:
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. In a linear system, the vertical excursion is proportional to the amplitude of the
signal.
:
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.
:
absolute measurement
Measurement made with an absolute coil.
:
absolute pressure
Pressure above absolute zero value, or pressure above that of empty space. Equal to sum of local atmospheric
pressure and gage atmosphere.
:
absolute temperature
Temperature measured from absolute zero temperature, expressed in Kelvin (K) in SI.
:
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.
:
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 .
:
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.
:
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.
:
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.
:
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.
:
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.
:
accuracy
The degree of conformity of a measurement to a standard or true value.
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.
:
acoustic emission activity
The number of bursts (or events, if the appropriate conditions are fulfilled) detected during an acoustic
emission test.
:
acoustic emission count
The number of times the signal amplitude exceeds the preset reference threshold.
:
acoustic emission event
A microstructural displacement that produces elastic waves in a material under load or stress.
:
acoustic emission rate
The number of times the amplitude has exceeded the threshold in a specified unit of time.
:
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.
:
acoustic microscopy
High resolution, high frequency ultrasonic techniques used to produce images of features beneath the surface
of a test object.
:
acuity
See neural acuity, vision acuity.
:
adaptive thresholding
Threshold value varying with inconstant background gray level.
:
adhesive wear
See wear, adhesive.
:
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.
:
agency
The organization selected by an authority to perform nondestructive testing, as required by a specification or
purchase order.
:
air dried
Drying of any item such as a core or mold without application of heat.
:
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.
:
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.
:
algorithm
A prescribed set of well defined rules or processes for the solution of a mathematical problem in a finite
number of steps.
:
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.
:
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.
:
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.
:
alternating current
An electrical current that reverses its direction of flow at regular intervals.
:
alternating current field
The varying magnetic field produced around a conductor by an alternating current flowing in the conductor.
:
alternating current magnetization
Magnetization by a magnetic field that is generated when alternating current is flowing.
:
ambient light
Light in the environment as opposed to illumination provided by a visual testing system.
:
ambient or atmospheric temperature
Temperature of surrounding atmosphere. Also called dry bulb temperature.
:
Ampere
A unit of electric current. Abbreviated A or amp.
:
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).
:
ampere turns
The product of the number of turns of a coil and the current in amperes flowing through the coil.
:
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.
:
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.
:
analog-to-digital converter
A circuit whose input is information in analog form and whose output is the same information in digital form.
:
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.
:
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.
:
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.
:
angle of refraction
The angle between the beam axis of a refracted wave and the normal to the refracting interface.
:
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.
:
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.
:
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.
:
anisotropy
The characteristic of exhibiting different values of a property (velocity, for example) in different directions in
the material.
:
annealing
Process of heating and cooling a material, usually to reduce residual stresses or to make it softer.
:
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.
:
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.
:
anomaly
A variation from normal material or product quality.
:
antinode
A point in a standing wave where certain characteristics of the wave field have maximum amplitude.
:
AOQ
Average outgoing quality.
:
AOQL
Average outgoing quality limit.
:
AQL
See acceptable quality level.
:
arbor
A bar or mandrel on which a core is built.
:
arc
A luminous high temperature discharge produced when an electric current flows across a gaseous gap.
arc strikes
:
Localized burn damage to an object from the arc caused by breaking an energized electric circuit. Also called
arc burns.
:
arc welding
See electric arc welding.
:
arcing
Current flow through a gap, often accompanied by intense heat and light.
:
Argand diagram
A graphical representation of a vector used in complex notation.
:
array
(1) A group of transducers used for source location. (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.
:
articulated pole pieces
On a magnetizing yoke, independently adjustable magnetic elements enabling the magnetization of irregular
test object profiles.
:
artifact
In nondestructive testing, an indication that may be interpreted erroneously as a discontinuity.
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. A manufactured material
anomaly. See acceptance standard and reference standard.
:
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.
:
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.
:
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 lb f·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.
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. (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. (3) The change in signal strength caused by an electronic device such as an
attenuator. (4) In radiography, the decrease in exposure rate of radiation caused by passage through material.
:
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.
:
attenuator
A device for causing or measuring attenuation. Usually calibrated in decibels.
:
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.
:
automated system
Acting mechanism that performs required tasks at a determined time and in a fixed sequence in response to
certain conditions.
:
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.
:
back draft
A reverse taper on the pattern that prevents its removal from the mold.
:
back reflection
The signal received from the far boundary or back surface of a test object.
:
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.
:
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.
:
background cylinder and difference cylinder
Two devices used to calculate illuminance by using the equivalent sphere illumination technique.
:
background fluorescence
Fluorescent residues observed over the general surface of the test object during fluorescent penetrant testing
and fluorescent magnetic particle testing.
:
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.
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.
:
backing board
A second bottom board where molds are opened.
:
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.
:
baked core
A core that has been heated or baked until it is thoroughly dry.
:
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.
:
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.
:
bandwidth
The difference between the lower and upper cutoff frequencies.
:
barium clay
A molding clay containing barium, used to eliminate or reduce the amount of scattered or secondary radiation
reaching the film.
:
barometer
Absolute pressure gage used to measure the atmospheric pressure at a specific location.
:
barometric pressure
Ambient pressure caused by the weight of the Earth's atmosphere. 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.
:
basin
A cavity on top of the cope into which metal is poured before it enters the sprue. Also called pouring basin.
:
basis calibration
Standardizing an ultrasonic testing instrument using calibration reflectors described in an application
document.
:
bath
The water or oil used as a vehicle for wet method magnetic particles. 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. See suspension.
:
bead
A half-round cavity in a mold or a half-round projection or molding on a casting.
:
beam exit point
See probe index.
:
beam spread
The divergence of the sound beam as it travels through a medium. Specifically, the solid angle which contains
the main lobe of the beam in the far field.
bearding
:
See furring.
:
bed-in
A method of ramming the drag mold without rolling over it.
:
bedding a core
Placing an irregularly shaped core on a bed of sand for drying.
:
bentonite
A plastic, adhesive clay that swells when wet. It is derived from decomposed volcanic ash and is used for
bonding molding sand.
:
Berthold penetrameter
A magnetic flux indicator containing an artificial discontinuity in the shape of a cross, mounted below an
adjustable cover plate.
:
beta particle
An electron or positron emitted from a nucleus during decay.
:
beta ray
A stream of high speed electrons of nuclear origin. This radiation is more penetrating than alpha radiation but
ionizes less strongly.
:
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.
:
billet
A solid semi finished round or square product that has been hot worked for forging, rolling or extrusion.
:
binary system
In metallurgy, a two element alloy system.
:
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.
:
birefringence
The splitting of a light beam into two parts through a translucent material.
:
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.
:
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.
black light intensity
See intensity.
:
:
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.
:
blacklight
See black light.
:
bleed
Refers to molten metal oozing out of a casting. Stripped or removed from the mold before complete
solidification.
:
bleedback
The ability of a penetrant to bleed out of a discontinuity subsequent to removal of the indication without
reapplying the penetrant.
:
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.
:
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.
:
blind riser
An internal riser that does not reach to the exterior of the mold.
:
blind spot
Portion of the retina where the optic nerve enters, without rods and cones and hence insensitive to light.
:
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.
:
blotch
(1) An irregularly spaced area of color change on a surface. (2) Nonuniform condition of a surface
characterized by such blotches.
:
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.
:
blowhole
A hole in a casting or a weld caused by gas entrapped during solidification.
:
blue hazard
Exposure to high frequency visible light at intensities and durations that may damage the retina, particularly
in conjunction with overheating.
bobbin coil
See ID coil.
:
:
bond
A cohesive material used to bind sand.
:
bond clay
Any clay suitable for use as a bonding material in molding sand.
:
bond strength
The degree of cohesiveness that the bonding agent exhibits in holding sand grains together.
:
book mold
A split mold hinged like a book.
:
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.
:
borescope, angulated
Borescope bent for viewing at forward oblique, right angle or retrospective angles for visual testing of surfaces
not accessible with conventional borescopes.
:
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.
:
borescope, microBorescope with an outside diameter generally from 1 to 5 mm (0.04 to 0.2 in.), typically using quartz filaments.
Compare borescope, miniature.
:
borescope, miniature
Borescope with an outside diameter generally less than 13 mm (0.5 in.). Sometimes called miniborescope. See
also borescope, micro-.
:
borescope, rigid
Borescope that does not bend, typically in order to keep the geometrical optics in alignment through a light
train system.
:
borescope, ultraviolet
Borescope equipped with ultraviolet lamps, filters and special transformers to transmit radiation of ultraviolet
wavelengths.
:
bottom board
The board or plate on which the mold rests.
:
bottom echo
See back reflection.
:
bottom pour mold
A mold grated at the bottom.
:
boundary echo
A reflection of an ultrasonic wave from an interface.
:
branch gates
Gates leading into a casting cavity from a single runner and sprue.
:
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.
:
bridging
Premature solidification of metal across a mold section before the metal below or beyond solidifies.
:
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.
:
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.
:
brittleness
The quality of a material that leads to crack propagation without appreciable plastic deformation.
:
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.
:
bubbler
See water column.
:
bucking coils
See differential coils.
:
buckle
Indentation in a casting, resulting from expansion of the sand.
:
bumper
A machine used for packing molding sand in a flask by repeated jarring or jolting.
:
bumping
Ramming sand in a flask by repeated jarring and jolting.
:
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.
:
burnt-in sand
A discontinuity consisting of a mixture of sand and metal cohering to the surface of a casting.
:
burr
A raised or turned over edge occurring on a machined part and resulting from cutting, punching or grinding.
:
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.
:
burst counting
A measurement of the number of bursts detected relative to specified equipment settings such as threshold
level or dead time.
:
burst duration
The interval between the first and last time the threshold was exceeded by the burst.
:
burst emission
A qualitative term applied to acoustic emission when bursts are observed.
:
burst rate
The number of bursts detected in a specified time.
:
burst rise time
The time interval between the first threshold crossing and the maximum amplitude of the burst.
:
butt weld or butt joint
Weld joining two metal pieces in the same plane.
:
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.
:
calibration reflector
A reflector with a known dimensioned surface established to provide an accurately reproducible reference
level.
:
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 × 10 12 Hz and that has a radiant intensity in that
direction of 1.4641 mW·sr 1 . Symbolized cd. Formerly known as candle.
:
candle
Former name for candela.
:
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.
:
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.
:
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.
:
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.
:
casing
The many strings of pipe that are used to line the hole during and after drilling of a gas or oil well.
:
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.
:
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.
:
cast structure
The internal physical structure of a casting evidenced by shape, orientation of grains and segregation of
impurities.
:
cast weld assembly
An assembly formed by welding one casting to another.
:
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).
:
casting strains
Strains in a casting caused by casting stresses that develop as the casting cools.
:
casting stresses
Stresses set up in a casting because of geometry and casting shrinkage.
:
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.
:
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.
:
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.
:
cavitation fatigue
A form of pitting caused by erosion from vibration and movement in liquid environments.
:
cavity
The die impression that gives a casting its external shape.
:
CCD
See charge coupled device.
:
cementite
Iron carbide (Fe 3 C), present in steels.
:
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.
:
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.
:
certification
The process of providing written testimony that an individual is qualified. See also certified.
:
certified
Having written testimony of qualification. See also certification.
:
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.
:
channels
In biology, mechanisms functioning as band pass filters in the visual cortex of mammals, causing sensitivity
to visual stimuli in particular frequencies and ranges.
:
chaplet
A metal support used to hold a core in place on a mold.
:
charge coupled device (CCD)
Solid state image sensor widely used in inspection systems because of their accuracy, high speed scanning
and long service life.
:
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.
:
chatter
(1) In machining or grinding, a vibration of the tool, wheel or work-piece producing a wavy surface on the
work. (2) The finish produced by such vibration.
:
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.
:
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.
:
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.
:
chuck
A small bar set between crossbars to hold sand in the cope.
:
circular magnetic field
The magnetic field surrounding an electrical conductor (test object) when a current is passed longitudinally
through the conductor.
:
circular magnetization
The magnetization in an object resulting from current passed longitudinally through the object itself or through
an inserted central conductor.
circumferential coil
See encircling coil.
:
circumferential magnetization
See circular magnetization.
:
:
cire perdue process
The lost wax process.
:
clean
Free from interfering solid or liquid contamination on the test surface and within voids or discontinuities.
:
cleaner
Volatile solvent employed to clean a surface before penetrant application. The cleaner is sometimes referred
to as the solvent remover.
:
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.
:
cleavage
The fracture of a crystal on a crystallographic plane of low index.
:
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.
closing
:
In image processing, dilation followed by erosion. A single pixel closing connects a broken feature separated
by one pixel. See also opening.
:
closure
Process by which a person cognitively completes patterns or shapes that are incompletely perceived.
:
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.
:
code
A standard enacted or enforced as a law.
:
coefficient of thermal expansion
The linear expansion or contraction per unit length per degree of temperature change between specified lower
and upper temperature limits.
:
coefficients of the filter
Values in a mask that serves as a filter in image processing.
:
coercive force
The reverse magnetizing force needed to remove remanent or residual magnetism and thereby demagnetize
the object.
:
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.
:
coil clearance
See liftoff.
:
coil shot
A technique of producing longitudinal magnetization by passing electric current through a coil encircling the
test object.
:
coil spacing
In electromagnetic testing, the axial distance between two encircling coils of a differential system.
:
coil technique
A method of magnetization in which all or a portion of the object is encircled by a current-carrying coil.
:
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). 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.
:
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.
:
cold light
Obsolete word for fluorescence.
cold shut
:
(1) Casting discontinuity caused by two streams of semi-molten 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. (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.
:
cold work
Permanent deformation produced by an external force in a metal at temperature below its recrystallization
temperature.
:
collimator
A device for limiting effects of beam spread.
:
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.
:
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.
:
color contrast penetrant
A penetrant incorporating a dye, usually nonfluorescent, sufficiently intensive to give good visibility to
discontinuity indications under visible light.
:
color discrimination
The perception of differences between two or more hues.
:
columnar structure
A coarse structure of parallel columns of grains, having the long axis perpendicular to the casting surface.
:
combination die
A die having two or more different cavities for different castings.
:
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.
:
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.
:
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.
:
compensator
An electrical matching network to compensate for electrical impedance differences.
:
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.
:
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.
:
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.
:
conditioned water
Water with an additive or additives that impart specific properties such as proper wetting, particle dispersion
or corrosion resistance.
:
conditioning agent
An additive to water suspensions that imparts specific properties such as proper wetting, particle dispersion
or corrosion resistance.
:
conductance
Property of a gas flow system that permits gas to flow.
:
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.
:
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.
:
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.
:
contact method
(1) The ultrasonic testing method in which the transducer makes direct contact with the test object through a
thin film of couplant. (2) The current flow technique in magnetic particle testing.
:
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.
:
contact transducer
The transducer used in the contact method.
:
continuous annealing furnace
A furnace in which castings are heat treated, by being passed through different heat zones kept at constant
temperatures.
:
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.
:
continuous emission
A qualitative term applied to acoustic emission when the bursts or pulses are not discernible.
:
continuous technique
Applying of magnetic particles to form satisfactory discontinuity indications while the magnetizing field is
simultaneously applied.
:
continuous wave
A single frequency wave that continues without interruption.
:
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.
:
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. (2) The difference in visibility (brightness or coloration) between an
indication and the surrounding surface.
:
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.
:
cooling stresses
Residual stresses resulting from nonuniform distribution of temperature during cooling.
:
cope
The upper or topmost section of a flask, mold or pattern.
:
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.
:
core blower
A machine for making foundry cores, using compressed air to blow and pack the sand into the core box.
:
core pin
A core, usually a circular section, having some taper or draft.
:
core plate
A plate on which a green core is baked.
:
core wash
A liquid with which cores are painted to produce smoother surfaces on the casting.
:
corner effect
The strong reflection obtained when an ultrasonic beam is directed toward the intersection of two or three
mutually perpendicular surfaces.
:
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.
:
corrosion, crevice
Type of galvanic corrosion caused by differences in metal ion concentrations in neighboring portions of the
corrodent.
:
corrosion embrittlement
The severe loss of ductility of a metal, resulting from corrosive attack, usually intergranular and often not
visually apparent.
:
corrosion fatigue
Fatigue cracking caused by repeated load applications on metal in a corrosive environment.
:
corrosion, fretting
Corrosion facilitated by fretting, particularly where a protective surface has been chafed in a corrosive
environment.
:
corrosion, poultice
Corrosion occurring under a layer of foreign material (e.g., under mud in automobile rocker panels).
:
corrosion-erosion
Simultaneous occurrence of erosion and corrosion.
:
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.
:
coupled
Two electric circuits that have an impedance in common so that a current in one causes a voltage in the other.
:
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.
:
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.
:
coupon
A piece of metal from which a test object is prepared, often an extra piece, as on a casting or forging.
:
cover half
The stationary half of a die casting die.
:
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) 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).
:
crack contaminant
Material that fills a crack and that may prevent penetrants from entering or from forming indications.
:
crack, base metal
Cracks existing in base metal before a manufacturing or welding operation or occurring in base metal during
the operation.
crack, cold
:
Cracks that occur in a casting after solidification, due to excessive stress generally resulting from nonuniform
cooling.
:
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.
:
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.
:
crack, forging
Cracks developed in the forging operation due to forging at too low a temperature, resulting in rupturing of
the steel.
:
crack, grinding
Thermal cracks caused by local overheating of the surface being ground.
:
crack, hot
Cracks that develop before the casting has completely cooled, as contrasted with cold cracks, that develop
after solidification.
:
crack, longitudinal
Cracks parallel to the length of the test object.
:
crack, machining
Cracks caused by too heavy a cut, a dull tool or chatter. Typically called machining tears.
:
crack, pickling
Cracks caused by immersing objects with high internal stresses in an acid solution.
:
crack, plating
Cracks similar to pickling cracks, but occurring during plating when the object is immersed in a strong
electrolyte.
:
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.
:
crack, transverse
Cracks at right angles to the length of the test object.
:
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.
:
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.
:
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.
:
creep strength
The constant nominal stress that will cause a specified creep rate at constant temperature.
:
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.
:
cross line grating
In moiré and grid nondestructive testing, a grating with bars, furrows or lines parallel to orthogonal xy axes.
:
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.
:
CRT
See cathode ray tube.
:
crush
A casting discontinuity caused by a partial destruction of the mold before the metal was poured.
:
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.
:
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.
:
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.
:
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.
:
cumulative bursts
The number of bursts detected from the beginning of the test.
:
cumulative characteristic distribution
A display of the number of times an acoustic emission signal exceeds a preselected characteristic as a function
of the characteristic.
:
cumulative count
The number of times the amplitude of an acoustic emission signal has exceeded the threshold since the start
of a test.
:
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.
:
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.
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).
:
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.
:
current induction technique
Magnetization in which a circulating current is induced in a ring component by the influence of a fluctuating
magnetic field.
:
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.
:
cycle
A single period of a waveform or other variable. See period.
:
damping
(1) Limiting the duration or decreasing the amplitude of vibrations, as when damping a transducer element.
(2) A deliberate introduction of energy absorbers to reduce vibrations.
:
damping capacity
A measure of ability of a material to dissipate mechanical energy.
:
damping material
A highly absorbent material used to cause rapid decay of vibration.
:
damping, transducer
A material bonded to the back of the piezoelectric element of a transducer to limit the duration of vibrations.
:
damping, ultrasonic
Decrease or decay of ultrasonic wave amplitude with respect to time or distance.
:
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) Process by which the retina becomes adapted to luminance
less than about 0.034 cd·m 2 .
dark adapted vision
See scotopic vision.
:
:
daubing
The act of filling cracks in cores.
:
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.
:
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.
:
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.
:
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.
:
deep drawing
The forming of deeply recessed parts by means of plastic flow of the material.
:
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.
:
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. Note that some discontinuities
may not affect serviceability and are therefore not defects. All defects are discontinuities. Compare
discontinuity and indication.
:
deformation
Change of shape under load. See also creep and elastic deformation.
:
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.
:
degassing
Removing gases from liquids or solids.
:
degreasing fluid
Solvents or cleaners employed to remove oil and grease from test surfaces before the liquid penetrant is
applied.
:
delamination
A laminar discontinuity, generally an area of unbonded materials.
:
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.
:
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.
:
delayed time base
See delayed sweep.
:
delta effect
Reradiation of energy from a discontinuity. The reradiated energy may include waves of both incident mode
and converted modes (longitudinal and shear).
:
delta ferrite
Solid solution with body centered cubic structure and iron as solvent. Also called delta iron.
:
delta iron
See delta ferrite.
:
delta t
The time interval between the detected arrival of an acoustic emission wave at two sensors.
:
demagnetization
The reduction of residual magnetism to an acceptable level.
:
demagnetizing coil
A coil of conductive material carrying alternating current used for demagnetization.
:
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.
:
dendrite
A crystal that has a treelike branching pattern, being most evident in cast metals slowly cooled through the
solidification range.
:
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.
:
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.
:
depth of fusion
The depth to which the base metal melted during welding.
:
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.
:
descaling
Removing the thick layer of oxides formed on some metals at elevated temperatures.
:
deseaming
Analogous to chipping, the discontinuities being removed by gas cutting.
:
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.
:
detector coil
See sensing coil.
:
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.
:
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.
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) In radiography, a chemical solution that reduces exposed silver halide crystals to
metallic silver.
:
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.
:
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.
:
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.
:
developer, wet
A penetrant developer usually supplied as dry particles that is mixed with water to form a suspension of
particles.
:
developing time
Elapsed time necessary for the applied developer to absorb and show indications from penetrant entrapments.
:
dewaxing
Removing the expendable wax pattern from an investment mold by heat or solvent.
:
dewetting
The flow and retraction of liquid on a surface, caused by contaminated surfaces or dissolved surface coatings.
:
diamagnetic material
A material whose relative permeability is less than unity. The intrinsic induction B i is oppositely directed to
applied magnetizing force H. A material with magnetic permeability less than 1.
:
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.
:
difference cylinder
See background cylinder.
:
differential amplifier
An amplifier whose output signal is proportional to the algebraic difference between two input signals.
:
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.
:
differential measurement
In electromagnetic testing, the imbalance in the system is measured using differential coils -in contrast to
absolute measurement and comparative measurement.
:
differentiated signal
In electromagnetic testing, an output signal proportional to the input signal's rate of change with respect to
time.
:
diffraction
In ultrasonic testing, the deflection of a wavefront when passing the edge of an ultrasonically opaque object.
:
diffuse indications
Indications that are not clearly defined as, for example, indications from surface contamination.
:
diffuse reflection
Scattered, incoherent reflections from rough surfaces.
:
diffusion
The process by which molecules intermingle as a result of concentration gradients or thermal motion.
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.
:
dip rinse
A means of removing excess surface penetrant in which the test objects are dipped into a tank of agitated water
or remover.
direct contact magnetization
See current flow technique.
:
:
direct current
An electric current flowing continually in one direction through a conductor.
:
direct current field
An active magnetic field produced by direct current flowing in a conductor or coil.
:
direct photometry
Simultaneous comparison of a standard lamp and an unknown light source.
:
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.
:
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.
:
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.
:
directional lighting
Lighting provided on the work plane or object predominantly from a preferred direction.
:
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.
:
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.
:
discernible image
Image capable of being recognized by sight without the aid of magnification.
discontinuity
:
An intentional or unintentional interruption in the physical structure or configuration of a part. After
nondestructive testing, unintentional discontinuities interpreted as detrimental in the host object may be called
flaws or defects. 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.
:
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.
:
discontinuity, primary processing
Material anomaly produced from the hot or cold working of an ingot into forgings, rod and bar.
:
discontinuity, secondary processing
Material anomaly produced during machining, grinding, heat treating, plating or other finishing operations.
:
discontinuity, service induced
Material anomaly caused by the intended use of the part.
:
dislocation
Void or discontinuity in the lattice of a metal crystalline structure. Two basic linear types are recognized (edge
dislocation and screw dislocation) but combinations and partial dislocations are most prevalent.
:
dispersion
The variation of phase velocity with frequency.
:
dispersive medium
A medium in which propagation velocity depends on the wave frequency.
:
displacement resolution
In moiré and grid nondestructive testing, measurement precision expressed as the smallest displacement that
can be determined with reasonable reliability.
:
dissociation
The breakdown of a substance into two or more constituents.
:
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.
:
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.
:
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.
:
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.
:
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.
:
dose rate
The radiation dose delivered per unit time and measured, for instance, in rems per hour. See also dose.
:
dosimeter
A device that measures radiation dose, such as a film badge or ionization chamber.
:
double crystal method
A method of ultrasonic testing that uses two transducers, one transmitting and the other receiving.
:
drag
The bottom section of a flask, mold or pattern.
:
dragout
The carryout or loss of penetrant materials as a result of their adherence to the test pieces.
:
drain time
That portion of the dwell time during which the excess penetrant, emulsifier, detergent remover or developer
drains off the test piece.
:
drop
A discontinuity in a casting due to a portion of the sand dropping from the cope or overhanging section of the
mold.
:
drop out
The falling away of green sand from the walls of a mold cavity when the mold is closed.
:
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.
:
dry bulb temperature
Alternate term for ambient or atmospheric temperature.
:
dry powder
Finely divided ferromagnetic particles selected and prepared for magnetic particle testing.
:
dry technique
A magnetic particle testing technique in which the ferromagnetic particles are applied in a dry powder form.
:
drying oven
An oven used for drying rinse water from test pieces.
:
drying time
The time allotted for a rinsed or cleaned test piece to dry.
:
dual response penetrant
A penetrant that produces discontinuity indications that can be seen under either ultraviolet light or visible
light.
:
dual transducer
A single transducer containing two piezoelectric elements, one for transmitting and one for receiving.
:
ductile crack propagation
Slow crack propagation that is accompanied by noticeable plastic deformation and requires energy to be
supplied from outside the body.
:
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.
:
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.
:
dynamic creep
Creep that occurs under conditions of fluctuating load or fluctuating temperature.
:
dynamic range
The ratio of maximum to minimum reflective areas that can be distinguished on the cathode ray tube at a
constant gain setting.
:
echo
A signal indicating reflected acoustic energy.
:
ECT
Eddy current testing.
:
eddy current
An electrical current induced in a conductor by a time varying magnetic field.
:
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.
:
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.
:
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. Depending on the
criteria, this minimum thickness is three to seven times the skin depth.
:
effective penetration
In ultrasonic testing, the maximum depth in a material at which discontinuities can be detected.
:
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.
:
elastic constants
Modulus of elasticity, either in tension, compression or shear and Poisson's ratio.
:
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.
:
elastic limit
The maximum stress to which a material may be subjected without any permanent strain remaining on
complete release of stress.
:
elasticity
The ability of a material to resume its former shape after deformation.
:
electric arc welding
Joining of metals by heating with electric arc. Also called arc welding.
:
electric field
A vector field of electric field strength or of electric flux density.
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.
:
electrical noise
Extraneous signals caused by externally radiated signals or electrical interferences within an ultrasonic
instrument. 10 A component of background noise.
:
electrochemical corrosion
Corrosion that occurs when current flows between cathodic and anodic areas on metallic surfaces.
:
electrode
A conductor by which a current passes into or out of a test object.
:
electromagnet
A soft iron core surrounded by a coil of wire that temporarily becomes a magnet when an electric current
flows through the wire.
:
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.
:
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.
:
electrostatic spraying
A technique of spraying wherein the material being sprayed is given a high electrical charge (potential) while
the test piece is grounded.
:
element
A chemical substance that cannot be divided into simpler substances by chemical means. Examples are
hydrogen, lead and uranium.
:
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.
:
EMAT
See electromagnetic acoustic transducer.
:
embrittlement
Reduction in the normal ductility of a metal due to a physical or chemical change.
:
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.
:
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.
:
emulsifier
A liquid that combines with an oil based penetrant to make it water washable.
:
emulsion
A dispersion of fine droplets of one liquid in another that can be stabilized by the addition of an emulsifier.
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. 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.
:
equilibrium diagram
A phase diagram showing the phases present at equilibrium in a material system.
:
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.
:
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.
:
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.
:
erosion-corrosion
Simultaneous occurrence of erosion and corrosion.
:
ET
Electromagnetic testing.
:
etch cracks
Shallow cracks in hardened steel containing high residual surface stresses produced by etching in an acid.
:
etching
A cleaning process for the controlled removal of surface material by chemical agents before liquid penetrant
application. Subjecting the surface of a metal to preferential chemical or electrolytic attack in order to reveal
structural details.
:
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.
:
eutectic liquid
A liquid having a proportion of metals such that two or more solid phases form at the same temperature during
cooling.
:
eutectic point
Temperature and proportion of metals at which two or more phases of a eutectic liquid form. Compare
eutectoid.
:
eutectoid
Similar to eutectic but in a solid system during cooling.
:
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.
evanescent wave
:
A disappearing wave.
:
event
A micro displacement giving rise to transient elastic waves. See acoustic emission event.
:
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.
:
event rate
The number of events detected in a specified unit of time. Term is restricted in the same way as event counting.
:
examination
The process of testing materials, interpreting and evaluating test indications to determine if the test object
meets specified acceptance criteria.
:
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.
:
excitation coil
Coil that carries the excitation current. Also called primary coil or winding. See detector coil.
:
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.
:
expanded sweep
A short duration horizontal sweep positioned to provide close examination of a particular signal or material
volume.
:
external discontinuities
Discontinuities on the outside or exposed surface of a test object.
:
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.
:
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.
:
false brinelling
Fretting wear indentations. Compare brinelling.
:
false indication
A test indication that could be interpreted as originating from a discontinuity but which actually originates
where no discontinuity exists. Distinct from nonrelevant indication. Compare defect.
:
family
An obsolete term, formerly denoting a complete series of materials from one manufacturer necessary to
perform a specific process of penetrant testing.
:
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.
:
far vision
Vision of objects at a distance, generally beyond arm's length. Compare near vision.
:
farsightedness
Vision acuity functionally adequate for viewing objects at a distance, generally beyond arm's length. Also
called hyperopia. Compare nearsightedness.
:
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.
:
feature extraction
From an enhanced image, derivation of some feature values, usually parameters for distinguishing objects in
the image.
:
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.
:
felicity effect
The appearance of significant acoustic emission at a stress level below the previous maximum applied.
:
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.
:
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. (2) Solid
solution of one or more other elements in alpha iron.
:
ferromagnetic material
Material such as iron, nickel or cobalt whose relative permeability is considerably greater than unity and
depends on the magnetizing force. Materials that are most strongly affected by magnetism are called
ferromagnetic.
:
fiber optic borescope
See borescope, fiber optic.
:
fiber optics
The technology of light transmission through crystalline fibers such as plastic, glass or quartz.
:
fiberscope
Jargon for fiber optic borescope.
:
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.
:
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.
:
field flow technique
See magnetic flow technique.
:
field of view
The range or area where things can be seen through an imaging system, lens or aperture. Compare depth of
field.
:
field of vision
The range or area where things can be perceived organoleptically at a point in time, assuming the eye to be
immobile.
:
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). 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.
:
fill factor effect
The effect of fill factor on coupling between coil and test object. See coupling coefficient.
:
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.
:
fillet weld
Weld at the corner of two metal pieces.
:
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.
:
film holder
A light tight carrier for films and screens.
:
film speed
Relative exposure required to attain a specified density.
:
filter
(1) A network that passes electromagnetic wave energy over a described range of frequencies and attenuates
energy at all other frequencies. (2) A processing component or function that excludes a selected kind of signal
or part of a signal.
:
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.
:
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.
:
fit up
To secure one or more joint members with special external fixturing to prevent movement during welding.
:
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. Also called shatter cracks and snowflakes.
:
flash magnetization
Magnetization by a current flow of brief duration. See capacitor discharge technique.
:
flash point
The lowest temperature at which vapors above a volatile, combustible substance ignite in air when exposed to
flame.
:
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.
:
flat bottom hole
A type of reflector commonly used in reference standards. The end (bottom) surface of the hole is the reflector.
:
flaw
A rejectable anomaly or unintentional discontinuity. See also defect and discontinuity.
:
flaw inversion
A method for measuring some dimensions of a discontinuity by the application of a mathematical algorithm
to the discontinuity signal.
:
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.
:
fluidity
The ability of molten metal to flow readily. Typically measured by the length of a standard spiral casting.
:
fluorescence
The emission of visible light from a material in response to ultraviolet or X-radiation. Formerly called cold
light.
:
fluorescent penetrant
A highly penetrating liquid used in the performance of liquid penetrant testing and characterized by its ability
to fluoresce under ultraviolet light.
:
fluorescent magnetic particle testing
The process using finely divided ferromagnetic particles that fluoresce when exposed to ultraviolet light (320
to 400 nm).
:
fluorescent penetrant testing
Technique of liquid penetrant testing that uses fluorescent penetrant.
:
flux density
See magnetic flux density.
:
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.
:
flux leakage
A local distortion of normal magnetic flux patterns in a magnetized test object. Can be caused by
discontinuities in the test object.
:
flux leakage field
The magnetic field that leaves or enters the surface of an object.
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.
:
flux lines
See lines of force.
:
flux method
See lumen method.
:
flux meter
An electronic device for measuring magnetic flux. 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.
:
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.
:
focus, principal plane of
The single plane actually in focus in a photographic scene.
:
focused beam
A sound beam that converges to a cross section smaller than that generated by a flat transducer.
:
focused transducer
A transducer that produces a focused sound beam.
:
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.
:
focusing, primary
Focusing of an image by the lens onto a fiber optic bundle at the tip of a probe.
:
focusing, secondary
Focusing at the eyepiece of a borescope or other optical instrument, specifically the manual refocusing needed
when the viewing distance changes.
:
foil
Metal in sheet form less than 0.15 mm (6 × 10 3 in.) thick.
:
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.
:
footlambert
Former unit of luminance. Measured in the SI system by candela per square meter.
:
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.
:
forging crack
Discontinuity formed during mechanical shaping of metal.
foundry
:
An establishment or building where metal castings are produced.
:
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.
:
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.
:
fracture
A break, rupture or crack large enough to cause a full or partial partition of a casting.
:
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.
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.
:
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.
:
frequency, pulse repetition
The number of pulses per second, in hertz (Hz).
:
frequency, test
The nominal ultrasonic wave test frequency used in a test.
:
Fresnel zone
See near field. Also called Fresnel field.
:
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.
:
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.
full-wave direct current
:
A single-phase or three-phase alternating current rectified to produce direct current characteristics of
penetration and flow.
:
furring
Buildup or bristling of magnetic particles resulting from excessive magnetization of the test object.
:
gage pressure
Pressure above (or below if measured from gage zero) atmospheric pressure at the measurement location.
:
gaggers
The metal supports that reinforce sand in the cope.
:
galling
A type of adhesive wear more gross than fretting.
:
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.
:
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.
:
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.
:
gas holes
Holes created by a gas evolving from molten metal. Appear as round or elongated, smooth edged dark spots,
occurring individually, in clusters or distributed throughout a casting.
:
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.
:
gas tungsten arc welding (GTAW)
Inert gas shielded arc welding using a tungsten electrode. Also called tungsten inert gas (TIG) welding.
:
gasket seal
Resilient ring, usually virgin polytetrafluoroethylene (PTFE), in a piping or tubing connection. Compare
interference sealing thread and metal-tometal seal.
:
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.
:
gated pattern
A pattern designed to include gating in the mold.
:
gauss
A customary or cgs unit of flux density or magnetic induction. See tesla.
:
gauss meter
A magnetometer that registers field strength in gauss (or Tesla).
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.
:
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.
:
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.
:
ghost
An indication arising from a combination of pulse repetition frequency and time base frequency. 18 See wrap
around.
:
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.
:
glare, blinding
Glare so intense that for an appreciable length of time after it has been removed, no object can be seen.
:
glare, direct
Glare resulting from high luminances or insufficiently shielded light sources in the field of view.
:
glare, reflected
Glare resulting from specular reflections of high luminances in polished or glossy surfaces in the field of view.
:
glossmeter
Reflectometer used to measure specular reflectance.
:
gooseneck
The pressure vessel or metal injection pump in an air injection casting machine.
:
gouge
Surface indentation caused by forceful abrasion or impact or flame cutting. Also called nick. Compare tool
mark.
:
grain boundary
Interface that forms between grains of solidifying metal as the random oriented crystal lattices meet. See grain.
:
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.
:
grain size
Size of the crystals in metal. When compared with a standard, usually referred to as being fine, medium or
coarse.
:
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.
:
grains
(1) Solid particle or crystal of metal. As molten metal solidifies grains grow and lattices intersect, forming
irregular grain boundaries. (2) Individual crystals that make up the crystalline structure of metal.
grass
:
See background noise.
:
grating
A grid superimposed on an optical test surface to measure displacement or deformation. See also reference
grating.
:
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.
:
graybody
Radiator whose spectral emissivity is uniform for all wavelengths but not 1.0. See blackbody.
:
green core
A sand casting core that has not been baked.
:
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.
:
green sand
Core sand intended for use in a damp state.
:
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.
:
grinding cracks
Shallow cracks formed in the surface of relatively hard materials because of excessive grinding heat or the
high sensitivity of the material. Grinding cracks typically are 90 degrees to the direction of grinding.
:
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.
:
group velocity
The rate at which the envelope of an ultrasonic pulse (many frequencies) propagates through the medium.
:
growth
The expansion of a casting because of aging.
:
Hadfield's steel
An austenitic manganese specialty steel that is easily work hardened.
:
half-wave direct current
A single-phase alternating current half-wave rectified to produce a pulsating unidirectional field. Also called
half-wave current.
:
halide
A compound of two or more elements, one of which is a halogen.
:
halitation
Rings of light visible around a spot on a video screen where an electron scanning beam is held.
:
Hall detector
A semiconductor element that produces an output electromotive force proportional to the product of the
magnetic field intensity and a biasing current.
:
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.
:
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. Also called a halogen
sensitive leak detector or a halide leak detector.
:
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.
:
halogen standard leak
A standard leak in which the contained gas is a halogen tracer gas compound.
:
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.
:
harmonic
A vibration frequency that is an integral multiple of the fundamental frequency.
:
harmonic analyzer
A mechanical device for measuring the amplitude and phase of the various harmonic components of a periodic
function from its graph.
:
harmonic distortion
Nonlinear distortion characterized by the appearance in the output of harmonics other than the fundamental
component when the input wave is sinusoidal.
:
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.
:
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.
:
heads
The clamping contacts on stationary magnetic particle systems.
:
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.
:
heat affected zone (HAZ)
Base metal not melted during brazing, cutting or welding, but whose microstructure and physical properties
were altered by the heat.
:
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.
:
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.
:
heat wave
Thermally produced variation in flue gas density that distorts images of objects in a firebox.
:
helium leak detector
A leak detector that responds to helium tracer gas.
:
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.
:
high temperature penetrant
A penetrant material specifically designed for use on high temperature surfaces where conventional penetrant
would be unsatisfactory.
:
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.
:
holes
Any void remaining in an object as a result of improper manufacturing processing. Often called gas holes,
cavities or air locks.
:
homogenizing
Holding at high temperature to eliminate or decrease chemical segregation by diffusion.
:
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.
:
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.
:
horn gate
A curved gate shaped like a horn and arranged to permit entry of molten metal at the bottom of casting cavity.
:
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.
:
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.
:
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. Cracks occurring in hot solid metals, caused
by stresses of thermal expansion or contraction and originating either internally or at the surface.
:
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.
:
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. Hot tears often occur where areas of different thickness
adjoin.
:
hot working
Deforming metal plastically at temperature and rate such that strain hardening does not occur. Low
temperature limit is recrystallization temperature.
:
hue
Characteristic of light at a particular bandwidth that gives a color its name.
:
hundred percent testing
See one hundred percent testing.
:
hydrogen embrittlement
A condition of low ductility in metals resulting from the absorption of hydrogen.
:
hydrophilic emulsifier or remover
Water base materials used for excess surface penetrant removal.
:
hyperthermia
Heating so excessive that it can damage or kill plant or animal cells.
:
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.
:
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.
:
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. The % IACS is equivalent to 172 divided by the material resistivity
in microohm centimeters.
:
icicles
A coalescence of metal protruding beyond the root of the weld. Sometimes called burn through.
:
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.
:
ideal gas
Gas that obeys the general gas laws for ideal gases. Also called perfect gas.
:
illuminance
The density of luminous flux on a surface. Measured in the SI system by lux.
:
illuminate
Shed light on.
:
illumination
The act of illuminating or state of being illuminated. See also illuminate. Compare illuminance.
:
image
Visual representation of a test object or scene.
:
image enhancement
Any of a variety of image processing steps, used singly or in combination to improve the detectability of
objects in an image.
:
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.
:
image orthicon
Television tube that uses the photoemission method. Compare vidicon tube.
:
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.
image quality indicator
Penetrameter.
:
:
image segmentation
Process in which the image is partitioned into regions, each homogeneous.
:
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. 1The transducer is not usually in contact with the test object.
:
impedance
The total opposition that a circuit presents to the flow of an alternating current, specifically the complex
quotient of voltage divided by current.
:
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.
:
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.
:
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.
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.
:
impurities
Elements or compounds whose presence in a material is unintentional.
:
in control
Within prescribed limits of process control.
:
in-motion radiography
Technique in which either the object being radiographed or the source of radiation is in motion during the
exposure.
:
incandescence
The emission of visible radiation due to thermal excitation.
:
incandescent
Emitting visible radiation as a result of heating.
:
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.
:
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.
:
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. Also called lack of fusion.
:
incremental permeability
The ratio of the change in magnetic induction to the corresponding change in magnetizing force when the
mean induction differs from zero.
:
indication
A nondestructive testing discontinuity response that requires interpretation to determine its relevance.
Compare defect, discontinuity and false indication.
:
indication, discontinuity
The visible evidence of a material discontinuity. Subsequent interpretation is required to determine the
significance of an indication.
:
indication, false
An indication produced by something other than a discontinuity. Can arise from improper test procedures.
:
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).
:
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.
:
induced current technique
See current induction technique.
:
induced magnetization
A magnetic field generated in an object when no direct electrical contact is made.
:
induction
The magnetism produced in a ferromagnetic body by some outside magnetizing force.
:
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.
:
inert gas
Gas that does not readily combine with other substances. Examples are helium, neon and argon.
:
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.
:
infrared
Below red, referring to radiation of frequency lower than the color red. See infrared radiation.
:
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.
:
infrared radiation
Radiant energy below the color red, of wavelengths longer than 770 nm, between the visible and microwave
regions of the electromagnetic spectrum.
:
infrared thermography
Imaging by infrared radiation. See infrared radiation. Compare thermography.
:
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).
:
inherent fluorescence
Fluorescence that is an intrinsic characteristic of a material.
:
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).
:
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.
:
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.
:
inserted coil
See ID coil. Also called inside coil.
:
insonification
Irradiation with sound.
:
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.
:
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.
:
interface triggering
In ultrasonic testing, triggering the sweep and auxiliary functions from an interface echo occurring after the
initial pulse. Also called IF synchronization.
:
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.
:
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.
:
intergranular corrosion
Corrosion occurring preferentially at grain boundaries.
:
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.
:
internal conductor
See central conductor.
:
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.
:
interstitial alloy
Alloy in which the atoms of the alloying element fit into the spaces between the atoms of the parent metal.
:
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.
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.
:
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.
:
investment compound
A mixture of graded refractory filler, a binder and a liquid vehicle, used to make molds for investment castings.
:
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.
:
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.
:
ionizing radiation
Any radiation that directly or indirectly displaces electrons from the outer domains of atoms. Examples include
alpha, beta and gamma radiation.
:
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.
:
irradiance
Power of electromagnetic radiant energy incident on the surface of a given unit area. Compare radiance.
:
IshiharaTM plates
Trade name for a kind of pseudoisochromatic plates.
:
isotropy
A condition in which significant medium properties (velocity, for example) are the same in all directions.
:
Jaeger eye chart
An eye chart used for near vision acuity examinations.
:
joint
The part of the mold where the cope and cheek, cope and drag or cheek and drag come together.
:
joint efficiency
The strength of a welded joint expressed as a percentage of the strength of the unwelded base metal.
:
joint penetration
The distance weld metal and fusion extend into a joint.
:
Kaiser effect
The absence of detectable acoustic emission until the previous maximum applied stress level has been
exceeded.
:
keeper
Ferromagnetic material placed across the poles of a permanent magnet to complete the magnetic circuit and
prevent loss of magnetism.
:
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.
:
laboratory microscope
Conventional compound microscope. See microscope and microscope, compound.
:
lack of fusion
Discontinuity due to lack of union between weld metal and parent metal or between successive weld beads.
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.
:
lambertian
Having a surface that diffuses light uniformly rather than reflecting it. Matte. Most objects have a lambertian
surface. Compare specular.
:
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. 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.
:
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.
:
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.
:
leak
An opening that allows the passage of a fluid.
:
leak detector
A device for detecting, locating, and/or measuring leakage.
:
leak testing (LT)
Nondestructive testing method for detecting, locating or measuring leaks or leakage in pressurized or
evacuated systems or components.
:
leakage
The measurable quantity of fluid escaping from a leak.
leakage design basis accident
:
The calculated peak containment internal pressure related to the design basis accident.
:
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.
:
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. See throughput.
:
leaker penetrant
A penetrant especially designed for leak detection.
:
leeches
Permanent magnets or electromagnets attached to electrodes carrying magnetizing current, to provide strong
electrode contact.
:
lens
Translucent object that refracts light passing through it in order to focus the light on a target.
:
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.
:
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. See level, acceptance.
:
lifting power
The ability of a magnet to lift a piece of ferritic steel by magnetic attraction alone.
:
liftoff
Distance between the probe coil and the test object.
:
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.
:
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.
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.
:
light metal
One of the low density metals such as aluminum, magnesium, titanium, beryllium or their alloys.
:
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.
:
lighting, flash
See lighting, strobe.
:
lighting, front
Placement of light source and image sensor on the same side of the test object.
:
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.
:
lighting, structured
Combining a light source with optical elements to form a line or sheet of light.
:
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.
:
line pair
Pair of adjacent, parallel lines used to evaluate the resolution of a specific imaging system. See also minimum
line pair.
:
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.
:
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.
:
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.
:
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.
:
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).
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.
:
logarithmic decrement
The natural logarithm of the ratio of the amplitudes of two successive cycles in a damped wave train.
:
longitudinal direction
The principal direction of flow in a worked metal.
longitudinal magnetic field
:
A magnetic field wherein the flux lines traverse the component in a direction essentially parallel with its
longitudinal axis.
:
longitudinal magnetization
Magnetization in which the flux lines traverse the component in a direction essentially parallel to its
longitudinal axis.
:
longitudinal wave
See compressional wave.
:
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.
:
loss of back reflection
Absence or significant reduction of an indication from the back surface of the test object.
:
lost-wax process
An investment casting process in which a wax pattern is used.
:
lot tolerance percent defective
In quality control, the percent defective at which there is a 10 percent probability of acceptance in a production
run.
:
low pass filtering
A linear combination of pixel values to smoothen abrupt transitions in a digital image. Also called smoothing.
:
LOX-safe penetrant
A penetrant material or system specifically designed to be compatible with or nonreactive in the presence of
liquid oxygen.
:
LT
Leak testing.
:
lumen
Luminous flux per steradian from a source whose luminous intensity is 1 candela. Symbolized lm.
:
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.
:
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.
:
luminosity
The luminous efficiency of radiant energy.
:
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.
:
luminous efficiency
See luminous efficacy.
:
luminous flux
Radiant energy's time rate of flow. Measured in lumens.
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.
:
lux
Unit of measure for illuminance in SI. Equivalent to lumens per square meter and symbolized lx. Formerly
known as meter-candle.
:
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.
:
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.
:
macrostructure
The structure of metals as revealed by examination of the etched surface of a polished object at a magnification
not exceeding ten diameters.
:
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.
:
magnetic circuit
The closed path followed by any group of magnetic flux lines.
:
magnetic field
Space in which the magnetic force is exerted within and surrounding a magnetized object.
:
magnetic field indicator
A device used to locate or determine relative intensity of a flux leakage field.
:
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.
:
magnetic flow technique
Closing the magnetic circuit of an electromagnet with a test object or portion of it. Resulting field is
longitudinal in direction. See longitudinal magnetization.
:
magnetic flux
The total number of lines of magnetic force existing in a magnetic circuit.
:
magnetic flux density
The normal magnetic flux per unit area. Expressed in tesla or gauss.
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.
:
magnetic particle test system
Equipment providing the electric current and magnetic flux necessary for magnetic particle discontinuity
detection.
:
magnetic particle testing (MT)
A nondestructive test method using magnetic leakage fields and indicating materials to disclose surface and
near surface discontinuities.
:
magnetic particles
Finely divided ferromagnetic material capable of being individually magnetized and attracted to flux leakage
fields.
magnetic permeability
See permeability.
:
:
magnetic powder
Magnetic particles in dry or powder form with size and shape suitable for discontinuity detection.
:
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.
:
magnetic saturation
That degree of magnetization where a further increase in magnetizing force produces no significant increase
in magnetic flux density in an object.
:
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.
:
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.
:
magnetization
The process by which elementary magnetic domains of a material are aligned predominantly in one direction.
:
magnetizing current
The electric current passed through or adjacent to an object that gives rise to a designated magnetic field.
:
magnetizing force
The magnetizing field strength applied to a ferromagnetic material to produce magnetism.
:
magnetometer
A device for measuring the strength of magnets or magnetic fields.
:
magnitude
The absolute value of a complex number without reference to the phase of the quantity.
:
malleability
The characteristic of metals that permits plastic deformation in compression without rupture.
:
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.
:
manipulator
In immersion testing, a device for angular orientations of the transducer.
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 Utube indicates the pressure difference.
:
manual zero
A control on a test instrument that allows the user to zero the instrument panel meter.
:
markers
In ultrasonic testing, a series of indications on the horizontal trace of a display screen that show increments of
time or distance.
:
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.
:
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.
:
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.
:
mass spectrometer leak detector
Mass spectrometer with design factors optimized to produce an instrument that has high sensitivity to a single
tracer gas.
:
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.
:
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.
:
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.
:
material noise
Random signals caused by the material structure of the test object. A component of background noise.
:
material, ferromagnetic
A material that exhibits the phenomena of magnetic hysteresis and saturation and whose magnetic
permeability is dependent on the magnetizing force.
:
material, nonferromagnetic
A material that is not magnetizable and not responsive to magnetic field tests.
:
mathematical morphology
Image processing technique of expanding and shrinking. The basic operators in mathematical morphology are
dilation (expanding), erosion (shrinking), opening and closing.
:
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.
maximum burst amplitude
:
The maximum signal amplitude within the duration of the burst.
:
Maxwell's equations
The fundamental equations of macroscopic electromagnetic field theory.
:
mean free path
Average distance a gas molecule travels between successive collisions with other molecules in the gas or vapor
state.
:
measurement system
The entire system from sensor to display inclusive.
:
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).
:
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.
:
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.
:
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 ).
:
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.
:
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).
:
metallograph
Short term for metallographic microscope.
:
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.
:
metallurgy
The science and technology of metals.
:
micro
A prefix that divides a basic unit of measure by one million.
:
microfissure
A crack of microscopic proportions.
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).
:
microporosity
Porosity visible only with the aid of a microscope.
:
microscope
An instrument that provides enlarged images of very small objects.
:
microscope, compound
Conventional microscope, using geometrical optics for magnification. Also called laboratory microscope.
:
microscope, interference
Magnifier using the wavelength of light as a unit of measure for surface contour and other characteristics.
:
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.
:
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.
:
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.
:
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.
:
microsegregations
(1) Segregation within a grain, crystal or small particle. Also called coring. (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.
:
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.
:
microstructure
The structure of polished and etched metal as revealed by a microscope at a magnification greater than ten
diameters.
:
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.
miniature angle beam block
:
A specific type of reference standard used primarily for angle beam, but also for straight beam and surface
wave calibration.
:
miniature borescope
See borescope, miniature.
:
miniborescope
Jargon for miniature borescope.
:
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.
:
misrun
A casting not fully formed, resulting from the metal solidifying before the mold is filled.
:
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.
:
mode
The manner in which an acoustic wave is propagated, as characterized by the particle motion in the wave
(shear, Lamb, surface or longitudinal).
:
mode conversion
A change of ultrasonic wave propagation mode upon reflection or refraction at an interface.
:
mode of vibration
Type of wave motion. Three common modes used in ultrasonic testing are longitudinal, transverse and surface
wave.
:
model, analytical
A representation of a process or phenomenon by a set of solvable equations.
:
modulus of elasticity
The ratio between stress and strain in a material deformed within its elastic range.
:
modulus of rupture
Nominal stress at fracture in a bend test or torsion test.
:
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.
:
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.
:
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.
:
mold jacket
Wood or metal form that is slipped over a sand mold for support during pouring.
:
mold wash
An aqueous or alcohol emulsion or suspension of various materials used to coat the surface of a mold cavity.
:
molding machine
A machine for making sand molds by mechanically compacting sand around a pattern.
:
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.
:
molecule
A group of atoms held together by chemical forces. The atoms in the molecule may be identical (H 2 and S 8
) or different (H 2 O and CO 2 ).
:
monochromatic light
Light from a very small portion of the visible spectrum.
:
monochromator
Device that uses prisms or gratings to separate or disperse the wavelengths of the spectrum into noncontinuous
lines or bands.
:
mottle
An apparently random positioning of metallic flakes that creates an accidental pattern.
:
MT
Magnetic particle testing.
:
multiaxial stresses
Any stress state in which two or three principal stresses are not zero.
:
multidirectional field
A periodic magnetic field that produces magnetization in two or more mutually perpendicular directions
during a single cycle.
:
multidirectional magnetization
Two or more magnetic fields in different directions imposed on a test object sequentially and in rapid
succession.
:
multifrequency
Two or more frequencies applied sequentially or simultaneously (as in a pulse).
:
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.
:
multiparameter
The many parameters of a test system. These parameters often affect test response and can often be
distinguished with a multifrequency technique.
:
multiphase alloy
Alloy in which several phases are present.
:
multiple back reflections
In ultrasonic testing, repetitive echoes from the far boundary of the test object.
:
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.
narrow banded
:
A relative term denoting a restricted range of frequency response.
:
NDC
Nondestructive characterization.
:
NDE
(1) Nondestructive evaluation. (2) Nondestructive examination.
:
NDI
Nondestructive inspection.
:
NDT
Nondestructive testing.
:
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.
:
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.
:
near ultraviolet radiation
Ultraviolet radiation with wavelengths ranging from about 320 to about 400 nm. Sometimes called black light.
:
near vision
Vision of objects nearby, generally within arm's length. Compare far vision.
:
nearsightedness
Vision acuity functionally adequate for viewing objects nearby, generally within arm's length but not at greater
distances. Also called myopia. Compare farsightedness.
:
necking down
Localized reduction in area of a specimen or structural member during welding or overloading.
:
negative sliding
The rolling and sliding of meshing gears or rollers when the rolling and sliding are in opposite directions.
:
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.
:
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.
:
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.
:
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.
:
nit
A former unit for measuring luminance, equivalent to one candela per square meter. Abbreviated nt.
noble metals
:
Cathodic metals (such as gold, platinum and silver), which strongly resist corrosion.
:
nodal points
In angle beam ultrasonic testing, the location of reflections at opposite surfaces as a wave progresses along a
test object.
:
node
A point in a standing wave where a given characteristic of the wave field has zero amplitude.
:
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.
:
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.
:
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.
:
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.
:
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.
:
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.
:
nonferromagnetic material
A material that is not magnetizable and essentially not affected by magnetic fields. Includes paramagnetic
materials and diamagnetic materials.
:
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.
:
normal induction
The maximum induction in a magnetic material that is symmetrically and cyclically magnetized.
:
normal permeability
The ratio of normal induction to the corresponding maximum magnetizing force. In anisotropic media, normal
permeability becomes a matrix.
:
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.
:
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.
:
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.
:
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.
:
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.
:
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.
:
OCTG
Oil country tubular goods.
:
oersted
The cgs unit of magnetic field strength, abbreviated Oe. In air, 1 Oe = 1 gauss. Replaced by SI's ampere per
meter.
:
oil country tubular goods (OCTG)
Hollow cylindrical components used to convey petroleum and related products.
:
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.
:
open sand casting
Any casting made in a mold that has no cope or other covering.
:
opening
Image processing operation of erosion followed by dilation. A single opening eliminates isolated single pixels.
See also closing.
:
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.
:
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.
:
organoleptic
Relying on or using sense organs, such as the human eye.
:
orientation
The angular relationship of a surface, plane, discontinuity or axis to a reference plane or surface.
:
orthicon
See image orthicon.
:
oscillogram
Common term for a record or photograph of data displayed on the cathode ray tube face.
:
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.
:
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.
:
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.
:
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.
:
parafoveal vision
See scotopic vision.
:
parallax
The apparent difference in position of an imaged point according to two differently positioned sensors.
:
parallel magnetization
A magnetic field induced in magnetizable material placed parallel to a conductor carrying an electric current.
Not a recommended practice for magnetic particle testing.
:
paramagnetic material
In electromagnetic testing, a material that has a relative permeability slightly greater than unity and is
practically independent of the magnetizing force.
:
parameter distribution
A display of the number of times the acoustic emission parameter falls between the values x and x + x as a
function of x. Typical parameters are amplitude, rise time and duration.
:
parasitic echo
See spurious echo.
:
particle motion
Movement of particles of material during wave propagation.
:
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.
:
parting sand
Fine sand for dusting on sand mold surfaces that are to be separated.
:
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 µ L/L is often used, with ppm to indicate proportion by
volume.
:
pass
In welding, a single bead along the entire weld length or the process of laying down that bead.
:
pattern
A form of wood, metal or other material, around which a molding material is placed to make a mold for casting
metals.
:
pearlite
Platelet mixture of cementite and ferrite in steels or in alpha and beta phases in nonferrous alloys.
:
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.
:
pencil source
An artificial source using the fracture of a brittle graphite lead in a suitable fitting to simulate an acoustic
emission event.
:
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.
:
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. 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.
:
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.
:
penetrant testing
Nondestructive testing method using penetrant.
:
penetrant, fluorescent
A penetrant characterized by its ability to fluoresce when excited by ultraviolet light.
:
penetrant, post emulsifiable
A penetrant that requires the application of a separate emulsifier to render the excess surface penetrant water
washable.
:
penetrant, visible
A penetrant characterized by an intense visible color dye that allows it to give contrasting indications on a
white developer background.
:
penetrant, water washable
A penetrant with built in emulsifier that makes it directly water washable.
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.
:
penetration, ultrasonic
Propagation of ultrasonic energy into a material. See also effective penetration.
:
period
The absolute value of the minimum interval after which the same characteristics of a periodic waveform or a
periodic feature return.
:
peripheral vision
The seeing of objects displaced from the primary line of sight and outside the central visual field.
:
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.
:
permanent mold
A metal mold of two or more parts used repeatedly for the production of many castings of the same form.
:
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. (2) The characteristic of materials that allows
gases or liquids to pass through them. (3) The ratio of flux density B to magnetizing field strength H. High
permeability materials are easier to magnetize than low permeability materials.
:
phantom
A reference standard used to verify the performance of ultrasound systems.
:
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.
:
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.
:
phase angle
The angular equivalent of the time displacement between corresponding points on two sine waves of the same
frequency.
:
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.
:
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.
:
phase shift
A change in the phase relationship between two alternating quantities of the same frequency.
phase velocity
:
The velocity of a single frequency continuous wave.
:
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.
:
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.
:
phasor quantity
Any quantity that is expressed as a complex number. See impedance.
:
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.
:
photoelasticity
The effect of a material's elastic properties on the way that it refracts or reflects light.
:
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.
:
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.
:
photometer
The basic measuring instrument of photometry. Accurate meters measuring radiant energy incident on a
receiver, producing measurable electrical quantities.
:
photometric brightness
The luminance of a light source.
:
photometry
The science and practice of the measurement of light or photon-emitting electromagnetic radiation. See also
relative photometry.
:
photon
Particle of light.
:
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.
:
photoreceptor
Light sensor.
:
physical properties
Nonmechanical properties such as density, electrical conductivity, heat conductivity and thermal expansion.
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.
:
pinhole porosity
Porosity, in either castings or metal formed by electrodeposition, resulting from numerous small holes
distributed throughout the metal.
:
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.
:
pitch and catch
Test technique in which ultrasonic energy is emitted by one transducer and received by another on the same
or opposite surface. Also called pitch-catch, two transducer technique or dual crystal method.
:
pitting
Discontinuity consisting of surface cavities. See also cavitation fatigue and pitting fatigue.
:
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.
:
pixel
A lighted point on the screen of a digital image. Picture element.
:
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.
:
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.
:
plastic deformation
Deformation that does or will remain permanent after removal of the load that caused it.
:
plate wave
See Lamb wave.
:
platelet
Flat crystallites in certain phases of steel.
:
plunger machines
Die casting machines having a plunger in continuous contact with molten metal.
:
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. See probe index.
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.
:
pores
(1) Small voids within a metal. (2) Minute cavities, sometimes intentional, in a powder metallurgy compact.
(3) Minute perforations in an electroplated coating.
:
porosity
A discontinuity in metal resulting from the creation or coalescence of gas. Very small pores are called
pinholes.
:
positive sliding
The rolling and sliding of meshing gears or rollers when directions of rolling and sliding are the same.
:
postcleaning
The removal of penetrant testing residues from the test piece after penetrant test processing is completed.
:
postemulsification
A penetrant removal technique employing a separate emulsifier applied over the surface penetrant to make it
removable with water spray.
:
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.
:
pouring
Transferring molten metal from a furnace or a ladle to a mold.
:
powder
See dry powder.
:
powder blower
A compressed air device used to apply dry magnetic particles over the surface of a test object.
:
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.
:
precleaning
The removal of surface contamination or smeared metal from the test piece so that it cannot interfere with the
penetrant testing process.
:
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.
:
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.
primary creep
:
First stage of creep, marked by elastic strain plus plastic strain.
:
primary radiation
Radiation emitting directly from the target of an X-ray tube or from a radioactive source.
:
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.
:
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.
:
probe coil
In electromagnetic testing, a small coil or coil assembly that is placed on or near the surface of test objects.
:
probe coil clearance
The perpendicular distance between adjacent surfaces of the probe and test object. See liftoff.
:
probe gas
A tracer gas that issues from a fine orifice so as to impinge on a restricted (small) test area.
:
probe index
The point on a shear wave or surface wave transducer through which the emergent beam axis passes.
:
process
Repeatable sequence of actions to bring about a desired result.
:
process control
Application of quality control principles to the management of a repeated process.
:
process testing
Initial product testing to establish correct manufacturing procedures and then by periodic tests to ensure that
the process continues to operate correctly.
:
prod magnetization
See current flow technique.
:
prods
Handheld electrodes for transmitting magnetizing current from a generating source to a test object.
production string
See tubing string.
:
:
propagation
Advancement of a wave through a medium.
:
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 µ L/L (ppm) tracer gas background contamination. It
proportions the amount of atmosphere allowed to enter the probe with its own (recirculating) fresh air supply.
:
pseudocolor
Image enhancement technique wherein colors are assigned to an image at several gray scale intervals.
:
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.
:
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.
:
PT
Liquid penetrant testing.
:
pull cracks
In a casting, cracks caused by residual stresses produced by cooling because of the object shape.
:
pulse
A transient electrical or ultrasonic signal that has a rapid increase in amplitude to its maximum value, followed
by an immediate return. An example is the signal that has propagated from the source to the transducer as
detected using a flat response transducer.
:
pulse echo method
An ultrasonic test method in which discontinuities are detected by return echoes of the transmitted pulses.
:
pulse length
A measure of pulse duration expressed in time or number of cycles.
:
pulse magnetization
Direct or indirect application of a high field intensity, usually by the capacitor discharge method.
:
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.
pulse repetition frequency
See repetition rate.
:
:
pulse tuning
Control of pulse frequency to optimize system response.
:
pulser transducer
In acoustic emission testing, a transducer used as an artificial source of acoustic energy.
:
pupil
Aperture in the center of an eye's iris, through which light focused by the lens passes.
:
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.
:
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.
:
Q of a coil
Ratio of reactance to resistance measured at the operating frequency.
:
quadrature
The relation between two periodic functions when the phase difference between them is one-fourth of a period.
:
qualification
Process of demonstrating that an individual has the required amount and the required type of training,
experience, knowledge and capabilities. See also qualified.
:
qualified
Having demonstrated the required amount and the required type of training, experience, knowledge and
abilities. See also qualification.
:
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.
:
quality assurance
Administrative actions that specify, enforce and verify a quality program.
:
quality control
Physical and administrative actions required to ensure compliance with the quality assurance program. May
include nondestructive testing in the manufacturing cycle.
:
quality of lighting
Level of distribution of luminance in a visual task or environment.
:
quartz Bourdon tube gage
High precision pressure measuring instrument containing a quartz helical Bourdon tube.
:
quasilongitudinal wave
A wave in which the direction of particle motion is not parallel to the direction of energy propagation.
:
quasishear wave
A wave in which the direction of particle motion is not perpendicular to the direction of energy propagation.
:
quenching of fluorescence
The extinction of fluorescence by causes other than removal of the ultraviolet light (the exciting radiation).
:
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.
:
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. 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.
:
radiant energy
Energy transmitted through a medium by electromagnetic waves. Also known as radiation.
:
radiant flux
Radiant energy's rate of flow, measured in watts.
:
radiant intensity
Electromagnetic energy emitted per unit time per unit solid angle. Measured in watts per steradian.
:
radiant power
Total radiant energy emitted per unit time.
:
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.
:
radio frequency display
The presentation of unrectified signals on a display screen. 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.
:
radiographic screens
Metallic or fluorescent sheets used to intensify the radiation effect on films.
:
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.
:
radiography
Radiographic testing.
:
radiology
That branch of medicine which uses ionizing radiation for diagnosis and therapy.
:
radiometer
Instrument for measuring radiant power of specified frequencies. Different radiometers exist for different
frequencies.
:
radiometric photometer
Radiometer for measuring radiant power over a variety of wavelengths.
:
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.
:
range
In ultrasonic testing, the maximum path length that is displayed. See also sweep length.
:
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.
:
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.
:
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.
:
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.
:
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.
:
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.
:
receiver
The section of an ultrasonic instrument that amplifies echoes returning from the test object. Also, a transducer
that picks up the echoes.
:
recommended practice
A set of guidelines or recommendations.
:
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.
:
recovery time
The time required for a test system to return to its original state after it has received a signal.
:
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.
:
rectified alternating current
A unidirectional electric current obtained by rectifying alternating current without the deliberate addition of
smoothing to remove the inherent ripples.
:
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.
:
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.
:
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.
reference grating
:
In moiré and grid nondestructive testing, an undeformed grating superimposed upon a specimen grating to
create the moiré.
:
reference number
Number associated with the impedance of a coil adjacent to a test sample.
:
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.
:
reflectance
The ratio of reflected wave energy to incident wave energy. Also known as reflectivity.
:
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.
:
reflection probe
A coil system that utilizes both an excitation and a detection or sensing coil on the same side of the sample.
:
reflectometer
Photometer used to measure diffuse, specular and total reflectance.
:
reflector
(1) In optical nondestructive testing, device used to redirect the luminous flux from a source by the process of
reflection. (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.
:
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.
:
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.
:
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.
:
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.
:
rejection level
See level, rejection.
:
relative permeability
The ratio of the permeability of the material to the permeability of vacuum. See permeability.
:
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.
:
relaxation
Relief of stress by creep. Diminishing stress by creep at constant strain frequently occurs in service.
:
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.
:
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.
:
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.
:
repeatability
Ability to reproduce a detectable indication in separate processings and tests from a constant source.
:
repetition rate
The number of pulses generated or transmitted per unit of time (usually seconds).
:
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.
:
replication
A method for copying the topography of a surface by making its impression in a plastic or malleable material.
:
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.
:
residual elements
Elements present in an alloy in small quantities, but not added intentionally.
:
residual magnetic field
The magnetism remaining in a ferromagnetic material after the magnetizing force is reduced to zero.
:
residual method
Using the residual magnetic field of high retentivity materials to trap magnetic particles and indicate
discontinuities.
:
residual technique
Ferromagnetic particles are applied to a test object after the magnetizing force has been discontinued.
:
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.
:
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.
:
resolution test
Procedure wherein a line is detected to verify a system's sensitivity.
:
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.
:
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.
:
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.
:
resonance method
A method using the resonance principle for determining velocity, thickness or presence of laminar
discontinuities.
:
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.
:
response factor
The response of the halogen leak detector to 3 × 10 7 Pa·m 3 ·s 1 (3 × 10 6 std cm 3 ·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).
:
response function
The ratio of response to excitation, both expressed as functions of the complex frequency.
:
retentivity
A material's property of retaining residual magnetism to a greater or lesser degree.
:
retina
In the eye, the tissue that senses light.
:
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.
:
ringing signals
(1) Closely spaced multiple signals caused by multiple reflections in a thin material. (2) Signals caused by
continued vibration of a transducer.
:
ringing time
The time that the mechanical vibrations of a transducer continue after the electrical pulse has stopped.
:
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.
:
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.
:
robotic system
Automated system programmed to perform purposeful movements in variable sequences.
:
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.
:
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.
:
root crack
A crack in either the weld or heat affected zone at the root of a weld.
:
root penetration
The depth to which weld metal extends into the root of a joint.
:
RT
Radiographic testing.
:
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.
:
runner box
A distribution box that divides the molten metal into several streams before it enters the mold cavity.
:
runout
The discontinuity in a casting caused by the escape of metal from the mold.
:
salvage tests
Testing after salvage operations or testing objects that can be repaired.
:
sampling probe
See detector probe.
:
sampling, partial
Testing of less than one hundred percent of a production lot. See one hundred percent testing.
:
sampling, random partial
Partial sampling that is fully random.
:
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.
:
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.
:
saturation
(1) A condition in which high amplitude signals on a display screen do not increase with increased gain and
appear flattened. (2) Relative or comparative color characteristic resulting from a hue's dilution with white
light.
:
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.
:
scalar
A quantity completely specified by a single number.
:
scale
Oxide formed on metal by chemical action of the surface metal with oxygen from the air.
:
scale pit
Shallow surface depression in metal, caused by scale.
:
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.
:
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.
:
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.
:
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.
:
Schlieren system
An optical system used for visual display of an ultrasonic beam passing through a transparent medium.
:
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.
:
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.
:
scrap
(1) Manufactured materials not suitable for sale. (2) Discarded metallic material that may be reclaimed through
melting and refining.
:
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.
:
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.
:
search coil
A detection coil that is usually smaller than the excitation coil.
:
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.
:
second stage replica
A positive replica made from the first cast to produce a duplicate of the original surface.
:
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.
:
secondary magnetic flux
magnetic flux due to induced flow of eddy currents.
:
seeability
The characteristic of an indication that enables an observer to see it against the adverse conditions of
background, outside light etc.
:
segregation
Nonuniform distribution of alloying elements, impurities or microphases.
:
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.
:
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.
:
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.
:
semipermanent mold
A permanent mold in which sand or plastic cores are used.
:
send/receive transducer
A transducer consisting of two piezoelectric elements mounted side by side separated by an acoustic barrier.
One element transmits, one receives.
:
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.
:
sensitivity
A measure of a sensor's ability to detect small signals. Limited by the signal-to-noise ratio.
:
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·m 3 ·s 1 or std cm 3 ·s 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).
:
sensitivity panel
A plated metal panel with cracks of known depth induced into the plating. Used to evaluate and compare
penetrant sensitivity.
:
sensitization
Precipitation of chromium carbides in the grain boundaries of a corrosion resistant alloy, resulting in
intergranular corrosion that would otherwise be resisted.
:
settling test
A procedure used to determine the concentration of particles in a magnetic particle bath.
:
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.
:
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.
:
shakeout
Removing castings from a sand mold.
:
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.
:
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.
:
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.
:
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.
:
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.
:
shear wave
A type of wave in which the particle motion is perpendicular to the direction of propagation.
:
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.
:
shell core
A shell molded sand core.
:
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.
:
shielding
A conducting or magnetic material placed so as to decrease susceptibility to interference and to increase
resolution.
:
shift
A casting discontinuity caused by mismatch of cope and drag or of cores and mold.
:
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. See also wedge.
:
shot
A short energizing cycle in a magnetic particle test.
:
shot peening
Cold working the surface of a metal by metal shot impingement. Used to clean a part surface before inspection.
:
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.
:
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.
:
shrink mark
A surface depression on a casting that sometimes occurs next to a thick section that cools more slowly than
adjacent sections.
:
shrinkage cavities
Cavities in castings caused by lack of sufficient molten metal as the casting cools.
:
shrinkage cracks
Hot tears associated with shrinkage cavities.
:
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.
:
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.
:
signal
Response containing relevant information.
:
signal electrode
Transparent conducting film on the inner surface of a vidicon's faceplate and a thin photoconductive layer
deposited on the film.
:
signal processing
Acquisition, storage, analysis, alteration and output of digital data through a computer.
:
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.
:
simple magnifier
A microscope having a single converging lens.
:
skim gate
A gating arrangement designed to prevent the passage of slag and other undesirable material into the casting.
:
skimmer
A tool for removing scum, slag and dross from the surface of molten metal.
:
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.
:
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.
:
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.
:
slag
A nonmetallic product resulting from the mutual dissolution of flux and nonmetallic impurities in smelting
and refining operations.
:
slag inclusions
Nonmetallic solid material entrapped in weld metal or between weld metal and base metal.
:
slag lines
Elongated cavities containing slag or other foreign matter in fusion welds.
:
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.
:
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.
:
slurry
A free-flowing pumpable suspension of a fine solid in a liquid.
:
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.
:
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.
:
snap flask
A hinged flask removed from the mold after the mold is made.
:
Snell's law
The physical law that defines the relationship between the angle of incidence and the angle of refraction.
:
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.
:
soaking
Prolonged holding at a selected temperature.
:
soldiers
Wooden blocks or sticks used to reinforce bodies of sand in the cope. They usually overhang the mold cavity.
:
solidification shrinkage
The decrease in volume of a metal during solidification.
:
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.
:
solvent action
The ability of a liquid to dissolve another material.
solvent cleaning
:
The process of removing excess penetrant from the surface of a test object by hand wiping with a solvent
dampened cloth.
:
solvent developer
A developer for penetrant tests in which the developing powder is applied as a suspension or solution in a
quick drying solvent.
:
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.
:
source
The location where an event takes place.
:
source location
The computed origin of acoustic emission signals.
:
spalling
Cracking or flaking of small particles of metal, usually in thin layers, from the surface of an object.
:
spalling fatigue
See subcase fatigue.
:
spatial resolution
Width of smallest region from which reliable data can be extracted.
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.
:
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.
:
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.
:
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.
:
spectral reflectance
The radiant flux reflected from a material divided by the incident radiant flux.
:
spectral transmittance
The radiant flux passing through a medium divided by the incident radiant flux.
:
spectrophotometer
Instrument used for spectrophotometry.
:
spectrophotometry
Measurement of electromagnetic radiant energy as a function of wavelength, particularly in the ultraviolet,
visible and infrared wavelengths.
:
spectroradiometer
Instrument used for spectroradiometry.
:
spectroradiometry
Measurement of electromagnetic radiant power and spectral emittance, used particularly to examine colors
and to measure the spectral emittance of light sources.
:
spectroscope
Instrument used for spectroscopy.
:
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.
:
spectrum
(1) The amplitude distribution of frequencies in a signal. (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.
:
spectrum response
The amplification (gain) of a receiver over a range of frequencies.
:
specular
Pertaining to a mirror-like reflective finish, as of a metal. Compare lambertian.
:
specular reflection
When reflected waves and incident waves form equal angles at the reflecting surface.
:
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.
:
speed of vision
The reciprocal of the duration of the exposure time required for something to be seen.
:
spherical wave
A wave in which points of the same phase lie on surfaces of concentric spheres.
:
spheroidizing
Heating and cooling to produce a spheroidal or globular form of carbide in steel.
:
split gate
A gate having the sprue axis in the die parting.
:
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.
:
spot examination
Local examination of welds or castings.
:
spray scrubber
Technique of pressure washing nonwater soluble penetrant from the surface by introducing a hydrophilic
emulsifier or detergent into the water wash.
:
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.
:
spurious echo
A general term used for any indication that cannot be associated with a discontinuity or boundary at the
location displayed.
:
squid
An acronym (superconducting quantum interference device). A sensitive detector of magnetic fields using a
quantum effect.
:
squint angle
The angle by which the ultrasonic beam axis deviates from the probe axis.
:
squirter
See water column.
:
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. (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.
:
standard atmospheric conditions
Atmospheric pressure of 101.325 kPa (14.6959 lb f ·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·ft3 ).
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.
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.
:
steady state
Thermal equilibrium, a condition of an object wherein the temperatures throughout the object remain constant.
:
steel
An iron alloy, usually with less than two percent carbon.
:
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 × 10 15 photon·s 1 ·m 2 ·K 2 .)
:
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.
:
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.
:
straight beam
An ultrasonic wave traveling normal to the test surface.
:
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.
:
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.
:
stress raiser
Contour or property change that causes local concentration of stress.
:
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.
:
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.
:
structural integrity test (SIT)
A test that demonstrates the capability of a vessel to withstand specified internal pressure loads.
:
subcase fatigue
Fatigue originating below the case depth. Compare case crushing. See also spalling fatigue.
subcase origin fatigue
See subcase fatigue.
:
:
substrate
Layer of metal underlying a coating, regardless of whether the layer is base metal.
:
subsurface discontinuity
Any discontinuity that does not extend through the surface of the object in which it exists. 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.
:
suppression
See reject.
:
surface wave
See Rayleigh wave.
:
survey meter
A portable instrument that measures dose rate of exposure or radiation intensity.
:
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. 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.
:
sweep delay
A delay in time of starting the sweep after the initial pulse. Also denotes the control for adjusting the time.
:
sweep length
The length of time or distance represented by the horizontal baseline on an A-scan.
:
swinging field
See multidirectional magnetization.
:
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.
:
tape head probe
The head of a tape recorder used as an eddy current coil. A type of horseshoe coil.
:
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.
:
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.
:
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.
:
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.
:
temperature diagram
See time temperature transformation (TTT) diagram.
:
temperature envelope
The temperature range over which a particular penetrant testing technique will operate.
:
tempering
Process of heating a material, particularly hardened steel, to below the austenite transformation temperature
to improve ductility.
:
tertiary creep
Third stage of creep, marked by steady increase in strain to the point of fracture under constant load.
:
tesla
The SI unit of measure for magnetic flux density. Abbreviated T. 1 T = 10,000 gauss.
:
tesla meter
A magnetometer that registers field strength in gauss (or tesla).
:
test coil
The section of a coil assembly that excites and/or detects the magnetic field in the material under
electromagnetic test.
:
test frequency
In electromagnetic testing, the number of complete cycles per unit time of the alternating current applied to
the primary test coil.
:
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.
:
test surface
The exposed surface of a test object.
:
thermal
Physical phenomenon of heat involving the movement of molecules. Compare infrared radiation.
:
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.
:
thermal diffusivity
The speed at which heat diffuses through an object. Expressed as the rate of temperature change with time and
represented by . Each material has its own characteristic value for , 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).
:
thermal equilibrium
Condition of an object wherein temperatures throughout the object remain constant.
:
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.
:
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.
:
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.
:
thresholding
Digital data processing technique that reduces a gray level image into a binary image.
:
throat, actual
Shortest distance from the root of a fillet weld to its face, as opposed to theoretical throat or weld size.
:
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.
:
throat, weld
Distance from the root of a fillet weld to its face. Compare weld size and throat, actual.
:
throttling
Reducing the net pumping speed of a pumping system by partially closing a valve or installing a section of
pipeline with low conductance.
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.
:
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.
:
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.
:
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.
:
time temperature transformation (TTT) diagram
A graph showing time required at any temperature to transform austenite to pearlite, bainite or martensite.
:
tip
In casual usage, the distal or objective end of a borescope.
:
toe crack
A base metal crack at the toe of a weld.
:
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.
:
tolerance
Permissible deviation or variation from exact dimensions or standards.
:
tone burst
A wave train consisting of several cycles of the same frequency.
:
tool mark
Shallow indentation or groove made by the movement of manufacturing tools over a surface. Compare gouge
or nick.
:
toroidal field
An induced magnetic field occurring in a ring test object when current is induced. See current induction
technique.
:
torr
Unit of absolute pressure nearly equal to 1.33332 kPa (1.000 mm Hg).
:
trace
Line formed by an electron beam scanning from left to right on a video screen to generate a picture.
:
tracer
In leak testing, a gas that is sensed as it escapes from confinement.
:
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.
:
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.
:
tracer standard leak
A standard leak in which the contained gas is a tracer gas compound.
:
transducer
(1) Any device that transforms energy from one form to another. (2) In electromagnetic testing, the test coil.
(3) An electroacoustical or magnetoacoustic device containing an element for converting electrical energy into
acoustical energy and vice versa. See search unit.
:
transducer relative sensitivity
The response of the transducer to a given and reproducible artificial source.
:
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.
:
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.
:
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.
:
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.
:
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.
:
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.
:
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.
:
transient heat flow
Heat flow occurring during the time it takes an object to reach thermal equilibrium or steady state.
:
transmission angle
The incident angle of a transmitted ultrasonic beam. It is zero degrees when the beam is perpendicular (normal)
to the test surface.
:
transmission characteristics
Test object characteristics that influence the passage of ultrasonic energy, including scattering, attenuation or
surface conditions.
:
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.
:
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.
:
troland
A unit of retinal illuminance equal to that produced by a surface whose luminance is 1 nit when the pupil
measures 1 mm 2 . 1 nit = 1 candela per square meter (1 cd·m 2 ).
:
true continuous method
Test technique in which magnetizing current is applied before application of magnetic particles and is
maintained without interruption throughout the examination.
:
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.
:
tungsten inclusions
Inclusions in welds resulting from solidified droplets, particles or splinters of tungsten from welding
electrodes.
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.
:
U shaped coil
See horseshoe coil.
:
ultrasonic
Pertaining to acoustic vibration frequencies greater than about 20 kHz.
:
ultrasonic absorption
The damping of ultrasonic waves as they pass through a medium. See attenuation coefficient.
:
ultrasonic spectroscopy
Analysis of the frequency content of an acoustic wave. Generally performed mathematically by using a fast
Fourier transform.
:
ultrasonic spectrum
Usually, the frequency of sound waves ranging from 20 kHz to 10 MHz, but may extend much higher in
special applications.
:
ultrasonic testing
Nondestructive testing using acoustic energy in the ultrasonic spectrum for interrogation.
:
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.
:
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.
:
underbead crack
A subsurface crack in the base metal adjacent to the weld fusion zone.
:
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.
:
unit die
A die block that contains several cavity inserts for making different kinds of die castings.
:
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.
:
upper confidence limit
A calculated value constructed from sample data with the intention of placing a statistical upper boundary on
a true leakage rate.
:
upset
A frame used to deepen either the cope or drag in a casting mold.
:
UT
Ultrasonic testing.
:
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.
:
vacuum
Space containing gas at a pressure below atmospheric pressure.
:
vacuum box
Device used to obtain a differential pressure across a weld or part of a pressure boundary that cannot be directly
pressurized.
:
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.
:
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. 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.
:
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.
:
variable standard leak
A device that permits a tracer gas to be introduced to the leak detector at a rate adjustable by the operator.
:
vector quantity
Any physical quantity that is specified with both magnitude and direction and that obeys the parallelogram
law of addition.
:
vehicle
A liquid medium for the suspension of magnetic particles, often a light petroleum distillate or conditioned
water. See carrier fluid.
:
vent
A small opening in a mold for the escape of gases.
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verification test
Tests intended to confirm the capability of the type A leak test method and equipment to determine the
containment leakage rate.
:
vertical limit
The readable level of vertical indication on an A-scan.
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.
:
video presentation
An electronic screen presentation in which radiofrequency signals have been rectified and usually filtered.
:
videoscope
Jargon for video borescope.
:
vidicon tube
Television tube that uses the photoconduction method. Compare image orthicon.
:
vigilance decrement
Degradation of reliability during performance of visual activities over a period of time. See also
psychophysics.
:
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.
:
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.
:
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.
:
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.
:
visible light
Radiant energy generated in the 400 to 700 nm wavelength range.
:
vision
Perception by eyesight. See far vision, machine vision, mesopic vision, near vision, peripheral vision, photopic
vision, scotopic vision and speed of vision.
:
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.
:
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.
:
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.
:
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.
:
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.
:
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.
:
visual performance
The quantitative assessment of the performance of a visual task, taking into consideration speed and accuracy.
:
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.
:
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.
:
visual testing
Method of nondestructive testing using electromagnetic radiation at visible frequencies.
:
voids
Hollow spots, depressions or cavities. See also discontinuity and dislocation.
:
VT
Visual and optical testing.
:
wash
A coating applied to the face of a mold prior to casting.
:
water break free
Rinse water, having the ability to cover an entire surface in an unbroken film.
:
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.
:
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.
:
water jet
An unsupported stream of water carrying ultrasonic signals between the transducer and the test object surface.
Also called a squirter.
:
water line
A tube or other passage through which water is circulated to cool a casting die.
:
water path
In immersion testing or with a water column, the distance from the transducer face to the test object's front
surface.
:
water tolerance
The amount of water that a penetrant or emulsifier can absorb before its effectiveness is impaired.
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.
:
wave train
A series of waves or groups of waves passing along the same course at regular intervals.
:
wavefront
In a wave disturbance, the locus of points having the same phase.
:
wavelength
The distance needed in the propagation direction for a wave to go through a complete cycle.
:
weak sand
Refers to sand that will not hold together when used to make a mold.
:
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.
:
wear oxidation
See wear, fretting.
:
wear, adhesive
Degradation of a surface because of micro-welding and consequent fracture due to the sliding of one surface
against another. Types include fretting, galling and scuffing.
:
wear, fretting
Surface degradation caused by micro-welding and micro-fractures on surfaces rubbing each other. Also called
chafing, friction oxidation and wear oxidation. See also cocoa and false brinelling.
:
wedge
A device used to direct ultrasonic energy into a test object at an acute angle. See also shoe.
:
weld bead
A deposit of filler metal from a single welding pass.
:
weld crack
A crack in weld metal.
:
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.
:
weld metal
That portion of a weld that has been melted during welding.
:
weld nugget
The weld metal in spot, seam or projection welding.
:
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.
weld throat
See throat.
:
:
welder's flash
Clinical condition, specifically keratoconjunctivitis, commonly caused by overexposure to ultraviolet
radiation of welding arc.
:
wet developer
A developer in which the developing powder is applied as a suspension or solution in a liquid, usually water
or solvent.
:
wet method
A testing technique in which magnetic particles are applied as a suspension in a liquid vehicle.
:
wet slurry technique
A magnetic particle test in which the particles are suspended in high viscosity vehicle.
:
wetting action
The ability of a liquid to spontaneously spread over and adhere to solid surfaces.
:
wetting agent
A substance that increases wetting action by reducing the surface tension of a liquid, thereby reducing the
formation of air bubbles.
:
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.
:
white light
Light combining all frequencies in the visible spectrum.
:
Wien's Displacement Law
For practical infrared imaging, Wien's Displacement Law gives the wavelength of maximum emittance.
:
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.
:
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.
:
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.
:
worm holes
Elongated or tubular cavities due to entrapped gas. Also called pipes.
:
wrap around
The display of misleading ultrasonic reflections from a previously transmitted pulse due to the use of excessive
pulse repetition frequency. See ghost.
:
X-ray
Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and
release energy. Radiation is non-isotopic in origin and is generated by bombarding a metallic target with high
speed electrons.
:
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.
:
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.