NDT
Glossary
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C
- C-scan
- a data presentation method applied to pulse echo and transmission techniques.
It yields a two-dimensional plan view of the object. No indication of depth
is given unless special gating procedures are used.
- Calibration
- The process whereby
the magnitude of the output of a measuring instrument is related to the magnitude
of the input force driving the instrument (i.e. Adjusting a weight scale to
zero when there is nothing on it).
- Calibration
Reflector - A reflector with a known dimensioned surface established
to provide an accurately reproducible reference measurement.
- Capacitance
- The property of an
electrical circuit that opposing a change in voltage. Capacitance enables
devices or circuits to hold an electrical change.
- Capacitive
Reactance - The opposition to alternating current
due to the capacitance of a capacitor, cable, or circuit.
- Capillary
Action - The phenomenon of a liquid such
as water spontaneously creeping up thin tubes and fibers, this is caused by
adhesive and cohesive forces and surface tension.
- Capillary
Pressure - The
difference in pressure across the interface between two immiscible fluids.
- Carbon Dating
-A method of using the half-life of Carbon-14 to find the approximate age
of an object that is up to 50,000 years old.
- Carbonitriding
- An evelated-temperature process (similar to carburizing) by which a ferrous
metal absorbs both carbon and nitrogen into the surface when exposed to an
atmosphere high in carbon and nitrogen. The carbon and nitrogen atoms diffuse
into the metal to form a high-carbon and high-nitrogen zone near the surface.
- Carburizing
- An elevated temperature process by which a ferrous metal absorbs carbon
into the surface when exposed to a high-carbon environment. Carbon atoms diffuse
into the metal to create a high-carbon zone near the surface.
- Case
- In a ferrous metal, the outer portion that has been made harder than the
interior, or core.
- Case
Depth - The depth of the case, or hardened surface region, of a metal.
- Cathode -
A negatively charged electrode, as of an electrolytic
cell, a storage battery, or an electron tube. The electrode at which
reduction (and practically no corrosion) occurs. It is the opposite of anode.
- Cathode
Ray Tube - A vacuum tube containing a screen on which ultrasonic
scans or oscilloscope traces may be displayed.
- Characteristic
Frequency Ratio
- It allows the test coil operating point to be specified
in terms of a single quantity rather than four independent variables.
- Chemical
Element - Any material that is composed of only one type of atom. It is
also called a basic element or just an element.
- Chemical
Formula - A formula used to describe the types of atoms and their numbers
in an element or compound.
- Circuit
-
A closed path followed or capable of being followed by an electric current.
- Circuit Diagrams
- A type of diagram that is a pictorial way of showing circuits.
- Circular
Magnetism - The circular magnetic field
around and inside a solid magnetic conductor when an electric current is passed
through it.
- Circumferential
- Around the circumference, or periphery, of circular or cylindrical object.
Also called tangential or hoop when referring to stresses.
- Circumferential
Coil - See encircling and internal probes.
- Cladding
- The outer layer, which provides corrosion protection or other desirable
property, to a composite metal. The metal layers can be bonded together by
rolling, welding, casting, heavy chemical deposition, or heavy electroplating.
- Cleavage
Fracture - A splitting fracture of a metal
(usually polycrystalline) across the grains (or crystals).
- Cloud Chamber
- (1) A station in a penetrant inspection processing line where the developer
is applied by creating a cloud of developer that envelops the test component.
(2) A device for detecting and measuring radioactivity and radiation. The
cloud chamber was invented by Charles Wilson in 1911 and it makes it possible
to visually see and photograph the path of ionizing radiation.
- Coefficients
- A constant chemical or physical property constant for a system with specific
conditions (i.e. Coefficient of Friction).
- Coefficient
of Thermal Expansion - The linear expansion or contraction per unit
length per degree temperatures between specified lower and upper temperatures.
- Coercive
Force
- The reverse magnetizing force necessary to remove residual magnetism and
demagnetize the part.
- Cohesive
Strength - The force that holds together the atoms in metal crystals.
Analogous to tensile strength, but on a submicroscopic scale.
- Coil
- More than one loop of a conductor wound in a spiral. Also called a solenoid.
- Coil
Shot - A short "shot" of magnetizing current passed through
a solenoid or coil for the purpose of producing a longitudinal magnetic field
in a test component.
- Cobalt
60 - A radioisotope of the element cobalt.
- Cold
Shut - (1) A discontinuity that appears on the surface of cast metal
as a result of two streams of liquid metal meeting but failing to unite. (2)
A lap on the surface of a forging or billet that was closed without fusion
during deformation. Same as forging lap.
- Cold
Work - Permanent deformation caused by application of an external
force to a metal below its recrystallization temperature.
- Collimating
Nozzle - A transducer assembly attachment designed to reduce the
ultrasonic beam spread.
- Collimation
- The process by which a beam of energy or particles
is aligned to form a parallel beam.
- Collimator
- A device for limiting the effects of beam spread.
- Color-Contrast
Penetrant - A penetrant incorporating a color dye or sufficient intensity
to give good color contrast in indications against the background of the surface
being tested, when viewed under white light.
- Columnar
Structure - A coarse structure of parallel columns of grains, having
the long axis perpendicular to the surface.
- Comparative
Test Block - A metal block specially cracked and having two separate,
but adjacent areas for the application of different penetrants so that a direct
comparison can be obtain.
- Compensator
- An electrical matching network to compensate for electrical impedance differences.
- Complex
Electrical Impedance
- In a typical AC circuit, resistance
R and reactance X combine in vector fashion to form a complex
impedance. Reactance is conventionally multiplied by the positive square root
of -1 (j), to express Z as a complex number of the form
R + jX.
- Composite
- A product that is produced by combining several different material
products to arrive at desired set of properties. Fiber glass, carbon graphite
epoxy, and carbon fiber are examples of composite
material.
- Compound
- Any material that is composed of more than one type of atom.
- Compression
- The act of forcing or pressing together.
- Compressional
Wave - A wave in which the particle motion in the material is parallel
to the wave propagation direction. Also called a longitudinal wave.
- Compressive
Strength - In compression testing, the ratio of maximum load to the
original cross-sectional area. Fracture may or may not occur, depending on
the applied forces and the properties of the material.
- Compton Scattering
- A process through which radiation is absorbed by the material it penetrates.
- Computed
Tomography - A radiographic technique in which the planar density data
is stretched out in a third dimension and combined similar data taken at various
angles to generate cross sectional images of the test component.
- Concentration
Cell - A cell involving an electrolyte and two identical electrodes,
with the electrical potential resulting from differences in the chemistry
of the environments adjacent to the two electrodes.
- Conductivity
- A measure of the ability of a material to conduct electrical current.
- Conductors
- Materials that have free electrons and allow electrical current to flow
easily.
- Consequent
Poles - Magnetic poles that exist where the specimen has been successively
magnetized in different sections to create more than two poles; e.g., two
north poles with one south pole between them.
- Constriction
- Squeezing in the lines of force; i.e., a narrowing of section in a magnetized
material.
- Constructive
Interference - The strengthening of waves that occurs when two waves interact
and in phase portions of each wave combine to create a wave with a higher
intensity.
- Contact
Method - The testing method in which the transducer face makes direct
contact with the test object through a thin film of couplant.
- Contact Transducers
- An ultrasonic transducer that is designed to be used in direct contact with
the surface of the test article.
- Contaminant
- Any foreign substance that interferes with a process or measurement.
- Continuous
Method - A magnetic particle inspection method in which the indicating
particles are on the part while the magnetizing current is being applied.
- Continuous
Wave
- A wave that continues without interruption.
- Continuum
-
The name used for the combination of all colors an object,
such as the Sun, emits, and also for the broad variation from color to color
in how much light is emitted.
- 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
(radiographic) - The measure of difference in the film or detector
density (darkness) from one area to another, resulting from various X-ray
intensities interacting with the detector.
- Contrast
Ratio - The relative difference in the film or detector density (darkness)
between the image background and a feature of interest.
- Contrast
Sensitivity -
Being able to differentiate between an object and its background
- Control
Echo - An ultrasonic reference signal from a constant reflector,
such as the back reflection from a smooth, regular surface. Loss of the control
echo indicates that the UT system is not functioning properly due to a problem
such as coupling loss.
- Controlled
Area - A defined area in which the occupational exposure of personnel
to radiation or to radioactive material is under the supervision of the individual
in charge.
- Cooling
Stresses - Residual stresses resulting from nonuniform distribution
of temperature during cooling.
- Corner
Effect
- The strong reflection obtained when an ultrasonic beam is directed toward
the intersection of two or three mutually perpendicular surfaces.
- Corrosion
- Deterioration of a metal by chemical or electrochemical reaction with
its environment.
- Corrosion
Embrittlement - The severe loss of ductility of a metal, resulting
from corrosive attack, usually intergranular and often not visually apparent.
- Corrosion
Fatigue - Cracking that initiates and propagates due to the application
of repeated or fluctuating stresses, and the initiation and propagation occurs
more rapidly due to the presence of a corrosive environment.
- Coulomb(ku`-lum)
- A charge that moves past a given point in one second. A coulomb is the charge
carried by 6.25 x 10^18 electrons.
- Couplant
- A substance (usually liquid) used between the transducer and the test surface
to permit or improve transmission of ultrasonic energy into the test object.
- Coupling
- (1) The physical connect of an ultrasonic transducer to the test component.
(2) The interaction of the coil's magnetic field with the test sample, which
results in the generation of eddy currents in the sample and, in turn, a change
in probe impedance.
- Coupon
- A piece of metal from which a test specimen is to be prepared. Often an
extra piece that is cut from a casting or forging.
- Crack
- A long narrow discontinuity
- Crack
Growth Rate - The change in crack length per number of fatigue
cycles.
- Crack Tip
Diffraction -
A process using a beam transducer to determine the length and height of a
crack
- Creep
- Time-dependent strain occurring under stress, or the change of shape that
occurs gradually under a steady load.
- Creep
Strength - (1) The constant nominal stress that will cause a specified
quantity of creep in a given time at constant temperature; (2) the constant
nominal stress that will cause a specified creep rate at constant temperature.
- Crevice
Corrosion - Localized corrosion resulting from the formation of a
concentration cell in a crevice between two surfaces.
- Critical
Angle - The first angel of the incident sound wave that generates a refracted
wave that travels along the incident surface. The first angle that results
in a surface following longitudinal wave is known as the 1st critical angle
and the first angle that results in surface following shear wave is known
as the 2nd critical angle.
- Cross
Talk
- The unwanted signal leakage (acoustical or electrical) across and 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.
- Crystal
- A three-dimensional array or atoms having a certain regularity in its arrangement.
A crystal is composed of many cells or lattices, in which the atoms are arranged.
In the field of metallurgy, a crystal is often called a grain.
- Cumulative
Dose (radiation) - The total dose (see threshold dose) resulting
from repeated exposure to radiation of the same region or of the whole body.
- Cup
Fracture (cup-and-cone-fracture) - Fracture, frequently seen in tensile
test pieces 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.
- Curie
- The basic unit of measure for describing the activity (radioactivity) of
a quantity of radioactive material. The amount of radioactive material
giving off 37 billion disintegrations per second. In the United States, the
picocurie (1 pCi = 0.037 d.p.s.) is the unit used for many measurements of
radioactive contamination.
- Current
(I) -
The flow of electrons. Measured in amperes.
- Current
Density - Current divided by the electrode
area (current per unit area of the electrode)
- Curvature
corrections - The method to account for degradation
of signal amplitude when using a flat ultrasonic transducer to inspect an
object with a curved surface.
- Cutoff
Frequency - The upper or lower frequency beyond
which no appreciable energy is transmitted.
- Cycle
(Hertz) - One complete set of recurrent values of a periodic quantity
comprises a cycle.
- Cyclic
Load - Repetitive loading of a material that sometimes leads to fatigue
fracture.
- Cyclotron
- A device that is capable of accelerating charged particles (protons)
in a circular path to energies that exceed 10 MeV. E.O. Lawrence developed
the Cyclotron in the early 1930’s, .
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