Penetrant testing methods are based on the penetration of liquid into defect cavities and its adsorption or diffusion from the defects. In this case, there is a difference in color or glow between the background and the surface area above the defect. Capillary methods are used to determine surface defects in the form of cracks, pores, hairlines and other discontinuities on the surface of parts.

Capillary flaw detection methods include the luminescent method and the paint method.

With the luminescent method, the test surfaces, cleaned of contaminants, are coated with a fluorescent liquid using a spray or brush. Such liquids can be: kerosene (90%) with auto scrap (10%); kerosene (85%) with transformer oil (15%); kerosene (55%) with machine oil(25%) and gasoline (20%).

Excess liquid is removed by wiping the controlled areas with a rag soaked in gasoline. To speed up the release of fluorescent liquids located in the defect cavity, the surface of the part is dusted with a powder that has adsorbing properties. 3-10 minutes after pollination, the controlled area is illuminated with ultraviolet light. Surface defects into which the luminescent liquid has passed become clearly visible by a bright dark green or green-blue glow. The method allows you to detect cracks up to 0.01 mm wide.

When testing using the paint method, the weld is pre-cleaned and degreased. A dye solution is applied to the cleaned surface of the welded joint. Red paints of the following composition are used as a penetrating liquid with good wetting:

The liquid is applied to the surface with a spray bottle or brush. Impregnation time - 10-20 minutes. After this time excess liquid wipe from the surface of the controlled area of ​​the seam with a rag soaked in gasoline.

After the gasoline has completely evaporated from the surface of the part, a thin layer of white developing mixture is applied to it. White developing paint is prepared from collodion with acetone (60%), benzene (40%) and thickly ground zinc white (50 g/l mixture). After 15-20 minutes, characteristic bright stripes or spots appear on a white background at the locations of defects. Cracks appear as thin lines, the degree of brightness of which depends on the depth of these cracks. Pores appear in the form of points of various sizes, and intercrystalline corrosion appears in the form of a fine mesh. Very small defects are observed under a magnifying glass of 4-10x magnification. At the end of the test, the white paint is removed from the surface by wiping the part with a rag soaked in acetone.

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-radiation absorption method
5. 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 controlled surface, visible to the naked eye, or with the help of special developers.

Stages of penetrant control

1. The control process using the capillary method can be divided into the following stages:
2. Preparation and pre-cleaning
3. Intermediate cleaning
4. Manifestation Process
5. Detection of welding defects
6. Drawing up a protocol in accordance with the results of the inspection

Final surface cleaning

Penetrant testing materials

The list of necessary materials for carrying out penetrant flaw detection is given in the table:	Indicator liquid	Intermediate cleaner
Developer Fluorescent liquids Colored liquids		Fluorescent colored liquids
	Dry developer	Oil based emulsifier Liquid developer on
	water based	Soluble Liquid Cleaner
	Aqueous developer in the form of a suspension
	Water sensitive emulsifier	Water or solvent

Liquid developer based on water or solvent for special applications

Preparation and preliminary cleaning of the surface to be tested 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.

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 the minimum size of 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

Fluorescent colored liquids

The developer is applied to the controlled surface in an even thin layer. 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.

Local accumulations of developer are unacceptable. Liquid developer based on aqueous suspension The developer is applied uniformly by immersing the controlled compound in it or by spraying it using a machine. Using

immersion method

, for best results, the duration of the dive 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

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. As auxiliary devices for optical inspection, they are used magnifying glasses

, or glasses with magnifying lenses.

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.

When using colored indicator liquids

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., 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"

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

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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 intact one increases, with the identification of quantitative and quality composition damage (up to thousandths of a 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 converter.

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 energy, rocketry, aviation, metallurgy, shipbuilding, chemical industry, in the construction of nuclear reactors, mechanical engineering, automotive, 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 method of non-destructive testing also for objects made of ferromagnetic materials, if their magnetic properties, 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 simple method control, it is possible not only to detect and identify surface and through defects, but also to obtain, from their location, shape, extent and orientation along the surface, complete 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 minimum size identified 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 ensured at the production level, the choice physical properties substances: density, surface tension, viscosity, penetrant under the action of capillary pressure, penetrates into the smallest discontinuities that have an open exit to 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.

manufacturers

Russia Moldova China Belarus Armada NDT YXLON International Time Group Inc.

Testo Sonotron NDT Sonatest SIUI SHERWIN Babb Co Rigaku RayCraft Proceq Panametrics Oxford Instrument Analytical Oy Olympus NDT NEC Mitutoyo Corp.

Micronics Metrel Meiji Techno Magnaflux Labino Krautkramer Katronic Technologies Kane JME IRISYS Impulse-NDT ICM HELLING Heine General Electric Fuji Industrial Fluke FLIR Elcometer Dynameters DeFelsko Dali CONDTROL COLENTA CIRCUTOR S.A. Buckleys Balteau-NDT Andrew AGFA Capillary control. Penetrant flaw detection. Penetrant non-destructive testing method. Capillary method for studying defects

is a concept that is based on the penetration of certain

liquid formulations into the surface layers of the necessary products, carried out using capillary pressure. Using this process, it is possible to significantly increase the lighting effects, which are able to more thoroughly identify all defective areas. Types of capillary research methods A fairly common occurrence that can occur in flaw detection , this is not a sufficiently complete identification of the necessary defects. Such results are very often so small that general visual inspection is not able to recreate all defective areas various products penetrant flaw detection. This method uses indicator liquids that completely penetrate the surface layers of the material under study and form indicator prints, with the help of which further registration occurs visually. You can familiarize yourself with it on our website.

Requirements for the capillary method

The most important condition for a high-quality method for detecting various defective violations in finished products similar to the capillary method is the acquisition of special cavities that are completely free from the possibility of contamination, and have additional access to the surface areas of objects, and are also equipped with depth parameters that far exceed the width of their opening. The values ​​of the capillary research method are divided into several categories: basic, which support only capillary phenomena, combined and combined, using a combination of several control methods.

Basic actions of penetrant control

Flaw detection, which uses the capillary inspection method, is designed to examine the most hidden and inaccessible defective areas. Such as cracks various types corrosion, pores, fistulas and others. This system used to correctly determine the location, length and orientation of defects. Its work is based on the thorough penetration of indicator liquids into the surface and heterogeneous cavities of the materials of the controlled object. .

Using the capillary method

Basic data of physical penetrant testing

The process of changing the saturation of the pattern and displaying the defect can be changed in two ways. One of them involves polishing upper layers controlled object, which subsequently performs etching using acids. Such processing of the results of the controlled object creates a filling with corrosion substances, which results in darkening and then manifestation on the light-colored material. This process has several specific prohibitions. These include: unprofitable surfaces that may be poorly polished. Also, this method of detecting defects cannot be used if non-metallic products are used.

The second process of change is the light output of defects, which implies their complete filling with special color or indicator substances, so-called penetrants. You definitely need to know that if the penetrant contains luminescent compounds, then this liquid will be called luminescent. And if the main substance is a dye, then all flaw detection will be called color. This control method contains dyes only in rich red shades.

Sequence of operations for capillary control:

Pre-cleaning	Mechanically, brush	Jet method	Hot steam degreasing	Solvent cleaning
Pre-drying
Application of penetrant	Immersion in the bath	Application by brush	Aerosol/spray application	Electrostatic application
Preparation and pre-cleaning	A lint-free cloth or sponge soaked in water	Water-soaked brush	Rinse with water	A lint-free cloth or sponge soaked in a special solvent
	Air dry	Wipe with a lint-free cloth	Blow with clean, dry air	Dry with warm air
Applying developer	Immersion (water-based developer)	Aerosol/spray application (alcohol based developer)	Electrostatic application (alcohol based developer)	Applying dry developer (for highly porous surfaces)
Surface inspection and documentation	Control in daylight or artificial light min. 500Lux (EN 571-1/EN3059) When using fluorescent penetrant: Lighting:< 20 Lux UV intensity: 1000μW/cm2	Documentation on transparent film	Photo-optical documentation	Documentation through photography or video

The main capillary methods of non-destructive testing are divided depending on the type of penetrating substance into the following:

· The method of penetrating solutions is a liquid method of capillary non-destructive testing, based on the use of a liquid indicator solution as a penetrating substance.

· The method of filterable suspensions is a liquid method of capillary non-destructive testing, based on the use of an indicator suspension as a liquid penetrating substance, which forms an indicator pattern from filtered particles of the dispersed phase.

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

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

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

Always in stock! With us you can (color flaw detection) at a low price from a warehouse in Moscow: penetrant, developer, cleaner Sherwin, capillary systemsHelling, Magnaflux, ultraviolet lanterns, ultraviolet lamps, ultraviolet illuminators, ultraviolet lamps and control (standards) for color defectoscopy of CDs.

We deliver Consumables for color flaw detection in Russia and the CIS transport companies and courier services.

Penetrant flaw detection

Penetrant control

Penetrant non-destructive testing method

CapillI flaw detectorAnd I - 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, for example, a magnifying glass or a 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 mark” can be used. Discontinuity depth is the size of the discontinuity in the direction inward of the test object from its surface. Discontinuity length - longitudinal dimension discontinuities 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.

Devices and equipment for capillary control:

• Penetrant inspection kits (cleaners, developers, penetrants)
• Sprayers
• Pneumohydroguns
• Ultraviolet lighting sources (ultraviolet lamps, illuminators)
• Test panels (test panel)

Control samples for color flaw detection

Sensitivity of the capillary flaw detection method

Penetrant Sensitivity– 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 defects with an opening width of more than 0.5 mm is not guaranteed by capillary inspection methods.

With class 1 sensitivity, penetrant flaw detection is used to control turbine engine blades, 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).

The sensitivity of flaw detection materials, the quality of intermediate cleaning and control of the entire capillary process are determined on control samples (standards for color CD flaw detection), i.e. on metal of a certain roughness with normalized artificial cracks (defects) applied to them.

The control sensitivity class is determined depending on the minimum size of detected defects. The perceived sensitivity, if necessary, is determined on natural objects or artificial samples with natural or simulated defects, the dimensions of which are specified by metallographic or other methods of analysis.

According to GOST 18442-80, the control sensitivity class is determined depending on the size of detected defects. 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. Since the depth and length of a defect also have a significant impact on the possibility of its detection (in particular, the depth should be significantly greater than the opening), these parameters are considered stable. The lower threshold of sensitivity, i.e. the minimum amount of disclosure of identified defects is limited by the fact that the amount of penetrant is very small; retained in the cavity of a small defect turns out to be insufficient to obtain a contrast indication at a given thickness of the developing agent layer. There is also an upper threshold of sensitivity, which is determined by the fact that from wide but shallow defects the penetrant is washed out when excess penetrant is removed from the surface.

5 sensitivity classes have been established (based on the lower threshold) depending on the size of the defects:

Sensitivity class	Defect opening width, µm
	Less than 1
	From 1 to 10
	From 10 to 100
	From 100 to 500
technological	Not standardized

Physical basis and methodology of the capillary control method

Capillary method of non-destructive testing (GOST 18442-80) is based on capillary penetration of an indicator liquid into a defect and is intended to identify defects that reach the surface of the test object. This method is suitable for identifying discontinuities with a transverse size of 0.1 - 500 microns, including through ones, on the surface of ferrous and non-ferrous metals, alloys, ceramics, glass, etc. Widely used to control the integrity of the weld.

A colored or dyeing penetrant is applied to the surface of the test object. Thanks to the special qualities that are ensured by the selection of certain physical properties of the penetrant: surface tension, viscosity, density, it, under the action of capillary forces, penetrates into the smallest defects that reach the surface of the test object

The developer, applied to the surface of the test object some time after carefully removing the penetrant from the surface, dissolves the dye located inside the defect and, due to diffusion, “pulls” the penetrant remaining in the defect onto the surface of the test object.

Existing defects are visible in sufficient contrast. Indicator marks in the form of lines indicate cracks or scratches, individual dots indicate pores.

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

Preliminary surface cleaning. 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.

Application of penetrant. The penetrant, usually red in color, is applied to the surface by spraying, brushing or dipping the OK in a bath, for good impregnation and complete coverage of the penetrant. As a rule, at a temperature of 5-50 0 C, for a period of 5-30 minutes.

Removing excess penetrant. Excess penetrant is removed by wiping with a cloth and rinsing with water. Or the same cleaner as at the pre-cleaning stage. In this case, the penetrant must be removed from the surface, but not from the defect cavity. The surface is then dried with a lint-free cloth or a stream of air. When using a cleaner, there is a risk of leaching out the penetrant and causing it to be incorrectly displayed.

Application of developer. After drying, a developer is immediately applied to the OK, usually white, thin even layer.

Control. QA inspection begins immediately after the end of the development process and ends, according to various standards, in no more than 30 minutes. The intensity of the color indicates the depth of the defect; the paler the color, the shallower the defect. Deep cracks have intense coloring. After testing, the developer is removed with water or a cleaner.
The coloring penetrant is applied to the surface of the test object (OC). Thanks to the special qualities that are ensured by the selection of certain physical properties of the penetrant: surface tension, viscosity, density, it, under the action of capillary forces, penetrates into the smallest defects that reach the surface of the test object. The developer, applied to the surface of the test object some time after carefully removing the penetrant from the surface, dissolves the dye located inside the defect and, due to diffusion, “pulls” the penetrant remaining in the defect onto the surface of the test object. Existing defects are visible in sufficient contrast. Indicator marks in the form of lines indicate cracks or scratches, individual dots indicate pores.

Sprayers, such as aerosol cans, are most convenient. The developer can also be applied by dipping. Dry developers are applied in a vortex chamber or electrostatically. After applying the developer, you should wait from 5 minutes for large defects to 1 hour for small defects. Defects will appear as red marks on a white background.

Through cracks on thin-walled products can be detected by applying developer and penetrant with different sides products. The dye that has passed through will be clearly visible in the developer layer.

Penetrant (penetrant from the English penetrate - to penetrate) is called a capillary flaw detection material that has the ability to penetrate discontinuities of the test object and indicate these discontinuities. Penetrants contain dyes (color method) or luminescent additives (luminescent method), or a combination of both. Additives make it possible to distinguish the area of ​​the developer layer above the crack impregnated with these substances from the main (most often white) continuous material of the object (background) without defects.

Developer (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. Thus, the role of the developer in capillary testing is, on the one hand, to extract the penetrant from defects due to capillary forces, on the other hand, the developer must create a contrasting background on the surface of the controlled object in order to confidently identify colored or luminescent indicators traces of defects. At the right technology manifestations, the width of the trace can be 10 ... 20 or more times greater than the width of the defect, and the brightness contrast increases by 30 ... 50%. This magnification effect allows experienced technicians to detect very small cracks even with the naked eye.

Sequence of operations for capillary control:

Pre-cleaning	Mechanically, brush	Jet method	Hot steam degreasing	Solvent cleaning
Pre-drying
Application of penetrant	Immersion in the bath	Application by brush	Aerosol/spray application	Electrostatic application
Intermediate cleaning	A lint-free cloth or sponge soaked in water	Water-soaked brush	Rinse with water	A lint-free cloth or sponge soaked in a special solvent
Drying	Air dry	Wipe with a lint-free cloth	Blow with clean, dry air	Dry with warm air
Applying developer	Immersion (water-based developer)	Aerosol/spray application (alcohol based developer)	Electrostatic application (alcohol based developer)	Applying dry developer (for highly porous surfaces)
Surface inspection and documentation	Control in daylight or artificial light min. 500Lux (EN 571-1/ EN3059) When using fluorescent penetrant: Lighting:< 20 Lux UV intensity: 1000μW/ cm 2	Documentation on transparent film	Photo-optical documentation	Documentation through photography or video

The main capillary methods of non-destructive testing are divided depending on the type of penetrating substance into the following:

· The method of penetrating solutions is a liquid method of capillary non-destructive testing, based on the use of a liquid indicator solution as a penetrating substance.

· The method of filterable suspensions is a liquid method of capillary non-destructive testing, based on the use of an indicator suspension as a liquid penetrating substance, which forms an indicator pattern from filtered particles of the dispersed phase.

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 recording the contrast of a color indicator pattern in visible radiation 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 recording the contrast in visible radiation of an achromatic pattern against the background of the surface of the test object.

Physical foundations of capillary flaw detection. Luminescent flaw detection (LD). Color flaw detection (CD).

There are two ways to change the contrast ratio between the image of the defect and the background. The first method consists of polishing the surface of the controlled product, followed by etching it with acids. With this treatment, the defect becomes clogged with corrosion products, turns black and becomes noticeable against the light background of the polished material. This method has whole line restrictions. In particular, in production conditions it is completely unprofitable to polish the surface of the product, especially welds. In addition, the method is not applicable when testing precision polished parts or non-metallic materials. The etching method is often used to control some local suspicious areas of metal products.

The second method is to change the light output of defects by filling them from the surface with special light- and color-contrast indicator liquids - penetrants. If the penetrant contains luminescent substances, i.e. substances that give a bright glow when irradiated with ultraviolet light, then such liquids are called luminescent, and the control method, accordingly, is luminescent (luminescent flaw detection - LD). If the penetrant is based on dyes that are visible in daylight, then the control method is called color ( color flaw detection- CD). In color flaw detection, bright red dyes are used.

The essence of penetrant flaw detection is as follows. The surface of the product is cleaned of dirt, dust, grease, flux residues, paint coatings etc. After cleaning, a layer of penetrant is applied to the surface of the prepared product and left for some time so that the liquid can penetrate into the open cavities of the defects. Then the surface is cleaned of liquid, some of which remains in the defect cavities.

In the case of fluorescent flaw detection The product is illuminated with ultraviolet light (ultraviolet illuminator) in a darkened room and inspected. Defects are clearly visible in the form of brightly glowing stripes, dots, etc.

With color flaw detection, it is not possible to identify defects at this stage, since the resolution of the eye is too low. To increase the detectability of defects, after removing the penetrant from it, a special developing material in the form of a quick-drying suspension (for example, kaolin, collodion) or varnish coatings are applied to the surface of the product. The developing material (usually white) draws the penetrant out of the defect cavity, which results in the formation of indicator marks on the developer. Indicator marks completely repeat the configuration of defects in plan, but are larger in size. Such indicator traces are easily visible to the eye even without the use of optical means. The deeper the defects, the greater the increase in the size of the indicator trace, i.e. the greater the volume of penetrant that fills the defect, and the more time has passed since the application of the developing layer.

The physical basis of capillary flaw detection methods is the phenomenon of capillary activity, i.e. the ability of liquid to be drawn into the smallest through holes and channels open at one end.

Capillary activity depends on the wetting ability of a solid by a liquid. In any body, each molecule is subject to molecular cohesion forces from other molecules. They are larger in a solid than in a liquid. Therefore, liquids, unlike solids, do not have elasticity of shape, but have high volumetric elasticity. Molecules located on the surface of the body interact both with molecules of the same name in the body, which tend to draw them into the volume, and with molecules of the environment surrounding the body and have the greatest potential energy. For this reason, an uncompensated force, called the surface tension force, arises perpendicular to the boundary in the direction inside the body. Surface tension forces are proportional to the length of the wetting contour and naturally tend to reduce it. The liquid on the metal, depending on the ratio of intermolecular forces, will spread over the metal or collect in a drop. A liquid wets a solid if the forces of interaction (attraction) of the liquid with the molecules of the solid are greater than the forces of surface tension. In this case, the liquid will spread over the solid body. If the forces of surface tension are greater than the forces of interaction with the molecules of the solid, then the liquid will gather into a drop.

When liquid enters a capillary channel, its surface is curved, forming a so-called meniscus. Surface tension forces tend to reduce the size of the free boundary of the meniscus, and it begins to act in the capillary extra strength, leading to the absorption of wetting fluid. The depth to which a liquid penetrates into a capillary is directly proportional to the coefficient of surface tension of the liquid and inversely proportional to the radius of the capillary. In other words, the smaller the radius of the capillary (defect) and the better the wettability of the material, the faster the liquid penetrates into the capillary and to a greater depth.

From us you can buy materials for penetrant testing (color flaw detection) at a low price from a warehouse in Moscow: penetrant, developer, cleaner Sherwin, capillary systemsHelling, Magnaflux, ultraviolet flashlights, ultraviolet lamps, ultraviolet illuminators, ultraviolet lamps and control samples (standards) for color flaw detection of CDs.

We deliver consumables for color flaw detection throughout Russia and the CIS by transport companies and courier services.

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