Standard Terminology for Nondestructive Examinations Part 3

ion source—in leak testing, that part of a leak detector tube in which tracer gas is ionized preliminary to being detected. ionization potential—the minimum energy, expressed in (electron) volts, required to remove an electron from an atom or molecule to form a positive ion. ionization vacuum gauge—a vacuum gauge comprising a means of ionizing the gas molecules, electrodes to facilitate the collection of the positive ions formed, and means of indicating the magnitude of the collected ion current. Various types of ionization gauges are distinguished in accordance with the method of producing the ionization. The common types are as follows: (a) hot-cathode ionization gauge—the ions are produced by collisions with electrons emitted from a hot filament (or cathode) and accelerated by an electric field. Also called hot-filament ionization gauge, or simply ion gauge. The Bayard-Alpert ionization gauge employs a tube with an electrode structure designed to minimize X-ray-induced electron emission from the ion collector. (b) cold-cathode ionization gauge—the ions are produced by a cold-cathode discharge, usually in the presence of a magnetic field which lengthens the path of the electrons between cathode and anode. The discharge tube is a transparent tube in which the color and form of a cold-cathode discharge (without the presence of a magnetic field) gives an indication of the pressure and the nature of the gas. The Phillips ionization gauge is a cold-cathode ionization gauge in which a magnetic field is directly parallel to the axis of an annular electrode (normally the anode) located between two plate electrodes perpendicular to the axis. Various modifications of the Penning gauge are named after the inventors, and certain types are referred to as magnetron vacuum gauges. (c) radioactive ionization gauge—the ions are produced by radiations (usually alpha particles) emitted from a radioactive source. isolation test—in leak testing, a method of determining whether a leak is present in a system, or of obtaining an estimate of its magnitude, by observing the rate of rise of pressure in the evacuated system when the system is isolated from the pump. (See also rate of rise.) Krypton 85—a tracer gas used to test for leakage when the radioisotope leak test method is used. leak—a hole, or void in the wall of an enclosure, capable of passing liquid or gas from one side of the wall to the other under action of pressure or concentration differential existing across the wall, independent of the quantity of fluid flowing. leak artifact—a device used to introduce gas into a system at a controlled rate, usually 10−7 mol/s or less. leak detector—a device for detecting, locating, or measuring, or combinations thereof, leakage. leak testing—comprises procedures for detecting or locating or measuring leakage, or combinations thereof. leakage rate—the flow rate of a liquid or gas through a leak at a given temperature as a result of a specified pressure difference across the leak. Standard conditions for gases are 25 °C and 100 kPa. Leakage rates are expressed in various units such as pascal cubic metres per second or pascal litres per second (see Table 3). low vacuum—see Table 2. 3 lusec—a unit of flow rate equal to 0.133 mPa·m /s. masking—in leak testing, the covering of a section of a test object so as to prevent tracer gas from entering leaks that may exist in the covered section. mass number—the whole number nearest to the atomic mass expressed in either atomic mass units or as (chemical) atomic weight. mass spectrometer (M.S.)—an instrument that is capable of separating ionized molecules of different mass to charge ratio and measuring the respective ion currents. The mass spectrometer may be used as a vacuum gauge that relates an output which is proportioned to the partial pressure of a specified gas, as a leak detector sensitive to a particular tracer gas, or as an analytical instrument to determine the percentage composition of a gas mixture. Various types are distinguished by the method of separating the ions. The principal types are as follows: (a) Dempster (M.S.)—The ions are first accelerated by an electric field through a slit, and are then deflected by a magnetic field through 180° so as to pass through a second slit. (b) Bainbridge-Jordan (M.S.)—The ions are separated by means of a radial electrostatic field and a magnetic field deflecting the ions through 60° so arranged that the dispersion of ions in the electric field is exactly compensated by the dispersion in the magnetic field for a given velocity difference. (c) Bleakney (M.S.)—The ions are separated by crossed electric and magnetic fields. Also called cross fields (M.S.). TABLE 3 Conversion Factors for Leak Testing To Convert from Leakage Rate: 3 atm·cm /s micron·litres/s micron·ft3 /h pascal·litres/s STD·cm 3/s torr·litres/s Pressure: atmosphere (std) bar micrometre of Hg micron millimetre of Hg 2 pounds·force/in. torr Viscosity: centipoise poise Volume: cm 3 3 ft litre To 3 Pa·m /s Pa·m 3 /s Pa·m 3 /s 3 Pa·m /s Pa·m 3 /s 3 Pa·m /s Pa Pa Pa Pa Pa Pa Pa Pa·s Pa·s m3 3 m m3 Multiply Column 1 by 1.10 1.33 1.05 1.00 1.01 1.33 × × × × × × − 1 10 10 − 4 10 − 4 − 3 10 10 − 1 − 1 10 5 1.01 × 10 1.00 × 10 5 1.33 × 10 − 1 1.33 × 10 − 1 1.33 × 10 2 3 6.89 × 10 1.33 × 10 2 1.00 × 10 1.00 × 10 − 3 − 1 1.00 × 10− 4 − 2 2.83 × 10 1.00 × 10− 3 (d) Nier (M.S.)—A modification of the Dempster (M.S.) in which the magnetic field deflects the ions. (e) Time of Flight (M.S.)—The gas is ionized by a pulsemodulated electron beam and each group of ions is accelerated toward the ion collector. Ions of different mass to charge ratios traverse their paths in different times. (f) Radio-Frequency (M.S.)—The ions are accelerated into a radio-frequency analyzer in which ions of a selected mass to charge are accelerated through openings in a series of spaced plates alternately attached across a radio-frequency oscillator. The ions emerge into an electrostatic field which permits only the ions accelerated in the analyzer to reach the collector. (g) Omegatron (M.S.)—The ions are accelerated by the cyclotron principle. mass spectrometer leak detector—a mass spectrometer adjusted to respond only to the tracer gas. mass spectrum—a record, graph, table, and so forth, that shows the relative number of ions of various mass that are produced when a given substance is processed in a mass spectrometer. mean free path—the average distance that a molecule travels between successive collisions with other molecules. medium vacuum—see Table 2. micrometre—a unit of length equal to one millionth of a metre. micron—a term for micrometre. micron of mercury—a unit of pressure equal to that exerted by a column of mercury standing one micrometre high. millimetre of mercury—a unit of pressure corresponding to a column of mercury exactly 1 mm high under standard acceleration of gravity. Sometimes called torr. minimum detectable leakage rate—the magnitude of the smallest leakage rate that can be unambiguously detected by a given leak detector in the presence of conditions existing at time of test. molecular flow—the flow of gas through a passage under conditions such that the mean-free path is greater than the largest dimension of a transverse section of the passage. molecular leak—a leak of such geometric configuration that gas flow through it obeys the laws of molecular flow (Knudsen’s law). The flow is proportional to the difference of the end pressures and inversely proportional to the square root of the molecular weight of the gas. newton (N)—the SI unit of force (kg·m/s2). noncondensable gas—a gas whose temperature is above its critical temperature, so that it cannot be liquefied by increase of pressure alone. occlusion—the trapping of undissolved gas in a solid during solidification. outgassing—the evolution of gas from a material in a vacuum. outlet pressure—see forepressure. palladium barrier leak detector—a leak detector using hydrogen as the tracer gas and using the principle of hydrogen diffusing through a hot palladium barrier into an evacuated vacuum gauge. partial pressure—the pressure caused by a gas, either by itself, or in the presence of other gases. When a second gas is not present, the partial pressure is the same as the total pressure. pascal (Pa)—one pascal is approximately equal to 1 × 10−5 atm or, more precisely, 1 Pa = 0.98692 × 10 −5 atm. pascal cubic metres per second (Pa·m 3/s)—the preferred unit of gas flow in the SI system. One Pa·m3/s is approximately equal to 10 atm cm 3/s or, more precisely, 1 Pa·m3/s = 9.8692 atm·cm3 /s. Penning gauge—see ionization vacuum gauge. perfect gas—see ideal gas. permeability coefficient—the steady-state rate of flow of gas through unit area and thickness of a solid barrier per unit pressure differential at a given temperature. Phillips ionization gauge—see ionization vacuum gauge. Pirani gauge—see thermal conductivity vacuum gauge. Poiseuille flow—the particular case of laminar viscous flow through a long pipe of circular cross section. pressure difference—in leak testing, the difference between the pressure on the inlet side of the leak and the pressure on the exit side of the leak. pressure dye test—(1) a form of leak test in which the item or items to be tested are filled with a liquid dye or fluorescent oil which is then pressurized for the purpose of driving the liquid through possible leakage paths with the presence of the leaks being visible when viewed from the exterior; (2) a form of leak test in which the item or items to be tested are immersed in a liquid dye or fluorescent oil which is then pressurized for the purpose of driving liquid into possible leakage paths with their presence being visible when the excess liquid has been removed from the exterior. pressure-evacuation test—a leak test in which one or more devices are placed under gas pressure for a period of time, the objective being to accumulate enough gas in those devices that may leak to permit an indication on a leak detector sensitive to the gas when the devices are placed in an evacuated system joined to the leak detector. pressure probe—see probe. pressure testing—a method of leak testing in which the component being tested is filled completely with a gas or liquid which is then pressurized. The outside of the component is examined for the detection of any leaks. probe—in leak testing, a tube having an opening at one end, used for directing or collecting a stream of tracer gas. probe gas—in leak testing, a tracer gas which issues from an orifice so as to impinge on a restricted test area. probe test—a leak test in which the tracer gas is applied by means of a probe so that the area covered by the tracer gas is localized. This enables the individual leaks to be located. sensitivity—in the case of a leak detector, the response of the detector to tracer gas leakage (that is, scale divisions per unit of leakage rate). proportioning probe—in leak testing, a probe that can vary sample to pure air ratios between 100 % sample and 100 % pure air without substantially changing the total flow from the probe. sensitivity of leak test—the smallest leakage rate that an instrument, method, or system is capable of detecting under specified conditions. (See minimum detectable leakage rate.) pump-down time—time of evacuation. sniffıng probe—same as sampling probe. sorption—the taking up of gas by absorption, adsorption, chemisorption, or any combination of these processes. pump-out tubulation—a tube extending from an evacuated device through which gas is pumped and which is usually permanently sealed off after the device has been evacuated. Sometimes called exhaust tubulation. radioisotope leak test system—a leak test system which uses a radioactive tracer gas and a detector for measuring the emission from the tracer. rate of rise—in leak testing, the time rate of pressure increase at a given time in a vacuum system which is suddenly isolated from the pump by a valve. The volume and temperature of the system are held constant during the rate of rise measurement. (See isolation test.) resistance (to flow)—the reciprocal of conductance. response factor—in leak testing, the response of the halogen leak detector 0.3 MPa·m3/s of refrigerant-12 (dichlorodifluoromethane, CCl2F2) or less, divided by the response to the same quantity of another halogen test gas. Thus, the actual leak rate of a detected leak will be the indication of the detector multiplied by the response factor. The response of mixture of a tracer and nonhalogen gases will be the response factor of the tracer divided by the fraction of tracer gas in the test gas. response time—the time required for a leak detector or leak testing system to yield a signal output equal to 63 % of the maximum signal attained when tracer gas is applied continuously to the system under test. Also called response. roughing—in leak testing, the initial evacuation of a vacuum system. roughing line—in leak testing, a line running from a mechanical pump to a vacuum chamber through which preliminary pumping is conducted in the rough vacuum range. roughing pump—in leak testing, a vacuum pump used for the initial evacuation of a vacuum system. sampling probe—in leak testing, a device used to collect tracer gas from an area of the test object and feed it to the leak detector at the reduced pressure required. Also called a sniffing probe. scattering—in leak testing, dispersion or diffusion in various directions due to intermolecular or ionic collisions as applied to the effect of the residual gas in a mass spectrometer tube or an ion beam traversing the tube. search-gas—same as tracer gas. spark coil leak detector—a high-frequency discharge coil of the Tesla type which indicates pin holes in glass vacuum systems by a spark jumping between the core of the coil and the pin hole. spectrometer tube—the sensing element of a mass spectrometer leak detector. spray probe—in leak testing, a device for directing a small jet of tracer gas on an object under vacuum testing. squealer—same as audible leak indicator. standard leak—a device that permits a tracer gas to be introduced into a leak detector or leak testing system at a known rate to facilitate calibration of the leak detector. standard leakage rate—the rate of flow of atmospheric air under conditions in which: inlet pressure is 0.1 MPa 6 5 %; outlet pressure is less than 1 kPa; temperature is 25 6 5 °C; and dew point is less than −25 °C. thermal conductivity vacuum gauge—a vacuum gauge containing two surfaces at different temperatures between which heat can be transported by the gas molecules so that changes in the temperature (or in the heating power required to maintain constant temperature) of one of the surfaces can be correlated with the gas pressure. Various types of thermal conductivity gauges are distinguished in accordance with the method of indicating the temperature change. The common types are listed below: (1) Pirani Gauge—an increase of pressure from the zero point causes a decrease in the temperature of a heated filament of material having a large temperature coefficient of resistance thus unbalancing a Wheatstone bridge circuit (or the circuit is adjusted to maintain the filament temperature constant). (2) Thermocouple Gauge—the decrease in temperature of a heated filament as the pressure rises is indicated by decreased emf in a thermocouple circuit having the junction in thermal contact with the center of the heated filament. (3) Thermistor Gauge—a form of Pirani gauge employing a thermistor as the heated element. (4) Bimetallic Strip Gauge—deflection of a bimetallic strip with changing temperature indicates the changes in pressure. thermocouple gauge—see thermal conductivity vacuum gauge. throttling—in leak testing, reducing the net pumping speed of a pumping system by partially closing a valve or installing a section of pipeline with low conductance. throughput—same as flow rate (1). tight—in leak testing, free from leaks in accordance with a given specification. torr—a unit of pressure equal to 1 ⁄ 760 of an atmosphere. tracer gas—a gas which, passing through a leak, can then be detected by a specific leak detector and thus disclose the presence of a leak. Also called search gas. tracer probe leak location—same as probe test. transition flow—in leak testing, the flow of gases under conditions intermediate between laminar viscous flow and molecular flow. ultra-high vacuum—see Table 2. ultrasonic leak detector—an instrument that detects ultrasonic energy produced by molecular turbulence that occurs in the transition from laminar to turbulent flow of a gas through an orifice and that converts this energy to a usable signal. vacuum—in vacuum technology a given space filled with gas at pressures below atmospheric pressure (see Table 2). vacuum testing—(1) a method of testing for leaks in which the object under test is evacuated and the tracer gas applied to the outside surface of the object; (2) a leak-testing procedure in which the enclosure under examination is evacuated, the tracer gas applied to the outside surface of the enclosure, and the gas detected after entering the enclosure. vapor pressure—the pressure exerted by the vapor of a solid or liquid when in equilibrium with the solid or liquid. very high vacuum—see Table 2. virtual leak—(1) the semblance of a leak in a vacuum system caused by slow release of trapped gas. (2) during a rate-of-rise test, the semblance of a leak in a vacuum system caused by slow release of sorbed or occluded gas or gases on or in the surfaces and pores of all materials in a system which has been exposed to atmospheric pressure prior to evacuation. viscous flow—the flow of gas through a duct under conditions such that the mean free path is very small in comparison with the smallest dimension of a transverse section of the duct. This flow may be either laminar or turbulent. viscous leak—a leak of such geometric configuration that gas flow through it is viscous in nature; that is, the flow obeys Poiseuille’s Law. The flow rate is proportional to the difference of the squares of the end pressures, and inversely proportional to the gaseous viscosity. Section F: Liquid Penetrant Testing (PT) Terms The terms defined in Section F are the direct responsibility of Subcommittee E07.03 on Liquid Penetrant and Magnetic Particle Methods. angstrom unit (Å)—a unit of length which may be used to express the wavelength of electromagnetic radiation, that is, light. One− 9angstrom unit is equal to 0.1 nanometres. (1 nm = 10 m.) background—the surface of the test part against which the indication is viewed. It may be the natural surface of the test part or the developer coating on the surface. black light—see UV-A. black light filter—see UV-A pass filter. bleedout—the action of an entrapped liquid penetrant in surfacing from discontinuities to form indications. blotting—the action of the developer in soaking up the penetrant from the discontinuity to accelerate bleedout. carrier—a liquid, either aqueous or nonaqueous, in which liquid penetrant testing materials are dissolved or suspended. class—the descriptive term for categorizing solvent removers with similar characteristics. detergent remover—a penetrant remover that is a solution of a detergent in water. developer—a material that is applied to the test surface to accelerate bleedout and to enhance the contrast of indications. developer, aqueous—a suspension of developer particles in water. developer, dry powder—a fine free-flowing powder used as supplied. developer, liquid film—a suspension of developer particles in a vehicle which leaves a resin/polymer film on the test surface after drying. developer, non-aqueous—developer particles suspended in a nonaqueous vehicle prior to application. developer, soluble—a developer completely soluble in its carrier, not a suspension of powder in a liquid, which dries to an absorptive coating. contaminant—any foreign substance present on the test surface or in the inspection materials which will adversely affect the performance of liquid penetrant materials. developing time—the elapsed time between the application of the developer and the examination of the part. When no developer is to be applied, the developing time is considered the elapsed time since the component is dry after the penetrant removal process. contrast—the difference in visibility (brightness or coloration) between an indication and the background. dragout—the carryout or loss of penetrant materials as a result of their adherence to the test pieces. clean—free of contaminants. drain time—that portion of the dwell time during which the excess penetrant or emulsifier drains from the part. drying oven—an oven used for increasing the evaporation rate of rinse water or an aqueous developer vehicle from test parts. drying time—the time required for a cleaned, rinsed or wet developed part to dry. dwell time—the total time that the penetrant or emulsifier is in contact with the test surface, including the time required for application and the drain time. electrostatic spraying—a technique for attaining a uniform coating in which the material sprayed is given an electrical charge. eluant—a liquid used to extract one material from another, as in chromatography. emulsification time—the time that an emulsifier is permitted to remain on the part to combine with the surface penetrant prior to removal. Also called emulsification dwell time. emulsifier—a liquid that interacts with an oily substance to make it water-washable. emulsifier, hydrophilic—a water-based liquid used in penetrant testing, which interacts with the penetrant oil rendering it water-washable. emulsifier, lipophilic—an oil based liquid used in penetrant testing, which interacts with the penetrant oil rendering it water-washable. etching—the removal of surface material by chemical or electrochemical methods. family—a complete series of penetrant materials required for the performance of a liquid penetrant testing. flash point—the temperature at which a vapor will ignite in the presence of an ignition source. fluorescence—the emission of visible light by a substance as a result of, and only during, the absorption of UV-A or other excitation source. footcandle (fc)—the illumination on a surface, 1 ft2 in area, on which is uniformly distributed a flux of 1 lm (lumen). It equals 10.8 lm/m2. form—the descriptive term for categorizing developers with similar characteristics. hold out sample—a sample of unused penetrant, emulsifier, or developer, or a combination of the three, set aside for future use in comparison testing. hydrophilic emulsifier—see emulsifier. immersion rinse—a means of removing excess surface penetrant in which the test part, test piece, or both, is immersed in an agitated tank of water. inspection—visual examination of the test part after completion of the liquid penetrant processing steps. known defect standard—a test piece with one or more defects used to verify the condition of the penetrant process. DISCUSSION—This test piece is used daily to verify the penetrant application, the removal of excess surface penetrant, the application of developer, the number and color of the indications that are produced. lipophilic emulsifier—see emulsifier lipophilic. liquid penetrant examination—see liquid penetrant testing. liquid penetrant testing—a nondestructive test that uses liquid penetrant materials to penetrate and detect various types of discontinuities open to the surface. overemulsification—excessive emulsifier dwell time which results in the removal of penetrants from some discontinuities. overwashing—too long or too vigorous washing, or both, which results in removal of penetrants from some discontinuities. penetrant—a solution or suspension of dye. penetrant comparator—an intentionally flawed specimen having separate but adjacent areas for the application of different liquid penetrant materials so that a direct comparison of their relative effectiveness can be obtained. DISCUSSION—It can also be used to evaluate liquid penetrant techniques, liquid penetrant systems, or test conditions. penetrant, fluorescent—a penetrant that fluoresces when excited by UV-A. penetrant, post emulsifiable—a liquid penetrant that requires the application of a separate emulsifier to render the excess surface penetrant water-washable. penetrant, solvent-removable—a liquid penetrant so formulated that most of the excess surface penetrant can be removed by wiping with a lint-free material, with the remaining surface penetrant traces removable by further wiping with a lint-free material lightly moistened with solvent remover. penetrant, visible—a liquid penetrant that is characterized by an intense color, usually red. penetrant, water-washable—a liquid penetrant with a built-in emulsifier. penetration time—same as dwell time. pooling—the existence of excessive amounts of penetrant, emulsifier or developer in an incompletely drained area. post-cleaning—the removal of residual liquid penetrant testing materials from the test part after the penetrant examination has been completed. post emulsification—a penetrant removal technique employing a separate emulsifier. precleaning—the removal of surface contaminants from the test part so that they will not interfere with the examination process. reference materials—the standard penetrant materials against which candidate materials for qualification are compared. rinse—the process of removing liquid penetrant testing materials from the surface of a test part by means of washing or flooding with another liquid, usually water. The process is also termed wash. sensitivity level—the descriptive term for identifying the capability of a penetrant system to indicate the presence of a surface-connected discontinuity. Ranging from 1⁄ 2 (ultra low) to 4 (ultra high). solvent remover—a volatile liquid used to remove excess penetrant from the surface being examined. temperature envelope—the temperature range over which a particular penetrant inspection test will operate. UV-A pass filter—a filter that transmits UV-A while absorbing other wavelengths. UV fading—the reduction of brightness of a fluorescent penetrant indication caused by excessive exposure to ultraviolet radiation. viscosity—the property of a fluid that presents a resistance to shearing flow. visible light—electromagnetic radiation in the 400 to 760 nm (4000 to 7600 Å) wavelength range. visual adaptation—the adjustment of the eyes when one passes from a bright to a darkened place. type—the descriptive term for designating a penetrant as either fluorescent (type 1) or visible (type 2). wash—same as rinse. water tolerance—the amount of water that a penetrant or emulsifier can absorb before its effectiveness is impaired. UV-A—electromagnetic radiation in the near-ultraviolet wavelength range, 320 to 400 nm (3200 to 4000 Å). wetting action—the ability of a liquid to spread over and adhere to solid surfaces. DISCUSSION—UV-A may also be referred to as “UV-A light” or “UV-A radiation.” Sources producing UV-A typically have a peak emission (radiation) intensity at 365 nm (3650 Å). white light—see visible light. Section G: Magnetic Particle Testing (MT) Terms The terms defined in Section G are the direct responsibility of Subcommittee E07.03 on Liquid Penetrant and Magnetic Particle Methods. ammeter shunt—a low-resistance precision resistor with high current carrying capacity connected in parallel with an ammeter. coil method—a method of magnetization in which part, or whole, of the component is encircled by a current-carrying coil. ampere turns—the product of the number of turns of a coil and the current in amperes flowing through the coil. coil technique—a technique of magnetization in which all, or a portion, of the part is encircled by a current-carrying coil. arc strikes—localized burn damage to a part from an arc caused by making or breaking an energized electrical circuit. conditioning agent—an additive to water suspensions that imparts specific properties such as: proper wetting, particle dispersion, corrosion resistance, biological resistance, or foam inhibition. background—the appearance of the surface of the test part against which indications are viewed. bath—see suspension. bipolar field—see field, bipolar. black light—see UV-A black light filter—see UV-A pass filter. carrier fluid—the fluid in which fluorescent and nonfluorescent magnetic particles are suspended to facilitate their application. central conductor—a conductor passed through a hollow part and used to produce circular magnetization within the part. circular field—see field, circular. circular magnetization—the magnetization in a part resulting from current passed directly through the part or through a central conductor. coercive force—the magnetizing force at which the magnetic flux density is equal to zero. The corresponding field intensity value is indicative of the ease of difficulty or demagnetization. contact head—electrode assembly used to clamp and support a part to facilitate passage of electrical current through the part for circular magnetization. contact pad—replaceable metal pad, usually of copper braid, placed on electrodes to give good electrical contact, thereby preventing damage, such as arc strikes, to the part under test. continuous method—a method wherein the indicating medium is applied while the magnetizing force is present. core (of an electromagnetic inspection circuit)—that part of the magnetic circuit which is within the electrical winding. Curie point—the temperature at which ferromagnetic materials can no longer be magnetized by outside forces, and at which they lose their residual magnetism (approximately 1200 to 1600 °F (649 to 871 °C) for many metals). current flow method—a method of magnetizing by passing a current through a component via prods or contact heads. The current may be alternating, rectified alternating, or direct. current induction method—a method of magnetizing in which a circulating current is induced in a ring component by the influence of a fluctuation magnetic field that links the component. field, resultant magnetic—(sometimes called vector): a magnetic field that is the result of two magnetizing forces impressed upon the same area of a magnetizable object. dark adaptation—the adjustment of the eyes when one passes from a bright to a darkened place. field strength—see magnetic field strength. fill factor—the ratio of the cross sectional area of the part being tested to the cross sectional area of the encircling coil. demagnetization—the reduction of residual magnetism to an acceptable level. flash magnetization—magnetization by a current flow of very brief duration. diffuse indications—indications that are not clearly defined as, for example, indications of subsurface defects. flash point—the lowest temperature at which vapors above a volatile combustible substance ignite in air when exposed to a flame. direct contact magnetization—a technique of magnetizing in which the current is passed through a part via prods or contact heads. dry method—magnetic particle inspection in which the ferromagnetic particles employed are in the dry powder form. dry powder—finely divided ferromagnetic particles suitably selected and prepared for magnetic particle inspection. dry technique—the examination technique in which the ferromagnetic particles are applied in the dry powder form. electromagnet—a soft iron core surrounded by a coil of wire that temporarily becomes a magnet when an electric current flows through the wire. energizing cycle—the application of a magnetizing force to a conductor. examination medium—a powder or suspension of magnetic particles that is applied to a magnetized test surface to determine the presence or absence of surface or slightly subsurface discontinuities. ferromagnetic—a term applied to materials that can be magnetized or strongly attracted by a magnetic field. field, bipolar—longitudinal magnetic field within a part that has two poles. field, circular magnetic—generally, the magnetic field surrounding any electrical conductor or part resulting from a current being passed through the part or conductor from one end to another. fluorescence—the emission of visible light by a substance as a result of, and only during, the absorption of UV-A or other excitation source. fluorescent examination method—the magnetic particle examination method employing a finely divided fluorescent ferromagnetic inspection medium. fluorescent magnetic particle inspection—the magnetic particle inspection process employing a finely divided fluorescent ferromagnetic inspection medium that fluoresces when activated by UV-A or other excitation source. flux density, magnetic—the strength of a magnetic field, expressed in flux lines per unit area. flux leakage field—the magnetic field that leaves or enters the surface of a part as the result of a discontinuity or a change in section. flux lines—see lines of force. flux penetration—the depth to which a magnetic flux exists in a part. footcandle (fc)—the illumination on a surface with an area of 1 ft2, on which a flux of 1 lm (lumen) is uniformly distributed. 1 fc is equal to 10.76 lux (lm/m2). full-wave direct current (FWDC)—a rectified three-phase alternating current. field, longitudinal magnetic—magnetic field wherein the flux lines traverse the component in a direction essentially parallel with its longitudinal axis. full-wave rectified current (FW)—this waveform is the result of rectifying a sinusoidal input by inverting the negative half-cycle of the sine wave so that the output contains two half-sine pulses for each input. This process may be applied to either single-phase or three-phase alternating current. Each can also be stated as full wave rectified alternating current. field, magnetic—the space, within and surrounding a magnetized part or a conductor carrying current, in which the magnetic force is exerted. furring—buildup or bristling of magnetic particles due to excessive magnetization of the component under examination resulting in a furry appearance. field, magnetic leakage—the magnetic field that leaves or enters the surface of a part at a discontinuity or change in section configuration of a magnetic circuit. gaussmeter, n—a device that measures magnetic flux density or magnetic induction (a quantity directly related to magnetic field strength or magnetic force); also known as a Tesla Meter or Magnetometer. field, residual magnetic—the field that remains in a piece of magnetizable material after the magnetizing force has been removed. gaussmeter (electronic), n—a gaussmeter that uses a hall effect probe to measure magnetic flux density. half-wave current (HW)—a rectified single-phase alternating current that produces a pulsating unidirectional field. or discontinuities due to the distortion of the magnetic lines of force in those areas. hall effect—a phenomenon in which a transverse electric field is produced in a current–carrying conductor placed in a magnetic field. magnetic particle field indicator—an instrument, typically a bi-metal (for example, carbon steel and copper) octagonal disk, containing artificial flaws used to verify the adequacy or direction, or both, of the magnetizing field. hysteresis—(1) the lagging of the magnetic effect when the magnetic force acting upon a ferromagnetic body is changed; (2) the phenomenon exhibited by a magnetic system wherein its state is influenced by its previous history. indirect magnetization—magnetization induced in a part when no direct electrical contact is made. induced current method—see current induction method. induced field—see indirect magnetization. inherent fluorescence—fluorescence that is an intrinsic characteristic of a material. inspection medium—see examination medium. leakage field—see field, magnetic leakage. leeches—permanent magnets or electromagnets that are attached to the electrodes carrying magnetizing current and that are strong enough to hold electrode contact firmly. light intensity—the light energy reaching a unit area of surface per unit time. lines of force—a conceptual representation of magnetic flux based upon the line pattern produced when iron filings are sprinkled on paper laid over a permanent magnet. local magnetization—magnetization of a prescribed volume or surface of a part. longitudinal magnetization—a magnetic field wherein the lines of force traverse the part in a direction essentially parallel with its longitudinal axis. magnet, permanent—see permanent magnet. magnetic field—the volume within and surrounding either a magnetized part or a current-carrying conductor wherein a magnetic force is exerted. magnetic field indicator—a pocket meter that is used to locate or determine the relative intensity of leakage field emanating from a part. magnetic field meter—an instrument designed to measure the flux density of magnetic fields. magnetic field strength—the measured intensity of a magnetic field at a point, expressed in oersteds or amperes per metre. magnetic hysteresis—in a magnetic material, as iron, a lagging in the values of resulting magnetization due to a changing magnetic force. (See also hysteresis.) magnetic particle examination—see magnetic particle testing. magnetic particle examination flaw indications—the accumulation of ferromagnetic particles along the areas of flaws magnetic particles—finely divided ferromagnetic material capable of being individually magnetized and attracted to distortion in a magnetic field. magnetic particle testing—a nondestructive test method utilizing magnetic leakage fields and suitable indicating materials to disclose surface and near-surface discontinuity indications. magnetic pole—one of two or more areas of flux leakage on a part. magnetic writing—a form of nonrelevant indication sometimes caused when the surface of a magnetized part comes in contact with another piece of ferromagnetic material. magnetization, circular—see field, circular. magnetization, longitudinal—see field, longitudinal. magnetizing current—the flow of either alternating or direct current used to induce magnetism into the part being inspected. magnetizing force—the magnetizing field applied to a ferromagnetic material to induce magnetization. multidirectional magnetization—the alternative application of magnetic fields in different directions during the same time frame. near surface discontinuity—a discontinuity not open to, but lying near, the surface of a part undergoing examination which produces broad, fuzzy, lightly held powder patterns. overall magnetization—magnetization of an entire part with a single energizing cycle. parallel magnetism—a form of induced magnetism that introduces a distorted field into the part under examination. It is derived from placing an external current carry conductor adjacent and parallel to the part under examination. permanent magnet—a magnet that retains a high degree of magnetization virtually unchanged for a long period of time (characteristic of materials with high retentivity). permeability—the ratio of flux density produced to magnetizing force (the ease with which a material can become magnetized). pole—the area on a magnetized part from which the magnetic field is leaving or returning into the part. polymer technique—the examination technique in which a polymer is used as the particle suspension vehicle. powder—see dry powder. powder blower—a compressed air device used to apply magnetic powder over the surface of a part undergoing inspection. prods—hand-held electrodes. quick break—a sudden interruption of the magnetizing current. residual magnetic field—the field that remains in ferromagnetic material after the magnetizing force has been removed. residual technique—the application of the magnetic particles after the magnetizing force has been discontinued. resultant field—see field, resultant. retentivity—the ability of a material to retain a portion of the applied magnetic field after the magnetizing force has been removed. saturation, magnetic—the total magnetization produced in a ferromagnetic material, at which point the incremental permeability has progressively decreased to approach unity. sensitivity—the degree of capability of a magnetic particle examination technique for indicating surface or near surface discontinuities in ferromagnetic materials. shot—a short energizing cycle in a magnetic particle examination. shunt meter test set—this device minimally consists of a specially prepared current shunt and the accompanying meter for measuring high current magnetizing pulses used in the magnetic particle examination process. These kits may contain either an analog or digital read-out style meter and may or may not be specifically designed to be used with one magnetizing waveform. These kits may be designed to display specific engineering units for each waveform type such as readings displayed in peak, RMS, or average. It is acceptable for a mathematical formula to be applied to the displaced value to derive the amperage units desired. skin effect—the phenomenon that causes the magnetization produced by alternating current to be contained near the surface of a ferromagnetic part. solenoid—an electrical conductor formed into a coil. subsurface discontinuity—any defect that does not open onto the surface of the part in which it exists. surge magnetization—use of a high initial current for a short period (less than a second), then a continuous reduced current while the inspection medium is applied. suspension—a two-phase system consisting of a finely divided solid dispersed in a liquid. swinging field—see multidirectional magnetization. tangential field—a magnetic field at an object’s surface, parallel and contiguous to the surface. This field may be either circular or longitudinal in direction. test piece—a specimen containing known artificial or natural defects used for checking the efficiency of magnetic particle flaw detection processes. test ring—a ring specimen containing artificial subsurface discontinuities which is used to evaluate and compare the overall performance and sensitivity of magnetic particle examination techniques. through-coil technique—see coil technique. true continuous technique—magnetic particle examination in which the magnetizing current is applied prior to the application of the magnetic particles and is maintained without interruption throughout the examination. UV-A—electromagnetic radiation in the near-ultraviolet wavelength range, 320 to 400 nm (3200 to 4000 Å). DISCUSSION—UV-A may also be referred to as “UV-A light” or “UV-A radiation.” Sources producing UV-A typically have a peak emission (radiation) intensity at 365 nm (3650 Å). UV-A pass filter—a filter that transmits UV-A while absorbing other wavelengths. vehicle—a liquid medium for the suspension of magnetic particles. visible light—electromagnetic radiation in the 400 to 760 nm (4000 to 7600 Å) wavelength range. water break test—a quality control test of conditioned water. wet slurry technique—a technique in which the magnetic particles are suspended in a high-viscosity vehicle. wet technique—the examination technique in which the magnetic particles are suspended in a liquid vehicle. white light—see visible light. yoke—a magnet that induces a magnetic field in the area of a part that lies between its poles. Yokes may be permanent magnets or either alternating-current or direct-current electromagnets. yoke magnetization—a longitudinal magnetic field induced in a part, or in an area of a part, by means of an external electromagnet shaped like a yoke. Section H: Neutron Radiologic Testing (NRT) Terms The terms defined in Section H are the direct responsibility of Subcommittee E07.05 on the Radiology (Neutron) Method. Additional radiological terms can be found in Section D. activation—the process of causing a substance to become artificially radioactive by subjecting it to bombardment by neutrons or other particles. attenuation coefficient—related to the rate of change in the intensity of a beam of radiation as it passes through matter. (See linear and mass attenuation coefficient.) attenuation cross section—the probability, expressed in barns, that a neutron will be totally absorbed by the atomic nucleus. barn—a unit of area used for expressing the area of nuclear cross sections. 1 barn 5 10 224 cm2 (3) cadmium ratio—the ratio of the neutron reaction rate measured with a given bare neutron detector to the reaction rate measured with an identical neutron detector enclosed by a particular cadmium cover and exposed in the same neutron field at the same or an equivalent spatial location. DISCUSSION—In practice, meaningful experimental values can be obtained in an isotropic neutron field by using a cadmium filter approximately 1-mm thick. cassette—a light-tight device for holding film or conversion screens and film in close contact during exposure. contrast agent—a material added to a component to enhance details by selective absorption of the incident radiation. conversion screen—a device that converts the imaged neutron beam to radiation or light that exposes the radiographic film. cross section—the apparent cross-sectional area of the nucleus as calculated on the basis of the probability of occurrence of a reaction by collision with a particle. It does not necessarily coincide with the geometrical cross-sectional area πr 2. It is given in units of area, 1 barn = 10−24 cm2. L/D ratio—one measure of the resolution capability of a neutron radiographic system. It is the ratio of the distance between the entrance aperture and the image plane (L) to the diameter of the entrance aperture (D). linear attenuation coefficient—a measure of the fractional decrease in radiation beam intensity per unit of distance traveled in the material (cm −1). low-energy photon radiation—gamma- and X-ray photon radiation having energy less than 200 keV (excluding visible and ultraviolet light). mass attenuation coefficient—a measure of the fractional decrease in radiation beam intensity per unit of surface density cm 2·gm−1. moderator—a material used to slow fast neutrons. Neutrons are slowed down when they collide with atoms of light elements such as hydrogen, deuterium, beryllium, and carbon. NC—effective thermal neutron content or neutron radiographic contrast. NC is the percent background film exposure due to unscattered thermal neutrons. neutron—a neutral elementary particle having an atomic mass close to 1. In the free state outside of the nucleus, the neutron is unstable having a half-life of approximately 10 min. neutron imaging, n—the process, science, and application of producing images (physically or in the form of data) of objects and phenomena by the means of neutron radiation. direct exposure imaging—in the direct exposure imaging method, the conversion screen and image recorder are simultaneously exposed to the neutron beam. neutron radiography—the process of producing a radiograph using neutrons as the penetrating radiation. electron volt—the kinetic energy gained by an electron after passing through a potential difference of 1 V. object scattered neutrons—neutrons scattered by the test objects that contribute to the film exposure. facility scattered neutrons—neutrons scattered in the facility that contribute to the film exposure. P—effective pair production content. P is the percent background exposure caused by pair production in 2 mm of lead. γ—effective gamma content. γ is the percent background film darkening caused by low-energy photon radiation absorbed by pair production in 2 mm of lead. pair production—the process whereby a gamma photon with energy greater than 1.02 MeV is converted directly into matter in the form of an electron-positron pair. Subsequent annihilation of the positron results in the production of two 0.511 MeV gamma photons. gamma ray—electromagnetic radiation having its origin in an atomic nucleus. half-life—the time required for one half a given number of radioactive atoms to undergo decay. half-value layer—the thickness of an absorbing material required to reduce the intensity of a beam of incident radiation to one-half of its original intensity. image quality indicator—a device or combination of devices whose image or images on a neutron radiograph provide visual or quantitative data, or both, concerning the radiographic sensitivity of the particular neutron radiograph. indirect exposure—a method in which only a gammainsensitive conversion screen is exposed to the neutron beam. After exposure, the conversion screen is placed in contact with the image recorder. process control radiograph—a radiograph which images a beam purity indicator and sensitivity indicator under identical exposure and processing procedures as the test object radiograph. A process control radiograph may be used to determine image quality parameters in circumstances of large or unusual test object geometry. radiograph—a permanent, visible image on a recording medium produced by penetrating radiation passing through the material being tested. radiographic inspection—the use of X-rays or nuclear radiation, or both, to detect discontinuities in material, and to present their images on a recording medium. radiography—the process of producing a radiograph using penetrating radiation.