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SECTION
NONDESTRUCTIVE TESTING
GLOSSARY
14
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Introduction
Most of the definitions in this glossary are adapted from
the text of Volumes 1 through 9 of the second edition Nondestructive Testing Handbook.1-9 The definitions in this
glossary have been modified to satisfy peer review and editorial style. For this reason, references given in this glossary
should be considered not attributions but rather acknowledgments and suggestions for further reading.
The definitions in this Nondestructive Testing Handbook
volume should not be referenced for inspections performed
according to standards or specifications or in fulfillment of
contracts. Standards writing bodies take great pains to
ensure that their documents are definitive in wording and
technical accuracy. People working to written contracts or
procedures should consult definitions referenced in real
standards when appropriate.
This glossary is provided for instructional purposes. No
other use is intended.
A
A-scan display: A display in which the received signal
amplitude is shown as a vertical excursion from the horizontal sweep time trace. The horizontal distance
between any two signals represents the material distance between the two conditions causing the signals.10
In a linear system, the vertical excursion is proportional
to the amplitude of the signal.7
absolute coil: A coil of electrically conductive wire that
responds to the electromagnetic properties of that region
of the test object that is within the magnetic field of the
coil, without comparison to the response of a second coil
at a different location on the same or similar material.4
absolute measurement: Measurement made with an
absolute coil.4
absolute pressure: Pressure above absolute zero value, or
pressure above that of empty space. Equal to sum of
local atmospheric pressure and gage atmosphere.1
absolute temperature: Temperature measured from absolute zero temperature, expressed in Kelvin (K) in SI.1
absorbed dose: The amount of energy imparted to matter
by an ionizing particle per unit mass of irradiated material at the place of interest. Absorbed dose is expressed
in Gray (Gy) or rads.11
absorption coefficient, linear: The fractional decrease in
transmitted intensity per unit of absorber thickness. It
is usually designated by the symbol µ and expressed in
units of cm–1.7,12
acceptable quality level (AQL): The maximum percent
defective (or the maximum number of units with
rejectable anomalies per hundred units) that, for the
purposes of sampling tests, can be considered satisfactory as a process average.8
acceptance criteria: The standard against which test
results are to be compared for purposes of establishing
the functional acceptability of a part or system being
examined.
acceptance level: A test level above or below which test
objects are acceptable in contrast to rejection level.4,13
acceptance standard: A specimen similar to the test
object containing natural or artificial discontinuities
that are well defined and similar in size or extent to the
maximum acceptable in the product. See reference
standard and standard.4,6,7
accommodation: Of the eye, adjustment of the lens’ focusing power by changing the thickness and curvature of
the lens by the action of tiny muscles attached to the
lens.8
accumulation test technique: Detecting the total amount
of leakage by enclosing the component under test
within a hood, bag, box, shroud or container. For pressure testing, any gas leaking from the component accumulates in the space (volume) between the component
and the enclosure. For vacuum testing, any gas leaking
into the component accumulates in the leak detector
sampling the evacuated component. Accumulation of
tracer gas in a measured time period provides a measure of the leakage rate.1
accuracy: The degree of conformity of a measurement to a
standard or true value.1
acoustic emission: The transient elastic waves resulting
from local internal micro displacements in a material.
The term also describes the technical discipline and
measurement technique relating to this phenomenon.5
acoustic emission activity: The number of bursts (or
events, if the appropriate conditions are fulfilled)
detected during an acoustic emission test.5
acoustic emission count: The number of times the signal
amplitude exceeds the preset reference threshold.5
acoustic emission event: A microstructural displacement
that produces elastic waves in a material under load or
stress.5
acoustic emission rate: The number of times the amplitude has exceeded the threshold in a specified unit of
time.5
acoustic emission testing (AE): Nondestructive test
method that uses acoustic emission.
acoustic impedance: A material property defined as the
product of sound velocity and density of the material.7,12
acoustic microscopy: High resolution, high frequency ultrasonic techniques used to produce images of features
beneath the surface of a test object.7
acuity: See neural acuity, vision acuity.
adaptive thresholding: Threshold value varying with inconstant background gray level.8
adhesive wear: See wear, adhesive.
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AE: Acoustic emission testing.
age hardening: A process of aging that increases hardness
and strength, but that ordinarily decreases ductility.
Also known as precipitation hardening.3
agency: The organization selected by an authority to perform nondestructive testing, as required by a specification or purchase order.2
air dried: Drying of any item such as a core or mold without application of heat.3
air injection machine: A die casting machine in which air
pressure acts directly on the surface of molten metal in a
closed pot (gooseneck) and forces the metal into a die.3
air flow: In leak testing, the flow of air from the probe inlet
to the sensitive element of the halogen leak detector that
carries the tracer gas from the leak to the sensing diode.1
algorithm: A prescribed set of well defined rules or processes for the solution of a mathematical problem in a
finite number of steps.4,14
alkali ion diode: A sensor for halogen gases. In this device,
positive ions (cations) of an alkali metal are produced on
the heated surfaces (usually platinum) of the diode. One
electrode is at a negative potential and attracts cations
that are released when a halogen gas passes between the
sensor electrodes. Provides an output current to operate
the indicator on the halogen leak detector.1
alpha ferrite: The form of pure iron that has a body centered cubic structure stable below 910 °C (1,670 °F).
Also called alpha iron.8
alpha particle: A positively charged particle emitted by
certain radioactive materials. It is made up of two neutrons and two protons; hence it is identical with the
nucleus of a helium atom.11
alternating current: An electrical current that reverses its
direction of flow at regular intervals.6
alternating current field: The varying magnetic field produced around a conductor by an alternating current
flowing in the conductor.6
alternating current magnetization: Magnetization by a
magnetic field that is generated when alternating current is flowing.6,15
ambient light: Light in the environment as opposed to illumination provided by a visual testing system.8
ambient or atmospheric temperature: Temperature of
surrounding atmosphere. Also called dry bulb temperature.
ampere: A unit of electric current. Abbreviated A or amp.6
ampere per meter: The SI base unit for magnetic field
strength in air at the center of a single-turn circular coil
having a diameter of 1 m, through which a current of
1 A is flowing. Abbreviated A·m–1 or A/m. 1 A·m–1 = 1.3
× 10–2 Oe (see oersted).6,15
ampere turns: The product of the number of turns of a coil
and the current in amperes flowing through the coil.6,16
amplitude distortion: See harmonic distortion.
amplitude response: That property of a test system
whereby the amplitude of the detected signal is measured without regard to phase. See also harmonic analyzer and phase analysis.4,13
amplitude, echo: The vertical height of a received signal on
an A-scan, measured from base to peak for video or peak
to peak for radio frequency presentation.7
analog-to-digital converter: A circuit whose input is
information in analog form and whose output is the
same information in digital form.4,14
angle: See field angle.
angle beam: An ultrasound beam traveling at an acute
angle into a medium. The angle of incidence or refraction after entry is measured from the normal to the
entry surface.7,12
angle of incidence: The included angle between the beam
axis of the incident wave and the normal to the surface
at the point of incidence.7,10
angle of reflection: The included angle between the beam
axis of the reflected wave and the normal to the reflecting surface at the point of reflection.7,10
angle of refraction: The angle between the beam axis of a
refracted wave and the normal to the refracting interface.7,10
angle testing: A method of ultrasonic testing in which
transmission of ultrasound is at an acute angle to the
entry surface. Usually called angle beam testing.7,10
angle transducer: A transducer that transmits or receives
ultrasonic energy at an acute angle to the surface. This
may be done to achieve special effects such as setting
up shear or surface waves by mode conversion at an
interface.7,10
angstrom: A unit of distance abbreviated Å and used to
express wavelengths of electromagnetic radiation. The SI
unit nanometer (nm) is now preferred; 1 nm = 10 Å.2,8
anisotropy: The characteristic of exhibiting different values
of a property (velocity, for example) in different directions in the material.2
annealing: Process of heating and cooling a material, usually to reduce residual stresses or to make it softer.2,3,8
annular coil clearance: The mean radial distance between
the inner diameter of an encircling coil assembly and
test object surface in electromagnetic examination. See
fill factor.4,13
anode: (1) In radiography, the positive electrode of an electron tube. (2) Negatively charged terminal, which may
corrode electrochemically during production of an
electric current. Compare cathode.8
anomaly: A variation from normal material or product
quality.4
antinode: A point in a standing wave where certain characteristics of the wave field have maximum amplitude.7,10
AOQ: Average outgoing quality.
AOQL: Average outgoing quality limit.
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AQL: See acceptable quality level.
arbor: A bar or mandrel on which a core is built.3
arc: A luminous high temperature discharge produced
when an electric current flows across a gaseous gap.6,15
arc strikes: Localized burn damage to an object from the arc
caused by breaking an energized electric circuit. Also
called arc burns.6,16
arc welding: See electric arc welding.
arcing: Current flow through a gap, often accompanied by
intense heat and light.6,17
Argand diagram: A graphical representation of a vector
used in complex notation.4,14
array: (1) A group of transducers used for source location.5
(2) An arrangement of sensors used for image building.
(3) A group of transducers arranged for beam shaping
or beam control.
array transducer: A transducer made up of several piezoelectric elements individually connected so that the signals they transmit or receive may be treated separately
or combined as desired.7
articulated pole pieces: On a magnetizing yoke, independently adjustable magnetic elements enabling the magnetization of irregular test object profiles.6
artifact: In nondestructive testing, an indication that may
be interpreted erroneously as a discontinuity.2
artificial discontinuity standard: See acceptance standard.
artificial discontinuity: Reference point, such as a hole,
groove or notch, that are introduced into a reference
standard to provide accurately reproducible sensitivity
levels for nondestructive test equipment.4,13 A manufactured material anomaly. See acceptance standard
and reference standard.6
artificial flaw standard: See acceptance standard.
artificial source: In acoustic emission, a point where elastic
waves are created to simulate an acoustic emission event.
The term also defines devices used to create the waves.5
ASNT: American Society for Nondestructive Testing.
ASNT Recommended Practice No. SNT-TC-1A: A set of
guidelines for employers to establish and conduct a
nondestructive testing personnel qualification and certification program. SNT-TC-1A was first issued in 1968
by the Society for Nondestructive Testing (SNT, now
ASNT) and has been revised every few years since.8
atmosphere: See standard atmospheric conditions.
atmospheric pressure: Ambient pressure caused by the
weight of the earth’s atmosphere. Because the weight of
the earth’s overlying atmosphere decreases with increase
in altitude, barometric pressure decreases at higher elevations above sea level. Also called barometric pressure.
At sea level, standard barometric pressure is taken as
101.325 kPa, equivalent to an absolute pressure of
14.696 lbf·in.–2. It is also equal to the pressure exerted by
a mercury column 760 mm (29.92 in.) high — that is,
equal to 760 mm Hg (29.92 in. Hg) or 760 torr.1
attenuation: (1) Decrease in energy or signal magnitude in
transmission from one point to another. Can be
expressed in decibels or as a scalar ratio of the input
magnitude to the output magnitude.4,14 (2) The loss in
acoustic energy that occurs between any two points of
travel. This loss may be caused by absorption, reflection, scattering or other material characteristics.10
(3) The change in signal strength caused by an electronic device such as an attenuator.7 (4) In radiography,
the decrease in exposure rate of radiation caused by
passage through material.11
attenuation coefficient: A factor which is determined by
the degree of diminution in sound wave energy per unit
distance traveled. Composed of two parts, one (absorption) proportional to frequency, the other (scattering)
dependent on the ratio of grain size or particle size to
wavelength.7,18
attenuator: A device for causing or measuring attenuation.
Usually calibrated in decibels.7,10
austenite: A solid solution with iron as the solvent in a face
centered cubic structure formed by slow cooling of
delta ferrite. Characteristic lattice structure is stable
between 906 °C (1,663 °F) and 1,390 °C (2,535 °F).
Also called gamma iron.8
automated system: Acting mechanism that performs
required tasks at a determined time and in a fixed
sequence in response to certain conditions.8
B
B-scan: A data presentation method typically applied to
pulse echo techniques. It produces a two-dimensional
view of a cross sectional plane through the test object.
The horizontal sweep is proportional to the distance
along the test object and the vertical sweep is proportional to depth, showing the front and back surfaces and
discontinuities between.7,12
back draft: A reverse taper on the pattern that prevents its
removal from the mold.3
back reflection: The signal received from the far boundary
or back surface of a test object.7,10
back scatter: See backscatter.
background: The surface of the test object on which the
indication is viewed in surface methods such as liquid
penetrant and magnetic particle testing. It may be the
natural surface of the object or the developer coating
on the object surface. This background may contain
irrelevant information that can interfere with the visibility of the indication.2,6,16
background contamination: Tracer gases that accumulate in the test area, making it difficult to keep a leak
detector zeroed. They may also be a health hazard.1
background cylinder and difference cylinder: Two
devices used to calculate illuminance by using the
equivalent sphere illumination technique.8,19
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background fluorescence: Fluorescent residues observed
over the general surface of the test object during fluorescent penetrant testing and fluorescent magnetic particle testing.2
background noise: The signals that originate from the test
object, the test instrument and their surroundings and
that interfere with test signals of interest. It has electrical and mechanical origins. Sometimes called grass or
hash.5,7,10
background signal: A steady or fluctuating output signal
of a test instrument caused by the presence of acoustic,
chemical, electrical or radiation conditions to which the
sensing element responds.1
backing board: A second bottom board where molds are
opened.3
backscatter: (1) In radiography, radiation scattered from
the floor, walls, equipment and other items in the area
of a radiation source.11 (2) In ultrasonic testing, scattered signals that are directed back to the
transmitter/receiver.7
baked core: A core that has been heated or baked until it is
thoroughly dry.3
baked permeability: The property of a molded mass of
sand heated at a temperature above 110 °C (230 °F)
until dry and cooled to room temperature to permit
passage of gasses.3
band pass filter: An electromagnetic frequency filter that
has a single transmission band between two cutoff frequencies, neither of the cutoff frequencies being zero
or infinity.4,14
bandwidth: The difference between the lower and upper
cutoff frequencies.4,14
barium clay: A molding clay containing barium, used to
eliminate or reduce the amount of scattered or secondary radiation reaching the film.3
barometer: Absolute pressure gage used to measure the
atmospheric pressure at a specific location.1
barometric pressure: Ambient pressure caused by the
weight of the Earth’s atmosphere.1 See atmospheric
pressure.
baseline: The horizontal trace across the A-scan cathode
ray tube display. It represents time and is generally
related to material distance or thickness.7
basin: A cavity on top of the cope into which metal is poured
before it enters the sprue. Also called pouring basin.3
basis calibration: Standardizing an ultrasonic testing
instrument using calibration reflectors described in an
application document.7
bath: The water or oil used as a vehicle for wet method
magnetic particles.6 The liquid penetrant testing materials (penetrant, emulsifier, developer) into which test
objects are immersed during the testing process and
penetrant materials retained in bulk in immersion tanks
intended for reuse.2 See suspension.
bead: A half-round cavity in a mold or a half-round projection or molding on a casting.3
beam exit point: See probe index.
beam spread: The divergence of the sound beam as it travels
through a medium.10 Specifically, the solid angle which
contains the main lobe of the beam in the far field.7
bearding: See furring.
bed-in: A method of ramming the drag mold without
rolling over it.3
bedding a core: Placing an irregularly shaped core on a
bed of sand for drying.3
bentonite: A plastic, adhesive clay that swells when wet. It
is derived from decomposed volcanic ash and is used
for bonding molding sand.3
Berthold penetrameter: A magnetic flux indicator containing an artificial discontinuity in the shape of a cross,
mounted below an adjustable cover plate.6,15
beta particle: An electron or positron emitted from a
nucleus during decay.11
beta ray: A stream of high speed electrons of nuclear origin. This radiation is more penetrating than alpha radiation but ionizes less strongly.11
betatron: A circular electron accelerator that is a source of
either high energy electrons or X-rays. The electrons
are injected by periodic bursts into a region of an alternating magnetic field. After acceleration, the electrons
are brought out directly or directed against a target to
produce X-rays.11
billet: A solid semifinished round or square product that
has been hot worked for forging, rolling or extrusion.2
binary system: In metallurgy, a two element alloy system.8
binder: A material used to hold the grains of sand together
in molds or cores. It may be cereal, oil, clay or natural
or synthetic resins.3
birefringence: The splitting of a light beam into two parts
through a translucent material.8
black body: See blackbody.
black light: Disfavored term for electromagnetic radiation
or light energy in the near ultraviolet range with wavelengths from 320 to 400 nm, just below the wavelengths
of visible light. Also a term for the ultraviolet light
source used in fluorescent nondestructive testing.
Black light sources often have a predominant wavelength of 365 nm. See the preferred term, ultraviolet
radiation.2,6,8,16
black light filter: A filter that transmits ultraviolet radiation
between 320 and 400 nm wavelengths while absorbing or
suppressing the transmission of the visible radiation and
hard ultraviolet radiation with wavelengths less than
320 nm.6,16
black light intensity: See intensity.
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blackbody: Hypothetical radiation source that yields the
maximum radiation energy theoretically possible at a
given temperature. A blackbody will absorb all incident
radiation falling upon it and has an emissivity of 1.0. See
also emissivity.9
blacklight: See black light.
bleed: Refers to molten metal oozing out of a casting.
Stripped or removed from the mold before complete
solidification.3
bleedback: The ability of a penetrant to bleed out of a discontinuity subsequent to removal of the indication
without reapplying the penetrant.2
bleedout: The action by which a penetrant exudes from
discontinuities onto the surface of a material. Action of
the entrapped penetrant in spreading out from surface
discontinuities to form an indication.2
blended sand: A mixture of sands of different grain sizes
and clay content that is needed to produce a sand possessing more suitable characteristics for foundry use.3
blind riser: An internal riser that does not reach to the
exterior of the mold.3
blind spot: Portion of the retina where the optic nerve
enters, without rods and cones and hence insensitive to
light.8
blister: A discontinuity in metal, on or near the surface,
resulting from the expansion of gas in a subsurface
zone. Very small blisters are called pinheads or pepper
blisters.2
blotch: (1) An irregularly spaced area of color change on a
surface. (2) Nonuniform condition of a surface characterized by such blotches.8
blotting: The action of the developer in soaking up the penetrant from the surface of a discontinuity so as to cause
maximum bleedout of the liquid penetrant for
increased contrast and sensitivity.2
blowhole: A hole in a casting or a weld caused by gas
entrapped during solidification.2,3
blue hazard: Exposure to high frequency visible light at
intensities and durations that may damage the retina,
particularly in conjunction with overheating.8
bobbin coil: See ID coil.
bond: A cohesive material used to bind sand.3
bond clay: Any clay suitable for use as a bonding material
in molding sand.3
bond strength: The degree of cohesiveness that the bonding agent exhibits in holding sand grains together.3
book mold: A split mold hinged like a book.3
borescope: An industrial endoscope; a periscope or telescope using mirrors, prisms, lenses, optic fibers or television wiring to transmit images from inaccessible
interiors for visual testing. Originally used in machined
apertures such as gun bores. There are both flexible
and rigid, fiber optic and geometric light borescopes.8
borescope, angulated: Borescope bent for viewing at forward oblique, right angle or retrospective angles for
visual testing of surfaces not accessible with conventional borescopes.8
borescope, fiber optic: Borescope that uses fiber optic
materials (such as glass or quartz) in the optical path
and for transmission of light to and from the test surface.8
borescope, micro-: Borescope with an outside diameter
generally from 1 to 5 mm (0.04 to 0.2 in.), typically
using quartz filaments. Compare borescope, miniature.8
borescope, miniature: Borescope with an outside diameter generally less than 13 mm (0.5 in.). Sometimes
called miniborescope. See also borescope, micro-.8
borescope, rigid: Borescope that does not bend, typically
in order to keep the geometrical optics in alignment
through a light train system.8
borescope, ultraviolet: Borescope equipped with ultraviolet lamps, filters and special transformers to transmit
radiation of ultraviolet wavelengths.8
bottom board: The board or plate on which the mold
rests.3
bottom echo: See back reflection.
bottom pour mold: A mold grated at the bottom.3
boundary echo: A reflection of an ultrasonic wave from an
interface.7,12
branch gates: Gates leading into a casting cavity from a
single runner and sprue.3
brazing: Joining of metals and alloys by fusion of nonferrous alloys that have melting points above 430 °C
(806 °F), but below melting points of materials being
joined.2
bridging: Premature solidification of metal across a mold
section before the metal below or beyond solidifies.3
brinell hardness: A measure of metal hardness. Determined by pressing a hard steel ball into the smooth surface under standard conditions.
brinelling: Stripe indentations made by a spherical object.
False brinelling refers to a type of surface wear.8
brittle crack propagation: A very sudden propagation of a
crack with the absorption of no energy except that
stored elastically in the body. Microscopic examination
may reveal some deformation even though it is not visible to the unaided eye.2
brittleness: The quality of a material that leads to crack
propagation without appreciable plastic deformation.2
broad banded: Having a relatively wide frequency bandwidth. Describes pulses that display a wide frequency
spectrum and receivers capable of amplifying them.
Opposite to narrow banded or tuned.7
bubbler: See water column.
bucking coils: See differential coils.
buckle: Indentation in a casting, resulting from expansion
of the sand.3
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bumper: A machine used for packing molding sand in a
flask by repeated jarring or jolting.3
bumping: Ramming sand in a flask by repeated jarring and
jolting.3
burning: Extreme overheating. Makes grains excessively
large and causes the more fusible constituents of steel
to melt and run into the grain boundaries or it may
leave voids between the grains. Steel may be oxidized to
the extent that it is no longer good and cannot be corrected by heat treating but it can be remelted.2
burnt-in sand: A discontinuity consisting of a mixture of
sand and metal cohering to the surface of a casting.3
burr: A raised or turned over edge occurring on a machined
part and resulting from cutting, punching or grinding.8,19
burst: (1) A signal whose oscillations have a rapid increase
in amplitude from an initial reference level (generally
that of the background noise), followed by a decrease
(generally more gradual) to a value close to the initial
value.5 (2) In metal, external or internal rupture caused
by improper forming.8
burst counting: A measurement of the number of bursts
detected relative to specified equipment settings such
as threshold level or dead time.5
burst duration: The interval between the first and last time
the threshold was exceeded by the burst.5
burst emission: A qualitative term applied to acoustic emission when bursts are observed.5
burst rate: The number of bursts detected in a specified
time.5
burst rise time: The time interval between the first threshold crossing and the maximum amplitude of the burst.5
butt weld or butt joint: Weld joining two metal pieces in
the same plane.8
C
C-scan: A data presentation technique applied to pulse
echo and transmission techniques. It yields a twodimensional plan view of the object but no depth indications unless special gating procedures are used.7,10,12
calibration reflector: A reflector with a known dimensioned surface established to provide an accurately
reproducible reference level.7
candela: Base unit of measure in SI for measuring luminous intensity. The luminous intensity in a given direction of a source that emits monochromatic radiation of
frequency 540 × 1012 Hz and that has a radiant intensity
in that direction of 1.4641 mW·sr –1. Symbolized cd.
Formerly known as candle.8
candle: Former name for candela.8
capacitor discharge technique: A single-shot magnetization technique using discharge from a bank of capacitors.
A means by which electrical charge is built up and stored
until a sufficient level is achieved to provide a predetermined magnetic field in a test object, usually saturation.6
capillary action: The tendency of liquids to penetrate or
migrate into small openings, such as cracks, pits or fissures. The positive force that causes movement of certain liquids along narrow or tight passages.2
carrier fluid: (1) A fluid that acts as a carrier for the active
materials. (2) The fluid in which fluorescent and visible
dyes are dissolved or suspended, in liquid penetrants or
leak tracers.2 (3) The liquid vehicle in which fluorescent or nonfluorescent magnetic particles are suspended for ease of application. See vehicle.6,16
case crushing: A mechanism producing fracture of the
case, like subcase fatigue but attributable to static overloading rather than to fatigue alone. In many instances
the movement of the subcase causes the case to crack
or spall.8
casing: The many strings of pipe that are used to line the
hole during and after drilling of a gas or oil well.8
casing string: Tubular structure on the outer perimeter of
a gas or oil well hole. The casing string is a permanent
part of the well and many are cemented into the formation.8
cassette: A lightproof container that is used for holding the
radiographic films in position during the radiographic
exposure and that may or may not contain intensifying
and/or filter screens.11
cast structure: The internal physical structure of a casting
evidenced by shape, orientation of grains and segregation of impurities.2,3
cast weld assembly: An assembly formed by welding one
casting to another.3
casting: Object of shape obtained by solidification of a substance in a mold.
casting shrinkage: Total shrinkage includes the sum of
three types: (1) liquid shrinkage (the reduction in volume of liquid metal as it cools to the liquidus); (2) solidification shrinkage (the change in volume of metal from
the beginning to ending of solidification); and (3) solid
shrinkage (the reduction in volume of metal from the
solidus to room temperature).2,3
casting strains: Strains in a casting caused by casting
stresses that develop as the casting cools.3
casting stresses: Stresses set up in a casting because of
geometry and casting shrinkage.3
cathode: (1) In radiography, the negative electrode of an
electron tube. (2) Positively charged terminal in an
arrangement that produces current by chemical reactions. Compare anode.8
cathode ray: A stream of electrons emitted by a heated filament and projected in a more or less confined beam
under the influence of a magnetic or electric field.7,12
cathode ray tube (CRT): A vacuum tube containing a
screen on which nondestructive testing or other signals
may be displayed. Used for ultrasonic A-scans or
B-scans.7,12
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cavitation fatigue: A form of pitting caused by erosion
from vibration and movement in liquid environments.8
cavity: The die impression that gives a casting its external
shape.3
CCD: See charge coupled device.
cementite: Iron carbide (Fe3C), present in steels.8
central conductor: An electric conductor passed through
the opening in a part with an aperture, or through a
hole in a test object, for the purpose of creating a circular magnetic field in the object.6,10
centrifugal casting: A casting made in a mold (sand, plaster or permanent) that rotates while the metal solidifies
under the pressure developed by centrifugal force.3
certification: The process of providing written testimony
that an individual is qualified. See also certified.8
certified: Having written testimony of qualification. See
also certification.8
chafing: See wear, fretting.
chalk test: A past method of locating cracks by applying
penetrating liquid to an object and then removing the
excess from the surface. The surface is coated with
whiting or chalk. After a short period of time the penetrant seeps out of the cracks into the whiting or chalk,
causing an appreciable difference in whiteness.2
channels: In biology, mechanisms functioning as bandpass
filters in the visual cortex of mammals, causing sensitivity to visual stimuli in particular frequencies and
ranges.8
chaplet: A metal support used to hold a core in place on a
mold.3
charge coupled device (CCD): Solid state image sensor
widely used in inspection systems because of their
accuracy, high speed scanning and long service life.8
Charpy test: A destructive mechanical test in which a
notched 10 × 10 × 55 mm rectangular bar, supported at
both ends as a simple beam, is broken by the impact of a
falling pendulum. Energy absorbed in breaking the bar is
a measure of the impact strength of the bar material and
indicates the material’s resistance to brittle fracture.2
chatter: (1) In machining or grinding, a vibration of the
tool, wheel or workpiece producing a wavy surface on
the work. (2) The finish produced by such vibration.2
checks: Numerous, very small cracks in metal or other material caused in processing. Minute cracks as in a die
impression, usually at a corner, caused by forging strains.
Also called grinding checks and check marks.2
chill: (1) A metal insert embedded in the surface of a sand
mold or core or placed in a mold cavity to increase the
cooling rate at that point. (2) White iron occurring on a
gray iron casting, such as the chill in the wedge test.3
chipping: (1) Removing seams and other surface discontinuities in metals manually with chisel or gouge or by
continuous machining, before further processing.
(2) Removing excessive metal.2,3
chuck: A small bar set between crossbars to hold sand in
the cope.3
circular magnetic field: The magnetic field surrounding
an electrical conductor (test object) when a current is
passed longitudinally through the conductor.6,16
circular magnetization: The magnetization in an object
resulting from current passed longitudinally through
the object itself or through an inserted central conductor.6,16
circumferential coil: See encircling coil.
circumferential magnetization: See circular magnetization.
cire perdue process: The lost wax process.3
clean: Free from interfering solid or liquid contamination
on the test surface and within voids or discontinuities.2
cleaner: Volatile solvent employed to clean a surface before
penetrant application. The cleaner is sometimes referred to as the solvent remover.2
cleanup or cleanup time: The time required for a leak
testing system to reduce its signal output to 37 percent
of the signal indicated when the tracer gas ceases to
enter the leak testing system.1
cleavage: The fracture of a crystal on a crystallographic
plane of low index.2
cleavage fracture: A fracture, usually of a polycrystalline
metal, in which most of the grains have failed by cleavage, resulting in bright reflecting facets. It is one type of
crystalline fracture. Contrast with shear fracture.2
closing: In image processing, dilation followed by erosion.
A single pixel closing connects a broken feature separated by one pixel. See also opening.8
closure: Process by which a person cognitively completes
patterns or shapes that are incompletely perceived.8
cocoa: Debris (usually oxides of the contacting metals) of
fretting wear, retained at or near the site of its formation — a condition especially helpful during visual tests.
With ferrous metals, the debris is brown, red or black,
depending on the type of iron oxide formed. For this
reason, ferrous debris is called cocoa or, when mixed
with oil or grease, red mud.8
code: A standard enacted or enforced as a law.8
coefficient of thermal expansion: The linear expansion
or contraction per unit length per degree of temperature change between specified lower and upper temperature limits.2
coefficients of the filter: Values in a mask that serves as a
filter in image processing.8
coercive force: The reverse magnetizing force needed to
remove remanent or residual magnetism and thereby
demagnetize the object.6
coil: One or more loops of a conducting material. In eddy
current testing, a single coil may be an exciter and
induce currents in the material or it may be a detector
or both simultaneously.4
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coil clearance: See liftoff.
coil shot: A technique of producing longitudinal magnetization by passing electric current through a coil encircling the test object.6,10
coil spacing: In electromagnetic testing, the axial distance
between two encircling coils of a differential system.4,13
coil technique: A method of magnetization in which all or
a portion of the object is encircled by a current-carrying
coil.6,16
cold cathode ionization gage: Discharge current results
from the application of a high voltage between anode
and cathode. The discharge current magnitude is a
function of the gaseous pressure within the gage chamber. The external permanent magnet facilitates ionization by forcing the electrons into a spiral path between
the two electrodes. The discharge current is displayed
on a meter over the absolute pressure range of less than
10 mPa (10–4 torr).1 Also known as Philips discharge
gage or Penning gage.
cold chamber machine: A die casting machine where the
metal chamber or plunger are not heated.3
cold cracks: Discontinuities appearing as straight lines usually continuous throughout their length and generally
existing singly. Cold cracks start at the surface and result
from cold working or stressing of metallic materials.2
cold light: Obsolete word for fluorescence.8
cold shut: (1) Casting discontinuity caused by two streams
of semimolten metal coming together inside a mold but
failing to fuse. Cold shuts are sometimes called misruns
but the latter term correctly describes incomplete filling of the mold.3 (2) A discontinuity that appears on the
surface of test metal as a result of two streams of liquid
meeting and failing to unite. A cracklike discontinuity
caused by forging, where two surfaces of metal fold
against each other to produce a discontinuity at the
point of folding. This is usually at some angle to the surface. It may also be a separate piece of metal forged
into the main component. See lap. (3) A portion of the
surface of a forging that is separated in part from the
main body of metal by oxide.2,3
cold work: Permanent deformation produced by an external force in a metal at temperature below its recrystallization temperature.2
collimator: A device for limiting effects of beam spread.7
color: Visual sensation by means of which humans distinguish light of differing hue (predominant wavelengths),
saturation (degree to which those radiations predominate over others) and lightness.
color blindness: Deficiency in the ability to perceive or
distinguish hues.8
color contrast dye: A dye that can be used in a penetrant
to impart sufficient color intensity to give good color
contrast indications against the background on a test
surface when viewed under visible light.2
color contrast penetrant: A penetrant incorporating a
dye, usually nonfluorescent, sufficiently intensive to
give good visibility to discontinuity indications under
visible light.2
color discrimination: The perception of differences
between two or more hues.8
columnar structure: A coarse structure of parallel columns
of grains, having the long axis perpendicular to the casting surface.2,3
combination die: A die having two or more different cavities for different castings.3
comparative measurement: In electromagnetic testing, a
measurement based on the unbalance in a system using
comparator coils. In contrast to differential and absolute measurements. See also comparator coils.4,13
comparative test block: A penetrant comparator in the
form of a block. See comparator, penetrant.
comparator coil: In electromagnetic testing, two or more
coils electrically connected in series opposition and
arranged so that there is no mutual induction (coupling) between them. Any electromagnetic condition
that is not common to the test object and the standard
will produce an unbalance in the system and thereby
yield an indication. See differential coils.4,13
comparator, penetrant: A test block or reference panel
with artificial cracks or special surface conditions, typically having two separate but adjacent areas for application of different penetrants or processing materials or
operation, so that a direct visual comparison can be made
between different penetrant processes or materials.2
compensator: An electrical matching network to compensate for electrical impedance differences.7,12
complete testing: Testing of an entire production lot in a
prescribed manner. Sometimes complete testing entails
the inspection of only the critical regions of a part. One
hundred percent testing requires the inspection of the
entire part by prescribed methods. Compare sampling,
partial.8
complex plane: A plane defined by two perpendicular reference axes, used for plotting a complex variable (such
as impedance) or functions of this variable (such as a
transfer function). See impedance analysis.4,14
compound microscope: See microscope, compound.
compressional wave: A wave in which particle motion in
the material is parallel to the wave propagation direction. Also called longitudinal wave.7
conditioned water: Water with an additive or additives
that impart specific properties such as proper wetting,
particle dispersion or corrosion resistance.6
conditioning agent: An additive to water suspensions that
imparts specific properties such as proper wetting, particle dispersion or corrosion resistance.6,16
conductance: Property of a gas flow system that permits
gas to flow.1
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conduction: Heat transfer occurring when warmer atomic
particles collide with — and thus impart some of their
heat energy to — adjacent cooler (slower moving) particles. This action is passed on from one atom (or free
electron) to the next in the direction of cooler regions.
Thus, heat always flows from a warmer to a cooler
region.9
cone: In biology, a retinal receptor that dominates the retinal response when the luminance level is high and provides the basis for the perception of color. Compare
rod.8,20
confidence level: The probability that the true leakage
rate will not exceed the upper confidence limit.1
constitution diagram: See phase diagram.
contact head: Electrode assembly used to clamp and support an object to facilitate passage of electric current
through the object for circular magnetization.6,16
contact method: (1) The ultrasonic testing method in
which the transducer makes direct contact with the test
object through a thin film of couplant.7,12 (2) The current flow technique in magnetic particle testing.6
contact pad: Replaceable metal pad, usually made of lead
or copper braid, placed on electrodes to give good electrical contact, thereby preventing damage such as arc
strikes to the test object.6,16
contact transducer: The transducer used in the contact
method.7
continuous annealing furnace: A furnace in which castings are heat treated, by being passed through different
heat zones kept at constant temperatures.3
continuous casting: A casting technique in which an ingot,
billet, tube or other shape is continuously solidified
while being poured so that its length is not determined
by mold dimensions.3
continuous emission: A qualitative term applied to acoustic emission when the bursts or pulses are not discernible.5
continuous technique: Applying of magnetic particles to
form satisfactory discontinuity indications while the
magnetizing field is simultaneously applied.6
continuous wave: A single frequency wave that continues
without interruption.7
contracted sweep: A misnomer that refers to extending
the duration of the sweep to permit viewing discontinuities or back reflections from deeper in the test object.
The sweep appears to be compressed.7
contrast: (1) In radiography, the measure of differences in
the film blackening resulting from various radiation
intensities transmitted by the object and recorded as
density differences in the image. Thus, difference in
film blackening from one area to another.11 (2) The difference in visibility (brightness or coloration) between
an indication and the surrounding surface.2
control: See in control, process control and quality control.
control echo: A reference signal from a constant reflector,
such as the back reflection from a smooth, regular surface.7,12
cooling stresses: Residual stresses resulting from nonuniform distribution of temperature during cooling.2,3
cope: The upper or topmost section of a flask, mold or pattern.3
core: (1) A specially formed material inserted in a mold to
shape the interior of another part of a casting that cannot be shaped as easily by the pattern. (2) In a ferrous
alloy, the inner portion that is softer than the outer portion or case.3
core blower: A machine for making foundry cores, using
compressed air to blow and pack the sand into the core
box.3
core pin: A core, usually a circular section, having some
taper or draft.3
core plate: A plate on which a green core is baked.3
core wash: A liquid with which cores are painted to produce smoother surfaces on the casting.3
corner effect: The strong reflection obtained when an
ultrasonic beam is directed toward the intersection of
two or three mutually perpendicular surfaces.7,12
corrosion: The deterioration of a metal by chemical or
electrochemical reaction with its environment.
Removal of material by chemical attack, such as the
rusting of automobile components.2
corrosion, crevice: Type of galvanic corrosion caused by
differences in metal ion concentrations in neighboring
portions of the corrodent.8
corrosion embrittlement: The severe loss of ductility of a
metal, resulting from corrosive attack, usually intergranular and often not visually apparent.2
corrosion fatigue: Fatigue cracking caused by repeated
load applications on metal in a corrosive environment.2
corrosion, fretting: Corrosion facilitated by fretting, particularly where a protective surface has been chafed in
a corrosive environment.8
corrosion, poultice: Corrosion occurring under a layer of
foreign material (e.g., under mud in automobile rocker
panels).8
corrosion-erosion: Simultaneous occurrence of erosion
and corrosion.8
count rate: See acoustic emission rate.
couplant: A substance (usually liquid) used between an
ultrasonic transducer and the test surface to permit or
improve transmission of ultrasonic energy into the test
object.7,12
coupled: Two electric circuits that have an impedance in
common so that a current in one causes a voltage in the
other.4,13
coupling: The percentage of magnetic flux from a primary
circuit that links a secondary circuit. The effectiveness
of a coil in inducing eddy currents in the test object.4
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coupling coefficient: (1) The fraction of magnetic flux
from one test coil that threads a second circuit (test
object). (2) The ratio of impedance of the coupling to
the square root of the product of the total impedances
of similar elements in the two meshes.4,14
coupon: A piece of metal from which a test object is prepared, often an extra piece, as on a casting or forging.3
cover half: The stationary half of a die casting die.3
crack: (1) A break, fissure or rupture, usually V shaped and
relatively narrow and deep. A discontinuity that has a
relatively large cross section in one direction and a
small or negligible cross section when viewed in a direction perpendicular to the first.2 (2) Propagating discontinuities caused by stresses such as heat treating or
grinding. Difficult to detect unaided because of fineness of line and pattern (may have a radial or latticed
appearance).6
crack contaminant: Material that fills a crack and that may
prevent penetrants from entering or from forming indications.2
crack, base metal: Cracks existing in base metal before a
manufacturing or welding operation or occurring in
base metal during the operation.2
crack, cold: Cracks that occur in a casting after solidification, due to excessive stress generally resulting from
nonuniform cooling.2
crack, cooling: Cracks in bars of alloy or tool steels resulting from uneven cooling after heating or hot rolling.
They are usually deep and lie in a longitudinal direction, but are usually not straight.2
crack, crater: A multisegment crack in a weld crater. Segments radiate from a common point, often called star
cracks.
crack, fatigue: Progressive cracks that develop in the surface and are caused by the repeated loading and
unloading of the object.2
crack, forging: Cracks developed in the forging operation
due to forging at too low a temperature, resulting in
rupturing of the steel.2
crack, grinding: Thermal cracks caused by local overheating of the surface being ground.2
crack, hot: Cracks that develop before the casting has completely cooled, as contrasted with cold cracks, that
develop after solidification.2
crack, longitudinal: Cracks parallel to the length of the
test object.2
crack, machining: Cracks caused by too heavy a cut, a dull
tool or chatter. Typically called machining tears.2
crack, pickling: Cracks caused by immersing objects with
high internal stresses in an acid solution.2
crack, plating: Cracks similar to pickling cracks, but occurring during plating when the object is immersed in a
strong electrolyte.2
crack, quenching: Ruptures produced during quenching
of hot metal due to more rapid cooling and contraction
of one portion of a test object than occurs in adjacent
portions.2
crack, transverse: Cracks at right angles to the length of
the test object.2
crack, weld: Cracks in weld fusion zones or adjacent base
metal. Usually a result of thermal expansion or contraction stresses related to temperature changes during
welding.2
crater: (1) In machining, a depression in the cutting tool
face eroded by chip contact. (2) In arc or gas fusion
welding, a cavity in the weld bead surface, typically
occurring when the heat source is removed and insufficient filler metal is available to fill the cavity.2
creep: Gradual and permanent change of shape in a metal
under constant load, usually at elevated temperature.
Occurs in three stages: primary creep, secondary creep
and tertiary creep. See also deformation.8
creep strength: The constant nominal stress that will cause
a specified creep rate at constant temperature.2
crevice corrosion: See corrosion, crevice.
critical angle: The incident angle of an ultrasound beam
above which a specific mode of refracted energy no
longer exists.7,10
cross line grating: In moiré and grid nondestructive testing, a grating with bars, furrows or lines parallel to
orthogonal xy axes.9
cross talk: The unwanted signal leakage (acoustical or electrical) across an intended barrier, such as leakage
between the transmitting and receiving elements of a
dual transducer. Also called cross noise and cross coupling.7,12
CRT: See cathode ray tube.
crush: A casting discontinuity caused by a partial destruction of the mold before the metal was poured.3
crushing: The pushing out of shape of a sand core or sand
mold when two parts of the mold do not fit properly
where they meet.3
crystal: See transducer.
crystal mosaic: Multiple crystals mounted in the same
plane on one holder and connected so as to cause all to
vibrate as one unit.7,12
crystal, X-cut: A cut such that the cut face is perpendicular to the X-direction of the piezoelectric crystal. In a
quartz slice so cut, a thickness mode of vibration
occurs when the slice is electrically stimulated in the
X-direction.7,12
crystal, Y-cut: In Y-cut, the cut face of the piezoelectric
crystal is perpendicular to the Y-direction. In quartz, a
shear mode of vibration is obtained when the slice is
electrically stimulated in the Y-direction.7,12
cumulative bursts: The number of bursts detected from
the beginning of the test.5
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cumulative characteristic distribution: A display of the
number of times an acoustic emission signal exceeds a
preselected characteristic as a function of the characteristic.5
cumulative count: The number of times the amplitude of
an acoustic emission signal has exceeded the threshold
since the start of a test.5
cumulative events: The number of events detected from
the beginning of a test. Use of this term is restricted in
the same way as event counting.5
cup fracture: Fracture, frequently seen in tensile test
places of a ductile material, in which the surface of failure on one portion shows a central flat area of failure in
tension, with an exterior extended rim of failure in
shear. Also called cup-and-cone fracture.2
Curie point: The temperature at which ferromagnetic
materials lose residual magnetism and can no longer be
magnetized by outside forces (between 650 and 870 °C
[1,200 and 1,600 °F] for most metals).6,16
current flow technique: Magnetizing by passing current
through an object using prods or contact heads. The
current may be alternating current or rectified alternating current.6,16
current induction technique: Magnetization in which a
circulating current is induced in a ring component by
the influence of a fluctuating magnetic field.6,16
cutoff frequency: Upper or lower spectral response of a
filter or amplifier, at a specified amount less (usually 3
or 6 dB) than the maximum response.7
cycle: A single period of a waveform or other variable. See
period.
D
damping: (1) Limiting the duration or decreasing the
amplitude of vibrations, as when damping a transducer
element.12 (2) A deliberate introduction of energy
absorbers to reduce vibrations.7
damping capacity: A measure of ability of a material to
dissipate mechanical energy.7,18
damping material: A highly absorbent material used to
cause rapid decay of vibration.7
damping, transducer: A material bonded to the back of
the piezoelectric element of a transducer to limit the
duration of vibrations.7,10
damping, ultrasonic: Decrease or decay of ultrasonic
wave amplitude with respect to time or distance.7,10
dark adaptation: (1) Adjustment of the eye over time to
reduced illumination, including increased retinal sensitivity, dilation of the pupil and other reflex physical
changes.2,6,16 (2) Process by which the retina becomes
adapted to luminance less than about 0.034 cd·m–2.8,20
dark adapted vision: See scotopic vision.
daubing: The act of filling cracks in cores.3
dead zone: In ultrasonic contact testing, the interval following the initial pulse at the surface of a test object to
the nearest inspectable depth.10 Any interval following
a reflected signal where additional signals cannot be
detected.7
deburring: Removing burrs, sharp edges or fins from metal
objects by filing, grinding or rolling the work in a barrel
with abrasives suspended in a suitable liquid medium.
Sometimes called burring.2,3
decarburization: The loss of carbon from the surface of a
ferrous alloy as a result of heating in a medium that
reacts with the carbon at the surface.2
decibel: A unit for expressing power relationships in sonic
and acoustic measurements. Equal to ten times the
base ten logarithm of the ratio of two powers. The unit
for voltages is twenty times the base ten logarithm of
the ratio of two voltages, provided the voltages are measured across equal impedances.7
deep drawing: The forming of deeply recessed parts by
means of plastic flow of the material.2
deep etching: Severe etching of a metallic surface for
examination at a magnification of ten diameters or less
to reveal gross features such as segregation, cracks,
porosity or grain flow.2
defect: A discontinuity whose size, shape, orientation or
location make it detrimental to the useful service of its
host object or which exceeds the accept/reject criteria
of an applicable specification.6,17 Note that some discontinuities may not affect serviceability and are therefore not defects.2 All defects are discontinuities.2
Compare discontinuity and indication.8,19
deformation: Change of shape under load. See also creep
and elastic deformation.8
degasifier: A substance that can be added to molten metal to
remove soluble gases that might otherwise be occluded
or entrapped in the metal during solidification.3
degassing: Removing gases from liquids or solids.3
degreasing fluid: Solvents or cleaners employed to
remove oil and grease from test surfaces before the liquid penetrant is applied.2
delamination: A laminar discontinuity, generally an area of
unbonded materials.7
delay line: A material (liquid or solid) placed in front of a
transducer to cause a time delay between the initial
pulse and the front surface reflection.7,12
delayed sweep: An A-scan or B-scan sweep, the start of
which has been delayed, thereby eliminating the
appearance of early response data on the screen.7,21
delayed time base: See delayed sweep.
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delta effect: Reradiation of energy from a discontinuity.12
The reradiated energy may include waves of both incident mode and converted modes (longitudinal and
shear).7
delta ferrite: Solid solution with body centered cubic
structure and iron as solvent. Also called delta iron.8
delta iron: See delta ferrite.
delta t (∆t): The time interval between the detected arrival
of an acoustic emission wave at two sensors.5
demagnetization: The reduction of residual magnetism to
an acceptable level.6,16
demagnetizing coil: A coil of conductive material carrying
alternating current used for demagnetization.6,15
demodulation: A modulation process wherein a wave
resulting from previous modulation is employed to
derive a wave having substantially the characteristics of
the original modulating wave.4,14
dendrite: A crystal that has a treelike branching pattern,
being most evident in cast metals slowly cooled through
the solidification range.2,3
deoxidizing: (1) The removal of oxygen from molten metals by use of suitable deoxidizers. (2) Sometimes refers
to the removal of undesirable elements other than oxygen by the introduction of elements or compounds that
readily react with them. (3) In metal finishing, the
removal of oxide films from metal surfaces by chemical
or electrochemical reaction.3
depth compensation: See distance amplitude correction.
depth of field: In photography, the range of distance over
which an imaging system gives satisfactory definition
when its lens is in the best focus for a specific distance.8
depth of fusion: The depth to which the base metal melted
during welding.2
depth of penetration: In electromagnetic testing, the
depth at which the magnetic field strength or intensity
of induced eddy currents has decreased to 37 percent
of its surface value. The square of the depth of penetration is inversely proportional to the frequency of the
signal, the conductivity of the material and the permeability of the material. Synonymous terms are standard
depth of penetration and skin depth. See joint penetration, root penetration and skin effect.2,4,13
descaling: Removing the thick layer of oxides formed on
some metals at elevated temperatures.2
deseaming: Analogous to chipping, the discontinuities
being removed by gas cutting.2
detail: In radiography, the degree of sharpness of outline of
the image. If a radiograph does not show a clear definition of the object or a discontinuity in the object, it is of
little value although it may have sufficient contrast and
density.11
detector coil: See sensing coil.4
detector probe: An adjustable or fixed device through
which air and/or tracer gas is drawn into the leak test
instrument and over the sensing element or detector.
Also called a sampling probe or a sniffer probe.1
detector probe test: A pressure leak test in which the
leakage of a component, pressurized with a tracer rich
mixture, is detected by scanning the test object boundary surface with a sniffer probe connected to an electronic leak detector. Leakage tracer gas is pulled from
the leak through the probe inlet to the sensing element
to cause a visible or audible signal on the indicator of
the leak test instrument.1 Also called sniffer test.
detergent remover: A penetrant remover that is a solution
of a detergent in water.2
developer: (1) In penetrant testing, a material that is
applied to the test piece surface after the excess penetrant has been removed and that is designed to enhance
the penetrant bleedout to form indications. May be a
fine powder, a solution that dries to form a dry powder
or a suspension (in solvent or water) that dries leaving
an absorptive film on the test surface.2 (2) In radiography, a chemical solution that reduces exposed silver
halide crystals to metallic silver.11
developer, dry: A dry, fine powder applied to the test piece
after the excess penetrant is removed and the surface
dried in order to increase the bleedout by means of
capillary action.2
developer, nonaqueous: See developer, solvent.
developer, soluble: Fine particles completely soluble in its
carrier (not a suspension of powder in a liquid) that
dries to form an adsorptive coating.2
developer, solvent: Fine particles suspended in a volatile
solvent. The volatile solvent helps to dissolve the penetrant out of the discontinuity and brings it to the surface. It then dries, fixing the indication.2
developer, wet: A penetrant developer usually supplied as
dry particles that is mixed with water to form a suspension of particles.2
developing time: Elapsed time necessary for the applied
developer to absorb and show indications from penetrant entrapments.2
dewaxing: Removing the expendable wax pattern from an
investment mold by heat or solvent.3
dewetting: The flow and retraction of liquid on a surface,
caused by contaminated surfaces or dissolved surface
coatings.8
diamagnetic material: A material whose relative permeability is less than unity. The intrinsic induction Bi is
oppositely directed to applied magnetizing force H.4,13
A material with magnetic permeability less than 1.6
die casting: (1) A casting made in a die. (2) A casting process where molten metal is forced under high pressure
into the cavity of a metal mold.3
difference cylinder: See background cylinder.
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differential amplifier: An amplifier whose output signal is
proportional to the algebraic difference between two
input signals.4,14
differential coils: Two or more physically adjacent but
mutually uncoupled coils connected in series opposition
such that an unbalance between them, causing a signal,
will be produced only when the electromagnetic conditions are different in the regions beneath two of the
coils. In contrast, comparator coils are not adjacent.4
differential measurement: In electromagnetic testing,
the imbalance in the system is measured using differential coils — in contrast to absolute measurement and
comparative measurement.4,13
differentiated signal: In electromagnetic testing, an output signal proportional to the input signal’s rate of
change with respect to time.4,13
diffraction: In ultrasonic testing, the deflection of a wavefront when passing the edge of an ultrasonically opaque
object.12
diffuse indications: Indications that are not clearly
defined as, for example, indications from surface contamination.2
diffuse reflection: Scattered, incoherent reflections from
rough surfaces.7,10
diffusion: The process by which molecules intermingle as a
result of concentration gradients or thermal motion.2
Spreading of a gas through other gases within a volume.
dilation: In image processing, the condition of a binary
image where the pixel in the output image is a 1 if any
of its eight closest neighbors is a 1 in the input image.
See also closing, erosion and opening.8
dip rinse: A means of removing excess surface penetrant in
which the test objects are dipped into a tank of agitated
water or remover.2
direct contact magnetization: See current flow technique.
direct current: An electric current flowing continually in
one direction through a conductor.6,17
direct current field: An active magnetic field produced by
direct current flowing in a conductor or coil.6,17
direct photometry: Simultaneous comparison of a standard lamp and an unknown light source.8,20
direct substitution alloy: Alloy in which the atoms of the
alloying element can occupy the crystal lattice spaces
normally occupied by the atoms of the parent metal.8
direct viewing: Viewing of a test object in the viewer’s
immediate presence. The term direct viewing is used in
the fields of robotics and surveillance to distinguish
conventional from remote viewing.8
direct vision instrument: Device offering a view directly
forward. A typical scene is about 19 mm (0.75 in.) wide
at 25 mm (1 in.) from the objective lens.8
directional lighting: Lighting provided on the work plane
or object predominantly from a preferred direction.8,20
directional properties: Properties whose magnitudes depend on the relation of the test axis to the specific
direction in the metal, resulting from preferred orientation or from fibering in the structure. See anisotropy.2
directional solidification: The solidification of molten
metal in a casting in such manner that feed metal is
always available for that portion that is just solidifying.3
discernible image: Image capable of being recognized by
sight without the aid of magnification.2
discontinuity: An intentional or unintentional interruption in the physical structure or configuration of a
part.6,8,16,22 After nondestructive testing, unintentional
discontinuities interpreted as detrimental in the host
object may be called flaws or defects.6 Compare defect,
dislocation and indication.
discontinuity, artificial: Reference discontinuities such as
holes, indentations, cracks, grooves or notches that are
introduced into a reference standard to provide accurately reproducible indications for determining sensitivity levels.2
discontinuity, inherent: Material anomaly originating
from solidification of cast metal. Pipe and nonmetallic
inclusions are the most common and can lead to other
types of discontinuities in fabrication.8,19
discontinuity, primary processing: Material anomaly
produced from the hot or cold working of an ingot into
forgings, rod and bar.8,19
discontinuity, secondary processing: Material anomaly
produced during machining, grinding, heat treating,
plating or other finishing operations.8,19
discontinuity, service induced: Material anomaly caused
by the intended use of the part.8
dislocation: Void or discontinuity in the lattice of a metal
crystalline structure.8 Two basic linear types are recognized (edge dislocation and screw dislocation) but combinations and partial dislocations are most prevalent.2
dispersion: The variation of phase velocity with frequency.7
dispersive medium: A medium in which propagation
velocity depends on the wave frequency.7
displacement resolution: In moiré and grid nondestructive testing, measurement precision expressed as the
smallest displacement that can be determined with reasonable reliability.9
dissociation: The breakdown of a substance into two or
more constituents.2
distal: In a manipulative or interrogating system, of or pertaining to the end opposite from the eyepiece and farthest from the person using the system. Objective; tip.8
distance amplitude correction (DAC): Compensation of
gain as a function of time for difference in amplitude of
reflections from equal reflectors at different sound
travel distances. Refers also to compensation by electronic means such as swept gain, time corrected gain,
time variable gain and sensitivity time control.7,12
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divergence: A term used to describe the spreading of
ultrasonic waves beyond the near field. It is a function
of transducer diameter and wavelength in the
medium.7
domain: A saturated macroscopic substructure in ferromagnetic materials where the elementary particles
(electron spins) are aligned in one direction by interatomic forces. A saturated permanent magnet.6,10
dose: The amount of ionizing radiation energy absorbed
per unit mass of irradiated material at a specific location, such as part of the human body. Measured in rems
and rads.11
dose rate: The radiation dose delivered per unit time and
measured, for instance, in rems per hour. See also
dose.11
dosimeter: A device that measures radiation dose, such as a
film badge or ionization chamber.11
double crystal method: A method of ultrasonic testing
that uses two transducers, one transmitting and the
other receiving.7,10
drag: The bottom section of a flask, mold or pattern.3
dragout: The carryout or loss of penetrant materials as a
result of their adherence to the test pieces.2
drain time: That portion of the dwell time during which
the excess penetrant, emulsifier, detergent remover or
developer drains off the test piece.2
drop: A discontinuity in a casting due to a portion of the
sand dropping from the cope or overhanging section of
the mold.3
drop out: The falling away of green sand from the walls of a
mold cavity when the mold is closed.3
dross: The scum that forms on the surface of molten metals
largely because of oxidation but sometimes because of
the rising of impurities to the surface.3
dry bulb temperature: Alternate term for ambient or atmospheric temperature.1
dry powder: Finely divided ferromagnetic particles selected and prepared for magnetic particle testing.6,10
dry technique: A magnetic particle testing technique in
which the ferromagnetic particles are applied in a dry
powder form.6,16
drying oven: An oven used for drying rinse water from test
pieces.2
drying time: The time allotted for a rinsed or cleaned test
piece to dry.2
dual response penetrant: A penetrant that produces discontinuity indications that can be seen under either
ultraviolet light or visible light.2
dual transducer: A single transducer containing two piezoelectric elements, one for transmitting and one for
receiving.7,12
ductile crack propagation: Slow crack propagation that is
accompanied by noticeable plastic deformation and
requires energy to be supplied from outside the body.2
ductility: The ability of a material to deform plastically
without fracturing, being measured by elongation or
reduction of area in a tensile test, by height of cupping
in an Erichsen test or by other means.2
dwell time: The total time that the penetrant or emulsifier
is in contact with the test surface, including the time
required for application and the drain time.2
dynamic creep: Creep that occurs under conditions of
fluctuating load or fluctuating temperature.2
dynamic range: The ratio of maximum to minimum reflective areas that can be distinguished on the cathode ray
tube at a constant gain setting.7,23,24
E
echo: A signal indicating reflected acoustic energy.7
ECT: Eddy current testing.
eddy current: An electrical current induced in a conductor
by a time varying magnetic field.4
eddy current testing: A nondestructive testing method in
which eddy current flow is induced in the test object.
Changes in the flow caused by variations in the object
are reflected into a nearby coil, coils, Hall effect device
or other magnetic flux sensor for subsequent analysis by
suitable instrumentation and techniques.4,13
edge or end effect: In electromagnetic testing, the disturbance of the magnetic field and eddy currents due to
the proximity of an abrupt change in geometry. The
effect generally results in the masking of discontinuities
within the affected region.4,13
effective depth of penetration: In electromagnetic testing, the minimum depth beyond which a test system
can no longer practically detect a further increase in
object thickness. If the minimum thickness for the frequency used is not exceeded or the object thickness is
not rigidly controlled, the test may be influenced by the
object thickness.13 Depending on the criteria, this minimum thickness is three to seven times the skin depth.4
effective penetration: In ultrasonic testing, the maximum
depth in a material at which discontinuities can be
detected.7,10
effective throat: In welding, the weld throat including the
amount of weld penetration but ignoring excess metal
between the theoretical face and the actual face.8
elastic constants: Modulus of elasticity, either in tension,
compression or shear and Poisson’s ratio.2
elastic deformation: Temporary change in shape under a
load. The material returns to its original size and shape
after the load is removed. Elastic deformation is the
state in which most metal components are used in service.8
elastic limit: The maximum stress to which a material may
be subjected without any permanent strain remaining
on complete release of stress.2
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elasticity: The ability of a material to resume its former
shape after deformation.8
electric arc welding: Joining of metals by heating with
electric arc. Also called arc welding.8
electric field: A vector field of electric field strength or of
electric flux density.4,14
electrical center: The center established by the electromagnetic field distribution within a test coil. A constant
intensity signal, irrespective of the circumferential position of a discontinuity, is indicative of electrical centering. The electrical center may be different from the
physical center of the test coil.4,13
electrical noise: Extraneous signals caused by externally
radiated signals or electrical interferences within an
ultrasonic instrument.10 A component of background
noise.7
electrochemical corrosion: Corrosion that occurs when
current flows between cathodic and anodic areas on
metallic surfaces.2
electrode: A conductor by which a current passes into or
out of a test object.6,15
electromagnet: A soft iron core surrounded by a coil of
wire that temporarily becomes a magnet when an electric current flows through the wire.6,16
electromagnetic acoustic transducer: An electromagnetic device using Lorentz forces and magnetostriction
in conductive and ferromagnetic materials to generate
and receive acoustic signals for ultrasonic nondestructive tests.7
electromagnetic testing (ET): A nondestructive test
method for materials, including magnetic materials,
that uses electromagnetic energy, both alternating and
direct current, to yield information regarding the quality and characteristics of the tested material.4,13
electrostatic spraying: A technique of spraying wherein
the material being sprayed is given a high electrical
charge (potential) while the test piece is grounded.2
element: A chemical substance that cannot be divided into
simpler substances by chemical means. Examples are
hydrogen, lead and uranium.2
elongation: In tensile testing, the increase in the gage
length, measured after fracture of the object within the
gage length, usually expressed as a percentage of the
original gage length.2
EMAT: See electromagnetic acoustic transducer.
embrittlement: Reduction in the normal ductility of a
metal due to a physical or chemical change.2
emissivity: Variable ratio of the total energy radiated by a
given surface at a given temperature to the total energy
radiated by a blackbody at the same temperature. Surface phenomenon depending on the surface condition
and composition. Smooth materials have lower emissivities than rough or corroded materials.9
emulsification time: In liquid penetrant testing, the
period of time that an emulsifier is permitted to combine with penetrant before removal. Also called emulsifier dwell time.2
emulsifier: A liquid that combines with an oil based penetrant to make it water washable.2
emulsion: A dispersion of fine droplets of one liquid in
another that can be stabilized by the addition of an
emulsifier.2
encircling coil: In electromagnetic testing, a coil or coil
assembly that surrounds the test object. Such coils are
also called annular, circumferential or feed-through
coils.4,13 See coil technique.
endoscope: Device for viewing the interior of objects.
From the Greek words for inside view, the term endoscope is used mainly for medical instruments. Nearly
every medical endoscope has an integral light source;
many incorporate surgical tweezers or other devices.
Compare borescope.8
equilibrium diagram: A phase diagram showing the
phases present at equilibrium in a material system.8
equivalent 20/20 near vision acuity: Vision acuity with
remote viewing or other nondirect viewing that approximates 20/20 direct viewing closely enough to be considered the same for visual testing purposes.8
equivalent sphere illumination: Level of perfectly diffuse (spherical) illuminance that makes the visual task
as photometrically visible within a comparison test
sphere as it is in the real lighting environment.8
erosion: (1) Loss of material or degradation of surface quality
through friction or abrasion from moving fluids, made
worse by solid particles in those fluids or by cavitation in
the moving fluid. See wear. (2) In image processing, condition of a binary image where the pixel in the output
image is a 1 if each of its eight neighbors is a 1 in the
input image. See also closing, dilation and opening.8
erosion-corrosion: Simultaneous occurrence of erosion
and corrosion.8
ET: Electromagnetic testing.
etch cracks: Shallow cracks in hardened steel containing
high residual surface stresses produced by etching in an
acid.2,8,19
etching: A cleaning process for the controlled removal of
surface material by chemical agents before liquid penetrant application.2 Subjecting the surface of a metal to
preferential chemical or electrolytic attack in order to
reveal structural details.2
eutectic alloy: The composition in a binary alloy system
that melts at a minimum temperature. More than one
eutectic composition may occur in a given alloy
system.2
eutectic liquid: A liquid having a proportion of metals such
that two or more solid phases form at the same temperature during cooling.8
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eutectic point: Temperature and proportion of metals at
which two or more phases of a eutectic liquid form.
Compare eutectoid.8
eutectoid: Similar to eutectic but in a solid system during
cooling.8
evaluation: Process of determining the magnitude and significance of a discontinuity after the indication has been
interpreted as relevant. Evaluation determines if the
test object should be rejected, repaired or accepted.
See indication and interpretation.2,6,7
evanescent wave: A disappearing wave.7
event: A micro displacement giving rise to transient elastic
waves. See acoustic emission event.5
event counting: A measurement of the number of acoustic
emission events. Because an event can produce more
than one burst, this term is used in its strictest sense
only when conditions allow the number of events to be
related to the number of bursts.5
event rate: The number of events detected in a specified
unit of time. Term is restricted in the same way as event
counting.5
examination: The process of testing materials, interpreting
and evaluating test indications to determine if the test
object meets specified acceptance criteria.6
examination medium: A powder or suspension of magnetic particles applied to a magnetized test surface to
determine the presence or absence of surface or
slightly subsurface discontinuities.6,16
excitation coil: Coil that carries the excitation current. Also
called primary coil or winding. See detector coil.4
exfoliation: Corrosion that progresses approximately parallel to the outer surface of the metal, causing layers of
the metal to be elevated by the formation of corrosion
product.2
expanded sweep: A short duration horizontal sweep positioned to provide close examination of a particular signal or material volume.7
external discontinuities: Discontinuities on the outside or
exposed surface of a test object.2
eye sensitivity curve: Graphic expression of vision sensitivity characteristics of the human eye. In the case of a
physical photometer, the curve should be equivalent to
the standard observer. The required match is typically
achieved by adding filters between the sensitive elements of the meter and the light source.8
F
facing: Any material applied in a wet or dry condition to the
face of a mold or core to improve the surface of the
casting.3
false brinelling: Fretting wear indentations. Compare
brinelling.8
false indication: A test indication that could be interpreted
as originating from a discontinuity but which actually
originates where no discontinuity exists.7 Distinct from
nonrelevant indication.2 Compare defect.8
family: An obsolete term, formerly denoting a complete
series of materials from one manufacturer necessary to
perform a specific process of penetrant testing.2
far field: The zone beyond the near field in front of the
transducer in which signal amplitude decreases monotonically in proportion to distance from the transducer.
Also called the Fraunhofer zone.7
far vision: Vision of objects at a distance, generally beyond
arm’s length. Compare near vision.8
farsightedness: Vision acuity functionally adequate for viewing objects at a distance, generally beyond arm’s length.
Also called hyperopia. Compare nearsightedness.8
fatigue fracture: The progressive fracture of a material that
begins at a discontinuity and increases under repeated
cycles of stress. The phenomenon leading to fracture
under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material.2
feature extraction: From an enhanced image, derivation
of some feature values, usually parameters for distinguishing objects in the image.8
feed-through coil: See encircling coil.
feeder: A reservoir of molten metal connected to, but not a
part of, the casting and designed to remain liquid while
the casting is solidifying. It is located so that it will feed
liquid metal to the larger portions of the casting that are
the last to solidify. Sprues, gates, risers and runners frequently function in this manner.3
felicity effect: The appearance of significant acoustic emission at a stress level below the previous maximum applied.5
felicity ratio: The measurement of the felicity effect. Ratio
between (1) the applied load or pressure at which
acoustic emission reappears during the next application
of loading and (2) previous maximum applied load.5
ferrite: (1) Any of several magnetic substances that consist
essentially of an iron oxide combined with one or more
metals (manganese, nickel or zinc) having high magnetic
permeability and high electrical resistivity.4,25 (2) Solid
solution of one or more other elements in alpha iron.8
ferromagnetic material: Material such as iron, nickel or
cobalt whose relative permeability is considerably
greater than unity and depends on the magnetizing
force.4,14 Materials that are most strongly affected by
magnetism are called ferromagnetic.2
fiber optic borescope: See borescope, fiber optic.
fiber optics: The technology of light transmission through
crystalline fibers such as plastic, glass or quartz.8
fiberscope: Jargon for fiber optic borescope.8
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field: In video technology, one of two video picture components that together make a frame. Each picture is
divided into two parts called fields because a frame at
the rate of thirty frames per second in a standard video
output would otherwise produce a flicker discernible to
the eye. Each field contains one half of the total picture
elements. Two fields are required to produce one complete picture or frame so the field frequency is sixty
fields per second and the frame frequency is thirty
frames per second.8
field angle: The included angle between those points on
opposite sides of the beam axis at which the luminous
intensity from a theatrical luminaire is 10 percent of the
maximum value. This angle may be determined from an
illuminance curve or may be approximated by use of an
incident light meter.8,20
field flow technique: See magnetic flow technique.6
field of view: The range or area where things can be seen
through an imaging system, lens or aperture. Compare
depth of field.8
field of vision: The range or area where things can be perceived organoleptically at a point in time, assuming the
eye to be immobile.8
fill factor: For encircling coil electromagnetic testing, the
ratio of the cross sectional area of the test object to the
effective cross sectional core area of the primary encircling coil (outside diameter of coil form, not inside
diameter that is adjacent to the object).4,6,13,15 For internal probe electromagnetic testing, the ratio of the
effective cross sectional area of the primary internal
probe coil to the cross sectional area of the tube interior.4,13
fill factor effect: The effect of fill factor on coupling
between coil and test object. See coupling coefficient.4
filled crack: A cracklike discontinuity, open to the surface,
but filled with some foreign material, such as oxide,
grease, etc., that tends to prevent penetrants from
entering.2
fillet weld: Weld at the corner of two metal pieces.8
film badge: A package of photographic film worn as a
badge by radiography personnel (and by workers in the
nuclear industry) to measure exposure to ionizing radiation. Absorbed dose can be calculated by degree of
film darkening caused by irradiation.11
film holder: A light tight carrier for films and screens.11
film speed: Relative exposure required to attain a specified
density.11
filter: (1) A network that passes electromagnetic wave
energy over a described range of frequencies and attenuates energy at all other frequencies.4,13 (2) A processing component or function that excludes a selected kind
of signal or part of a signal.8
filtering: See low pass filtering.
fine crack: A discontinuity in a solid material with a very
fine opening to the surface, but possessing length and
depth greater than the width of this opening. Usually
the depth is many times the width.2
finite element analysis: A numerical technique for the
analysis of a continuous system whereby that system is
decomposed into a collection of finite sized elements.4
fit up: To secure one or more joint members with special
external fixturing to prevent movement during welding.8,19
flakes: Short discontinuous internal fissures in ferrous metals attributed to stresses produced by localized transformation and/or decreased solubility of hydrogen during
cooling usually after hot working. On a fractured surface, flakes appear as bright silvery areas; on an etched
surface they appear as short, discontinuous cracks.8,19
Also called shatter cracks and snowflakes.2
flash magnetization: Magnetization by a current flow of
brief duration. See capacitor discharge technique.6,16
flash point: The lowest temperature at which vapors above
a volatile, combustible substance ignite in air when
exposed to flame.6,16
flask: A metal or wood frame for making and holding a sand
mold. The upper part is called the cope and the lower
part is called the drag.3
flat bottom hole: A type of reflector commonly used in
reference standards. The end (bottom) surface of the
hole is the reflector.7
flaw: A rejectable anomaly or unintentional discontinuity.
See also defect and discontinuity.2
flaw inversion: A method for measuring some dimensions
of a discontinuity by the application of a mathematical
algorithm to the discontinuity signal.4
flaw location scale: A specially graduated ruler that can be
attached to an angle beam transducer to relate the position of an indication on the cathode ray tube screen to
the actual location of a discontinuity within the test
object.7
fluidity: The ability of molten metal to flow readily. Typically
measured by the length of a standard spiral casting.3
fluorescence: The emission of visible light from a material
in response to ultraviolet or X-radiation. Formerly
called cold light.8
fluorescent penetrant: A highly penetrating liquid used
in the performance of liquid penetrant testing and
characterized by its ability to fluoresce under ultraviolet light.2
fluorescent magnetic particle testing: The process using
finely divided ferromagnetic particles that fluoresce
when exposed to ultraviolet light (320 to 400 nm).6,17
fluorescent penetrant testing: Technique of liquid penetrant testing that uses fluorescent penetrant.
flux density: See magnetic flux density.
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flux indicator: A small device, generally a metal strip or
disk, containing artificial discontinuities. Used to determine when correct magnetizing conditions and/or magnetic field direction have been achieved.6
flux leakage: A local distortion of normal magnetic flux
patterns in a magnetized test object. Can be caused by
discontinuities in the test object.6
flux leakage field: The magnetic field that leaves or enters
the surface of an object.6,16
flux leakage method: A method for the detection and analysis of a surface discontinuity or near-surface discontinuity using the flux that leaves a magnetically saturated,
or nearly saturated, test object at a discontinuity.4,6
flux lines: See lines of force.
flux method: See lumen method.
flux meter: An electronic device for measuring magnetic
flux.6 See also gauss meter.
focal zone: The distance before and after the focal point in
which the intensity differs a specified amount (usually 6
dB) from the focal intensity. Also called depth of field or
depth of focus.7
focus: Position of a viewed object and a lens system relative
to one another to offer a distinct image of the object as
seen through the lens system. See accommodation and
depth of field.8
focus, principal plane of: The single plane actually in
focus in a photographic scene.8
focused beam: A sound beam that converges to a cross section smaller than that generated by a flat transducer.7
focused transducer: A transducer that produces a focused
sound beam.7
focusing, automatic: (1) Feature of camera, usually
incorporating a range finder, whereby the lens system
adjusts to focus on an object in part of the field of
view. (2) Metaphorical attribute of a borescopic
instrument’s depth of field (the range of distance in
focus). The depth of field is so great in the case of
video borescopes that focusing is unnecessary for most
applications.8
focusing, primary: Focusing of an image by the lens onto a
fiber optic bundle at the tip of a probe.8
focusing, secondary: Focusing at the eyepiece of a
borescope or other optical instrument, specifically the
manual refocusing needed when the viewing distance
changes.8
foil: Metal in sheet form less than 0.15 mm (6 × 10–3 in.)
thick.2
footcandle: Former unit of measure for illumination,
equivalent to one lumen evenly distributed over a
square foot or to a surface illumination at a distance of
one foot from a point of one candela. Abbreviated ftc or
fc. See also lux.8
footlambert: Former unit of luminance. Measured in the
SI system by candela per square meter.8
foreign materials: They may appear as isolated, irregular
or elongated variations of film density not corresponding to variations in thickness of material or to cavities.
May be sand, slag, oxide or dross metal or any material
included in the material being examined.3
forging crack: Discontinuity formed during mechanical
shaping of metal.8
foundry: An establishment or building where metal castings are produced.3
fovea centralis: Region of sharpest vision in the retina,
where the layer of blood vessels, nerve fibers and cells
above the rods and cones is far thinner than in peripheral regions.8
foveal vision: See photopic vision.
fractography: Descriptive treatment of fracture, especially
in metals, with specific reference to photographs of the
fracture surface. Macrofractography involves photographs at low magnification, microfractography at
high magnification.2
fracture: A break, rupture or crack large enough to cause a
full or partial partition of a casting.2,3
frame: A complete raster scan projected on a video screen.
There are thirty frames per second in a standard video
output. A frame may be comprised of two fields, each
displaying part of the total frame. See also field.8
Fraunhofer zone: See far field.
free carbon: The part of the total carbon in steel or cast
iron that is present in the elemental form as graphite or
temper carbon.3
frequency: The number of complete wave cycles passing a
given point per second or the number of vibrations per
second.7 Measured in hertz (Hz).
frequency, fundamental: In resonance testing, the frequency at which the wavelength is twice the thickness
of the test material.7,12
frequency, pulse repetition: The number of pulses per
second, in hertz (Hz).7
frequency, test: The nominal ultrasonic wave test frequency used in a test.7,12
Fresnel zone: See near field. Also called Fresnel field.7
fretting: Action that results in surface damage, especially in
a corrosive environment, when there is low amplitude
motion between solid surfaces in contact under pressure. Also called fretting corrosion.2
fretting corrosion: See corrosion, fretting.
fretting wear: See wear, fretting.
friction oxidation: See wear, fretting.
front surface: The first surface of a test object encountered by the incident ultrasonic beam. See interface.7
full-wave direct current: A single-phase or three-phase
alternating current rectified to produce direct current
characteristics of penetration and flow.6
furring: Buildup or bristling of magnetic particles resulting
from excessive magnetization of the test object.6,16
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G
gage pressure: Pressure above (or below if measured from
gage zero) atmospheric pressure at the measurement
location.1
gaggers: The metal supports that reinforce sand in the
cope.3
galling: A type of adhesive wear more gross than fretting.8
galvanic series: List of metals, alloys and graphite (a nonmetal) in sequence with the most anodic (easiest corroded) in liquids at one end and the most cathodic
(least easily corroded) at the other end.8
gamma iron: Iron with face centered cubic structure
formed by slow cooling of delta ferrite. This characteristic lattice structure is stable between 906 °C (1,663 °F)
and 1,390 °C (2,535 °F). Also called austenite.8
gamma rays: High energy, short wavelength electromagnetic radiation emitted by a nucleus. Energies of gamma
rays are usually between 0.01 and 10 MeV. X-rays also
occur in this energy range but are of non-nuclear origin.
Gamma radiation usually accompanies alpha and beta
emissions and always accompanies fission. Gamma rays
are very penetrating and are best attenuated by dense
materials like lead and depleted uranium.11
gas holes: Holes created by a gas evolving from molten
metal.2 Appear as round or elongated, smooth edged
dark spots, occurring individually, in clusters or distributed throughout a casting.3
gas porosity: Gas pockets or voids in metal. Refers to
porous sections in metal that appear as round or elongated dark spots corresponding to minute voids usually
distributed through the entire casting.3 Spherical or
elongated internal cavities caused by evolution of dissolved gasses from molten metal or slag trapped during
cooling and solidification of castings or fusion welds.2
gas tungsten arc welding (GTAW): Inert gas shielded arc
welding using a tungsten electrode. Also called tungsten inert gas (TIG) welding.8
gasket seal: Resilient ring, usually virgin polytetrafluoroethylene (PTFE), in a piping or tubing connection.
Compare interference sealing thread and metal-tometal seal.8
gate: (1) In ultrasonic testing, an electronic device for monitoring signals in a selected segment of the trace on an
A-scan display. (2) The interval along the baseline that
is monitored.7 (3) In casting, the channel through which
molten metal enters a mold cavity. Sometimes called
ingate.3
gated pattern: A pattern designed to include gating in the
mold.3
gauss: A customary or cgs unit of flux density or magnetic
induction. See tesla.6
gauss meter: A magnetometer that registers field strength
in gauss (or Tesla).6
general examination: A test or examination of a person’s
knowledge, typically (in the case of nondestructive testing personnel qualification) a written test on the basic
principles of a nondestructive testing method and general knowledge of basic equipment used in the method.
(According to ASNT’s guidelines, the general examination should not address knowledge of specific equipment, codes, standards and procedures pertaining to a
particular application.) Compare practical examination
and specific examination.8
geometric moiré techniques: Moiré techniques that can
be explained by geometric optics, mainly by the
mechanical obstruction of light or the scalar addition of
light.9
geometrical optics: The mathematical study of how light
rays are reflected and refracted and practical techniques based on such understanding, including the
transmission of images by lenses and mirrors. Also
called lens optics.8
ghost: An indication arising from a combination of pulse
repetition frequency and time base frequency.18 See
wrap around.7
glare: Excessive brightness (or brightness varying by more
than 10:1 within the field of view) which interferes with
clear vision, critical observation and judgment.8
glare, blinding: Glare so intense that for an appreciable
length of time after it has been removed, no object can
be seen.8,20
glare, direct: Glare resulting from high luminances or
insufficiently shielded light sources in the field of
view.8,20
glare, reflected: Glare resulting from specular reflections
of high luminances in polished or glossy surfaces in the
field of view.8,20
glossmeter: Reflectometer used to measure specular
reflectance.8,20
gooseneck: The pressure vessel or metal injection pump in
an air injection casting machine.3
gouge: Surface indentation caused by forceful abrasion or
impact or flame cutting. Also called nick. Compare tool
mark.8
grain boundary: Interface that forms between grains of
solidifying metal as the random oriented crystal lattices
meet. See grain.8
grain refiner: Any material, usually a metal from a special
group, added to a liquid metal or alloy to produce a
finer grain in the hardened metal.3
grain size: Size of the crystals in metal. When compared
with a standard, usually referred to as being fine,
medium or coarse.2
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graininess: A film characteristic that consists of the grouping or clumping together of the countless small silver
grains into relatively large masses visible to the naked
eye or with slight magnification.11
grains: (1) Solid particle or crystal of metal. As molten
metal solidifies grains grow and lattices intersect, forming irregular grain boundaries.8 (2) Individual crystals
that make up the crystalline structure of metal.2
grass: See background noise.
grating: A grid superimposed on an optical test surface to
measure displacement or deformation. See also reference grating.9
gray: SI unit for measurement of absorbed radiation dose,
absorbed by matter at a particular location and expressed in joules per kilogram (J·kg –1). Replaces the
rad.
gray level: Integer number representing the brightness or
darkness of a pixel or, as a composite value, of an image
comprised of pixels.8
graybody: Radiator whose spectral emissivity is uniform for
all wavelengths but not 1.0. See blackbody.8
green core: A sand casting core that has not been baked.3
green rot: Form of attack due to simultaneous carburization and oxidation of stainless heating elements common to nickel chromium and nickel chromium iron
alloys, especially in furnace environments.8
green sand: Core sand intended for use in a damp state.3
grid: In moiré and grid nondestructive testing, cross hatch
pattern of two sets of parallel lines, one set of lines
being perpendicular to the other; the lines in each set
are parallel to each other and spaced at fixed intervals.
The term grid also refers to the physical or real cross
line grating.9
grinding cracks: Shallow cracks formed in the surface of
relatively hard materials because of excessive grinding
heat or the high sensitivity of the material.2 Grinding
cracks typically are 90 degrees to the direction of grinding.8,19
gross porosity: In weld metal or in a casting, pores, gas
holes or globular voids that are larger and in greater
number than obtained in good practice.2,3
group velocity: The rate at which the envelope of an ultrasonic pulse (many frequencies) propagates through the
medium.7
growth: The expansion of a casting because of aging.3
H
Hadfield’s steel: An austenitic manganese specialty steel
that is easily work hardened.8
half-wave direct current: A single-phase alternating current half-wave rectified to produce a pulsating unidirectional field. Also called half-wave current.6,16
halide: A compound of two or more elements, one of which
is a halogen.1
halitation: Rings of light visible around a spot on a video
screen where an electron scanning beam is held.8
Hall detector: A semiconductor element that produces an
output electromotive force proportional to the product
of the magnetic field intensity and a biasing current.4
Hall effect: A potential difference developed across a conductor at right angles to the direction of both the magnetic field and the electric current. Produced when a
current flows along a rectangular conductor subjected
to a transverse magnetic field.6,15
halogen: Any of the nonmetallic elements — fluorine,
chlorine, bromine and iodine — or any gaseous chemical component containing one or more of these elements.
halogen leak detector: A leak detector that responds to
halogen containing tracer gases. Normally not very sensitive to the elemental halogen gases, but are very good
when they are used with a gas that contains halogen.1
Also called a halogen sensitive leak detector or a halide
leak detector.1
halogen sniffer test: A pressure leak test in which the
leakage of a component, pressurized with a halogen
rich mixture, is detected by scanning over the test
object boundary surface with a probe connected to a
halogen leak detector. Halogen gas is pulled from the
leak through the probe inlet to the sensing element to
cause a visible or audible signal on the indicator of the
leak test instrument.1
halogen standard leak: A standard leak in which the contained gas is a halogen tracer gas compound.1
hardness: Resistance of metal to plastic deformation, usually by indentation. However, the term may also refer to
stiffness or temper or to resistance to scratching, abrasion or cutting.2
harmonic: A vibration frequency that is an integral multiple of the fundamental frequency.7,10
harmonic analyzer: A mechanical device for measuring
the amplitude and phase of the various harmonic components of a periodic function from its graph.4,14
harmonic distortion: Nonlinear distortion characterized
by the appearance in the output of harmonics other
than the fundamental component when the input wave
is sinusoidal.4,13
hash: See background noise.
head shot: Producing circular magnetization by passing
current directly through the test object. Commonly
done while holding the object between the headstock
and tailstock of a wet horizontal magnetic particle testing system.6
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heading: Upsetting wire, rod or bar stock in dies to form
parts having some of the cross sectional area larger than
the original. Examples are bolts, rivets and screws.8,19
heads: The clamping contacts on stationary magnetic particle systems.6,10
heat: The energy associated with the random and chaotic
motions of the atomic particles from which matter is
composed. All materials (hot or cold) contain heat and
radiate infrared energy. The unit for measuring heat is
the joule (J), equal to about 0.24 calorie (cal) or
9.481 × 10 –4 British thermal units (BTUs). Compare
infrared radiation and temperature.9
heat affected zone (HAZ): Base metal not melted during
brazing, cutting or welding, but whose microstructure
and physical properties were altered by the heat.2
heat checking: Surface cracking caused when metal
rapidly heated (or cooled and heated repeatedly) is prevented from expanding freely by colder metal below
the surface. Friction may produce the heat. Sometimes
called thermal fatigue.8
heat treatment: Heating and cooling a metal or alloy in
such a way as to obtain desired conditions or properties.
Heating for the sole purpose of working is excluded
from the meaning of this definition.2,3
heat wave: Thermally produced variation in flue gas density that distorts images of objects in a firebox.8
helium leak detector: A leak detector that responds to
helium tracer gas.1
helium mass spectrometer leak detector: Mass spectrometer constructed to be peaked for response to
helium gas.
hertz: The unit of frequency equivalent to one cycle per
second.4,7,10,14
high temperature penetrant: A penetrant material specifically designed for use on high temperature surfaces
where conventional penetrant would be unsatisfactory.2
hindered contraction: Contraction where the geometry
will not permit a casting to contract in certain regions in
keeping with the coefficient of expansion of the metal
being cast.3
holes: Any void remaining in an object as a result of
improper manufacturing processing. Often called gas
holes, cavities or air locks.2
homogenizing: Holding at high temperature to eliminate
or decrease chemical segregation by diffusion.2
hood test: A quantitative leak test in which a test object
under vacuum test is enclosed by a hood filled with
tracer gas so as to subject all parts of the test object to
examination for leakage at one time. A form of dynamic
leak testing in which the entire enclosure or a large portion of its external surface is exposed to the tracer gas
while the interior is connected to a leak detector with
the objective of determining the existence of leakage.1
horizontal linearity: In ultrasonic testing, a measure of
the proportionality between the positions of the indications appearing on the horizontal trace and the positions of their sources.7
horn gate: A curved gate shaped like a horn and arranged
to permit entry of molten metal at the bottom of casting
cavity.3
horseshoe coil: A probe coil in which the ferrite core of the
coil is horseshoe shaped. Also called a U coil or U-core
coil.4
horseshoe magnet: A bar magnet bent into the shape of a
horseshoe so that the two poles are adjacent. Usually
the term applies to a permanent magnet.6,10
hot cracks: Ragged dark lines of variable width and
numerous branches. They have no definite line of continuity and may exist in groups. They may originate
internally or at the surface.3 Cracks occurring in hot
solid metals, caused by stresses of thermal expansion
or contraction and originating either internally or at
the surface.2
hot thermionic ionization gage: Positive ion current
flowing from a tungsten or thorium coated filament to
a cylindrical grid collector is proportional to gas density over the absolute pressure range below 100 mPa
(10–3 torr).
hot spot: The point of retarded solidification caused by an
increased mass of metal at the juncture of two sections.
It frequently results in shrinkage and inferior mechanical properties at this location.2,3
hot tear: A fracture formed in a metal during solidification
because of hindered contraction. Surface cracks on
castings produced by contraction of the metal during
cooling.2,3 Hot tears often occur where areas of different thickness adjoin.8
hot working: Deforming metal plastically at temperature
and rate such that strain hardening does not occur. Low
temperature limit is recrystallization temperature.2
hue: Characteristic of light at a particular bandwidth that
gives a color its name.8
hundred percent testing: See one hundred percent testing.
hydrogen embrittlement: A condition of low ductility in
metals resulting from the absorption of hydrogen.2
hydrophilic emulsifier or remover: Water base materials
used for excess surface penetrant removal.2
hyperthermia: Heating so excessive that it can damage or
kill plant or animal cells.8
hysteresis: (1) The lagging of the magnetic effect when the
magnetizing force acting on a ferromagnetic body is
changed. (2) The phenomenon exhibited by a magnetic
system wherein its state is influenced by its previous
history.6
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hysteresis loop: A curve showing flux density B plotted as a
function of magnetizing force H as magnetizing force is
increased to the saturation point in both negative and
positive directions sequentially. The curve forms a characteristic S shaped loop. Intercepts of the loop with the
B-H axis and points of minimum and maximum magnetizing force define important magnetic characteristics
of a material.6,10
I
IACS: The International Annealed Copper Standard. A
conductivity measurement system in which the conductivity of annealed, unalloyed copper is arbitrarily rated
at 100 percent and the conductivities of other materials
are expressed as percentages of this standard.26 The
% IACS is equivalent to 172 divided by the material
resistivity in microohm centimeters.4
icicles: A coalescence of metal protruding beyond the root
of the weld. Sometimes called burn through.2
ID coil: A coil or coil assembly used for electromagnetic
testing by insertion into the test piece, as with an inside
probe for tubing. Also called inside coils or bobbin
coils.4,13
ideal gas: Gas that obeys the general gas laws for ideal
gases. Also called perfect gas.1
illuminance: The density of luminous flux on a surface.
Measured in the SI system by lux.8
illuminate: Shed light on.8
illumination: The act of illuminating or state of being illuminated. See also illuminate. Compare illuminance.8,20
image: Visual representation of a test object or scene.8
image enhancement: Any of a variety of image processing
steps, used singly or in combination to improve the
detectability of objects in an image.8
image guide: Fiber bundle that carries the picture formed
by the objective lens at the distal end of a fiber optic
borescope back to the eyepiece.8
image orthicon: Television tube that uses the photoemission method. Compare vidicon tube.8
image processing: Actions applied singly or in combination to an image, in particular the measurement and
alteration of image features by computer. Also called
picture processing.8
image quality indicator: Penetrameter.
image segmentation: Process in which the image is partitioned into regions, each homogeneous.8
immersion technique: The ultrasonic technique in which
the test object and the transducer are submerged in a
liquid (usually water) that acts as the coupling
medium.12 The transducer is not usually in contact with
the test object.7
impedance: The total opposition that a circuit presents to
the flow of an alternating current, specifically the complex quotient of voltage divided by current.4,13
impedance analysis: In electromagnetic testing, an analytical method that consists of correlating changes in the
amplitude, phase, quadrature components or all of
these, of a complex test signal voltage to the electromagnetic conditions within the test object.4,13
impedance plane diagram: A graphical representation
(real part along the horizontal axis and imaginary part
along the vertical axis) of the locus of points indicating
the variations in the impedance of a test coil as a function of basic test parameters.4,13
impedance, acoustic: A mathematical quantity used in
computation of acoustic reflection and transmission
characteristics at boundaries. It is expressed as the
product of wave velocity and density.7,21
impregnation: (1) The treatment of porous castings with a
sealing medium to stop pressure leaks. (2) The process
of filling the pores of a sintered compact, usually with a
liquid such as a lubricant. (3) The process of mixing
particles of a nonmetallic substance in a matrix of metal
powder, as in diamond impregnated tools.3
impurities: Elements or compounds whose presence in a
material is unintentional.2,3
in control: Within prescribed limits of process control.8
in-motion radiography: Technique in which either the
object being radiographed or the source of radiation is
in motion during the exposure.3,11
incandescence: The emission of visible radiation due to
thermal excitation.8
incandescent: Emitting visible radiation as a result of heating.8
inclusion: Foreign particles or impurities, usually oxides,
sulfides, silicates and such, that are retained in metal
(welds or castings) during solidification or that are
formed by subsequent reaction of the solid metal.2,3
incomplete fusion: Fusion that is less than complete. Failure of weld metal to fuse completely with and bond to
the base metal or preceding bead.2
incomplete penetration: In welding, root penetration that
is less than complete or failure of a root pass and a backing pass to fuse with each other.2 Also called lack of
fusion.2
incremental permeability: The ratio of the change in
magnetic induction to the corresponding change in
magnetizing force when the mean induction differs
from zero.4,14
indication: A nondestructive testing discontinuity response
that requires interpretation to determine its relevance.
Compare defect, discontinuity and false indication.8
indication, discontinuity: The visible evidence of a material discontinuity. Subsequent interpretation is required
to determine the significance of an indication.2
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indication, false: An indication produced by something
other than a discontinuity. Can arise from improper test
procedures.6
indication, nonrelevant: An indication due to misapplied
or improper testing. May also be an indication caused
by an actual discontinuity that does not affect the
usability of the object (a change of section, for
instance).2
indication, relevant: An indication from a discontinuity
(as opposed to a nonrelevant indication) requiring evaluation by a qualified inspector, typically with reference
to an acceptance standard, by virtue of the discontinuity’s size or location.8,22
induced current technique: See current induction technique.
induced magnetization: A magnetic field generated in an
object when no direct electrical contact is made.6,16
induction: The magnetism produced in a ferromagnetic
body by some outside magnetizing force.6,10
inductor: A device consisting of one or more associated
windings, with or without a magnetic core, for introducing inductance into an electric circuit or material.4,14
inert gas: Gas that does not readily combine with other
substances. Examples are helium, neon and argon.1
inert gas shielded arc welding: Joining of metals by heating them with an electric arc between the electrode(s)
and the work piece, using an inert gas to shield the electrode(s). See also gas tungsten arc welding.8
infrared: Below red, referring to radiation of frequency
lower than the color red. See infrared radiation.9
infrared and thermal testing: Nondestructive testing that
uses heat or infrared radiation as interrogating energy.
infrared cameras: Radiometer that collects infrared radiation to create an image.9
infrared radiation: Radiant energy below the color red, of
wavelengths longer than 770 nm, between the visible
and microwave regions of the electromagnetic spectrum.8,9,20
infrared thermography: Imaging by infrared radiation.
See infrared radiation. Compare thermography.9
ingate: See gate.
inherent discontinuities: Discontinuities that are produced in the material at the time it is formed (for example, during solidification from the molten state).2
inherent fluorescence: Fluorescence that is an intrinsic
characteristic of a material.6,16
initial permeability: The slope of the induction curve at
zero magnetizing force as the test object is removed
from a demagnetizing condition (slope at the origin of
the B-H curve before hysteresis is observed).4,13
initial pulse: The electrical pulse applied to excite an ultrasonic transducer. The first indication on the screen if
the sweep is undelayed. Also called the main bang. May
also refer to the acoustic pulse generated by the electrical pulse.7
inlet: The opening, flange, connection or coupling on a leak
detector or leak testing system through which tracer gas
may enter from a leak in a test object.1
inserted coil: See ID coil. Also called inside coil.4,13
insonification: Irradiation with sound.7
inspection medium: See examination medium.
inspection: See examination.
integrated leakage rate test (ILRT): The leakage test
performed for an entire system or component by pressurizing the system to the calculated peak containment
internal pressure related to the design and determining
the overall integrated leakage rate.1
intensity, radiant: The luminous flux per steradian emanating from a visible source, measured in lm·sr–1. Also,
from a nonvisible source, the radiant flux per steradian
emanating from that source and measured in W·sr–1.
interface: The boundary between two adjacent media.7,10
interface triggering: In ultrasonic testing, triggering the
sweep and auxiliary functions from an interface echo
occurring after the initial pulse. Also called IF synchronization.7
interference fitted thread: See interference sealing
thread.
interference objective: Small, metallized glass mounted
in contact with the test object and adjustable for tilt to
control fringe spacing.8
interference sealing thread: Piping seal using a tapered
connection made under great pressure, forcing mating
surfaces together more tightly than is possible by hand
alone. Compare gasket seal and metal-to-metal seal.8
intergranular corrosion: Corrosion occurring preferentially at grain boundaries.2
intergranular stress corrosion cracking: An anomaly
caused by intergranular corrosion as a result of sensitized material, stress and corrosive environment (typical in the heat affected zone of stainless steel welds).
interlaced scanning: A process whereby the picture
appearing on a video screen is divided into two parts.
Interlaced scanning reduces flicker by increasing the
electron beam’s downward rate of travel so that every
other line is sent. When the bottom is reached, the
beam is returned to the top and the alternate lines are
sent. The odd and even line scans are each transmitted
at 1/60 s, totaling 1/30 s per frame and retaining the
standard rate of 30 frames per second. The eye’s persistence of vision allows the odd and even lines to appear
as a single image without flicker.8
internal conductor: See central conductor.
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interpretation: The determination of the significance of
test indications from the standpoint of their relevance
or irrelevance. The determination of the cause of an
indication or the evaluation of the significance of discontinuities from the standpoint of whether they are
detrimental or inconsequential.2
interstitial alloy: Alloy in which the atoms of the alloying
element fit into the spaces between the atoms of the
parent metal.8
inverse segregation: Segregation in cast metal in which an
excess of lower melting constituents occurs in the earlier freezing portions, apparently the result of liquid
metal entering cavities developed in the earlier solidified metal.3
inverse square law: From a point source of radiation, the
intensity of energy arriving at a point of interest varies
as the inverse square of distance from source.3,11
investment casting: (1) Casting metal into a mold produced by surrounding (investing) an expendable pattern with a refractory slurry that sets at room
temperature after which the wax, plastic or frozen mercury pattern is removed. Also called precision casting or
lost wax process. (2) A casting made by the process.3
investment compound: A mixture of graded refractory
filler, a binder and a liquid vehicle, used to make molds
for investment castings.3
investment molding: A method of molding by using a pattern of wax, plastic or other material invested or surrounded by a molding medium in slurry or liquid form.
After the molding medium has solidified, the pattern is
removed by subjecting the mold to heat. Also called lost
wax process or precision molding.3
ion current: The current that flows at all times from the
positive emitter (heater) to the negative cathode collector of the heated anode (alkali ion) halogen vapor
detector. This current increases in the presence of halogenated gases.1
ionizing radiation: Any radiation that directly or indirectly
displaces electrons from the outer domains of atoms.
Examples include alpha, beta and gamma radiation.11
IQI: Image quality indicator. See penetrameter.
IR: Infrared and thermal testing.
iris: Ring of variable area around the pupil and in front of
the lens of the eye. The surface area of the iris adjusts
spontaneously to change the amount of light entering
the eye.8
irradiance: Power of electromagnetic radiant energy incident on the surface of a given unit area. Compare radiance.8
Ishihara™ plates: Trade name for a kind of pseudoisochromatic plates.8
isotropy: A condition in which significant medium properties
(velocity, for example) are the same in all directions.7
J
Jaeger eye chart: An eye chart used for near vision acuity
examinations.8
joint: The part of the mold where the cope and cheek, cope
and drag or cheek and drag come together.3
joint efficiency: The strength of a welded joint expressed
as a percentage of the strength of the unwelded base
metal.2
joint penetration: The distance weld metal and fusion
extend into a joint.2
K
Kaiser effect: The absence of detectable acoustic emission
until the previous maximum applied stress level has
been exceeded.5
keeper: Ferromagnetic material placed across the poles of
a permanent magnet to complete the magnetic circuit
and prevent loss of magnetism.6,15
kinetic vision acuity: Vision acuity with a moving target.
Studies indicate that 10 to 20 percent of visual efficiency can be lost by target movement.8
L
laboratory microscope: Conventional compound microscope. See microscope and microscope, compound.8
lack of fusion: Discontinuity due to lack of union between
weld metal and parent metal or between successive
weld beads.2 Also called incomplete penetration.
Lamb wave: A type of ultrasonic wave propagation in
which the wave is guided between two parallel surfaces
of the test object. The mode and velocity depend on the
product of the test frequency and the separation
between the surfaces. Also called plate waves.7
lambertian: Having a surface that diffuses light uniformly
rather than reflecting it. Matte. Most objects have a
lambertian surface. Compare specular.8
laminated pole pieces: See articulated pole pieces.
lamination: Discontinuity in plate, sheet or strip caused by
pipe, inclusions or blowholes in the original ingot. After
rolling, laminations are usually flat and parallel to the
outside surface. Laminations may also result from pipe,
blisters, seams, inclusions or segregation elongated and
are made directional by working. Lamination discontinuities may also occur in metal powder compacts.2 May
appear in the form of rectangles or plates as inclusion
stringers between rolled surfaces. Short, intermittent
laminations may be detrimental if the object is subjected to high bending stresses in service.6
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lap: Surface discontinuity, usually parallel to the surface,
appearing as a fold or tangential seam in a wrought
product and caused by folding over of a hot metal fin or
sharp corner in a thin plate, then rolling or forging it
into the surface but not welding it. See also cold shut.2,6
laser: An acronym (light amplification by stimulated emission of radiation). The laser produces a highly monochromatic and coherent (spatial and temporal) beam of
radiation. A steady oscillation of nearly a single electromagnetic mode is maintained in a volume of an active
material bounded by highly reflecting surfaces, called a
resonator. The frequency of oscillation varies according
to the material used and by the methods of initially
exciting or pumping the material.8,20
leak: An opening that allows the passage of a fluid.1,27
leak detector: A device for detecting, locating, and/or
measuring leakage.1
leak testing (LT): Nondestructive testing method for detecting, locating or measuring leaks or leakage in pressurized
or evacuated systems or components.1
leakage: The measurable quantity of fluid escaping from a
leak.1
leakage design basis accident: The calculated peak containment internal pressure related to the design basis
accident.1
leakage field: See magnetic leakage field.
leakage flux: Magnetic flux of the coil that does not link
with the test object. The magnetic flux that leaves a saturated or nearly saturated object at a discontinuity.4
leakage rate: The quantity of leakage fluid per unit time
that flows through a leak at a given temperature as a
result of a specified pressure difference across the
leak.1 See throughput.
leaker penetrant: A penetrant especially designed for leak
detection.2
leeches: Permanent magnets or electromagnets attached to
electrodes carrying magnetizing current, to provide
strong electrode contact.6,16
lens: Translucent object that refracts light passing through
it in order to focus the light on a target.8
lens optics: See geometrical optics.
level, acceptance: In contrast to rejection level, test level
above or below which, depending on the test parameter, test objects are acceptable.2
level, rejection: The value established for a test signal
above or below which, depending on the test parameter, test objects are rejectable or otherwise distinguished from the remaining objects.2 See level,
acceptance.
lifting power: The ability of a magnet to lift a piece of ferritic steel by magnetic attraction alone.6,15
liftoff: Distance between the probe coil and the test
object.4
liftoff effect: In an electromagnetic test system output, the
effect observed due to a change in magnetic coupling
between a test object and a probe coil whenever the
distance between them is varied.4,13
light: Radiant energy that can excite the retina and produce
a visual sensation. The visible portion of the electromagnetic spectrum, from about 380 to 770 nm.8,20
light adapted vision: See photopic vision.
light guide bundle: Bundle of filaments, usually glass, that
carries noncoherent light from a high intensity source
through a fiber optic borescope to illuminate the
object.8
light metal: One of the low density metals such as aluminum, magnesium, titanium, beryllium or their
alloys.2
lighting, back: Placement of light source and image sensor
on opposite sides of the test object, used when the silhouette of a feature is important.8
lighting, flash: See lighting, strobe.
lighting, front: Placement of light source and image sensor
on the same side of the test object.8
lighting, strobe: Lighting that flashes 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.8
lighting, structured: Combining a light source with optical elements to form a line or sheet of light.8
limited certification: Individuals who are certified only for
specific operations are usually called limited Level (I, II
or III) or are designated as having limited certification
because they are not qualified to perform the full range
of activities expected of personnel at that level of qualification.8
line pair: Pair of adjacent, parallel lines used to evaluate
the resolution of a specific imaging system. See also
minimum line pair.8
linearity, amplitude: A measure of the proportionality of
the signal input to the receiver and the amplitude of the
signal appearing on the display of an ultrasonic instrument or on an auxiliary display.7,23,24
linearity, area: In ultrasonic testing, constant proportionality between the signal amplitude and the areas of equal
discontinuities located at the same depth in the far
field. Necessarily limited by the size of the ultrasonic
beam and configuration of the reflector.7
lines of force: A conceptual representation of magnetic flux
based on the line pattern produced when iron filings are
sprinkled on paper laid over a permanent magnet.6,16
lipophilic removers: An oil base material that disperses
into a penetrant through solvent action, creating a mixture that is emulsifiable in water, facilitating its removal
by a water wash.2
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liquid crystals: Cholesteric liquids whose optical properties cause them to reflect vivid spectral colors for temperature changes. Their adjustable response is sensitive
and can be made to change from red to blue over a temperature gradient as small as 1 °C (1.8 °F).9
liquid penetrant: See penetrant.
liquid penetrant testing (PT): Nondestructive testing
method using penetrant.
location plot: A representation of acoustic emission
sources computed using an array of transducers.5
logarithmic decrement: The natural logarithm of the
ratio of the amplitudes of two successive cycles in a
damped wave train.7
longitudinal direction: The principal direction of flow in a
worked metal.2
longitudinal magnetic field: A magnetic field wherein
the flux lines traverse the component in a direction
essentially parallel with its longitudinal axis.6,16
longitudinal magnetization: Magnetization in which the
flux lines traverse the component in a direction essentially parallel to its longitudinal axis.6,15
longitudinal wave: See compressional wave.7
loose piece: A core positioned near, but not fastened to, a
die and arranged to be ejected with the casting. The
loose piece may be removed and used repeatedly for
the same purpose. Also, it is similarly used in or on patterns, core boxes and permanent molds.3
loss of back reflection: Absence or significant reduction of
an indication from the back surface of the test object.7,10
lost-wax process: An investment casting process in which a
wax pattern is used.3
lot tolerance percent defective: In quality control, the
percent defective at which there is a 10 percent probability of acceptance in a production run.8
low pass filtering: A linear combination of pixel values to
smoothen abrupt transitions in a digital image. Also
called smoothing.8
LOX-safe penetrant: A penetrant material or system
specifically designed to be compatible with or nonreactive in the presence of liquid oxygen.2
LT: Leak testing.
lumen: Luminous flux per steradian from a source whose
luminous intensity is 1 candela. Symbolized lm.8
lumen method: A lighting design procedure used for predetermining the relation between the number and
types of lamps or luminaires, the room characteristics
and the average illuminance on the work plane. It takes
into account both direct and reflected flux. Also called
flux method.8,20
luminance: The ratio of a surface’s luminous intensity in a
given direction to a unit of projected area. Measured in
candela per square meter.8
luminosity: The luminous efficiency of radiant energy.8
luminous efficacy: The ratio of the total luminous flux of a
light source to the total radiant flux or to the power
input. Sometimes called luminous efficiency.8
luminous efficiency: See luminous efficacy.
luminous flux: Radiant energy’s time rate of flow. Measured in lumens.8
luminous intensity: Luminous flux on a surface normal to
the direction from its light source, divided by the solid
angle the surface subtends at the source. Measured in
candela. Also known as candlepower.8
lux: Unit of measure for illuminance in SI. Equivalent to
lumens per square meter and symbolized lx. Formerly
known as meter-candle.8
M
machine vision: Automated system function of acquiring,
processing and analyzing images to evaluate a test object
or to provide information for human interpretation. A
typical system consists of a light source, a video camera,
a video digitizer, a computer and an image display.8
macroshrinkage: A casting discontinuity, detectable at
magnifications not exceeding ten diameters, consisting
of voids in the form of stringers shorter than shrinkage
cracks. This discontinuity results from contraction during solidification where there is not an adequate opportunity to supply filler material to compensate for the
shrinkage. It is usually associated with abrupt changes
in section size.2,3
macrostructure: The structure of metals as revealed by
examination of the etched surface of a polished object
at a magnification not exceeding ten diameters.2
macular lutae: Irregular, diffuse ring of yellow pigment
which partly overlaps the fovea and surrounds it to
around 10 degrees and which absorbs blue light, thus
changing the color of the light reaching receptors
beneath.8
magnetic circuit: The closed path followed by any group
of magnetic flux lines.6,15
magnetic field: Space in which the magnetic force is
exerted within and surrounding a magnetized object.6,10
magnetic field indicator: A device used to locate or determine relative intensity of a flux leakage field.6,16
magnetic field leakage: See flux leakage field.
magnetic field strength: The measured intensity of a
magnetic field at a specific point. Expressed in amperes
per meter or oersted.6
magnetic flow technique: Closing the magnetic circuit of
an electromagnet with a test object or portion of it.
Resulting field is longitudinal in direction.6 See longitudinal magnetization.
magnetic flux: The total number of lines of magnetic force
existing in a magnetic circuit.6,15
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magnetic flux density: The normal magnetic flux per unit
area. Expressed in tesla or gauss.6,15
magnetic flux leakage: See flux leakage field.
magnetic leakage field: See flux leakage field.
magnetic leakage flux: Exiting of magnetic lines of force
from the surface of a test object.4,14
magnetic particle test system: Equipment providing the
electric current and magnetic flux necessary for magnetic particle discontinuity detection.6,15
magnetic particle testing (MT): A nondestructive test
method using magnetic leakage fields and indicating
materials to disclose surface and near surface discontinuities.6,16
magnetic particles: Finely divided ferromagnetic material
capable of being individually magnetized and attracted
to flux leakage fields.6,16
magnetic permeability: See permeability.
magnetic powder: Magnetic particles in dry or powder
form with size and shape suitable for discontinuity
detection.6,15
magnetic rubber: A specially formulated testing medium
containing magnetic particles. Used to obtain replica
castings of component surfaces with discontinuities
being reproduced within the replica.6,15
magnetic saturation: That degree of magnetization where a
further increase in magnetizing force produces no significant increase in magnetic flux density in an object.4,13
magnetic writing: A nonrelevant indication sometimes
caused when the surface of a magnetized object comes
in contact with another piece of ferromagnetic material
or a current carrying cable.6,16
magnetism: (1) The ability of a magnet to attract or repel
another magnet or to attract a ferromagnetic material.
(2) A force field surrounding conductors carrying electric current.6,17
magnetization: The process by which elementary magnetic domains of a material are aligned predominantly
in one direction.6
magnetizing current: The electric current passed through
or adjacent to an object that gives rise to a designated
magnetic field.6
magnetizing force: The magnetizing field strength applied
to a ferromagnetic material to produce magnetism.6,16
magnetometer: A device for measuring the strength of
magnets or magnetic fields.6,17
magnitude: The absolute value of a complex number without reference to the phase of the quantity.4
malleability: The characteristic of metals that permits plastic deformation in compression without rupture.2
malleable cast iron: A cast iron made by a prolonged
anneal of white cast iron in which decarburization or
graphitization or both, take place to eliminate some or
all of the cementite. The graphite is in the form of temper carbon.3
manipulator: In immersion testing, a device for angular orientations of the transducer.7,21
manometer: Instrument, usually a U shaped tube containing water or mercury, for measuring pressure (or pressure differentials) of gases and vapors. The difference
in liquid column height in the two vertical arms of the
U-tube indicates the pressure difference.1
manual zero: A control on a test instrument that allows the
user to zero the instrument panel meter.1
markers: In ultrasonic testing, a series of indications on the
horizontal trace of a display screen that show increments
of time or distance.7,21
martensite: (1) Acicular (needlelike) microstructure produced by fast cooling or quenching of metals and alloys
such as steel. (2) The hard steel with such microstructure produced by fast cooling of austenite.8
mask: (1) A spatial filter in the sensing unit of a surface
inspection system. (2) An n × n square matrix with different values that serves as a filter in image processing.8
masking: The covering of a portion of a test object so as to
prevent tracer gas from entering leaks that may exist in
the covered section.1
mass spectrometer leak detector: Mass spectrometer
with design factors optimized to produce an instrument
that has high sensitivity to a single tracer gas.1
match bend effect: Optical illusion whereby an area of
uniform brightness appears to be nonuniform because
of contrast with the brightness of an adjacent area.8
match plate pattern: A sand molding pattern partly on the
cope side and partly on the drag side of the plate that
forms the parting between the cope and drag sections
of the molding flask. Permanent forms for runners,
gates, sprue and riser locations and sometimes complete risers, are included. Such a pattern usually is
made of aluminum and is used extensively with molding
machines.3
match plate: A plate of metal or other material on which
patterns for metal castings are mounted or formed as an
integral part so as to facilitate the molding operation.
The pattern is divided along its parting plane by the
plate.3
material noise: Random signals caused by the material
structure of the test object.10 A component of background noise.7
material, ferromagnetic: A material that exhibits the phenomena of magnetic hysteresis and saturation and
whose magnetic permeability is dependent on the magnetizing force.2
material, nonferromagnetic: A material that is not magnetizable and not responsive to magnetic field tests.2
mathematical morphology: Image processing technique
of expanding and shrinking. The basic operators in
mathematical morphology are dilation (expanding),
erosion (shrinking), opening and closing.8
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matte: Tending to diffuse light rather than reflect it; not
shiny. Also called lambertian. The term matte is generally applied to smooth surfaces or coatings. Compare
specular.8
maximum burst amplitude: The maximum signal amplitude within the duration of the burst.5
Maxwell’s equations: The fundamental equations of macroscopic electromagnetic field theory.4,14
mean free path: Average distance a gas molecule travels
between successive collisions with other molecules in
the gas or vapor state.1
measurement system: The entire system from sensor to
display inclusive.1
mechanical properties: The properties of a material that
reveal its elastic and inelastic behavior where force is
applied, thereby indicating its suitability for mechanical
applications (for example, modulus of elasticity, tensile
strength, elongation, hardness and fatigue limit).2
melting point coatings: Coatings that melt at some specific temperature. Anomalies are usually associated
with a temperature increase, so the materials melt first
over anomalies. Melting point compounds also are
comparatively insensitive and require relatively high
surface temperatures.9
meniscus method: A convex glass lens placed in contact
with an optically flat glass platen. A dyed liquid
between lens and platen forms a meniscus shaped film
of liquid. This film has zero thickness at the central
point of contact between lens and platen. A nonfluorescent or colorless spot appears at this point of contact,
the spot diameter being a function of a dye constant
and dye concentration.2
mesopic vision: Vision adapted to a level of light between
photopic at 3.4 × 10–2 cd·m–2 (3.2 × 10–3 cd·ft–2) and
scotopic at 3 × 10–5 cd·m–2 (2.7 × 10–6 cd·ft–2).8
metal-to-metal seal: Piping seal in which the mating surfaces on the external connection (the pin) and internal
connection (the box) are machined to provide a pressured interference fit 360 degrees around the connection. Compare gasket seal and interference sealing
thread.8
metallic discontinuity: A break in the continuity of the
metal of an object. May be located on the surface (e.g.,
a crack) or deep in the interior of the object (e.g., gas
pocket).2
metallograph: Short term for metallographic microscope.8
metallographic microscope: See microscope, metallographic.
metallography: The science dealing with the constitution
and structure of metals and alloys as revealed by the
unaided eye or by such tools as low powered magnifications, optical microscope, electron microscope and
X-ray diffraction.2
metallurgical microscope: See microscope, metallurgical.
metallurgy: The science and technology of metals.2
micro: A prefix that divides a basic unit of measure by one
million.2
microborescope: See borescope, micro-.
microfissure: A crack of microscopic proportions.2
micrograph: A graphic reproduction of the surface of a
prepared object, usually etched, at a magnification
greater than ten diameters. If produced by photographic means it is called a photomicrograph (not a
microphotograph).2
microporosity: Porosity visible only with the aid of a
microscope.2
microscope: An instrument that provides enlarged images
of very small objects.8
microscope, compound: Conventional microscope, using
geometrical optics for magnification. Also called laboratory microscope.8
microscope, interference: Magnifier using the wavelength of light as a unit of measure for surface contour
and other characteristics.8
microscope, metallographic: Metallurgical microscope
designed for both visual observation and photomicrography of prepared surfaces of opaque materials at magnifications ranging from about 25 to about 3,000
diameters.2 Also called a metallograph.
microscope, metallurgical: Microscope designed with
features suited for metallography.8
microscope, phase contrast: Laboratory microscope with
two additional optical elements to transmit both
diffracted and undiffracted light, revealing refractive
index discontinuities in a completely transparent test
object.8
microscope, polarizing: Microscope with polarizing elements to restrict light vibration to a single plane for
studying material with directional optical properties. As
fibers, crystals, sheet plastic and materials under strain
are rotated between crossed polarizers on the microscope stage, they change color and intensity in a way
that is related to their directional properties.8
microscopic stresses: Residual stresses that vary from tension to compression in a distance (presumably approximating the grain size) that is small compared to the
gage length in ordinary strain measurement. Hence,
not detectable by dissection method. Can sometimes
be measured by X-ray shift.2
microsegregations: (1) Segregation within a grain, crystal
or small particle. Also called coring.2 (2) Extremely narrow cracks, usually long and straight, on the surfaces of
highly finished wrought metals. Often very shallow,
their identity must be established to ensure that the
indications are not from detrimental cracks, deep laps
or long inclusion stringers.6
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microshrinkage: A casting discontinuity, not detectable at
magnifications lower than ten diameters, consisting of
interdendritic voids. This discontinuity results from
contraction during solidification where there is not an
adequate opportunity to supply filler material to compensate for shrinkage. Alloys with a wide solidification
temperature range are particularly susceptible.2,3
microstructure: The structure of polished and etched
metal as revealed by a microscope at a magnification
greater than ten diameters.2
microwave testing: Nondestructive testing method that
uses, for its probing energy, electromagnetic radiation
of frequencies from 0.3 to 300 GHz, with wavelengths
from 1 mm to 1 m.4
miniature angle beam block: A specific type of reference
standard used primarily for angle beam, but also for
straight beam and surface wave calibration.7,12
miniature borescope: See borescope, miniature.
miniborescope: Jargon for miniature borescope.8
minimum line pair: The closest distance that a specific imaging system can resolve between a pair of adjacent, parallel
lines (line pair) used to evaluate system resolution.8
misrun: A casting not fully formed, resulting from the
metal solidifying before the mold is filled.3
MKSA: A system of units for mechanics and electromagnetics in which the basic units are meter, kilogram, second
and ampere. It is a constituent part of the SI system of
units.4,14
mode: The manner in which an acoustic wave is propagated, as characterized by the particle motion in the
wave (shear, Lamb, surface or longitudinal).7,10
mode conversion: A change of ultrasonic wave propagation mode upon reflection or refraction at an interface.7
mode of vibration: Type of wave motion. Three common
modes used in ultrasonic testing are longitudinal, transverse and surface wave.7,21
model, analytical: A representation of a process or phenomenon by a set of solvable equations.4,14
modulus of elasticity: The ratio between stress and strain
in a material deformed within its elastic range.8
modulus of rupture: Nominal stress at fracture in a bend
test or torsion test.2
moiré: Optical patterns caused by the beating of two
superimposed gratings. Moiré fringes usually appear
as alternating bright and dark bands on the image of
the specimen. The gratings can be real or virtual. For
analysis of in-plane deformations, a deformed specimen grating and an undeformed reference grating are
superimposed.9
moiré interferometry: All moiré techniques that require
physical optics for their explanation, particularly
diffraction and interference of light waves. It is known
by other names, including interferometric moiré, high
sensitivity moiré and diffraction moiré.9
mold: A form or cavity into which molten metal is poured
to produce a desired shape. Molds may be made of
sand, plaster or metal and frequently require the use of
cores and inserts for special applications.2,3
mold jacket: Wood or metal form that is slipped over a
sand mold for support during pouring.3
mold wash: An aqueous or alcohol emulsion or suspension
of various materials used to coat the surface of a mold
cavity.3
molding machine: A machine for making sand molds by
mechanically compacting sand around a pattern.3
molecular flow: Phenomenon occuring when mean free
path length of gas molecules is greater than the largest
cross sectional dimension of a leak or the tube through
which flow is occurring.1
molecule: A group of atoms held together by chemical
forces. The atoms in the molecule may be identical (H2
and S8) or different (H2O and CO2).2
monochromatic light: Light from a very small portion of
the visible spectrum.8
monochromator: Device that uses prisms or gratings to
separate or disperse the wavelengths of the spectrum
into noncontinuous lines or bands.8
mottle: An apparently random positioning of metallic flakes
that creates an accidental pattern.8
MT: Magnetic particle testing.
multiaxial stresses: Any stress state in which two or three
principal stresses are not zero.2
multidirectional field: A periodic magnetic field that produces magnetization in two or more mutually perpendicular directions during a single cycle.6
multidirectional magnetization: Two or more magnetic
fields in different directions imposed on a test object
sequentially and in rapid succession.6,15
multifrequency: Two or more frequencies applied sequentially or simultaneously (as in a pulse).4
multifrequency technique: Utilization of the response of
a test object to more than one frequency, usually to separate effects that would be indistinguishable at a single
frequency.4
multiparameter: The many parameters of a test system.
These parameters often affect test response and can
often be distinguished with a multifrequency technique.4
multiphase alloy: Alloy in which several phases are present.8
multiple back reflections: In ultrasonic testing, repetitive
echoes from the far boundary of the test object.7,10
multivariable: See multiparameter.
mutual inductance: The common property of two electrical circuits whereby an electromotive force is induced in
one circuit by a change of current in the other circuit.4,14
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N
narrow banded: A relative term denoting a restricted
range of frequency response.7,12
NDC: Nondestructive characterization.
NDE: (1) Nondestructive evaluation. (2) Nondestructive
examination.8
NDI: Nondestructive inspection.8
NDT: Nondestructive testing.8
near field: The distance immediately in front of a transducer in which the ultrasonic beam exhibits complex
and changing wavefronts. Also called the Fresnel field
or Fresnel zone.7,10
near surface discontinuity: A discontinuity not open to
but near the surface of a test object. Produces broad,
fuzzy, lightly held dry magnetic particle indications.6,16
near ultraviolet radiation: Ultraviolet radiation with
wavelengths ranging from about 320 to about 400 nm.
Sometimes called black light.8
near vision: Vision of objects nearby, generally within arm’s
length. Compare far vision.8
nearsightedness: Vision acuity functionally adequate for
viewing objects nearby, generally within arm’s length
but not at greater distances. Also called myopia. Compare farsightedness.8
necking down: Localized reduction in area of a specimen
or structural member during welding or overloading.8,19
negative sliding: The rolling and sliding of meshing gears
or rollers when the rolling and sliding are in opposite
directions.8
neper: The natural logarithm of a ratio of two amplitudes
(equal to 8.686 dB) used as a measure of attenuation.
Power ratios are expressed as half the natural logarithm.7
neural acuity: The ability of the eye and brain together to
discriminate patterns from background. Discrimination
is influenced by knowledge of the target pattern, by the
scanning technique and by the figure/ground relationship of a discontinuity.8
neutron: An uncharged elementary particle with a mass
nearly equal to that of the proton. The isolated neutron
is unstable and decays with a half-life of about 13 minutes into an electron, proton and neutrino.11
neutron radiography: Radiographic nondestructive testing using neutrons as the interrogating particles.
nick: Surface indentation caused by forceful abrasion or
impact. Also called gouge. Compare tool mark.8
nit: A former unit for measuring luminance, equivalent to
one candela per square meter. Abbreviated nt.8
noble metals: Cathodic metals (such as gold, platinum and
silver), which strongly resist corrosion.8
nodal points: In angle beam ultrasonic testing, the location
of reflections at opposite surfaces as a wave progresses
along a test object.7
node: A point in a standing wave where a given characteristic of the wave field has zero amplitude.7
nodular cast iron: A cast iron that has been treated while
molten with a master alloy containing an element such
as magnesium or cerium to give primary graphite in the
spherultic form.3
noise: Any undesired signals that tend to interfere with normal reception or processing of a desired signal. The origin may be an electrical or acoustic source, small
discontinuities or abrupt changes in properties of the
test material.7,12
nondestructive characterization (NDC): Branch of nondestructive testing concerned with the description and
prediction of material properties and behaviors of components and systems.
nondestructive evaluation (NDE): Another term for
nondestructive testing. In research and academic communities, the word evaluation is often preferred
because it emphasizes interpretation by knowledgeable
personnel.8
nondestructive examination (NDE): Another term for
nondestructive testing. In the utilities and nuclear
industry, examination is sometimes preferred because
testing can imply performance trials of pressure containment or power generation systems.8
nondestructive inspection (NDI): Another term for nondestructive testing. In some industries (utilities, aviation), the word inspection often implies maintenance
for a component that has been in service.8
nondestructive testing (NDT): The determination of the
physical condition of an object without affecting that
object’s ability to fulfill its intended function. Nondestructive testing techniques typically use a probing
energy form to determine material properties or to
indicate the presence of material discontinuities (surface, internal or concealed). See also nondestructive
evaluation, nondestructive examination and nondestructive inspection.8
nonferromagnetic material: A material that is not magnetizable and essentially not affected by magnetic fields.
Includes paramagnetic materials and diamagnetic materials.4,13
nonrelevant indication: See indication, nonrelevant.
normal incidence: (1) A condition in which the axis of an
ultrasonic beam is perpendicular to the entry surface of
the test object. (2) A condition where the angle of incidence is zero.7
normal induction: The maximum induction in a magnetic
material that is symmetrically and cyclically magnetized.4,14
normal permeability: The ratio of normal induction to the
corresponding maximum magnetizing force. In anisotropic media, normal permeability becomes a matrix.4,14
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normalized impedance diagram: In electromagnetic
testing, an impedance curve from which the effects of
frequency on a probe in air have been removed. Usually
the plotted data are (1) the measured reactance divided
by the reactance of the coil in air versus (2) the measured resistance less the resistance in air divided by the
coil reactance in air.4
normalizing: Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in
air to a temperature substantially below the transformation range.3
NR: Neutron radiographic testing.
null: To adjust a bridge circuit so that the test sample and
reference arms produce equal and opposite currents
through the detector.4
null signal: A fixed component of a test coil signal that is
subtracted from the output signal leaving only that part
of the signal that varies with test object conditions.4
numerical analysis: A technique to generate numbers as
the solution to a mathematical model of a physical system. Used in place of a closed form analytic expression.
Usually requires digital computation.4
organoleptic: Relying on or using sense organs, such as the
human eye.8
orientation: The angular relationship of a surface, plane,
discontinuity or axis to a reference plane or surface.7,10
orthicon: See image orthicon.
oscillogram: Common term for a record or photograph of
data displayed on the cathode ray tube face.7,12
ounces per year (oz /yr): Units defining the size of a leak
as the weight of refrigerant gas that will pass through
the leak in one year.1
outgassing: Forms of gas coming from material in a vacuum system. Includes gases adsorbed on the surface,
dissolved in material, trapped in pockets and those due
to evaporation or condensation.1
overall integrated leakage rate: The total leakage
through all leakage paths including containment welds,
valves, fittings and components that penetrate a primary reactor containment system, expressed in weight
percent of contained air mass per day.1
O
pancake coil: A probe coil whose axis is normal to the surface of the test material and whose length is not larger
than the radius.4
parafoveal vision: See scotopic vision.
parallax: The apparent difference in position of an imaged
point according to two differently positioned sensors.8
parallel magnetization: A magnetic field induced in magnetizable material placed parallel to a conductor carrying an electric current.10 Not a recommended practice
for magnetic particle testing.6
paramagnetic material: In electromagnetic testing, a
material that has a relative permeability slightly greater
than unity and is practically independent of the magnetizing force.4,13
parameter distribution: A display of the number of times
the acoustic emission parameter falls between the values x and x + δx as a function of x. Typical parameters
are amplitude, rise time and duration.5
parasitic echo: See spurious echo.
particle motion: Movement of particles of material during
wave propagation.7
parting line: The mark left on the casting where the die
halves meet. Also, the surface between the cover and
ejector portions of the die.3
parting sand: Fine sand for dusting on sand mold surfaces
that are to be separated.3
parts per million (ppm): Concentration of a specific gas in
another gas or gas mixture. For example, a tracer gas
concentration might be 10 ppm in air or nitrogen. The
more specific term µL/L is often used, with ppm to
indicate proportion by volume.1
objective: In discussion of a lens system (camera,
borescope, microscope, telescope), of or pertaining to
the end or lens closest to the object of examination —
at the end opposite from the eyepiece. Distal; tip.8
OCTG: Oil country tubular goods.8
oersted: The cgs unit of magnetic field strength, abbreviated Oe. In air, 1 Oe = 1 gauss. Replaced by SI’s ampere
per meter.6,15
oil country tubular goods (OCTG): Hollow cylindrical
components used to convey petroleum and related
products.8
one hundred percent testing: Testing of all parts of an
entire production lot in a prescribed manner. Sometimes, complete testing entails the testing of only the
critical portions of the part. Compare sampling, partial.8
open sand casting: Any casting made in a mold that has no
cope or other covering.3
opening: Image processing operation of erosion followed
by dilation. A single opening eliminates isolated single
pixels. See also closing.8
opsin: See visual purple.
optic disk: Area in the retina through which the fibers from
the various receptors cross the inner (vitreous humor)
side of the retina and pass through it together in the optic
nerve bundle. This transitional area is completely blind.8
optimum frequency: The frequency that provides the
highest signal-to-noise ratio compatible with the detection of a specific discontinuity. Each combination of
discontinuity type and material may have a different
optimum frequency.7,12
P
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pass: In welding, a single bead along the entire weld length
or the process of laying down that bead.8
pattern: A form of wood, metal or other material, around
which a molding material is placed to make a mold for
casting metals.3
pearlite: Platelet mixture of cementite and ferrite in steels
or in alpha and beta phases in nonferrous alloys.8
peeling: (1) The dropping away of sand from the casting
during shakeout. (2) The detaching of one layer of a
coating from another or from the basic metal, because
of poor adherence.3
pencil source: An artificial source using the fracture of a
brittle graphite lead in a suitable fitting to simulate an
acoustic emission event.5
penetrability: The condition of being penetrable so that
liquid can enter into very fine openings such as cracks.
Often erroneously used to describe the property of a
penetrant that causes it to find its way into very fine
openings.2
penetrameter: A strip of metal the same composition as
that of the metal being tested, representing a percentage of object thickness and provided with a combination of steps, holes or slot or alternatively made as a
wire. When placed in the path of the rays, its image
provides a check on the radiographic technique
employed.3,11 Also called image quality indicator.
penetrant: A liquid capable of entering discontinuities
open to the test surface and that is adapted to the penetrant test process by being made highly visible in small
traces. Fluorescent penetrants fluoresce brightly under
ultraviolet light and visible penetrants are intensely colored to be readily visible on developer backgrounds
when illuminated with visible light.2
penetrant comparator: See comparator, penetrant.
penetrant leak testing: A technique of penetrant testing
in which the penetrant is applied to one surface of a test
material while the opposite surface is tested for indications that would identify a through leak or void passing
through the material thickness.2
penetrant testing: Nondestructive testing method using
penetrant.
penetrant, fluorescent: A penetrant characterized by its
ability to fluoresce when excited by ultraviolet light.2
penetrant, post emulsifiable: A penetrant that requires
the application of a separate emulsifier to render the
excess surface penetrant water washable.2
penetrant, visible: A penetrant characterized by an intense
visible color dye that allows it to give contrasting indications on a white developer background.2
penetrant, water washable: A penetrant with built in
emulsifier that makes it directly water washable.2
penetration time: The time allowed, after penetrant has
been applied to a surface, for the penetrant to enter discontinuities that may be present. The length of time
elapsing between the application of the penetrant to
the test object and the removal of the penetrant.2
penetration, ultrasonic: Propagation of ultrasonic energy
into a material. See also effective penetration.7
period: The absolute value of the minimum interval after
which the same characteristics of a periodic waveform
or a periodic feature return.4,14
peripheral vision: The seeing of objects displaced from
the primary line of sight and outside the central visual
field.8,20
permanent magnet: An object possessing the ability to
retain an applied magnetic field for a long period of
time after the active power of the field has been
removed.6,10
permanent mold: A metal mold of two or more parts used
repeatedly for the production of many castings of the
same form.3
permeability: (1) A general term for various relationships
between magnetic induction and magnetizing force.
These relationships are: (a) absolute permeability (the
quotient of a change in magnetic induction divided by
the corresponding change in magnetizing force) or
(b) specific (relative) permeability (a pure number that
is the same in all unit systems). The value and dimension of absolute permeability depend on the system of
units employed. In anisotropic media, permeability
becomes a matrix.4,14 (2) The characteristic of materials
that allows gases or liquids to pass through them.3
(3) The ratio of flux density B to magnetizing field
strength H. High permeability materials are easier to
magnetize than low permeability materials.6
phantom: A reference standard used to verify the performance of ultrasound systems.7
phase: In metallurgy, a physically homogeneous portion of
a material system, specifically the portion of an alloy
characterized by its microstructure at a particular temperature during melting or solidification.8
phase analysis: An analytical technique that discriminates
between variables in an object undergoing electromagnetic testing by the different phase angle changes that
these conditions produce in the test signal. See also
phase detection.4,13
phase angle: The angular equivalent of the time displacement between corresponding points on two sine waves
of the same frequency.4,13
phase contrast microscope: See microscope, phase contrast.
phase detection: The derivation of a signal whose amplitude is a function of the phase angle between two alternating currents, one of which is used as a reference.4,13
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phase diagram: Graph showing the temperature, pressure
and composition limits of phase fields in a material system. Also called a constitution diagram. Compare equilibrium diagram.8
phase shift: A change in the phase relationship between
two alternating quantities of the same frequency.4,13
phase velocity: The velocity of a single frequency continuous wave.7
phase-sensitive system: A system whose output signal is
dependent on the phase relationship between the voltage returned from a pickup or sensing coil and a reference voltage.4,13
phased array: A mosaic of transducer elements in which
the timing of the elements’ excitation can be individually controlled to produce certain desired effects, such
as steering the beam axis or focusing the beam.7
phasor quantity: Any quantity that is expressed as a complex number. See impedance.4,15
photoconduction: Method by which a vidicon television
camera tube produces an electrical image, in which conductivity of the photosensitive surface changes in relation to intensity of the light reflected from the scene
focused onto the surface. Compare photoemission.8
photoelasticity: The effect of a material’s elastic properties
on the way that it refracts or reflects light.8
photoelectric effect: Emission of electrons from a surface
bombarded by sufficiently energetic photons. Such
emissions may be used in an illuminance meter and
may be calibrated in lux.8,20
photoemission: Method by which an image orthicon television camera tube produces an electrical image, in
which a photosensitive surface emits electrons when
light reflected from a viewed object is focused on that
surface. Compare photoconduction.8
photometer: The basic measuring instrument of photometry. Accurate meters measuring radiant energy incident
on a receiver, producing measurable electrical quantities.8
photometric brightness: The luminance of a light source.8
photometry: The science and practice of the measurement
of light or photon-emitting electromagnetic radiation.
See also relative photometry.8
photon: Particle of light.8
photopic vision: Vision adapted to daylight and mediated
mainly by the cones. Vision is wholly photopic when the
luminance of the test surface is above 0.034 cd·m–2
(0.0032 cd·ft–2). Also known as foveal vision and light
adapted vision. Compare mesopic vision and scotopic
vision.8,20
photoreceptor: Light sensor.8
physical properties: Nonmechanical properties such as
density, electrical conductivity, heat conductivity and
thermal expansion.2
picture element: See pixel.
picture processing: See image processing.
piezoelectric effect: The ability of certain materials to
convert electrical energy into mechanical energy and
vice versa.7,12
pinhole porosity: Porosity, in either castings or metal
formed by electrodeposition, resulting from numerous
small holes distributed throughout the metal.3
pipe: (1) The central cavity formed during solidification of
metal, especially ingots, by thermal contraction. (2) The
discontinuity in wrought or cast products resulting from
such a cavity. (3) An extrusion discontinuity due to the
oxidized surface of the billet flowing toward the center
of the rod at the back end. (4) A cast, wrought or
welded metal tube.2
pitch and catch: Test technique in which ultrasonic energy
is emitted by one transducer and received by another on
the same or opposite surface.12 Also called pitch-catch,
two transducer technique or dual crystal method.7
pitting: Discontinuity consisting of surface cavities. See
also cavitation fatigue and pitting fatigue.8
pitting fatigue: Discontinuity consisting of surface cavities
typically due to fatigue and abrasion of contacting surfaces undergoing compressive loading. See also cavitation fatigue and pitting.8
pixel: A lighted point on the screen of a digital image. Picture element.8
Planck’s Distribution Law: The distribution criterion for
blackbody radiation.
plane of focus: See focus, principal plane of.
plane wave: A wave in which points of same phase lie on
parallel plane surfaces.7,18
plaster molding: Molding where a gypsum bonded aggregate flour in the form of a water slurry is poured over a
pattern, permitted to harden and is thoroughly dried
after removal of the pattern. The technique is used to
make smooth nonferrous castings of accurate size.3
plastic deformation: Deformation that does or will remain
permanent after removal of the load that caused it.2
plate wave: See Lamb wave.
platelet: Flat crystallites in certain phases of steel.8
plunger machines: Die casting machines having a plunger
in continuous contact with molten metal.3
point of incidence: In ultrasonic testing, the point at
which the center of the sound beam leaves the plastic
wedge of an angle beam transducer and enters the test
object.12 See probe index.7
polarizing microscope: See microscope, polarizing.
pole: See magnetic pole.
poling: The process of reorienting crystal domains in certain materials by applying a strong electric field at elevated temperatures. Materials (usually ceramics) so
treated exhibit piezoelectric behavior.7
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pores: (1) Small voids within a metal. (2) Minute cavities,
sometimes intentional, in a powder metallurgy compact.
(3) Minute perforations in an electroplated coating.2
porosity: A discontinuity in metal resulting from the creation or coalescence of gas. Very small pores are called
pinholes.8,19
positive sliding: The rolling and sliding of meshing gears
or rollers when directions of rolling and sliding are the
same.8
postcleaning: The removal of penetrant testing residues
from the test piece after penetrant test processing is
completed.2
postemulsification: A penetrant removal technique
employing a separate emulsifier applied over the surface penetrant to make it removable with water spray.2
poultice corrosion: See corrosion, poultice.
pouring basin: A basin on top of a mold to receive the
molten metal before it enters the sprue or downgate.3
pouring: Transferring molten metal from a furnace or a
ladle to a mold.3
powder: See dry powder.
powder blower: A compressed air device used to apply dry
magnetic particles over the surface of a test object.6,16
practical examination: In certification of nondestructive
testing personnel, a hands-on examination using test
equipment and sample test objects. Compare general
examination and specific examination.8
precleaning: The removal of surface contamination or
smeared metal from the test piece so that it cannot
interfere with the penetrant testing process.2
pressure testing:. A technique of leak testing objects pressurized with a tracer gas with the subsequent detection
and location of any existing leaks with a sampling probe
(a qualitative test). Tests performed by increasing the
pressure inside a test boundary to a level greater than
the surrounding atmosphere and detecting leakage by
systematic examination of the outside of the test surface. Leaks are located at time of detection; however, it
is impossible to accurately determine a total leakage
rate for the object being tested.1
prewash technique: Penetrant system in which major portion of a nonwater washable penetrant is removed with
a water spray prior to application of the remover.2
primary creep: First stage of creep, marked by elastic
strain plus plastic strain.8
primary radiation: Radiation emitting directly from the
target of an X-ray tube or from a radioactive source.11
primary reference response level: The ultrasonic
response from the basic calibration reflector at the
specified sound path distance, electronically adjusted to
a specified percentage of full screen height.7
principal plane of focus: See focus, principal plane of.
probe: In leak testing, the physical means for sensing a
gaseous leak, typically a tube having a fine opening at
one end, used for directing or collecting a stream of
tracer gas. Detector probes are used for pressure testing
and tracer probes are used for vacuum testing.1 In ultrasonic testing, see search unit.7
probe coil: In electromagnetic testing, a small coil or coil
assembly that is placed on or near the surface of test
objects.4,13
probe coil clearance: The perpendicular distance between
adjacent surfaces of the probe and test object. See liftoff.4,13
probe gas: A tracer gas that issues from a fine orifice so as
to impinge on a restricted (small) test area.1
probe index: The point on a shear wave or surface wave
transducer through which the emergent beam axis
passes.7,18
process: Repeatable sequence of actions to bring about a
desired result.8
process control: Application of quality control principles
to the management of a repeated process.8
process testing: Initial product testing to establish correct
manufacturing procedures and then by periodic tests to
ensure that the process continues to operate correctly.2
prod magnetization: See current flow technique.
prods: Handheld electrodes for transmitting magnetizing
current from a generating source to a test object.6,15
production string: See tubing string.
propagation: Advancement of a wave through a
medium.7,10
proportioning probe: A probe that can vary the tracer gas
concentration in the sample at the sensor, typically by
mixing pure air with sample gas from the probe inlet
port. Ratios of mixture between 100 percent pure air
(obtained from an outdoors source or by filtering ambient air through charcoal) and 100 percent leak sample
gas are attainable without great changes in total flow
from the probe. The proportioning probe used in halogen leak testing lets the user operate in an atmosphere
with up to 1,000 µL/L (ppm) tracer gas background
contamination. It proportions the amount of atmosphere allowed to enter the probe with its own (recirculating) fresh air supply.1
pseudocolor: Image enhancement technique wherein colors
are assigned to an image at several gray scale intervals.8
pseudoisochromatic plates: Color plates used for color
vision examinations. Each plate bears an image which
may be difficult for the examinee to see if his or her
color vision is impaired.8
psychophysics: Interaction between vision performance
and physical or psychological factors. One example is
the so-called vigilance decrement, the degradation of
reliability based on performing visual and/or repetitive
activities over a period of time.8
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PT: Liquid penetrant testing.
pull cracks: In a casting, cracks caused by residual stresses
produced by cooling because of the object shape.3
pulse: A transient electrical or ultrasonic signal that has a
rapid increase in amplitude to its maximum value, followed by an immediate return.7,21 An example is the
signal that has propagated from the source to the transducer as detected using a flat response transducer.5
pulse echo method: An ultrasonic test method in which
discontinuities are detected by return echoes of the
transmitted pulses.7
pulse length: A measure of pulse duration expressed in
time or number of cycles.7,21
pulse magnetization: Direct or indirect application of a
high field intensity, usually by the capacitor discharge
method.6
pulse method: Multifrequency technique in which a
broadband excitation such as an impulse is used. Either
the frequency components are extracted and analyzed
or the interpretation is based directly on characteristics
of the time domain waveform.4
pulse repetition frequency: See repetition rate.
pulse tuning: Control of pulse frequency to optimize system response.7
pulser transducer: In acoustic emission testing, a transducer used as an artificial source of acoustic energy.5
pupil: Aperture in the center of an eye’s iris, through which
light focused by the lens passes.8
pure air supply: In leak testing, air that has been cleaned
of halogen contamination by means of an activated
charcoal filter. This term is sometimes also used to
describe any nonreactive gas, such as nitrogen, that
contains no halogen contamination and to which the
leak detector is not sensitive.1
purple: See visual purple.
pyrometry: Type of radiation thermometer, giving readings
for one point at a time, rather than imaging a scene in
the manner of an infrared video camera. The word
pyrometry means fire measurement. As the name
implies, pyrometers are used for hot applications, such
as the monitoring of furnace or foundry conditions.
Pyrometers today are digital devices with liquid crystal
temperature readouts. They may be mounted in place
or available as hand held units.9
Q
Q of a coil: Ratio of reactance to resistance measured at the
operating frequency.4,14
quadrature: The relation between two periodic functions
when the phase difference between them is one-fourth
of a period.4,14
qualification: Process of demonstrating that an individual
has the required amount and the required type of training, experience, knowledge and capabilities. See also
qualified.8
qualified: Having demonstrated the required amount and
the required type of training, experience, knowledge
and abilities. See also qualification.8
quality: The ability of a process or product to meet specifications or to meet the expectations of its users in terms
of efficiency, appearance, longevity and ergonomics.8
quality assurance: Administrative actions that specify,
enforce and verify a quality program.8
quality control: Physical and administrative actions required to ensure compliance with the quality assurance
program. May include nondestructive testing in the
manufacturing cycle.8
quality of lighting: Level of distribution of luminance in a
visual task or environment.8
quartz Bourdon tube gage: High precision pressure measuring instrument containing a quartz helical Bourdon
tube.1
quasilongitudinal wave: A wave in which the direction of
particle motion is not parallel to the direction of energy
propagation.7
quasishear wave: A wave in which the direction of particle
motion is not perpendicular to the direction of energy
propagation.7
quenching of fluorescence: The extinction of fluorescence by causes other than removal of the ultraviolet
light (the exciting radiation).2
quick break: A sudden interruption of magnetizing current. Used in magnetic particle tests for materials with
high residual longitudinal magnetism and limited to
three-phase fullwave rectified alternating current.6,16
R
rad: Radiation absorbed dose. A unit of absorbed dose of
ionizing radiation. One rad is equal to the absorption of
10 –5 J (100 ergs) of radiation energy per gram of matter.11 Replaced by the gray (Gy).
radiance: Radiant flux per unit solid angle and per unit
projected area of the source. Measured in watts per
square meter steradian. Compare irradiance.8
radiant energy: Energy transmitted through a medium by
electromagnetic waves. Also known as radiation.8
radiant flux: Radiant energy’s rate of flow, measured in
watts.8
radiant intensity: Electromagnetic energy emitted per
unit time per unit solid angle. Measured in watts per
steradian.8
radiant power: Total radiant energy emitted per unit time.8
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radiation safety officer: An individual engaged in the
practice of providing radiation protection. The representative appointed by the licensee for liaison with the
applicable regulatory agency.11
radio frequency display: The presentation of unrectified
signals on a display screen.7,12 Also called RF display.
See also video presentation.
radiographic interpretation: The determination of the
cause and significance of subsurface discontinuities
indicated on a radiograph. The evaluation as to the
acceptability or rejectability of the material is based on
the judicious application of the radiographic specifications and standards governing the material.11
radiographic screens: Metallic or fluorescent sheets used
to intensify the radiation effect on films.11
radiographic testing (RT): The use of radiant energy in
the form of X-rays or gamma rays for nondestructive
testing of opaque objects in order to produce graphical
records on a medium that indicates the comparative
soundness of the object being tested.11
radiography: Radiographic testing.
radiology: That branch of medicine which uses ionizing
radiation for diagnosis and therapy.11
radiometer: Instrument for measuring radiant power of
specified frequencies. Different radiometers exist for
different frequencies.8
radiometric photometer: Radiometer for measuring radiant power over a variety of wavelengths.8
radioscopy: A radiographic testing technique in which
gamma rays or X-rays are used to produce an instantaneous image on a video or screen display as opposed to
a latent image on a film. The test object may be
remotely manipulated in real time to present a moving
radiographic image.
ramoff: A casting discontinuity resulting from the movement of sand away from the pattern because of
improper ramming.3
range: In ultrasonic testing, the maximum path length that
is displayed. See also sweep length.7,12
rarefaction: The thinning or separation of particles in a
propagating medium due to the relaxation phase of an
ultrasonic cycle. Opposite of compression. A compressional wave is composed of alternating compressions
and rarefactions.7,10
raster: A repetitive pattern whereby a directed element (a
robotic arm or a flying dot on a video screen) follows
the path of a series of adjacent parallel lines, taking
them successively in turn, always in the same direction
(from top to bottom or from left to right), stopping at
the end of one line and 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.8
rat’s tooth principle: (1) The tendency for hard material
on a tooth’s front surface to wear more slowly than soft
material on the back surface, keeping the edge sharp.
(2) Mechanism of wear whereby adjacent hard and soft
surfaces wear at different rates, producing a self sharpening edge.8
Rayleigh wave: An ultrasonic wave that propagates along
the surface of a test object. The particle motion is elliptical in a plane perpendicular to the surface, decreasing
rapidly with depth below the surface. The effective
depth of penetration is considered to be about one
wavelength.7
real grating: In moiré and grid nondestructive testing, a
physical grating on glass or other substrate. Two types
are the amplitude grating (or bar-and-space grating)
consisting of opaque bars and clear spaces for use with
transmitted light, or reflective bars and nonreflective
spaces for use with reflected light; and the phase grating consisting of an array of furrows on the surface of a
transparent or opaque body.9
recarburize: (1) To increase the carbon content of molten
cast iron or steel by adding carbonaceous material, high
carbon pig iron or a high carbon alloy. (2) To carburize
a metal object to return surface carbon lost in processing.3
receiver: The section of an ultrasonic instrument that
amplifies echoes returning from the test object. Also, a
transducer that picks up the echoes.7
recommended practice: A set of guidelines or recommendations.8
Recommended Practice SNT-TC-1A: See ASNT Recommended Practice No. SNT-TC-1A.
recovery: Reduced stress level and increased ductility of
metal after work hardening. See creep.8
recovery time: The time required for a test system to
return to its original state after it has received a signal.4,13
recrystallization: (1) The change from one grain structure
to another, as occurs on heating or cooling through a
critical temperature. (2) The formation of a new, strain
free grain structure from that existing in cold worked
metal, usually accomplished by heating.2
rectified alternating current: A unidirectional electric
current obtained by rectifying alternating current without the deliberate addition of smoothing to remove the
inherent ripples.6,15
red mud: Debris (usually oxides of the contacting metals)
of fretting wear, mixed with oil or grease and retained at
or near the site of its formation. See also cocoa.8
reference blocks: A block of material containing artificial
or actual cracks of various depths and widths used for
reference in defining the size and location of defective
areas in materials.2
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reference coil: In electromagnetic testing, the section of
the coil assembly that excites or detects the electromagnetic field in the reference standard of a comparative
system.4,13
reference grating: In moiré and grid nondestructive testing, an undeformed grating superimposed upon a specimen grating to create the moiré.9
reference number: Number associated with the impedance of a coil adjacent to a test sample.4
reference standard: A typical test object with known artificial or natural discontinuities of various specific sizes,
used as a basis for test comparisons, equipment calibration or determining the efficiency of the discontinuity
detection process. Also called reference or test panel,
reference or test block and reference or test piece.2 See
also acceptance standard.
reference threshold: A preset voltage level that has to be
exceeded before an acoustic emission signal is detected
and processed. This threshold may be adjustable, fixed
or floating.5
reflectance: The ratio of reflected wave energy to incident
wave energy. Also known as reflectivity.8
reflection: A general term for the process by which the
incident flux leaves a surface or medium from the incident side, without change in frequency. Reflection is
usually a combination of specular and diffuse reflection.8,20
reflection probe: A coil system that utilizes both an excitation and a detection or sensing coil on the same side of
the sample.4
reflectometer: Photometer used to measure diffuse, specular and total reflectance.8
reflector: (1) In optical nondestructive testing, device used
to redirect the luminous flux from a source by the process of reflection.8,20 (2) In ultrasonic testing, a discontinuity or object surface from which acoustic energy
returns to the sensor.
refracted beam: A beam that occurs in the second
medium when an ultrasonic beam is incident at an
acute angle on the interface between two media having
different sound velocities.7,12
refraction: The change in direction of a wave as a beam
passes from one medium into another having a different sound velocity. A change in direction and mode may
occur at any angle of incidence. At small angles of incidence, the original mode and a converted mode may
exist in the second medium.7
refractive index: The ratio of the velocity of an incident
wave to that of a refracted wave. It is known as the
refractive index of the second medium with respect to
the first.7
reinforcement of weld: (1) In a butt joint, weld metal on
the face of the weld that extends out beyond a surface
plane common to the members being welded. (2) In a
fillet weld, weld metal that contributes to convexity.
(3) In a flash, upset or gas pressure weld, weld metal
exceeding base metal diameter or thickness.2
reject: An instrument function or control used for minimizing or eliminating low amplitude signals (electrical or
material noise) so that other signals may be further
amplified. Use of this control can reduce vertical linearity. Also called suppression.7,12
rejection level: See level, rejection.
relative permeability: The ratio of the permeability of the
material to the permeability of vacuum. See permeability.4
relative photometry: (1) Evaluation of a desired photometric characteristic based on an assumed lumen output of a test lamp. (2) Measurement of an uncalibrated
light source relative to another uncalibrated light
source.8
relaxation: Relief of stress by creep. Diminishing stress by
creep at constant strain frequently occurs in service.2
relay amplifier: An optional electronic module in some
heated anode (alkali ion) halogen vapor detector systems that amplifies the leak signal and initiates an automatic control. The control then either sounds an
audible alarm, flashes a signal light, stops a conveyor or
operates whatever other control actuator the user connects to this relay output signal.1
relevant indication: See indication, relevant.
rem: Roentgen equivalent man. A unit of absorbed radiation dose in biological matter. It is equal to the
absorbed dose in rads multiplied by the relative biological effectiveness of the radiation.11
remanent magnetism: See residual magnetic field.
remote viewing: Viewing of a test object not in the viewer’s
immediate presence. The word remote previously
implied either closed circuit television or fiber optic
systems remote enough so that, for example, the eyepiece and the objective lens could be in different
rooms. High resolution video and digital signals can
now be transmitted around the world with little loss of
image quality. Compare direct viewing.8
repeatability: Ability to reproduce a detectable indication
in separate processings and tests from a constant
source.1,2
repetition rate: The number of pulses generated or transmitted per unit of time (usually seconds).7
replica: Piece of malleable material, such as polyvinyl or
polystyrene plastic film, molded to a test surface for the
recording or analysis of the surface microstructure.8
replication: A method for copying the topography of a surface by making its impression in a plastic or malleable
material.8
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reserve vision acuity: The ability of an individual to maintain vision acuity under poor viewing conditions. A
visual system with 20/20 near vision acuity under
degraded viewing conditions has considerable reserve
vision acuity compared to that of an individual with
20/70 near vision acuity.8
residual elements: Elements present in an alloy in small
quantities, but not added intentionally.2
residual magnetic field: The magnetism remaining in a
ferromagnetic material after the magnetizing force is
reduced to zero.6,10
residual method: Using the residual magnetic field of high
retentivity materials to trap magnetic particles and indicate discontinuities.6
residual technique: Ferromagnetic particles are applied
to a test object after the magnetizing force has been discontinued.6
resolution: An aspect of image quality pertaining to a system’s ability to reproduce objects, often measured by
resolving a pair of adjacent objects or parallel lines. See
also minimum line pair and resolving power.8
resolution, discontinuity: The property of a test system
that enables the separation of indications due to discontinuities located in close proximity to each other in a
test object.2
resolution test: Procedure wherein a line is detected to
verify a system’s sensitivity.8
resolution threshold: Minimum distance between a pair of
points or parallel lines when they can be distinguished as
two, not one, expressed in minutes of arc. Vision acuity
in such a case is the reciprocal of one half of the period
expressed in minutes.8,20
resolving power: The ability of detection systems to separate two points in time or distance. Resolving power
depends on the angle of vision and the distance of the
sensor from the test surface. Resolving power in vision
systems is often measured using parallel lines. Compare
resolution.8
resonance: The condition in which the frequency of a forcing vibration (ultrasonic wave) is the same as the natural vibration frequency of the propagation body (test
object), resulting in large amplitude responses at that
frequency.7,10
resonance method: A method using the resonance principle for determining velocity, thickness or presence of
laminar discontinuities.7
resonant frequency: The frequency at which a body vibrates, that frequency being sympathetic to the energy
causing the vibration.
response or response time: The time (time-constant)
required for a leak detector or leak testing system to yield
a signal output equal to 63 percent of the maximum signal attained when tracer gas is applied continuously for
an indefinitely long period to the leak detector probe.1
response factor: The response of the halogen leak detector to 3 × 10–7 Pa·m3·s–1 (3 × 10–6 std cm3·s–1) of tracer
R-12 or less, divided by the response to the same quantity of another tracer gas. Thus, the actual leakage rate
of a detected leak will equal the indication of the detector multiplied by the response factor of the specific
halogen tracer gas used. The response factor of a mixture of tracer and nontracer gases will be the response
factor of the tracer divided by the fraction of tracer gas
in the test gas (by volume).1
response function: The ratio of response to excitation,
both expressed as functions of the complex frequency.4,14
retentivity: A material’s property of retaining residual magnetism to a greater or lesser degree.6,10
retina: In the eye, the tissue that senses light.8
retinene: See visual purple.
RF display: See radio frequency display.
rhodopsin: See visual purple.
ring standard: See test ring.
ringdown count: See acoustic emission count.
ringing method: A test method for bonded structures in
which disbonds are indicated by increased amplitude of
ringing signals.7,12
ringing signals: (1) Closely spaced multiple signals caused
by multiple reflections in a thin material. (2) Signals
caused by continued vibration of a transducer.7,12
ringing time: The time that the mechanical vibrations of a
transducer continue after the electrical pulse has
stopped.7,12
rinse: The process of removing liquid penetrant testing
materials from the surface of a test object by means of
washing or flooding with another liquid, usually water.
Also called wash.2
riser: A reservoir of molten metal connected to the casting
to provide additional metal to the casting, required as
the result of shrinkage before and during solidification.3
robotic system: Automated system programmed to perform purposeful movements in variable sequences.8
rod: Retinal receptor that responds at low levels of luminance even below the threshold for cones. At these levels there is no basis for perceiving differences in hue
and saturation. No rods are found in the fovea centralis.8,20
roof angle: In a dual element delay line transducer, the
angle by which the top surfaces of the delay line are
tilted horizontally to direct the beams of the two elements to intersect at a specified zone in the medium.7
root crack: A crack in either the weld or heat affected zone
at the root of a weld.2
root penetration: The depth to which weld metal extends
into the root of a joint.2
RT: Radiographic testing.
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runner: (1) A channel through which molten metal flows
from one receptacle to another. (2) The portion of the
gate assembly that connects the downgate sprue or riser
with the casting. (3) Parts of patterns and finished castings corresponding to the described portion of the gate
assembly.3
runner box: A distribution box that divides the molten
metal into several streams before it enters the mold
cavity.3
runout: The discontinuity in a casting caused by the escape
of metal from the mold.3
S
salvage tests: Testing after salvage operations or testing
objects that can be repaired.2
sampling probe: See detector probe.
sampling, partial: Testing of less than one hundred percent of a production lot. See one hundred percent testing.8
sampling, random partial: Partial sampling that is fully
random.8
sampling, specified partial: Partial sampling in which a
particular frequency or sequence of sample selection is
prescribed. An example of specified partial sampling is
the testing of every fifth unit.8
sand: A granular material resulting from the disintegration
of rock. Foundry sands are mainly silica. Bank sands are
found in sedimentary deposits and contains less than 5
percent clay. Dune sand occurs in wind blown deposits
near large bodies of water and is very high in silica content. Molding sand contains more than 5 percent clay,
usually between 10 and 20 percent. Silica sand is a
granular material containing at least 95 percent silica
and often more than 99 percent. Sand core is nearly
pure silica. Miscellaneous types of sand include zircon,
olivine, calcium carbonate, lava and titanium minerals.3
saturation: (1) A condition in which high amplitude signals
on a display screen do not increase with increased gain
and appear flattened.7 (2) Relative or comparative color
characteristic resulting from a hue’s dilution with white
light.8
saturation level: See magnetic saturation.
scab: A flat volume of metal joined to a casting through a
small area. Usually set in a depression, a flat side being
separated from the metal of the casting proper by a thin
layer of sand.3
scalar: A quantity completely specified by a single number.4,14
scale: Oxide formed on metal by chemical action of the surface metal with oxygen from the air.2
scale pit: Shallow surface depression in metal, caused by
scale.2
scaling: (1) Forming a layer of oxidation product on metals,
usually at high temperatures. (2) Deposition of insoluble constituents on a metal surface, as in cooling tubes
and water boilers.8,19
scanning: Movement of the transducer over the surface of
the test object in a controlled manner so as to achieve
complete coverage. May be either contact or immersion method.7
scarfing: Cutting surface areas of metal objects, ordinarily
by using a gas torch. The operation permits surface discontinuities to be cut from ingots, billets or the edges of
plate that is to be beveled for butt welding.3
scattering: (1) Random reflection and refraction of radiation caused by interaction with material it strikes or
penetrates. (2) Random reflection of ultrasonic waves
by small discontinuities or surface irregularities.7
Schlieren system: An optical system used for visual display
of an ultrasonic beam passing through a transparent
medium.7,9,12
scoring: (1) Marring or scratching of any formed part by
metal pickup on a punch, die or guide. (2) Reducing the
thickness of a part along a line to weaken it purposely at
a specific location.8,19
scotopic vision: Dark adapted vision, using only the rods in
the retina, where differences in brightness can be detected but differences in hue cannot. Vision is wholly
scotopic when the luminance of the test surface is
below 3 × 10–5 cd·m–2 (2.7 × 10–6 cd·ft–2). Also known as
parafoveal vision. Compare mesopic vision and photopic vision.8
scrap: (1) Manufactured materials not suitable for sale.
(2) Discarded metallic material that may be reclaimed
through melting and refining.3
scuffing: A type of adhesive wear.
sea level atmospheric pressure or sea level barometric
pressure: See atmospheric pressure.
sealing: (1) Closing pores in anodic coatings to render them
less absorbent. (2) Plugging leaks in a casting by introducing thermosetting plastics into porous areas and
subsequently setting the plastic with heat.3
seam: (1) On the surface of metal, an unwelded fold or lap
that appears as a crack, usually resulting from a discontinuity obtained in casting or working. (2) Mechanical
or welded joints.3 (3) Longitudinal surface discontinuity on metal originating from a surface crack or blowhole near the surface of the ingot, that is drawn out
during rolling and follows the rolling direction. Also
due to overfill while rolling. After forging, seams generally follow the direction of flow lines.2
search coil: A detection coil that is usually smaller than the
excitation coil.4
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search unit: An assembly comprising a piezoelectric element, backing material (damping), wear plate or wedge
(optional) and leads enclosed in a housing. Also called
transducer or probe.7
second stage replica: A positive replica made from the
first cast to produce a duplicate of the original surface.8
secondary creep: Second stage of creep, where deformation proceeds at a constant rate and less rapidly than as
in primary creep. Essentially an equilibrium condition
between the mechanisms of work hardening and recovery.8
secondary magnetic flux: magnetic flux due to induced
flow of eddy currents.4
seeability: The characteristic of an indication that enables
an observer to see it against the adverse conditions of
background, outside light etc.2
segregation: Nonuniform distribution of alloying elements, impurities or microphases.2,3
selectivity: The characteristic of a test system that is a measure of the extent to which an instrument is capable of
differentiating between the desired signal and disturbances of other frequencies or phases.4,13
self emulsifiable: Describes a penetrant that spontaneously emulsifies into water, a property that allows it to be
rinsed off with water, with more control than if it actually dissolved in the rinse water. Also called water washable. See penetrant, water washable.2
self inductance: The property of an electric circuit whereby an electromotive force is induced in that circuit by a
change of current in the circuit.4,14
semipermanent mold: A permanent mold in which sand
or plastic cores are used.3
send/receive transducer: A transducer consisting of two
piezoelectric elements mounted side by side separated
by an acoustic barrier. One element transmits, one
receives.7,10
sensing coil: A coil that detects changes in the magnetic
field produced by the flow of eddy currents in a test
specimen, induced by an excitation coil. Sensing and
excitation coils can be one and the same.4
sensitivity: A measure of a sensor’s ability to detect small
signals. Limited by the signal-to-noise ratio.7
sensitivity of leak detector: Response of a leak detector
to tracer gas leakage (typically panel meter pointer
deflection in scale divisions; leak sensitivity is measured
in units of Pa·m3·s–1 or std cm3·s–1).1
sensitivity of leak test: The smallest leakage rate that an
instrument, technique or system can detect under specified conditions (implies minimum detectable leakage
rate).1
sensitivity panel: A plated metal panel with cracks of
known depth induced into the plating. Used to evaluate
and compare penetrant sensitivity.2
sensitization: Precipitation of chromium carbides in the
grain boundaries of a corrosion resistant alloy, resulting
in intergranular corrosion that would otherwise be
resisted. 8
settling test: A procedure used to determine the concentration of particles in a magnetic particle bath.6
SH wave: See shear horizontal wave.
shadow: A region in a test object that cannot be reached by
ultrasonic energy traveling in a given direction. Caused
by geometry or the presence of intervening large discontinuities.7
shadow casting: Nondestructive technique of vapor
depositing a thin metal film onto a replica at an oblique
angle in order to obtain a micrograph of a test surface of
an opaque specimen.8
shakeout: Removing castings from a sand mold.3
shallow discontinuity: A discontinuity open to the surface
of a solid object that possesses little depth in proportion
to the width of this opening. A scratch or nick may be a
shallow discontinuity in this sense.2
shear: A force that tends to cause two contiguous parts of
the same body to slide in a direction parallel to their
plane of contact.2
shear break: Open break in metal at the periphery of a
bolt, nut, rod or member at approximately a 45 degree
angle to the applied stress. Occurs most often with
flanged products. Also called shear crack.8,19
shear crack: See shear break.
shear horizontal wave: A shear wave in which the particle
vibration is parallel to the incidence surface. Abbreviated SH wave.7
shear vertical wave: A shear wave in which the particle
vibration is perpendicular to the direction of wave
propagation but essentially normal to the incidence surface. Abbreviated SV wave.7
shear wave: A type of wave in which the particle motion is
perpendicular to the direction of propagation.7,12
shear wave transducer: An angle beam transducer or
straight beam transducer designed to cause mode converted shear waves to propagate at a nominal angle in a
specified test medium.7
shell core: A shell molded sand core.3
shell molding: Forming a mold from thermosetting resin
bonded sand mixtures brought in contact with preheated metal patterns, resulting in a firm shell with a
cavity corresponding to the outline of a pattern.3
shielding: A conducting or magnetic material placed so as to
decrease susceptibility to interference and to increase
resolution.4
shift: A casting discontinuity caused by mismatch of cope
and drag or of cores and mold.3
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shoe: A device used to adapt a straight beam transducer for
use in a specific type of testing, including angle beam or
surface wave tests and tests on curved surfaces.12 See
also wedge.7
shot: A short energizing cycle in a magnetic particle test.6,16
shot peening: Cold working the surface of a metal by
metal shot impingement. Used to clean a part surface
before inspection.3
shoulder: Cylindrical metal component surface, machined
to receive threading indentations but in fact not
threaded, where the thread stops on the outside surface
of the pipe.8
shrink: Internal rupture occurring in castings due to contraction during cooling, usually caused by variations in
solidification rates in the mold. Includes shrinkage
sponge, small voids (stringers or bunches) or a fingerprint pattern of semifused seams. Also applied to surface shrinkage cracks.2,6
shrink mark: A surface depression on a casting that sometimes occurs next to a thick section that cools more
slowly than adjacent sections.3
shrinkage cavities: Cavities in castings caused by lack of
sufficient molten metal as the casting cools.2,3
shrinkage cracks: Hot tears associated with shrinkage cavities.2,3
shrinkage porosity or sponge: Porous metal often with a
network of fine cracks formed during solidification of
molten metal. At surface, may form a localized, lacy or
honeycombed penetrant indication.2
SI: The International System of units of measurement. An
international system of measurement based on seven
units: meter (m), kilogram (kg), second (s), kelvin (K),
ampere (A), candela (cd) and mole (mol). See also
MKSA.4,14
signal: Response containing relevant information.4,13
signal electrode: Transparent conducting film on the inner
surface of a vidicon’s faceplate and a thin photoconductive layer deposited on the film.8
signal processing: Acquisition, storage, analysis, alteration
and output of digital data through a computer.8
signal-to-noise ratio: The ratio of signal values (responses
that contain relevant information) to baseline noise values (responses that contain nonrelevant information).
See noise.4,7,13
simple magnifier: A microscope having a single converging lens.8
skim gate: A gating arrangement designed to prevent the
passage of slag and other undesirable material into the
casting.3
skimmer: A tool for removing scum, slag and dross from
the surface of molten metal.3
skin: A thin outside metal layer, not formed by bonding as
in cladding or electroplating, that differs in composition, structure or other characteristic from the main
mass of metal.3
skin depth: See depth of penetration.
skin effect: The phenomena wherein the depth of penetration of electrical currents into a conductor decreases as
the frequency of the current is increased. At very high
frequencies, the current flow is restricted to an
extremely thin outer layer of the conductor. See depth
of penetration.4,13
skip distance: In angle beam tests of plate or pipe, the distance from the sound entry point to the first reflection
point on the same surface. See V-path.7,12
slag: A nonmetallic product resulting from the mutual dissolution of flux and nonmetallic impurities in smelting
and refining operations.3
slag inclusions: Nonmetallic solid material entrapped in
weld metal or between weld metal and base metal.2,3
slag lines: Elongated cavities containing slag or other foreign matter in fusion welds.2,3
slide: Part of a die generally arranged to move parallel to
the parting line, the inner end forming a part of the die
cavity wall and involving one or more undercuts and
sometimes including a core or cores.3
sliver: A discontinuity consisting of a very thin elongated
piece of metal attached by only one end to the parent
metal into whose surface it has been rolled.2
slurry: A free-flowing pumpable suspension of a fine solid
in a liquid.6
slush casting: A casting made by pouring an alloy into a
metal mold, allowing it to remain long enough to form a
thin shell and then pouring out the remaining liquid.3
smoothing: In image processing, use of positive coefficients in a linear combination of pixel values to
smoothen abrupt transitions in a digital image. Also
called low pass filtering.8
snap flask: A hinged flask removed from the mold after the
mold is made.3
Snell’s law: The physical law that defines the relationship
between the angle of incidence and the angle of refraction.7
sniffer probe: See detector probe.
sniffer test: See detector probe test.
SNT-TC-1A: See ASNT Recommended Practice No.
SNT-TC-1A.
soak time: The period of time when the emulsifier remains
in contact with the liquid penetrant on the surface of the
test object. Soak time ceases when the penetrant emulsifier is quenched with water or completely removed by
water rinsing. Also called emulsification time.2
soaking: Prolonged holding at a selected temperature.3
soldiers: Wooden blocks or sticks used to reinforce bodies of
sand in the cope. They usually overhang the mold cavity.3
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solidification shrinkage: The decrease in volume of a
metal during solidification.2,3
solution heat treatment: A heat treatment that causes the
hardening constituent of an alloy to go into solid solution, followed by a quench to retain it temporarily in a
supersaturated solution state at lower temperatures.3
solvent action: The ability of a liquid to dissolve another
material.2
solvent cleaning: The process of removing excess penetrant from the surface of a test object by hand wiping
with a solvent dampened cloth.2
solvent developer: A developer for penetrant tests in
which the developing powder is applied as a suspension
or solution in a quick drying solvent.2
solvent remover: A volatile liquid that can dissolve penetrant and that is used to remove excess surface penetrant from test objects by appropriate hand wiping
techniques.2
source: The location where an event takes place.5
source location: The computed origin of acoustic emission
signals.5
spalling: Cracking or flaking of small particles of metal,
usually in thin layers, from the surface of an object.2
spalling fatigue: See subcase fatigue.
spatial resolution: Width of smallest region from which
reliable data can be extracted.9
specific acoustic impedance: See acoustic impedance.
specific examination: In certification of nondestructive
testing personnel, a written examination that addresses
the specifications and products pertinent to the application. Compare general examination and practical examination.8
specification: A set of instructions or standards invoked by
a specific customer to govern the results or performance of a specific set of tasks or products.8
specimen grating: In moiré and grid nondestructive testing, a real grating, usually crossed lines, printed or
embossed on the surface of a specimen. It deforms with
the specimen as the specimen is loaded.9
spectral power distribution: The radiant power per unit
wavelength as a function of wavelength. Also known as
spectral energy distribution, spectral density and spectral distribution.8
spectral reflectance: The radiant flux reflected from a
material divided by the incident radiant flux.8
spectral transmittance: The radiant flux passing through a
medium divided by the incident radiant flux.8
spectrophotometer: Instrument used for spectrophotometry.8
spectrophotometry: Measurement of electromagnetic
radiant energy as a function of wavelength, particularly
in the ultraviolet, visible and infrared wavelengths.8
spectroradiometer: Instrument used for spectroradiometry.8
spectroradiometry: Measurement of electromagnetic
radiant power and spectral emittance, used particularly
to examine colors and to measure the spectral emittance of light sources.8
spectroscope: Instrument used for spectroscopy.8
spectroscopy: Spectrophotometry or spectroradiometry in
which the spectrum, rather than being analyzed only by
a processing unit, is presented in a visible form to the
operator for organoleptic examination.8
spectrum: (1) The amplitude distribution of frequencies in
a signal.7 (2) Representation of radiant energy in adjacent bands of hues in sequence according to the
energy’s wavelengths or frequencies. A rainbow is a well
known example of a visible spectrum.8
spectrum response: The amplification (gain) of a receiver
over a range of frequencies.7
specular: Pertaining to a mirror-like reflective finish, as of a
metal. Compare lambertian.8
specular reflection: When reflected waves and incident
waves form equal angles at the reflecting surface.8
speed of light: The speed of all radiant energy, including
light, is 2.997925 × 10 8 m· s–1 in vacuum (approximately
186,000 mi· s–1). In all materials the speed is less and
varies with the material’s index of refraction, which
itself varies with wavelength.8,20
speed of vision: The reciprocal of the duration of the exposure time required for something to be seen.8,20
spherical wave: A wave in which points of the same phase
lie on surfaces of concentric spheres.18,7
spheroidizing: Heating and cooling to produce a
spheroidal or globular form of carbide in steel.3
split gate: A gate having the sprue axis in the die parting.3
spot check tests: Testing a number of objects from a lot to
determine the lot’s quality, the sample size being chosen arbitrarily, such as five or ten percent. This does not
provide accurate assurance of the lot’s quality.2
spot examination: Local examination of welds or castings.2
spray scrubber: Technique of pressure washing nonwater
soluble penetrant from the surface by introducing a hydrophilic emulsifier or detergent into the water wash.2
sprue: (1) The channel that connects the pouring basin with
the runner. (2) Sometimes used to mean all gates, risers, runners and similar scrap. Also called downsprue or
downgate.3
spurious echo: A general term used for any indication that
cannot be associated with a discontinuity or boundary
at the location displayed.7
squid: An acronym (superconducting quantum interference device). A sensitive detector of magnetic fields
using a quantum effect.4
squint angle: The angle by which the ultrasonic beam axis
deviates from the probe axis.7
squirter: See water column.
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standard: (1) A physical object with known material characteristics used as a basis for comparison or calibration.
(2) A concept established by authority, custom or agreement to serve as a model or rule in the measurement of
quantity or the establishment of a practice or procedure.7,12 (3) Document to control and govern practices
in an industry or application, applied on a national or
international basis and usually produced by consensus.
See also acceptance standard, working standard and
reference standard.4,8,13
standard atmospheric conditions: Atmospheric pressure
of 101.325 kPa (14.6959 lbf·in.–2). Temperature of 20 °C
(293.15 K, 68 °F or 527.67 °R). The density of dry air at
these conditions is 1.2041 kg·m–3 (0.07517 lb·ft–3).1
standard barometric pressure at sea level: See atmospheric pressure.
standard depth of penetration: See depth of penetration.
standard leak: A device that permits a tracer gas to be
introduced into a leak detector or a leak testing system
at a known rate to facilitate tune up and calibration of
the leak detector or test system.1
standard observer response curve: See eye sensitivity
curve.
standing wave: A wave in which the energy flux is zero at
all points. Such waves result from the interaction of
similar waves traveling in opposite directions as when
reflected waves meet advancing waves. A particular
case is that of waves in a body whose thickness is an
integral multiple of half-wavelengths, as in resonance
testing.7,10,12
steady state: Thermal equilibrium, a condition of an object
wherein the temperatures throughout the object
remain constant.9
steel: An iron alloy, usually with less than two percent carbon.8
Stefan-Boltzmann Law: Relationship governing the wavelength independent rate of emission of radiant energy
per unit area. The law relates the total radiation intensity to the fourth power of absolute temperature and
emissivity of the material surface. For example, intensity (heat flow) from a copper block at 100 °C (212 °F)
is 300 W·m–2 (95 BTU·ft–2·h–1). (Stefan-Boltzmann
constant for photon emission = 1.52041 × 1015 photon·s–1·m–2·K–2.)9
stepped wedge: A device used, with appropriate penetrameters on each step, for the inspection of parts having great variations in thickness or complex geometries.
The stepped wedge must be made of material radiographically similar to that being radiographed.11
stereo photography: Close range photogrammetric technique involving the capture and viewing of two images
of the same object in order to reconstruct a three
dimensional image of the object.8
straight beam: An ultrasonic wave traveling normal to the
test surface.7,12
strain: The alteration of the shape of a material by external
forces.
stress: (1) In physics, the force in a material that resists
external forces such as tension and compression.
(2) Force per unit area.8
stress corrosion cracking: Failure by cracking under
combined action of corrosion and stress, either applied
or residual. Cracking may be either intergranular or
transgranular, depending on the metal and corrosive
medium.2
stress raiser: Contour or property change that causes local
concentration of stress.8
stress relieving: Heating to a suitable temperature, holding long enough to reduce residual stresses and then
cooling slowly enough to minimize the development of
new residual stresses.3
stress riser: See stress raiser.
stringer: In wrought materials, an elongated configuration
of microconstituents or foreign material aligned in the
direction of working. Commonly, the term is associated
with elongated oxide or sulfide inclusions in steel.2
structural integrity test (SIT): A test that demonstrates
the capability of a vessel to withstand specified internal
pressure loads.1
subcase fatigue: Fatigue originating below the case depth.
Compare case crushing. See also spalling fatigue.8
subcase origin fatigue: See subcase fatigue.
substrate: Layer of metal underlying a coating, regardless
of whether the layer is base metal.2
subsurface discontinuity: Any discontinuity that does not
extend through the surface of the object in which it
exists.2 See near surface discontinuity.
subsurface fatigue: Fatigue cracking that originates below
the surface. Usually associated with hard surfaced or
shot peened parts but may occur anytime subsurface
stresses exceed surface stresses.8
suppression: See reject.
surface wave: See Rayleigh wave.
survey meter: A portable instrument that measures dose
rate of exposure or radiation intensity.11
suspension: (1) A two-phase system comprising finely
divided magnetic particles dispersed in a liquid vehicle.2 (2) Liquid bath, often a petroleum distillate, in
which solid particles are suspended.4,6 See vehicle.
SV wave: See shear vertical wave.
sweep: The uniform and repeated movement of a spot
across the screen of the cathode ray tube to form the
horizontal baseline.7
sweep delay: A delay in time of starting the sweep after the
initial pulse. Also denotes the control for adjusting the
time. 7,12
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sweep length: The length of time or distance represented
by the horizontal baseline on an A-scan.7,12
swinging field: See multidirectional magnetization.
T
tangential field: Magnetic field at the object’s surface parallel to the surface. The tangential field runs uniformly
along the material/air interface and is generally weaker
than the field in the object. Measurement can be influenced by external fields.6
tape head probe: The head of a tape recorder used as an
eddy current coil. A type of horseshoe coil.4
Tarasov etching technique: Way of visually inspecting for
the presence of deleterious effects in hardened steels
by using specific etching solutions and methods of
inspection.8
temper: (1) In heat treatment, reheating hardened steel or
hardened cast iron to some temperature below the
eutectoid temperature for the purpose of decreasing
the hardness and increasing the toughness. The process
also is sometimes applied to normalized steel. (2) In
tool steels, temper is inadvisedly used to denote the carbon content. (3) In nonferrous alloys and in some ferrous alloys (steels that cannot be hardened by heat
treatment), the hardness and strength produced by
mechanical or thermal treatment or both are characterized by a certain structure, mechanical properties or
reduction in area during cold working.3
temper brittleness: Brittleness that results when certain
steels are held within, or are cooled slowly through, a
certain range of temperature below the transformation
range. The brittleness is revealed by notched bar
impact tests at or below room temperature.3
temperature: A measure of the intensity of particle motion
in degrees Celsius (°C) or degrees Fahrenheit (°F) or,
in the absolute scale, kelvin (K) or degrees Rankine (°R), where 1 K = 1 °C = 1.8 °R = 1.8 °F. Compare
heat.9
temperature diagram: See time temperature transformation (TTT) diagram.
temperature envelope: The temperature range over
which a particular penetrant testing technique will
operate.2
tempering: Process of heating a material, particularly hardened steel, to below the austenite transformation temperature to improve ductility.8
tertiary creep: Third stage of creep, marked by steady
increase in strain to the point of fracture under constant
load.8
tesla: The SI unit of measure for magnetic flux density.
Abbreviated T. 1 T = 10,000 gauss.6
tesla meter: A magnetometer that registers field strength
in gauss (or tesla).6
test coil: The section of a coil assembly that excites and/or
detects the magnetic field in the material under electromagnetic test.4,13
test frequency: In electromagnetic testing, the number of
complete cycles per unit time of the alternating current
applied to the primary test coil.4,13
test piece: A part subjected to testing.
test quality level: See level, rejection.
test ring: A ring specimen typically made of tool steel, containing artificial subsurface discontinuities used to evaluate and compare the performance and sensitivity of
magnetic particles.6,16
test surface: The exposed surface of a test object.2,7
thermal: Physical phenomenon of heat involving the movement of molecules. Compare infrared radiation.9
thermal conductivity vacuum gage: Instrument that
operates on principle that as gas molecules are removed
from a system, the amount of heat transfer by conduction is reduced. This relationship is used to indicate
absolute pressure.1
thermal diffusivity: The speed at which heat diffuses
through an object. Expressed as the rate of temperature
change with time and represented by α. Each material
has its own characteristic value for α, combining the
overall influence of thermal conductivity, density and
specific heat. In a practical sense, thermal diffusivity
determines how fast a material will heat up or cool
down. The rate of temperature change with time is
more rapid in a material with a high thermal diffusivity
(e.g., metals) and slower in a material with a lower diffusivity (e.g., plastics).9
thermal equilibrium: Condition of an object wherein
temperatures throughout the object remain constant.9
thermography: Imaging or viewing of an object or process
through sensing of infrared radiation emitted by it. The
temperature patterns on the material surface produce
corresponding radiation patterns. Thus, heat flow by
both conduction and radiation may be observed and
used to locate material discontinuities.9
three-way sort: An electromagnetic sort based on a test
object signal response above or below two levels established by three or more calibration standards.4,13
threshold: See adaptive thresholding, resolution threshold
and threshold level.
threshold level: The setting of an instrument that causes it
to register only those changes in response greater or
less than a specified magnitude.4,13
thresholding: Digital data processing technique that
reduces a gray level image into a binary image.8
throat, actual: Shortest distance from the root of a fillet
weld to its face, as opposed to theoretical throat or
weld size.8
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throat, theoretical: The distance from the beginning of
the root of the weld perpendicular to the hypotenuse of
the largest right triangle that can be inscribed within
the cross section of the fillet weld. Compare weld size.8
throat, weld: Distance from the root of a fillet weld to its
face. Compare weld size and throat, actual.8
throttling: Reducing the net pumping speed of a pumping
system by partially closing a valve or installing a section
of pipeline with low conductance.1
through-coil method: See coil method.
throughput: Quantity of gas, or total number of molecules
at a specific temperature, passing a section of a vacuum
system per unit of time. See leakage rate.1
through-transmission: A test technique in which magnetic or ultrasonic energy is transmitted through the
test object and received by a second transducer on the
opposite side. Changes in received signal amplitude are
evaluated as indications of variations in material continuity.7
tie rod: A bar used in a casting machine to hold dies locked
against pressure and, in general, also to serve as a way
along which the movable die platen slides.3
TIG welding: Tungsten inert gas welding.
time base: See sweep.
time delay: See sweep delay.
time differential: See delta t.
time of flight: The time for an acoustic wave to travel
between two points. For example, the time required for
a pulse to travel from the transmitter to the receiver via
diffraction at a discontinuity edge or along the surface
of the test object.7
time temperature transformation (TTT) diagram: A
graph showing time required at any temperature to
transform austenite to pearlite, bainite or martensite.8
tip: In casual usage, the distal or objective end of a
borescope.8
toe crack: A base metal crack at the toe of a weld.2
toggle: The linkage in a casting machine employed to multiply pressure mechanically in locking the dies. Also,
linkage used for core locking and withdrawal in a die.3
tolerance: Permissible deviation or variation from exact
dimensions or standards.2
tone burst: A wave train consisting of several cycles of the
same frequency.7
tool mark: Shallow indentation or groove made by the
movement of manufacturing tools over a surface. Compare gouge or nick.8
toroidal field: An induced magnetic field occurring in a
ring test object when current is induced. See current
induction technique.6
torr: Unit of absolute pressure nearly equal to 1.33332 kPa
(1.000 mm Hg).1
trace: Line formed by an electron beam scanning from left
to right on a video screen to generate a picture.8
tracer: In leak testing, a gas that is sensed as it escapes from
confinement.8
tracer gas: A gas that can be detected by a specific leak
detector and thus disclose the presence of a leak in a
system. Also called search gas.1
tracer probe test: A leak test in which a tracer gas is
applied by means of a probe to an accessible test surface on an evacuated test object so that the area covered by the tracer gas is localized. A leak detector in the
line to the vacuum pump enables individual leaks to be
located when they admit tracer gas.1
tracer standard leak: A standard leak in which the contained gas is a tracer gas compound.1
transducer: (1) Any device that transforms energy from one
form to another. (2) In electromagnetic testing, the test
coil.4 (3) An electroacoustical or magnetoacoustic device
containing an element for converting electrical energy
into acoustical energy and vice versa. See search unit.7,12
transducer relative sensitivity: The response of the transducer to a given and reproducible artificial source.5
transducer, differential: A piezoelectric twin element or
dual pole transducer, the output poles of which are isolated from the case and are at a floating potential.5
transducer, flat response: A transducer whose frequency
response has no resonance within its specified frequency band (the bandwidth to –3 dB being defined),
the ratio between the upper and lower limits of its band
being typically not less than 10.5
transducer, resonant: A transducer that uses the mechanical amplification due to a resonant frequency (or
several close resonant frequencies) to give high sensitivity in a narrow band, typically ±10 percent of the
principal resonant frequency at the –3 dB points.5
transducer, single ended: A piezoelectric single element
transducer, the output pole of which is isolated from
the case, the other pole being at the same potential as
the case.5
transducer, wideband: A transducer that uses the mechanical amplification due to the superposition of multiple resonances to give high sensitivity in several narrow
bands within a specified wide band.5
transfer function: Description of changes to the waves
arising as they propagate through the medium or, for a
transducer, the relationship between the transducer
output signal and the physical parameters of the wave.5
transformation diagram: See time temperature transformation (TTT) diagram.
transition flow: Phenomenon that occurs when the mean
free path of gas is about equal to the cross sectional
dimension of a leak or the tube through which flow is
occurring.1
transient heat flow: Heat flow occurring during the time it
takes an object to reach thermal equilibrium or steady
state.9
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transmission angle: The incident angle of a transmitted
ultrasonic beam. It is zero degrees when the beam is
perpendicular (normal) to the test surface.7,10
transmission characteristics: Test object characteristics
that influence the passage of ultrasonic energy, including scattering, attenuation or surface conditions.7
transmission technique: See through-transmission.
transmitter: (1) The transducer that emits ultrasonic
energy. (2) The electrical circuits that generate the signals emitted by the transducer.7
transverse wave: See shear wave.
trimming: (1) In forging or die casting, removing the parting line flash and gates by shearing. (2) In castings, the
removal of gates, risers and fins.3
troland: A unit of retinal illuminance equal to that produced by a surface whose luminance is 1 nit when the
pupil measures 1 mm2. 1 nit = 1 candela per square
meter (1 cd·m–2).8
true continuous method: Test technique in which magnetizing current is applied before application of magnetic
particles and is maintained without interruption
throughout the examination.6,16
TTT: Time temperature transformation.
tubing string: Pipe with which oil or gas has contact as it is
brought to the earth’s surface. Also called production
string.8
tungsten inclusions: Inclusions in welds resulting from
solidified droplets, particles or splinters of tungsten
from welding electrodes.2
tungsten inert gas (TIG) welding: See gas tungsten arc
welding.
two-way sort: An electromagnetic sort based on a test
object signal response above or below a level established by two or more calibration standards.4,13
U
U shaped coil: See horseshoe coil.
ultrasonic: Pertaining to acoustic vibration frequencies
greater than about 20 kHz.7,12
ultrasonic absorption: The damping of ultrasonic waves
as they pass through a medium.10 See attenuation coefficient.7
ultrasonic spectroscopy: Analysis of the frequency content of an acoustic wave. Generally performed mathematically by using a fast Fourier transform.7
ultrasonic spectrum: Usually, the frequency of sound
waves ranging from 20 kHz to 10 MHz, but may extend
much higher in special applications.7
ultrasonic testing: Nondestructive testing using acoustic
energy in the ultrasonic spectrum for interrogation.7
ultraviolet borescope: See borescope, ultraviolet.
ultraviolet radiation: (1) Electromagnetic radiation with
wavelengths ranging from about 4 to about 400 nm,
between visible light and X-rays. Compare near ultraviolet radiation.8 (2) The range of wavelengths used for
fluorescent nondestructive testing is typically between
320 and 400 nm. Shorter wavelengths are very hazardous. Compare black light.6
ultraviolet radiometer: A meter, usually calibrated at
365 nm, used in fluorescent liquid penetrant and magnetic particle testing to measure the output of ultraviolet lamps.8
underbead crack: A subsurface crack in the base metal
adjacent to the weld fusion zone.2
undercut: Undesirable depression or groove left unfilled
by weld metal, created by melting during welding and
located in base material at the toe of a weld.2,8
unit die: A die block that contains several cavity inserts for
making different kinds of die castings.3
unsharpness, geometric: The fuzziness or lack of definition in a radiographic image resulting from the source
size, object-to-film distance and the source-to-object
distance.11
upper confidence limit: A calculated value constructed
from sample data with the intention of placing a statistical upper boundary on a true leakage rate.1
upset: A frame used to deepen either the cope or drag in a
casting mold.3
UT: Ultrasonic testing.
V
V-path: In angle beam tests of plate or cylindrical sections,
the path of the ultrasonic beam in the test object from
point of entry on the front surface to the back surface
and reflecting to the front surface again. See also skip
distance.7
vacuum: Space containing gas at a pressure below atmospheric pressure.1
vacuum box: Device used to obtain a differential pressure
across a weld or part of a pressure boundary that cannot
be directly pressurized.1
vacuum melting: Melting in a vacuum to prevent contamination from air, as well as to remove gases already dissolved in the metal. The solidification may also be
carried out in a vacuum or at low pressure.3
vacuum pressure testing: A leak testing procedure in
which the test object containing tracer gas is placed
within an evacuated enclosure and the tracer gas is
detected after entering the enclosure.1 Also called bell
jar testing.
vacuum testing: Method of testing for leaks in which the
object under test is evacuated and the tracer gas is
applied to the outside surface of the test object.
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vapor pressure: The pressure exerted by the vapor of a liquid when in equilibrium with the surface of the liquid.
These limiting pressures can restrict the levels of pressurization of enclosures with these tracer gases during
pressure leak testing.1,2
variable standard leak: A device that permits a tracer gas
to be introduced to the leak detector at a rate adjustable
by the operator.1
vector quantity: Any physical quantity that is specified
with both magnitude and direction and that obeys the
parallelogram law of addition.4,14
vehicle: A liquid medium for the suspension of magnetic
particles, often a light petroleum distillate or conditioned water. See carrier fluid.6,16
vent: A small opening in a mold for the escape of gases.3
verification test: Tests intended to confirm the capability
of the type A leak test method and equipment to determine the containment leakage rate.1
vertical limit: The readable level of vertical indication on
an A-scan.7
vertical linearity: See linearity, amplitude.
video: Pertaining to the transmission and display of images
in an electronic format that can be displayed on a
screen.8
video presentation: An electronic screen presentation in
which radiofrequency signals have been rectified and
usually filtered.7,12
videoscope: Jargon for video borescope.8
vidicon tube: Television tube that uses the photoconduction method. Compare image orthicon.8
vigilance decrement: Degradation of reliability during
performance of visual activities over a period of time.
See also psychophysics.8
virtual grating: In moiré and grid nondestructive testing,
closely spaced walls (or planes) of light separated by
darkness, created by the alternating constructive and
destructive interference of two intersecting beams of
coherent light.9
virtual leak: Emission of vapors within a vacuum system
that result from condensible or trapped vapors. They
gradually evaporate from surfaces or escape from pockets raising the absolute pressure in the same manner as
a real leak.1
viscous flow: The flow of gas or gas mixtures through a leak
or duct under conditions such that the mean free path is
smaller than the cross section of the leak or opening.
Viscous flow may be either laminar or turbulent and is
most likely to occur during leak tests at atmospheric or
higher pressures. With vacuum conditions, the flow of
tracer gases to the leak detector element is usually by
diffusion, resulting in slow response to leaks being
probed by a tracer jet.1
visibility: The quality or state of being perceivable by the
eye. In many outdoor applications, visibility is defined in
terms of the distance at which an object can be just perceived by the eye. In indoor applications it usually is
defined in terms of the contrast or size of a standard test
object, observed under standardized viewing conditions,
having the same threshold as the given object.8,20
visible light: Radiant energy generated in the 400 to
700 nm wavelength range.6,16
vision: Perception by eyesight. See far vision, machine
vision, mesopic vision, near vision, peripheral vision,
photopic vision, scotopic vision and speed of vision.8
vision acuity: The ability to distinguish fine details visually.
Quantitatively, it is the reciprocal of the minimum
angular separation in minutes of two lines of width subtending one minute of arc when the lines are just
resolvable as separate.8,20
visual acuity: See vision acuity.
visual angle: The angle subtended by an object or detail at
the point of observation. It usually is measured in minutes of arc.8,20
visual background noise: Formations on or signals from a
test object that constitutes the background to a discontinuity. The higher the level of visual background noise,
the more difficult it is to distinguish a discontinuity.8
visual efficiency: Reliability of a visual system. The term
visual efficiency uses 20/20 near vision acuity as a baseline for 100 percent visual efficiency.8
visual field: The locus of objects or points in space that can
be perceived when the head and eyes are kept fixed.
The field may be monocular or binocular.8,20
visual perception: The interpretation of impressions
transmitted from the retina to the brain in terms of
information about a physical world displayed before the
eye. Visual perception involves any one or more of the
following: recognition of the presence of something
(object, aperture or medium); identifying it; locating it
in space; noting its relation to other things; identifying
its movement, color, brightness or form.8,20
visual performance: The quantitative assessment of the
performance of a visual task, taking into consideration
speed and accuracy.8,20
visual purple: Chromoprotein called rhodopsin, the photosensitive pigment of rod vision. The mechanism of
converting light energy into nerve impulses is a photochemical process in the retina. Chromoprotein is transformed by the action of radiant energy into a succession
of products, finally yielding the protein called opsin
plus the carotenoid known as retinene.8
visual task: The appearance and immediate background of
those details and objects that must be seen for the performance of a given activity. The term visual task is a
misnomer because it refers to the visual display itself
and not the task of extracting information from it.8,20
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visual testing: Method of nondestructive testing using
electromagnetic radiation at visible frequencies.8
voids: Hollow spots, depressions or cavities. See also discontinuity and dislocation.8
VT: Visual and optical testing.
W
wash: A coating applied to the face of a mold prior to casting.3
water break free: Rinse water, having the ability to cover
an entire surface in an unbroken film.2
water break test: A quality control test for conditioned
water. Verifies that the water’s surface tension has been
sufficiently reduced by a wetting agent to satisfactorily
cover test objects and disperse magnetic particles. May
also be used to establish surface cleanliness before
testing.6
water column: A tube filled with water and attached to the
front of a transducer to couple an ultrasonic beam to a
test object. A delay line between the initial pulse and
the front surface signal. Also serves as a coupling
device. See also delay line.7
water jet: An unsupported stream of water carrying ultrasonic signals between the transducer and the test object
surface. Also called a squirter.7
water line: A tube or other passage through which water is
circulated to cool a casting die.3
water path: In immersion testing or with a water column,
the distance from the transducer face to the test object’s
front surface.7,12
water tolerance: The amount of water that a penetrant or
emulsifier can absorb before its effectiveness is
impaired.2
wave interference: The production of a series of maxima
and minima of sound pressure as a consequence of the
superposition of waves having different phases.7,12
wave train: A series of waves or groups of waves passing
along the same course at regular intervals.7
wavefront: In a wave disturbance, the locus of points having the same phase.7,12
wavelength: The distance needed in the propagation direction for a wave to go through a complete cycle.7,10
weak sand: Refers to sand that will not hold together when
used to make a mold.3
wear: See erosion; rat’s tooth principle; wear, adhesive; and
wear, fretting.
wear face: A protective material on the face of a transducer
to prevent wear of the piezoelectric element.7,12
wear oxidation: See wear, fretting.
wear, adhesive: Degradation of a surface because of
microwelding and consequent fracture due to the sliding of one surface against another. Types include fretting, galling and scuffing.8
wear, fretting: Surface degradation caused by microwelding and microfractures on surfaces rubbing each other.
Also called chafing, friction oxidation and wear oxidation. See also cocoa and false brinelling.8
wedge: A device used to direct ultrasonic energy into a test
object at an acute angle.12 See also shoe.7
weld bead: A deposit of filler metal from a single welding
pass.2
weld crack: A crack in weld metal.2
weld line: The junction of the weld metal and the base
metal or the junction of base metal parts when filler
metal is not used.2
weld metal: That portion of a weld that has been melted
during welding.2
weld nugget: The weld metal in spot, seam or projection
welding.2
weld size: Thickness of weld metal — in a fillet weld the
distance from the root to the toe of the largest isosceles
right triangle that can be inscribed in a cross section of
the weld.8
weld throat: See throat.
welder’s flash: Clinical condition, specifically keratoconjunctivitis, commonly caused by overexposure to ultraviolet radiation of welding arc.8
wet developer: A developer in which the developing powder is applied as a suspension or solution in a liquid,
usually water or solvent.2
wet method: A testing technique in which magnetic particles are applied as a suspension in a liquid vehicle.6,16
wet slurry technique: A magnetic particle test in which
the particles are suspended in high viscosity vehicle.6,16
wetting action: The ability of a liquid to spontaneously
spread over and adhere to solid surfaces.2
wetting agent: A substance that increases wetting action
by reducing the surface tension of a liquid, thereby
reducing the formation of air bubbles.2
wheel transducer: A device that couples ultrasonic
energy to a test object through the rolling contact area
of a wheel containing a liquid and one or more transducers.7,12
white light: Light combining all frequencies in the visible
spectrum.8
Wien’s Displacement Law: For practical infrared imaging, Wien’s Displacement Law gives the wavelength of
maximum emittance.9
wobble: In electromagnetic testing, an effect that produces
variations in an output signal of a test system and arises
from variations in coil spacing due to lateral motion of
the test object in passing through an encircling coil.4,13
work hardening: Increase in hardness accompanying
plastic deformation of a metal. Usually caused in a
metal by repeated bending or flexing. Compare creep
and recovery.8
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working standard: Work piece or energy source calibrated
and used in place of expensive reference standards. In
the calibrating of photometers, the standard would be a
light source.8
worm holes: Elongated or tubular cavities due to
entrapped gas. Also called pipes.2
wrap around: The display of misleading ultrasonic reflections from a previously transmitted pulse due to the use
of excessive pulse repetition frequency.21 See ghost.7
Y
yoke: A U shaped magnet that induces a field in the area of
the test object that lies between its poles (magnetic particle or flux leakage testing). Yokes may be permanent
magnets, alternating current electromagnets or direct
current electromagnets.4,6,13
X
Z
X-ray: Penetrating electromagnetic radiation emitted when
the inner orbital electrons of an atom are excited and
release energy. Radiation is nonisotopic in origin and is
generated by bombarding a metallic target with high
speed electrons.11
zircon sand: A highly absorptive material used as a blocking or masking medium for drilled holes, slots and
highly irregular geometries to reduce scattering during
radiography.3
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REFERENCES
1. Nondestructive Testing Handbook, second edition:
Vol. 1, Leak Testing. Columbus, OH: American Society for Nondestructive Testing (1982).
2. Nondestructive Testing Handbook, second edition:
Vol. 2, Liquid Penetrant Tests. Columbus, OH: American Society for Nondestructive Testing (1982).
3. Nondestructive Testing Handbook, second edition:
Vol. 3, Radiography and Radiation Testing. Columbus, OH: American Society for Nondestructive Testing (1985).
4. Nondestructive Testing Handbook, second edition:
Vol. 4, Electromagnetic Testing. Columbus, OH:
American Society for Nondestructive Testing (1986).
5. Nondestructive Testing Handbook, second edition:
Vol. 5, Acoustic Emission Testing. Columbus, OH:
American Society for Nondestructive Testing (1987).
6. Nondestructive Testing Handbook, second edition:
Vol. 6, Magnetic Particle Testing. Columbus, OH:
American Society for Nondestructive Testing (1989).
7. Nondestructive Testing Handbook, second edition:
Vol. 7, Ultrasonic Testing. Columbus, OH: American
Society for Nondestructive Testing (1991).
8. Nondestructive Testing Handbook, second edition:
Vol. 8, Visual and Optical Testing. Columbus, OH:
American Society for Nondestructive Testing (1993).
9. Nondestructive Testing Handbook, second edition:
Vol. 9, Special Nondestructive Testing Methods.
Columbus, OH: American Society for Nondestructive Testing (1995).
10. Weismantel, E. “Glossary of Terms Frequently Used
in Nondestructive Testing.” Materials Evaluation.
Vol. 33, No. 4. Columbus, OH: American Society for
Nondestructive Testing (1975).
11. NDT Terminology. Wilmington, DE: E.I. du Pont de
Nemours & Company, Photo Products Department
(n.d.).
12. Nondestructive Testing Methods. TO33B-1-1
(NAVAIR 01-1A-16) TM43-0103. Washington, DC:
Department of Defense United States Air Force
(June 1984): p 1.25.
13. E 268-81, Definitions Approved for Use by Agencies
of the Department of Defense as Part of Federal Test
Method Standard No. 151b and for Listing in the
DoD Index of Specifications and Standards. Philadelphia, PA: American Society for Testing and Materials
(1981).
14. IEEE Standard Dictionary of Electrical and Electronic
Terms. New York, NY: Institute of Electrical and Electronics Engineers (distributed by Wiley-Interscience, a
division of John Wiley and Sons) (1984).
15. Glossary of Terms Used in Nondestructive Testing,
Part 2. London, United Kingdom: British Standards
Institute (November 1984).
16. E 269-89, Standard Definitions of Terms Relating to
Magnetic Particle Examination. Philadelphia, PA:
American Society for Testing and Materials (1989).
17. API RP5A5, Recommended Practice for Field Inspection of New Casing, Tubing and Plain End Drill Pipe,
third edition. Washington, DC: American Petroleum
Institute (1987).
18. “Ultrasonic Flaw Detection.” The Glossary of Terms
Used in Nondestructive Testing. British Standard
3683, Part 4. London, England: British Standards
Institute (1985).
19. EPRI Learning Modules. Charlotte, NC: Electric
Power Research Institute (various years).
20. IES Lighting Handbook: Reference Volume. New
York, NY: Illuminating Engineering Society of North
America (1984).
21. MIL-STD-371, Glossary of Terms and Definitions for
Ultrasonic Testing Procedures. Washington, DC
(Department of Defense): United States Army
(October 1987).
22. 1992 Annual Book of ASTM Standards. Section 3,
Metals Test Methods and Analytical Procedures:
Vol. 03.03, Nondestructive Testing. Philadelphia, PA:
American Society for Testing and Materials (1992).
23. E 1316, Standard Terminology for Nondestructive
Examinations. Philadelphia, PA: The American Society for Testing and Materials (1993).
24. E 500-85, Standard Definitions of Terms Relating to
Ultrasonic Testing. Philadelphia, PA: American Society for Testing and Materials (1985).
25. Mish, Frederick C., ed. Webster’s Ninth New Collegiate Dictionary. Springfield, MA: Merriam-Webster
(1984).
26. “Nondestructive Inspection and Quality Control.”
Metals Handbook. Vol. 11. Metals Park, OH: American Society for Metals (1976).
27. ANSI/ANS-58.6. New York, NY: American National
Standards Institute (1981).
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