Types and methods of flaw detection. Classification

Physical non-destructive methods are widely used for flaw detection of building structures and joints. They are also used in the examination and control of products to identify hidden defects.

The most widely used methods of flaw detection: ultrasonic, x-ray, radiation, magnetic and electromagnetic, capillary, radio wave, thermal and optical.

IN ultrasonic methods flaw detection uses the property of ultrasonic vibrations to propagate in a homogeneous medium and be reflected at the boundary of two media or at the area of ​​discontinuity. Ultrasonic methods are used for flaw detection of reinforced concrete and metal structures in order to detect internal cracks, voids, large pores, foreign inclusions and delaminations; are used to control welded joints made of low-carbon and low-alloy steels, aluminum and its alloys, as well as plastics. Among the methods of ultrasonic flaw detection, the shadow and pulse echo methods are the most common.

Shadow the method is based on the attenuation of the ultrasonic pulse in the presence of a defect that forms an ultrasonic shadow inside the structure. When sounding through the element on the screen of the cathode-ray tube, the phase of the oscillations changes and the magnitude of the signal entering the receiving head decreases (Fig. 4.1 a, b).

Pulse echo method consists in sending and reflecting ultrasonic pulses from the border of the product or defect (Fig. 4.1, V, G). Test heads of the combined type alternately perform the function of the emitter and receiver of ultrasound. At the moment of sending the pulse, the initial signal appears on the screen of the cathode-ray tube - a surge of the pulse in the left corner. The bottom echo signal is shifted to the right relative to the initial one by the time of passage and reflection of the pulse from the bottom face of the element. If a defect is encountered along the pulse path, the signal from it is reflected earlier. The height of the burst and its location between the initial and bottom signals characterize the size and depth of the defect.

Rice. 4.1. Scheme of ultrasonic flaw detection:

A- shadow method in the absence of a defect; b- if there is a defect;

V- echo method in the absence of a defect; G- if there is a defect;

H- initial signal; P- the signal entering the receiving head;

D- bottom echo signal; Df- defect signal

For ultrasonic flaw detection of building structures, other methods are also used: resonant, shock wave, traveling wave and free vibrations.

X-ray and radiation methods of scanning controlled elements with X-ray or gamma rays (Fig. 4.2) and recording the uneven attenuation of the rays by photographic, visual or ionization methods make it possible to determine not only the size and depth of defects, but also their nature by the degree of blackening of the X-ray film, by visual comparison of the image contrast with a standard of sensitivity or intensity of radiation measured by an ionization counter.

X-ray and radiation methods are used for flaw detection of welded joints made of metals and plastics. They allow you to identify lack of penetration, shells, pores, cracks, slag and gas inclusions, study the structure of the metal and determine the type of crystal lattice.

Magnetic methods controls are based on the registration of magnetic fields formed in the defect zone of ferromagnetic elements after their magnetization (Fig. 4.3). These methods are most often used to control the quality of welds in metal structures. Among the magnetic methods, the most widespread are: magnetic particle, magnetographic, magnetoferrosonde, induction and magnetic semiconductor. A highly sensitive electromagnetic method with the excitation of eddy currents has been developed for sorting metal by grades and identifying internal defects.

Rice. 4.2. Scheme of X-ray or radiation flaw detection:

1- source of radiation; 2 - diaphragm; 3 - rays; 4 - controlled

element; 5 - defect; 6 - x-ray film; 7 - image of the defect on the film

Rice. 4.3. Magnetic flux in a defective weld:

1 - controlled element; 2 - welded seam;

3 - defect; 4 - magnetic lines; 5 - electromagnet

Capillary methods flaw detection is associated with the penetration of the indicator liquid into surface defects of welded structures made of metals and plastics. These methods can be divided into three types: 1) color with the use of an indicator liquid, giving a red defect pattern on a white background of the developer; 2) luminescent with the use of a luminescent liquid that glows under the action of ultraviolet rays; 3) luminescent-color, which allows to detect defects in daylight and in ultraviolet light without the use of optical instruments.

Various phosphors are used as indicator liquids, for example, Lum-6 or a solution consisting of kerosene (volume fraction 50%), gasoline (25%), transformer oil (25%), aniline or other dye (0.03%). It is more convenient to apply liquids in aerosol packaging. The method of capillary flaw detection includes: degreasing the controlled surface; application of indicator liquid with subsequent removal of its excess; applying a developing liquid or a dry developer; interpretation of control results.

radio wave flaw detection methods are based on the use of radio waves of ultrahigh frequency - microwave range. These methods are used to control the quality of thin products made of plastics, wood and concrete.

Radio wave control is carried out by methods of reflected radiation (echo method) or transmitted radiation (shadow method) and allows you to fix the smallest defects in the product and the nature of their development over time by changing the phase, amplitude or features of the polarization of radio waves.

Thermal control methods are based on changing the nature of thermal contrasts in the presence of defects in the element. Radiated or reflected heat is measured with infrared radiometers. Thermal images of the object under study can also be converted into visible ones using liquid-crystal compounds for this, which makes it possible to use thermal methods for a qualitative assessment of controlled products.

Optical methods based on the registration of light or infrared radiation are less sensitive than radio waves. However, the advent of lasers made it possible to use them for high-precision measurements.

Holography is a method of obtaining an image of an object based on the interference of coherent waves. Coherent waves are called waves of the same length, the phase difference of which does not change with time.

Holographic methods can fix both the amplitude and phase of oscillations, and then reproduce them at any time in the form of a hologram. To do this, the laser beam is directed to the element under study. The light scattered by the laser hits the photographic film. Part of the light waves is also reflected on it by an opaque mirror (Fig. 4.4). Due to the superposition of light waves on the film, an interference pattern of the element appears, which remains unchanged if its position does not change. If the resulting hologram is illuminated with a laser beam of the same frequency that was received during the initial observation, we will obtain a reconstructed holographic image of the element. The imposition of a force, ultrasonic, thermal or radio wave field on the element under study leads to a change in the interference pattern on the hologram.

Holographic methods can be used to measure deformations of an element and record the smallest structural changes in materials. When comparing reference holograms of defect-free products with those obtained for controlled elements, existing defects are detected with high accuracy.

Rice. 4.4. Scheme:

A- obtaining a hologram; b- reproduction of the hologram;

1- laser; 2 - element under study; 3 - mirror;

4 - hologram; 5 - reproduction of the element; 6 - observer

LECTURE 5. NON-DESTRUCTIVE TESTING METHODS

Methods using penetrating media.

These are methods for monitoring the tightness of connections in tanks, gas tanks, pipelines and other similar structures. There are methods of leak detection and capillary.

Leak detection methods.

1. Water test. The container is filled with water to a mark slightly higher than the operational one, and the condition of the seams is monitored. In closed vessels, the liquid pressure can be increased by additional injection of water or air. The state of the seam can also be checked with a strong jet of water from a fire hose at a pressure of 1 atm, directed normally to the surface of the seam.

2. Kerosene test. Due to its low viscosity and low surface tension compared to water, kerosene easily penetrates through the smallest pores. If the surface of the seam on one side is abundantly moistened with kerosene, and the opposite side is whitewashed in advance with an aqueous solution of chalk, then if there is a defect, characteristic rusty spots will appear on a light background.

3. Test with compressed air. The seam on one side is coated with soapy water, and on the opposite side it is blown with compressed air under a pressure of 4 at.

4. Vacuum test. The seam on one side is coated with soapy water. Then, a metal cassette is attached to the seam on the same side in the form of a flat box without a bottom, but bordered on the bottom with a rubber gasket, with a transparent top. A vacuum pump creates a slight vacuum in the cassette.

capillary method.

A special liquid (indicator penetrant) is applied to the structure, which fills the cavities of surface defects under the action of capillary forces. The liquid is then removed from the surface of the structure. If there was powder in the liquid, then it will be filtered out and accumulate in defects; when using a liquid without powder, after removing the liquid, a developer is applied to the structure - chalk (in the form of a powder or an aqueous suspension), which reacts with the liquid in defects and forms an indicator pattern of high color contrast. When using reagents, even patterns are formed that can luminesce in ultraviolet rays and in daylight.

acoustic methods.

Ultrasonic method.

Defect control is carried out with the help of through-sounding of the object. In areas without defects, the speed of the ultrasonic wave does not decrease, and in the area with defects containing air, the wave completely attenuates or its speed noticeably decreases.

Quality control of welded joints of butt joints is carried out as follows. To detect slag inclusions, shells, gas pores, cracks, lack of penetration, the echo method is most often used, when the source and receiver of waves are combined in one transducer (the wave is started and received alternately). The transducer is prismatic, which allows you to start and receive a wave at an angle to the vertical. Move the transducer zigzag along the weld. The reflection of the wave from the opposite face of structural elements connected by welding (the wave velocity, on the forward and reverse path of which the defect may have been encountered) is compared with the reference reflections (velocities) obtained on pre-welded reference fragments of joints with artificially made defects.

Acoustic emission method is based on the registration of acoustic waves in a metal during its plastic deformation.

By recording the speed of wave movement, it is possible to detect the accumulation of dangerous damage (zones of stress concentration) in the process of loading structures and their operation. Special equipment "hears" the crackle of metal.

Methods using ionizing radiation.

radiographic method using X-ray or -radiation:

When transilluminated, the defect is projected onto the film in the form of a dark spot, from which it is possible to determine the position of the defect in the plan and its magnitude in the direction perpendicular to the transillumination direction. The magnitude of the defect in the transmission direction is judged by comparing the intensity of the darkening of the spot with the intensities of the darkenings obtained on the film from cuts of different depths on the sensitivity standard. The depth of the defect is determined by shifting the radiation source parallel to the film and starting the flow at a new angle to it, as already described for concrete structures.

Starting the flow at a new angle has another goal: to reveal defects that are elongated perpendicular to the original flow direction, intersected by it along a shorter distance and, as a result, remained “unnoticed”.

Magnetic, electrical and electromagnetic methods.

Magnetic methods are based on the registration of stray fields above defects or on the determination of the magnetic properties of controlled products. Distinguish methods: magnetic particle, magnetographic, fluxgate, Hall transducer, induction and ponderomotive.

Magnetic particle method. Any ferromagnetic part consists of very small spontaneously magnetized areas - domains. In the demagnetized state, the magnetic fields of the domains are arbitrarily directed and compensate each other; the total magnetic field of the domains is equal to zero. If the part is placed in a magnetizing field, then under its influence the fields of individual domains are set in the direction of the external field, the resulting magnetic field of the domains is formed, and the part is magnetized.

The magnetic flux in the defect-free zone propagates in a straight line in the direction of the resulting magnetic field. If the magnetic flux encounters an open or hidden defect (a layer of air or a non-ferromagnetic inclusion), then it encounters a large magnetic resistance (a region with reduced magnetic permeability), the magnetic flux lines are bent and some of them come to the surface of the structure. Where they leave the structure and enter it, local poles N, S and a magnetic field appear above the defect.

If the magnetizing field is removed, the local poles and the magnetic field above the defect will still remain.

The greatest perturbing effect and the largest local magnetic field will cause a defect oriented perpendicular to the direction of the magnetic flux lines. If a current is simultaneously passed through the structure under study, direct and alternating, this will create a variable direction of magnetization and reveal differently oriented defects.

To register local magnetic fields over defects, finely ground iron minium, scale, etc. are used, choosing the color of the powder as contrasting with the color of the previously cleaned surface of the structure; the powder is applied dry (spraying) or in the form of a suspension - water (which is preferable for building structures) or kerosene-oil. Due to magnetization and attraction of powder particles to each other, it settles over defects in the form of noticeable accumulations.

To register local magnetic fields (defects) in welds, use magnetographic method. Magnetization is carried out by a solenoid, the turns of which are parallel to the seam on both sides; a magnetic tape (similar to that used in sound recording, but slightly wider) is superimposed on the seam. The local magnetic field will be recorded on the tape. Listen to the recording on the audio indicator.

Ferroprobe method is based on the conversion of the magnetic field strength into an electrical signal. Moving two probes over the surface of the structure after its demagnetization, they look for local magnetic fields above the defects; the electromotive force arising in these places will be fixed by the device.

hall effect lies in the fact that if a rectangular plate of a semiconductor (germanium, antimonite, indium arsenide) is placed in a magnetic field perpendicular to the intensity vector and a current is passed through it in the direction from one face to the opposite opposite, then an electromotive force proportional to the intensity will appear on the other two faces magnetic field. Plate dimensions 0.7x0.7 mm, thickness 1 mm. Local magnetic fields above defects are sought out by moving the device along the structure after its demagnetization.

induction method. Searching for local magnetic fields over defects in welds is carried out using a core coil, which is powered by alternating current and is an element of a bridge circuit. The electromotive force arising above the defect is amplified and converted into an audio signal or fed to a recorder or oscilloscope.

ponderomotive method. An electric current flows through the frame of the device, forming a magnetic field around itself. The device is installed on a railway rail subjected to magnetization by an external magnetic field. Magnetic fields interact with each other, the frame rotates and takes some position. When moving along the rail and detecting a scattering flux over a defect, the frame changes its initial position.

1. Defectoscopy is a set of physical methods that allow to control the quality of materials, semi-finished products, parts and components of vehicles without destroying them. Methods of flaw detection make it possible to evaluate the quality of each individual part and carry out their complete (100%) control.

The task of flaw detection, along with the detection of defects such as cracks and other discontinuities, is to control the dimensions of individual parts (usually with one-sided access), as well as to detect leaks in specified areas. Flaw detection is one of the methods to ensure the safe operation of vehicles; the scope and choice of the type of flaw detection depend on the conditions of its operation.

2. Methods of flaw detection are based on the use of penetrating radiation (electromagnetic, acoustic, radioactive), the interaction of electric and magnetic fields with materials, as well as the phenomena of capillarity, light and color contrast. In the areas where defects are located in the material, due to changes in the structural and physical characteristics of the material, the conditions for its interaction with the indicated radiations, physical fields, as well as with substances applied to the surface of the controlled part or introduced into its cavity, change. By registering these changes with the help of appropriate equipment, it is possible to judge the presence of defects that represent a violation of the integrity of the material or the uniformity of its composition and structure, determine their coordinates and estimate the dimensions. With sufficiently high accuracy, it is also possible to measure the thickness of the walls of hollow parts and protective and other coatings applied to the products.

In the modern practice of the automotive industry and automotive service, the following methods of flaw detection of materials, semi-finished products, parts and assemblies have found application.

Optical methods- these are methods carried out visually (to detect surface cracks and other defects larger than 0.1 ... 0.2 mm) or using optical devices - endoscopes (Fig. 1), which allow detecting similar defects larger than 30 ... surfaces and hard to reach areas. Optical methods usually precede other methods and are used to control all parts of aircraft structures at all stages of manufacture and operation.

Rice. 1.

Examination with an endoscope is used, for example, to search for cracks on the inside of the side members of car frames.

radiation methods, using X-ray, gamma and other (for example, electrons) penetrating radiation of various energies, obtained using X-ray machines, radioactive isotopes and other sources, make it possible to detect internal defects larger than 1 ... 10% of the thickness of the translucent section in products with a thickness (for steel) up to 100 mm (when using X-ray equipment) and up to 500 mm (when using fast electrons). Radiation methods are used to control cast, welded and other parts of aircraft structures made of metallic and non-metallic materials, as well as to control defects in the assembly of various assemblies (Fig. 2).

Rice. 2.

In the automotive industry, radiation flaw detection is used to control the quality of liners and pistons.

Radio wave methods are based on changes in intensities, shifts in time or phase, and other parameters of electromagnetic waves in the centimeter and millimeter ranges when they propagate in products made of dielectric materials (rubber, plastics, and others). At a depth of 15...20 mm, it is possible to detect delaminations with an area of ​​more than 1 cm 2 .

In the automotive industry, the radio wave method measures the thickness of dielectric coatings

Thermal methods- these are methods that use infrared (thermal) radiation of a heated part to detect the inhomogeneity of its structure (discontinuity in multilayer products, in welded and soldered joints). The sensitivity of modern equipment (thermal imagers, Fig. 3) makes it possible to register a temperature difference on the surface of a controlled part of less than 1 °C.

Rice. 3.

In the automotive industry, thermal methods are used to control the quality of welds, for example, when welding air brake reservoirs.

Magnetic methods are based on the analysis of stray magnetic fields arising in the areas of location of surface and subsurface defects in magnetized parts made of ferromagnetic materials. Under optimal conditions, when the defect is located perpendicular to the direction of the magnetizing field, rather thin defects can be detected, for example, grinding cracks (in steel) with a depth of 25 µm and an opening of 2 µm. Magnetic methods can also measure, with an error not exceeding 1...10 µm, the thickness of protective (non-magnetic) coatings deposited on a part made of ferromagnetic material (Fig. 4).

In the automotive industry and automotive service, magnetic flaw detection is used to control the quality of grinding of critical parts, for example, crankshaft journals.

Acoustic (ultrasonic) methods- these are methods that use elastic waves of a wide frequency range (0.5 ... 25 MHz), introduced into the controlled part at different angles. Propagating in the material of the part, elastic waves attenuate to varying degrees, and when they encounter defects, they are reflected, refracted, and scattered. Analyzing the parameters (intensity, direction, and others) of transmitted and (or) reflected waves, one can judge the presence of surface and internal defects of various orientations larger than 0.5 ... 2 mm 2 . Control can be carried out with one-way access.

Rice. 4.

It is also possible to measure the thickness of hollow products with an error of no more than 0.05 mm (limitations are the significant curvature of the surface of the part and the strong attenuation of ultrasonic waves in the material). Acoustic methods (at low frequencies) can detect delaminations with an area of ​​more than 20 ... 30 mm 2 in glued and brazed structures with metal and non-metal fillers (including honeycomb), in laminated plastics, as well as in clad sheets and pipes. Using the so-called acoustic emission method, it is possible to detect developing (i.e., the most dangerous) cracks in the loaded elements of automotive units, selecting them from less dangerous, non-developing defects detected by other methods (Fig. 5). In this case, the control zones are formed using a different arrangement of sensors on the structure. Wire gauges are installed in the control zone so that their direction does not coincide with the direction of fatigue crack development.

Rice. 5.

Eddy current (electroinductive) methods are based on the interaction of eddy current fields, excited by a flaw detector sensor in a product made of electrically conductive material, with the field of the same sensor. These flaw detection methods allow in the automotive industry to detect discontinuities (cracks with a length of more than 1 ... 2 mm and a depth of more than 0.1 ... 0.2 mm, films, non-metallic inclusions), measure the thickness of protective coatings on metal, judge the inhomogeneities of the chemical composition and structure material, internal stresses. Equipment for testing by eddy current methods is highly productive and allows you to automate sorting.

Electrical Methods based on the use of mainly weak direct currents and electrostatic fields; they make it possible to detect surface and subsurface defects in products made of metallic and non-metallic materials and to distinguish between some grades of alloys. flaw detection technological product production

Capillary methods are based on the phenomenon of capillarity, that is, on the ability of certain substances to penetrate into small cracks. Treatment with such substances increases the color and light contrast of the part of the product containing surface cracks relative to the undamaged surface surrounding this part. These methods make it possible to detect surface cracks with an opening of more than 0.01 mm, a depth of 0.03 mm and a length of 0.5 mm in parts made of non-porous materials, including complex-shaped parts, when the use of other methods is difficult or excluded (Fig. .6).

Rice. 6.

In the automotive industry, capillary methods are used to control the quality of welds, for example in the manufacture of tanks. The above methods of flaw detection individually are not universal, and therefore the most critical parts are usually checked using several methods, although this leads to additional time. To improve the reliability of inspection results and labor productivity, automated systems are being introduced, including the use of computers to control inspection and process information received from flaw detector sensors.

DEFECTOSCOPY(from lat. defectus - a flaw, a flaw and the Greek skopeo - I consider, I observe) - a complex of physical. methods and means of non-destructive quality control of materials, blanks and products in order to detect defects in their structure. D. methods make it possible to more fully evaluate the quality of each product without destroying it and to carry out complete control, which is especially important for critical products. destinations, for which the methods of selective destructive testing are insufficient.

Non-compliance with the specified technol. parameters in the processing of complex chemical material. and phase composition, the impact of aggressive environments and exploitation. loads during storage of the product and during its operation can lead to the appearance of decomp. in the material of the product. kind of defects - discontinuities or homogeneity, deviations from a given chemical. composition, structure or dimensions that impair the performance of the product. Depending on the size of the defect in the area of ​​its location, physical changes change. material properties - density, electrical conductivity, magnetic, elastic characteristics, etc.

D.'s methods are based on the analysis of the distortions introduced by a defect in the physical devices applied to a controlled product. fields diff. nature and on the dependence of the resulting fields on the properties, structure and geometry of the product. Information about the resulting field allows you to judge the presence of a defect, its coordinates and size.

D. includes the development of non-destructive testing methods and equipment - flaw detectors, devices for testing, systems for processing and fixing the information received. Optical, radiation, magnetic, acoustic, electromagnet are used. (eddy current), electric and other methods.

Optical D. is based on direct. inspection of the surface of the product with the naked eye (visually) or with the help of optical. instruments (loupe, microscope). To inspect the inside surfaces, deep cavities and hard-to-reach places apply special. endoscopes are diopter tubes containing light guides made of fiber optics, equipped with miniature illuminators, prisms and lenses. Optical methods. D. in the visible range, only surface defects (cracks, films, etc.) can be detected in products made of materials that are opaque to visible light, as well as surface and internal defects. defects - in transparent. Min. the size of the defect, visually detected by the naked eye, is 0.1-0.2 mm, when using optical. systems - tens of microns. Projectors, profilometers and microinterferometers are used to control the geometry of parts (eg, thread profile, surface roughness). The new implementation of the optical A method that makes it possible to significantly increase its resolution is laser D., which uses the diffraction of a coherent laser beam with indication using photoelectronic devices. When automating optical control methods are used by television. image transmission.

Radiation D. is based on the dependence of the absorption of penetrating radiation on the length of the path traveled by it in the material of the product, on the density of the material and the atomic number of the elements that make up it. The presence in the product of discontinuities, foreign inclusions, changes in density and thickness leads to decomp. weakening of the rays in decomp. its sections. By registering the distribution of the intensity of the transmitted radiation, you can get information about the internal. product structure, including judging the presence, configuration and coordinates of defects. In this case, penetrating radiation decomp can be used. hardness: roentgen. radiation with energies of 0.01-0.4 MeV; radiation received in linear (2-25 MeV) and cyclic. (betatron, microtron 4-45 MeV) accelerators or in an ampoule with -active radioisotopes (0.1-1 MeV); gamma radiation with energies of 0.08-1.2 MeV; neutron radiation with energies 0.1-15 MeV.

Registration of the intensity of the transmitted radiation is carried out by decomp. ways - photographic. method with obtaining an image of a translucent product on a photographic film (film radiography), on a reusable xeroradiographic. plate (electroradiography); visually, observing images of a translucent product on a fluorescent screen (radioscopy); using electron-optical converters (X-ray television); measurement of radiation intensity spec. indicators, the action of which is based on the ionization of gas by radiation (radiometry).

Sensitivity of Radiation Methods. D. is determined by the ratio of the length of a defect or zone with a different density in the direction of transillumination to the thickness of the product in this section and for decomp. materials is from 1 to 10% of its thickness. The use of X-ray D. effective for products cf. thicknesses (steel up to ~80 mm, light alloys up to ~250 mm). Superhard radiation with an energy of tens of MeV (betatron) makes it possible to shine through steel products with a thickness of up to ~500 mm. Gamma-D. characterized by a more compact source of radiation, which makes it possible to control hard-to-reach areas of products with a thickness of up to ~250 mm (steel), moreover, in conditions where the X-ray D. is difficult. Neutron D. naib. effective for the control of products of small thickness from materials of low density. One of the new ways of X-ray control is to calculate. tomography based on the processing of radiometric. information with the help of a computer, obtained by repeatedly transilluminating products at different angles. At the same time, it is possible to visualize images in layers in layers. product structure. When working with sources of ionizing radiation, an appropriate biol must be provided. protection.

Radio wave D. is based on a change in the parameters of the electric magnet. waves (amplitudes, phases, directions of the polarization vector) of the centimeter and millimeter range when they propagate in products made of dielectric materials (plastics, rubber, paper).

The source of radiation (usually coherent, polarized) is a microwave generator (magnetron, klystron) of low power, feeding a waveguide or special. an antenna (probe) that transmits radiation to the controlled product. The same antenna, when receiving reflected radiation, or a similar one located on the opposite side of the product, when receiving transmitted radiation, sends the received signal through the amplifier to the indicator. The sensitivity of the method makes it possible to detect delaminations in dielectrics at a depth of up to 15-20 mm with an area of ​​​​1 cm 2, to measure the moisture content of paper, bulk materials with an error of less than 1%, the thickness of the metal. sheet with an error of less than 0.1 mm, etc. It is possible to visualize the image of the controlled area on the screen (radio imager), fix it on photographic paper, and also use holographic. image capturing methods.

Thermal (infrared) D. is based on the dependence of the temperature of the body surface both in stationary and non-stationary fields on the presence of a defect and inhomogeneity of the body structure. In this case, infrared radiation is used in the low-temperature range. The temperature distribution on the surface of the controlled product, which occurs in transmitted, reflected or intrinsic radiation, is an IR image of this part of the product. By scanning the surface with a radiation receiver sensitive to IR rays (thermistor or pyroelectric), on the screen of the device (thermal imager), you can observe the entire cut-off or color image, the distribution of temperature over sections, or, finally, select individual parts. isotherms. The sensitivity of thermal imagers makes it possible to register a temperature difference of less than 1 ° C on the surface of the product. The sensitivity of the method depends on the size ratio d defect or inhomogeneity to depth l its occurrence is approximately like ( d/l) 2, as well as on the thermal conductivity of the material of the product (inversely proportional dependence). Using the thermal method, it is possible to control products that heat up (cool down) during operation.

Magnetic D. can be used only for products made of ferromagnet. alloys and is sold in two versions. The first one is based on the analysis of magnetic parameters. stray fields arising in the areas of location of surface and subsurface defects in magnetized products, the second - on the dependence of the magnetic. properties of materials from their structure and chemical. composition.

In the first method, the product is magnetized using electromagnets, solenoids, by passing current through the product or a rod passed through a hole in the product, or by inducing current in the product. For magnetization, constant, variable and pulsed magnetic fields are used. Optimal control conditions are created when the defect is oriented perpendicular to the direction of the magnetizing field. For hard magnetic materials, control is carried out in the field of residual magnetization, for soft magnetic materials - in the applied field.

Magnet indicator. field defect can serve as a magnet. powder, eg. magnetite of high dispersity (magnet powder method), sometimes coloring (to control products with a dark surface) or fluorescent (to increase sensitivity) components are added to Krom. Powder particles after sprinkling or watering with a suspension of a magnetized product settle on the edges of defects and are observed visually. The sensitivity of this method is high - cracks with a depth of ~25 µm and an opening of -2 µm are detected.

With a magnetographic Magnet serves as an indicator in the method. tape, which is pressed against the product and magnetized along with it. The culling is carried out according to the results of the analysis of the record on the magnet. tape. The sensitivity of the method to surface defects is the same as that of the powder method, and to deep defects it is higher - at a depth of up to 20-25 mm, defects are detected with a depth extension of 10-15% of the thickness.

Passive inductive transducers can be used as an indicator of the defect field. Product moving with relative. speed up to 5 m/s and more, after passing through the magnetizing device, it passes through the transducer, inducing in its coils a signal containing information about the parameters of the defect. This method is effective for testing metal during the rolling process, as well as for testing railway rails.

Ferroprobe indication method uses active transducers - fluxgates, in which coils are wound on a thin permalloy core: an exciting one, the field of which interacts with the field of the defect, and a measuring one, according to the emf, the field strength of the defect or the gradient of this field is judged. The fluxgate indicator makes it possible to detect in products of a simple shape, moving at a speed of up to 3 m/s, at a depth of up to 10 mm, defects with a length (in depth) of ~10% of the thickness of the product. To indicate the defect field, converters based on hall effect and magnetoresistor. After carrying out control by methods of magnetic D. the product has to be carefully demagnetized.

The second group of methods of magn. D. serves to control the structural state, thermal modes. processing, mechanical material properties. So, coercive force carbon and low-alloy. steel is correlated with carbon content and hence hardness, magnetic permeability- with the content of the ferrite component (os-phase), the limiting content of which is limited due to the deterioration of the mechanical. and technological material properties. Specialist. devices (ferritometers, a-phase meters, coercimeters, magnetic analyzers) that use the relationship between the magnetic. characteristics and other properties of the material, also allow you to practically solve the problem of magnetic. D.

Magnet methods. D. are also used to measure the thickness of protective coatings on ferromagnetic products. materials. Devices for these purposes are based either on ponderomotive action - in this case, the force of attraction (separation) is measured. magnet or electromagnet from the surface of the product, to which it is pressed, or on the measurement of the magnetic strength. fields (with the help of Hall sensors, ferroprobes) in the magnetic circuit of an electromagnet installed on this surface. Thickness gauges allow measurements in a wide range of coating thicknesses (up to hundreds of microns) with an error not exceeding 1-10 microns.

acoustic(ultrasonic) D. uses elastic waves (longitudinal, shear, surface, normal, bending) of a wide frequency range (main sample of the ultrasonic range), emitted in a continuous or pulsed mode and introduced into the product using a piezoelectric. (less often - e-magnetoacoustic.) converter excited by the generator e-magn. fluctuations. Propagating in the material of the product, elastic waves decay in decomp. degree, and encountering defects (disturbances in the continuity or homogeneity of the material), they are reflected, refracted and scattered, while changing their amplitude, phase, and other parameters. Accept them the same or otd. converter and after appropriate processing, the signal is fed to the indicator or recording device. There are several acoustic options. D., to-rye can be used in decomp. combinations.

The echo method is an ultrasound location in a solid medium; this is naib. universal and widespread method. Ultrasonic frequency pulses of 0.5-15 MHz are injected into the controlled product and the intensity and time of arrival of echo signals reflected from the surfaces of the product and from defects are recorded. Echo-method control is carried out with one-sided access to the product by scanning its surface with a finder at a given speed and step at optimum. ultrasonic input angle. The method possesses high sensitivity, edges is limited by structural noise. In the opt. conditions can be detected defects with sizes of several. tenths of mm. The disadvantage of the echo method is the presence of an uncontrolled dead zone near the surface, the extent of which is swarm (depth) is determined by Ch. arr. the duration of the emitted pulse and is usually 2-8 mm. The echo method effectively controls ingots, shaped castings, metallurgical. semi-finished products, welded, glued, soldered, riveted joints and other structural elements in the process of manufacture, storage and operation. Detected superficial and vnutr. defects in blanks and products decomp. shapes and dimensions of metals and non-metallic. materials, zones of violation of the homogeneity of crystalline. structure and corrosion damage to metal. products. The thickness of the product can be measured with high accuracy with one-sided access to it. A variant of the echo method using lamb waves, which have a full-flowing nature of distribution, allows you to control sheet semi-finished products of great length with high productivity; the limitation is the requirement for the constancy of the thickness of the controlled semi-finished product. Control using Rayleigh waves allows you to detect surface and near-surface defects; the limitation is the requirement for high surface smoothness.

The shadow method provides for the input of ultrasound from one side of the product, and the reception from the opposite side. The presence of a defect is judged by a decrease in the amplitude in the zone of the sound shadow formed behind the defect, or by a change in the phase or time of reception of the signal that envelopes the defect (a temporary version of the method). With one-sided access to the product, a mirror version of the shadow method is used, with which the defect indicator is a decrease in the signal reflected from the bottom of the product. In terms of sensitivity, the shadow method is inferior to the echo method, but its advantage is the absence of a dead zone.

The resonance method is used by Chap. arr. to measure the thickness of a product. Exciting ultrasonic vibrations in the local volume of the wall of the product, they are modulated in frequency within 2-3 octaves, the values ​​of the resonant frequencies (when an integer number of half-waves fit along the wall thickness) determine the wall thickness of the product with an error of approx. 1%. When vibrations are excited in the entire volume of the product (an integrated version of the method), one can also judge the presence of defects or a change in the elastic characteristics of the material of the product by changing the resonant frequency.

The method of free vibrations (integral version) is based on shock excitation of elastic vibrations in a controlled product (eg, a lively low-frequency vibrator) and subsequent measurement using a piezoelectric element. fluctuations, according to the change in the spectrum to-rykh, the presence of a defect is judged. The method has been successfully used to control the quality of gluing low-quality materials (textolite, plywood, etc.) between themselves and with metal. sheathing.

The impedance method is based on the measurement of the local mechanical resistance (impedance) of the controlled product. The sensor of the impedance flaw detector, operating at a frequency of 1.0-8.0 kHz, being pressed to the surface of the product, reacts to the reaction force of the product at the point of pressing. The method makes it possible to determine delaminations with an area of ​​20-30 mm 2 in glued and brazed structures with metal. and non-metallic filling, in laminated plastics, as well as in clad sheets and pipes.

The velocimetric method is based on changing the speed of propagation of bending waves in a plate depending on the thickness of the plate or on the presence of delaminations inside a multilayer glued structure. The method is implemented at low frequencies (20-70 kHz) and makes it possible to detect delaminations with an area of ​​2-15 cm 2 (depending on depth), occurring at a depth of up to 25 mm in products made of laminated plastics.

Acoustic-topographic. The method is based on the observation of vibration modes, including "Chladni figures", with the help of a thin-diameter powder during excitation of bending vibrations in a controlled product with a modulated (within 30-200 kHz) frequency. Powder particles, moving from surface areas oscillating with max. amplitude, to areas where this amplitude is minimal, outline the contours of the defect. The method is effective for testing products such as multilayer sheets and panels and makes it possible to detect defects with a length of 1–1.5 mm.

Acoustic method. emission (related to passive methods) is based on the analysis of signals characterizing the stress waves emitted during the occurrence and development of cracks in the product during its mechanical. or thermal loading. Signals are received piezoelectrically. finders located on the surface of the products. The amplitude, intensity, and other parameters of the signals contain information about the initiation and development of fatigue cracks, stress corrosion, and phase transformations in the material of structural elements decomp. types, welds, pressure vessels, etc. Acoustic method. emissions allows you to detect developing, ie, max. dangerous, defects and separate them from defects detected by other methods, non-developing, less dangerous for the further operation of the product. The sensitivity of this method when using special. measures to protect the receiving device from the effects of external noise interference is quite high and allows you to detect cracks at the beginning. stages of their development, long before the resource of the product is exhausted.

Promising directions for the development of acoustic. control methods are sound vision, including acoustic. holography, acoustic tomography.

eddy current(electroinductive) D. is based on the registration of changes in electric. parameters of the sensor of an eddy current flaw detector (impedance of its coil or emf), caused by the interaction of the field of eddy currents excited by this sensor in a product made of electrically conductive material, with the field of the sensor itself. The resulting field contains information about the change in electrical conductivity and magnetic. permeability due to the presence of structural inhomogeneities or discontinuities in the metal, as well as the shape and size (thickness) of the product or coating.

The sensors of eddy current flaw detectors are made in the form of inductance coils placed inside the controlled product or surrounding it (through-through sensor) or superimposed on the product (attached sensor). In screen-type sensors (through and overhead) the controlled product is located between the coils. Eddy current D. does not require mechanical. contact of the sensor with the product, which makes it possible to control them at high speeds. displacement (up to 50 m/s). Eddy current flaw detectors are divided into a trace. main groups: 1) devices for detecting discontinuities with pass-through or clamp-on sensors operating in a wide frequency range - from 200 Hz to tens of MHz (increasing the frequency increases the sensitivity to the length of cracks, since small-sized sensors can be used). This allows you to identify cracks, non-metallic captivity. inclusions and other defects with a length of 1-2 mm at a depth of 0.1-0.2 mm (attachment sensor) or a length of 1 mm at a depth of 1-5% of the diameter of the product (through sensor). 2) Devices for controlling dimensions - thickness gauges, with the help of which they measure the thickness of dec. coatings applied to the base from dec. materials. Determination of the thickness of non-conductive coatings on electrically conductive substrates, which is essentially a measurement of the gap, is carried out at frequencies up to 10 MHz with an error within 1-15% of the measured value.

To determine the thickness of electrically conductive galvanic. or plakirs. coatings on an electrically conductive base, eddy current thickness gauges are used, in which special are implemented. schemes for suppressing the influence of changes in beats. electrical conductivity of the base material and changes in the size of the gap.

Eddy current thickness gauges are used to measure the wall thickness of pipes, cylinders made of non-ferromagnet. materials, as well as sheets and foils. Measurement range 0.03-10 mm, error 0.6-2%.

3) Eddy current structurometers allow, by analyzing the values ​​of beats. electrical conductivity and magnet. permeability, as well as the parameters of higher voltage harmonics, to judge the chem. composition, structural state of the material, the size of the internal. voltages, sort products by grades of material, quality thermal. processing, etc. It is possible to identify zones of structural heterogeneity, fatigue zones, to evaluate the depth of decarburized layers, thermal layers. and chemical-thermal. processing, etc. For this, depending on the specific purpose of the device, either low-frequency fields of high strength, or high-frequency fields of low strength, or two- and multi-frequency fields are used. In structure meters, to increase the amount of information taken from the sensor, as a rule, multifrequency fields and spectral analysis of the signal is carried out. Devices for the control of ferromagnet. materials operate in the low-frequency range (50 Hz-10 kHz), to control non-ferromagnetic - in the high-frequency range (10 kHz-10 MHz), due to the dependence of the skin effect on the value of the magnetic. permeability.

Electric D. is based on the use of weak posts. currents and e-static. fields and is carried out by e-contact, thermoelectric, triboelectric. and e-static. methods. El-contact method allows you to detect surface and subsurface defects by changing the electrical resistance on the surface of the product in the area where this defect is located. With the help of special contacts located at a distance of 10-12 mm from one another and tightly pressed to the surface of the product, a current is applied, and on another pair of contacts located on the current line, a voltage is measured proportional to the resistance in the area between them. The change in resistance is used to judge the violation of the homogeneity of the structure of the material or the presence of a crack. The measurement error is 5-10%, which is due to the instability of the current resistance and will measure. contacts.

Thermoelectric The method is based on measuring the thermoelectromotive force (TEMF) that occurs in a closed circuit when the contact point of two dissimilar metals is heated. If one of these metals is taken as a standard, then for a given temperature difference between hot and cold contacts, the value and sign of TEMF will be determined by the properties of the second metal. This method can determine the grade of metal from which the workpiece or structural element is made, if the number of possible options is small (2-3 grades).

Triboelectric The method is based on measuring the triboEMF that occurs when dissimilar metals rub against each other. By measuring the potential difference between the reference and test metals, it is possible to distinguish between brands of certain alloys. Change in chem. composition of the alloy within the limits allowed by tech. conditions, leads to a spread in the readings of thermo- and triboelectric. appliances. Therefore, both of these methods can be applied only in cases of a sharp difference in the properties of sorted alloys.

E l. fields in which the product is placed. To detect surface cracks in a metallic coating. its products are pollinated with a fine powder of chalk from a spray gun with an ebonite tip. Chalk particles, when rubbed against ebonite, are positively charged due to triboelectric. effect and settle at the edges of the cracks, since near the latter, the inhomogeneity of the e-static. the field is expressed at the most. noticeably. If the product is made of non-conductive materials, then it is pre-wetted with an ionic penetrant and, after removing its excess from the surface of the product, a charge is powdered. chalk particles, which are attracted by the liquid that fills the cavity of the crack. In this case, it is possible to detect cracks that do not extend to the surface being inspected.

capillary D. is based on the arts. increasing the color and light contrast of the part of the product containing surface cracks relative to the surrounding surface. It is being carried out. arr. luminescent and color methods, allowing to detect cracks, the identification of which with the naked eye is impossible due to their small size, and the use of optical. devices is inefficient due to insufficient image contrast and a small field of view at the required magnifications.

To detect a crack, its cavity is filled with a penetrant - an indicator liquid based on phosphors or dyes, penetrating into the cavity under the action of capillary forces. After that, the surface of the product is cleaned of excess penetrant, and the indicator liquid is removed from the crack cavity using a developer (sorbent) in the form of a powder or suspension, and the product is examined in a darkened room in UV light (luminescent method). The luminescence of the indicator solution absorbed by the sorbent gives a clear picture of the location of cracks with min. with an opening of 0.01 mm, a depth of 0.03 mm and a length of 0.5 mm. The color method does not require dimming. The penetrant containing the dye additive (usually bright red), after filling the cavity of the crack and cleaning the surface of its excess, diffuses into a white developing varnish applied in a thin layer on the surface of the product, clearly outlining the cracks. The sensitivity of both methods is approximately the same.

The advantage of capillary D. is its versatility and uniformity of technology for parts decomp. shapes, sizes and materials; disadvantage - the use of materials with high toxicity, explosion and fire hazard, which imposes special safety requirements.

Meaning D. D. methods are used in decomp. areas of the national economy, helping to improve the technology of manufacturing products, improve their quality, extend their service life and prevent accidents. Some methods (ch. arr. acoustic) allow for periodic. in the control of products during their operation, to assess the damageability of the material, which is especially important for predicting the residual life of critical products. In this regard, the requirements for the reliability of information obtained by using D.'s methods, as well as for the performance of control, are constantly increasing. T. to. characteristics of flaw detectors are low and their readings are affected by many random factors, the assessment of the results of testing can only be probabilistic. Along with development of new methods D., osn. the direction of improving the existing ones is the automation of control, the use of multi-parameter methods, the use of computers for processing the information received, the improvement of metrological. characteristics of the equipment in order to improve the reliability and performance of control, the use of visualization methods ext. product structure and defects.

Lit.: Shraiber D.S., Ultrasonic flaw detection, M., 1965; Non-destructive testing. (Handbook), ed. D. McMaster, trans. from English, book. 1-2, M.-L., 1965; Falkevich A. S., Khusanov M. X., Magnetographic control of welded joints, M., 1966; Dorofeev A.L., Electroinductive (induction) flaw detection, M., 1967; Rumyantsev S.V., Radiation flaw detection, 2nd ed., M., 1974; Devices for non-destructive testing of materials and products, ed. V. V. Klyueva, [vol. 1-2], M., 1976; Non-destructive testing of metals and products, ed. G. S. Samoilovich, M., 1976. D. S. Schreiber.

Defectoscopy I Defectoscopy (from lat. defectus - lack and ... scopy)

a set of methods and tools for non-destructive testing of materials and products in order to detect defects. D. includes: the development of methods and equipment (defectoscopes, etc.); drawing up control methods; processing of indications of flaw detectors.

Due to the imperfection of the manufacturing technology or as a result of operation in difficult conditions, various defects appear in the products - violations of the continuity or uniformity of the material, deviations from the specified chemical composition or structure, as well as from the specified dimensions. Defects change the physical properties of the material (density, electrical conductivity, magnetic, elastic properties, etc.). Existing D. methods are based on the study of the physical properties of materials exposed to X-ray, infrared, ultraviolet, and gamma rays, radio waves, ultrasonic vibrations, magnetic and electrostatic fields, and so on.

The simplest method of D. is visual - with the naked eye or with the help of optical instruments (for example, a magnifying glass). To inspect internal surfaces, deep cavities and hard-to-reach places, special tubes with prisms and miniature illuminators (diopter tubes) and television tubes are used. Lasers are also used to control, for example, the quality of the surface of thin wire, etc. Visual D. makes it possible to detect only surface defects (cracks, films, etc.) in metal products and internal defects in products made of glass or plastics that are transparent to visible light. The minimum size of defects detected by the naked eye is 0.1-0.2 mm, and when using optical systems - tens micron.

X-ray flaw detection is based on the absorption of X-rays (See X-rays), which depends on the density of the medium and the atomic number of the elements that form the material of the medium. The presence of defects such as cracks, cavities, or inclusions of foreign material leads to the fact that rays passing through the material ( rice. 1 ) are attenuated to varying degrees. By registering the intensity distribution of the transmitted rays, it is possible to determine the presence and location of various material inhomogeneities.

The intensity of the rays is recorded by several methods. Photographic methods take a picture of the detail on the film. The visual method is based on observing the image of a part on a fluorescent screen. This method is more effective when using electron-optical converters (See. Electron-optical converter). With the xerographic method, images are obtained on metal plates coated with a layer of a substance whose surface is charged with an electrostatic charge. On plates that can be used repeatedly, contrast images are obtained. The ionization method is based on measuring the intensity of electromagnetic radiation by its ionizing effect, for example, on a gas. In this case, the indicator can be installed at a sufficient distance from the product, which allows you to control products heated to a high temperature.

The sensitivity of X-ray flaw detection methods is determined by the ratio of the length of the defect in the direction of transmission to the thickness of the part in this section and for various materials is 1-10%. The use of X-ray flaw detection is effective for parts of relatively small thickness, because the penetrating power of x-rays increases slightly with increasing energy. X-ray flaw detection is used to determine shells, coarse cracks, segregation inclusions in cast and welded steel products with a thickness of up to 80 mm and in products made of light alloys up to 250 mm. To do this, use industrial x-ray installations with radiation energy from 5-10 to 200-400 kev (1 ev= 1.60210 10 -19 j). Thick products (up to 500 mm) shine through with superhard electromagnetic radiation with an energy of tens mev obtained in the Betatron e.

Gamma flaw detection has the same physical foundations as X-ray flaw detection, but uses the radiation of gamma rays emitted by artificial radioactive isotopes of various metals (cobalt, iridium, europium, etc.). Use radiation energy from several tens kev up to 1-2 mev for transillumination of thick parts ( rice. 2 ). This method has significant advantages over X-ray flaw detection: the equipment for gamma flaw detection is relatively simple, the radiation source is compact, which makes it possible to examine hard-to-reach parts of products. In addition, this method can be used when the use of X-ray flaw detection is difficult (for example, in the field). When working with sources of X-ray and gamma radiation, biological protection must be provided.

Radio flaw detection is based on the penetrating properties of radio waves (see radio waves) of the centimeter and millimeter ranges (microradio waves), and makes it possible to detect defects mainly on the surface of products, usually from non-metallic materials. Due to the low penetrating power of microradio waves, radiodefectoscopy of metal products is limited (see Skin effect). This method determines defects in steel sheets, bars, wires during their manufacture, and also measures their thickness or diameter, the thickness of dielectric coatings, etc. From a generator operating in a continuous or pulsed mode, microradio waves penetrate the product through horn antennas (See Horn antenna) and, having passed the received signal amplifier, are registered by a receiving device.

Infrared D. uses infrared (thermal) rays (see. Infrared radiation) to detect inclusions that are opaque to visible light. The so-called infrared image of the defect is obtained in the transmitted, reflected or intrinsic radiation of the product under study. This method controls products that heat up during operation. Defective areas in the product change the heat flux. A stream of infrared radiation is passed through the product and its distribution is recorded by a heat-sensitive receiver. The heterogeneity of the structure of materials can also be studied by the ultraviolet D method.

Magnetic D. is based on the study of magnetic field distortions that occur at the sites of defects in products made of ferromagnetic materials. An indicator can be a magnetic powder (ferrous oxide) or its suspension in oil with a particle size of 5-10 micron. When the product is magnetized, the powder settles at the location of defects (magnetic powder method). The stray field can be recorded on a magnetic tape, which is applied to the investigated area of ​​the magnetized product (magnetographic method). Small-sized sensors (flux probes) are also used, which, when moving along the product at the defect site, indicate changes in the current pulse recorded on the oscilloscope screen (flux probe method).

The sensitivity of the method of magnetic D. depends on the magnetic characteristics of the materials, the indicators used, the modes of magnetization of products, etc. The method of magnetic powder can detect cracks and other defects at a depth of up to 2 mm (rice. 3 ), the magnetographic method mainly controls the welds of pipelines with a thickness of up to 10-12 mm and detect thin cracks and lack of fusion. The fluxgate method is the most appropriate for detecting defects at a depth of up to 10 mm and in some cases up to 20 mm in products of the correct form. This method allows you to fully automate the control and sorting. Magnetization of products is carried out by magnetic flaw detectors ( rice. 4 ), which create magnetic fields of sufficient strength. After the inspection, the products are carefully demagnetized.

Magnetic D. methods are used to study the structure of materials (magnetic structurometry) and to measure thickness (magnetic thickness measurement). Magnetic structurometry is based on the determination of the main magnetic characteristics of a material (coercive force, induction, residual magnetization, magnetic permeability). These characteristics, as a rule, depend on the structural state of the alloy subjected to various heat treatments. Magnetic structurometry is used to determine the structural components of the alloy, which are in it in small quantities and differ significantly from the alloy base in their magnetic characteristics, to measure the depth of carburization, surface hardening, etc. Magnetic thickness measurement is based on measuring the force of attraction of a permanent magnet or electromagnet to the surface of a product made of ferromagnetic material, on which a layer of non-magnetic coating is applied, and allows you to determine the thickness of the coating.

Electroinductive (eddy current) D. is based on the excitation of eddy currents by an alternating magnetic field of a flaw detector sensor. Eddy currents create their own field, opposite in sign to the exciting one. As a result of the interaction of these fields, the impedance of the sensor coil changes, which is indicated by the indicator. The indicator readings depend on the electrical conductivity and magnetic permeability of the metal, the dimensions of the product, as well as changes in electrical conductivity due to structural inhomogeneities or discontinuities in the metal.

The sensors of eddy current flaw detectors are made in the form of inductance coils, inside of which the product is placed (pass-through sensors), or which are applied to the product (overhead sensors). The use of eddy current D. makes it possible to automate the quality control of wire, rods, pipes, and profiles moving at high speeds during their manufacture, and to conduct continuous measurement of dimensions. Eddy current flaw detectors can control the quality of heat treatment, evaluate the contamination of highly electrically conductive metals (copper, aluminum), determine the depth of chemical-thermal treatment layers with an accuracy of up to 3%, sort some materials into grades, measure the electrical conductivity of non-ferromagnetic materials with an accuracy of 1%, detect surface cracks a few deep micron with a length of several tenths mm.

Thermoelectric D. is based on the measurement of the electromotive force (see electromotive force) (thermoelectric power) that occurs in a closed circuit when the contact point of two dissimilar materials is heated. If one of these materials is taken as a standard, then for a given temperature difference between hot and cold contacts, the value and sign of the thermoelectric power will be determined by the chemical composition of the second material. This method is usually used in cases where it is required to determine the grade of material that makes up a semi-finished product or structural element (including in a finished structure).

Triboelectric D. is based on the measurement of the electromotive force that occurs during the friction of dissimilar materials (see Tribometry). By measuring the potential difference between the reference and test materials, it is possible to distinguish the grades of some alloys.

Electrostatic D. is based on the use of an electrostatic field (See Electrostatic field), in which the product is placed. To detect surface cracks in products made of non-conductive materials (porcelain, glass, plastics), as well as from metals coated with the same materials, the product is dusted with fine chalk powder from a spray gun with an ebonite tip (powder method). In this case, the chalk particles receive a positive charge. As a result of the inhomogeneity of the electrostatic field, chalk particles accumulate at the edges of cracks. This method is also used to control products made of insulating materials. Before pollination, they must be moistened with an ionic liquid.

Ultrasonic D. is based on the use of elastic vibrations (see Elastic waves), mainly in the ultrasonic frequency range. Violations of the continuity or homogeneity of the medium affect the propagation of elastic waves in the product or the vibration mode of the product. Main methods: echo method, shadow method, resonant method, velosymmetric method (actually ultrasonic methods), impedance method and free vibration method (acoustic methods).

The most versatile echo method is based on sending short pulses of ultrasonic vibrations ( rice. 5 ) and recording the intensity and time of arrival of echo signals reflected from defects. To control the product, the echo flaw detector sensor scans its surface. The method makes it possible to detect surface and deep defects with different orientations. Industrial installations have been created ( rice. 6 ) to control various products. Echo signals can be observed on the oscilloscope screen or registered with a self-recording device. In the latter case, the reliability, objectivity of the assessment, productivity and reproducibility of the control increase. The sensitivity of the echo method is very high: under optimal control conditions at a frequency of 2-4 MHz it is possible to detect defects whose reflecting surface has an area of ​​about 1 mm 2.

With the shadow method, ultrasonic vibrations, having met a defect on their way, are reflected in the opposite direction. The presence of a defect is judged by a decrease in the energy of ultrasonic vibrations or by a change in the phase of ultrasonic vibrations that envelop the defect. The method is widely used to control welds, rails, etc.

The resonance method is based on the determination of natural resonant frequencies of elastic oscillations (frequency 1-10 MHz) when excited in the product. This method measures the wall thickness of metal and some non-metal products. With the possibility of measuring on one side, the measurement accuracy is about 1%. In addition, this method can identify zones of corrosion damage. Resonance flaw detectors carry out manual control and automated control with recording instrument readings.

The velocimetric method of echo flaw detection is based on measuring changes in the velocity of propagation of elastic waves in the area of ​​defects in multilayer structures, and is used to detect areas of debonding between metal layers.

The impedance method is based on measuring the mechanical resistance (impedance) of a product with a sensor that scans the surface and excites elastic vibrations of sound frequency in the product. This method can detect defects in adhesive, soldered, and other joints, between thin skin and stiffeners or fillers in multilayer structures. Detectable defects with an area of ​​15 mm 2 and more are marked with a signaling device and can be recorded automatically.

The method of free oscillations (see. Natural oscillations) is based on the analysis of the spectrum of free oscillations of a controlled product excited by an impact; is used to detect areas of broken connections between elements in multilayer glued structures of considerable thickness from metallic and non-metallic materials.

Ultrasonic diagnosing, which uses several variable parameters (frequency range, types of waves, radiation modes, contact methods, etc.), is one of the most universal methods of nondestructive testing.

Capillary D. is based on an artificial increase in the light and color contrast of a defective area relative to an undamaged one. Capillary D. methods make it possible to detect with the naked eye thin surface cracks and other material discontinuities that form during the manufacture and operation of machine parts. The cavities of surface cracks are filled with special indicator substances (penetrants), which penetrate into them under the action of capillary forces. For the so-called luminescent method, penetrants are based on phosphors (kerosene, noriol, etc.). A thin powder of a white developer (magnesium oxide, talc, etc.), which has sorption properties, is applied to the surface cleaned of excess penetrant, due to which the penetrant particles are removed from the crack cavity to the surface, outline the crack contours and glow brightly in ultraviolet rays. With the so-called color control method, penetrants are based on kerosene with the addition of benzene, turpentine and special dyes (for example, red paint). To control products with a dark surface, a magnetic powder colored with phosphors (magnetoluminescent method) is used, which facilitates the observation of fine cracks.

The sensitivity of capillary D. makes it possible to detect surface cracks with an opening of less than 0.02 mm. However, the wide application of these methods is limited due to the high toxicity of penetrants and developers.

D. is an equal and inalienable link in technological processes, which makes it possible to increase the reliability of manufactured products. However, D.'s methods are not absolute, because many random factors influence the control results. The absence of defects in the product can only be said with varying degrees of probability. The reliability of control is facilitated by its automation, the improvement of methods, as well as the rational combination of several methods. The suitability of products is determined on the basis of rejection standards developed during their design and manufacturing technology. The rejection rates are different for different types of products, for the same type of products operating in different conditions, and even for different areas of the same product, if they are subjected to different mechanical, thermal or chemical effects.

The use of diamonds in the process of production and operation of products gives a great economic effect by reducing the time spent on processing workpieces with internal defects, saving metal, etc. In addition, diamonds play a significant role in preventing the destruction of structures, helping to increase their reliability and durability. .

Lit.: Trapeznikov A. K., X-ray flaw detection, M., 1948; Zhigadlo A. V., Control of parts by the method of magnetic powder, M., 1951; Tatochenko L.K., Medvedev S.V., Industrial gamma-defectoscopy, M., 1955; Defectoscopy of metals. Sat. Art., ed. Edited by D. S. Schreiber. Moscow, 1959. Modern methods of control of materials without destruction, ed. S. T. Nazarova. Moscow, 1961. Kiefer I.I., Testing of ferromagnetic materials, 2nd ed., M. - L., 1962; Gurvich A. K., Ultrasonic flaw detection of welded joints, K., 1963; Shraiber D.S., Ultrasonic flaw detection, M., 1965; Non-destructive testing. Handbook, ed. R. McMaster, trans. from English, book. 1-2, M. - L., 1965; Dorofeev A. L., Electroinductive (induction) flaw detection, M., 1967.

D. S. Schreiber.

Rice. 2. Photograph in gamma radiation (left) and photograph of the profit cut (right) of an ingot weighing about 500 kg; shrinkage shell is visible.

II Defectoscopy ("Defectoscopy")

a scientific and technical journal published by the USSR Academy of Sciences in Sverdlovsk since 1965. Created on the basis of the Institute of Metal Physics. Published 6 times a year. "D." publishes original articles on research in the field of theory and technology of non-destructive quality control of materials and products, on the results of laboratory and industrial testing of flaw detectors. It highlights the experience of using control equipment at factories, the experience of controlling building structures and materials, etc. Circulation (1972) 3.5 thousand copies. Reprinted in English in New York (USA).

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

Synonyms:

See what "Defectoscopy" is in other dictionaries:

Defectoscopy … Spelling Dictionary- (from defect and ... scopy) generalizing name of non-destructive methods for testing materials (products); used to detect discontinuities or homogeneity of the macrostructure, deviations in the chemical composition and other purposes. Most… … Big Encyclopedic Dictionary

Defectoscopy- - a method for obtaining information about the internal state of the equipment being diagnosed to detect defects without destroying the product based on non-destructive testing methods. Note. Non-destructive testing methods include magnetic, ... ... Encyclopedia of terms, definitions and explanations of building materials

Defectoscopy- (from defect and ... scopy), a generalized name for non-destructive testing methods used to detect violations of the structure, chemical composition and other defects in products and materials. Main methods: X-ray, gamma flaw detection, ... ... Illustrated Encyclopedic Dictionary

Exist., number of synonyms: 3 gamma flaw detection (1) radio flaw detection (1) ... Synonym dictionary

defectoscopy- A method for obtaining information about the internal state of the equipment being diagnosed to detect defects without destroying the product based on non-destructive testing methods. Note Non-destructive testing methods include magnetic, ... ... Technical Translator's Handbook

- (from Latin defectus defect and Greek skopeo I consider, observe * a. flaw detection; n. Defektoskopie, zerstorungsfreie Werkstoffprufung; f. defectoscopie, detection des defauts; i. defectoscopia, deteccion de defectos) control ... ... Geological Encyclopedia, E. S. Lev, N. K. Lopyrev. Leningrad, 1957. River transport. Publisher's binding. The safety is good. The book discusses the physical methods of control of materials and products without their destruction, in relation to ..., A.P. Markov. The monograph summarizes the results of research and development of laboratory and industrial vizoscopes, automated tools for remote flaw detection of complex contour extended products ... eBook