Glossary of terms

Abrasion test

The process of grinding or wearing away through the use of abrasives; a roughening or scratching of a surface due to abrasive wear.

Abrasive wear

The general category of abrasive wear can be characterized by a single key word - cutting.

Abrasive wear

The removal of material from a surface when hard particles slide or roll across the surface under pressure. The particles may be loose or may be part of another surface in contact with the surface being abraded. Compare with adhesive wear.

Absorbed Does

The amount of energy, imparted to matter by an ionizing particle per unit mass of irradiated material at the place of interest. It is expressed in rads.


The taking up of energy from the medium through which it passes.

Absorption Coefficient

The ratio of energy absorbed by a medium or material to the energy incident on the surface. If a flux through a material decreases with distance x in proportion to e-ax, then a is called the absorption coefficient. Also known as the absorption factor; absorption ratio; coefficient of absorption.

Absorption Coefficient, Linear

The fractional decrease in transmitted intensity per unit of absorber thickness. It is usually designated by the symbol µ and expressed in units of (cm-1.2).

Acceptance Standard

A controlled specimen containing natural or artificial discontinuities that are well defined and similar to the maximum acceptable discontinuity, in size and extent, in the product.

Acoustic Emission Testing (AE)

A nondestructive testing method that "listens" for transient elastic-waves generated due to a rapid release of strain energy caused by a structural alteration in a solid material. 

Acoustic Impedance (Z)

The resistance of a material to the passage of sound waves. The value of this material property is the product of the material density and sound velocity. The acoustic impedance of a material determines how much sound will be transmitted and reflected when the wave encounters a boundary with another material. The larger the difference in acoustic impedance between two materials, the larger the amount of reflected energy will be.

Acoustic Properties

 Intrinsic characteristics of any particular material that describe how sound travels through it. Such characteristics include the density, acoustic impedance, and sound velocity.

Adhesive wear

The removal or displacement of material from a surface by the welding together and subsequent shearing of minute areas of two surfaces that slide across each other under pressure. Compare with abrasive wear.

Adhesive wear

Like abrasive wear, adhesive wear can also be characterized by a single word. In the case of adhesive wear, the word is "welding," or more precisely, "microwelding." 

Adjustment of a measuring system

Adjustment of a measuring system: set of operations carried out on a measuring system so that it provides prescribed indications corresponding to given values of a quantity to be measured.

Aging tests and conditionings

The plastic and composite materials are used also in situations of exposure to atmospheric agents (UV radiations, oxygen, ozone ...) and this can cause a rapid drop of the mechanical properties; to contrast these effects  it is necessary to empower polymers with stabilizing substances. 

Alligator skin

See orange peel.


The longitudinal splitting of flat slabs in a piane parallel to the rolled surface. Also called fishmouthing.

Alpha Radiation

A stream of fast-moving helium nuclei. This is a strongly ionizing radiation with very weak penetration (e.g. cannot penetrate a piece of paper).

Alternating Current (AC)

 Electric current that reverses direction periodically (usually many times per second).


Surrounding; usually used in relation to temperature, as "ambient temperature" surrounding a certain part or assembly.


A term used to describe the strength of electric current. The number of electrons moving past a fixed point in a conductor in one second. Measured in amperes. The term amps is often used for short.


A standard unit of measure for electric current or the flow of electrons. The amount of current sent by one volt through a resistance of one ohm.

Analysis by Auger spectroscopy

The Auger spectroscopy allows to characterize the chemical composition of the sample surface both qualitatively and quantitatively.

Analysis by Auger spectroscopy for depth profiles

Using this technique can only be detected chemical elements present on the sample surface to a depth of about  1-5 nanometers.
It is possible to select the exact area of ​​interest on which perform the analysis.

Analysis by SEM-FIB

The SEM-FIB is an electron microscope with a resolution of 2nm, which allows to dig without damaging the surface of a sample and look at his section.

Analysis by XPS

The technique X-Ray Photoelectron Spectroscopy (XPS) allows to characterize the surface of a sample from a compositional point of view...

Analysis of additives and combustion gases

The most common polymeric and composite materials are highly flammable, and if it were not for the addition of specific anti-flame additives, the use of these materials would precluded in many fields.
The knowledge, for example, of the index of oxygen in a polymer as well as the level of damage regarding combustion fumes, may direct the purchase of the material according to intended use.

Analysis of phases

Metallic materials have a wide range of mechanical properties and this determines their particular versatility.
Using various techniques and processes, the related properties can be varied by changing peculiar characteristics such as, for example, the resistance.

Analysis of sensitisazion

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.

Analysis of surface heat treatments

The heat treatment, whether it is a massive treatment or a superficial one, gives the material the desired characteristics in terms of mechanical properties, surface resistance and tonicity and therefore it guides the behavior in exercise and the mechanical and chemical response that the component presents in exercise conditions.

Analysis of the charges

Analysis through XRD (x-ray diffraction)

The analysis of a X-ray diffraction spectrum of (XRD), while not providing direct information on the chemical composition of a sample, allows to define and quantify the crystalline phases present in any material in the first 20 microns in surface.

Analysis through XRD (x-ray diffraction)

The analysis of a X-ray diffraction spectrum of (XRD), while not providing direct information on the chemical composition ...

Angle Beam Testing

An ultrasound testing technique that uses an incidence wave angle other than 90 degrees to the test surface. The refracted angle of the sound energy is calculated using Snell's law.

Angle Beam Transducers

A device used generated sound energy, send the energy into a material at angle other than 90 degrees to the surface, and receive reflected energy and convert it to electrical pulses.

Angle of Incidence

The angle between the direction of propagation of an electromagnetic or acoustic wave (or ray) incident on a body and the local normal to that body.

Angle of Reflection

The angle between the direction of propagation of an electromagnetic or acoustic wave (or ray) reflected by a body and the local normal to that body.

Angle of Refraction

The angle between the direction of propagation of an electromagnetic or acoustic wave (or ray) refracted by an optically homogeneous body and the local normal to that body.

Angular Frequency

For any oscillation, the number of vibrations per unit time, multiplied by 2π. Also known as angular velocity and radian frequency.

Annealing twin

A twin formed in a crystal during recrystallization.


The electrode of an electrolytic cell at which oxidation occurs. Contrast with cathode.


(1) The positive terminal or the collector of electrons in an electrical system (i.e. the positive terminal of a battery) (2) The electrode at which oxidation or corrosion occurs. It is the opposite of cathode.

Arrest lines (marks)

See beach marks.

A-Scan Display

A data presentation method in which signal amplitude is plotted along the y-axis versus time on the x-axis. 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.


In tribology, a protuberance in the small-scale topographical irregularities of a solid surface.

Atmospheric corrosion

The metals ordinarily used in equipment and structures corrode at a negligibie rate when exposed in to the atmosphere in the absence of moisture to serve as an electrolyte. 

Atomic Number

A number representing the positive charge or number of protons in the nucleus of an atom.


The reduction in the level of a quantity, such as the intensity of a wave or radiation.

Attenuation Coefficient

A factor which is determined by the degree of reduction in sound wave energy per unit distance traveled. It is composed of two parts, one (absorption) proportional to frequency, the other (scattering) dependent on the ratio of grain size or particle size to wavelength.

Auger spectroscopy

The Auger spectroscopy allows to characterize the chemical composition of the sample surface both qualitatively and quantitatively.


A nonmagnetic solid solution of ferric carbide or carbon in iron. An elevated-temperture parent phase in ferrous metals from which all other low-temperature structures are derived. The normal structures are derived. The normal condition of certain types of stainless steels.

Authorized qualifying body

Body, independent of the employer, authorized by the certification body to prepare and administer qualification examinations.


Longitudinal, or parallel to the axis or centerline of a part. Usually refers to axial compression or axial tension.

Axial strain

Increase (or decrease) in length resulting from a stress acting parallel to the longitudinal axis of a test specimen.

Back Reflection

The signal received from the far boundary or back surface of a test object.

Back Scatter

 Scattered signals that are directed back to the transmitter/receiver.

Background indication

Background indication: indication obtained from a phenomenon, body, or substance similar to the one under investigation, but for which a quantity of interest is supposed not to be present, or is not contributing to the indication.


Material placed at the reverse side of a joint preparation for the purpose of supporting molten weld metal.

Bacterial and bio-fouling corrosion

Biological organisms affect corrosion processes on metals by directly influencing anodic and cathodic reactions, by affecting protective surface films on metals, by producing corrosive substances and by producing solid deposits. 


An intermediate transformation product from austenite in the heat treatment of steel. Bainite can somewhat resemble pearlite or martensite, depending on the transformation temperature.

Banded structure

A segregrated structure consisting of alternating, nearly parallel bands of different composition, typically aligned in the direction of primary hot working.

Base gas

Major or only component of a pure or mixed gas.

Base quantity

Quantity in a conventionally chosen subset of a given system of quantities, where no subset quantity can be expressed in terms of the others

Basic examination

Esame di livello 3 che dimostra la conoscenza del candidato sulla tecnologia e sulla scienza dei materiali, relative al settore di attività del candidato, del sistema di qualificazione e di certificazione e dei principi di base dei metodi PND come
richiesto per il livello 2.

Beach marks

Macroscopic (visible) progression marks on a fracture surface that indicate
successive position of the advancing crack front. The classic appearance is of irregular elliptical or semielliptical rings, radiating outward from one or more origins. Beach marks (also known as clamshell marks, tide marks, or arrest marks) are typically found on service fractures where the part is loaded randomly, intermittently, or with periodic variations in mean stress or alternating stress. Not to be confused with striations, which are microscopic and form differently.


"Beachmarks" are a unique feature found in many fatigue fractures, and their presence is a positive means of identifying fatigue fractures.

Beam Alignment Measurements

Measurements that provide data on the degree of alignment between the sound beam axis and the transducer housing. This information is particularly useful in applications that require a high degree of certainty regarding beam positioning with respect to a mechanical reference surface.

Beam Exit Point

See probe index.

Beam Profiles

A measurement of the intensity of the beam across its width (or profile). It provides valuable information about transducer sound field characteristics.

Beam Spread

The divergence of the sound beam as it travels through a medium. Specifically, the solid angle that contains the main lobe of the beam in the far field.


See ultraviolet light.

Blank indication

Blank indication: indication obtained from a phenomenon, body, or substance similar to the one under investigation, but for which a quantity of interest is supposed not to be present, or is not contributing to the indication.

Bottom Echo

See back reflection.

Breaking stress

See rupture stress.

Brinell hardness HB

A number related to the applied load and to the surface area of the permanent impression made by a ball indenter.

Brinell hardness test

A test for determining the hardness of a material by forcing a hard steel or carbide bali of specified diameter into it under a specified load. The result is expressed as the Brinell hardness number.


Damage to a solid bearing surface characterized by one or more plastically formed indentations brought about by overload. This term is often applied in the case of rolling-element bearings. See also false brinelling.


Permitting little or no plastic (permanent) deformation prior to fracture.

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 not noticeable to the unaided eye. Contrast with ductile crack propagation.

Brittle erosion behavior

Erosion behavior having characteristic properties (e. g., little or no plastic flow, the formation of cracks) that can be associated with brittle fracture of the exposed surface. The maximum volume removal occurs at an angle near 90°, in contrast to approximately 25° for ductile erosion behavior.

Brittle fracture

Separation of a solid accompanied by little or no macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture.

Brittle fracture of ductile steels

Brittle fracture of normally ductile steels has occurred primarily in large, continuous, box-like structures such as box beams, pressure vessels, tanks, pipes, ships, bridges, and other restrained structures, frequently joined with welded construction.


The tendency of a material to fracture without first undergoing significant plastic deformation. Contrast with ductility.


A data presentation method 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.


(1)An indented valley in the surface of a sand casting due to expansion of the molding Band. (2) A local waviness in metal bar or sheet, usually transverse to the direction of rolling.


A compression phenomenon that occurs when, after some critical level of load, a bulge, bend, bow, kink, or other wavy condition is produced in a beam, column, plate, bar, or sheet product form.


Buckling is defined as collapse due to compressive instability. It is most common when long, slender columns are compressed in an axial direction, or when thin-walled tubes are compressed in either an axial direction or a diagonal direction as a result of torsional loading.

Bulk modulus

See bulk modulus of elasticity.

Bulk modulus of elasticity, K

The measure of resistance to change in volume; the ratio of hydrostatic stress to the corresponding unit change in volume.

C/S and O/N/H analyzers


Individual seeking qualification and certification who gains experience under the supervision of suitably qualified personnel.

Capping run

In multi layer welding, the run(s) visible on the weld face(s) after completion of welding.

Carbon flotation

Segregation in which free graphite has separated from the molten iron. This defect tends to occur at the upper surfaces of the cope of the castings.

Casting shrinkage

See liquid shrinkage, shrinkage cavity, solidification shrinkage, and solid shrinkage.
Catastrophic wear. Rapidly occurring or accelerating surface damage, deterioration, or change of shape caused by wear to such a degree that the service life of a part is appreciably shortened or its function is destroyed.

Causes of brittle fracture

Brittle fractures that occur in service are invariably initiated by defects that are initially present in the manufactured product or fabricated structure or by defects that develop during service.

Causes of distorsion failure

Distorsion failure occurs when a structure or component is deformed so that it no longer can support the load it was intended to carry, is incapable of performing its intended function, or interferes with the operation of another component.


Document issued by the certification body under the provisions of this European Standard, indicating that the named person has demonstrated the competence(s) defined on the certificate.


Procedure used by the certification body to confirm that the qualification requirements for a method, level and sector have been fulfilled, leading to the issuing of a certificate.

Certification body

Body that administers procedures for certification according to the requirements of this European Standard and which fulfils the requirements of EN ISO/IEC 17024.

Characteristics of the brittle failure

Brittle fractures have certain characteristics that permit them to be properly identified:

Characteristics of the ductile failure

Ductile fractures have characteristics that are different from those of brittle fractures. However, it must be recognized that many fractures contain some of the characteristics of both types. 

Classification of graphite

A microstructural examination is performed in order to define the type, distribution and dimension of graphite in cast irons.


(1) Fracture of a crystal by crack propagation across a crystallographic piane of low index. (2) The tendency to cleave or split along definite crystallographic planes.


The metallic coatings consist of thicknesses of metal applied (methods: electrochemical, chemical or immersion in the metal led to the melting temperature) on metallic or non-metallic substrates in order to improve the corrosion resistance, mechanical properties but also for aesthetic purposes. the coatings applied to the material (either metallic or otherwise) can be either of metallic type (chrome-plating, zinc-plating, nickel -plating), of inorganic type (paints and varnishes) or (but only in the case of metallic substrates) may be related to changes carried out on the surface layer (surface conversions, anodizing in the case of aluminum).

Cobalt 60

A radioisotope of the element cobalt.

Coefficient of Thermal Expansion

The linear expansion or contraction per unit length per degree temperatures between specified lower and upper temperatures.


A constant chemical or physical property constant for a system with specific conditions (i.e. Coefficient of Friction).

Coherent derived unit

Coherent derived unit: derived unit that, for a given system of quantities and for a chosen set of base units, is a product of powers of base units with no other proportionality factor than one.


More than one loop of a conductor wound in a spiral. Also called a solenoid.


The process by which a beam of energy or particles is aligned to form a parallel beam.

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.

Combined standard measurement uncertainty

Combined standard measurement uncertainty: standard measurement uncertainty that is obtained using the individual standard measurement uncertainties associated with the input quantities in a measurement model.

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.

Comparison of Maths

Software used is HOLOS and allows to compare the object under inspection with its CAD math. The measurement is performed by manual control or in CNC mode.


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.

Compression fatigue

A seemingly puzzling type of fatigue crack is one that grows in a part, or a region of a part, that is stressed in compression when the part is under load.

Compressional Wave

A wave in which the particle motion in the material is parallel to the wave propagation direction. Also called a longitudinal wave.

Concentration cell-corrosion

If a piece of metal is immersed in an electrolyte and there is a difference in concentration of one or more dissolved compounds or gases in the electrolyte, two areas of metal in contact with solution differing in concentration will ordinarily differ in solution potential, forming a concentration cell.


Tests can be conducted to determine the behavior of paints and other types of coatings to prolonged exposure to conditions of temperature / humidity defined in accordance with the requirements of the coating or product specifications.


A measure of the ability of a material to conduct electrical current.


Materials that have free electrons and allow electrical current to flow easily.

Contact Transducers

An ultrasonic transducer that is designed to be used in direct contact with the surface of the test article.

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.

Conversion factor between units

Conversion factor between units: ratio of two measurement units for quantities of the same kind.


Correction: compensation for an estimated systematic effect.


Definition of corrosion: the chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties


Deterioration of a metal by chemical or electrochemical reaction with its environment.

Corrosion and conditioning tests

Corrosion, which is the unintended destructive chemical or electrochemical reaction of a material with its environment, frequently leads to service failures of metal parts or renders them susceptible to failure by some other mechanism. 

Corrosion fatigue

As if fatigue itself were not a complicated enough type of failure, it is further complicated by the addition of a corrosive environment. 

Corrosion of buried metals

Major influences on the corrosion of uncoated metallic objects buried in the earth include galvanic effects; chemical composition, oxygen content, and pH of the soil; alloy selection; and stray currents.

Coverage factor

Coverage factor: number larger than one by which a combined standard measurement uncertainty is multiplied to obtain an expanded measurement uncertainty A coverage factor is usually symbolized k.

Coverage interval

Coverage interval: interval containing the set of true quantity values of a measurand with a stated probability, based on the information available.

Coverage probability

Coverage probability: probability that the set of true quantity values of a measurand is contained within a specified coverage interval.

Crevice corrosion

A crevice in a metal surface at a joint between two metallic surfaces or between a metallic and a nonmetallic surface or a crevice beneath a particle of solid matter on a metallic surface provides conditions that are conducive to the development of the type of concentration-cell corrosion called crevice corrosion. 

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.


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.


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. 


Limiting the duration or decreasing the amplitude of vibrations.

Dead band

Dead band: maximum interval through which a value of a quantity being measured can be changed in both directions without producing a detectable change in the corresponding indication.


A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.


 Loss of carbon from the surface layer of a carbon-containing alloy due to reaction with one or more chemical substances in a medium that contacts the surface.


A logarithmic unit for expressing power relationships. n = 10 log10(I1/I2) where n is the difference of decibels of intensities 1 & 2. 


The removal of radioactive contaminants from surfaces.


A discontinuity or other imperfection causing a reduction in the quality of a material or component.


The sharpness of features on a radiograph that correspond to boundaries from thickness or material density changes in the radiographed component.


Deformation within the elastic range caused by a load or force that does not exceed the elastic limit of the material. Temporary deformation such as that of a spring.


A change in the form of a body due to stress, thermal change, change in moisture, or other causes. Measured in units of length.

Deformation bands

 Bands produced within individual grains during cold working which differ variably in orientation from the matrix.


A laminar discontinuity such as an area of unbonded materials.


The process of removing existing magnetism from a part.


A crystal that has a tree-like branching pattern, being most evident in cast metals slowly cooled through the solidification range.


A crystal with a treelike branching pattern. Dendrites are most evident in cast metals slowly cooled through the solidification range.


Corrosion in which nickel is selectively leached from nickel-containing alloys. Most commonly observed in coppernickel alloys after extended service in fresh water. See also selective leaching.


An instrument used to measure the degree of darkening of developed radiographic film.


The mass of a substance per unit volume.


Selective removal of one component of an alloy, usually from the surface or preferentially from grain-boundary regions. See also selective leaching.

Deposit attack

See poultice corrosion. deposit corrosion. See poultice corrosion.
Dezincification. Corrosion in which zinc is selectively leached from zinc-containing alloys. Most commonly found in copper-zinc alloys containing less than 85% Cu after extended service in water containing dissolved oxygen. See also selective leaching.

Deposit attack.

See poultice corrosion. deposit corrosion. See poultice corrosion.
Dezincification. Corrosion in which zinc is selectively leached from zinc-containing alloys. Most commonly found in copper-zinc alloys containing less than 85% Cu after extended service in water containing dissolved oxygen. See also selective leaching.

Depth Compensation

See distance amplitude correction.

Depth of Fusion

The depth to which the base metal melted and fused during welding.

Depth of Penetration (Standard)

The depth to which the eddy current density has decreased to 1/e or 36.8% of the surface density. Also known as skin depth.

Derived quantity

Derived quantity: quantity, in a system of quantities, defined in terms of the base quantities of that system.

Detection limit

Detection limit: measured quantity value, obtained by a given measurement procedure, for which the probability of falsely claiming the absence of a component in a material is ß, given a probability ß of falsely claiming its presence.


Detector: device or substance that indicates the presence of a phenomenon, body, or substance when a threshold value of an associated quantity is exceeded.


A device that determines the presence of or measures the amount of energy, such as radiation.

Determination of anions (chlorides, bromides, fluorides, nitrites, nitrates, phosphates and sulphates)

The technique allows the recognition and the simultaneous determination of one or more cations or anions in aqueous solution. It is based on the separation of ions through ion exchange columns that use the different affinities of the analytes in solution for the eluent phase and the stationary phase contained in the chromatographic column.

Determination of anions and cations by Ion Chromatography

The technique allows the recognition and the simultaneous determination of one or more cations or anions in aqueous solution. It is based on the separation of ions through ion exchange columns that use the different affinities of the analytes in solution for the eluent phase and the stationary phase contained in the chromatographic column.

Determination of austenitic and ferritic grain size

The microstructural examination is performed in order to define the size of austenitic-ferritic grain.

Determination of cations (ammonium, calcium, magnesium, potassium, lithium, sodium)

The technique allows the recognition and the simultaneous determination of one or more cations or anions in aqueous solution. It is based on the separation of ions through ion exchange columns that use the different affinities of the analytes in solution for the eluent phase and the stationary phase contained in the chromatographic column.

Determination of chromium hexavalent

The method wants to verify the content of hexavalent chromium in surface coatings of metallic particulars through a colorimetric / spectrophotometric analysis according to ISO 3613 of 15/06/2000.

Determination of kinematic viscosity at 100 °C

Viscosity is one of the most important characteristics of an oil. In fact, this characteristic influences the  thickness of the oil film which is interposed between the parts to be lubricated.

Determination of kinematic viscosity at 40 °C

Viscosity is one of the most important characteristics of an oil. In fact, this characteristic influences the  thickness of the oil film which is interposed between the parts to be lubricated.

Determination of the content of humidity Karl Fischer

Karl Fischer titration is used for the determination of water content (or humidity) for liquid and solid samples.

Determination of the content of water by Karl Fisher method

Karl Fischer titration is used for the determination of water content (or humidity) for liquid and solid samples.

Developer (Penetrant)

A finely divided powder applied over the surface of a part to help bring out penetrant indications.

Developing Time

The time between the application of the developer and the examination of the part for indications.


Corrosion in which zinc is selectively leached from zinc-containing alloys. Most commonly found in copper-zinc alloys containing less than 85% Cu after extended service in water containing dissolved oxygen. See also selective leaching.

Diamagnetic Materials

Materials that have all paired electrons in the atoms and thus have no net magnetic moment. The magnetic permeability of diamagnetic materials is usually very close to 1.

Diamond pyramid hardness test

See Vickers hardness test.

Differential Probe

A probe having two sensing coils located side-by-side allowing it to convert a floating signals to a low voltage ground referenced signal to be displayed on a ground referenced oscilloscope.

Differential temperature cells

In electrolytic cells of the differential-temperature type, the anode and cathod consist of the same metal and differ only in temperature.


Any redistribution in space of the intensity of waves that results from the presence of an object causing variations of either the amplitude or phase of the waves.

Dimensional testing

The software used by TEC Eurolab is CALYPSO which allows to define dimensional errors, geometric errors, errors of position and shape. The measurement can be done in manual probing, which does not provide scanning, or in CNC mode using a control program on which it is possible to insert measurement strategies in continuous scanning.
The report issued by the software can be of graphic-type, for geometric and form errors, or of table-type for dimensional errors.
Programming can also be performed in Autorun mode, which allows the palletising of a program. In essence, a program can be repeated several times in the Y axis and more times in the X axis, at a steady pace, so that it is possible to control more particulars in series, saving precious time.
The reliability of measurement is guaranteed by the extreme precision of CALYPSO software, of the CMM ZEISS PRISMO measuring machine and the VAST XT head.

Dimensional testing in contact

Through contact dimensional measurements, errors can be defined, of dimensional, geometric, position and shape type as well as it is possible to compare the object under inspection with the related mathematics.

Dimpled rupture fracture

A fractographic term describing ductile fracture that occurs through the formation and coalescence of microvoids (dimples) along the fracture path. The fracture surface of such a ductile fracture appears dimpled when observed at high magnification and usually is most clearly resolved when viewed in a scanning electron microscope.

Direct Current (DC)

 Electrical current that flows in only one direction in a circuit. 


A break in the continuity of a medium or material.

Discrimination threshold

Discrimination threshold: largest change in a value of a quantity being measured that causes no detectable change in the corresponding indication.


The variation of phase velocity with frequency. In general, any process separating radiation into components having different frequencies, energies, velocities, or other characteristics.

Displaying measuring instrument

Displaying measuring instrument: indicating measuring instrument where the output signal is presented in visual form.

Dissimilar material joint

Welded joint in which the parent materials have significant differences in mechanical properties and/or chemical composition.

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.

Distance-Amplitude Blocks

A set of ultrasonic reference specimens in which each specimen has a different metal path length to a equal-sized reflector. The specimens are used to develop distance amplitude response curves.

Distance-Amplitude Response Curve

A curve showing the relationship between signal amplitude and equal-sized reflecting surfaces at various distances from the transducer. Standard blocks are used to obtain such curve.

Distorsion failures

The term "failure," means the inability of a part or assembly to perform its intended function for any reason. We usually think of failure in terms of fracture, wear, or corrosion. Even in the absence of any of these three factors, however, a part can also fail when distortion of size or shape prevents the performance of its intended function.

Distorted Field

A magnetic field that does not follow a straight path or have a uniform distribution due to the irregular in shape of the magnetized test object. The direction of a magnetic field in a symmetrical object will be substantially uniform if produced by a uniformly applied magnetizing force, as in the case of a bar magnetized in a solenoid.


 Any deviation from an original size, shape, or contour that occurs because of the application of stress or the release of residual stress.


An improper 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.


The amount of ionizing radiation energy absorbed per unit mass of irradiated material at a specific location, such as a part of the human body. Measured in reps, rems per hour.


A device that measures radiation dose, such as a film badge or ionization chamber.

Ductile crack propagation

Slow crack propagation that is accompanied by noticeable plastic deformation and requires energy to be supplied from outside the body. Contrast with brittle crack propagation.

Ductile erosion behaviour

Erosion behaviour having characteristic properties (i.e., considerable plastic deformation) that can be associated with ductile fracture of the exposed solid surface. A characteristic ripple pattern forms on the exposed surface at low values of angle of attack. Contrast with brittle erosion behaviour.

Ductile fracture

racture characterized by tearing of metal accompanied by appreciable gross plastic deformation and expenditure of considerable energy. Contrast with brittle fracture.


The ability of a material to deform plastically before fracturing. Measured by elongation or reduction of area in a tension test, by height of cupping in a cupping test, or by the radius or angle of bend in a bend test. Contrast with brittleness; see also plastic deformation.


Moving, or having high velocity. Frequently used with high strain rate (>0.1 s-') testing of metal specimens. Contrast with static.


A signal indicating reflected acoustic energy.

Eddy Current Inspection

An electromagnetic technique used on conductive materials for crack detection or the rapid sorting of small components for either flaws, size variations, or material variation, as well as other applications. 

Eddy Current Method

An electromagnetic NDT Method based on the process of inducing electrical currents into a conductive material and observing the interaction between the currents and the material.

EDS micro-analysis

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings

EDS microscopy

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings.

Elastic constants

The factors of proportionality that relate elastic displacement of a material to applied forces. See also bulk modulus of elasticity, modulus of elasticity, Poisson's ratio, and shear modulus.
elastic deformation. A change in dimensions directly proportional to and in phase with an increase or decrease in applied force.

Elastic limit

The maximum stress a material is capable of sustaining without any permanent strain (deformation) remaining upon complete release of the stress. See also proportional limit.
Elastic strain. See elastic deformation.


 The property of a material by virtue of which deformation caused by stress disappears upon removal of the stress. A perfectly elastic body completely recovers its original shape and dimensions after release of stress.

Electrical Current

The movement of electrons between atoms.

Electrical Impedance

The total opposition that a circuit presents to an alternating current.

Electrical Noise

Extraneous signals caused by externally radiated signals or electrical interferences within an ultrasonic instrument. A component of background noise.


A naturally occurring force that exists all around us. 

Electrochemical Corrosion

Corrosion which occurs when current flows between cathodic and anodic areas on metallic surfaces.

Electromagnetic Field

A field that is created when energy from a power source such as a battery is applied to a circuit, making the electrons flow through a conductor, a new type of field is developed around the wire.

Electromagnetic Induction

A process by which electrical current is induced in an electrical conductor by a changing magnetic field that acts upon the conductor.

Electromagnetic Radiation

Energy in a wave form that possesses both electrical and magnetic characteristics. EMR radiates in the form of a wave which can accelerate charged particles. Electromagnetic radiation can travel through a vacuum and its energy varies greatly; radio waves have the longest wavelengths and the lowest frequency and energy, while X-rays and gamma rays have the shortest wavelengths and highest frequencies and energies. 

Electromagnetic Spectrum

The entire range of wavelengths or frequencies of electromagnetic radiation extending from gamma rays to the longest radio waves.

Electromagnetic Testing

A nondestructive way to test materials by using electromagnetic energy. 


The production of a magnetic field by current flowing in a conductor.

Electromotive Force

The work or energy which causes the flow of an electric current. Expressed as volts. It should be noted that the term "force" is a misnomer. However, the term is so well established that its use continues in spite of its being incorrect.


A term used in mechanical testing to describe the amount of extension of a test piece when stressed. See also elongation, percent and stress.

Elongation, percent

The extension of a uniform section of a specimen expressed as percentage of the original gage length.


The severe loss of ductility and/or toughness of a material, usually a metal or alloy.

Embrittlement of steels

Strain-age embrittlement. Most susceptible to the phenomenon of strain-age embrittlement are low-carbon rimmed or capped steels that are severely cold worked during forming processes. Subsequent moderate heating during manufacture (as in galvanizing, enameling, or paint baking) or aging at ambient temperature during service may cause embrittlement.

Emulsion Penetrant

A mixture of water and oil produced by the addition of a third material, the liquid penetrant emulsifier.

Endurance limit

The maximum stress below which a material can presumably endure an infinite number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare with fatigue limit.


Destruction of materials by the abrasive action of moving fluids, usually accelerated by the presence of solid particles carried with the fluid. See also erosion-corrosion.
Erosion-corrosion. A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material.

Erosive wear

Erosive wear (or erosion) occurs when particles in a fluid or other carrier slide and roll at relatively high velocity against a surface.

Essential variable

Welding condition that requires qualification.

Estensimetric test

The strain gauge is one of the techniques that allow to measure the surface deformation state of a component in operation; this technique allows to reconstruct experimentally the stress distribution of the same.


The process of deciding the severity of a condition after an indication has been interpreted. Evaluation determines if the test object should be rejected, repaired or accepted. See indication and interpretation.

Evaluation of non-metallic inclusions

A microstructural examination is performed in order to define the presence of non-metallic inclusions in steel.

Examination centre

Centre approved by the certification body where qualification examinations will be carried out.


Person certified to level 3 in the method and product or industrial sector for which he is authorized by the certification body to conduct, supervise and grade the qualification examination.

Examining body

Organisation that has been appointed to verify compliance with the applicable standard.


Corrosion that proceeds laterally from the sites of initiation along planes parallel to the surface, generally at grain boundaries, forming corrosion products that force metal away from the body of the material, giving rise to a layered appearance.

Expanded measurement uncertainty

Expanded measurement uncertainty: product of a combined standard measurement uncertainty and a factor larger than the number one.


A general term used to imply that a part in service (1) has become completely inoperable, (2) is still operable but is incapable of satisfactorily performing its intended function, or (3) has deteriorated seriously, to the point that it has become unreliable or unsafe for continued use.

False brinelling

Damage to a solid bearing surface characterized by indentations not caused by plastic deformation, resulting from overload but thought to be due to other causes such as fretting corrosion. See also brinelling.


The phenomenon leading to fracture under repeated or fluctuating stresses having
a maximum value less than the ultimate tensile strength of the material. See also fatigue failure, high-cycle fatigue, low-cycle fatigue, and ultimate strength.

Fatigue crack growth rate, da/dN

The rate of crack extension caused by constant-amplitude fatigue loading, expressed in terms of crack extension per cycle of load application.

Fatigue failure

Fatigue life

The number of stress cycles that can be sustained prior to failure under a stated test condition.

Fatigue limit

The maximum stress that presumably leads to fatigue fracture in a specified number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare with endurance limit.

Fatigue notch factor

The ratio of the fatigue strength of an unnotched specimen to the fatigue strength of a notched specimen of the same material and condition; both strengths are determined at the same number of stress cycles.

Fatigue notch factor

The ratio of the fatigue strength of an unnotched specimen to the fatigue strength of a notched specimen of the same material and condition; both strengths are determined at the same number of stress cycles.

Fatigue notch sensitivity

An estimate of the effect of a notch or hole of a given size and shape on the fatigue properties of a material; measured by q = (Kf - 1)/( Kt - 1), where Kf is the fatigue notch factor and Kt is the stress-concentration factor. A material is said to be fully notch sensitive if q approaches a value of 1.0; it is not notch sensitive if the ratio approaches 0.

Fatigue ratio

The fatigue limit under completely reversed flexural stress divided by the tensile strength for the same alloy and condition.

Fatigue strength

The maximum stress that can be sustained for a specified number of stress cycles without failure, the stress being completely reversed within each cycle unless otherwise stated.

Fatigue striation

See striation.

Fatigue test

Fatigue wear

Wear of a solid surface caused by fracture arising from material fatigue.


Tubular cored metal arc welding with active gas shield; flux cored arc welding /USA/


Essentially pure iron in the microstructure of an iron or steel specimen. It may have a small amount of carbon (less than 0.02 wt%). Also called alpha iron.


It is a measure of coupling between the coil and test object.

Ferromagnetic Materials

Materials that can be magnetized.


Describing a metal that is more than 50% iron, such as steel, stainless steel, cast iron, ductile (nodular) cast iron, etc.


(1) The characteristic of wrought metal that indicates directional properties. It is revealed by etching of a longitudinal section or is manifested by the fibrous or woody appearance of a fracture. It is caused chiefly by extension of the constituents of the metal, both metallic and non-metallic, in the direction of working. (2) The pattern of preferred orientation of metal crystals after a given deformation process, usually wiredrawing. See also texture.

Fiber stress

Local stress through a small area (a point or line) on a section where the stress is not uniform, as in a beam under a bending load.

Fiber-reinforced composite

A material consisting of two or more discrete physical phases, in which a fibrous phase is dispersed in a continuous matrix phase. The fibrous phase may be macro-, micro-, or submicroscopic, but it must retain its physical identity so that it could conceivably be removed from the matrix intact.

Fibrous fracture

 A gray and amorphous fracture that results when a metal is sufficiently ductile for the crystals to elongate before fracture occurs. When a fibrous fracture is obtained in an impact test, it may be regarded as definite evidence of toughness of the metal. See also crystalline fracture and silky fracture.

Fibrous structure

(1) In forgings, a structure revealed as laminations, not necessarily detrimental, on an etched section or as a ropy appearance on a fracture. (2) In wrought iron, a structure consisting of slag fibers embedded in ferrite. (3) In rolled steel plate stock, a uniform, lamination-free, fine-grained structure on a fractured surface.

Field Intensity

A term used to describe the strength of the electromagnetic field. 

Filiform corrosion

Corrosion that occurs under some coatings in the form of randomly distributed threadlike filaments.

Filled Crack

A crack-like discontinuity, open to the surface, but filled with some foreign material-oxide, grease, etc.- which tends to prevent penetrants from entering.

Filling run

In multi layer welding, the run(s) deposited after the root run(s) and before the capping run(s).


A layer of absorption material that is placed in the beam of radiation for the purpose of absorbing rays of certain wavelengths and thus controlling the quality of the radiograph.

Filters in Radiography

Filters are placed in the x-ray beam to produce a cleaner image by absorbing the lower energy x-ray photons that tend to scatter more. 


A discontinuity found on the fracture surface of a weld in steel that consists of a small pore or inclusion surrounded by an approximately round, bright area.


See alligatoring.


 A short, discontinuous internal crack in ferrous metals attributed to stresses produced by localized transformation and hydrogen solubility effects during cooling after hot working. In fracture surfaces, flakes appear as bright, silvery areas with a coarse texture. In deep acid-etched transverse sections, they appear as discontinuities that are usually in the midway to center location of the section. Also termed hairline cracks and shatter cracks.

Flat Bottom Hole

A type of reflector commonly used in reference standards. The end (bottom) surface of the hole is the reflector.


A defect.

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.


Movement (slipping or sliding) of essentially parallel planes within an element of a material in parallel directions; occurs under the action of shear stress. Continuous action in this manner, at constant volume and without disintegration of the material, is termed yield, creep, or plastic deformation.

Flow lines

Texture showing the direction of metal flow during hot or cold working. Flow lines often can be revealed by etching the surface or a section of a metal part.

Fluorescence, Penetrant

Property of emitting light as the result of, and only during the absorption of radiation from some other energy source.


A bright vivid color that glows under a black light.

Fluorescent Dye Penetrant

A highly penetrating liquid used in performance of of liquid penetrant testing and characterized by its ability to fluoresce under black light.


A type of pitting in which cavities occur in a regular pattern, forming grooves or flutes. Fluting is caused by fretting or by electric arcing.

Focal-Film Distance (ffd)

The distance in inches between the focal spot of the x-ray tube, or the radiation source, and the film.


 A defect in metal, usually on or near the surface, caused by continued fabrication of overlapping surfaces.

Forward Scatter

Radiation scattered in approximately the same direction of the primary beam.


Descriptive explanation of a fracture process, especially in metals, with specific reference to photographs of the fracture surface. Macrofractography involves low magnification (<25 x); microfractography, at high magnification (>25 x ).


A break, or separation, of a part into two or more pieces.


The irregular surface produced when a piece of metal is broken. See also crystalline fracture, fibrous fracture, granular fracture, intergranular fracture, silky fracture, and transgranular fracture.

Fracture mechanic

 See linear elastic fracture mechanics.

Fracture Mechanics

A quantitative analysis for evaluating structural behavior in terms of applied stress, crack length, and specimen or machine component geometry.

Fracture stress

See rupture stress.

Fracture surfaces analysis – fractographic

The analysis of the failure surface allows to examine and investigate, using optical and scanning electron (SEM) microscopes, the morphology that has been generated on the failure surface during the damage. 

Fracture test

Test in which a specimen is broken and its fracture surface is examined with the unaided eye or with a low-power microscope to determine such factors as composition, grain size, case depth, or discontinuities.

Fracture toughness

A generic term for measures of resistance to extension of a crack. The term is sometimes restricted to results of fracture mechanics tests, which are directly applicable in fracture control. However, the terra commonly includes results from simple tests of notched or precracked specimens not based on fracture mechanics analysis. Results from tests of the latter type are often useful for fracture control, based on either service experience or empirical correlations with fracture mechanics tests. See also stress-intensity factor.

Fracture Toughness

A generic term for measures of resistance to extension of a crack. The term is sometimes restricted to results of fracture mechanics tests, which are directly applicable in fracture control. 


The number of waves that pass a given point in a specified unit of time.

Frequency, Pulse Repetition

The number of pulses per second.


Wear that occurs between tight-fitting surfaces subjected to oscillation at very small amplitude. This type of wear can be a combination of oxidative wear and abrasive wear. See also fretting corrosion.

Fretting corrosion

 The deterioration at the interface between contacting surfaces as the result of corrosion and slight oscillatory slip between the two surfaces.

Fretting fatigue

Fatigue fracture that initiates at a surface area where fretting has occurred.

Fretting wear

Fretting wear is quite similar to adhesive wear in that microwelding occurs on mating surfaces.


This is a particular process, also known as charged particle bombardment, that yields radioisotopes that are not readily available by the neutron bombardment or fission process.


A condition whereby excessive friction between high spots results in localized welding with subsequent spalling and a further roughening of the rubbing surfaces of one or both of two mating parts.

Galvanic corrosion

When dissimilar metals are in electrical contact in an electrolyte, the less noble metal (anode) is attacked to a greater degree than if it vere exposed alone, and the more noble metal (cathode) is attacked to a lesser degree than if it avere exposed alone.

Galvanic corrosion

Accelerated corrosion of a metal because of an electrical contact with a more noble metal or non-metallic conductor in a corrosive electrolyte.

Gamma Radiation

High-energy, short wavelength electromagnetic radiation emitted by a nucleus. Energies of gamma rays are usually between 0.010 and 10 mev. X-rays also occur in this energy range, but are 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 Component

Gaseous substance that is essential to the performance of the gas mixture.

Gas Container

Vessel used for the shipment and/or storage of pure or mixed gases in a gaseous or liquid state.

Gas designation

Classification plus the symbols for all chemical components plus the nominal composition in volume percent.

Gas hole

A hole in a casting or weld formed by gas escaping from molten metal as it solidifies. Gas holes may occur individually or in clusters, or may be distributed throughout the solidified metal.

Gas Holes

Holes created by a gas escaping from molten metal.

Gas Holes (on radiograph)

Appear as round or elongated, smooth-edged dark spots, occurring individually, in clusters or distributed throughout the casting.

Gas impurity

Gaseous substance with chemical composition different from the base gas, component or gas mixture.

Gas mixture

Gas consisting of two or more components.

Gas Porosity

A cavity caused by entrapped gas. Essentially a smooth-sided bubble within the metal, where the metal solidified before the gas could escape to the atmosphere. Also called gas pocket.

Gas porosity

Fine holes or pores within a metal that are caused by entrapped gas or by evolution of dissolved gas during solidification.


An electronic device for monitoring signals in a selected segment of the trace on an A-scan display.

Gauging wear

This type of wear is caused by extremely high-stress battering or impact that tends to cut or gouge large wear fragments from the surface of the metal. 

Gauss (B)

Unit of flux density or induction. The strength of field induced in a ferromagnetic body is described as being so many gausses. Numerically, one gauss is one line of flux per square centimeter of area.

Geiger Counter

A radiation detection and measuring instrument. It contains a gas filled tube which discharges electrically when ionizing radiation passes through it. Discharges are counted to measure the radiation's intensity.

General corrosion

 A form of deterioration that is distributed more or less uniformly over a surface. See also corrosion.

General examination

Written examination, at level 1 or 2, concerned with the principles of an NDT method.


See slip.


An individual crystal in a polycrystalline metal or alloy, including twinned regions or sub grains if present.

Grain boundary

An interface separating two grains at which the orientation of the lattice changes from that of one grain to that of the other. When the orientation change is very small the boundary is sometimes referred to as a sub-boundary structure.

Grain flow

Fiberlike lines on polished and etched sections of forgings caused by orientation of the constituents of the metal in the direction of working during forging. Grain flow produced by proper die design can improve required mechanical properties of forgings.

Grain-boundary corrosion

Same as intergranular corrosion; see also corrosion and interdendritic corrosion.

Granular fracture

A type of irregular surface produced when metal is broken that is characterized by a rough, grainlike appearance, rather than a smooth or fibrous one. It can be sub classified as transgranular or intergranular. This type of fracture is frequently called crystalline fracture; however, the inference that the metal broke because it "crystallized" is not justified, because all metals are crystalline in the solid state. See also fibrous fracture and silky fracture.

Graphitic corrosion

Deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products, leaving the graphite intact; it occurs in relatively mild aqueous solutions and in buried pipe and fittings. The term "graphitization" is commonly used to identify this form of corrosion, but is not recommended because of its use in metallurgy for the decomposition of carbide to graphite.

Grinding wear

The principal characteristics of grinding wear are that it is caused primarily by particles under high stress that cut, or plow, many very small grooves at relatively low speed across a metal surface. 

Hairline crack

 See flake.


A measure of the resistance of a material to surface indentation or abrasion; may be thought of as a function of the stress required to produce some specified type of surface deformation. There is no absolute scale for hardness; therefore, to express hardness quantitatively, each type of test has its own scale of arbitrarily defined hardness. Indentation hardness can be measured by Brinell, Knoop, Rockwell, Scleroscope, and Vickers hardness tests.

Hardness Brinell - HB

The hardness test is carried out to evaluate the state of a metal alloy supply.
For metal alloys, TEC Eurolab uses the following hardness scales: Brinell, Vickers and Rockwell.

Hardness Microvickers

The hardness test is carried out to evaluate the state of a metal alloy supply.
For metal alloys, TEC Eurolab uses the following hardness scales: Brinell, Vickers and Rockwell.

Hardness Rockwell - HR

The hardness test is carried out to evaluate the state of a metal alloy supply.
For metal alloys, TEC Eurolab uses the following hardness scales: Brinell, Vickers and Rockwell.

Hardness Vickers - HV

The hardness test is carried out to evaluate the state of a metal alloy supply.
For metal alloys, TEC Eurolab uses the following hardness scales: Brinell, Vickers and Rockwell.

Hartmann lines

See Lueders lines.

Heat input

Energy introduced into the weld region during welding.

Heat-affected zone

That portion of the base metal that was not melted during brazing, cutting, or welding, but whose microstructure and mechanical properties were altered by the heat.

Herringbone pattern

See chevron pattern.

High-cycle fatigue

Fatigue that occurs at relatively large numbers of cycles. The arbitrary, but commonly accepted, dividing line between high-cycle fatigue and low-cycle fatigue is considered to be about 10.000 to 100.000 cycles. In practice, this distinction is made by determining whether the dominant component of the strain imposed during cyclic loading is elastic (high cycle) or plastic (low cycle), which in turn depends on the properties of the metal and on the magnitude of the nominal stress.


Any void remaining in a specimen as a result of improper manufacturing processing. Often called gas holes, cavities, or air locks.

Homogeneous joint

Welded joint in which the weld metal and parent material have no significant differences in mechanical properties and/or chemical composition.

Hooke's law

A material in which stress is linearly proportional to strain is said to obey Hooke's law. This law is valid only up to the proportional limit, or the end of the straight-line portion of the stress-strain diagram. See also modulus of elasticity.

Hot crack

See solidification shrinkage crack.

Hot Cracks

Appear as ragged dark lines of variable width and numerous branches internally or at the surface.

Hot tear

A crack or fracture formed before completion of solidification because of hindered contraction. A hot tear is frequently open to the surface of the casting and thus exposed to the atmosphere. This may result in oxidation, decarburization, or other metal-atmosphere reactions at the tear surface.

HPLC liquid chromatography

The techniqueallows the recognition and the simultaneous determination of one or more cations or anions in aqueous solution. It is based on the separation of ions through ion exchange columns that use the different affinities of the analytes in solution for the eluent phase and the stationary phase contained in the chromatographic column.

Hydrogen blistering

The formation of blisters on or below a metal surface from excessive internal hydrogen pressure. Hydrogen may be formed during cleaning, plating, corrosion, etc.

Hydrogen damage

A general terra for the embrittlement, cracking, blistering, and hydride formation that can occur when hydrogen is present in some metals.

Hydrogen embrittlement

A condition of low ductility or hydrogen-induced cracking in metals resulting from the absorption of hydrogen. See also hydrogen-induced delayed cracking.

Hydrogen-induced delayed cracking

A term sometimes used to identify a form of hydrogen embrittlement in which a metal appears to fracture spontaneously under a steady stress less than the yield stress. There is usually a delay between the application of stress (or exposure of the stressed metal to hydrogen) and the onset of cracking. Also referred to as static fatigue.

Hydrophilic Emulsifiers

A process to remove the excess penetrant with mechanical and chemical action but no diffusion takes place. Hydrophilic emulsifiers are basically detergents that contain solvents and surfactants.

Hydrostatic modulus

See bulk modulus of elasticity.

ICP analysis

The plasma emission spectrometry is a "destructive" technique useful to determine quantitatively the majority of the chemical elements of the periodic table even in very low concentrations (ppm) .

Impact energy

The amount of energy required to fracture a material, usually measured by means of an Izod test or Charpy test. The type of specimen and test conditions affect the values and therefore should be specified.

Impact load

An especially severe shock load such as that caused by instantaneous arrest of a falling mass, by shock meeting of two parts (in a mechanical hammer, for example), or by explosive impact, in which there can be an exceptionally rapid build-up of stress.

Impact strength

See impact energy.


The total opposition in an electrical circuit to flow of alternating current.

Impedance Method

Eddy current method, which monitors the change in prove impedance; both phase and amplitude.

Impedance, Acoustic

See acoustic impedance.


Discontinuity in the weld or a deviation from the intended geometry.

Impingement attack

Corrosion associated with turbulent flow of liquid. May be accelerated by entrained gas bubbles. See also erosion-corrosion.


Nonmetallic particles, usually compounds in a metal matrix. Usually considered undesirable, though in some cases, such as in free machining metals, inclusions may be deliberately introduced to improve machinability.


A particle of foreign material in a metallic matrix. The particle is usually a compound (such as an oxide,' sulphide, or silicate), but may be of any substance that is foreign to (and essentially insoluble in) the matrix. Inclusions are usually considered undesirable, although in some cases-such as in free-machining metals-manganese sulphides, phosphorus, selenium, or tellurium may be deliberately introduced to improve machinability.

Incomplete Fusion

Welding fusion which is less than compete. Failure of weld metal to fuse completely with the base metal or preceding bead.

Incomplete Joint Penetration (Lack of Fusion)

Welding fusion that fails to penetrate to complete thickness of the materials being joined. Appears as elongated darkened lines of varying length and width which may occur in any part of the welding groove.

Incomplete Penetration

Welding root penetration which is less than complete or failure of a root pass and backing pass to fuse with each other.

Indicating measuring instrument

Indicating measuring instrument: measuring instrument providing an output signal carrying information about the value of the quantity being measured.


Indication: quantity value provided by a measuring instrument or a measuring system.


In nondestructive testing, the response from or the evidence of a discontinuity in material condition or structure.

Indication interval

Indication interval: set of quantity values bounded by extreme possible indications.

Industrial experience

Experience, acceptable to the certification body, gained under qualified supervision, in the application of the NDT method in the sector concerned, needed to acquire the skill and knowledge to fulfil the provisions of qualification.

Instrumental measurement uncertainty

Instrumental measurement uncertainty: component of measurement uncertainty arising from a measuring instrument or measuring system in use.


The amount of energy a sound has over an area. The same sound is more intense if you hear it in a smaller area. In general, sounds with a higher intensity are louder. 


See intergranular.

Intercrystalline corrosion

See intergranular corrosion.

Intercrystalline cracking

See intergranular cracking.

Interdendritic corrosion

Corrosive attack that progresses preferentially along interdendritic paths. This type of attack results from local differences in composition commonly encountered in alloy castings. See also corrosion.


The boundary between two contacting parts or regions of parts.


Between crystals or grains. Also termed intercrystalline. Contrast with transgranular.

Intergranular corrosion

Corrosion occurring preferentially at grain boundaries, usually with slight or negligible attack on the adjacent grains. See also interdendritic corrosion.

Intergranular corrosion

Intergranular corrosion is preferential dissolution of the grain-boundary phases or the zones immediately adiacent to them, usually with slight or negligible attack on the main body of the grains. 

Intergranular Corrosion

Corrosion occurring preferentially at grain boundaries.

Intergranular cracking

Cracking or fracturing that occurs between the grains or crystals in a polycrystalline aggregate. Contrast with transgranular cracking.

Intergranular fracture

Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Contrast with transgranular fracture.

Intergranular Fracture

Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Contrasted to transgranular fracture.

Intergranular stress-corrosion cracking

Stress-corrosion cracking in which the cracking occurs along grain boundaries.

Internal oxidation

(1) The formation of isolated particles of corrosion products beneath the metal surface. This occurs as the result of preferential oxidation of certain alloy constituents by inward diffusion of oxygen, nitrogen, sulphur, etc. Also called subsurface corrosion. (2) Preferential in situ oxidation of certain components of phases within the bulk of a solid alloy accomplished by diffusion of oxygen into the body. This is commonly used to prepare electrical contact materials.

International measurement standard

International measurement standard: measurement standard recognized by signatories to an international agreement and intended to serve worldwide.

International System of Quantities (ISQ)

International System of Quantities (ISQ): system of quantities based on the seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

International System of Unit SI

International System of Units SI: system of units, based on the International System of Quantities, their names and symbols, including a series of prefixes and their names and symbols, together with rules for their use, adopted by the General Conference on Weights and Measures (CGPM).


The determination of the source and relevancy of an ultrasonic indication.

Interpretation of fracture surface

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings.


See transgranular.

Intracrystalline cracking

See transgranular cracking.


Person authorized by the certification body to supervise examinations.


This process of radiation absorption.

Ionizing Radiation

Radiation of sufficiently high energy to knock electrons out of the orbits of atoms and molecules, often creating more ionizing radiation and adversely affecting living tissues. Biologically significant radiation is an ionizing dose of radiation above 155 ev which may have carcinogenic, mutagenic, or other health effects in humans. 

Iridium 192

A radioactive isotope of the element Iridium which has a half-life of 75 days. It is used extensively as a source of gamma radiation.


Exposure to radiation, as in a nuclear reactor.


 One of two or more atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. Most elements have more than one naturally occurring isotope.

Izod test

A type of impact test in which a V-notched specimen, mounted vertically, is subjected to a sudden blow delivered by the weight at the end of a pendulum arm. The energy required to break off the free end is a measure of the impact strength or toughness of the material. Contrast with Charpy test.


A mathematical expression; a line or surface integral that encloses the crack front from one crack surface to the other, used to characterize the fracture toughness of a material having appreciable plasticity before fracture. The J-integral eliminates the need to describe the behaviour of the material near the crack tip by considering the local stress-strain field around the crack front; Jk is the critical value of the J-integral required to initiate growth of a pre-existing crack.

Job-specific training

Training, provided by the employer (or his agent) to the certificate holder in those aspects of non-destructive testing specific to the employer’s products, NDT equipment, NDT procedures, and applicable codes, standards, specifications and procedures, leading to the award of operating authorizations.

Joint Penetration

The distance weld metal and fusion extend into a joint.


1,000 ev (see electron volt)

Kilovolt (kv)

Unit of electromotive force or potential equal to 100 volts.

Knoop hardness number, HK

A number related to the applied load and to the projected area of the permanent impression made by a rhombic-based pyramidal diamond indenter having included edge angles of 172° 30' and 130° 0'

Knoop hardness test

An indentation hardness test using calibrated machines to force a rhombic-based pyramidal diamond indenter having specified edge angles, under specified conditions, into the surface of the material under test and to measure the long diagonal after removal of the load.

Laboratory heat treatments

The heat treatment, whether it is a massive treatment or a superficial one, gives the material the desired characteristics in terms of mechanical properties, surface resistance and tonicity and therefore it guides the behavior in exercise and the mechanical and chemical response that the component presents in exercise conditions.

Lack of deformation

Since initiation of fatigue fracture does not require a high stress, there is usually little or no deformation in a part or specimen that has fractured by fatigue.

Lack of Fusion

Discontinuity due to lack of union between weld metal and parent metal.

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.


Plate-like; made of a number of parallel plates or sheets. Usually applied to microstructure. The most common lamellar microstructure is pearlite in ferrous metals.


(1) A type of discontinuity with separation or weakness generally aligned parallel to the worked surface of a metal. (2) In electrical components such as motors, a blanked piece of electrical sheet that is stacked up with several other identical pieces to make a stator or rotor.


Metal defects with separation or weakness generally aligned parallel to the worked surface of the metal. May be the result of pipe, blisters, seams, inclusions or segregation elongated and made directional by working. Lamination defects may also occur in metal-powder compacts.


(1) A surface imperfection on worked metal caused by folding over a fin overfill or similar surface condition, then impressing this into the surface by subsequent working without welding it. (2) A fiat surface that holds an abrasive for polishing operations.


See selective leaching.
linear-elastic fracture mechanics. A method of fracture analysis that can determine the stress (or load) required to induce fracture instability in a structure containing a crack-like flaw of known size and shape. See also stress-intensity factor.

Leak Test

A test on sealed sources to assure that radioactive material is not being released.

Leak Testing (LT)

Techniques are used to detect and locate leaks in pressure containment parts, pressure vessels, and structures. 

Linear Accelerator

A particle accelerator designed to move charged particles at high velocities along a straight path to a target.

Linear Accelerator (linac)

An apparatus used to accelerate electrons to high velocities by means of a high frequency electrical wave traveling along a tube in the linear direction of the electron beam.

Liquid metal embrittlement

The decrease in ductility of a metal caused by contact with a liquid metal.

Liquid Penetrant Inspection (LPI)

A method that is used to reveal surface breaking flaws by bleedout of a colored or fluorescent dye from the flaw.

Liquid shrinkage

The reduction in volume of liquid metal as it cools to the liquidus.

Longitudinal direction

That direction parallel to the direction of maximum elongation in a worked material. See also normal direction and transverse direction.

Longitudinal Wave (Velocity)

Rate of propagation of a wave parallel to the direction of motion of the particles.

Longitudinal Waves

 Commonly used term for compressional wave.

Low-cycle fatigue

Fatigue that occurs at relatively small numbers of cycles «10' cycles). Low-cycle fatigue may be accompanied by some plastic, or permanent, deformation. Compare with high-cycle fatigue.

Lubricant fluids

Lueders lines

Elongated surface markings or depressions, often visible to the unaided eye, that form along the length of a tension specimen at an angle of approximately 45° to the loading axis. Caused by localized plastic deformation, they result from discontinuous (inhomogeneous) yielding. Also known as Lueders bands, Hartmann lines, Piobert lines, or stretcher strains.


 Visible at magnifications at or below 25 x.

Macroscopic characteristics of fatigue failure

Information can be learned about a fatigue fracture with only macroscopic examination.


Isolated, clustered, or interconnected voids in a casting that are detectable macroscopically. Such voids are usually associated with abrupt changes in section size and are caused by feeding that is insufficient to compensate for solidification shrinkage.


The structure of metals as revealed by macroscopic examination of a specimen. The examination may be carried out using an as-polished or a polished and etched specimen.


Metal active gas welding; MAG welding; gas metal arc welding /USA/.


Any piece of iron, steel or magnetite that has the property of attracting iron or steel. 

Magnetic Discontinuity

This refers to a break in the magnetic uniformity of the part-a sudden change in permeability. A magnetic discontinuity may not be related to any actual physical break in the metal, but it may produce a magnetic particle indication.

Magnetic Domain

A region in which the magnetic fields of atoms are grouped together and aligned.

Magnetic Field

The space in which a magnetic force is exerted. This space exists within and around a magnetized material and a conductor carrying electrical current.

Magnetic Particle Inspection

A method of detecting cracks or defects by establishing a magnetic field in the object and using iron filings to see if the field lines are constant.

Magnetic Particle Testing

(see Magnetic Particle Inspection) 


The force of attraction or repulsion in a material.


The property and the extent of being magnetized. Quantitatively, the magnetic moment per unit volume of a substance.


Deformation of a ferromagnetic material (such as iron and steel) subjected to a magnetic field. 


The ratio of the length of a line in the image plane (for example, ground glass or a photographic plate) to the length of the same line in the object. Magnifications are usually expressed in linear terms and in units called diameters.

Main-method examination

Written examination, at level 3, which demonstrates the candidate’s general and specific knowledge, and the ability to write NDT procedures for the NDT method as applied in the industrial or product sector(s) for which certification is sought.


The characteristic of metals that permits plastic deformation in compression without fracture. See also ductility.


Person or organization responsible for the welding production.

Manufacturer of consumables

Party who manufactures the consumables totally or performs the final part of production, which determines the quality of the consumables.

Material measure

Material measure: measuring instrument reproducing or supplying, in a permanent manner during its use, quantities of one or more given kinds, each with an assigned quantity value.


The continuous or principal phase in which another constituent is dispersed.

Maximum permissible error limit of error

Maximum permissible error limit of error: extreme value of measurement error, with respect to a known reference quantity value, permitted by specifications or regulations for a given measurement, measuring instrument, or measuring system.

Maximum permissible measurement error

Maximum permissible measurement error: extreme value of measurement error, with respect to a known reference quantity value, permitted by specifications or regulations for a given measurement, measuring instrument, or measuring system.

Maximum strength

See ultimate strength.


Measurand: quantity intended to be measured.

Measured quantity value

Measured quantity value: quantity value representing a measurement result.


Measurement: process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity.

Measurement accuracy

Measurement accuracy: closeness of agreement between a measured quantity value and a true quantity value of a measurand. The concept ‘measurement accuracy’ is not a quantity and is not given a numerical quantity value. A measurement is said to be more accurate when it offers a smaller measurement error.

Measurement bias

Measurement bias: estimate of a systematic measurement error.

Measurement error

Measurement error: measured quantity value minus a reference quantity value.

Measurement method

Measurement method: generic description of a logical organization of operations used in a measurement.

Measurement model

Measurement model: mathematical relation among all quantities known to be involved in a measurement.

Measurement of density of streaks

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings.

Measurement of the thickness of coatings and metal oxide layers

A microstructural examination is performed in order to define the thickness of metal coatings or oxide layers.

Measurement precision

Measurement precision: closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions.

Measurement principle

Measurement principle: phenomenon serving as a basis of a measurement.

Measurement procedure

Measurement procedure: detailed description of a measurement according to one or more measurement principles and to a given measurement method, based on a measurement model and including any calculation to obtain a measurement result.

Measurement repeatability

Measurement repeatability: measurement precision under a set of repeatability conditions of measurement.

Measurement reproducibility

Measurement reproducibility: measurement precision underreproducibility conditions of measurement.

Measurement result

Measurement result: set of quantity values being attributed to a measurand together with any other available relevant information.

Measurement standard

Measurement standard: realization of the definition of a given quantity, with stated quantity value and associated measurement uncertainty, used as a reference.

Measurement uncertainty

Measurement uncertainty: non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used.

Measuring chain

Measuring chain: series of elements of a measuring system constituting a single path of the signal from a sensor to an output element.

Measuring instrument

Measuring instrument: device used for making measurements, alone or in conjunction with one or more supplementary devices.

Measuring system

Measuring system: set of one or more measuring instruments and often other devices, including any reagent and supply, assembled and adapted to give information used to generate measured quantity values within specified intervals for quantities of specified kinds.

Measuring transducer

Measuring transducer: device, used in measurement, that provides an output quantity having a specified relation to the input quantity.

Mechanical (cold) crack

A crack or fracture in a casting resulting from rough handling or from thermal shock, such as may occur at shakeout or during heat treatment.

Mechanical properties

The properties of a material that reveal its elastic and inelastic (plastic) behaviour when force is applied, thereby indicating its suitability for mechanical (load-bearing) applications. Examples are elongation, fatigue limit, hardness, modulus of elasticity, tensile strength, and yield strength. Compare with physical properties.

Mechanical twin

A twin formed in a crystal by simple shear under external loading.

metal alloy

A metal alloy is an aggregate of two or more chemical elements that has metallic properties. To know a metal alloy and its properties it is necessary to perform some analysis in order to determine the structure, the percentages and quantities of its components and characteristics that distinguish it.

Metal penetration

An imperfection on the surface of a casting caused by the penetration of molten metal into voids between refractory particles of the mold.


Metallography is the study of the physical structure and components of metals, typically using microscopy.
Metallographic, micrographic and macrographic inspections are among the most important analytic techniques to evaluate the characteristics of metallic materials.

Metallographic test ferrous metal materials

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.

Metallographic test non ferrous metal materials

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.


Metallurgical band examination

A morphological evaluation is performed in order to define the directional distribution (bands) of the ferrite and pearlite in case hardening steels (carburizing).


The science and technology of metals.

Metals wear

It is possible to analyze the wear metals in lubricating oils according to ASTM D5185.
It takes just 10 ml of used oil (it is always good to analyse also the new oil for comparison).


A crack of microscopic proportions. Also termed microfissure.


 See microcrack.


A graphic reproduction of the surface of a prepared specimen, usually etched, at a magnification greater than ten diameter. If produced by photographic means it is called a photomicrograph ( not a microphotograph).


Extremely fine porosity in castings.


Visible only at magnifications above 25 x .

Microscopic characteristics of fatigue failure

Striations are the most characteristic microscopic evidence of fatigue fracture, although striations are not always present on fatigue fracture surfaces, as will be seen.


A casting imperfection consisting of interdendritic voids. Microshrinkage results from contraction during solidification where the opportunity to supply filler material is inadequate to compensate for shrinkage. Alloys with wide ranges in solidification temperature are particularly susceptible.


A casting defect, not detectable at magnifications lower than ten diameters, consisting of interdendritic voids. This defect results from contraction during solidification where there is not an adequate opportunity to supply filler material to compensate for shrinkage. Alloys with a wide range in solidification temperature are particularly susceptible.

Microstructrural aspects

Brittle fractures usually propagate by either or both of two fracture modes:

Microstructrural aspects

It is on a microscopic scale that the characteristics of ductile deformation and fracture really become unique. It is necessary to examine both the changes that are visible with a light microscope and those that can be examined only with an electron microscope at magnifications unattainable by a light microscope.


The structure of metals and alloys as revealed after polishing and etching a specimen, at magnifications greater than 25 x.

Microstructure analysis

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.


Metal inert gas welding; MIG welding; gas metal arc welding /USA/

Migration testing for metals and alloys in contact with foodstuffs


Unit of electric current equal to one thousandth of an ampere.


A casting not fully formed because of solidification of metal before the mold is filled.


111 Manual metal arc welding (metal arc welding with covered electrode); shielded metal arc welding /USA/


One of the three classes of crack (surface) displacements adjacent to the crack tip. These displacement modes are associated with stress-strain fields around the crack tip and are designated I, II, and III. See also crack-tip plane strain and crack opening displacement.

Mode Conversion

The change of ultrasonic wave propagation mode upon reflection and/or refraction at an interface.

Mode of combined fracture

It must not be assumed that brittle fracture always occurs solely by the cleavage or the intergranular fracture mode as described above.

Mode of Vibration

Type of wave motion. Three common modes used in ultrasonic testing are longitudinal, transverse and surface wave.

Modulus of elasticity

(1) The measure of rigidity or stiffness of a meta]; the ratio of stress, below the proportional limit, to the corresponding strain. In terms of the stress-strain diagram, the modulus of elasticity is the slope of the stress-strain curve in the range of linear proportionality of stress to strain. Also known as Young's modulus. (2) For materials that do not conform to Hooke's law throughout the elastic range, the slope of either the tangent to the stress-strain curve at the origin or at low stress, the secant drawn from the origin to any specified point on the stress-strain curve, or the chord connecting any two specific points on the stress-strain curve is usually taken to be the modulus of elasticity. In these cases, the modulus is referred to as the tangent modulus, secant modulus, or chord modulus, respectively.

Modulus of rigidity

See shear modulus.

Modulus of rupture

Nominal stress at fracture in a bend test or torsion test. In bending, modulus of rupture is the bending moment at fracture divided by the section modulus. In torsion, modulus of rupture is the torque at fracture divided by the polar section modulus. See also modulus of rupture in bending and modulus of rupture in torsion.

Modulus of rupture in bending

The value of maximum tensile or compressive stress (whichever causes failure) in the extreme fiber on a beam loaded to failure in bending

Modulus of rupture in torsion

The valve of maximum shear stress in the extreme fiber of a member of circular cross section loaded to failure in torsion.

Multiple of a unit

Multiple of a unit: measurement unit obtained by multiplying a given measurement unit by an integer greater than one.

Multiple-choice examination question

Wording of a question giving rise to four potential replies, only one of which is correct, the remaining three being incorrect or incomplete.


National measurement standard

National measurement standard: measurement standard recognized by national authority to serve in a state or economy as the basis for assigning quantity values to other measurement standards for the kind of quantity concerned.


Acronym for Nondestructive Evaluation


Acronym for Nondestructive Testing.

NDT instruction

Written description of the precise steps to be followed in testing to an established standard, code, specification or NDT procedure

NDT method

Discipline applying a physical principle in non-destructive testing EXAMPLE Ultrasonic testing.

NDT Methods

A process used to test an object for flaws and other defects that does not harm the object. 

NDT procedure

Written description of all essential parameters and precautions to be applied when non-destructively testing products in accordance with standard(s), code(s) or specification(s).

NDT training

Process of instruction in theory and practice in the NDT method in which certification is sought, which takes the form of training courses to a syllabus approved by the certification body.

Near Field

The distance immediately in front of the transducer in which the ultrasonic beam exhibits complex and changing wavefronts. Also called the Fresnel Field or Fresnel Zone.


(1) Reduction of the cross-sectional area of metal in a localized area by stretching. (2) Reduction in the diameter of a portion of the length of a cylindrical shell or tube.

Neutron embrittlement

Embrittlement resulting from bombardment with neutrons, usually encountered in metals that have been exposed to a neutron flux in the core of a reactor. In steels, neutron embrittlement is evidenced by a rise in the ductile-to-brittle transition temperature. See also radiation damage.


Any undesired signal that obscures the signal of interest.

Nominal indication interval

Nominal indication interval: set of quantity values, bounded by rounded or approximate extreme indications, obtainable with a particular setting of the controls of a measuring instrument or measuring system and used to designate that setting.

Nominal quantity value

Nominal quantity value: rounded or approximate value of a characterizing quantity of a measuring instrument or measuring system that provides guidance for its appropriate use.

Nominal strength

See ultimate strength.

Nominal value

Percentage value of a component, quoted by the manufacturer or supplier, which corresponds to the general composition given by the designation.

Non essential variable

Welding condition addressed in the WPS but not requiring qualification.

Non-contact Dimensional testing

Through not-in-contact dimensional measurements, it is possible to compare the object under inspection with the related mathematics as well as to perform the reverse engineering.

Nondestructive Evaluation (NDE)

The use of non-invasive techniques to determine the integrity of a material, component or structure, or to quantitatively measure some characteristic of an object. (Making quantitative measurements is what distinguishes NDE from NDT.)

Non-destructive testing

Non-destructive tests (N.D.T.) are inspections, checks and surveys carried out by means of methods that do not alter the material and do not require the destruction or removal of test samples from the concerned structure. 

Nondestructive Testing (NDT)

Testing to detect defects in materials using techniques that do not damage or destroy the items being tested.


Describing a metal that is less than 50% iron, such as aluminum, copper, magnesium, and zinc and their alloys.

Normal direction

That direction perpendicular to the plane of working in a worked material.
See also longitudinal direction and transverse direction.


See stress concentration.

Notch acuity

Relates to the severity of the stress concentration produced by a given notch in a particular structure. If the depth of the notch is very small compared with the width (or diameter) of the narrowest cross section, acuity may be expressed as the ratio of the notch depth to the notch root radius. Otherwise, acuity is defined as the ratio of one-half the width (or diameter) of the narrowest cross section to the notch root radius.

Notch brittleness

Susceptibility of a material to brittle fracture at points of stress concentration. For example, in a notch tension test, the material is said to be notch brittle if the notch strength is less than the tensile strength of an unnotched specimen. Otherwise, it is said to be notch ductile.

Notch depth

The distance from the surface of a test specimen to the bottom of the notch. In a cylindrical test specimen, the percentage of the original cross-sectional area removed by machining an annular groove.

Notch rupture strength

The ratio of applied load to original area of the minimum cross section in a stress-rupture test of a notched specimen.

Notch sensitivity

A measure of the reduction in strength of a metal caused by the presence of stress.

Notch strength

The maximum load on a notched tension-test specimen divided by the minimum cross-sectional area (the area at the root of the notch). Also called notch tensile strength.

Notch tensile strength

See notch strength.

Numerical quantity value

Numerical quantity value: number in the expression of a quantity value, other than any number serving as the reference.

Observation with scanning electron microscope

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings.

Observations with scanning electron microscope SEM

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings.

Off-system measurement unit

Off-system measurement unit: measurement unit that does not belong to a given system of units.

Operating authorization

Written statement issued by the employer, based upon the scope of certification, authorizing the individual to carry out defined tasks.
NOTE Such authorization can be dependent on the provision of job-specific training.

Optic emission spectrometry (EOS)

The emission spectrometry analysis allows to verify the chemical composition of the metallic alloy.

Orange peel

A surface roughening in the form of a pebble-grained pattern where a metal of unusually coarse grain is stressed beyond its elastic limit. Also known as pebbles and alligator skin.
original crack size, a0. The physical crack size at the start of testing.

Ordinal quantity

Ordinal quantity: quantity, defined by a conventional measurement procedure, for which a total ordering relation can be established, according to magnitude, with other quantities of the same kind, but for which no algebraic operations among those quantities exist.


A device that displays how a voltage or current signal varies over time.


(1) A reaction in which there is an increase in valence resulting from a loss of electrons. Contrast with reduction. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.

Oxidative wear

A type of wear resulting from the sliding action between two metallic components that generates oxide films on the metal surfaces. These oxide films prevent the formation of a metallic bond between the sliding surfaces, resulting in fine wear debris and low wear rates.


Paint is a material which, once applied (as a liquid or powder) on the substrate (which may be metallic or other material), forms a solid film for a protective and/or aesthetic purpose.


A material property or instrument variable.

Parent material

Material(s) to be joined by welding.

Parent material thickness

Nominal thickness of the materials to be welded.

Particle size

With the particle size analysis it is possible to determine the average size of particles that compose a sediment, a powder or a residue.


The selective corrosion of one or more components of a solid-solution alloy.


See orange peel.


The property of a penetrant that causes it to find its way into very fine openings, such as cracks.


A fluid (usually a liquid but can be a gas) which possesses unique properties that render it highly capable of entering small openings, a characteristic which makes this fluid especially suitable for use in the detection of surface discontinuities which may be present.

Penetrant Testing (PT)

Method that is used to reveal surface breaking flaws by bleedout of a colored or fluorescent dye from the flaw.

Penetration, Ultrasonic

Propagation of ultrasonic energy into a material. See also effective penetration.


The shadow cast when the incident radiation is partly, but not wholly cut off by an intervening body; the space of partial illumination between the umbra, or perfect shadow or all side and the full light. A marginal region on borderland or partial obscurity.


The ease with which a magnetic flux can be established in a given magnetic circuit.

Permeability (Magnetic)

Ratio between flux density, B, and magnetizing force, H. Permeability describes the intrinsic willingness of a material to conduct magnetic flux lines.

Perpendicular lines

The term "ratchet marks" is used to describe features that are very useful in identification of fatigue fractures and in locating and counting the number of fatigue origins. 


The pH is a scale of acidity or alkalinity of a solution. The pH value is determined by using a potentiometric method using a glass electrode as a sensor combined with a suitable reference electrode.

Phase Angle

The difference in phase between two sinusoidal varying quantities. 

Phase 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.


A vector describing sinusoidal signals; It has both amplitude and phase.

Physical crack size, ap.

The distance from a reference plane to the observed crack front. This distance may represent an average of several) measurements along the crack front. The reference plane depends on the specimen form, and it is normally taken to be either the boundary or a plane containing either the load line or the centerline of a specimen or plate.

Physical properties

Properties of a metal or alloy that are relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of thermal expansion, magnetic permeability, and lattice parameter. Does not include chemical reactivity. Compare with mechanical properties.

Physical tests

Piezoelectric Effect

The ability of certain materials to convert electrical energy into mechanical energy and vice versa.


A small, rounded hole just below the surface of a casting, sometimes visible only after machining. Such holes, often localized, have bright interior surfaces.

Piobert lines

See Lueders lines.


(1) then central cavity formed by contraction in metal, especially ingots, during solidification; (2) the defect in wrought or cast products resulting from such a cavity; (3) an extrusion defect due to the oxidized surface of the billet flowing toward the center of the rod at the back end; (4) a tubular metal product, cast or wrought.


Small cavities in a metal surface by nonuniform electrodeposition or by corrosion.


(1) Corrosion of a metal surface, confined to a point or small area, that takes the form of cavities. (2) In tribology, a type of wear characterized by the presence of surface cavities formed by processes such as fatigue, local adhesion, or cavitation.

Pitting corrosion

Pitting of metals is extremely localized corrosion that generally produces sharply defined holes. 

Plane strain

The stress condition in linear elastic fracture mechanics in which there is zero strain in a direction normal to both the axis of applied tensile stress and the direction of crack growth (Le., parallel to the crack front); most nearly achieved in loading thick plates along a direction parallel to the plate surface. Under plane-strain conditions, the plane of fracture instability is normal to the axis of the principal tensile stress.

Plane stress

The stress condition in linear elastic fracture mechanics in which the stress in the thickness direction is zero; most nearly achieved in loading very thin sheet along a direction parallel to the surface of the sheet. Under plane-stress conditions, the plane of fracture instability is inclined 45° to the axis of the principal tensile stress.

Plane Wave

Wave in which points of same phase lie on parallel plane surfaces.

Plane-strain fracture toughness

The crack extension resistance under conditions of crack-tip plane strain. See also stress intensity factor.

Plane-stress fracture toughness

The value of the crack-extension resistance at the instability condition determined from the tangency between the R-curve and the critical crack-extension force curve of the specimen. See also stress-intensity factor.

Plastic Deformation

Deformation that remains after removal of the load or force that caused the deformation, or change of shape. Same as permanent deformation.

Plastic Deformation

The permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.


In tribology, the formation of grooves by plastic deformation of the softer of two surfaces in relative motion.

PMI method

The X-ray fluorescence spectrometry allows to perform non-destructive quantitative chemical analysis on site.

Poisson's ratio

The absolute value of the ratio of the transverse strain to the corresponding axial strain, in a body subjected to uniaxial stress; usually applied to elastic conditions.


Comprising an aggregate of more than one crystal and usually a large number of crystals.


Polymers are materials made of macromolecules, that are sequences of basic fondamental units called monomers held together by the repetition of the same type of bond (covalent). The high molecular weight reached by polymers gives them mechanical and technical properties, significantly higher than those of non-polymeric materials; in some particular cases, for some applications, polymers may compete with metallic materials. There are various types of polymers: Synthetic (eg, polyethylene, polyester) - Natural (wool, cellulose, starch, DNA, etc..) - Conductors (used in the manufacture of microchips) - very rigid or super-flexible types (used in the aerospace and the automotive industry) - Elastic, resistant to flame, to heat, to chemicals etc..Polymers are generally classified into 3 categories: Thermoplastics - Thermosets - Elastomers (or rubbers). Furthermore, for each type of polymer, they may be subjected to various processing techniques (extrusion, injection molding, blow molding, thermoforming, etc.) that allow you to create products with different characteristics.


(1) A small void in the body of a metal. (2) A minute cavity in a powder metallurgy compact, sometimes intentional. (3) A minute perforation in an electroplated coating.


(1) Small voids in the body of a metal; (2) In powder metallurgy - minute cavities in a compact, sometimes intentional; (3) minute perforations in an electroplated coating.


The property of being porous.


Fine holes or pores within a metal.

Poultice corrosion

A term used in the automotive industry to describe the corrosion of vehicle body parts due to the collection of road salts and debris on ledges and in pockets that are kept moist by weather and washing. Also called deposit attack or deposit corrosion.

Preferred orientation

A condition of a polycrystalline aggregate in which the crystal orientations are not random, but rather exhibit a tendency for alignment with a specific direction in the bulk material, commonly related to the direction of working. See also fiber and texture.

Preliminary welding procedure specification (pWPS)

A document containing the required variables of the welding procedure which has to be qualified.

Pre-production welding test

Welding test having the same function as a welding procedure test, but based on a non-standard test piece representative of the production conditions.

Presence of metals by ICP

The plasma emission spectrometry is a "destructive" technique useful to determine quantitatively the majority of the chemical elements of the periodic table even in very low concentrations (ppm).

Primary creep

The first, or initial, stage of creep, or time-dependent deformation.
principal stress (normal). The maximum or minimum value of the normal stress at a point in a plane considered with respect to all possible orientations of the considered plane. On such principal planes the shear stress is zero. There are three principal stresses on three mutually perpendicular planes. The state of stress at a point may be: (1) uniaxial, a state of stress in which two of the three principal stresses are zero; (2) biaxial, a state of stress in which only one of the three principal stresses is zero; or (3) triaxial, a state of stress in which none of the principal stresses is zero. Multiaxial stress refers to either biaxial or triaxial stress.

Primary measurement standard

Primary measurement standard: measurement standard established using a primary reference measurement procedure, or created as an artifact, chosen by convention.


Eddy current transducer.


 Advancement of a wave through a medium.

Proportional limit

The maximum stress at which strain remains directly proportional to stress; the upper end of the straight-line portion of the stress-strain or load-elongation curve. See also elastic limit.

Prove custom

Prove fatica

Prove impatto

Pulse-Echo Test

A test that can determine the location of a discontinuity by measuring the time required for a short ultrasonic pulse to travel through the material. 


Demonstration of physical attributes, knowledge, skill, training and experience required to properly perform NDT tasks.

Qualification examination

Examination, administered by the certification body or the authorized qualifying body, which assesses the general, specific and practical knowledge and the skill of the candidate.

Qualified supervision

Supervision of candidates gaining experience by NDT personnel certified to this European Standard or by non-certified personnel who, in the opinion of the certification body, possess the knowledge, skill, training and experience required to properly perform such supervision


Quantity: property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference.

Quantity calculus

Quantity calculus: set of mathematical rules and operations applied to quantities other than ordinal quantities.

Quantity dimension

Quantity dimension: expression of the dependence of a quantity on the base quantities of a system of quantities as a product of powers of factors corresponding to the base quantities, omitting any numerical factor.

Quantity equation

Quantity equation: mathematical relation between quantities in a given system of quantities, independent of measurement units.

Quantity value

Quantity value: number and reference together expressing magnitude of a quantity.

Quantity-value scale (measurement scale)

Quantity-value scale (measurement scale): ordered set of quantity values of quantities of a given kind of quantity used in ranking, according to magnitude, quantities of that kind.

Quasi-cleavage fracture

A fracture mode that combines the characteristics of cleavage fracture and dimpled rupture fracture. An intermediate type of fracture found in certain high-strength metals.

Quenching crack

A crack formed as a result of thermal stresses produced by rapid cooling from a high temperature.

Radial marks

Lines on a fracture surface that radiate from the fracture origin and are visible to the unaided eye or at low magnification. Radial marks result from the intersection and connection of brittle fractures propagating at different levels. Also known as shear ledges. See also chevron pattern.


 Energy traveling in the form of electromagnetic waves or photons. 

Radiation Absorbed Dose (RAD)

The quantity that expresses the amount of energy which ionizing radiation imparts to a given mass of matter.

Radiation damage.

A general term for the alteration of properties of a material arising from exposure to ionizing radiation (penetrating radiation), such as x-rays, gamma rays, neutrons, heavy-particle radiation, or fission fragments in nuclear fuel material. See also neutron embrittlement.

Radioactive Material

Includes any such material whether or not subject to licensing control by the commission.


Any individual who performs or who, in attendance at the site where the sealed source or sources are being used, personally supervises radiographic operations and who is responsible to the licensee for assuring compliance with the requirements of these regulations and the conditions of the licenses.

Radiographic Film

A type of film that is sensitive to a certain type of radiation allow an image to form when exposed. 

Radiographic Interpretation

The determination of the cause and significance of subsurface discontinuities indicated on the radiograph. The evaluation as to the acceptability or rejectibility of the materials is based upon the judicious application of the radiographic specifications and standards governing the material.


The process of making a radiograph

Random measurement error

Random measurement error: component of measurement error that in replicate measurements varies in an unpredictable manner.

Range of a nominal indication interval

Range of a nominal indication interval: absolute value of the difference between the extreme quantity values of a nominal indication interval.

Range of interval

The range of the interval [a; b] is the difference b - a and is denoted by r[a; b].

Range of qualification

Extent of qualification for an essential welding variable.

Ratchet marks

Lines on a fatigue fracture surface that result from the intersection and connection of fatigue fractures propagating from multiple origins. Ratchet marks are parallel to the overall direction of crack propagation and are visible to the unaided eye or at low magnification.

Rated operating condition

Rated operating condition: operating condition that must be fulfilled during measurement in order that a measuring instrument or measuring system perform as designed.


A shallow, indented, and irregular line on a casting surface due to sand expansion.


A plot of crack-extension resistance as a function of stable crack extension, which is the difference between either the physical crack size or the effective crack size and the original crack size. R-curves normally depend on specimen thickness and, for some materials, on temperature and strain rate.


(1) In cupping and deep drawing, a measure of the percentage decrease from blank diameter to cup diameter, or of diameter reduction in redrawing. (2) In forging, rolling, and drawing, either the ratio of the original to final cross-sectional area or the percentage decrease in cross-sectional area. (3) A reaction in which there is a decrease in valence resulting from a gain in electrons. Contrast with oxidation.

Reduction of area

The difference between the original cross-sectional area of a tension specimen and the smallest area at or after fracture as specified for the material being tested. Also known as reduction in area.

Reference operating condition

Reference operating condition: operating condition prescribed for evaluating the performance of a measuring instrument or measuring system or for comparison of measurement results.

Reference Radiographs

A group of radiographs containing images of discontinuities. These can be used as comparison "standards" for acceptability of materials.

Reference Standards

A reference object containing known reflectors representing accept or reject criteria.


The change in direction of an acoustic wave as the ultrasonic beam passes from one medium into another having a different sound velocity. A change in both direction and mode occurs at acute angles of incidence. At small angles of incidence, the original mode and a converted mode may exist in the second medium. 

Relative standard measurement uncertainty

Relative standard measurement uncertainty: standard measurement uncertainty divided by the absolute value of the measured quantity value.

Repeatability condition of measurement

Repeatability condition of measurement: condition of measurement, out of a set of conditions that includes the same measurement procedure, same operators, same measuring system, same operating conditions and same location, and replicate measurements on the same or similar objects over a short period of time.

Reproducibility condition of measurement

Reproducibility condition of measurement: condition of measurement, out of a set of conditions that includes different locations, operators, measuring systems, and replicate measurements on the same or similar objects.

Research of secondary phases

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.  

Residual stress

Stress present in a body that is free of external forces or thermal gradients.

Resistance to aging

Resistance to chemical agents

For coatings, resistance tests to chemical agents are useful for the determination of the resistance to liquids and/or chemical agents but in particular these tests are used for paints. 


Resolution: smallest change in a quantity being measured that causes a perceptible change.

Resolution of a displaying device

Resolution of a displaying device: smallest difference between displayed indications that can be meaningfully distinguished.

River pattern

A characteristic pattern of cleavage steps running parallel to the local direction of crack propagation on the fracture surfaces of grains that have separated by cleavage.

Rock candy fracture

A fracture that exhibits separated-grain facets; most often used to describe an intergranular fracture in a largegrained metal.

Rockwell hardness number, HR

A number derived from the net increase in the depth of impression as the load on an indenter is increased from a fixed minor load to a major load and then returned to the minor load. Rockwell hardness numbers are always quoted with a scale symbol representing the penetrator, load, and dial used.

Rockwell hardness test

An indentation hardness test using a calibrated machine that utilizes the depth of indentation, under constant load, as a measure of hardness. Either a 120° diamond cone with a slightly rounded point or a 1.6- or 3.2-mm diam steel ball is used as the indenter.

Root run

In multi layer welding, the run(s) of the first layer deposited in the root.

Rupture stress

The stress at failure. Also known as breaking stress or fracture stress.


A corrosion product consisting primarily of hydrated iron oxide. A term properly applied only to ferrous alloys.


Submerged arc welding with one wire electrode.


A raised and rough area on the surface of a casting due to sand being dislodged from the surface of the mold.

Scale of a displaying measuring instrument

Scale of a displaying measuring instrument: part of a displaying measuring instrument, consisting of an ordered set of marks together with any associated quantity values.


Movement of the transducer over the surface of the test object in a controlled manner so as to achieve complete coverage. May be either contract or immersion method. 


Random reflection of ultrasonic waves by small discontinuities or surface irregularities. 


Random reflection of ultrasonic waves by small discontinuities or surface irregularities.

Scleroscope hardness number, HSc or HSd

A number related to the height of rebound of a diamond-tipped hammer dropped on the material being tested. It is measured on a scale determined by dividing into 100 units the average rebound of the hammer from a quenched (to maximum hardness) and untempered AISI W-5 tool steel test block.

Scleroscope hardness test

 A dynamic indentation hardness test using a calibrated instrument that drops a diamond-tipped hammer from a fixed height onto the surface of the material being tested. The height of rebound of the hammer is a measure of the hardness of the material.


In tribology, a severe form of wear characterized by the formation of extensive grooves and scratches in the direction of sliding.


In tribology, the mechanical removal and/or displacement of material from a surface by the action of abrasive particles or protuberances sliding across the surfaces. See also plowing.


A form of adhesive wear that produces superficial scratches or a high polish on the rubbing surfaces. It is observed most often on inadequately lubricated parts.


An unfused fold or lap that appears as a crack on a metal surface.

Season cracking

Cracking resulting from the combined effects of corrosion and internal stress. A terra usually applied to stress-corrosion cracking of brass.

Secant modulus

The slope of the secant drawn from the origin to any specified point on a stress-strain curve. See also modulus of elasticity.

Secondary creep

See creep.


Particular section of industry or technology where specialized NDT practices are used, requiring specific product-related knowledge, skill, equipment or training.
NOTE A sector can be interpreted to mean a product (welded products, castings) or an industry (aerospace,
in-service testing). See Annex A.


Nonuniform distribution of alloying elements, impurities, or phases.

Selective leaching

Selective leaching is the removal of an element from an alloy by corrosion. 

Selective leaching.

Corrosion in which one element is preferentially removed from an alloy, leaving a residue (often porous) of the elements that are more resistant to the particular environment. See also decarburization, denickelification, dezincification, and graphitic corrosion.


Sensitivity: quotient of the change in an indication of a measuring system and the corresponding change in a value of a quantity being measured.


A measure of the ability to detect small signals. Limited by the signal-to-noise ratio.


In austenitic stainless steels, the precipitation of chromium carbides, usually at grain boundaries, on exposure to temperatures of about 550 to 850 ¢XC (1000 to 1550 ¢XF), leaving the grain boundaries depleted of chromium and therefore susceptible to preferential attack by a corroding (oxidizing) medium.


Sensor: element of a measuring system that is directly affected by a phenomenon, body, or substance carrying a quantity to be measured.

Shatter crack

See fake.


A narrow, slanting ridge along the edge of a fracture surface. The terra sometimes also denotes a narrow, often crescentshaped, fibrous region at the edge of a fracture that is otherwise of the cleavage type, even though this fibrous region is in the same plane as the rest of the fracture surface.

Shear bands

Bands in which deformation has been concentrated inhomogeneously in sheets that extend across regional groups of grains. Only one system is usually present in each regional group of grains, different systems being present in adjoining groups. The bands are noncrystallographic and form on planes of maximum shear stress (55¢X to the compression direction). They carry most of the deformation at large strains.

Shear fracture

A ductile fracture in which a crystal (or a polycrystalline mass) has separated by sliding or tearing under the action of shear stresses. See also shear stress.

Shear ledges

See radial marks.

Shear modulus

The ratio of shear stress to the corresponding shear strain for shear stresses below the proportional limit of the material. Values of shear modulus are usually determined by torsion testing. Also known as modulus of rigidity.

Shear strain

The tangent of the angular change, due to force, between two lines originally perpendicular to each other through a point in a body.

Shear strength

The maximum shear stress that a material is capable of sustaining. Shear strength is calculated from the maximum load during a shear or torsion test and is based on the original dimensions of the cross section of the specimen.

Shear stress

(1) A stress that exists when parallel planes in metal crystals slide across each other. (2) The stress component tangential to the plane on which the forces act. Also known as tangential stress.

Shock load

The sudden application of an external force that results in a very rapid build-up of stress-for example, piston loading in internal combustion engines.


See casting shrinkage.

Shrinkage Cavity

Cavities in castings caused by lack of sufficient molten metal as the casting cools. A small bubble in metal that appears as dendritic, filamentary, or jagged darkened area on a radiograph film.

Shrinkage cavity

A void left in cast metals as a result of solidification shrinkage. Shrinkage cavities occur in the fast metal to solidify after casting.

Shrinkage Cracks

Hot tears associated wit shrinkage cavities.

Shrinkage Porosity or Sponge

A localized lacy, or honeycombed, darkened area on a film that indicates porous metal.


A change in eddy current instrument output voltage; It has amplitude and phase.

Significant interruption

Absence or change of activity which prevents the certified individual from practising the duties corresponding to the level in the method and the sector(s) within the certified scope, for either a continuous period in excess of one year or two or more periods for a total time exceeding two years.
NOTE Legal holidays or periods of sickness or courses of less than thirty days are not taken into account when calculating the interruption.

Silky fracture

A metal fracture in which the broken metal surface has a fine texture, usually dull in appearance. Characteristic of tough and strong metals. Contrast with crystalline fracture and granular fracture.

Slag Inclusions

Nonmetallic solid material entrapped in weld metal or between weld metal and base metal. 

Slant fracture

A type of fracture appearance, typical of plane-stress fractures, in which the plane of metal separation is inclined at an angle (usually about 45¢X) to the axis of the applied stress.


Plastic deformation by the irreversible shear displacement (translation) of one part of a crystal relative to another in a definite crystallographic direction and usually on a specific crystallographic plane. Sometimes called glide. See also flow.

S-N curve

A plot of stress (S) against the number of cycles to failure (N). The stress can be the maximum stress (Smax) or the alternating stress amplitude (Sa). The stress values are usually nominal stress; i.e., there is no adjustment for stress concentration. The diagram indicates the S-N relationship for a specified value of the mean stress (Sm) or the stress ratio (A or R) and a specified probability of survival. For N a log scale is almost always used. For S a linear scale is used most often, but a log scale is sometimes used. Also known as S-N diagram.

S-N diagram

See S-N curve.

Solid shrinkage

The reduction in volume of metal from the solidus to room temperature.

Solidification shrinkage

The reduction in volume of metal from beginning to end of solidification.

Solidification shrinkage crack

A crack that forms, usually at elevated temperature, because of the internal (shrinkage) stresses that develop during solidification of a metal casting. Also termed hot crack.

Solvent Cleaning

The process of removing the excess penetrant from the surface of a part by washing or wiping with a solvent for the penetrant.

Solvent Developer

A developer in which the developing powder is applied as a suspension in a quick-drying solvent.

Solvent Remover

A nonaqueous liquid employed in removal of surface penetrant from parts or for removal of unwanted background porosity indications.

Sound Wave Propagation

The way sound vibrations travel through different mediums. 


The cracking and flaking of particles out of a surface.

Specific examination

Written examination, at level 1 or 2, concerned with testing techniques applied in a particular sector(s), including knowledge of the product(s) tested and of codes, standards, specifications, procedures and acceptance criteria.


Sample used in practical examinations, possibly including radiographs and data sets, which is representative of products typically tested in the applicable sector.
NOTE It can include more than one area or volume to be tested.

Specimen master report

Model answer, indicating the optimum result for a practical examination given a defined set of conditions (equipment type, settings, technique, specimen, etc.) against which the candidate’s test report will be graded.


 See water column.

Stages of fatigue failure

The definition above refers to fracture "under repeated or fluctuating stresses having a maximum value less than the tensile strength." 

Standard measurement uncertainty

Standard measurement uncertainty: measurement uncertainty expressed as a standard deviation.


Stationary or very slow. Frequently used in connection with routine tension testing of metal specimens. Contrast with dynamic. 

Static fatigue

See hydrogen-induced delayed cracking.

Steady-rate creep

See creep.

Strain hardening

An increase in hardness and strength caused by plastic deformation at temperatures below the recrystallization range. Also known as work hardening.

Stray-current corrosion

Corrosion caused by electric current from a source external to the intended electrical circuit, for example, extraneous current in the earth.


The intensity of the internally distributed forces or components of forces that resist a change in the volume or shape of a material that is or has been subjected to external forces. Stress is expressed in force per unit area and is calculated on the basis of the original dimensions of the cross section of the specimen. Stress can be either direct (tension or compression) or shear. Usually expressed in pounds per square inch (psi) or megapascals (MPa).

Stress amplitude

One-half the algebraic difference between the maximum and minimum stress in one cycle of a repetitively varying stress.

Stress concentration

A change in contour or a discontinuity that causes local increases in stress in materials under load. Typical are sharp-cornered grooves or notches, threads, fillets, holes, etc. Also called stress raiser.

Stress Corrosion

Preferential attack area under stress in a corrosive environment, where such an environment alone would not have caused corrosion.

Stress cycle

The smallest segment of the stress-time function that is repeated periodically.

Stress raiser

See stress concentration.

Stress ratio, A or R

The algebraic ratio of two specified stress values in a stress cycle. Two commonly used stress ratios are (1) the ratio of the alternating stress amplitude to the mean stress, A = Sa/Sm, and (2) the ratio of the minimum stress to the maximum stress, R = Smin/Smaxs 

Stress-concentration factor, Kt

A multiplying factor for applied stress that allows for the presence of a structural discontinuity such as a notch or hole; Kt equals the ratio of the greatest stress in the region of the discontinuity to the nominal stress for the entire section. Also known as theoretical stressconcentration factor.

Stress-corrosion cracking, SCC.

A cracking process that requires the simultaneous action of a corrodent and sustained tensile stress. This excludes corrosion-reduced sections that fail by fast fracture. It also excludes intergranular or transgranular corrosion, which can disintegrate an alloy without applied or residual stress. See also corrosion.

Stress-intensity factor, K

A scaling factor used in linear-elastic fracture mechanics to describe the intensification of applied stress at the tip of a crack of known size and shape. At the onset of rapid crack propagation in any structure containing a crack, the factor is called the critical stress-intensity factor, or the fracture toughness.

Stress-rupture strength

See creep-rupture strength.

Stress-strain curve

See stress-strain diagram.

Stress-strain diagram

A graph in which corresponding values of stress and strain are plotted against each other. Values of stress are usually plotted vertically (ordinate or y axis) and values of strain horizontally (abscissa or x axis). Also known as deformation curve and stress-strain curve.

Stretcher strains

See Lueders lines.


A fatigue fracture feature often observed in electron micrographs that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front across that crystal during one stress cycle, and a line normal to the striation
indicates the direction of local crack propagation. Not to be confused with beach marks, which are much larger (macroscopic and form differently.

Striations or beachmarks?

Both striations and beachmarks identify the position of the tip of the fatigue crack at a given point in time. 


In wrought materials, an elongate configuration of microconstituents or foreign material aligned in the direction of working The term is commonly associated with clot gated oxide or sulfide inclusions in steel.

Sub-boundary structure (subgrain structure)

A network of low-angle boundaries usually with misorientations less than 1 within the main grains of a microstructure.


A portion of a crystal or grain, wit an orientation slightly different from the orientation of neighboring portions of the same crystal.

Submultiple of a unit

Measurement unit obtained by dividing a given measurement unit by an integer greater than one.


The reaction of a metal or alloy with a sulfur-containing species to produce sulfur compound that forms on or beneath the surface of the metal or alloy.

Sulfide stress cracking, SSC

Brittle failure b cracking under the combined action of tensile stress and corrosion in the presence of water and hydrogen sulfide.

Superficial hardness Rockwell - HR

The hardness test is carried out to evaluate the state of a metal alloy supply.
For metal alloys, TEC Eurolab uses the following hardness scales: Brinell, Vickers and Rockwell.


Act of directing the application of NDT performed by other NDT personnel, which includes the control of actions involved in the preparation of the test, performance of the test and reporting of the results.

Surface analysis

Surface hardness

The hardness test is carried out to evaluate the state of a metal alloy supply.
For metal alloys, TEC Eurolab uses the following hardness scales: Brinell, Vickers and Rockwell.

Surface microstructure

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.


Surface textures

The microanalysis performed by using probe EDS, allows precise qualitative analysis of small size components (inclusions) and the analysis of coatings.

System of units

System of units: set of base units and derived units, together with their multiples and submultiples, defined in accordance with given rules, for a given system of quantities.

Systematic measurement error

Systematic measurement error: component of measurement error that in replicate measurements remains constant or varies in a predictable manner.

Tangent modulus

The slope of the stress-strain curve at any specified stress or strain. Se also modulus of elasticity.

Tangential stress

See shear stress.

Target measurement uncertainty

Target measurement uncertainty: measurement uncertainty specified as an upper limit and decided on the basis of the intended use of measurement results.

Temper brittleness

Brittleness that result when certain steels are held within, or at cooled slowly through, a certain range c temperature below the transformation range The brittleness is manifested as an upward shift in ductile-to-brittle transition temperature, but only rarely produces a low value c reduction of area in a smooth-bar tension test of the embrittled material.

Temporary distorsion

Also serious is the permanent distortion that results from yielding during service, from creep, and from buckling (or compression instability).

Tensile strength

In tension testing, the ratio c maximum load to the original cross-section, area. See also ultimate strength; compare with yield strength.

Tensile stress

A stress that causes two parts c an elastic body, on either side of a typical, stress plane, to pull apart. Contrast wit compressive stress.

Tensile testing

See tension testing.

Tension testing

A method of determining the behavior of materials subjected to uniaxial, loading, which tends to stretch the metal. A longitudinal specimen of known length an diameter is gripped at both ends an stretched at a slow, controlled rate until rupture occurs. Also known as tensile testing.

Tertiary creep

See creep.

Test piece

Welded assembly which is used for testing purposes.

Test specimen

Part or portion cut from the test piece in order to perform a specified destructive test.

Tested welding consumable

Welding consumable or consumable combination tested according to appropriate standards for testing of welding consumables.


In a polycrystalline aggregate, the state of distribution of crystal orientations. In the usual sense, it is synonymous with preferred orientation, in which the distribution is not random. See also fiber.

Theoretical stress-concentration factor

See stress-concentration factor.

Thermal analysis

Thermal analysis are useful to determine the material properties in function of the temperature and these tests can also be carried out on paints.
The thermal characterization provides the parameters relevant for the evaluation of the properties of the material in exercise such as the weight change at a certain temperature for a certain time, in order to detect the chemical and physical changes that are generated.

Thermal fatigue

Fracture resulting from the presence of temperature gradients that vary with time in such a manner as to produce cyclic stresses in a structure.

Thermal fatigue

A somewhat similar type of fatigue fracture is caused not by repetitive mechanical stresses but by cyclic thermal stresses. 

Thermal shock

The development of a steep temperature gradient and accompanying high stresses within a structure.

Thermal stresses

Stresses in metal resulting from nonuniform temperature distribution.

Thermomechanical analysis

The thermo-mechanical properties represent a help to determine the causes of breakage or dimensional changes of various materials when these are subjected to more or less intense heat sources.

Tide marks

See beach marks.


Tungsten inert gas welding; TIG welding; gas tungsten arc welding /USA/


A twisting action applied to a shaftlike or cylindrical member. The twisting may be either reversed (back and forth) or unidirectional (one way).

Torsional stress

The shear stress on a transverse cross section resulting from a twisting action.

Total dissolved solids

The term total dissolved solids means the residue that remains in a capsule, after evaporation of a water sample, previously filtered, and subsequent dried in an oven.

Total suspended solids

The term total suspended solids means all the non-dissolved substances present in the water sample to be tested.


See transgranular.

Transcrystalline cracking

See transgranular cracking.


Through or across crystals or grains. Also called intracrystalline or transcrystalline.

Transgranular cracking.

Cracking or fracturing that occurs through or across a crystal or grain. Also called transcrystalline cracking. Contrast with intergranular cracking.

Transgranular fracture

Fracture through or across the crystals or grains of a metal. Also called transcrystalline fracture or intracrystalline fracture. Contrast with intergranular fracture.

Transient creep

See creep and primary creep.

Transitions ductile-fragile

Body-centered cubic (bcc) metals, such as ferritic steels as well as some hexagonal close-packed (hcp) metals, undergo a ductile-to-brittle transition in their fracture behavior. 

Transverse direction

Literally, "across," usually signifying a direction or plane perpendicular to the direction of working. In rolled plate or sheet, the direction across the width is often called long transverse; the direction through the thickness, short transverse.

Travelling measurement standard

Travelling measurement standard: measurement standard, sometimes of special construction, intended for transport between different locations.


The science concerned with the design, friction, lubrication, and wear of contacting surfaces that move relative to each other.

True quantity value

True quantity value: quantity value consistent with the definition of a quantity.


The formation of localized corrosion products that appear on a surface as knoblike prominences (tubercules).


Two portions of a crystal with a definite orientation relationship; one may be regarded as the parent, the other as the twin. The orientation of the twin is a mirror image of the orientation of the parent across a twinning plane or an orientation that can be derived by rotating the twin portion about a twinning axis. See also annealing twin and mechanical twin.

Twin bands

Bands across a crystal grain, observed on a polished and etched section, where crystallographic orientations have a mirror-image relationship to the orientation of the matrix grain across a composition plane that is usually parallel to the sides of the band.

Two-Film Technique

A procedure wherein two films of different relative speeds are used simultaneously to radiograph both the thick and the thin sections of an item.

Type A evaluation of measurement uncertainty

Type A evaluation of measurement uncertainty: evaluation of a component of measurement uncertainty by a statistical analysis of measured quantity values obtained under defined measurement conditions.

Type B evaluation of measurement uncertainty

Type B evaluation of measurement uncertainty: evaluation of a component of measurement uncertainty determined by means other than a Type A evaluation of measurement uncertainty.

Types of distorsion failure

Distortion failures may be classified in different ways. One way is to consider them either as size distortion (change of volume, either growth or shrinkage) or as shape distortion (such as stretching, bending, twisting, or buckling).

Ultimate strength

The maximum stress (tensile, compressive, or shear) a material can sustain without fracture, determined by dividing maximum load by the original cross-sectional area of the specimen. Also known as nominal strength or maximum strength.


A term referring to acoustic vibration frequencies greater than about 20,000 hertz.

Uncertainty budget

Uncertainty budget: statement of a measurement uncertainty, of the components of that measurement uncertainty, and of their calculation and combination.

Uniform corrosion

Corrosion of metals by uniform chemical attack is the simplest and most common form of corrosion, and it occurs in the atmosphere, in liquids, and in soil, frequently under normal service conditions. 

Unit equation

Unit equation: mathematical relation between base units, coherent derived units or other measurement units.


Abbreviation for the ultrasonic method of nondestructive testing.


Validation: verification, where the specified requirements are adequate for an intended use.


Act of demonstrating that a verified procedure will work in practice and fulfil its intended function, normally achieved by actual witnessing, demonstration, field or laboratory tests or selected trials.


Distance traveled per unit time.


Verification: provision of objective evidence that a given item fulfils specified requirements.

Verification of the microstructure of surface treatments

A  microstructural analysis is performed in order to evaluate the microstructure in a metal alloy.

Vickers hardness number, HV

A number related to the applied load and the surface area of the permanent impression made by a square-based pyramidal diamond indenter having included face angles of 136°.

Vickers hardness test.

An indentation hardness test employing a 136° diamond pyramid indenter (Vickers) and variable loads, enabling the use of one hardness scale for all ranges of hardness-from very soft lead to tungsten carbide. Also known as diamond pyramid hardness test.

Volumetric modulus of elasticity

See bulk modulus of elasticity.

Wallner lines

A distinct pattern of intersecting sets of parallel lines, usually producing a set of V-shaped lines, sometimes observed when viewing brittle fracture surfaces at high magnification in an electron microscope. Wallner lines are attributed to interaction between a shock wave and a brittle crack front propagating at high velocity. Sometimes Wallner lines are misinterpreted as fatigue striations.

Water hardness

Water hardness is determined by complexometric  titration with EDTA until the color change of a specific indicator based on Eriochrome black modified and stabilized.


Wave Propagation

The way in which a wave travels through a medium.


Damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting surface or substance.

Wear rate

The rate of material removal or dimensional change due to wear per unit of exposure parameter-for example, quantity of material removed (mass, volume, thickness) in unit distance of sliding or unit time.

Weld metal thickness

Thickness of the weld metal excluding any reinforcement.


Person who holds and manipulates the electrode holder, welding torch or blowpipe by hand.

Welding consumable

Materials consumed in the making of a weld, including filler metals and auxiliary materials.

Welding co-ordination personnel

Personnel who have responsibilities in the manufacturing operation for welding and welding related activities whose competence and knowledge has been demonstrated by e.g. training, education and/or relevant manufacturing experience.

Welding procedure

Specified course of action to be followed in making a weld, including the welding process(es), reference to materials, welding consumables, preparation, preheating (if necessary), method and control of welding and post-weld heat treatment (if relevant), and necessary equipment to be used.

Welding procedure qualification record (WPQR)

Record comprising all necessary data needed for qualification of a preliminary welding procedure specification.

Welding procedure specification (WPS)

A document that has been qualified by one of the methods described in clause 6 and provides the required variables of the welding procedure to ensure repeatability during production welding.

Welding procedure test

Making and testing of a standardized test piece, as indicated in the pWPS, in order to qualify a welding procedure.

Welding process

For the welding processes, the nomenclature and definitions given in ISO 857-1 are followed in this standard.


(1) Metallic filamentary growths, often microscopic in size, that attain very high strengths. (2) Oxide whiskers, such as sapphire, which because of their strength and inertness at high temperatures are used as reinforcements in metal-matrix composites.

Work hardening

 See strain hardening.

Work instruction

Simplified specification of the welding procedure, suitable for direct application in the workshop.

Working measurement standard

Working measurement standard: measurement standard that is used routinely to calibrate or verify measuring instruments or measuring systems.

X-RAY Photoelectron Spectroscopy (XPS)

The technique X-Ray Photoelectron Spectroscopy (XPS) allows to characterize the surface of a sample from a compositional point of view...


A form of electromagnetic radiation with wavelengths shorter than those of ultraviolet light. 


Evidence of plastic deformation in structural materials. See also creep and flow.

Yield point

The first stress in a material, usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. Only certain metals-those that exhibit a localized, heterogeneous type of transition from elastic to plastic deformation-produce a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The load at which a sudden drop in the flow curve occurs is called the upper yield point. The constant load shown on the flow curve is the lower yield point.

Yield strength

The stress at which a material exhibits a specified deviation from proportionality of stress and strain. The specified deviation is usually 0.2% for most metals. Compare with tensile strength.

Yield stress

The stress level of highly ductile materials, such as structural steels, at which large strains take place without further increase in stress.

Young's modulus

See modulus of elasticity.

Zero adjustment of a measuring system

Zero adjustment of a measuring system: adjustment of a measuring system so that it provides a null indication corresponding to a zero value of a quantity to be measured. - Internet Partner
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