Capillary control. Color flaw detection. Capillary method non-destructive testing.

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Penetrant flaw detection- a flaw detection method based on the penetration of certain contrast substances into the surface defective layers of a controlled product under the influence of capillary (atmospheric) pressure; as a result of subsequent processing with a developer, the light and color contrast of the defective area relative to the undamaged one increases, with the identification of the quantitative and qualitative composition of the damage (up to thousandths millimeter).

There are luminescent (fluorescent) and color methods of capillary flaw detection.

Mainly by technical requirements or conditions it is necessary to detect very small defects (up to hundredths of a millimeter) and it is simply impossible to identify them during a normal visual inspection with the naked eye. The use of portable optical instruments, such as a magnifying glass or microscope, does not allow identifying surface damage due to the insufficient visibility of the defect against the background of the metal and the lack of field of view at multiple magnifications.

In such cases, the capillary control method is used.

During capillary testing, indicator substances penetrate into the cavities of surface and through defects in the material of the test objects, and subsequently the resulting indicator lines or points are recorded visually or using a transducer.

Testing by the capillary method is carried out in accordance with GOST 18442-80 “Non-destructive testing. Capillary methods. General requirements."

The main condition for detecting defects such as a violation of the continuity of a material by the capillary method is the presence of cavities that are free from contamination and other technical substances, with free access to the surface of the object and a depth several times greater than the width of their opening at the outlet. A cleaner is used to clean the surface before applying penetrant.

Purpose of penetrant testing (penetrant flaw detection)

Penetrant flaw detection (penetration testing) is intended for detection and inspection of surface and through defects invisible or poorly visible to the naked eye (cracks, pores, lack of fusion, intercrystalline corrosion, cavities, fistulas, etc.) in inspected products, determining their consolidation, depth and orientation on the surface.

Application of the capillary method of non-destructive testing

The capillary testing method is used to control objects of any size and shape made of cast iron, ferrous and non-ferrous metals, plastics, alloy steels, metal coatings, glass and ceramics in the energy sector, rocketry, aviation, metallurgy, shipbuilding, chemical industry, and in the construction of nuclear power plants. reactors, in mechanical engineering, automotive industry, electrical engineering, foundry, medicine, stamping, instrument making, medicine and other industries. In some cases, this method is the only one for determining the technical serviceability of parts or installations and allowing them to operate.

Penetrant flaw detection is used as a non-destructive testing method also for objects made of ferromagnetic materials, if they magnetic properties, the shape, type and location of damage do not allow achieving the sensitivity required by GOST 21105-87 using the magnetic particle method or the magnetic particle testing method is not allowed to be used according to technical specifications operation of the facility.

Capillary systems are also widely used for leakage monitoring, in conjunction with other methods, when monitoring critical facilities and facilities during operation. The main advantages of capillary flaw detection methods are: simplicity of operations during testing, ease of use of devices, a wide range of controlled materials, including non-magnetic metals.

The advantage of penetrant flaw detection is that with the help of a simple testing method it is possible not only to detect and identify surface and through defects, but also to determine their location, shape, extent and orientation along the surface full information about the nature of the damage and even some of the reasons for its occurrence (concentration of power stresses, non-compliance with technical regulations during manufacturing, etc.).

Organic phosphors are used as developing liquids - substances that emit bright radiation when exposed to ultraviolet rays, as well as various dyes and pigments. Surface defects are detected using means that allow the penetrant to be removed from the defect cavity and detected on the surface of the controlled product.

Instruments and equipment used in capillary control:

Sets for penetrant flaw detection Sherwin, Magnaflux, Helling (cleaners, developers, penetrants)
. Sprayers
. Pneumohydroguns
. Sources of ultraviolet lighting (ultraviolet lamps, illuminators).
. Test panels (test panel)
. Control samples for color flaw detection.

The "sensitivity" parameter in the capillary flaw detection method

The sensitivity of penetrant testing is the ability to detect discontinuities of a given size with a given probability when using a specific method, control technology and penetrant system. According to GOST 18442-80, the control sensitivity class is determined depending on the minimum size of detected defects with a transverse size of 0.1 - 500 microns.

Detection of surface defects with an opening size of more than 500 microns is not guaranteed by capillary testing methods.

Sensitivity class Defect opening width, µm

II From 1 to 10

III From 10 to 100

IV From 100 to 500

technological Not standardized

Physical basis and methodology of the capillary control method

The capillary method of non-destructive testing (GOST 18442-80) is based on the penetration of an indicator substance into a surface defect and is intended to identify damage that has free access to the surface of the test product. The color flaw detection method is suitable for detecting discontinuities with a transverse size of 0.1 - 500 microns, including through defects, on the surface of ceramics, ferrous and non-ferrous metals, alloys, glass and other synthetic materials. Found wide application when monitoring the integrity of solders and welds.

Colored or dyeing penetrant is applied with a brush or spray to the surface of the test object. Thanks to the special qualities that are provided at the production level, the choice of physical properties of the substance: density, surface tension, viscosity, penetrant under the action of capillary pressure, penetrates into the smallest discontinuities that have open exit onto the surface of the controlled object.

The developer, applied to the surface of the test object after a relatively short time after careful removal of the unassimilated penetrant from the surface, dissolves the dye located inside the defect and, due to mutual penetration into each other, “pushes” the penetrant remaining in the defect onto the surface of the test object.

Existing defects are visible quite clearly and in contrast. Indicator marks in the form of lines indicate cracks or scratches, individual color dots indicate single pores or outlets.

The process of detecting defects using the capillary method is divided into 5 stages (performing capillary testing):

1. Preliminary cleaning of the surface (use a cleaner)
2. Application of penetrant
3. Removing excess penetrant
4. Application of developer
5. Control

Capillary control. Color flaw detection. Penetrant non-destructive testing method.

Non-destructive testing acquires important, when the development of the coating has already been completed and you can move on to it industrial applications. Before a coated product goes into service, it is checked for strength and the absence of cracks, discontinuities, pores or other defects that could cause destruction. The more complex the object being coated, the greater the likelihood of defects. Table 1 presents and describes below existing non-destructive methods for determining the quality of coatings.

Table 1. Non-destructive methods for quality control of coatings before their use.

VISUAL INSPECTION

The simplest quality assessment is an external inspection of a coated product. Such control is relatively simple, it becomes especially effective in good lighting, when using a magnifying glass. In general, external inspection should be performed by qualified personnel and in combination with other methods.

SPRAYING WITH PAINT

Cracks and depressions on the surface of the coating are revealed by the absorption of paint. The surface to be tested is sprayed with paint. It is then thoroughly wiped and an indicator is sprayed onto it. After a minute, paint comes out of cracks and other minor defects and colors the indicator, thus revealing the outline of the crack.

FLUORESCENT CONTROL

This method is similar to the paint absorption method. The test sample is immersed in a solution containing fluorescent dye, which gets into all the cracks. After cleaning the surface, the sample is coated with a new solution. If the coating has any defects, the fluorescent paint in this area will be visible under ultraviolet irradiation.

Both absorption-based techniques are used only to detect surface defects. Internal defects are not detected. Defects lying on the surface itself are difficult to detect, since wiping the surface before applying the indicator removes the paint from them.

RADIOGRAPHIC CONTROL

Penetrating radiation inspection is used to identify pores, cracks and cavities within the coating. X-rays and gamma rays pass through the material being tested and onto the photographic film. The intensity of x-rays and gamma radiation changes as they pass through the material. Any pores, cracks or changes in thickness will be recorded on the photographic film, and by appropriate decoding of the film, the position of any internal defects can be determined.

Radiographic testing is relatively expensive and slow. The operator must be protected from radiation. Difficult to analyze products complex shape. Defects are determined when their size is more than 2% of the total coating thickness. Therefore, radiographic technique is not suitable for detecting small defects in large structures complex shape, it gives good results on less complex products.

EDGE CURRENT CONTROL

Surface and internal defects can be determined using eddy currents induced in the product by introducing it into the electromagnetic field of the inductor. When a part moves in an inductor, or an inductor relative to a part, the induced eddy currents interact with the inductor and change its impedance. The induced current in a sample depends on the presence of conduction defects in the sample, as well as its hardness and size.

By using appropriate inductances and frequencies, or a combination of both, defects can be identified. Eddy current monitoring is not practical if the product configuration is complex. This type of inspection is not suitable for detecting defects on edges and corners; in some cases from uneven surface the same signals as from the defect may be received.

ULTRASONIC CONTROL

In ultrasonic testing, ultrasound is passed through a material and changes in the sound field caused by defects in the material are measured. The energy reflected from defects in the sample is sensed by a transducer, which turns it into an electrical signal and is fed to an oscilloscope.

Depending on the size and shape of the sample, longitudinal, transverse or surface waves are used for ultrasonic testing. Longitudinal waves propagate through the test material in a straight line until they encounter a boundary or discontinuity. The first boundary that the incoming wave encounters is the boundary between the transducer and the product. Part of the energy is reflected from the boundary, and a primary pulse appears on the oscilloscope screen. The remaining energy travels through the material until it encounters a defect or the opposing surface, the position of the defect being determined by measuring the distance between the signal from the defect and from the front and rear surfaces.

Discontinuities can be positioned so that they can be identified by directing radiation perpendicular to the surface. In this case, the sound beam is introduced at an angle to the surface of the material to create transverse waves. If the entry angle is increased sufficiently, surface waves are formed. These waves follow the contour of the sample and can detect defects near its surface.

There are two main types of ultrasonic testing units. Resonance testing uses radiation with a variable frequency. When the natural frequency corresponding to the thickness of the material is reached, the amplitude of the oscillations increases sharply, which is reflected on the oscilloscope screen. The resonance method is mainly used to measure thickness.

With the pulse echo method, pulses of constant frequency lasting a fraction of a second are introduced into the material. The wave passes through the material and the energy reflected from the defect or back surface is incident on the transducer. The transducer then sends out another pulse and receives the reflected one.

To identify defects in the coating and to determine the adhesion strength between the coating and the substrate, the transmission method is also used. In some coating systems, reflected energy measurement does not adequately identify the defect. This is due to the fact that the boundary between the coating and the substrate is characterized by such a high reflection coefficient that the presence of defects changes the total reflection coefficient little.

The use of ultrasonic testing is limited. This can be seen from following examples. If the material has a rough surface, the sound waves are scattered so much that the test becomes meaningless. To test objects of complex shape, transducers are needed that follow the contour of the object; Surface irregularities cause blips to appear on the oscilloscope screen, making it difficult to identify defects. Grain boundaries in metal act similarly to defects and scatter sound waves. Defects located at an angle to the beam are difficult to detect, since reflection occurs mainly not in the direction of the converter, but at an angle to it. It is often difficult to distinguish discontinuities located close to one another. In addition, only those defects are detected whose dimensions are comparable to the length sound wave.

Conclusion

Selection tests are undertaken during initial stage coating development. Because during the search period optimal mode the number of different samples is very large, a combination of test methods is used to weed out unsatisfactory samples. This selection program usually consists of several types of oxidation tests, metallographic examination, flame testing and tensile testing. Coatings that successfully pass selection tests are tested under conditions similar to operational ones.

Once a particular coating system has been determined to pass field testing, it can be applied to protect the actual product. It is necessary to develop a technique for non-destructive testing of the final product before putting it into operation. Non-destructive techniques can be used to identify surface and internal holes, cracks and discontinuities, as well as poor adhesion between the coating and the substrate.

COMPLETED: LOPATINA OKSANA

Penetrant flaw detection - a flaw detection method based on the penetration of certain liquid substances into surface defects of a product under the action of capillary pressure, as a result of which the light and color contrast of the defective area relative to the undamaged area increases.

Penetrant flaw detection (penetrant testing) designed to identify invisible or weakly visible to the naked eye surface and through defects (cracks, pores, cavities, lack of fusion, intercrystalline corrosion, fistulas, etc.) in test objects, determining their location, extent and orientation along the surface.

Indicator liquid(penetrant) is a colored liquid designed to fill open surface defects and subsequently form an indicator pattern. The liquid is a solution or suspension of dye in a mixture of organic solvents, kerosene, oils with the addition of surfactants (surfactants) that reduce the surface tension of water located in defect cavities and improve the penetration of penetrants into these cavities. Penetrants contain dyes (color method) or luminescent additives (luminescent method), or a combination of both.

Cleaner– serves for preliminary cleaning of the surface and removal of excess penetrant

Developer is a flaw detection material designed to extract penetrant from a capillary discontinuity in order to form a clear indicator pattern and create a contrasting background. There are five main types of developers used with penetrants:

Dry powder; - aqueous suspension; - suspension in solvent; - solution in water; - plastic film.

Devices and equipment for capillary control:

Materials for color flaw detection, Luminescent materials

Kits for penetrant flaw detection (cleaners, developers, penetrants)

Sprayers, Pneumatic-hydraulic guns

Sources of ultraviolet lighting (ultraviolet lamps, illuminators).

Test panels (test panel)

Control samples for color flaw detection.

The penetrant testing process consists of 5 stages:

1 – preliminary cleaning of the surface. To ensure that the dye can penetrate into defects on the surface, it must first be cleaned with water or an organic cleaner. All contaminants (oils, rust, etc.) and any coatings (paintwork, metallization) must be removed from the controlled area. After this, the surface is dried so that no water or cleaner remains inside the defect.

2 – application of penetrant. The penetrant, usually red in color, is applied to the surface by spraying, brushing or dipping the test object into a bath to ensure good penetration and complete coverage of the penetrant. As a rule, at a temperature of 5...50°C, for a time of 5...30 minutes.

3 - removal of excess penetrant. Excess penetrant is removed by wiping with a cloth, rinsing with water, or with the same cleaner as at the pre-cleaning stage. In this case, the penetrant should be removed only from the control surface, but not from the defect cavity. Then the surface is dried with a lint-free cloth or a stream of air.

4 – application of developer. After drying, a developer (usually white) is immediately applied to the control surface in a thin, even layer.

5 - control. Identification of existing defects begins immediately after the end of the development process. During control, indicator traces are identified and recorded. The intensity of the color indicates the depth and width of the defect; the paler the color, the smaller the defect. Deep cracks have intense coloring. After testing, the developer is removed with water or a cleaner.

To the disadvantages capillary testing should include its high labor intensity in the absence of mechanization, the long duration of the control process (from 0.5 to 1.5 hours), as well as the complexity of mechanization and automation of the control process; decreased reliability of results at subzero temperatures; subjectivity of control - dependence of the reliability of the results on the professionalism of the operator; limited shelf life of flaw detection materials, dependence of their properties on storage conditions.

The advantages of capillary control are: simplicity of control operations, simplicity of equipment, applicability to a wide range of materials, including non-magnetic metals. The main advantage of capillary flaw detection is that with its help it is possible not only to detect surface and through defects, but also to obtain, from their location, extent, shape and orientation along the surface, valuable information about the nature of the defect and even some of the reasons for its occurrence (stress concentration, non-compliance technology, etc.).

Flaw detection materials for color flaw detection are selected depending on the requirements for the controlled object, its condition and control conditions. The transverse size of the defect on the surface of the test object is taken as a defect size parameter - the so-called defect opening width. The minimum value of disclosure of detected defects is called the lower sensitivity threshold and is limited by the fact that a very small amount of penetrant retained in the cavity of a small defect is insufficient to obtain a contrast indication for a given thickness of the developing substance layer. There is also an upper sensitivity threshold, which is determined by the fact that the penetrant is washed out of wide but shallow defects when excess penetrant is removed from the surface. The detection of indicator traces corresponding to the main characteristics indicated above serves as the basis for an analysis of the admissibility of the defect in terms of its size, nature, and position. GOST 18442-80 establishes 5 sensitivity classes (lower threshold) depending on the size of defects

Class 1 sensitivity controls the blades of turbojet engines, sealing surfaces of valves and their seats, metal sealing gaskets of flanges, etc. (detectable cracks and pores up to tenths of a micron in size). Class 2 tests reactor housings and anti-corrosion surfacing, base metal and welded connections of pipelines, bearing parts (detectable cracks and pores up to several microns in size). Class 3 tests the fasteners of a number of objects, with the ability to detect defects with an opening of up to 100 microns; class 4 – thick-walled castings.

Capillary methods, depending on the method of identifying the indicator pattern, are divided into:

· Luminescent method, based on recording the contrast of a visible indicator pattern luminescent in long-wave ultraviolet radiation against the background of the surface of the test object;

· contrast (color) method, based on registration of color contrast in visible radiation indicator pattern against the background of the surface of the test object.

· fluorescent color method, based on recording the contrast of a color or luminescent indicator pattern against the background of the surface of the test object in visible or long-wave ultraviolet radiation;

· luminance method, based on registering the contrast in visible radiation of an achromatic pattern against the background of the object’s surface.

PERFORMED BY: VALYUKH ALEXANDER

Penetrant control

Penetrant non-destructive testing method

CapillIflaw detectorAndI - flaw detection method based on the penetration of certain liquid substances into surface defects of the product under the action of capillary pressure, as a result of which the light and color contrast of the defective area relative to the undamaged area increases.

There are luminescent and color methods of capillary flaw detection.

In most cases, according to technical requirements, it is necessary to identify defects so small that they can be noticed when visual inspection almost impossible with the naked eye. The use of optical measuring instruments, such as a magnifying glass or microscope, does not allow identifying surface defects due to insufficient contrast of the image of the defect against the background of the metal and a small field of view at high magnifications. In such cases, the capillary control method is used.

During capillary testing, indicator liquids penetrate into the cavities of surface and through discontinuities in the material of the test objects, and the resulting indicator traces are recorded visually or using a transducer.

Testing by the capillary method is carried out in accordance with GOST 18442-80 “Non-destructive testing. Capillary methods. General requirements."

Capillary methods are divided into basic, using capillary phenomena, and combined, based on a combination of two or more non-destructive testing methods of different physical nature, one of which is penetrant testing (penetrant flaw detection).

Purpose of penetrant testing (penetrant flaw detection)

Penetrant flaw detection (penetrant testing) designed to identify invisible or weakly visible to the naked eye surface and through defects (cracks, pores, cavities, lack of fusion, intercrystalline corrosion, fistulas, etc.) in test objects, determining their location, extent and orientation along the surface.

Capillary methods of non-destructive testing are based on capillary penetration of indicator liquids (penetrants) into the cavities of surface and through discontinuities of the material of the test object and registration of the resulting indicator traces visually or using a transducer.

Application of the capillary method of non-destructive testing

The capillary testing method is used to control objects of any size and shape made of ferrous and non-ferrous metals, alloy steels, cast iron, metal coatings, plastics, glass and ceramics in the energy sector, aviation, rocketry, shipbuilding, the chemical industry, metallurgy, and in the construction of nuclear power plants. reactors, in the automotive industry, electrical engineering, mechanical engineering, foundry, stamping, instrument making, medicine and other industries. For some materials and products, this method is the only one for determining the suitability of parts or installations for work.

Penetrant flaw detection is also used for non-destructive testing of objects made of ferromagnetic materials, if their magnetic properties, shape, type and location of defects do not allow achieving the sensitivity required by GOST 21105-87 using the magnetic particle method and the magnetic particle testing method is not allowed to be used due to the operating conditions of the object.

A necessary condition for identifying defects such as a violation of the continuity of a material by capillary methods is the presence of cavities that are free from contaminants and other substances that have access to the surface of objects and a depth of distribution that significantly exceeds the width of their opening.

Penetrant testing is also used for leak detection and, in combination with other methods, for monitoring critical facilities and facilities during operation.

The advantages of capillary flaw detection methods are: simplicity of control operations, simplicity of equipment, applicability to a wide range of materials, including non-magnetic metals.

The advantage of penetrant flaw detection is that with its help it is possible not only to detect surface and through defects, but also to obtain, from their location, extent, shape and orientation along the surface, valuable information about the nature of the defect and even some of the reasons for its occurrence (stress concentration, non-compliance with technology, etc.). ).

Organic phosphors are used as indicator liquids - substances that produce a bright glow of their own when exposed to ultraviolet rays, as well as various dyes. Surface defects are detected using means that make it possible to extract indicator substances from the defect cavity and detect their presence on the surface of the controlled product.

Capillary (crack), facing the surface of the test object only on one side is called a surface discontinuity, and connecting the opposite walls of the test object is called through. If surface and through discontinuities are defects, then it is permissible to use the terms “surface defect” and “through defect” instead. The image formed by the penetrant at the location of the discontinuity and similar to the cross-sectional shape at the exit to the surface of the test object is called an indicator pattern, or indication.

In relation to a discontinuity such as a single crack, instead of the term “indication”, the term “indicator trace” can be used. Discontinuity depth is the size of the discontinuity in the direction inward of the test object from its surface. Discontinuity length is the longitudinal size of a discontinuity on the surface of an object. Discontinuity opening is the transverse size of the discontinuity at its exit to the surface of the test object.

A necessary condition for the reliable detection of defects that reach the surface of an object by the capillary method is their relative freedom from contamination by foreign substances, as well as a depth of distribution that significantly exceeds the width of their opening (minimum 10/1). A cleaner is used to clean the surface before applying penetrant.

Capillary flaw detection methods are divided into into basic ones, using capillary phenomena, and combined ones, based on a combination of two or more non-destructive testing methods that are different in physical essence, one of which is capillary testing.

Penetrant testing of welded joints is used to identify external (surface and through) and. This method of testing allows you to identify defects such as hot and incomplete cooking, pores, cavities and some others.

Using penetrant flaw detection, it is possible to determine the location and size of the defect, as well as its orientation along the metal surface. This method applies to both . It is also used in welding plastics, glass, ceramics and other materials.

The essence of the capillary testing method is the ability of special indicator liquids to penetrate into the cavities of seam defects. By filling defects, indicator liquids form indicator traces, which are recorded during visual inspection or using a transducer. The procedure for penetrant control is determined by standards such as GOST 18442 and EN 1289.

Classification of capillary flaw detection methods

Penetrant testing methods are divided into basic and combined.

The main ones involve only capillary control with penetrating substances.

Combined ones are based on the combined use of two or more, one of which is capillary control.

1. Basic control methods

• The main control methods are divided into:
• Depending on the type of penetrant:

1. penetrant testing

• testing using filter suspensions
• Depending on the method of reading information:
• brightness (achromatic)
• color (chromatic)

luminescent

luminescent-colored.

1. Combined methods of penetrant control
2. Combined methods are divided depending on the nature and method of exposure to the surface being tested. And they happen:
3. Capillary-electrostatic
4. Capillary-electroinduction
5. Capillary-magnetic

Capillary-radiation absorption method

Capillary radiation method. Penetrant flaw detection technology Before performing penetrant testing, the surface to be tested must be cleaned and dried. After this, an indicator liquid - panetrant - is applied to the surface.

This liquid penetrates into the surface defects of the seams and after some time, intermediate cleaning is carried out, during which excess indicator liquid is removed. Next, a developer is applied to the surface, which begins to draw the indicator liquid from the weld defects. Thus, defect patterns appear on the tested surface, visible

naked eye

1. , or using special developers.
2. Stages of penetrant control
3. The control process using the capillary method can be divided into the following stages:
4. Preparation and pre-cleaning
5. Intermediate cleaning
6. Manifestation Process

Detection of welding defects

Drawing up a protocol in accordance with the results of the inspection

Water sensitive emulsifier

If necessary, contaminants such as scale, rust, oil stains, paint, etc. are removed from the controlled surface of the weld. These contaminants are removed using mechanical or chemical cleaning, or a combination of these methods.

Mechanical cleaning is recommended only in exceptional cases, if there is a loose film of oxides on the controlled surface or there are sharp differences between the weld beads or deep undercuts. Mechanical cleaning has received limited use due to the fact that when it is carried out, surface defects are often closed as a result of rubbing, and they are not detected during inspection.

Chemical cleaning involves the use of various chemical cleaning agents that remove contaminants such as paint, oil stains, etc. from the surface being tested. Residues of chemical reagents can react with indicator liquids and affect the accuracy of control. That's why chemical substances after preliminary cleaning, they should be washed off the surface with water or other means.

After preliminary cleaning of the surface, it must be dried. Drying is necessary to ensure that no water, solvent, or any other substances remain on the outer surface of the seam being tested.

Application of indicator liquid

The application of indicator liquids to the controlled surface can be carried out in the following ways:

1. By capillary method. In this case, filling of weld defects occurs spontaneously. The liquid is applied by wetting, dipping, jetting or spraying compressed air or inert gas.
2. Vacuum method. With this method, a rarefied atmosphere is created in the defect cavities and the pressure in them becomes less than atmospheric, i.e. a kind of vacuum is obtained in the cavities, which absorbs the indicator liquid.
3. Compression method. This method is the opposite of the vacuum method. Filling of defects occurs under the influence of pressure on the indicator liquid exceeding Atmosphere pressure. Under high pressure, the liquid fills the defects, displacing air from them.
4. Ultrasonic method. Filling of defect cavities occurs in an ultrasonic field and using the ultrasonic capillary effect.
5. Deformation method. Defect cavities are filled under the influence of elastic vibrations of a sound wave on the indicator liquid or under static loading, which increases minimum size defects.

For better penetration indicator liquid in the defect cavity, the surface temperature should be in the range of 10-50°C.

Intermediate surface cleaning

Substances for intermediate surface cleaning should be applied in such a way that the indicator liquid is not removed from surface defects.

Cleaning with water

Excess indicator liquid can be removed by spraying or wiping with a damp cloth. At the same time, mechanical impact on the controlled surface should be avoided. The water temperature should not exceed 50°C.

Solvent cleaning

First, remove excess liquid using a clean, lint-free cloth. After this, the surface is cleaned with a cloth moistened with a solvent.

Cleaning with emulsifiers

Water-sensitive emulsifiers or oil-based emulsifiers are used to remove indicator liquids. Before applying the emulsifier, it is necessary to wash off excess indicator liquid with water and immediately apply the emulsifier.

After emulsification, it is necessary to rinse the metal surface with water.

Combined cleaning with water and solvent

With this cleaning method, excess indicator liquid is first washed off from the monitored surface with water, and then the surface is cleaned with a lint-free cloth moistened with a solvent.

Drying after intermediate cleaning

• To dry the surface after intermediate cleaning, you can use several methods:
• by wiping with a clean, dry, lint-free cloth
• evaporation at ambient temperature drying at
• elevated temperature
• air drying

a combination of the above drying methods.

The drying process must be carried out in such a way that the indicator liquid does not dry out in the cavities of the defects. To do this, drying is performed at a temperature not exceeding 50°C.

The process of manifestation of surface defects in a weld The developer is applied evenly to the controlled surface. thin layer

Fluorescent liquids

. The development process should begin as soon as possible after intermediate cleaning.

The use of dry developer is only possible with fluorescent indicator liquids. The dry developer is applied by spraying or electrostatic spraying. The controlled areas should be covered uniformly and evenly.

The developer is applied uniformly by immersing the controlled compound in it or by spraying it using a machine. When using the immersion method, to obtain the best results, the duration of the immersion should be as short as possible. The compound to be tested must then be evaporated or blast dried in an oven.

Solvent based liquid developer

The developer is sprayed onto the controlled surface so that the surface is evenly wetted and a thin and uniform film is formed on it.

Liquid developer in the form of an aqueous solution

Uniform application of such a developer is achieved by immersing the controlled surfaces in it, or by spraying with special devices.

The immersion should be short-term; in this case, the best test results are achieved. After this, the controlled surfaces are dried by evaporation or blowing in an oven.

Duration of the development process

The duration of the development process lasts, as a rule, for 10-30 minutes. In some cases, an increase in the duration of manifestation is allowed. The development time countdown begins: for dry developer immediately after its application, and for liquid developer - immediately after drying the surface.

Detection of welding defects as a result of penetrant flaw detection

If possible, inspection of the controlled surface begins immediately after applying the developer or after drying it. But the final control occurs after the development process is completed. Magnifying glasses or glasses with magnifying lenses are used as auxiliary devices for optical inspection.

When using fluorescent indicator liquids

The use of photochromatic glasses is not permitted. It is necessary for the inspector's eyes to adapt to the darkness in the test booth for a minimum of 5 minutes.

Ultraviolet radiation should not reach the inspector's eyes. All monitored surfaces must not fluoresce (reflect light). Also, objects that reflect light under the influence of ultraviolet rays should not fall into the controller’s field of view. General ultraviolet lighting may be used to allow the inspector to move around the test chamber without obstruction.

All controlled surfaces are inspected in daylight or artificial light. The illumination on the surface being tested must be at least 500 lux.

At the same time, there should be no glare on the surface due to light reflection.

Repeated capillary control If there is a need for re-inspection, then the entire penetrant flaw detection process is repeated, starting with the pre-cleaning process. To do this, it is necessary, if possible, to provide more favorable conditions

control. For repeated control, it is allowed to use only the same indicator liquids, from the same manufacturer, as during the first control. Using other liquids, or the same liquids but different manufacturers

, not allowed. In this case, it is necessary to thoroughly clean the surface so that no traces of the previous inspection remain on it.

According to EN571-1, the main stages of penetrant testing are presented in the diagram:

Video on the topic: "Capillary flaw detection of welds"

Penetrant testing (capillary / fluorescent / color flaw detection, penetrant testing) Penetrant inspection, penetrant flaw detection, luminescent / color flaw detection - these are the most common names among specialists for the method of non-destructive testing with penetrating substances, -.

penetrants - Capillary control method the best way detection of defects appearing on the surface of products. Practice shows the high economic efficiency of penetrant flaw detection, the possibility of its use in a wide variety of forms and controlled objects

, ranging from metals to plastics. At a relatively low cost Supplies

, equipment for fluorescent and color flaw detection is simpler and less expensive than for most other non-destructive testing methods.

Penetrant test kits

Kits for color flaw detection based on red penetrants and white developers

Standard set for operation in the temperature range -10°C ... +100°C

High temperature set for operation in the range 0°C ... +200°C

Kits for penetrant flaw detection based on luminescent penetrants

Standard set for operation in the temperature range -10°C ... +100°C in visible and UV light

High temperature kit for operation in the range 0°C ... +150°C using a UV lamp λ=365 nm.

Penetrant flaw detection - review

Historical reference

Method for studying the surface of an object penetrating penetrants, which is also known as penetrant flaw detection(capillary control), appeared in our country in the 40s of the last century. Penetrant control was first used in the aircraft industry. Its simple and clear principles have remained unchanged to this day.

Abroad, around the same time, a red-white method for detecting surface defects was proposed and soon patented. Subsequently, it received the name - liquid penetrant testing method. In the second half of the 50s of the last century, materials for penetrant flaw detection were described in the US military specification (MIL-1-25135).

Penetrant quality control

Possibility of quality control of products, parts and assemblies using penetrating substances - - these are the most common names among specialists for the method of non-destructive testing with penetrating substances, - exists due to such a physical phenomenon as wetting. The flaw detection liquid (penetrant) wets the surface and fills the mouth of the capillary, thereby creating conditions for the appearance of a capillary effect.

Penetrating ability is a complex property of liquids. This phenomenon is the basis of capillary control. Penetration ability depends on the following factors:

• properties of the surface under study and the degree of its cleaning from contaminants;
• physical and chemical properties of the material of the test object;
• properties penetrant(wettability, viscosity, surface tension);
• temperature of the test object (affects the viscosity of the penetrant and wettability)

Among other types of non-destructive testing (NDT), the capillary method plays a special role. Firstly, in terms of the totality of qualities, it is perfect way surface control for the presence of microscopic discontinuities invisible to the eye. It is distinguished from other types of NDT by its portability and mobility, the cost of monitoring a unit area of ​​the product, and the relative ease of implementation without the use of complex equipment. Secondly, capillary control is more universal. If, for example, it is used only for testing ferromagnetic materials with a relative magnetic permeability of more than 40, then penetrant flaw detection is applicable to products of almost any shape and material, where the geometry of the object and the direction of defects do not play a special role.

Development of penetrant testing as a non-destructive testing method

The development of surface flaw detection methods, as one of the areas of non-destructive testing, is directly related to scientific and technological progress. Manufacturers industrial equipment have always been concerned about saving materials and human resources. At the same time, the operation of equipment is often associated with increased mechanical loads on some of its elements. Let's take turbine blades as an example. aircraft engines. Under intense loads, it is cracks on the surface of the blades that pose a known danger.

In this particular case, as in many others, capillary control came in handy. Manufacturers quickly appreciated it, it was adopted and received a sustainable vector of development. The capillary method has proven to be one of the most sensitive and popular non-destructive testing methods in many industries. Mainly in mechanical engineering, serial and small-scale production.

Currently, the improvement of capillary control methods is carried out in four directions:

• improving the quality of flaw detection materials aimed at expanding the sensitivity range;
• decline harmful effects materials on the environment and humans;
• the use of electrostatic spraying systems of penetrants and developers for a more uniform and economical application of them to the controlled parts;
• implementation of automation schemes in the multi-operational process of surface diagnostics in production.

Organization of a color (fluorescent) flaw detection area

The organization of the area for color (luminescent) flaw detection is carried out in accordance with industry recommendations and enterprise standards: RD-13-06-2006. The site is assigned to the non-destructive testing laboratory of the enterprise, which is certified in accordance with the Certification Rules and the basic requirements for non-destructive testing laboratories PB 03-372-00.

Both in our country and abroad, the use of color flaw detection methods at large enterprises is described in internal standards, which are completely based on national ones. Color flaw detection is described in the standards of Pratt&Whitney, Rolls-Royce, General Electric, Aerospatiale and others.

Penetrant control - pros and cons

Advantages of the capillary method

1. Low costs for consumables.
2. High objectivity of control results.
3. Can be used for almost all solid materials (metals, ceramics, plastics, etc.) with the exception of porous ones.
4. In most cases, penetrant testing does not require the use of technologically complex equipment.
5. Carrying out control anywhere under any conditions, including stationary ones, using appropriate equipment.
6. Thanks to the high monitoring performance, it is possible quick check large objects with a large surface area under study. Using this method At enterprises with a continuous production cycle, in-line control of products is possible.
7. The capillary method is ideal for detecting all types of surface cracks, providing clear visualization of defects (when properly inspected).
8. Ideal for inspection of complex geometries, light metal parts such as turbine blades in the aerospace and energy industries, and engine parts in the automotive industry.
9. Under certain circumstances, the method can be used for leak testing. To do this, the penetrant is applied to one side of the surface and the developer to the other. At the point of leakage, the penetrant is drawn to the surface by the developer. Leak testing to detect and locate leaks is extremely important for products such as tanks, containers, radiators, hydraulic systems and so on.
10. Unlike X-ray testing, penetrant flaw detection does not require special safety measures, such as the use of radiation protection equipment. During research, it is enough for the operator to exercise basic caution when working with consumables and use a respirator.
11. Absence special requirements regarding the knowledge and qualifications of the operator.

Limitations for color flaw detection

1. The main limitation of the capillary inspection method is the ability to detect only those defects that are open to the surface.
2. A factor that reduces the effectiveness of capillary testing is the roughness of the test object - the porous structure of the surface leads to false readings.
3. Special cases, although quite rare, include the low wettability of the surface of some materials with penetrants both water-based and organic solvent-based.
4. In some cases, the disadvantages of the method include the difficulty of performing preparatory operations associated with the removal paint coatings, oxide films and drying of parts.

Penetrant control - terms and definitions

Penetrant non-destructive testing

Penetrant non-destructive testing is based on the penetration of penetrants into cavities that form defects on the surface of products. Penetrant is a dye. Its trace, after appropriate surface treatment, is recorded visually or using instruments.

In capillary control apply various ways testing based on the use of penetrants, surface preparation materials, developers and for penetrant studies. There are now a sufficient number of consumables for penetrant testing on the market that allow the selection and development of techniques that satisfy essentially any sensitivity, compatibility and environmental requirements.

Physical basis of penetrant flaw detection

The basis of penetrant flaw detection- this is a capillary effect, as a physical phenomenon, and a penetrant, as a substance with certain properties. The capillary effect is influenced by such phenomena as surface tension, wetting, diffusion, dissolution, and emulsification. But in order for these phenomena to work for results, the surface of the test object must be well cleaned and degreased.

If the surface is properly prepared, a drop of penetrant that falls on it will quickly spread, forming a stain. This indicates good wetting. Wetting (adhesion to a surface) refers to the ability liquid body form a stable interface at the interface with a solid body. If the interaction forces between the molecules of a liquid and a solid exceed the interaction forces between the molecules inside the liquid, then wetting of the surface of the solid occurs.

Pigment particles penetrant, many times smaller in size than the width of the opening of microcracks and other damage to the surface of the object under study. In addition, the most important physical property of penetrants is low surface tension. Due to this parameter, penetrants have sufficient penetrating ability and wet well different kinds surfaces - from metals to plastics.

Penetrant penetration into discontinuities (cavities) of defects and subsequent extraction of the penetrant during the development process occurs under the action of capillary forces. And deciphering a defect becomes possible due to the difference in color (color flaw detection) or glow (luminescent flaw detection) between the background and the surface area above the defect.

Thus, under normal conditions, very small defects on the surface of the test object are not visible to the human eye. In the process of step-by-step surface treatment special compounds, on which capillary flaw detection is based, an easily readable, contrasting indicator pattern is formed above the defects.

In color flaw detection, due to the action of the penetrant developer, which “pulls” the penetrant to the surface by diffusion forces, the size of the indication usually turns out to be significantly larger than the size of the defect itself. The size of the indicator pattern as a whole, subject to the control technology, depends on the volume of penetrant absorbed by the discontinuity. When assessing the control results, we can draw some analogy with the physics of the “amplification effect” of signals. In our case, the “output signal” is a contrasting indicator pattern, which can be several times larger in size than the “input signal” - an image of a discontinuity (defect) that is unreadable by the eye.

Flaw detection materials

Flaw detection materials for penetrant testing, these are means that are used for testing with liquid (penetration testing) penetrating into the surface discontinuities of the products being tested.

Penetrant

Penetrant is an indicator liquid, a penetrating substance (from the English penetrate - to penetrate) .

Penetrants are capillary flaw detection materials that are capable of penetrating into surface discontinuities of a controlled object. Penetrant penetration into the damage cavity occurs under the action of capillary forces. As a result of low surface tension and the action of wetting forces, the penetrant fills the void of the defect through an orifice open to the surface, thereby forming a concave meniscus.

Penetrant is the main consumable material for penetrant flaw detection. Penetrants are distinguished by the method of visualization into contrast (color) and luminescent (fluorescent), by the method of removal from the surface into water-washable and removable with a cleaner (post-emulsifiable), by sensitivity into classes (in descending order - I, II, III and IV classes according to GOST 18442-80)

Foreign standards MIL-I-25135E and AMS-2644, in contrast to GOST 18442-80, divide the sensitivity levels of penetrants into classes in ascending order: 1/2 - ultra-low sensitivity, 1 - low, 2 - medium, 3 - high, 4 - ultra-high .

Penetrants are subject to a number of requirements, the main one being good wettability. The next important parameter for penetrants is viscosity. The lower it is, the less time is required to completely saturate the surface of the test object. Penetrant testing takes into account such properties of penetrants as:

• wettability;
• viscosity;
• surface tension;
• volatility;
• flash point (flash point);
• specific gravity;
• solubility;
• sensitivity to pollution;
• toxicity;
• smell;
• inertia.

The composition of the penetrant usually includes high-boiling solvents, pigment-based dyes (luminophores) or soluble ones, surfactants, corrosion inhibitors, and binders. Penetrants are produced in cans for aerosol application (the most suitable form of release for field work), plastic canisters and barrels.

Developer

Developer is a material for capillary non-destructive testing, which, due to its properties, extracts the penetrant located in the defect cavity to the surface.

The penetrant developer is typically white in color and acts as a contrasting background for the indicator image.

The developer is applied to the surface of the test object in a thin, uniform layer after it has been cleaned (intermediate cleaning) of penetrant. After the intermediate cleaning procedure, a certain amount of penetrant remains in the defect area. The developer, under the influence of the forces of adsorption, absorption or diffusion (depending on the type of action), “pulls” the penetrant remaining in the capillaries of the defects to the surface.

Thus, the penetrant, under the influence of the developer, “tints” the surface areas above the defect, forming a clear defectogram - an indicator pattern that repeats the location of defects on the surface.

Based on the type of action, developers are divided into sorption (powders and suspensions) and diffusion (paints, varnishes and films). Most often, developers are chemically neutral sorbents made of silicon compounds, white in color. Such developers, covering the surface, create a layer with a microporous structure into which, under the action of capillary forces, the coloring penetrant easily penetrates. In this case, the developer layer above the defect is painted in the color of the dye (color method), or is moistened with a liquid containing a phosphor additive, which begins to fluoresce in ultraviolet light (luminescent method). In the latter case, the use of a developer is not necessary - it only increases the sensitivity of the control.

The correct developer should provide uniform surface coverage. The higher the sorption properties of the developer, the better it “pulls” the penetrant from the capillaries during development. These are the most important properties of the developer that determine its quality.

Penetrant control involves the use of dry and wet developers. In the first case we are talking about powder developers, in the second about water-based developers (aqueous, water-washable), or based on organic solvents (non-aqueous).

The developer in the flaw detection system, like other materials in this system, is selected based on sensitivity requirements. For example, to identify a defect with an opening width of up to 1 micron, in accordance with the American standard AMS-2644 for the diagnosis of moving parts gas turbine unit Powder developer and fluorescent penetrant should be used.

Powder developers have good dispersion and are applied to the surface by electrostatic or vortex method, forming a thin and uniform layer necessary to guarantee the extraction of a small volume of penetrant from the cavities of microcracks.

Water-based developers do not always provide a thin and uniform layer. In this case, if there are small defects on the surface, the penetrant does not always come to the surface. Too much thick layer developer may mask the defect.

Developers can react chemically with indicator penetrants. Based on the nature of this interaction, developers are divided into chemically active and chemically passive. The latter are the most widespread. Chemically active developers react with the penetrant. Detection of defects, in this case, is carried out by the presence of reaction products. Chemically passive developers act only as a sorbent.

Penetrant developers are available in aerosol cans (the most suitable form of release for field work), plastic canisters and barrels.

Penetrant emulsifier

Emulsifier (penetrant absorber according to GOST 18442-80) is a flaw detection material for penetrant testing, used for intermediate surface cleaning when using post-emulsifying penetrant.

During the emulsification process, the penetrant remaining on the surface interacts with the emulsifier. Subsequently, the resulting mixture is removed with water. The purpose of the procedure is to clean the surface from excess penetrant.

The emulsification process can have a significant impact on the quality of visualization of defects, especially when inspecting objects with rough surface. This is expressed in obtaining a contrasting background of the required purity. To obtain a clearly readable indicator pattern, the background brightness should not exceed the display brightness.

Lipophilic and hydrophilic emulsifiers are used in capillary control. A lipophilic emulsifier is made on an oil basis, while a hydrophilic emulsifier is made on a water basis. They differ in their mechanism of action.

The lipophilic emulsifier, covering the surface of the product, passes into the remaining penetrant under the influence of diffusion forces. The resulting mixture is easily removed from the surface with water.

The hydrophilic emulsifier acts on the penetrant in a different way. When exposed to it, the penetrant is divided into many particles of smaller volume. As a result, an emulsion is formed, and the penetrant loses its ability to wet the surface of the test object. The resulting emulsion is removed mechanically (washed off with water). The basis of hydrophilic emulsifiers is a solvent and surfactants (surfactants).

Penetrant cleaner(surfaces)

Penetrant Cleaner is an organic solvent for removing excess penetrant (intermediate cleaning), cleaning and degreasing the surface (pre-cleaning).

A significant influence on the wetting of the surface is exerted by its microrelief and the degree of purification from oils, fats and other contaminants. In order for the penetrant to penetrate even the smallest pores, in most cases, mechanical cleaning is not enough. Therefore, before testing, the surface of the part is treated with special cleaners made from high-boiling solvents.

The most important properties Modern surface cleaners for penetrant control are:

• degreasing ability;
• absence of non-volatile impurities (the ability to evaporate from the surface without leaving traces);
• minimal content of harmful substances that affect humans and the environment;
• Operating temperature range.

Penetrant testing consumable compatibility

Flaw detection materials for penetrant testing by physical and chemical properties must be compatible both with each other and with the material of the test object. Components of penetrants, cleaning agents and developers must not lead to loss of operational properties controlled products and damage to equipment.

Compatibility table for Elitest consumables for penetrant testing:

⚫ - recommended to use; ∨ - can be used; × - can not use
Download the compatibility table of consumables for capillary and magnetic particle testing:

Penetrant testing equipment

Equipment used in penetrant testing:

• reference (control) samples for penetrant flaw detection;
• sources of ultraviolet lighting (UV lanterns and lamps);
• test panels (test panel);
• air-hydraulic pistols;
• sprayers;
• cameras for penetrant control;
• systems for electrostatic application of flaw detection materials;
• water purification systems;
• drying cabinets;
• tanks for immersion application of penetrants.

Detected defects

Penetrant flaw detection methods make it possible to identify defects that appear on the surface of a product: cracks, pores, cavities, lack of fusion, intergranular corrosion and other discontinuities with an opening width of less than 0.5 mm.

Control samples for penetrant flaw detection

Control (standard, reference, test) samples for penetrant testing are metal plates with artificial cracks (defects) of a certain size applied to them. The surface of the control samples may have roughness.

Control samples are manufactured according to foreign standards, in accordance with European and American standards EN ISO 3452-3, AMS 2644C, Pratt & Whitney Aircraft TAM 1460 40 (the standard of the company - the largest American manufacturer of aircraft engines).

Control samples use:

• to determine the sensitivity of test systems based on various flaw detection materials (penetrant, developer, cleaner);
• to compare penetrants, one of which can be taken as a model;
• to assess the washability quality of luminescent (fluorescent) and contrast (color) penetrants in accordance with AMS 2644C standards;
• for general assessment of the quality of penetrant testing.

The use of control samples for penetrant testing is not regulated in Russian GOST 18442-80. However, in our country, control samples are actively used in accordance with GOST R ISO 3452-2-2009 and enterprise standards (for example, PNAEG-7-018-89) to assess the suitability of flaw detection materials.

Penetrant testing techniques

To date, we have accumulated enough great experience application of capillary methods for the purpose of operational control of products, assemblies and mechanisms. However, the development of a working methodology for carrying out penetrant testing often has to be carried out separately for each specific case. This takes into account factors such as:

1. sensitivity requirements;
2. object state;
3. the nature of the interaction of flaw detection materials with the controlled surface;
4. compatibility of consumables;
5. technical capabilities and conditions for performing work;
6. the nature of the expected defects;
7. other factors affecting the effectiveness of penetrant control.

GOST 18442-80 defines the classification of the main capillary control methods depending on the type of penetrant - penetrant (solution or suspension of pigment particles) and depending on the method of obtaining primary information:

1. brightness (achromatic);
2. color (chromatic);
3. luminescent (fluorescent);
4. luminescent-colored.

Standards GOST R ISO 3452-2-2009 and AMS 2644 describe six main methods of penetrant testing by type and groups:

Type 1. Fluorescent (luminescent) methods:

• method A: water-washable (Group 4);
• method B: subsequent emulsification (Groups 5 and 6);
• method C: organosoluble (Group 7).

Type 2. Color methods:

• method A: water-washable (Group 3);
• method B: subsequent emulsification (Group 2);
• method C: organosoluble (Group 1).