Method of illuminating parts. X-ray inspection of welded joints Fig. 7. Transmission of the spherical dome of the air heater casing and similar structures

Inactive

BUILDING STANDARDS

Instructions for control methods used in quality testing
welded joints of steel building structures and pipelines

Date of introduction 1968-07-01

"Instructions for control methods used when checking the quality of welded joints of steel building structures and pipelines" was developed by the All-Union Research Institute for the Construction of Main Pipelines of the Ministry of Gas Industry together with the institutes TsNIIProektstalkonstruktsiya of the USSR State Construction Committee, Orgenergostroy of the USSR Ministry of Energy and Electrification and VNIIMontazhspetsstroy of the Ministry of Assembly and Special construction work in the USSR.

The instructions are intended to provide guidance in checking the quality of welded joints without their destruction. The adopted control methods comply with the requirements established by the Construction Norms and Rules (SNiP) for checking the quality of welds of sheet and lattice structures and pipelines.

The following took part in the development of the instructions:

Eng. I.E. Neufeld, Ph.D. tech. Sciences A.S. Falkevich, Ph.D. tech. Sciences K.I. Zaitsev, engineer M.X. Khusanov (VNIIST);

Eng. N.N.Belous, Ph.D. tech. Sciences A.S. Chesnokov, Ph.D. tech. Sciences A.S. Dovzhenko (TsNIIProektstalkonstruktsiya of the USSR State Construction Committee);

Eng. V.P. Pushkin, S.S. Yakobson, Ph.D. tech. Sciences Kontorovsky (Orgenergostroy);

Ph.D. tech. Sciences A.M. Gofner (NIIMontazhspetsstroy).

INTRODUCED by the USSR Ministry of Gas Industry

APPROVED by the State Committee of the USSR Council of Ministers for Construction on July 26, 1967.

1. GENERAL PART

1.1. This Instruction is a guide to the selection and application of methods for quality control of welded joints of steel building structures and pipelines without destruction of the controlled joints.

This Instruction does not apply to the inspection of welded joints made by press welding methods.

1.2. The control methods given in these Instructions are applied in accordance with the requirements Building codes and rules of chapters: SNiP III-B.5-62* "Metal structures. Rules for manufacturing, installation and acceptance", SNiP III-G.9-62 " Process pipelines. Rules for the production and acceptance of work", SNiP III-D.10-62** "Main pipelines. Rules for organizing construction, production and acceptance into operation", SNiP III-G.7-66 "Gas supply. External networks and structures. Rules for the organization and production of work. Acceptance for operation" etc., as well as in accordance with the rules of Gosgortekhnadzor for quality control of welded joints.
________________
* In the territory Russian Federation GOST 23118-99 is valid;
** SNiP 2.05.06-85 is in force on the territory of the Russian Federation. - Database manufacturer's note.

1.3. Testing methods without disturbing welded joints are intended to identify internal macrodefects of the weld and heat-affected zone (cracks, lack of fusion, slag inclusions and gas pores), as well as to check the tightness of these joints.

1.4. The number and length of controlled welded joints are established by the Building Codes and Rules and Technical specifications for this design.

1.5. Welded joints or areas thereof that are subject to inspection are determined by the operator together with the technical supervisor of the work being performed. For inspection, you should select welded joints or areas made in the least favorable conditions and various welders.

Table 1


Control methods	Thickness of controlled connections in mm	Type of welded joints
Continuity control
1. Transillumination:
a) x-rays		Butt, corner and lap joints
b) gamma rays
2. Ultrasonic testing	10-15 and above	Butt and fillet welds of non-austenitic steels
3. Magnetographic control		Butt welds of ferromagnetic metals with a width of welded parts of at least 150 mm
Leak control
1. Vacuum method	Up to 16 mm	Butt lap and corner joints
2. Chemical reactions
3. Kerosene test

1.7. Conclusions on the quality of welded joints and seams must be made by a person (operator, inspector) who has special training and a certificate to carry out these works.

1.8. Theoretical training and practical training of persons appointed to work on welding quality control can be carried out only in a training organization according to special approved programs.

Testing the knowledge of persons (operators, supervisors) involved in welding control must be carried out at least once a year. If there is a break in control work for more than 6 months, the person resuming control work must be subject to a test of knowledge and practical skills.

A representative of Gosgortekhnadzor must be included in the qualification commission for the certification of inspectors-operators allowed to work on monitoring and assessing the quality of welds at facilities supervised by Gosgortekhnadzor.

2. TRANSPLAY WITH X-RAYS AND GAMMA RAYS

2.1. Transmission of welds must be carried out in accordance with the requirements of GOST 7512-55 "Welded seams. Methods of control by radiography and gamma graphing" and this Instruction.

2.2. The main sources of gamma radiation used for gamma flaw detection of welded joints are the following isotopes: cobalt-60, cesium-137, iridium-192 and thulium-170.

Characteristics of isotopes and recommended areas of application are given in Table 2.

table 2


Isotope name	Average radiation energy of MEV	Half-life in years
Cobalt-60			Welded joints made of steel and heavy metals with a thickness of 20-200 mm
Cesium-137			Welded connections made of steel 5-100 mm thick
Iridium-192			The same, 3-50 mm
Thulium-170			The same, 1-20 mm and light alloys

2.3. For gamma flaw detection, flaw detectors of the GUP-Cesium 1-2 types manufactured by the Mosrentgen plant, RID-21G of VNIIRT and other types of flaw detectors approved by the sanitary inspection authorities are used.

2.4. X-ray examination of welded seams of metal structures up to 60 mm thick can be performed using X-ray machines RUP-200-20 and RUP-200-5, having a maximum operating voltage of 200 kV at a current of 5-20 mA and similar ones.

For structures with a metal thickness of up to 30 mm, it is rational to use devices RUP-120-5, RAP-150-5 and IRA-1, etc. (manufactured by the Mosrentgen and Burevestnik factories).

Note. From imported equipment, you can use any similar devices designed for X-ray flaw detection of metals.

2.5. When working with X-ray equipment, you must follow the appropriate operating instructions.

Materials used

2.6. When scanning welds, domestic X-ray films of the RT and RM types are used. X-ray films of the Agfa-Duro, Agfa-Sino, and Agfa-Tex types (GDR) are also used.

RT-type film with a double-sided emulsion of increased layer thickness is designed specifically for hard gamma radiation and is used both with and without intensifying screens.

Film type PM-1 also has a double-sided emulsion.

2.7. To check the quality of films, a control film is taken from each batch, but not more than 20 packs, which is developed for the time specified in the recipe for this film, then fixed.

If there are no veils, spots, stripes or other emulsion defects on the film, this batch of film is considered suitable and allowed for use.

2.8. The width of the films used for transillumination must be equal to the width of the seam and adjacent areas on each side, at least 20 mm.

2.9. Films should be stored in packs placed on edge in special rooms that provide protection from dampness, ignition and exposure to penetrating radiation. In addition, film storage facilities must meet the following conditions:

a) the room temperature should be 10-25 °C;

b) boxes with film should be placed at a distance of at least 1 m from heating devices and should be protected from direct sunlight;

c) harmful gases should not penetrate into the room: hydrogen sulfide, carbon monoxide, ammonia, as well as vapors of aromatic substances;

d) there should be no acids, gasoline, kerosene or other flammable liquids in the room.

2.10. Intensifying screens have a layer of calcium tungstate emulsion and are used to reduce exposure time during transillumination. Exposure time when using these screens is reduced by up to 40 times, depending on the severity of the radiation.

2.11. Reinforcing screens must have clean surface no cracks, stains or scratches. The edges of the screens must be carefully glued with collodion to prevent the fluorescent composition from falling off and getting on the film.

2.12. In order to increase image clarity, screens made of lead foil with a thickness of 0.1-0.2 mm are used.

Lead foil should have a smooth, clean surface free of scratches, dents and wrinkles.

Preparing for candling

2.13. Places for scanning welds at the site are designated in accordance with clause 1.5 of these Instructions.

2.14. Before X-ray testing, all welds intended for inspection must be thoroughly cleaned of slag, splashes, and dirt and accepted for external inspection. Welds that are not accepted by external inspection are not subject to X-ray examination.

2.15. Before X-raying, welds are marked into separate sections, marked with chalk and then marked with oil paint or branded with metal stamps knocked out next to the seam. The marking is applied to the expanded illumination pattern.

2.16. Using a device, appropriate stamps (marks) made of lead are installed on the cassettes.

If it is impossible to install markings, it is allowed to carry out transillumination without them. At the same time, the number of the cassette is written in ink on the intensifying screens and, when transilluminated, this number is projected on the image. It is allowed to mark the photograph with a simple pencil on the photograph itself before developing it.

2.17. To protect the X-ray film from exposure, it is placed in a cassette made of light-proof material (black paper, leatherette, rubber or aluminum). The simplest is a cassette made of black opaque paper, consisting of two envelopes placed one inside the other. The inner envelope is placed inside the outer one with the open end facing inward.

2.18. Charging and discharging cassettes should be done in a darkened and ventilated photo room.

2.19. X-ray film, intensifying and lead screens are placed in the cassette in various combinations depending on the requirements for the image. Charging circuits for cassettes in accordance with GOST 7512-55 are shown in Fig. 1.

Fig.1. Cassette charging circuits

Lead screens

X-ray film

Intensifying screens

Fig.1. Cassette charging circuits

2.20. Charging and discharging cassettes must be done without damaging the film emulsion and intensifying screens. Films with a damaged layer and contaminated surface are not allowed to be used.

Charging and discharging cassettes should be done on a dry table separately from the cuvettes with developer and fixer. In this case, the films are placed on clean paper, previously laid on the table.

2.21. Reinforcing screens that have traces of dirt, stains, cracks and scratches on the surface of the emulsion are not allowed for use. Traces of dirt or stains should be washed off carefully with warm soapy water.

2.22. Before installation in the cassette, lead screens are smoothed, if necessary, to remove folds and unevenness on their surface.

X-ray and gamma radiography technique

2.23. X-ray and gamma radiography consists of the following stages:

a) installation of a sensitivity standard, lead indicators and markings on the translucent area;

b) installation and fastening of the cassette on the area of the translucent seam on the side opposite to the location of the radiation source. In this case, the cassette should be pressed against the surface of the controlled seam;

c) installing the radiation source at a given focal length (at a distance from the radiation source to the middle of the cassette) and securing it on a tripod or special device for gamma graphing;

d) exposure at a given exposure time.

Notes:

1. The radiation source and the controlled object with the pressed cassette must be securely secured from displacement and vibration during exposure.

2. The focal length must be taken to be no less than the length of the seam section being illuminated at the same time.

2.24. The sensitivity standard - a flaw meter (Fig. 2) - and markings are installed on the side of the radiation source next to the weld seam parallel to the latter so that they are not projected onto the controlled part of the seam.

Fig.2. Sensitivity standard - defect meter

2.25. The exposure time is determined according to special graphs (Fig. 3, 4), and then clarified experimentally.

Fig.3. Exposure time graph when shining steel with cobalt-60 gamma rays

Focal length in mm

Fig.4. Exposure time graph when shining steel with Cesium-137 gamma rays

Focal length in mm

To do this, several test images are taken with at different times exposures, and after development the sensitivity of the image is determined. Maximum sensitivity indicates optimal time exposure for given conditions.

2.26. Welded seams of butt joints without beveled edges or with grooved edges are illuminated, as a rule, with a beam directed perpendicular to the seam.

2.27. Recommended patterns for scanning butt joints with different edge preparations are shown in Fig. 5. If it is necessary to identify lack of penetration along the bevels of the edges, it is permissible to perform transillumination in such a way that the rays coincide with the direction of the edges (Fig. 6).

Fig.5. Schemes for X-raying butt welded joints with various preparations

Fig.6. Scheme for scanning welded joints with X-shaped preparation of edges to detect defects along the bevel of the edges

2.28. Welded seams of butt joints of sheet cylindrical or spherical metal structures of small diameters (up to 10 m) can be translucent with one installation of the source. To do this, a source with high activity is installed in the center of the product (Fig. 7), and the entire circumference is illuminated in one installation of the source.

Fig.7. Transmission of the spherical dome of the air heater casing and similar structures

Cassette; - radiation source

2.29. X-raying of welded joints of pipelines is carried out in three ways.

a) The radiation source is placed inside the pipe, in its center (Fig. 8). Placing the source inside the pipe is the most efficient and makes it possible to monitor the entire joint in one installation. However, this method can only be used for x-raying pipes with a diameter of over 200 mm.

Fig.8. Panoramic scanning of welded joints of pipelines with the radiation source located in the center of the pipe

Radiation source; - film

b) The radiation source is placed outside the pipe: in this case, a cassette with X-ray film is installed on the joint area intended for scanning, and the radiation source is placed on the back side of the pipe. The focal length in this case is selected depending on the diameter of the pipe, and the radiation source can be located directly on the pipe or at the required distance from it, but not less than 300 mm (Fig. 9).

Fig.9. Examination of a welded pipe joint through two walls

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To control welded joints of various types, choose one of the transmission schemes shown in Fig. 2.2. Single-sided butt welded joints without edge preparation, as well as with a V-shaped groove, are usually visible through the normal to the plane of the elements being welded (see Fig. 2.2, diagram 1). It is more advisable to illuminate seams made by double-sided welding with a K-shaped groove on the edges according to scheme 2, using in some cases two exposures. In this case, the direction of the central beam must coincide with the cutting line of the edges. It is also possible to translucent these seams according to scheme 1.

Rice. 2.2 Transmission schemes.

When inspecting lap seams, T-joints and corner connections the central beam is directed, as a rule, at an angle of 45° to the plane of the sheet (schemes 3 - 8). A pipes large diameter(more than 200 mm) are illuminated through one wall, and the radiation source is installed outside or inside the product with the direction of the axis of the working beam perpendicular to the seam (diagrams 9, 11).

When shining through two walls of welded joints of small-diameter pipes, in order to avoid overlapping the image of the seam section facing the radiation source with the image of the seam section facing the film, the source is shifted from the plane of the welded joint (Diagram 10) by an angle of up to 20... 25 °.

When choosing a scanning scheme, it is necessary to remember that lack of penetration and cracks can be detected only if the planes of their opening are close to the direction of scanning (0 ... 10°), and their opening is ≥0.05 mm.

Selecting focal length.

After selecting the illumination scheme, set the focal length F. With its increase, the sensitivity of the method increases slightly, but the exposure time increases (proportionally to the square of the distance).

Typically, the focal length is chosen in the range of 300...750 millimeters.

Choice of exposure time.

X-ray exposure is expressed as the product of tube current and time; γ-radiation - as the product of the activity of the radiation source, expressed in the γ-equivalent of radium, and time.

In this work, we will use the nomogram for RT-1 film with a metal screen as a base one, with further recalculation of exposures for other films and screens.

Exposure time is calculated as:

where i is the tube current, E is the exposure value selected according to the nomogram, k is a coefficient depending on the type of screen (only for RT-type films). Coefficient value To selected according to table 2.

Table 2.

When changing the focal length, the exposure is recalculated as follows:

Appendix 1 presents the characteristics of films and nomograms for the MART-200 device, as well as nomograms for selecting exposures during transillumination various materials using RT-1 film.

BIBLIOGRAPHY

1. Shcherbinsky V.G., Aleshin N.P. Ultrasonic testing of welded joints. – M.: Publishing house of MSTU im. N.E. Bauman, 2000. – 496 p.

2. Aleshin N.P. Physical methods of non-destructive testing of welded joints: textbook. – M.: Mechanical Engineering, 2006. -368 p.

3. Aleshin N.P., Shcherbinsky V.G. Radiation, ultrasonic and magnetic flaw detection.. M., graduate School, 1989.- 250 p.

4. Brekhovskikh L.M., Goncharov V.V. Introduction to continuum mechanics. - M.: Nauka, 1982. - 335 p.

5. Shelikhov G.S. Magnetic particle flaw detection of parts and assemblies: a practical guide. M.: Scientific and Technical Center “Expert”, 1995.

6. Login V.V. Control and testing in mechanical engineering. Textbook / M.: MIIT, 2003.

7. Maslov B.G. Non-destructive testing of welded joints and products in mechanical engineering. Textbook for universities. - M.: Mechanical Engineering, 2008. - 272 p.

8. V.I. Kapustin, V.M. Zuev, V.I. Ivanov, A.V. Oak Radiographic control. Information aspects. – M. Nauchtekhizdat, 2010. – 367 p.

Let us briefly consider its operations using the example of radiographic testing of welded joints.

Radiographic testing of welded joints has the following sequence of basic operations:

selection of radiation source,
selection of radiographic film + determination of optimal transmission modes;
illumination of an object;
carrying out photo processing of photographs and their decoding;
registration of control results.

Selecting a radiation source determined by technical feasibility and economic efficiency. The main factors determining the choice of source are: specified sensitivity; thickness and density of the material of the controlled product; performance control; configuration of the controlled part; its availability for control, etc.

For example, when inspecting products that may have large defects, it is more advisable to use high-energy isotopes that provide short transmission times. For critical products, X-ray radiation is used and only as an exception isotopes that have the lowest possible radiation energy.

Selection of radiographic film is carried out according to the thickness and density of the material of the object being scanned, as well as according to the required performance and specified control sensitivity.

Rice. 1. Nomograms of the areas of application of radiographic films when x-raying steel: I - RT-5, RT-4; II - PT-l, RT-3; III - RT-2.

RT-1 film is used mainly for testing welded joints of large thickness, as it has high contrast and sensitivity to radiation. The universal screen film RT-2 is used for illuminating parts of various thicknesses, and the illumination time is the shortest in comparison with other types of films. High-contrast films RT-Z and RT-4 are suitable for testing products made of aluminum alloys or alloys of ferrous metals of small thickness. For flaw detection of critical compounds, RT-5 film is used. This film has a fairly high contrast and allows you to detect minor defects, although it has the lowest sensitivity to radiation, which increases the exposure time during inspection. It is advisable to select an approximate radiographic film according to nomograms (Fig. 1).

To control welded joints of various types, choose one of the transmission schemes shown in Fig. 2. Single-sided butt welded joints without edge preparation, as well as with a V-shaped groove, are usually visible through the normal to the plane of the elements being welded (see Fig. 2, Scheme 1). It is more advisable to illuminate seams made by double-sided welding with a K-shaped groove on the edges according to scheme 2, using in some cases two exposures. In this case, the direction of the central beam must coincide with the cutting line of the edges. It is also possible to translucent these seams according to scheme 1.

Rice. 2. Schemes of radiographic inspection of welded joints.

When inspecting lap seams, T-joints and corner joints, the central beam is directed, as a rule, at an angle of 45° to the plane of the sheet (Diagrams 3 - 8). Large-diameter pipes (more than 200 mm) are illuminated through one wall, and the radiation source is installed outside or inside the product with the direction of the axis of the working beam perpendicular to the seam (diagrams 9, 11).

When choosing a scanning scheme, it is necessary to remember that lack of fusion and cracks can be detected only if their opening planes are close to the scanning direction (0 ... 10°), and their opening is ≥0.05 mm.

To control circumferential welded joints of pipes, a panoramic transmission scheme is often used (Scheme 11), in which a source with panoramic radiation is installed inside the pipe on the axis and the joint is scanned in one exposure. The condition for using this transmission scheme is as follows: the size of the active part F of the radiation source, at which it can be used to control the weld in a panoramic way, is determined by the formula

Ф ≤ (u - R) / (r - 1),

where u is the maximum permissible value of geometric blur of the image of defects in the image (in mm), specified, as a rule, by the current documentation on ; R and r are the outer and inner radii of the controlled connection, respectively, mm.

After selecting the illumination scheme, set the focal length F. Increasing it slightly increases the sensitivity of the method, but increases (proportionally to the square of the distance) the exposure time.

The focal length is selected depending on the transmission scheme, the thickness of the material and the size of the active part (focal spot) of the radiation source. For example, for schemes 1 - 8 (see Fig. 2), the focal length should be F ≥ (Ф / u + 1)(s + H), where s is the thickness of the welded joint in the direction of transmission, mm; H is the distance from the film to the surface of the product facing it. Typically, the focal length is chosen in the range of 300...750 millimeters.

Exposure time and length When monitoring according to the given schemes, the area controlled for one exposure should be such that:

The density of blackening of the image of the controlled area of the seam, OSZ and sensitivity standards was ≥1.0 and ≤3.0 units. optical density;
the decrease in the density of blackening of any area in the image compared to the density of blackening at the site where the sensitivity standard was installed was ≤0.4 ... 0.6 units. optical density depending on the film contrast ratio, but nowhere should the blackening density be<1,5 eд.;
the distortion of the image of defects at the edges of the image in relation to their image in its center did not exceed 10 and 25% for straight and curved sections, respectively.

Usually length l rectilinear and close to rectilinear sections controlled in one exposure should be ≤0.8ƒ, where ƒ is the distance from the radiation source to the surface of the controlled section.

The selection of exposure when transilluminating products is carried out according to nomograms (Fig. 3), and it is clarified using test images. X-ray exposure is expressed as the product of tube current and time; γ - radiation - as the product of the activity of the radiation source, expressed in γ -equivalent to radium, for a time. Nomograms are given for a specific type of film, focal length and radiation source.

Fig. 3. Nomograms for determining the exposure time of steel transillumination: a - X-ray radiation at F = 750 mm and PT-1 film; 6 - γ - radiation with RT-1 film and F = 500 mm; 1 - thulium; 2 - strontium-75; 3 - iridium-192; 4 - cesium-135; 5 - europium-152; 6 - cobalt-60.

Preparation of the controlled object to transillumination consists of a thorough inspection and, if necessary, cleaning the object of slag and other contaminants. External defects must be removed, as their appearance on photographs may obscure the image of internal defects. The welded joint is divided into control sections, which are marked so that after scanning it is possible to accurately indicate the location of identified internal defects. Cassettes and those loaded in them must be marked in the same order as the corresponding control areas. The selected film is loaded into a cassette, after which the cassette is secured to the product and installed on the side of the radiation source. In cases where it is impossible to place it this way, for example, when scanning pipes through two walls, it is allowed to place the standard on the side of the detector (film cassette).

After completing the above operations and ensuring safe working conditions, they begin to X-ray the products. In this case, the radiation source must be installed in such a way that during transillumination it cannot vibrate or move, otherwise the image on the film will be blurred. After the exposure time has passed, the film cassettes are removed and the exposed film is subjected to photo processing.

The process of photographic film processing includes the following operations:

manifestation,
intermediate rinsing
image capture,
washing in still water,
final washing, film drying.

When developed, silver bromide crystals are reduced to metallic silver. The film is developed in a special developer solution. The development time is indicated on the film and solution packaging. After development, the film is rinsed in a cuvette with water. This intermediate rinsing prevents the developer from getting into the fixing solution. Undeveloped grains of silver bromide dissolve in the fixer, and the reduced metallic silver does not undergo any changes.

After fixing, the film must be washed in non-flowing water, followed by extraction and collection of silver. Then the film is washed in a bath with running water for 20-30 minutes to remove any chemical reagents remaining after fixation. After washing the film, it is dried for 3...4 hours. The drying temperature should not exceed 35°C.

Decoding images- the most important stage of photo processing. The interpreter's task is to identify defects and determine their types and sizes. X-ray images are deciphered in transmitted light on a negotoscope - a device in which there are lighting lamps covered with milky or frosted glass to create a uniformly diffused light flux. The decoding room is darkened so that the surface of the film does not reflect the incident light. Modern negotoscopes regulate the brightness of the illuminated field and its size. If the illumination of the negotoscope is not adjusted, then if the light is too bright, small defects with insignificant changes in the optical density of the blackening of the film may be missed.

Interpretation of radiographs consists of three main stages:

image quality assessment,
analyzing the image and finding defects in it,
drawing up a conclusion about the quality of the product.

The quality of the image is primarily assessed by the absence of defects on it caused by improper photo processing or careless handling of the film: the radiogram should not have spots, stripes, dirt or damage to the emulsion layer that make decoding difficult.

Then the optical density is assessed, which should be 2.0 ... 3; check whether the elements of the sensitivity standard are visible, guaranteeing the detection of unacceptable defects; Is there an image of markings in the picture? Optical density is measured using densitometers or microphotometers.

The conclusion about the quality of the inspected welded joint is given in accordance with the technical conditions for the manufacture and acceptance of the product. In this case, the quality of the product is assessed only by a dry photograph if it meets the following requirements:

The X-ray image clearly shows the image of the welded joint along the entire length of the image;
There are no stains, scratches, fingerprints, or streaks on the photo due to poor washing of the film and improper handling of it;
The images of the standards are visible in the picture.

Otherwise, re-examination is performed.

To shorten the entry control results abbreviated designations for defects found in the image are used: T - cracks; H - lack of penetration; P - pores; Ш - slag inclusions; B - tungsten inclusions; Pdp - undercut; Skr - edge offset; O - oxide inclusions in the weld. Based on the nature of the distribution, the detected defects are combined into the following groups: individual defects, chains of defects, clusters of defects. The chain includes ≥3 defects located on the same line with a distance between them equal to three times the size of the defect or less. A cluster of defects includes clustered defects in an amount of at least three with a distance between them equal to three times the size of the defect or less. The size of the defect is considered to be the largest linear size of its image on the image in millimeters. If there is a group of defects of different sizes of the same type, indicate the average or predominant size of the defect in the group, as well as the total number of defects.

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X-ray inspection of welded joints

24.05.2017

Among all possible types of NDT of welds, radiographic testing (RT) of welded joints is one of the most accurate. It is in great demand in the professional field, where high-quality products are produced that are designed to withstand significant loads, since they are not allowed to contain any defects: lack of fusion, microcracks, cavities, pores and other types of defects.

Methods of scanning parts, or methods of penetrating radiation, are based on the interaction of penetrating radiation with the controlled object. For flaw detection purposes, ionizing radiation is used - short-wave electromagnetic oscillations propagating in a vacuum at the speed of light (2.998 10 8 m/s). These radiations, passing through a substance, ionize its atoms and molecules, i.e. positive and negative ions and free electrons are formed. Therefore, these radiations are called ionizing. Possessing high energy, ionizing radiation penetrates layers of matter of varying thickness. In this case, electromagnetic radiation loses its intensity depending on the properties of the medium, since the rays are absorbed to one degree or another by the material. The degree of absorption depends on the type of material, its thickness, and also on the intensity (hardness) of the radiation. The greater the thickness of the translucent part, made of a homogeneous material, the greater the degree of absorption for a given initial radiation, and the flux of rays behind the part will be weakened to a greater extent. If an object of unequal thickness and density is transilluminated, then in areas where the transilluminated object has a greater thickness or greater density of material, the intensity of the transmitted rays will be less than in areas with a lower density or less thickness.

Thus, if there is any defect in the irradiation zone in the part, the attenuation of the rays in the defect zone will be less if it is a discontinuity (sink, gas bubble). If the defect is a denser inclusion in the material of the part, the radiation attenuation will be greater. In Fig. 3.63 diagram of the radiation intensity behind the part gives an idea of the nature of the change in intensity. When rays pass through a dense inclusion, the intensity decreases; when passing through a hollow shell, the radiation intensity is greater. An area with greater thickness causes a greater drop in radiation intensity.

The intensity of the rays passing through the controlled part must be measured or recorded in some way and, based on the decoding results, the condition of the object must be assessed.

Rice. 3.63.

7 - radiation intensity diagram; 2 - dense inclusion in the material of the part; 3 - X-ray tube; 4 - controlled part; 5 - hollow shell

in the part material

The method is intended to identify internal macrodefects, such as pores, lack of fusion, undercuts, slag inclusions, burn-throughs, porosity, cavities, looseness, gas bubbles, and deep corrosion. Cracks can be detected provided that they have a sufficiently large opening and are oriented (by the opening plane) along the beam shining through the part. The method is also used to control the quality of assembly of units, sealing of cables in tips, sealing of hose tips, quality of riveted joints, and cleanliness of closed channels.

For transillumination of products, mainly two types of radiation are used: x-ray and gamma radiation. The fundamental difference between these two types of radiation lies in the nature of their occurrence. X-ray arises as a result of a change in the speed of movement (braking) of electrons flying from the hot cathode to the tungsten mirror of the anode of the X-ray tube. Gamma radiation is the result of nuclear transformations and occurs when the nucleus of an atom of an unstable isotope transitions from one energy state to another. X-ray and gamma radiation, when passing through a material, lose their energy due to scattering and conversion into kinetic energy of electrons. The shorter the wavelength of x-ray or gamma radiation, the greater its penetrating power. Short-wave radiation is called hard, and long-wave radiation is called soft. Short-wave radiation carries more energy than long-wave radiation.

X-rays They have relatively low rigidity, so they are used for shining through thin-walled structures: combustion chambers, rivet seams, cladding, etc. The X-ray method allows you to control steel parts with a thickness of up to 150 mm, and parts made of light alloys - up to 350 mm.

Industrial X-ray machines are used as a source of X-ray radiation. Recently, small-sized pulsed devices have become increasingly widespread, making it possible to illuminate fairly large thicknesses at low power due to the short pulse time (1-3 μs) at a relatively high current (100-200 A) (Fig. 3.64). The device consists of an X-ray tube, a high-voltage generator and a control system. An X-ray tube is an electric vacuum device designed to produce X-ray radiation. Structurally, the tube is a glass or glass-metal cylinder with insulated electrodes - anode and cathode. The pressure in the cylinder is approximately 10“ 5 -10 -7 mmHg. Art. Free electrons in the tube are formed due to thermionic emission of the cathode, heated by electric current from a low-voltage source. The current density of thermionic emission in the tube, as well as the intensity of X-ray radiation, increases (up to a certain limit) with increasing cathode temperature and voltage between the cathode and anode. As the voltage increases, the wavelength of the X-ray radiation decreases, and its penetrating power (the hardness of the rays) increases accordingly. Thus, X-ray installations make it possible to change the radiation hardness over a wide range, which is undoubtedly an advantage of this method. X-ray control is more sensitive than gamma control.

Rice. 3.64.

A- RAP 160-5; 6 - "Arina-9"

Almost all the energy (about 97%) consumed by the tube is converted into heat, which heats the anode, so the tubes are cooled with a stream of water, oil, air, or periodically turned off. High-voltage generators of X-ray machines provide power to the tubes with a high, adjustable voltage - 10-400 kV. The generator consists of a high-voltage transformer, a filament tube transformer and a rectifier. The control system of the device provides regulation and control of the voltage and anode current of the X-ray tube, signaling of the operation of the device, its shutdown after the set exposure time has expired, and emergency shutdown in the event of malfunctions, interruption of the coolant supply or opening of the equipment room doors. The presence of so many additional elements makes X-ray machines bulky, and this, in turn, makes it difficult to approach controlled objects directly on an aircraft with X-ray tubes.

Gamma rays(y-rays) have great penetrating power, therefore they are used to illuminate massive parts or assembled units. Radioactive isotopes placed in the protective casing of a gamma flaw detector are used as a source of gamma radiation. The most widely used isotopes in flaw detection are cesium-137, iridium-192, and cobalt-60. The gamma flaw detector consists of a container (protective casing, radiation head) for storing the radioactive source in the non-working position, a device for remotely moving the source to the working position, and an alarm system about the position of the source. Gamma flaw detectors can be portable, mobile or stationary; as a rule, they are self-contained devices and do not require power from external sources. Based on this, gamma flaw detectors can be used in the field to examine products in hard-to-reach places and in closed areas, including explosion and fire hazardous areas. However, gamma radiation is more dangerous for humans, unlike X-rays. Adjusting the radiation energy of a specific isotope during gamma flaw detection is impossible. The penetrating power of gamma radiation is higher than X-ray radiation, so parts of greater thickness can be illuminated. The gamma method allows you to control steel parts up to 200 mm thick, but the sensitivity of the control is lower, the difference between defective and non-defective is less noticeable. Based on this, the area of application of gamma flaw detection is the inspection of products of large thickness (small defects in this case are less dangerous).

Modern Gammarid gamma flaw detectors (Fig. 3.65) are designed for radiographic testing of metal and welded joints using ionizing radiation sources based on selenium-75, iridium-192 and cobalt-60 radionuclides. Panoramic and frontal scanning of products, relatively small dimensions and weight of the radiation head, and the ability to move the source in the ampoule over considerable distances make these flaw detectors extremely convenient for working in field, hard-to-reach and cramped conditions. Radiation heads of flaw detectors comply with the requirements of Russian and international standards and IAEA regulations. A modern source blocking system and a uranium protection unit provide increased safety in the operation of defective

Rice. 3.65.

toscopes. The use of a highly active, high-focus source of ionizing radiation based on the radionuclide selenium-75, which has no analogues on the world market, makes it possible to ensure the reliability of radiographic testing at a level approaching the level of radiographic testing in the most common range of controlled metal thicknesses.

X-rays and gamma rays propagate in straight lines, have, as already mentioned, high penetrating power, including passing through metals, are absorbed to varying degrees by substances with different densities, and also cause effects in photographic emulsions, ionize gas molecules, and cause glow some substances. These properties of penetrating radiation are used to record the intensity of radiation after it passes through the controlled part.

Depending on the method of presenting the final information, the following X-ray and gamma flaw detection methods are distinguished:

photographic (radiographic) with obtaining an image on x-ray film, which is then analyzed by the controller;
visual (radioscopic) with obtaining an image on a screen (scintillation, electroluminescent or television);
ionization (radiometric), based on measuring the intensity of radiation passed through products using an ionization chamber, the current value in which is recorded by a galvanometer or electrometer.

The most convenient method for monitoring products under operating conditions is the radiographic method, since it is the most sensitive to defects, is technologically advanced and provides good documentation (the resulting radiograph can be stored for a long time). When using the photo method, the radiographic image of an object is converted by an X-ray film emulsion (after its photoprocessing) into a visible light-and-shadow image. The degree of blackening of the film is proportional to the duration and intensity of the X-ray or gamma radiation acting on it. The film is a transparent substrate made of nitrocellulose or cellulose acetate, on which a layer of photographic emulsion is applied, topped with a layer of gelatin to prevent damage. For greater radiation absorption, the emulsion layer is applied on both sides. The sensitivity of the radiographic method depends on the nature of the defects of the object being examined, the conditions of its examination, and the characteristics of sources and radiation recorders (for example, film). All these factors affect the clarity and contrast of the radiograph and its quality. Consequently, the sensitivity of the method is directly dependent on the quality of the radiograph.

To evaluate and check the quality of radiographs, standards are used, which are a set of wires of various diameters (wire standards), plates with grooves of various depths (standards with grooves) and standards with holes or holes. The quality of the images and the detection of natural defects will be higher, the more clearly and contrastingly the standards taken simultaneously with the controlled object are developed on the X-ray image. The clarity of the image is greatly influenced by the geometric conditions of illumination of objects, and its contrast is influenced by the energy of the primary radiation and its spectral composition. Negative results are caused by violation of the technology of photoprocessing of exposed films.

Radiographic control products in operation are produced by transportable, lightweight x-ray and gamma devices. These include portable devices of the RUP-120-5 and RUP-200-5 types, as well as relatively new devices of the RAP-160-10P and RAP-160-1-N types.

The radiographic testing process includes the following main operations:

Structural and technological analysis of the subject to control

object and preparing it for transillumination;

selection of radiation source and photographic materials;
determination of modes and illumination of the object;
chemical-photographic processing of exposed film;
decoding of photographs with the design of received materials.

The task of a flaw detector inspector is to obtain a radiographic image suitable for assessing the quality of an object. In preparation for inspection, parts must be cleaned of slag and contaminants, inspected and marked into separate areas with chalk or colored pencil. Then, based on the purpose of control, the configuration of the part and the convenience of approaching the radiation source and film, the direction of illumination of the part or its section is selected. The choice of radiation source and photographic materials depends on the area of application of X-ray and gammagraphy and the testability of the product. The main technical requirement for choosing a radiation source and X-ray film is to ensure high sensitivity. The choice of film for transillumination is determined by the minimum size of defects to be detected, as well as the thickness and density of the material of the translucent part. When inspecting objects of small thickness and especially light alloys, it is advisable to use high-contrast and fine-grained films. When screening larger thicknesses, a more sensitive film should be used. There are four classes of X-ray films of varying sensitivity, contrast and grain size.

Cassettes are used to protect films from exposure to visible light and to place them. When choosing cassettes, it is assumed that the film fits more tightly to the area of the part being scanned. Soft cassettes are used if the film needs to be bent. Such cassettes are envelopes made of light-proof paper. Rigid cassettes made from aluminum alloy provide a tighter fit and clearer images. The duration of exposure is determined by nomograms, where the thickness of the transilluminated material is plotted along the abscissa axis, and the exposure time is plotted along the ordinate axis. Nomograms are compiled on the basis of experimental data obtained by illuminating objects made of specific materials with specific radiation sources. Chemical-photographic processing of film includes developing, intermediate washing, fixing, rinsing and final washing or drying of the image. The film is processed in a darkroom (in a dark room) under inactive lighting. Interpretation of X-ray and gamma images is carried out by viewing them in transmitted light on a X-ray viewer. When deciphering, it is necessary to be able to distinguish defects in parts from defects in the film, including those caused by improper handling or design features of the part. Simultaneously with examining the image, it is advisable to inspect the part being inspected, as well as compare the image with the reference one obtained by scanning the usable parts (Fig. 3.66).

The advantages of the radiographic method are its clarity, the ability to determine the nature, boundaries, configuration and depth of defects. The disadvantages of the method include low sensitivity for detecting fatigue cracks, high consumption of X-ray film and photographic materials, as well as inconveniences associated with the need to process films in the dark.

Using radioscopic method fluoroscopic is used as a radiation intensity detector

Direction of Transillumination

Rice. 3.66.

A- circumferential seams in cylindrical or spherical products; 6 - corner connections; V- using a compensator and a lead mask; TO- cassette with film (for radiography); 7 - translucent product; 2 - compensator; 3 - lead mask

screen. The method has low sensitivity, and the control results are largely subjective. Significant progress has been made in the field of creating X-ray introscopes - “intravision” devices. Electro-optical X-ray introscopes use the conversion of X-ray radiation passed through a controlled object into an optical image observed on the output screen. In X-ray television introscopes, this image is transmitted by the television system to the kinescope screen.

At radiometric (ionization) method control, the object is illuminated with a narrow beam of radiation, which sequentially moves along the controlled areas (Fig. 3.67). The radiation passing through the controlled area is converted by a detector, at the output of which an electrical signal appears,

Direction

movements

Rice. 3.67.

7 - source; 2,4 - collimators; 3 - controlled object; 5 - scintillation sensitive element; b - photomultiplier; 7 - amplifier; 8 - recording device

proportional to the radiation intensity. The electrical signal is sent through an amplifier to a recording device.

The radiometric method has high productivity and can be easily automated. However, using this method it is difficult to judge the nature and shape of defects, and it is also impossible to determine the depth of their occurrence.

In addition to the above methods of radiation monitoring of parts, there are also xeroradiography method, based on the action of X-rays and gamma rays passing through the controlled object on the photosensitive semiconductor layer, on which an electrostatic charge is induced before shooting. During exposure, the charge decreases in proportion to the irradiation energy, as a result of which a latent electrostatic image of the illuminated object is formed in the layer. It is manifested using electrified dry powder, transferred to paper and fixed in vapors of an organic solvent or by heating. For testing, for example, plates consisting of an aluminum substrate and a selenium layer deposited on it are used. X-ray images obtained on such a plate are not inferior in basic parameters to images obtained on X-ray film.

Radiation thickness measurements, which use X-ray, y- and (3-radiation())

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