3MT - asnt.org

Richard D. Lopez, Center for NondestructiveEvaluation, Iowa State University, Ames, Iowa

16C H A P T E R

Magnetic Testing Glossary

From Nondestructive Testing Handbook, Third Edition: Volume 8, Magnetic Particle Testing Testing © 2008. Reprinted with permission of The American Society for Nondestructive Testing Inc.

kbalkin

Cross-Out

kbalkin

Cross-Out

Introduction

PurposeStandards writing bodies take great painsto ensure that their standards aredefinitive in wording and technicalaccuracy. People working to writtencontracts or procedures should consultdefinitions referenced in standards whenappropriate. For example, persons whowork in accordance with standardspublished by ASTM International arerequired to refer to definitions in theASTMBook of Standards.1

The definitions in this NondestructiveTesting Handbook volume should not bereferenced for tests performed accordingto standards or specifications or infulfillment of contracts. This glossary isprovided for instructional purposes. Noother use is intended.

On ReferencesMany definitions in this glossary areadapted from other volumes of theNondestructive Testing Handbook series.Many definitions from the secondedition’s Magnetic Particle Testing (1989)2

are reprinted but not referenced below.Definitions from three volumes of thethird edition are referenced.3-5

Some terms apply generally tonondestructive testing and are not specificto magnetic techniques — terms onsubjects such as metallurgy, qualitycontrol and personnel qualification. Mostof these definitions come from the secondedition volume Nondestructive TestingOverview (1996),6 and some are rephrasedin the most recent volume, the thirdedition’s Ultrasonic Testing (2007).4

All definitions in this glossary havebeen modified to satisfy peer review andeditorial style. For these reasons,references in this glossary should beconsidered not attributions but ratheracknowledgments and suggestions forfurther reading.

Definitions

A

acceptance criterion: Benchmark againstwhich test results are to be comparedfor purposes of establishing thefunctional acceptability of a part orsystem being examined.4

acceptance level: Measured value orvalues above or below which testobjects are acceptable in contrast torejection level.4

acceptance limit: Test signal value usedin electromagnetic testing,establishing the group to which amaterial under test belongs.4

acceptance standard: (1) Specimen,similar to the product to be tested,containing natural or artificialdiscontinuities that are well definedand similar in size or extent to themaximum acceptable in the product.4(2) Document defining acceptablediscontinuity size limits.5 See alsostandard.

accommodation: Of the eye, adjustmentof the lens’ focusing power bychanging the thickness and curvatureof the lens through the movement oftiny muscles.3

ACGIH: American Conference ofGovernmental Industrial Hygienists.

agglomeration: Clustering where smallerparticles collide and adhere as groups.

alternating current: Electric waveformthat changes cyclically in magnitudeand direction.7

alternating current magnetization:Inducing of a magnetic state by acyclically reversing waveform, a stategenerally characterized by its formfollowing ability and by shallowpenetration.

ampere (A): SI unit of electric current.4ampere per meter (A·m–1): SI derived

unit of magnetic field intensity. Themeasurement 1 A·m–1, for example,describes a current of 1 A flowingthrough a coil of 1 m diameter.4

ampere turn: Unit for expressing themagnetomotive force required formagnetization using a coil in terms ofthe product of the number of coilturns and the current in amperesflowing through the coil.

376 Magnetic Testing

PART 1. Terms


angstrom (Å): Disused unit of length.1Å= 0.1 nm.

anomaly: In nondestructive testing, anunintentional or undesired materialcondition that may qualify as a defect.Compare defect; discontinuity. Someanomalies, such as inadequate casehardening or rough surface finish,may be defects but, because there is nointerruption in the material structure,are not discontinuities.

apposing field: See bucking field.arc: Current flow across a gap, producing

intense heat and light.arc strikes: Localized heat damage to an

object sometimes caused by poor arcweld initiation technique or by poorcoupling between a test object andcontact pads or prods.

arc welding: See electric arc welding.articulated pole pieces: Independently

adjustable legs of an electromagneticyoke enabling satisfactory contact onirregular test object profiles.

ASNT: American Society forNondestructive Testing.

ASNT Recommended PracticeNo.-SNT-TC-1A: See RecommendedPractice No. SNT-TC-1A.

automated system: Acting mechanismthat performs required tasks at adetermined time and in a fixedsequence in response to certainconditions.4

axial: Of or pertaining to a directionalong the length of an oblong objectand perpendicular to its radius — forexample, down the length of acylinder. Compare radial; tangential.

B

background: (1) In magnetic particletesting, the appearance or brightnessof the surrounding area acting toreduce the contrast of an indication.(2) Nonrelevant signal that tends tointerfere with the normal reception orinterpretation of the target beingsought.

bath: Combination of well agitated waterbased or oil based carrier fluid with acontrolled concentration of suspendedmagnetic particles.

bearding: See furring.berthold penetrameter: Shared flux

indicator of magnetic field orientation,for use during continuousmagnetization. Similar to a pie gagebut containing an cover plate withheight adjustable to vary the magneticflux density required to form anindication. See also shared fluxindicator.

black light: Disfavored term for ultravioletradiation. The term is misleadingbecause the phenomenon is not blackand is not light and has also beenapplied to the lamp.

blind spot: Portion of the retina wherethe optic nerve enters the eye and nophotoreceptors (rods and cones) arepresent.

blister: Discontinuity in metal, on or nearthe surface, resulting from theexpansion of gas in a subsurface zone.Very small blisters are called pinheadsor pepper blisters.4

blowhole: Hole in a casting or a weldcaused by gas entrapped duringsolidification.4

blue light hazard: Danger posed to theeye due to long term exposure to highintensity visible light.

borescope: Industrial endoscope;electronic and/or optical device thatallows the inspector to view normallyinaccessible interior surfaces.

borescope, fiber optic: Industrialendoscope, or fiber optic borescope,that uses glass or quartz fibers totransmit light and the optical path toand from the test object.

bucking field: Magnetic flow techniqueconfiguration where poles of likepolarity are induced on the ends of atest object to force magnetization intoextremities that are normally fieldfree.

butt weld: Weld that joins the edges ofwork pieces in the same plane.

C

calibration: (1) Determination of thecorrelation between a known inputvalue and an output value from ameasurement device. (2) Act ofreturning an instrument to thecondition of the original equipmentmanufacturer.

candela (cd): Base SI unit of luminousintensity, in a given direction, of amonochromatic radiation source thathas a frequency of 5.4 × 1014 Hz andthat has a radiant intensity in thatdirection of 1.464 mW·sr–1.

capacitor discharge technique:Magnetization technique generallycharacterized by a short duration, highintensity electrical pulse, oftenperformed on oil field components.

carrier fluid: Water based or oil basedcomponent of the bath, the agitationof which holds magnetic particles insuspension.

central conductor: See internal conductor.centrifuge tube: Vial that holds liquids

and has graduations to indicate theconcentration of solids that settle outof a known suspension volume.

377Magnetic Testing Glossary


certification: With respect tonondestructive test personnel, theprocess of providing written testimonythat an individual has met therequirements of a specific practice orstandard. See also certified andqualified.5

certified: With respect to nondestructivetest personnel, having writtentestimony of qualification. See alsocertification and qualification.5

CGS system: Obsolete measurementsystem based on the centimeter, gramand second. Compare SI.

checks: See grinding crack.circular magnetic field: Active or

residual magnetization oriented alongthe circumference. See also circularmagnetization, current flow techniqueand right hand rule.

circular magnetization: Result of currentflow or internal conductor techniqueswhere flux lines are oriented along thecircumference of the test object.

circumferential magnetization: Seecircular magnetization.

coercive force: Reverse external magneticfield intensity required to reduce thetest object’s bulk magnetism to zero.

coercivity: See coercive force.code: Standard enacted or enforced as a

law.3coil technique: Magnetization technique

using an encircling current carryingsolenoid that imparts a longitudinalmagnetic field in ferromagneticcomponents with a length-to-diameterratio greater than 3. See also L·D–1 ratioand self-demagnetizing factor.

coil shot: See coil technique. One instanceof the coil technique; one pulse ofcurrent in the coil technique.

color: Visual sensation by means of whichhumans distinguish light of differinghue (predominant wavelengths),saturation (degree to which thoseradiations predominate over others)and lightness.3

color blindness: Deficiency in ability toperceive or distinguish hues.3

conditioning agent: Additive to waterbased carrier fluid aiding withdefoaming, surface wetting, particledispersion, pH or corrosivity, orantifungal properties.

conductance (G): Transmission of electriccurrent through material. Measured insiemens (S). Inversely related toelectrical resistance (R):4

(1)

conductivity (σ): Ability of material totransmit electric current, measured insiemens per meter. Reciprocal orinverse of resistivity ρ:4

(2)

cone cells: Common name for three colorsensitive photoreceptors concentratedat the inner region of the retina.Cones assist with mesopic vision andare responsible for photopic vision.Compare rod cells.

confidence level: Level of assurance fordetecting a specified discontinuity sizewith a specified probability.3 See alsoprobability of detection.

contact technique: See current flowtechnique.

contact pad: Replaceable metal pad,usually made of braided copper and/orlead, that prevents electrical arcingbetween the headstock and test objectduring a head shot.

continuous technique: Technique ofmagnetic particle testing, a testsequence where the particles flow overthe test object only during activemagnetization.

contour probe: In magnetic particletesting, yoke with legs adjustable fortest objects of various shapes.

contrast: Difference in color or brightnessbetween indication and background.

cosine law: Physical law stating that theillumination of a surface varies as thecosine of the incidence angle.Maximum illumination is obtainedwhen the source is perpendicular tothe surface.

coupling: Percentage of magnetic fluxfrom a primary circuit that links asecondary circuit; effectiveness of acoil in inducing eddy currents in thetest object.4

crack: (1) Break, fissure or rupture,sometimes V shaped in cross sectionand relatively narrow. By convention,a discontinuity is called a crack if it isat least three times longer than it iswide. (2) Propagating discontinuitycaused by fatigue, corrosion or stressessuch as heat treating or grinding. Maybe difficult to detect unaided becauseof fineness of line and pattern (mayhave a radial or latticed appearance).5,6

curie point (Tc): Temperature at which aphase transformation causesferromagnetic materials to lose theirmagnetic properties.

σρ

= 1

GR

= 1



current flow technique: Circularmagnetization of a test object within ashort period of time by passing electricpower through the test object withprods, or the headstock and tailstockof a stationary unit. See also circularmagnetization and right hand rule.Compare magnetic flow technique.

current induction technique: See toroidalmagnetization.

cycle: Single period of a waveform orother variable.4

D

dark adaptation: Time required for thepupils to dilate and for the two typesof photoreceptors in the retina tochange chemical balance. After a finiteamount of time, an inspector willtransition from photopic vision tomesopic or scotopic low illuminationvision.

defect: Discontinuity whose size, shape,orientation or location (1) makes itdetrimental to the useful service of itshost object or (2) exceeds anaccept/reject criterion of an applicablespecification. Some discontinuities donot exceed an accept/reject criterionand are therefore not defects.Compare crack; discontinuity;indication.5,6

demagnetization: Reduction of residualmagnetism to an acceptable level,generally less than 0.2 to 1.0 mT (2 to10 G). See also demagnetizing coil anddirect current downcycle demagnetization.

demagnetizing coil: Solenoid or coilcarrying the current to be used fordemagnetization. Current waveformmay be alternating for pass-throughsolenoids, or a rectified current whena multiple-step downcycledemagnetization process is used. Someresidual magnetization may remain inlarge parts magnetized with directcurrent or rectified current, butsubsequently demagnetized withalternating current. See also directcurrent downcycle demagnetization.

demagnetizing factor: Seeself-demagnetizing factor.

density: Mass per unit volume, measuredin kilograms per cubic meter (kg·m–3).

depth of penetration: See skin effect.diamagnetic material: Substance with a

magnetic permeability less than 1 thatweakly repels an external magneticfield.

diffuse indication: Particle cluster notclearly defined — for example,indication from a subsurfacediscontinuity.

direct current: Electricity that flowscontinuously in one direction througha conductor. The only true source ofdirect current is a battery, althoughsome rectified power waveforms mayresemble direct current. See alsofull-wave current and half-wave current.

direct current downcycledemagnetization: Massaging themagnetism of a component down toan acceptable level through a 25-stepto 30-step process, where thepersistence of one polarity is overcomein decreasing steps by a field reversingat each step.

discontinuity: Interruption in thephysical structure or configuration of atest object. After nondestructivetesting, a discontinuity indication canbe interpreted to be a flaw or a defect.10

Compare defect; indication.5,6

discontinuity, artificial: Referencediscontinuity such as hole,indentation, crack, groove, or notchintroduced into a reference standardto provide accurately reproducibleindications for determining sensitivitylevels.4

domain: Macroscopic dipole substructurewithin a ferromagnetic materialpermanently magnetically saturated.Domains are randomly oriented in ademagnetized material, but theirorientation may be preferentiallyrotated through the application of anexternal field.

downcycle: See direct current downcycledemagnetization.

dry powder: Ferromagnetic particles,larger than those used in wetsuspensions, introduced to the testobject surface by dusting or puffing.

dry technique: Magnetic particle testtechnique, generally used withportable equipment, where theferromagnetic particles are applied aspowder.

dual-use particle: Magnetic particlecoated with pigment that providescontrast when viewed undercontrolled levels of ambient whitelight but that also fluoresces underultraviolet radiation. Testing withfluorescent particles is performedunder low ambient lighting andcontrolled ultraviolet radiation.Compare dual-use particle; visibleparticle.



E

eddy current: Electrical current inducedin a conductor by a time varyingmagnetic field.4

electric arc welding: Joining of metals byheating with electric arc. Also calledarc welding.3

electromagnet: Ferromagnetic coresurrounded by a coil of wire thattemporarily becomes a magnet whenan electric current flows through thewire.4

encircling coil: See coil technique.endoscope: See borescope.equivalent 20/20 near vision acuity:

Vision acuity with remote viewing orother nondirect viewing thatapproximates 20/20 direct viewingclosely enough to be considered thesame for visual testing purposes.3

equivalent sphere illumination: Level ofperfectly diffuse (spherical)illuminance that makes the visual taskas photometrically visible within acomparison test sphere as it is in thereal lighting environment.3

evaluation: Process of deciding theseverity of a condition after anindication has been interpreted.Evaluation determines if the testobject should be rejected or accepted.See also indication and interpretation.5

eye sensitivity curve: See photopic vision.

F

false indication: Test indication thatcould be interpreted as originatingfrom a discontinuity but that actuallyoriginates where no discontinuityexists in the test object. Distinct froma nonrelevant indication. Compare alsodefect.4

farsightedness: Vision acuity functionallyadequate for viewing objects at adistance, generally at or farther thanan arm’s length. Also calledhyperopia.3 Compare nearsightedness.

ferromagnetic material: Material such asiron, nickel or cobalt whose relativepermeability is considerably greaterthan unity, depends on themagnetizing force and often exhibitshysteresis. Materials that are moststrongly affected by magnetism arecalled ferromagnetic.4

field flow technique: See magnetic flowtechnique.

fill factor: Convenient quantity forcharacterizing how closely the outsidediameter of a specimen matches theinside diameter of the magnetizingcoil. With a high fill factor, the ratioof the cross sectional area of the coildivided by the cross sectional area ofthe specimen is less than 2;intermediate, 2 to 10; low, greaterthan 10.

fillet weld: Weld that joins the edges ofworkpieces at right angles.

flash magnetization: See capacitordischarge technique.

flash point: Lowest temperature at whicha substance will form an ignitablemixture in air. The value varies withcircumstances.

flaw: Rejectable or unintentionalanomaly.4 See also defect anddiscontinuity.4

fluorescence: Luminescent phenomenonexhibited by some substances wherehigher energy electromagnetic wavesare absorbed and reemitted as lowerenergy waves. The emission ceases assoon as the exciting energy isremoved. Different fromphosphorescence, which will continueto emit after the exciting energy isremoved. In magnetic particle testing,pigments coating the magneticparticles are excited by invisible UV-Aradiation and emit visible light.

fluorescent particle: Magnetic particlecoated with pigment that fluoresceswhen excited with UV-A radiation.Testing with fluorescent particles isperformed under low ambient lightingand controlled ultraviolet radiation.Compare dual-use particle; visibleparticle.

flux: Convenient concept for visualizingthe vector field of magnetic inductionthat comprises a magnetic field. Fluxlines form closed loops that do notcross. Magnetic flux is governed by thedensity of flux lines. The number offlux lines is expressed in weber (Wb),where 1 Wb = 108 maxwell (Mx). Thedensity of flux lines is expressed intesla (T), where 1T = 104 gauss (G).

flux density: See magnetic flux density.flux indicator: See shared flux indicator.flux leakage field: Magnetic field that

leaves or enters the surface of anobject.4

flux leakage technique: Electromagnetictest technique for the detection andanalysis of a surface discontinuity ornear-surface discontinuity using theflux that leaves a magneticallysaturated, or nearly saturated, testobject at a discontinuity.4

flux meter: Device that measures totalchange in magnetic flux density bymonitoring the voltage induced in acoil.8 See also tesla meter.



footcandle (ftc): Non-SI unit ofilluminance, where1 ftc=1 lm·ft–2 =10.76 lx.

footlambert (ftl): Non-SI unit ofluminance, where 1 ftl = 3.426 cd·m–2.

fracture mechanics: Field of solidmechanics that deals with behavior ofcracked bodies subjected to stress andstrain.

frequency: Number of times per secondthat a cyclical waveform repeats. Theunit of frequency is hertz (Hz).

full-wave current: Single-phase orthree-phase alternating currentconverted to produce unidirectionalcurrent. Rectified current containsmore amplitude variation, or ripple,than direct current from a battery.

furring: Buildup of dry magnetic particlesat magnetic poles resulting fromovermagnetization of the test object.

G

gas metal arc welding: Inert gas shieldedmetal joining process that uses acontinuous and consumable wireelectrode. Also called MIG (metal inertgas) welding. Compare gas tungsten arcwelding and shielded metal arc welding.

gas tungsten arc welding: Inert gasshielded metal joining process thatuses a nonconsumable tungstenelectrode. Filler material, whenneeded, is manually fed into themolten weld puddle. Also calledtungsten inert gas welding. Compare gasmetal arc welding; shielded metal arcwelding.

gauss (G): Old CGS unit of magnetic fluxdensity denoting one flux line, ormaxwell, passing through one squarecentimeter. The preferred unit of fluxdensity is the tesla (T), where1T=104 G.

gauss meter: See tesla meter.general examination: In personnel

qualification, a test or examination ofa person’s knowledge, typically (in thecase of nondestructive testingpersonnel qualification) a written teston the basic principles of anondestructive test method andgeneral knowledge of basic equipmentused in the method. (According toASNT’s guidelines, the generalexamination should not addressknowledge of specific equipment,codes, standards and procedurespertaining to a particularapplication.)4

glare: Excessive brightness (or brightnessvarying by more than 10:1 within thefield of view) that interferes withobservation or interpretation of a testresponse. Glare may be caused byreflection, whether specular (smoothsurface) or diffuse (rough surface), oflight or radiation sources.

grinding crack: Shallow crack formed inthe surface of relatively hard materialsbecause of excessive grinding heat orthe high sensitivity of the material.Grinding cracks typically are oriented90degrees to the direction ofgrinding.4

Hhalf-wave current: Power waveform

rectified from single-phase alternatingcurrent to produce a pulsatingunidirectional field.

hall effect: Potential difference developedacross a conductor at right angles tothe direction of both the magneticfield and the electric current. Producedwhen current flows along arectangular conductor subjected to atransverse magnetic field.4

hall effect detector: Semiconductorelement that produces an outputelectromotive force proportional tothe product of the magnetic fieldintensity and a biasing current.4

headstock: One of two points on a wethorizontal unit, often equipped with apneumatic ram, which contacts andsupports the test object duringapplication of the current flowtechnique.

head shot: See current flow technique.heat affected zone: Base metal that was

not melted during brazing, cutting orwelding but whose microstructure andphysical properties were altered by theheat.4

heat treatment: Heating and cooling ametal or alloy in such a way as toobtain desired conditions orproperties. Heating for the solepurpose of working is excluded fromthis definition.3

hertz (Hz): Measurement unit offrequency, equivalent to one cycle persecond.4

horseshoe magnet: U shaped bar magnet.See also keeper.

human factors: Factors in the overall testsensitivity based upon mental andphysical condition of the inspector,training, experience level and thephysical conditions under which theinspector must work.

hyperopia: See farsightedness.



hysteresis: Lagging of a ferromagnetic testobject’s magnetization under theinfluence of a changing externalmagnetic field intensity; phenomenonexhibited by a magnetic systemwherein its state is influenced by itsprevious history.4

hysteresis loop: Curve showing fluxdensity B plotted as a function ofmagnetizing force H as H is increasedto the saturation point in bothnegative and positive directionssequentially. The curve forms acharacteristic loop.4

I

IACS: International Annealed CopperStandard.

illuminance: Intensity of radiant energyin the visible light spectrum.Illuminance is measured infootcandles or lux.

incremental permeability: Ratio of thechange in magnetic induction to thecorresponding change in magnetizingforce.4

indication: Nondestructive testequipment response to a discontinuitythat requires interpretation todetermine its relevance.4 In magneticparticle testing, a visible accumulationof magnetic particles that serves asevidence of a magnetic leakage field.See also defect, discontinuity, falseindication and nonrelevant indication.

induced current magnetization:Noncontact means for testing delicatering shaped objects for circumferentialdiscontinuities. The technique is basedon the fact that a time varying currentpassing through an internalconductor, often a soft iron orlaminated core, self-induces anencircling magnetic field. This timevarying magnetic field will induce asecondary current circling through thering. This secondary current thenself-induces the toroidal magnetic fieldused for testing. See also right handrule.

inductance: Property of electric circuit, bywhich current in it or in a nearbycircuit creates magnetic flux in theother circuit. Inductance is measuredin henries, where one henry equalsone weber per ampere (1 H = 1Wb·A–1). See also self-inductance.

initial permeability: Slope of theinduction curve at zero magnetizingforce as a test object begins to bemagnetized from a demagnetizedcondition (slope at the origin of theBH curve before hysteresis isobserved).4

internal conductor: Rod of conductivematerial threaded through a hole in acylindrical test object to inducecircular magnetic flux. An internalconductor may be centered in the hole(a central conductor) or be offset nearor touching one side of the cylinder’sinside surface.

intergranular stress corrosion crack:Anomaly caused by intergranularcorrosion as a result of sensitizedmaterial, stress and corrosiveenvironment (typical in the heataffected zone of stainless steel welds).4

International Annealed CopperStandard (IACS): Conductivitymeasurement system in which theconductivity of annealed, unalloyedcopper is arbitrarily rated at100percent and in which theconductivities of other materials areexpressed as percentages of thisstandard.4

interpretation: Determination of thesource, significance and relevance oftest indications.5,6

inverse square law: Physical law for apoint source of energy. The quantityor strength is inversely proportional tothe square of the distance from theorigin.

iris: Ring of variable area around thepupil and in front of the lens of theeye. The surface area of the iris adjustsspontaneously to change the amountof light entering the eye.3

irradiance: Radiant power falling upon aknown surface area at a given angle.In nondestructive testing, the unit forirradiance of a UV-A source ismicrowatt per centimeter squared(μW·cm–2) and maximum irradianceoccurs when the source and surfaceare perpendicular. See also radiometer.

J

jaeger eye chart: Eye chart used for nearvision acuity examinations.3

K

keeper: Ferromagnetic material placedacross the pole faces of a permanenthorseshoe magnet to reduce thereluctance of the gap and to preventloss of magnetism.

ketos ring: See test ring.kinematic viscosity: Ratio of absolute

viscosity divided by the liquid’sdensity. Kinematic viscosity is oftenreported in centistokes.



L

L·D–1 ratio: Convenient means forexpressing the shape of a test object interms of length L divided by diameterD. In magnetic particle testing, ratioused to judge whether a test object isappropriate for coil magnetization ordemagnetization alone or whetherpole extensions or stacking is required.See also self-demagnetizing factor.

lambert cosine law: See cosine law.laminated pole pieces: See articulated pole

pieces.leach: See leech.leaked visible light: Unwanted

electromagnetic radiation that has awavelength between 400 and 800 nmthat is generated by the UV-A sourcebut not filtered out of the emissionspectrum. Leaked visible light isgenerally perceived as purple or darkblue light and will not be accuratelymeasured using a photometric sensor.See also light contamination, photometer,radiometer, UV-A, UV-A filter and visiblelight.

leakage field: See flux leakage field.leech: Permanent magnetic or

electromagnetic accessory used toensure adequate electrical contactduring current flow magnetization.Sometimes spelled leach.

lifting power: In magnetic particletesting, the mass of a ferromagneticbar that a yoke can suspend throughattraction. Often this mass is providedas a minimum that the yoke mustmeet or exceed.

light: Electromagnetic radiation that fallswithin the human eye’s responserange. See also photopic vision.

light contamination: Unwanted visiblelight present in darkened test area.Sources may include gaps in curtains,leaked visible light from the UV-Asource or fluorescence from theinspector’s clothing.

light meter: See photometer. Compareradiometer.

limited certification: Individuals certifiedonly for specific operations; usuallycalled limited Level (I, II or III) ordesignated as having limitedcertification because they are notqualified to perform the full range ofactivities expected of personnel at thatlevel of qualification.3

lines of force: See flux.longitudinal magnetic field: Active or

residual magnetization oriented alongthe longest axis of the part. See alsolongitudinal magnetization and magneticflow technique.

longitudinal magnetization: Result ofmagnetic flow technique whereinduced flux lines flow between thepoles of an electromagnet or pair ofpermanent magnets.

lumen (lm): SI photometric unit ofluminous flux, weighted according tothe photopic vision response. Onelumen equals the light emitted by onecandela (cd) point source into onesteradian (sr) solid angle(1 lm=1cd·sr–1).

luminance: Photometric brightness of alight source as defined by the densityof its luminous intensity. Luminanceis a measure of the luminous flux perunit solid angle per unit area in agiven direction and is reported incandela per square meter (cd·m–2).

luminous intensity: Measure of a lightsource’s power output per unit solidangle emitted or reflected from apoint, when weighted by the photopicspectral luminous efficiency responsecurve. Luminous intensity is measuredin candela. Compare luminance.

lux (lx): SI unit of illuminance, equal toone lumen per square meter(1 lx=1 lm·m–2).

M

magnetic circuit: Path followed by fluxlines that may include the test object,any air gaps and an electromagnetic orpermanent magnet yoke.

magnetic field: Energy vector fieldsurrounding a magnet or electriccircuit.

magnetic field indicator: See pocket fieldindicator.

magnetic field intensity (H): Magnitudeof the vector field surrounding amagnetic dipole,9 in ampere per meter.Sometimes called magnetic fieldstrength.

magnetic flow technique: Longitudinalmagnetization technique where atleast part of the test object completes amagnetic circuit. See also longitudinalmagnetization and yoke.

magnetic flux: See flux lines.magnetic flux density (B): Amount of

magnetic induction passingperpendicularly through a given area,measured in tesla.

magnetic flux leakage testing:Nondestructive test technique whereinduced magnetism in a ferromagneticsample forms localized poles atsurface. Near-surface discontinuitiesare indicated by a signal in aninduction coil or hall element; if theyare indicated by magnetic particles,the technique is called magnetic particletesting.



magnetic gradient: Change in magneticfield intensity (A·m–2).

magnetic particle testing:Nondestructive test technique whereinduced magnetism in a ferromagneticsample forms localized poles at surfaceand near-surface discontinuitiesindicated by a finely divided ironbased powder. Compare magnetic fluxleakage testing.

magnetic particles: Finely dividedferromagnetic powder of proper size,shape, relative permeability, visibilityand retentivity for use in a test.

magnetic pole: One of two opposite endsof a dipole where flux enters or leavesa magnetized object. Any locationwhere flux enters or leaves the testobject.

magnetic rubber: Replica casting mediumcontaining magnetic particles, whichwhen cured and removed from aproperly magnetized recess, provides apermanent mold with visibleindications.

magnetic saturation: Result of completedomain alignment where an increasein the coercive field H produces nochange in flux density B.

magnetic stripe card: In magneticparticle testing, a credit card sizeddevice with encoded magneticreversals of varying strength forregular evaluation of bath sensitivity.See also particle concentration. Comparesettling test.

magnetic writing: Nonrelevantindication that may be caused whentwo magnetized objects come intocontact.

magnetization: (1) Induced dipolemoment per unit volume of a solid.(2) Act of inducing a magnetic field ina ferromagnetic object.

magnetizing force: Magnetomotive forceper unit length of a magnetic circuit.Measured in ampere turns per meter(At·m–1).

magnetomotive force: Magnetic fieldintensity, measured in air or vacuumin ampere turns.

magnetometer: See pocket field indicator.magnitude: Absolute value of a complex

quantity (number) without referenceto the phase of the quantity.4

material safety data sheet (MSDS):Document that contains informationon safety and health in storage,handling, use, cleanup and disposal ofsubstances. Manufacturers of testingmaterials are required to providematerial safety data sheets to users inaccordance with the OSHA HazardCommunication Standard.

Maxwell’s equations: Fundamentalequations of electromagnetic fieldtheory:

(3)

(4)

(5)

(6)

where B is magnetic flux density,D is electric flux density, E is electricfield intensity, H is magnetic fieldintensity, J is current density, t is time,ρ isvolume charge density and � is thedel operator.4

mesopic vision: Intermediate state ofdark adaptation where retinal conesand rods work together in semidarkconditions. This state would beexpected in typical fluorescentnondestructive evaluationapplications. See also photopic visionand scotopic vision.

MIG welding: See gas metal arc welding.model, analytical: Mathematical

representation of a process orphenomenon.4

multidirectional magnetization: Two ormore magnetic fields in differentdirections imposed on a test objectsequentially and in rapid successionthrough phase control of the suppliedcurrent. See also phase and swingingfield magnetization.

myopia: See nearsightedness.

N

NDE: (1) Nondestructive examination.(2) Nondestructive evaluation. Seenondestructive testing.

NDI: Nondestructive inspection. Seenondestructive testing.

NDT: See nondestructive testing.nearsightedness: Vision acuity

functionally adequate for viewingobjects nearby, generally within anarm’s length. Also called myopia.3Compare farsightedness.

near-surface discontinuity: Subsurfaceinterruption in the physical structureor configuration of a test object that isclose to, but not breaking, the testobject’s surface. (This sense of nearsurface differs from that in methodsthat distinguish a test object’s nearsurface from its far surface, adistinction rarely made in magneticparticle testing.)

noise: Component of physical quantity,such as voltage, that providesnonrelevant information. Comparesignal.

=∇ ⋅ D ρ

= 0∇ ⋅ B

∇ × ∂∂

+HD

J=t

∇ × − ∂∂

EB

=t



nondestructive testing (NDT):Determination of the physicalcondition of an object withoutaffecting that object’s ability to fulfillits intended function. Nondestructivetest methods typically use anappropriate form of energy todetermine material properties or toindicate the presence of materialdiscontinuities (surface, internal orconcealed).5,6 Sometimes callednondestructive evaluation, nondestructiveexamination or nondestructive inspection.

nonferromagnetic material: Material notmagnetizable and essentially notaffected by magnetic fields.4

nonrelevant indication: Test responsecaused by sample geometry or by aphysical condition that is not adiscontinuity.

numerical analysis: Technique togenerate numbers as the solution to amathematical model of a physicalsystem; used in place of a closed formanalytic expression; usually requiresdigital computation.4

O

oersted (Oe): Obsolete CGS measurementunit of magnetizing force, or magneticfield intensity. Replaced in SI byampere per meter, or ampere turns permeter: 1Oe= 79.57747 A·m–1.

ohm (Ω ): Measurement unit of electricalresistance.4

oil country tubular goods (OCTGs):Hollow cylindrical components, suchas pipes, used to convey petroleumand related products.4

P

parallel magnetization: Dubious practiceof imparting circular magnetization ina sample near a current carryingconductor. Compare internal conductor.

paramagnetic material: Inelectromagnetic testing, a materialthat has a relative permeability slightlygreater than unity and is practicallyindependent of the magnetizingforce.4

particle concentration: Amount ofpowder suspended within a knownsample volume of bath. Typicallymeasured using a settling test, orthrough evaporation and weighing.See also centrifuge tube.

percent International Annealed CopperStandard (%IACS): Traditionalmeasurement of conductivity σ as apercentage of the conductivity of purecopper, arbitrarily rated at100percent.4 In SI, conductivity ismeasured in siemens per meter(S·m–1). See also conductivity;International Annealed Copper Standard.

period: Absolute value of the minimuminterval after which the samecharacteristics of a periodic waveformor a periodic feature repeat.4

permanent magnet: Material with highretentivity, which maintainsmagnetization after a coercive fieldhas been removed. In magneticparticle testing, permanent magnetyokes must also have a high coercivity.

permeability (µ): (1) Ability of a materialto be magnetized, measured asincrease in flux density. (2) Ratio ofmagnetic induction B overmagnetizing force H. Absolutepermeability in SI units is measured inhenries per meter (H·m–1). See alsorelative permeability and permeability offree space.

permeability of free space (µ0):Calculation constant describing theratio of magnetic induction B tomagnetizing force H within a vacuum.1 μ0 = 4 × 10–7 H·m–1. See alsopermeability and relative permeability.

pH: A measure of the acidity or alkalinityof a solution. Negative of log C, whereC is the concentration of hydrogenions. Values lower than 7.0 are acidic;values equal to 7.0 are neutral; valueshigher than 7.0 are alkaline.

phase: (1) A circuit conductor carryingalternating current of a givenfrequency, as in one-phase orthree-phase power. (2) Point on a360-degree harmonic power waveform(thyristors, for example, vary totalpower output through phase control).

photochromic lens: Eyeglass materialthat automatically darkens to reducelight transmission when exposed toultraviolet radiation.

photometer: Device used to measureilluminance. The sensor is filteredsuch that its response closely matchesthe spectral responsivity curve of thehuman eye. In nondestructive testing,photometers measure lux. Compareradiometer.

photometry: Study and measurement ofelectromagnetic radiation withwavelengths between 400 and 800nm,within the human eye’s spectralresponsivity. See also photometer andphotopic vision. Compare radiometry.



photopic vision: Average spectralresponsivity curve of the human eyewhen adapted to well lit conditions(greater than 0.034 cd·m–2). Thephotopic spectral luminous efficiencyresponse curve is governed by anaveraged retinal cone response withsensitivity peaks centered at about555nm.

pie gage: One type of shared fluxindicator in the form of a handlemounted disk comprised offerromagnetic wedges surrounded by acopper matrix. When properlydemagnetized before use the spacebetween wedges provides artificialdiscontinuities at 0, 45 and 90 degreesand provides a measure of magneticflux direction during dry powdertesting.

pocket field indicator: Small, hand helddevice used to display the intensity ofuniform external magnetic flux asangular deflection of a display needle.The device contains a permanentreference magnet coupled to amovable, field sensing magnet, andsome units may be calibrated.

pole: See magnetic pole.powder blower: Compressed air device

used to deliver a cloud of drymagnetic particles to the surface of atest object.

powder bulb: Container compressed byhand to deliver a cloud of drymagnetic particles to the surface of atest object.

practical examination: In certification ofnondestructive testing personnel, ahands-on examination using testequipment and sample test objects.3Compare general examination andspecific examination.

probability of detection (PoD): Statisticalanalysis of a specific test procedureindicating how likely a givendiscontinuity length may be reliablyfound.

probe: See transducer.prod magnetization: See current flow

technique.prods: Handheld electrodes for

transmitting magnetizing current froma portable power source to the testobject. See also leech.

pseudoisochromatic plates: Testingdevice used for color visionexaminations. Each plate bears animage that would be difficult for theexaminee to see if their color visionwas impaired.3

pulse magnetization: See capacitordischarge technique.

pupil: Aperture in the center of an eye’siris, through which light focused bythe lens passes.3

Q

qualification: Process of demonstratingthat an individual has the requiredamount and the required type oftraining, experience, knowledge andabilities.5,6 See also certification andqualified.

qualified: Having demonstrated therequired amount and the requiredtype of training, experience,knowledge and abilities.5,6 See alsocertified and qualification.

quality: Ability of a process or product tomeet specifications or to meet theexpectations of its users in terms ofefficiency, appearance, reliability andergonomics.5,6

quality assurance: Administrative actionsthat specify, enforce and verifyquality.5,6

quality control: Physical andadministrative actions required toensure compliance with a qualityassurance program. Quality controlmay include nondestructive testing inthe manufacturing cycle.5,6

quantitative quality indicator (QQI):Shim that has an artificialdiscontinuity and is held in intimatecontact with a test object’s surfaceduring active magnetization toindicate that proper magnitude anddirection of magnetic induction havebeen obtained for testing. The artificialdiscontinuity may be circular or linearand is defined in terms of percent oftotal shim thickness.

quick break: Sudden cessation ofmagnetizing current. A quick break isneeded when using three-phasefull-wave rectified alternating currentduring coil or induced currentmagnetization. The rapid change incurrent produces strong magneticinduction during toroidalmagnetization and reduces thedisturbing flux near poles for sensitivetesting of the test object’s ends in coilmagnetization.

R

radial: Of or pertaining to direction fromcenter of a sphere or cross section of acylindrical object to its surface, andperpendicular to its axis. Compareaxial and tangential.

radiometer: Device used to measureirradiance. In nondestructive testing,radiometers are used to measure UV-Aoutput, or leaked visible light, inmicrowatt per square centimeter(μW·cm–2). See also irradiance.Compare photometer.



radiometry: Study and measurement ofelectromagnetic radiation emitted by asource or falling upon a surface.

recommended practice: Set of guidelinesor recommendations.4

Recommended Practice No. SNT-TC-1A:Set of guidelines published by theAmerican Society for NondestructiveTesting, for employers to establish andconduct a nondestructive testingpersonnel qualification andcertification program.4

recommended practice: Set of guidelinesor recommendations.5,6

Recommended Practice No. SNT-TC-1A:Set of guidelines published by theAmerican Society for NondestructiveTesting, for employers to establish andconduct a qualification andcertification program fornondestructive testing personnel.5,6

rectified alternating current: Seehalf-wave current and full-wave current.

reference standard: (1) Test objectcontaining known discontinuitiesrepresenting accept or reject criteria.(2) Sample test object selected forreference.5

relative permeability (µr): Unitless ratioof a material’s permeability to thepermeability of free space.

relevant indication: In nondestructivetesting, an indication from adiscontinuity or condition andrequiring evaluation.5

reluctance: Resistance of a material tochanges in magnetization. Reciprocalof permeability.

rejection level: Value established for atest signal above or below which testobjects are rejectable or otherwisedistinguished from the remainingobjects. This level is different from therejection level as defined for ultrasonicand other test systems.4

remanent magnetism: See residualmagnetic field.

residual magnetic field: Magnetizationremaining in a ferromagnetic materialafter magnetizing force H is reduced tozero.

residual technique: Testing procedureused only with highly retentivematerials where a remnant magneticfield is relied on to attract magneticparticles. Compare continuoustechnique.

resistance, electrical (R): Opposition toflow of electric current throughmaterial; ratio of voltage to current.Measured in ohms (Ω). Inverselyrelated to conductance:

(7)

where A is the conductor’s crosssectional area (square meter), G isconductance (siemens), L is the lengthof the conductor (meter) and ρ isresistivity (ohm meter).4

resistivity (ρ): Ability of material to resistelectric current. Measured in ohmmeter (Ω·m), which is the resistance ofa cube made of the material whosedimensions are 1 m on each side.Inversely related to conductivity σ(siemens per meter):4

(8)

resolution: An aspect of image qualitypertaining to a system’s ability toreproduce objects, often measured byresolving a pair of adjacent objects orparallel lines.6

retentivity: Material’s ability to maintainremnant magnetism in the absence ofa coercive field.

retina: Rear portion of the eyeball,opposite the pupil, where lightsensitive rods and cones are present.

right hand rule: Technique for visualizingthe relationship between a flowingcurrent and its induced magnetic field.When the right hand is closed in a fistwith the thumb extended and whencurrent flows out along the thumb,the fingers represent the self-inducedmagnetic field.

rise time: Amount of time for a currentsource to reach its set point.

rod cells: Low light photoreceptorsconcentrated toward the outer regionof the retina. Rods assist with mesopicvision and are responsible for scotopicnight vision. Compare cone cells.

root mean square (rms): Statisticalmeasure of the magnitude of a varyingquantity, such as current. Square rootof the mean square of a set ofmeasures, usually a time series.

ρσ

= 1

RG

LA

= =1 ρ



S

saturation: See magnetic saturation.scalar: Quantity completely specified by a

single number and unit.4scotopic vision: Average spectral

responsivity curve of the human eyewhen adapted to very dark conditions(less than 3 × 10–5 cd·m–2).Illumination levels for scotopic visionare below the sensitivity of retinalcones, so no color perception ispossible.

self-demagnetizing factor: Estimate ofthe resistance of a test object tomagnetization due to the proximity ofmagnetic poles of opposite polarity.For coil magnetization, the internalmagnetization within a low L·D–1 ratiotest object is opposite of the coil’smagnetic field and a lower distancebetween poles results in a greaterinternal resistance.

self-inductance: Ratio of magnetic fluxformed around a conductor to theamount of current passing through astraight or coiled conductor.Self-inductance is measured in henries,where one henry equals one weber perampere (1 H = 1 Wb·A–1). See alsoinductance.

sensitivity: See probability of detection.sensor: Device that detects a material

property or mechanical behavior (suchas radiation or displacement) andconverts it to an electrical signal.Probe; transducer.5

settling test: One procedure used todetermine the concentration ofmagnetic particles in a new bath or tocheck for contamination or other bathproblems. See also centrifuge tube andparticle concentration. Comparemagnetic stripe card.

shared flux indicator: Device held inintimate contact with test objectduring active magnetization to showthe direction of magnetic induction.Examples include the bertholdpenetrameter, magnetic flux indicatorstrip and pie gage.

shielded metal arc welding: Metaljoining process that uses a consumableflux coated electrode. The flux bothcovers the molten weld pool andforms the protective shielding gas.Also called stick welding. Compare gasmetal arc welding and tungsten metal arcwelding.

shim: Indicator of magnetic fieldorientation, consisting of thin foil ofhigh permeability material havingartificial notch discontinuities.

shot: In magnetic particle testing, theperiod of time when current is flowingthrough the test object. Shot durationand the number of shots required fortesting may be varied. See also currentflow technique.

SI (International System of Units):Measurement system in which thefollowing seven units are basic: meter,mole, kilogram, second, ampere,kelvin and candela.5,6

siemens per meter (S·m–1): SI unit ofconductivity.

signal: Physical quantity, such as voltage,that contains relevant information.4

signal-to-noise ratio: Ratio of signalvalues (responses that contain relevantinformation) to baseline noise values(responses that contain nonrelevantinformation).4

silicon controlled rectifier: Solid stateelectronic component used to varypower output in an arcless manner.The power waveform from a siliconcontrolled rectifier will contain spikesand conversion between peak, rootmean square and average is notstraightforward across the outputrange.

skin depth: In electromagnetic testing,the depth at which the magnetic fieldintensity or intensity of induced eddycurrents has decreased to 37 percent ofits surface value. The square of thedepth of penetration is inverselyproportional to the frequency of thesignal, the conductivity of the materialand the permeability of the material.4See also skin effect.

skin effect: Term used to describe thepenetration ability of cyclical currentor magnetization as a function offrequency, conductivity and relativepermeability. In magnetic particletesting, skin effect refers to alternatingcurrent’s inability to penetrate deeperthan 1 to 3 mm (0.04 to 0.12 in.) withtypical testing variables.10 See also skindepth.

slurry: See bath.SNT-TC-1A: See Recommended Practice

No. SNT-TC-1A.specific examination: In certification of

nondestructive testing personnel, awritten examination that addresses thespecifications and products pertinentto the application.3 Compare generalexamination and practical examination.

specific gravity: Unitless ratio of thedensity of a material divided by thedensity of water. Water has a densityof about 1 g·cm–3, or 1000 kg·m–3.

specification: Set of instructions orstandards invoked to govern theresults or performance of a specific setof tasks or products.5,6



spectral irradiance: Measure of energyemitted by a radiation source asfunction of wavelength. Units ofspectral irradiance are in watts permeter squared and are often plottedversus wavelength.

spectral luminous efficiency: See spectralresponsivity.

spectral responsivity: Measure of aphotometric or radiometric sensor’ssensitivity over a wavelength range ofinterest, often presented as percentversus wavelength. Photometricsensors should exhibit a bell shapedspectral responsivity curve over thevisible light range, whereasradiometric sensors may exhibit a flator other response curve.

standard: (1) Reference object used as abasis for comparison or calibration.(2)Concept established by authority,custom or agreement to serve as amodel or rule in the measurement ofquantity or the establishment of apractice or procedure.5,11

standard depth of penetration: See skindepth.

standardization, instrument: Adjustmentof instrument readout before use to aspecified reference value.4

stick welding: See shielded metal arcwelding.

stress concentration: Region where forceper unit area is elevated, often becauseof geometric factors or cracks. Alsoknown as a stress raiser.

stringer: In wrought materials, anelongated configuration ofmicroconstituents or foreign materialaligned in the direction of working.Commonly, the term is associatedwith elongated oxide or sulfideinclusions in steel.3

subsurface discontinuity: Discontinuitynot open to the surface. See alsonear-surface discontinuity.

susceptibility: Dimensionless propertydescribing a material’s response to anexternal magnetic field.

suspension: See bath.suspension vehicle: See carrier fluid.swinging field magnetization: One form

of multidirectional magnetizationwhere two time varying magneticfields are combined such that theresultant vector magnetization rapidlyrotates through an angle. See alsomultidirectional magnetization.

T

tangential: Of or pertaining to a directionimpinging on a curved surface of anobject and perpendicular to the radiusat the point where it impinges.Compare axial and radial.

tesla (T): SI derived unit of measure formagnetic flux density. 1T=1Wb·m–2 =104 G.

tesla meter: Magnetometer used tomeasure active or residual magneticinduction in the location anddirection of interest. See also fluxmeter, hall effect.

test object: Hollow, ring shapedspecimen, typically made of 01 toolsteel, containing artificial subsurfacedrilled through-hole discontinuities.The ring is used to compare the dailyperformance of a wet horizontal testunit or to evaluate the sensitivity ofdry powders when magnetized usingthree-phase full-wave rectified current.

test object: Physical part or specimensubject to nondestructive testing.

threshold level: Setting of an instrumentthat causes it to register only thosechanges in response greater or lessthan a specified magnitude.4

thyristor: See silicon controlled rectifier.TIG welding: See gas tungsten arc welding.toroidal magnetization: See induced

current magnetization.transducer: Device by means of which

energy can flow from one or moretransmission systems or media to oneor more other transmission systems ormedia; sensor or probe.4

tubing string: Pipe with which oil or gashas contact as it is brought to theearth’s surface.4

U

ultraviolet radiation: Electromagneticradiation with wavelengths between100 and 400 nm. See also irradianceand UV-A. Fluorescent nondestructivetesting uses UV-A and safe exposurelimits for ultraviolet radiation andblue light hazard are available throughthe American Conference ofGovernmental Industrial Hygienists.

ultraviolet source: Term for the deviceproviding excitation energy forfluorescent materials. See UV-Aradiation source.

Unified Numbering System:Alphanumeric system for identifyingalloys according to a registrymaintained by ASTM Internationaland SAE International.4



UV-A: Electromagnetic radiation withwavelengths between 315 and 400nm.Fluorescent nondestructive testing hashistorically used ultraviolet energycentered at 365 nm. See also irradianceand radiometer.

UV-A filter: Device that is used to modifythe emission spectrum from aradiation source to eliminate visiblelight and higher energy ultravioletenergy, while allowing the desiredlong wavelength ultraviolet radiationto pass through.

UV-A radiation source: Preferred term forthe device providing excitation energyfor fluorescent materials.

V

vector quantity: Any physical quantitywhose specification involves bothmagnitude and direction and thatobeys the parallelogram law ofaddition.4

viscosity: Measure of the resistance ofliquid to deform under shear stress.See also kinematic viscosity.

visible light: Radiant energy with awavelength between 400 and 800 nmas measured in photometric units oflux.

visible particle: Common term describingfinely divided powder for use innonfluorescent magnetic particle tests.The particles may be their naturalcolor or may be coated to enhancecontrast. Testing using visible particlesis performed under a controlled levelof ambient lighting and typically doesnot need any ultraviolet light.

vision acuity: Quantitative measure ofthe acuteness of vision.

visual efficiency: Reliability of a visualsystem. The term visual efficiency uses20/20 near vision acuity as a baselinein the United States for 100 percentvisual efficiency.3

visual field: Locus of objects or points inspace that can be perceived when headand eyes are kept fixed. The field maybe monocular or binocular.3

visual perception: Interpretation ofimpressions transmitted from theretina to the brain in terms ofinformation about a physical worlddisplayed before the eye. Visualperception involves any one or moreof the following: recognition of thepresence of something (object,aperture or medium); identifying it;locating it in space; noting its relationto other things; identifying itsmovement, color, brightness or form.3

visual performance: Quantitativeassessment of the performance of avisual test, taking into considerationspeed and accuracy.3

visual task: Appearance and immediatebackground of those details andobjects that must be seen for theperformance of a given activity. Theterm visual task is a misnomer becauseit refers to the visual display itself andnot the task of extracting informationfrom it.3

volt (V): Measurement unit of electricpotential.4

W

water, break free: Rinse water, having theability to cover an entire surface in anunbroken film.3

wavelength: Distance between repeatingunits of a wave. For example, thedistance from one peak to the nextpeak.

wet horizontal unit: Stationaryequipment that provides a measuredamount of electric current to aheadstock and tailstock, allows bathapplication and may be equipped witha rigid multiple-turn magnetizing coil.

wet technique: Testing procedure inwhich the suspended magneticparticles are applied as a well agitatedbath.

wetting action: Action of liquid inspontaneously spreading over andadhering to solid surfaces.3

white light: Light combining allfrequencies in the visible spectrumand in equal proportions.3

working standard: Work piece or energysource calibrated and used in place ofexpensive reference standards. Incalibrating of photometers, thestandard would be a light source.3

Y

yoke: Portable U shaped electromagnet orpermanent magnet that induceslongitudinal magnetization in theregion of the test object between itsmagnetic poles. See also articulated polepieces and magnetic flow technique.




PART 2. Symbols

TABLE 1. Symbols and units used in electromagnetics.

Symbol Property SI Unit SI Symbol

A magnetic vector potential weber per meter Wb·m–1

Ax, Ay, Az, AR, Ar, Aθ, Aφ components of vectorAt (unit) ampere turn AtB magnetic flux density tesla TD electric flux density coulomb per square meter C·m–2

ds differential area (vector) square meter m2

d�� differential length (vector) meter mE electric field intensity volt per meter V·m–1

F force newton Nf frequency cycles per second HzG conductance siemens SH magnetic field intensity ampere per meter A·m–1

I (electric) current ampere AJ current density ampere per square meter A·m–2

Js surface current density ampere per square meter A·m–2

L inductance henry H� length, distance meter mM magnetization ampere per meter A·m–1

m magnetic moment ampere per meter A·m–2

n normal (component of vector)n, Q, R, r, x, y, z, θ, φ unit vectors meter mP power watt WPd dissipated power watt WP poynting vector watt per cubic meter W·m–3

q electric charge coulomb CR resistance ohm ΩR position vector meter mS area square meter m2

t time second sV (electric) potential, voltage volt VVm electromotive force ampere turn Atv velocity, speed meter per second m·s–1

W work joule Jw energy density joule per cubic meter J·m–3

We electric stored energy joule JWm magnetic stored energy joule Jδ skin depth meter m�, �0, �r (electric) permittivity farad per meter F·m–1

Λ flux linkageµ, µ0, µr (magnetic) permeability henry per meter H·m–1

ρ resistivity ohm meter Ω·mρ charge density coulomb per square meter C·m–2

ρs surface charge density coulomb per square meter C·m–2

σ conductivity siemens per meter S·m–1

τ tangential component of vectorΧ [chi] magnetic susceptibilityω angular frequency radian per second rad·s–1


Tables 1 and 2 list physical quantities forelectromagnetics.

By convention, symbols for constantsand variables from the Roman alphabetare printed in italic; vectors representingfour-dimensional information are printedin bold. Measurement units are covered inthe introduction to this volume.

For physical quantities and propertiesin materials science, the reader is servedby reference books such as the CRCHandbook of Chemistry and Physics12 andLeonard Mordfin’s Handbook of ReferenceData for Nondestructive Testing.13

Measurement units and their symbolsare covered in the introduction to thisvolume.


TABLE 2. Physical constants for electromagnetism.

Symbol Property Value

�0 permittivity of free space 8.8542 × 10–12 F·m–1

µ0 permeability of free space 4π × 10–7 H·m–1

e charge on one electron –1.602 × 10–19 Cc speed of light (vacuum) 2.99792 × 108 m·s–1


1. ASTM E 1316, Standard Terminology forNondestructive Examinations. WestConshohocken, PA: ASTMInternational (2007).

2. Nondestructive Testing Handbook, thirdedition: Vol. 6, Magnetic ParticleTesting. Columbus, OH: AmericanSociety for Nondestructive Testing(1989).

3. Nondestructive Testing Handbook, thirdedition: Vol. 2, Liquid Penetrant Testing.Columbus, OH: American Society forNondestructive Testing (1999).

4. Nondestructive Testing Handbook, thirdedition: Vol. 5, Electromagnetic Testing.Columbus, OH: American Society forNondestructive Testing (2004).

5. Nondestructive Testing Handbook, thirdedition: Vol. 7, Ultrasonic Testing.Columbus, OH: American Society forNondestructive Testing (2007).

6. Nondestructive Testing Handbook,second edition: Vol. 10, NondestructiveTesting Overview. Columbus, OH:American Society for NondestructiveTesting (1996).

7. Shull, P. Nondestructive Evaluation:Theory, Techniques, and Applications.New York, NY: Marcel Dekker (2002).

8. Betz, C.E. Principles of Magnetic ParticleTesting. Chicago, Illinois:Magnaflux (1967).

9. Jiles, D. Introduction to Magnetism andMagnetic Materials. New York, NY:Chapman & Hall (1998).

10. Lovejoy, D. Magnetic Particle Inspection:A Practical Guide. New York, NY:Chapman & Hall (1993).

11. TO33B-1-1 (NAVAIR 01-1A-16)TM43-0103, Nondestructive TestingMethods. Washington, DC: UnitedStates Department of Defense, UnitedStates Air Force (June 1984): p 1.25.

12. CRC Handbook of Chemistry andPhysics, 89th edition. Baton Rouge, LA:CRC Press (2007).

13. Mordfin, L., ed. Handbook of ReferenceData for Nondestructive Testing.WestConshohocken, PA:ASTMInternational (2002).


References

3


3MTGL_375_394.qxd 10/03/2008 1:40 PM Page 396


3MT - asnt.org

Documents

Transcript of 3MT - asnt.org