, rivets and process control. 1 screws. incandescence: Emission of visible heat affected zone: Portion of base metal radiation as a result of heating. not melted during brazing, cutting or indication: Nondestructive test response welding but with mechanical that requires interpretation to 4 properties altered by the heat. determine its relevance.4 See also heat checking: Surface cracking caused defect; discontinuity; false indication; when metal rapidly heated (or cooled nonrelevant indication. and heated repeatedly) is prevented indication, nonrelevant: Indication that from expanding freely by colder metal has no relation to a discontinuity that below the surface. Friction may might constitute a defect.1 Test produce the heat. Heat checking is response caused by geometry or by a sometimes called thermal fatigue. physical condition that is not a heat wave: Thermally produced variation discontinuity. in flue gas density that distorts images indication, relevant: Indication from a of objects in a firebox. discontinuity (as opposed to a false hot tear: Fracture formed in a cast metal indication) requiring evaluation by a during solidification and due to qualified inspector, typically with extensive tensile stress associated with reference to an acceptance standard, volumetric shrinkage. Hot tears often by virtue of the discontinuity’s size or occur where areas of different location.1 thicknesses adjoin. indirect viewing: Viewing of a test object hue: Characteristic of light at a particular during which the light image is bandwidth; commonly associated with mediated through a system of two or the color’s name. more lenses (as in a borescope) or human factors: Factors in the overall test transduced through an electronic sensitivity based upon mental and signal (as with a charge coupled physical condition of the inspector, camera). Compare direct viewing; remote training, experience level and the viewing. physical conditions under which the infrared radiation: Electromagnetic inspector must work. radiant energy of wavelengths longer hyperopia: See farsightedness. than 770 nm.2,6 hyperthermia: Heating so excessive that interference fitted thread: See interference it can damage or kill plant or animal sealing thread. cells.

Visual Testing Glossary 311 interference objective: In a microscope, a K small, metallized glass mounted in contact with the test object and kinetic vision acuity: Vision acuity with adjustable for tilt to control fringe a moving target. Studies indicate that spacing. 10 to 20 percent of visual efficiency interference sealing thread: Piping seal can be lost by target movement. using a tapered connection made up under great pressure, forcing the mating surfaces together more tightly L than is possible with a spiral thread. laboratory microscope: Conventional Compare gasket seal. compound microscope. See microscope. interlaced scanning: Process whereby the lambert cosine law: See cosine law. picture appearing on a video screen is lambertian: Having a surface that reflects divided into two parts. Interlaced light diffusely and uniformly rather scanning reduces flicker by increasing than specularly. See matte. Most the electron beam’s downward rate of objects have a lambertian surface. travel so that every other line is sent. Compare specular. When the bottom is reached, the lap: Forging discontinuity caused by a beam is returned to the top and the folding over of metal. Laps are found alternate lines are sent. The odd and in rolled bar stock and at or near even line scans are each transmitted at diameter changes.2,5 1/60 s, totaling 1/30 s per frame and laser: Acronym (light amplification by retaining the standard rate of stimulated emission of radiation). A 30 frames per second. The eye’s device, the laser that produces a persistence of vision allows the odd highly monochromatic and coherent and even lines to appear as a single (spatial and temporal) beam of image without flicker. radiation.2 interpretation: Determination of the leaked visible light: Unwanted cause, significance and relevance of electromagnetic radiation that has a test indications. wavelength between 400 and 800 nm interstitial alloy: Alloy in which the that is generated by a UV-A source but atoms of the alloying element fit into not filtered out of the emission the spaces between the atoms of the spectrum. Leaked visible light is parent metal. generally perceived as purple or dark inverse square law: Physical law for a blue light and not accurately measured point source of energy. The quantity using a photometric sensor.4 or strength is inversely proportional to the square of the distance from the lens: Transparent object that refracts light origin. passing through it in order to focus iris: Ring of variable area around the the light. pupil and in front of the lens of the lens optics: See geometrical optics. eye. The surface area of the iris adjusts light adapted vision: See photopic vision. spontaneously to change the amount light guide bundle: Bundle of filaments, of light entering the eye. usually glass, that carries noncoherent irradiance: Radiant power falling upon a light from a high intensity source known surface area at a given angle. through a fiber optic borescope to Compare radiance. See also radiometer. illuminate an object. light: Radiant energy that can excite the IshiharaTM plates: Trade name for a kind retina and produce a visual sensation. of pseudoisochromatic plates, used for The visible portion of the color differentiation vision testing. electromagnetic spectrum extends isomorphous binary system: Two from about 400 to 800 nm.2,6 element alloy system in which both lighting, back: Placement of light source elements are completely soluble in and image sensor on opposite sides of each other in the liquid and the solid the test object, used when the states, in all proportions at all silhouette of a feature is important. temperatures. lighting, flash: See lighting, strobe. lighting, front: Placement of light source J and image sensor on the same side of the test object. jaeger eye chart: Eye chart used for near lighting, strobe: Lighting that flashes vision acuity examination. intermittently at a rate that may be adjusted and is often perceived as a flicker, used to image moving objects or still objects with potential movement.

312 Visual Testing lighting, structured: Combining a light lux (lx): SI unit of illuminance, equal to source with optical elements to form a one lumen per square meter line or sheet of light. (1 lx =1lm·m–2). light meter: See photometer. Compare radiometer. limited certification: Of a person, M certified only for specific operations; usually called limited Level (I or II) or machine vision: Automated system designated as having limited function of acquiring, processing and certification because they are not analyzing images to evaluate a test qualified to perform the full range of object or to provide information or activities expected of personnel at that interpretation for human level of qualification, for a given interpretation. A typical machine method. vision system consists of a light line pair: Pair of adjacent, parallel lines source, a video camera, a video used to evaluate the resolution of a digitizer, a computer and an image specific imaging system. See also display. minimum line pair. macula lutea: Irregular, diffuse ring of lot tolerance percent defective: In yellow pigment which partly overlaps quality control, the percent defective the fovea and surrounds it out to at which there is a 10 percent around 10 degrees and which absorbs probability of acceptance in a blue light, thus changing the color of production run. the light reaching receptors beneath. low pass filtering: In image processing, martensite: (1) Acicular (needlelike) linear combination of pixel values to microstructure produced by fast smoothen abrupt transitions in a cooling or quenching of metals and digital image. Also called smoothing. alloys such as steel. (2) The hard steel lumen (lm): SI photometric unit of with such microstructure produced by luminous flux, weighted according to fast cooling of austenite. Martensite is the photopic vision response. One a constituent commonly found in lumen equals the light emitted by one quenched steel. candela (cd) point source into one martensite finish temperature: steradian (sr) solid angle (1 lm = Temperature at which martensite 1 cd·sr–1). formation is completed as steel cools. lumen method: Lighting design martensite start temperature: procedure used for predetermining the Temperature at which martensite starts relation between the number and to form as steel cools. types of lamps or luminaires, the room mask: (1) A spatial filter in the sensing unit of a surface inspection system. characteristics and the average × illuminance on the work plane. It (2) An n n square matrix with takes into account both direct and different values that serves as a filter reflected flux. Also called flux in image processing. method.2,6 match bend effect: Optical illusion luminance: Photometric brightness of a whereby an area of uniform brightness light source defined by the density of appears to be nonuniform because of its luminous intensity, measured as contrast with the brightness of an luminous flux per unit solid angle per adjacent area. unit area in a given direction. mathematical morphology: Image Reported in candela per square meter processing technique of expanding (cd·m–2). and shrinking. The basic operators in luminosity: Luminous efficiency of mathematical morphology are dilation radiant energy. (expanding), erosion (shrinking), luminous efficacy: Ratio of the total opening and closing. luminous flux of a light source to the matte: Having a surface that reflects light total radiant flux or to the power diffusely rather than at an angle equal input. Sometimes called luminous to the angle of incidence; not shiny. efficiency. Also called lambertian. The term matte luminous efficiency: See luminous is generally applied to smooth surfaces efficacy. or coatings. Compare specular. luminous flux: Radiant energy’s time rate mesopic vision: Vision adapted to a level of flow. Measured in lumens. of light between photopic at × –2 –2 × –3 –2 luminous intensity: Measure of a light 3.4 10 cd·m (3.2 10 cd·ft ) × –5 –2 source’s power output per unit solid and scotopic at 3 10 cd·m × –6 –2 angle emitted or reflected from a (2.7 10 cd·ft ). point, when weighted by the photopic metallograph: Short term for spectral luminous efficiency response metallographic microscope. curve. Luminous intensity is measured metallographic microscope: See in candela. Compare luminance.4 microscope, metallographic.

Visual Testing Glossary 313 metallography: Science and practice of monochromatic: Light from a very small microscopic testing, inspection and portion of the spectrum. analysis of a metal’s structure, monochromator: Device that uses prisms typically at magnifications from 50 × or gratings to separate or disperse the to 2500 ×. wavelengths of the spectrum into one metallurgical microscope: See microscope, band. metallurgical. morphology: See mathematical microborescope: See borescope, micro-. morphology. microscope: Instrument that provides mottle: Apparently random positioning of enlarged images of small objects. metallic flakes that creates an microscope, compound: Conventional accidental pattern. microscope, using geometrical optics multipass weld: Weld made by many for magnification. Also called passes, one pass at a time. laboratory microscope. multiphase alloy: Alloy in which several microscope, interference: Magnifier phases are present. using the wavelength of light as a unit of measure for surface contour and other characteristics. N microscope, metallographic: Metallurgical microscope NDE: (1) Nondestructive evaluation. incorporating a camera. Also called a (2) Nondestructive examination. See metallograph. Most metallographic nondestructive testing. microscopes share these features: NDI: Nondestructive inspection. See (a) stand with concealed shock nondestructive testing. absorbers, (b) intense light source, NDT: See nondestructive testing. (c) inverted stand so that the test near ultraviolet radiation: Ultraviolet object is face down, (d) viewing radiation with wavelengths ranging screens for prolonged tasks such as dirt from about 320 to about 400 nm. count or grain size measurements, Formerly called black light. (e) bright, dark and polarized near vision: Vision of objects nearby, illumination options. generally within arm’s length. microscope, metallurgical: Microscope Compare far vision. designed with features suited for nearsightedness: Vision acuity metallography. functionally adequate for viewing microscope, phase contrast: Laboratory objects nearby, generally within arm’s microscope with two additional length. Also called myopia. Compare optical elements to transmit both farsightedness. diffracted and undiffracted light, necking down: Localized reduction in revealing refractive index area of a specimen or structural member during welding under discontinuities in a completely 2,5 transparent test object. overload. microscope, polarizing: Microscope with negative sliding: Rolling and sliding of polarizing elements to restrict light meshing gears or rollers when the vibration to a single plane for studying rolling and sliding are in opposite material with directional optical directions. properties. As fibers, crystals, sheet neural acuity: Ability of the eye and plastic and materials under strain are brain together to discriminate patterns rotated between crossed polarizers on from background. Discrimination is the microscope stage, they change influenced by knowledge of the target color and intensity in a way that is pattern, by the scanning technique related to their directional properties. and by the figure-to-ground MIG welding: See gas metal arc welding. relationship of a discontinuity. The miniature borescope: See borescope, figure/ground relationship can be miniature. referred to as having a level of visual miniborescope: Jargon for miniature background noise. borescope. nick: Surface indentation caused by minimum line pair: Closest distance that forceful abrasion or impact. Also called a specific imaging system can resolve gouge. Compare tool mark. between a pair of adjacent, parallel nit: Obsolete unit for measuring lines (line pair) used to evaluate luminance, equivalent to one candela system resolution. per square meter. Abbreviated nt. modulus of elasticity: Ratio between noble metals: Cathodic metals (such as stress and strain in a material gold, platinum and silver), which deformed within its linear elastic strongly resist corrosion. range.

314 Visual Testing nondestructive evaluation (NDE): optic disk: Area in the retina through Another term for nondestructive which the fibers from the various testing. In research and academic receptors cross the inner (vitreous communities, the word evaluation is humor) side of the retina and pass often preferred because it emphasizes through it together in the optic nerve interpretation by knowledgeable bundle. This transitional area is personnel. completely blind. nondestructive examination (NDE): optics: Physical science of the Another term for nondestructive transmission of radiation, especially of testing. In the utilities and nuclear light. See geometrical optics. industry, examination is sometimes organoleptic: Relying on or using sense preferred because testing can imply organs, such as the human eye. performance trials of pressure orthicon: See image orthicon. containment or power generation systems. nondestructive inspection (NDI): P Another term for nondestructive testing. In some industries (utilities, parafoveal vision: See scotopic vision. aviation), the word inspection often parallax: Apparent difference in position implies maintenance for a component of an imaged point according to two that has been in service. differently positioned sensors. nondestructive testing (NDT): pass: In welding, a single bead of weld Determination of the physical metal along the entire joint or the condition of an object without process of laying down that bead. affecting that object’s ability to fulfill pearlite: Platelet mixture of cementite its intended function. Nondestructive and ferrite in steels or in alpha and test methods typically use an beta phases in nonferrous alloys. appropriate form of energy to peripheral vision: Seeing of objects determine material properties or to displaced from the primary line of sight and outside the central visual indicate the presence of material 2,6 discontinuities (surface, internal or field. concealed). Sometimes called phase: In metallurgy, a physically nondestructive evaluation, nondestructive homogeneous portion of a material examination or nondestructive inspection. system, specifically the portion of an nonferromagnetic material: Material not alloy characterized by its magnetizable and essentially not microstructure at a particular affected by magnetic fields.4 temperature during melting or nonrelevant indication: See indication, solidification. nonrelevant. phase contrast microscope: See numerical analysis: Technique to microscope, phase contrast. generate numbers as the solution to a phase diagram: Graph showing the mathematical model of a physical temperature, pressure and composition system; used in place of a closed form limits of phase fields in a material analytic expression; usually requires system. Also called a constitution digital computation.4 diagram. Compare equilibrium diagram. photochromic lens: Eyeglass material that automatically darkens to reduce O light transmission when exposed to ultraviolet radiation. objective: In discussion of a lens system photoconduction: Method by which a (camera, borescope, microscope, vidicon television camera tube telescope), of or pertaining to the end produces an electrical image, in which or lens closest to the object of the conductivity of the photosensitive examination — at the end opposite surface changes in relation to the from the eyepiece. Distal; tip. intensity of the light reflected from OCTG: Oil country tubular goods. the scene focused onto the surface. oil country tubular goods: Hollow Compare photoemission. cylindrical components, such as pipes, photoelasticity: Effect of a material’s used in petroleum wells to case the elastic properties on the way that it hole and to convey petroleum and refracts or reflects light. related products.4 photoelectric effect: Emission of opening: Image processing operation of electrons from a surface bombarded by erosion followed by dilation. A single sufficiently energetic photons. Such opening eliminates isolated single emissions may be used in an pixels. See also closing. illuminance meter and can be opsin: See visual purple. calibrated in lux.2,6

Visual Testing Glossary 315 photoemission: Method by which an positive sliding: Rolling and sliding of image orthicon television camera tube meshing gears or rollers when the produces an electrical image, in which directions of rolling and sliding are a photosensitive surface emits the same. electrons when light reflected from a poultice corrosion: See corrosion, poultice. viewed object is focused on the practical examination: In certification of surface. Compare photoconduction. nondestructive testing personnel, a photometer: Device used to measure hands-on examination using test illuminance. The sensor is filtered equipment and sample test objects. such that its response closely matches Compare general examination; specific the spectral responsivity curve of the examination. human eye. In nondestructive testing, primary creep: First stage of creep, photometers measure lux. Compare marked by elastic strain plus plastic radiometer. strain. photometric brightness: Luminance of a principal plane of focus: See focus, light source. principal plane of. photometry: Study and measurement of probability of detection (PoD): Statistical electromagnetic radiation with statement from a specific test approximate wavelengths between 400 procedure indicating how likely a and 800 nm, within the human eye’s given discontinuity length may be spectral responsivity. See also reliably found. photometer; photopic vision; radiometry; process: Repeatable sequence of actions to relative photometry. bring about a desired result. photon: Particle of light, hypothesized to process control: Application of quality explain those behaviors of light in control principles to the management which its behavior is corpuscular of a repeated process. rather than wavelike. pseudocolor: Image enhancement photopic vision: Average spectral technique wherein colors are assigned responsivity curve of the human eye to an image at several gray scale when adapted to well lit conditions intervals. (greater than 0.034 cd·m–2). The pseudoisochromatic plate: Image used photopic spectral luminous efficiency for color vision examinations. Each response curve is governed by an plate bears an image which may be averaged retinal cone response with difficult for the examinee to see if his sensitivity peaks centered at about or her color vision is impaired. See 555 nm. Also known as foveal vision also Ishihara™ plates. and light adapted vision. Compare psychophysics: Interaction between mesopic vision and scotopic vision.2,6 vision performance and physical or photoreceptor: Light sensor. psychological factors. One example is picture element: See pixel. the so-called vigilance decrement, the picture processing: See image processing. degradation of reliability based on pipe: Longitudinal centerline performing visual activities over a discontinuity inherent in ingots, period of time. imparted to some rolled metal and pupil: Black aperture in the center of the consisting of a concavity or voids. eye’s lens, through which light enters pitting: Discontinuity consisting of the lens to impinge on the retina. surface cavities. See also cavitation purple: See visual purple. fatigue. pixel: Addressable point on the screen of a digital image. The image from a Q conventional computer is an array of pixels, each of which has a numerical qualification: Process of demonstrating value. The higher the number for a that an individual has the required pixel, the brighter it is. Formerly called amount and the required type of training, experience, knowledge and picture element. 4-6 plane of focus: See focus, principal plane abilities. See also certification and of. qualified. platelet: Flat crystallites in certain phases qualified: Having demonstrated the of steel. required amount and the required polarizing microscope: See microscope, type of training, experience, polarizing. knowledge and abilities. See also porosity: Discontinuity in metal resulting certified and qualification. from the creation or coalescence of quality: Ability of a process or product to gas. Very small pores open to the meet specifications or to meet the surface are called pinholes.2,5 expectations of its users in terms of efficiency, appearance, reliability and ergonomics.4-6

316 Visual Testing quality assurance: Administrative actions rat’s tooth principle: (1) The tendency that specify, enforce and verify for hard material on a tooth’s front quality.4-6 surface to wear more slowly than soft quality control: Physical and material on the back surface, keeping administrative actions required to the edge sharp. (2) Mechanism of wear ensure compliance with a quality whereby adjacent hard and soft assurance program. Quality control surfaces wear at different rates, may include nondestructive testing in producing a self-sharpening edge. the manufacturing cycle.4-6 Recommended Practice No. SNT-TC-1A: quality of lighting: Level of luminance in Set of guidelines published by the a visual task or environment. American Society for Nondestructive Testing, for employers to establish and conduct a qualification and R certification program for nondestructive testing personnel.4-6 radial: Of or pertaining to direction from recommended practice: Set of guidelines center of a circle (or a sphere or cross or recommendations.4-6 section of a cylindrical object) to its recovery: Reduced stress level and surface, and perpendicular to its axis. increased ductility of metal after work Compare axial. hardening. See creep. radiance: Radiant flux per unit solid recrystallization: Changes in angle and per unit projected area of microstructure and properties upon the source. Measured in watts per heating of cold worked metal. square meter steradian. Compare red mud: Debris (usually oxides of the irradiance. contacting metals) of fretting wear, radiant energy: Energy transmitted mixed with oil or grease and retained through a medium by electromagnetic at or near the site of its formation. See waves. Also known as radiation. also cocoa. radiant flux: Radiant energy’s rate of reference standard: Object containing flow, measured in watts. known discontinuities at known radiant intensity: Electromagnetic energy distances and representing accept or emitted per unit time per unit solid reject criteria. angle. Measured in watts per steradian. reflectance: Ratio of reflected wave radiant power: Total radiant energy energy to incident wave energy. Also emitted per unit time. known as reflectivity. radiometer: Device used to measure reflection: General term for the process irradiance. In nondestructive testing, by which the incident energy leaves a radiometers are used to measure UV-A surface or medium from the incident output, or leaked visible light, in side, without change in frequency. microwatt per square centimeter –2 Reflection is usually a combination of (µW·cm ). See also irradiance. specular and diffuse reflection.2,6 Compare photometer. reflectometer: Photometer used to radiometric photometer: Radiometer for measure diffuse, specular and total measuring radiant power over a reflectance. variety of wavelengths. reflector: Device used to redirect the radiometry: Study and measurement of luminous flux from a source by the electromagnetic radiation emitted by a process of reflection.2,6 source or falling upon a surface. refraction: Reorientation of radiation’s raster: Repetitive pattern whereby a path by the medium through which it directed element (a robotic arm or a passes. flying dot on a video screen) follows relative photometry: (1) Evaluation of a the path of a series of adjacent parallel desired photometric characteristic lines, taking them successively in turn, based on an assumed lumen output of always in the same direction (from top a test lamp. (2) Measurement of an to bottom or from left to right), uncalibrated light source relative to stopping at the end of one line and another uncalibrated light source. beginning again at the start of the next line. Following a raster pattern makes it possible for electron beams to form video pictures or frames and for a sensor-bearing armature to cover a predetermined part of the surface of a test object.

Visual Testing Glossary 317 remote viewing: (1) Indirect viewing of a rhodopsin: See visual purple. test object far from the viewer’s robotic system: Automated system immediate presence — for example, programmed to perform purposeful viewing with telemetry or crawlers. actions in variable sequences. The term remote viewing is used in the rod: Retinal receptor that responds at low fields of robotics and surveillance to levels of luminance even down below distinguish conventional from distant the threshold for cones. At these levels viewing tasks. (2) Viewing of a test there is no basis for perceiving object during which the light image is differences in hue and saturation. No mediated through a system of two or rods are found in the fovea centralis.2,6 more lenses (as in a borescope) or Concentrated toward the outer region transduced through an electronic of the retina, rods assist with mesopic signal (as with a charge coupled vision and are responsible for scotopic camera). This use of the term remote night vision. Compare cone. viewing in some specifications is a root mean square (rms): Statistical misnomer, intended merely to measure of the magnitude of a varying distinguish borescopy from direct quantity, such as current. Square root viewing. Compare borescope; direct of the mean square of a set of viewing; indirect viewing. measures, usually a time series. replica: Piece of malleable material, such as polyvinyl or polystyrene plastic film, molded to a test surface for the S recording or analysis of the surface microstructure. sampling, partial: Testing of less than replica, metallographic: Replica suitable 100 percent of a production lot. for microscopic examination. See sampling, random partial: Partial metallography. sampling that is fully random. replication: Method for copying the sampling, specified partial: Partial topography of a surface by making its sampling in which a particular impression in a plastic or malleable frequency or a sequence of sample material. selection is prescribed. An example of reserve vision acuity: Ability of an specified partial sampling is the testing individual to maintain vision acuity of every fifth unit. under poor viewing conditions. A saturation: Relative or comparative color visual system with 20/20 near vision characteristic resulting from a hue’s acuity under degraded viewing dilution with white light. scalar: Quantity completely specified by a conditions has considerable reserve 4 vision acuity compared to that of an single number and unit. individual with 20/70 near vision scaling: (1) Forming a layer of oxidation acuity. product on metals, usually at high resolution: Aspect of image quality temperature. (2) Deposition of pertaining to a system’s ability to insoluble constituents on a metal surface, as in cooling tubes and water depict objects, often measured by 2,5 distinguishing (resolving) a pair of boilers. adjacent objects or parallel lines. scoring: (1) Marring or scratching of any resolution test: Procedure wherein a line formed part by metal pickup on a is detected to verify a system’s punch, die or guide. (2) Reducing sensitivity. the thickness of a part along a line to weaken it purposely at a specific resolution threshold: Minimum distance 2,5 between a pair of points or parallel location. lines when they can be distinguished scotopic vision: Dark adapted vision, as two, not one, expressed in minutes using only the rods in the retina, of arc. Vision acuity, in such a case, is where differences in brightness can be the reciprocal of one-half of the period detected but differences in hue expressed in minutes.2,6 cannot. Vision is wholly scotopic resolving power: Ability of vision or when the luminance of the test × –5 –2 other detection system to separate two surface is below 3 10 cd·m × –6 –2 points. Resolving power depends on (2.7 10 cd·ft ). Also known as the angle of vision and the distance of parafoveal vision. Compare mesopic the sensor from the test surface. vision and photopic vision. Resolving power is often measured scuffing: Type of adhesive wear. using parallel lines. Compare seam: Linear discontinuity formed by a resolution. lack of metal from folds produced by retina: In the eye, the tissue on back, an underfilled pass during metal inside surface of the eyeball, opposite rolling. Squeezed tight on subsequent the pupil, where light sensitive rods passes, the underfill runs parallel to and cones sense light. the longitudinal axis of the bar. retinene: See visual purple.

318 Visual Testing second stage replica: Positive replica simple magnifier: Microscope having a made from the first cast to produce a single converging lens. duplicate of the original surface. smoothing: In image processing, linear secondary creep: Second stage of creep, combination of pixel values to smooth in which deformation proceeds at a abrupt transitions in a digital image. constant rate and less rapidly than in Also called low pass filtering. primary creep. Essentially an SNT-TC-1A: See Recommended Practice No. equilibrium condition between the SNT-TC-1A. mechanisms of work hardening and spalling fatigue: See subcase fatigue. recovery. See also defect and specific examination: In certification of discontinuity.4 nondestructive testing personnel, a sensitivity: Ability of a sensor or system written examination that addresses the to distinguish a signal or indication specifications and products pertinent from background noise. See also to the application. Compare general probability of detection. examination and practical examination. sensitization: Precipitation of chromium specific gravity: Unitless ratio of the carbides in the grain boundaries of a density of a material divided by the corrosion resistant alloy, resulting in density of water. Water has a density intergranular corrosion that would of about 1 g·cm–3, or 1000 kg·m–3. otherwise be resisted. specification: Set of instructions or sensor: Device that detects a material standards invoked to govern the property or mechanical behavior (such properties, results or performance of a as radiation or displacement) and specific set of tasks or products.4-6 converts it to an electrical signal. spectral irradiance: Measure of energy shadow casting: Nondestructive emitted by a radiation source as technique of vapor depositing a thin function of wavelength. Units of metal film onto a replica at an oblique spectral irradiance are watts per square angle in order to obtain a micrograph meter and are often plotted versus of a test surface of an opaque test wavelength. object. spectral power distribution: Radiant shear break: Open break in metal at the power per unit wavelength as a periphery of a bolt, nut, rod or function of wavelength. Also known member at approximately a 45 degree as spectral energy distribution, spectral angle to the applied stress. Shear density and spectral distribution. breaks occur most often with flanged spectral reflectance: Radiant flux products. Also called shear crack.2,5 reflected from a material divided by shear crack: See shear break. the incident radiant flux. shielded arc welding: Joining of metals spectral responsivity: Measure of a by heating them with an electric arc photometric or radiometric sensor’s between electrode(s) and the work sensitivity over a wavelength range of piece, using an inert gas to shield the interest, often presented as percent electrode(s). See also gas tungsten arc versus wavelength. Photometric welding. sensors should exhibit a bell shaped shoulder: Cylindrical metal component spectral responsivity curve over the (pipe) surface, machined to receive visible light range, whereas threading indentations but in fact not radiometric sensors may exhibit a flat threaded, where the thread stops on or other response curve. the outside surface of the pipe. spectral transmittance: Radiant flux SI (International System of Units): passing through a medium divided by Measurement system in which the the incident radiant flux. following seven units are basic: meter, spectrophotometer: Instrument used for mole, kilogram, second, ampere, spectrophotometry. kelvin and candela. spectrophotometry: Measurement of signal electrode: Transparent conducting electromagnetic radiant energy as a film on the inner surface of a vidicon’s function of wavelength, particularly in faceplate and a thin photoconductive the ultraviolet, visible and infrared layer deposited on the film. wavelengths. signal processing: Acquisition, storage, spectroradiometer: Instrument used for analysis, alteration and output of spectroradiometry. digital or analog data. spectroradiometry: Measurement of signal-to-noise ratio: Ratio of signal electromagnetic radiant power and values (responses that contain relevant spectral emittance, used particularly to information) to baseline noise values examine colors and to measure the (responses that contain nonrelevant spectral emittance of light sources. information).4 spectroscope: Instrument used for signal: Physical quantity, such as voltage, spectroscopy. that contains relevant information.4

Visual Testing Glossary 319 spectroscopy: Spectrophotometry or stringer: In wrought materials, an spectroradiometry in which the elongated configuration of spectrum, rather than being analyzed microconstituents or foreign material only by a processing unit, is presented aligned in the direction of working. in a visible form to the operator for Commonly, the term is associated organoleptic examination. with elongated oxide or sulfide spectrum: Representation of radiant inclusions in steel. energy in adjacent bands of hues in subcase fatigue: Fatigue originating below sequence according to the energy’s the case depth. wavelengths or frequencies. A rainbow subcase origin fatigue: See subcase is a well known example of a visible fatigue. spectrum. subsurface fatigue: Fatigue cracking that specular: Pertaining to a mirrorlike originates below the surface. Usually reflective finish, as of a metal. associated with hard surfaced or shot Compare lambertian. peened parts but may occur any time specular reflection: When reflected subsurface stresses exceed surface waves and incident waves form equal stresses. angles at the reflecting surface. speed of light: Speed of all radiant energy, including light, is T 299 792 458 × 108 m·s–1 in vacuum. In all materials the speed is less and tarasov etching technique: Way of varies with the material’s index of visually inspecting for the presence of refraction, which itself varies with deleterious effects in hardened steels wavelength.2,6 by using specific etching solutions and speed of vision: Reciprocal of the methods of inspection. duration of the exposure time required temperature diagram: See time for something to be seen.2,6 temperature transformation (TTT) standard: Object, document or concept diagram. established by authority, custom or tempering: Process of heating a material, agreement to serve as a model or rule particularly hardened steel to below in the measurement of quantity or the the austenite transformation establishment of a practice or temperature, to improve ductility. procedure.4,8 See also reference standard tertiary creep: Third stage of creep, and acceptance standard. marked by steady increase in strain to standardization, instrument: Adjustment the point of fracture under constant of instrument readout before use to a load. specified reference value.4 test object: Physical part or specimen standard observer response curve: See subject to nondestructive testing. eye sensitivity curve. threshold: (1) A value in a phenomenon steel: Iron alloy, usually with less than where a large change of output occurs. two percent carbon. (2) Setting of an instrument that stereo photography: Close range causes it to register only those changes in response greater or less than a photogrammetric technique involving 4 the capture and viewing of two images specified magnitude. See adaptive of the same object in order to thresholding, resolution threshold. reconstruct a three dimensional image thresholding: Digital data processing of the object. technique that reduces a gray level stick welding: See shielded metal arc image into a binary image. welding. throat, actual: Shortest distance from the strain: Deflection or alteration of the root of a fillet weld to its face, as shape of a material by external forces. opposed to theoretical throat or weld stress: (1) In physics, the action in a size. material that resists external forces throat, effective: In fillet welds, the weld such as tension and compression. throat including the amount of weld (2) Load per unit of area. penetration but ignoring excess metal stress concentration: Region where force between the theoretical face and the per unit area is elevated, often because actual face. of geometric factors or cracks. Also throat, theoretical: Distance from the known as a stress raiser. beginning of the root of a fillet weld stress raiser: Contour or property change perpendicular to the hypotenuse of that locally increases stress magnitude. the largest right triangle that can be stress riser: See stress raiser. inscribed within the cross section of the fillet weld. Compare weld size.

320 Visual Testing throat, weld: Distance from the root of a V fillet weld to its face. Compare weld size and throat, actual. video: Pertaining to the transmission and TIG welding: Tungsten inert gas welding. display of images in an electronic See gas tungsten arc welding. format that can be displayed on a time temperature transformation (TTT) monitor or screen. diagram: Graph showing time videoscope: Jargon for video borescope. See required at any temperature to borescope, video. transform austenite to pearlite, bainite vidicon tube: Analog television tube that or martensite. uses the photoconduction method. tip: Distal or objective end of a borescope. Compare image orthicon. tool mark: Shallow indentation or groove vigilance decrement: Degradation of made by the movement of reliability during performance of manufacturing tools over a surface. visual activities over a period of time. Compare gouge or nick. See also psychophysics. trace: Line formed by electron beam visibility: Quality or state of being scanning from left to right on a video perceivable by the eye. In many screen to generate a picture. outdoor applications, visibility is tracer: In leak testing, a gas that is sensed defined in terms of the distance at as it escapes from confinement. which an object can be just perceived transformation diagram: See time by the eye. In indoor applications it temperature transformation (TTT) usually is defined in terms of the diagram. contrast or size of a standard test troland: Unit of retinal illuminance equal object, observed under standardized to that produced by a surface whose view conditions, having the same luminance is 1 cd·m–2 when the pupil threshold as the given object.2,6 measures 1 mm2. visible light: Radiant energy with a tubing string: Pipe with which oil or gas wavelength between 400 and 800 nm has contact as it is brought to the as measured in photometric units of Earth’s surface.4 lux. tungsten inert gas (TIG) welding: See gas vision: Perception by eyesight. See far tungsten arc welding. vision, machine vision, mesopic vision, near vision, peripheral vision, photopic vision, scotopic vision, and speed of U vision. vision acuity: Ability to distinguish fine ultraviolet borescope: See borescope, details visually at a given distance. ultraviolet. Quantitatively, it is the reciprocal of ultraviolet radiation: Electromagnetic the minimum angular separation in radiation with wavelengths between minutes of two lines of width 40 and 400 nm. See also irradiance and subtending one minute of arc when UV-A. the lines are just resolvable as ultraviolet radiometer: Meter, usually separate.2,6 calibrated at 365 nm, used in visual acuity: See vision acuity. fluorescent liquid penetrant and visual angle: Angle formed by lines magnetic particle testing to measure drawn from center of eye subtended output of ultraviolet lamp. by an object or detail at the point of undercut: Undesirable groove left unfilled observation. It usually is measured in by weld metal, created during welding minutes of arc.2,6 and located in base plate at the toe of visual background noise: Formations on a weld. or signals from a test object that Unified Numbering System: constitutes the background to a Alphanumeric system for identifying discontinuity. The higher the level of alloys according to a registry visual background noise, the more maintained by ASTM International difficult it is to distinguish a 4 and SAE International. discontinuity. UV-A: Electromagnetic radiation with visual efficiency: Reliability of a visual wavelengths between 315 and system. The term visual efficiency uses 400 nm. Fluorescent nondestructive 20/20 near vision acuity as a baseline testing has historically used ultraviolet in the United States for 100 percent energy centered at 365 nm. See also visual efficiency. irradiance and radiometer.

Visual Testing Glossary 321 visual field: Locus of objects or points in W space that can be perceived when head and eyes are fixed. The field may be wavelength: Distance between repeating monocular or binocular.2,6 values of a wave. For example, the visual perception: Interpretation of distance from one peak to the next impressions transmitted from the peak on a sine wave. retina to the brain in terms of wear: See erosion; rat’s tooth principle; wear, information about a physical world adhesive; and wear, fretting. displayed before the eye. Visual wear oxidation: See wear, fretting. perception involves any one or more wear, adhesive: Degradation of a surface of the following: recognition of the by microwelding and consequent presence of something (object, fracture due to the sliding of one aperture or medium); identifying it; surface against another. Types include locating it in space; noting its relation fretting, galling and scuffing. to other things; identifying its wear, fretting: Surface degradation by movement, color, brightness or microwelding and microfractures on form.2,6 surfaces rubbing each other. Also visual performance: Quantitative called chafing, friction oxidation and assessment of the performance of a wear oxidation. See also cocoa and false visual task, taking into consideration brinelling. speed and accuracy.2,6 weld size: Thickness of weld metal — in a visual purple: Chromoprotein called fillet weld the distance from the root rhodopsin, the photosensitive pigment to the toe of the largest isosceles right of rod vision. The mechanism of triangle that can be inscribed in a converting light energy into nerve cross section of the weld. impulses is a photochemical process in weld throat: See throat, weld. the retina. Chromoprotein is welder’s flash: Clinical condition, transformed by the action of radiant specifically keratoconjunctivitis, energy into a succession of products, commonly caused by overexposure to finally yielding the protein called opsin ultraviolet radiation of welding arc. plus the carotenoid known as retinene. white light: Light combining all visual task: Appearance and immediate frequencies in the visible spectrum background of those details and (wavelengths from 380 to 780 nm) objects that must be seen for the and in equal proportions. performance of a given activity. The work hardening: Increase in hardness term visual task is a misnomer because accompanying plastic deformation of it refers to the visual display itself and a metal. Usually caused in a metal by not the task of extracting information repeated impacting, bending or from it. See visual field. flexing. Compare creep and recovery. visual testing: Method of nondestructive working standard: Work piece or energy testing using electromagnetic radiation source calibrated and used in place of at visible frequencies. expensive reference standards. In voids: Hollow spots, depressions or calibrating of photometers, the cavities. See also discontinuity. standard would be a light source. volt (V): Measurement unit of electric potential.4 VT: Visual testing.

322 Visual Testing References

1. ASTM E 1316, Standard Terminology for Nondestructive Examinations. West Conshohocken, PA: ASTM International (2007). 2. Nondestructive Testing Handbook, second edition: Vol. 8, Visual and Optical Testing. Columbus, OH: American Society for Nondestructive Testing (1993). 3. Nondestructive Testing Handbook, second edition: Vol. 10, Nondestructive Testing Overview. Columbus, OH: American Society for Nondestructive Testing (1996). 4. Nondestructive Testing Handbook, third edition: Vol. 8, Magnetic Testing. Columbus, OH: American Society for Nondestructive Testing (2008). 5. EPRI Learning Modules. Charlotte, NC: Electric Power Research Institute. 6. IES Lighting Handbook: Reference Volume. New York, NY: Illuminating Engineering Society of North America (1984). 7. Lovejoy, D. Magnetic Particle Inspection: A Practical Guide. New York, NY: Chapman & Hall (1993). 8. TO33B-1-1 (NAVAIR 01-1A-16) TM43-0103, Nondestructive Testing Methods. Washington, DC: United States Department of Defense, United States Air Force (June 1984).