Recently, government bodies of the Russian Federation have declared a “turn to the East” and potential close cooperation between Russian manufacturers/customers and Chinese ones. For high-quality collaboration with representatives of the PRC, it is necessary to speak the same language with them, and in particular, to navigate the terminology and standard regulatory documentation used by both parties. In this article, we would like to summarize our experience of interaction with colleagues from the People's Republic of China on one local issue - diagnosing casing strings, and, using its example, consider the similarities and differences in the regulatory documentation of the Russian Federation and the People's Republic of China.

Casing pipes are used to secure oil and gas wells during their construction and operation. The casing pipes are connected to each other using coupling or couplingless (integral) threaded connections. At the construction site, multi-stage construction quality control is always carried out, consisting of the following operations: control of the availability of accompanying documentation (certificate); checking compliance of certificate data with pipe markings; visual control; instrumental control; unbrakable control; mandrel control; hydraulic test.

All quality control activities shall be specified by the manufacturer's instructions, which shall include the appropriate procedure and quantitative or qualitative acceptance criteria. Non-destructive testing instructions must comply with the requirements of these specifications and the requirements of national and international standards selected by the manufacturer.

On the territory of the Russian Federation, the main GOST 632-1980 and GOST 53366-2009 are currently in force (Cancelled, from 01/01/2015 use GOST 31446-2012. By order of the Federal Agency for Technical Regulation and Metrology dated 10/22/2014 No. 1377-st - restored on the territory of the Russian Federation from 01/01/2015 to 01/01/2017), regulating the requirements for non-destructive testing and control levels of seamless and electric-welded pipes. All casing pipes must be checked for defects along the entire length (from end to end) using non-destructive testing methods.

Casing pipes must not have defects that, according to GOST R 53366-2009, are considered unacceptable defects, and must meet the requirements established in this standard. Standard Methods for Non-Destructive Testing of Pipe are traditional, proven methods and provide non-destructive testing procedures that are widely used for the inspection of tubular products throughout the world. However, it is possible to use other non-destructive testing methods and procedures that can detect defects, for example, for the use of pipes in wells with special operating conditions. In such cases, it is recommended to use other non-destructive testing methods that make it possible to confirm the required quality of pipes and their suitability for lowering into the well.

Let's consider non-destructive testing methods for casing strings used in the Russian Federation and China:

1) Ultrasonic testing (ultrasonic method)

Ultrasound propagates throughout the entire circumference of the material. The acoustic characteristics of the material and internal structural changes are reflected in the propagation of ultrasonic waves. Signal recording and analysis gives an idea of ​​the degree of damage to the material. GOST 53366-2009 specifies only international standards, in accordance with which casing strings must be inspected: ISO 9303, ISO 9503 and ASTM E 213. However, GOST 13680-2011 for identifying delaminations, the projection area of ​​which on the outer surface is no more than 260 mm 2, it is proposed to act in accordance with ISO 10124:1994 (Table 1).

At the same time, standard methods of ultrasonic non-destructive testing are in effect in Russia: GOST R ISO 10332-99 “Seamless and welded steel pressure pipes (except for pipes made by submerged arc welding)”, GOST 12503-75 “Steel. Ultrasonic testing methods. General requirements", GOST 14782-86 "Non-destructive testing. Welded connections. Ultrasonic methods" (Repealed on the territory of the Russian Federation from July 1, 2015. Use GOST R 55724-2013), GOST R ISO 10893-12-2014 "Seamless and welded steel pipes. Part 12. Ultrasonic method for automated monitoring of wall thickness along the entire circumference,” however, they are not used to identify defects in casing strings. The international standards of the ultrasonic non-destructive testing method listed above are mainly used, while in the PRC the integrity of casing pipes is monitored in accordance with international and/or its own standards 1 .

Table 1 presents the most important standards for ultrasonic testing of casing strings, from the standard methods of non-destructive testing of pipes, used both in Russia and in China.

Table 1

2) Magnetic control (magnetic flux leakage method)

The next non-destructive testing method, which is recommended to be used in accordance with the requirements of GOST 53366-2009, is the magnetic flux scattering method.

Magnetic flaw detection of casing pipes using the leakage flux method is based on the detection of magnetic leakage fluxes in a ferromagnetic material with high magnetic permeability by measuring the variable characteristics after magnetization of the product. After magnetization, the magnetic flux, spreading through the object under study and encountering a defect on its way, bends around it due to the fact that the magnetic permeability of the defect is significantly lower than the magnetic permeability of the base metal. As a result, part of the magnetic field lines is displaced by the defect to the surface, forming a local magnetic leakage flux.

Magnetic testing methods cannot detect defects that cause disturbances in the distribution of magnetic flux lines without the formation of a local leakage flux. The flux disturbance depends on the size and shape of the defect, its depth and its orientation relative to the direction of the magnetic flux. Surface defects located perpendicular to the magnetic flux create significant leakage fluxes; defects oriented along the direction of magnetic field lines practically do not cause the appearance of stray fluxes. The presence of longitudinal and transverse defects leads to the need to carry out double testing using combined magnetization.

Table 2 presents the standards for magnetic flaw detection using the magnetic flux leakage method. Table 2 does not present standard non-destructive testing methods in force in the Russian Federation: GOST R 55680-2013 “Non-destructive testing. Fluxgate method" (valid from 07/01/2015, replacing GOST 21104-75); GOST R ISO 10893-3-2016 “Seamless and welded steel pipes. Part 3. Automated testing using the magnetic flux scattering method over the entire surface of ferromagnetic steel pipes to detect longitudinal and (or) transverse defects” (effective date 01.11.2016).

table 2

3) Eddy current testing (eddy current method)

Eddy current testing is a field of eddy currents generated by a ferromagnetic coil located near the surface of the tested object; analysis of changes in the electromagnetic field of eddy currents under the influence of certain defects. The method is only applicable to conductive material. Eddy current testing can be used to test pipes, welds and cracks in the surface layer of the deposit, and indirectly measure the length of the defect.

Table 3 presents testing standards using the eddy current method; there are no Russian and Chinese specialized standards for flaw detection of casing strings using this method. However, a number of standards are in force on the territory of the Russian Federation: GOST 24289-80 “Non-destructive eddy current testing. Terms and definitions", GOST R ISO 15549-2009 "Non-destructive testing. Eddy current testing. Basic provisions”, GOST R ISO 12718-2009 “Non-destructive testing. Eddy current testing. Terms and definitions", GOST R 55611-2013 "Non-destructive eddy current testing. Terms and Definitions". On the territory of the People's Republic of China, this method is standardized only for pipes of other classes (sizes).

Table 3

4) Magnetic testing (magnetic particle method)

Magnetic particle testing - the use of magnetic powder, which is adsorbed in places of defects, forming a “magnetic mark” - rolls of black magnetic powder, control is carried out visually. The method reflects surface and internal defects, while the sensitivity of the method does not depend on the color and metallization of the surface. The magnetic particle method is preferable for ferromagnetic materials compared to the penetrating substance method, as it is more efficient and easier to use. The main disadvantage is limited access to ferromagnetic material; in order to fully examine the surface, special equipment and a power source are required. After testing, residual magnetization is observed, which is difficult to eliminate. Table 4 shows international standards for the magnetic particle method of inspection of casing strings, Chinese standards for inspection by this method, used in mechanical engineering: quality control of equipment under pressure using the magnetic particle method. Table 4 also does not include standards in force in Russia, because there were no references to them in the defining GOST 53366-2009: GOST R 56512-2015 “Non-destructive testing. Magnetic particle method. Typical technological processes" (date of implementation 01.11.2016), GOST R ISO 9934-1-2011 "Non-destructive testing. Magnetic particle method. Part 1. Basic requirements”, GOST R ISO 9934-2-2011 “Non-destructive testing. Magnetic particle method. Part 2. Flaw detection materials”, GOST 21105-87 “Non-destructive testing. Magnetic particle method”, GOST R ISO 10893-5-2016 “Seamless and welded steel pipes. Part 5. Magnetic particle testing of ferromagnetic steel pipes to detect surface defects” (effective date 11/01/2016).

Table 4

5) Inspection by penetrating substances (capillary flaw detection)

The penetrant method is based on the penetration of a special liquid - penetrant - into the cavities of surface and through discontinuities of the test object, with subsequent extraction of the penetrant from the defects. The most common method is the capillary method, which is suitable for diagnosing objects made of metals and ceramics. The duration of flaw detection depends on the physical properties of the liquid, the nature of the detected defects and the method of filling the defect cavities with liquid. Within half an hour, surface fatigue, stress corrosion cracking and weld defects can be detected, and the method can determine the size of the crack.

GOST 53366-2009 does not specify standards for the capillary testing method for identifying defects in the casing, but this standard allows the use of other methods and methods of non-destructive testing. At the same time, GOST R ISO 13680-2011 recommends using ISO 12095 or ASTM E 165, which are listed in Table 5. Internal Russian standards for non-destructive testing using the penetrating liquid method have been developed and are in force, but until now they have not been used for inspecting casing strings: GOST R ISO 3059-2015 “Non-destructive testing. Penetrating testing and magnetic particle method. Selection of inspection parameters" (date of implementation 06/01/2016), GOST R ISO 3452-1-2011 "Non-destructive testing. Penetrating control. Part 1. Basic requirements”, GOST R ISO 3452-2-2009 “Non-destructive testing. Penetrating control. Part 2. Testing of penetrants”, GOST R ISO 3452-3-2009 “Non-destructive testing. Penetrating control. Part 3. Test samples”, GOST R ISO 3452-4-2011 “Non-destructive testing. Penetrating control. Part 4. Equipment”, GOST R ISO 12706-2011 “Non-destructive testing. Penetrating control. Dictionary”, GOST 18442-80 “Non-destructive testing Capillary methods General requirements”.

Table 5 presents standards related to this casing diagnostic method. There are no domestic Chinese standards for casing penetrant testing.

Table 5

6) X-ray control (radiographic method)

The radiographic method involves the use of X-ray radiation passing through the weld metal and creating an image on a radiographic film that shows the presence of various defects. The degree of exposure of the film will be greater in areas where defects are located.

In accordance with GOST ISO 3183-2012 “Steel pipes for pipelines in the oil and gas industry. General technical conditions”, the welded seam of each pipe end must be subjected to radiographic testing at a distance of at least 200 mm from the end of the pipe. The following pipes are subjected to this control method:

• with one or two longitudinal seams or one spiral seam, obtained by combining gas metal arc welding and submerged arc welding;
• with one or two longitudinal seams or one spiral seam, obtained by submerged arc welding.

Table 6 presents the relevant standards related to radiographic inspection of casing welds. Some standards for inspection of pipe welds are not specified.

Table 6

1. In the Russian Federation and China, when inspecting casing pipes for defects using various non-destructive testing methods, they are mainly guided by international ISO and ASTM standards.
2. Non-destructive testing of casing pipes is carried out in accordance with at least the same international standard in both Russia and China.
3. The main methods of non-destructive testing of casing strings in accordance with GOST 632-1980 and GOST 53366-2009 are: ultrasonic method, magnetic flux scattering method, eddy current method and magnetic particle method.
4. On the territory of the Russian Federation and the People's Republic of China, internal standards for non-destructive testing have been developed, which are not used to identify defects in casing pipes, but are used in other industrial areas.
5. In current internal standards and newly adopted ones, you can find references to canceled or outdated (there are replacement) versions of international and internal standards.
6. The radiographic non-destructive testing method is used only for flaw detection of casing pipe welds.

XU Jin-long, CAO Biao, HONG Wu-xing, LU Shan-sheng, FENG Jun-han, HUA Bin, YANG Shu-jie Domestic and international standards for non-destructive testing methods for casing strings / “Non-destructive testing methods” 2014, Vol 36 , No. 10, pp. 72-77

Tags: eddy current testing, penetrant flaw detection, penetrant testing, magnetic testing, magnetic particle testing, magnetic flux dispersion method, non-destructive testing, non-destructive testing of casing pipes, casing pipe, radiographic testing, X-ray testing, ultrasonic testing

Welded joints are new formations on any structure and their further safe operation largely depends on the quality of their application, and this, in turn, can only be revealed by a special check. The quality of welds of metal joints is checked using various flaw detection techniques. Of all the variety of flaw detection types that exist today, we can highlight ultrasonic testing of welded joints, which is the most accessible and inexpensive diagnostic method. Moreover, ultrasonic testing is practically not inferior in measurement accuracy to such types of non-destructive testing as fluoroscopy, gamma-scopy, radioscopy and others.

The technique of ultrasonic non-destructive testing is not a new type of flaw detection and was first put into practice in 1928, and with the development of technical progress and industrial technologies it began to be used in many areas of human activity.

The entire effect of ultrasonic testing is based on the fact that acoustic ultrasonic waves, when passing through a homogeneous medium, do not change their rectilinear trajectory of movement, but when separating media that have different structures and have different values ​​of specific acoustic resistance, they are partially reflected. Moreover, the more significant the difference in the physical and chemical properties of materials, the greater the sound resistance at the interface between the media, the more noticeable and noticeable the effect when reflecting sound waves.

For example, when a weld is formed, a mixture of gases usually remains in the metal structure, which did not have time to escape during solidification. At the same time, the gaseous medium has actually five times less wave resistance to the passage of ultrasonic vibrations than a metal crystal lattice, which allows ultrasonic vibrations to be almost completely reflected.

Ultrasonic testing or flaw detection of welded joints is a non-destructive method for searching for internal structures that have chemical or physical deviations from specified standards, which, if unacceptable in magnitude, are defined as mechanical defects in welds.

Advantages of ultrasonic testing

Ultrasonic testing techniques are used to diagnose all types of welding, soldering and gluing, which makes it possible to identify joint defects such as:

• air voids and pores,
• delamination in the deposited weld metal,
• heat-affected cracks,
• chemically heterogeneous inclusions,
• slag deposits,
• heterogeneity of structure,
• distortion of geometric dimensions.

The main advantages of ultrasonic flaw detection include the ability to control:

• connections from both homogeneous and dissimilar materials;
• structures consisting of both metals and non-metals;
• without destruction or damage to the test samples;
• with high mobility;
• with high research speed;
• at low cost;
• without dangerous factors for personnel in comparison with X-ray or radio flaw detection.

Disadvantages of ultrasonic testing

The use of ultrasonic testing has a number of features, namely, it requires significant preparation of the test surfaces for the passage of ultrasonic waves from piezoelectric transducers through the metal structure. Necessary:

• creation of class 5 roughness on the surface of the welded joint with the direction of the stripes perpendicular to the seam;
• applying a contact mass (in the form of water, oils) to the area under study to completely eliminate the air gap, and in the case of a vertical or strongly inclined surface, use thick pastes that are incapable of rapid drainage;

Directly the disadvantages of this flaw detection technique include:

• the need to use special piezoelectric transducers with a radius of curvature of the base in the range of +-10% of the radius of the object under study for diagnosing rounded shapes with a structure with a diameter of less than 200 mm;
• significant difficulties in studying coarse-grained structures of metals, for example, cast iron or austenite with a thickness of more than 60 mm, associated with significant attenuation and significant dispersion of ultrasonic vibrations;
• impossibility of inspecting parts with small and complex shapes;
• difficulty in assessing connections of different types of steels, which is associated with the heterogeneity of the base metals and the weld;
• the impossibility of establishing the actual sizes of various types of defects due to their shape, physical properties and location in the structure of the weld.

Types of ultrasonic inspection of seams

Ultrasonic flaw detection technology is based on the ability of high-frequency acoustic vibrations, about 20 kHz, to pass through a homogeneous structure and partially reflect from various obstacles in the form of pores, cracks and other inhomogeneities. There are several methods for obtaining the reflection of an ultrasonic signal, namely:

• shadow, which determines the difference in amplitude between transmitted and reflected vibrations;
• specular-shadow, based on determining the attenuation coefficient of reflected waves;
• echo-mirror or tandem, using two devices for its operation;
• delta method, which consists in determining the energy of vibrations reflected from a defect;
• pulse echo, which is based on the registration of reflected ultrasonic waves.

The most common are two types of flaw detection of welds using ultrasound - shadow and echo-pulse testing methods.

Methodology for ultrasonic testing

Despite the existence of several methods of ultrasonic flaw detection, their implementation is almost similar and differs only in the set of diagnostic equipment. Thus, the flaw detection procedure can be described by the following sequence:

1. Careful preparation of the surface under study is carried out by mechanically removing residual slag, paint and rust from the weld seam. In addition, 50 mm strips are cleaned on both sides of it.
2. The flaw detection site is generously covered with a liquid mass in the form of water, mineral oils or thick special pastes - this is necessary to allow the unhindered passage of ultrasonic waves.
3. The device is pre-configured for a specific technique designed to solve specific problems.
4. The ultrasonic piezoelectric transducer sequentially begins to move along a zigzag path along the weld seam.
5. After receiving a stable signal, it is necessary to periodically rotate the piezoelectric transducer in different directions around its axis so as to obtain a signal with maximum image clarity on the device screen.
6. When defects are detected, they are recorded and the corresponding coordinates are recorded.
7. If necessary, ultrasonic testing of welds is carried out in one or several passes.
8. The obtained flaw detection results are recorded in the inspection log.

In construction, pipes with Ø from 28 to 1420 mm with a wall thickness from 3 to 30 mm are used. The entire range of diameters according to flaw detection can be divided into 3 groups:

1. Ø from 28 to 100 mm and H from 3 to 7 mm
2. Ø from 108 to 920 mm and H from 4 to 25 mm
3. Ø from 1020 to 1420 mm and H from 12 to 30 mm

According to studies that were carried out at MSTU. N.E. Bauman recently, in the process of developing methods for ultrasonic testing of welded pipe joints, one should take into account such a very important factor as the anisotropy of the elastic characteristics of the pipe material.

Anisotropy of pipe steel, its features

Anisotropy- this is the difference in the properties of a medium (for example, physical: thermal conductivity, elasticity, electrical conductivity, etc.) in different directions within a given medium.

In the process of ultrasonic testing of welded joints of main gas pipelines assembled from pipes of domestic and foreign production, the omission of serious root defects, inaccurate assessment of their coordinates, and a significant level of acoustic noise were discovered.

It turned out that if optimal control parameters are observed and during its implementation, the main reason for missing a defect is the presence of significant anisotropy in the elastic properties of the base material. It affects the speed, attenuation and deviation from straightness of the ultrasonic beam.

During the sounding of metal, more than 200 pieces of pipes according to the scheme shown in Fig. 1, it turned out that the standard deviation of the wave speed with this direction of motion and polarization is equal to 2 m/s (for transverse waves). Deviations of velocities from the table values ​​of 100 m/s or more are not random and are probably associated with the production technology of rolled products and pipes. Such deviations have a strong influence on the propagation of polarized waves. In addition to the indicated anisotropy, inhomogeneity of the speed of sound across the thickness of the pipe wall was also discovered.

Rice. 1. Designations of deposits in the pipe metal: X, Y, Z. - directions of ultrasound propagation: x. y.z: - polarization directions; Y - rolling direction: Z - perpendicular to the plane of the pipe

The structure of rolled sheets is layered, consisting of metal fibers and other inclusions elongated during deformation. In addition, due to the effect of the thermomechanical rolling cycle on the metal, sections of the sheet that are uneven in thickness are subject to various deformations. These features cause the speed of sound to additionally depend on the depth of the sound layer.

Features of control of welded seams of pipes of various diameters

Pipes Ø from 28 to 100 mm

A distinctive feature of welded seams of pipes Ø from 28 to 100 mm with H from 3 to 7 mm is the occurrence of sagging inside the pipe. This causes false echo signals from them to appear on the screen of the flaw detector during testing with a direct beam, which coincide in time with the echo signals reflected from the root defects found by a single reflected beam. Due to the fact that the effective width of the beam is comparable to the thickness of the pipe wall, it is extremely difficult to identify the reflector by the location of the finder relative to the reinforcement roller. There is also an uncontrolled zone in the center of the seam due to the large width of the seam bead. All this is the reason for the low probability (10-12%) of detecting unacceptable volumetric defects, although unacceptable planar defects are detected much better (~ 85%). The main characteristics of sagging - depth, width and angle of contact with the surface of the object - are random variables for this standard size of pipe; the average values ​​are respectively 2.7 mm; 6.5 mm and 56°30".

Rolled steel behaves as an anisotropic and inhomogeneous medium with rather complex dependences of the velocities of elastic waves on the direction of polarization and sounding. The speed of sound changes approximately symmetrically with respect to the middle of the sheet section, and in the region of this middle the transverse wave speed can greatly (up to 10%) decrease compared to the surrounding areas. The shear wave speed in the controlled objects varies in the range from 3070 to 3420 m/s. At a depth of up to 3 mm from the surface of the rolled product, the speed of the transverse wave may increase slightly (up to 1%).

Noise immunity of control increases significantly in the case of using inclined separate-combined probes of the RSN type (Fig. 2), which are called chordal. They were designed at MSTU. N.E. Bauman. A special feature of the inspection is that there is no need for cross scanning when searching for defects. It is performed only along the perimeter of the pipe at the moment the front face of the converter is pressed against the seam.

Rice. 2. Inclined chord RSN-PEP: 1 - emitter: 2 - receiver

Pipes Ø from 108 to 920 mm

Pipes with Ø from 108 to 920 mm with H from 4 to 25 mm are also connected by one-sided welding without back welding. Until recently, the control of these connections was carried out using combined probes according to a method developed for pipes with Ø from 28 to 100 mm. But such a control technique requires the presence of a fairly large zone of coincidence (zone of uncertainty). This significantly reduces the accuracy of connection quality assessment. In addition, combined probes are characterized by a high level of reverberation noise, which makes it difficult to decipher signals, as well as uneven sensitivity, which cannot always be compensated by available means. The use of chordal separate-combined probes for the purpose of monitoring this standard size of welded joints is impractical, since due to the limited values ​​of the input angles of ultrasonic vibrations from the surface of the welded joint, the dimensions of the transducers increase significantly, and the area of ​​acoustic contact becomes larger.

At MSTU. N. E. Bauman created inclined probes with leveled sensitivity to perform inspection of welded joints with a diameter of 100 mm or more. Sensitivity equalization ensures that the rotation angle 2 is selected in such a way that the upper part and middle of the seam are sounded by the central once reflected beam, and the lower part by direct peripheral rays that fall on the defect at an angle Y from the central one. In Fig. Figure 3 shows a graph of the dependence of the angle of introduction of the transverse wave on the angle of rotation and opening of the directional pattern Y. In such probes, the incident and reflected waves from the defect are horizontally polarized (SH-wave).

Rice. 3. Changing the input angle alpha, within the limit of half the opening angle of the RSN-PEP radiation pattern, depending on the rotation angle delta.

It is clear from the graphs that when testing objects with a wall thickness of 25 mm, the uneven sensitivity of the RS-probe reaches 5 dB, while for a combined probe it can reach 25 dB. RS-PEP is characterized by an increased signal-to-interference level and, therefore, increased absolute sensitivity. For example, the RS-PEP easily detects a defect with an area of ​​0.5 mm2 during the inspection of a welded joint 10 mm thick with both direct and once reflected beams with a useful signal/interference ratio of 10 dB. The procedure for performing control with probe data is the same as for a combined probe.

Pipes Ø from 1020 to 1420 mm

Welded joints of pipes Ø from 1020 to 1420 mm with H from 12 to 30 mm are performed by double-sided welding or with back welding of the seam bead. In seams that are made by double-sided welding, usually, false signals from the trailing edge of the reinforcement roller do not cause as much interference as in single-sided seams. Their amplitude is not so great due to the smoother contours of the roller. In addition, they are further along the scan. For this reason, this is the most suitable pipe size for flaw detection. But the results of research conducted at MSTU named after. N. E. Bauman show that the metal of these pipes is characterized by the greatest anisotropy. To reduce the effect of anisotropy on defect detection, a 2.5 MHz probe should be used with a prism angle of 45°, rather than 50°, as specified in most regulatory documents. The highest control accuracy was achieved using probes of the RSM-N12 type. Unlike the methodology compiled for pipes with Ø from 28 to 100 mm, there is no zone of uncertainty when monitoring these connections. The rest of the control method is similar. When using an RS-PET, it is also recommended to adjust the scanning speed and sensitivity for vertical drilling. The scanning speed and sensitivity of inclined combined probes should be adjusted using corner reflectors of the appropriate size.

When inspecting welds, it must be remembered that in the heat-affected zone there are metal delaminations, which make it difficult to determine the coordinates of the defect. The area in which the defect was found by an inclined probe must be additionally checked by a direct probe in order to clarify the nature of the defect and identify the exact value of the depth of the defect.

In the nuclear, petrochemical and nuclear power industries, clad steels are often used in the manufacture of pipelines, apparatus and vessels. For cladding the inner wall of these structures, austenitic steels are used, which are applied by surfacing, rolling or explosion in a layer of 5 to 15 mm.

The process of monitoring these welded joints involves analyzing the continuity of the pearlite part of the weld, as well as the fusion zone with restorative anti-corrosion surfacing. In this case, the continuity of the body of the surfacing itself is not controlled.

But due to the difference in the acoustic characteristics of the base metal and austenitic steel, echo signals appear from the interface during ultrasonic testing, preventing the detection of defects, for example, cladding delaminations and sub-cladding cracks. In addition, the presence of cladding and its characteristics have a significant impact on the parameters of the acoustic path of the probe.

For this reason, standard technological solutions are ineffective in inspecting thick-walled welds of clad pipelines.

After many years of research, scientists have figured out the main features of the acoustic tract. Recommendations were received for optimizing its characteristics and a technology for performing ultrasonic analysis of welds with austenitic cladding was developed.

In particular, scientists have found that when a beam of ultrasonic waves is reflected from the boundary of pearlite-austenitic cladding, the radiation pattern almost does not change in the case of rolling cladding and changes significantly in the case of surfacing cladding. Its width increases significantly, and within the main lobe there are oscillations of 15-20 dB, depending on the surfacing method. There is a significant movement of the reflection exit point from the beam cladding boundary compared to its location, and the velocity of the shear waves in the transition zone also changes.

When developing technology for monitoring welded joints of clad pipelines, all this was taken into account. This technology provides for a preliminary mandatory determination of the thickness of the pearlite part (the depth of penetration of the anti-corrosion surfacing).

For more accurate detection of planar defects (lack of fusion and cracks), it is better to use a probe with an input angle of 45° and a frequency of 4 MHz. More accurate detection of vertically oriented defects at an input angle of 45°, in contrast to angles of 60 and 70°, is explained by the fact that during sounding of the latter, the angle at which the beam meets the defect is close to the third critical angle, at which the transverse wave reflection coefficient is minimal.
When the pipe is sounded outside at a frequency of 2 MHz, echo signals from defects are screened by an intense and long-lasting noise signal. The resistance to interference of the probe at a frequency of 4 MHz is on average 12 dB higher. For this reason, the useful signal from a defect located in close proximity to the deposit boundary will be better read against the background of noise. And vice versa, when sounding the pipe from the inside through the surfacing, better resistance to interference will be provided by a probe at a frequency of 2 MHz.

The technology for monitoring pipeline welds with surfacing is regulated by Gosatomnadzor document RFPNAEG-7-030-91.

In the construction industry, pipes with a diameter of 28 to 1420 mm and a wall thickness of 3 to 30 mm are used. Based on flaw detection, the entire range of pipe diameters can be divided into three groups:

1. 28...100 mm and H = 3...7 mm
2. 108...920 mm and H= 4...25 mm
3. 1020...1420 mm and H= 12...30 mm

Conducted by specialists from MSTU. N.E. Bauman's research shows that it is necessary to take into account the anisotropy of the elastic properties of the material when developing methods for ultrasonic testing of welded pipe joints.

Features of anisotropy of pipe steel.

It is assumed that the speed of propagation of transverse waves does not depend on the direction of sounding and is constant over the cross section of the pipe wall. But ultrasonic testing of welded joints of main gas pipelines made from foreign and Russian pipes revealed a significant level of acoustic noise, the omission of large root defects, as well as incorrect assessment of their coordinates.

It has been established that if optimal control parameters are observed and the testing procedure is followed, the main reason for missing a defect is the presence of a noticeable anisotropy in the elastic properties of the base material, which affects the speed, attenuation, and deviation from straightness of the ultrasonic beam propagation.

Having sounded the metal of more than 200 pipes according to the scheme shown in Fig. 1, it was revealed that the standard deviation of the wave speed for a given direction of propagation and polarization is 2 m/s (for transverse waves). Deviations of speeds from the table by 100 m/s or more are not accidental and are most likely associated with the production technology of rolled products and pipes. Deviations on such scales significantly affect the propagation of polarized waves. In addition to the described anisotropy, inhomogeneity of the speed of sound across the thickness of the pipe wall was revealed.

Rice. 1. Designations of deposits in the pipe metal: X, Y, Z. - directions of ultrasound propagation: x. y.z: - polarization directions; Y - rolling direction: Z - perpendicular to the plane of the pipe

Rolled sheets have a layered texture, consisting of fibers of metal and non-metallic inclusions, elongated during deformation. Sheet zones of unequal thickness are subject to various deformations as a result of the influence of the thermomechanical rolling cycle on the metal. This leads to the fact that the speed of sound is additionally affected by the depth of the sounding layer.

Inspection of welded seams of pipes of various diameters.

Pipes with a diameter of 28...100 mm.

Welded seams in pipes with a diameter of 28 to 100 mm and a height of 3 to 7 mm have such a feature as the formation of sagging inside the pipe, this, when inspected with a direct beam, leads to the appearance of false echo signals on the screen of the flaw detector, which coincide in time with the echo signals, reflected from root defects, which are detected by a single reflected beam. Since the effective width of the beam is commensurate with the thickness of the pipe wall, the reflector usually cannot be found by the location of the finder relative to the reinforcement roller. There is also an uncontrolled zone in the center of the seam due to the large width of the seam bead. All this leads to the fact that the probability of detecting unacceptable volumetric defects is low (10-12%), but unacceptable planar defects are determined much more reliably (~ 85%). The main parameters of sagging (width, depth and angle of contact with the surface of the product) are considered random variables for a given pipe size; the average parameter values ​​are 6.5 mm; 2.7 mm and 56°30" respectively.

Rolled products behave like an inhomogeneous and anisotropic medium with rather complex dependences of the velocities of elastic waves on the direction of sounding and polarization. The change in sound speed is closely symmetrical relative to the middle of the sheet section, and near this middle the transverse wave speed can decrease significantly (up to 10%) relative to the surrounding areas. The shear wave speed in the objects under study varies in the range of 3070...3420 m/s. At a depth of up to 3 mm from the surface of the rolled product, a slight (up to 1%) increase in the shear wave speed is likely.

The noise immunity of control is significantly enhanced when using inclined separate-combined probes of the RSN type (Fig. 2), called chord probes. They were created at MSTU. N.E. Bauman. The peculiarity of the inspection is that when identifying defects, transverse scanning is not necessary; it is only needed along the perimeter of the pipe when the front face of the transducer is pressed against the seam.

Rice. 2. Inclined chord RSN-PEP: 1 - emitter: 2 - receiver

Pipes with a diameter of 108...920 mm.

Pipes with a diameter of 108-920 mm and with H in the range of 4-25 mm are also performed by one-sided welding without back welding. Until recently, control over these connections was controlled by combined probes according to the methodology outlined for pipes with a diameter of 28-100 mm. But the known control technique assumes the presence of a significantly large zone of coincidence (zone of uncertainty). This leads to insignificant reliability of assessing the quality of the connection. Combined probes have a high level of reverberation noise, which complicates the decoding of signals, and uneven sensitivity, which cannot always be compensated for by available means. The use of chordal separate-combined probes for monitoring a given standard size of welded joints is not effective due to the fact that due to the limited values ​​of the input angles of ultrasonic vibrations from the surface of the welded joint, the dimensions of the transducers increase disproportionately, and the area of ​​acoustic contact increases.

Created at MSTU. N.E. Bauman inclined probes with equalized sensitivity are used to control welded joints with a diameter of more than 10 cm. Equalization of sensitivity is achieved by choosing a rotation angle of 2 so that the middle and upper part of the weld is sounded by a central, single-reflected beam, and the lower part is examined by direct peripheral rays incident on the defect at an angle Y, from central. In Fig. 3. shows a graph of the dependence of the angle of input of the transverse wave on the angle of rotation and opening of the directional pattern Y. Here in the probe, the waves incident and reflected from the defect are horizontally polarized (SH-wave).

Rice. 3. Changing the input angle alpha, within the limit of half the opening angle of the RSN-PEP radiation pattern, depending on the rotation angle delta.

The graph shows that when testing products H = 25 mm, the uneven sensitivity of the RS-probe can be up to 5 dB, and for a combined probe it can reach 25 dB. RS-PEP has an increased signal level and has increased absolute sensitivity. The RS-PEP clearly reveals a notch with an area of ​​0.5 mm2 when inspecting a welded joint 1 cm thick with both a direct and a single reflected beam at a useful signal/interference ratio of 10 dB. The process of monitoring the considered probes is similar to the procedure for conducting combined probes.

Pipes with a diameter of 1020...1420 mm.

To make welded joints of pipes with a diameter of 1020 and 1420 mm with H in the range from 12 to 30 mm, double-sided welding or welding with back welding of the seam bead is used. In seams made by double-sided welding, false signals from the trailing edge of the reinforcement bead most often have less interference than in single-sided welds. They are smaller in amplitude due to the smoother contours of the roller further along the sweep. In this regard, this is the most convenient pipe size for flaw detection. But conducted at MSTU. N.E. Bauman's research shows that the metal of these pipes is characterized by the greatest anisotropy. In order to minimize the effect of anisotropy on the detection of defects, it is best to use a probe at a frequency of 2.5 MHz with a prism angle of 45°, and not 50°, as advised in most regulatory documents for testing such connections. Higher control reliability was achieved when using RSM-N12 type probes. But unlike the method outlined for pipes with a diameter of 28-100 mm, there is no zone of uncertainty when monitoring these connections. Otherwise, the control principle remains the same. When using the RS-PEP, it is recommended to adjust the scan speed and sensitivity according to vertical drilling. The scanning speed and sensitivity of inclined combined probes should be adjusted using corner reflectors of the appropriate size.

When inspecting welds, it is necessary to remember that metal delamination may occur in the heat-affected zone, which complicates the determination of the coordinates of the defect. The area with a defect found by an inclined probe must be checked with a direct probe to clarify the characteristics of the defect and identify the true value of the depth of the defect.

In the petrochemical industry and nuclear energy, clad steels are widely used for the production of pipelines and vessels. Austenitic steels applied by surfacing, rolling or explosion with a thickness of 5-15 mm are used as cladding for the inner wall of such structures.

The method of monitoring these welded joints involves assessing the continuity of the pearlite part of the weld, including the fusion zone with restorative anti-corrosion surfacing. The continuity of the surfacing body itself is not subject to control.

But due to the difference in the acoustic properties of the base metal and austenitic steel from the interface during ultrasonic testing, echo signals appear that interfere with the detection of defects such as cladding delaminations and sub-cladding cracks. The presence of cladding significantly affects the parameters of the acoustic path of the probe.

In this regard, standard technological solutions for monitoring thick-walled welds of clad pipelines do not give the desired result.

Long-term research by a number of specialists: V.N. Radko, N.P. Razygraeva, V.E. Bely, V.S. Grebennik and others made it possible to determine the main features of the acoustic path, develop recommendations for optimizing its parameters, and create a technology for ultrasonic testing of welds with austenitic cladding.

In the works of specialists, it was established that when a beam of ultrasonic waves is re-reflected from the pearlite-austenitic cladding boundary, the directional pattern almost does not change in the case of rolling cladding and is significantly deformed in the case of surfacing cladding. Its width increases sharply, and within the main lobe oscillations of 15-20 dB appear, depending on the type of surfacing. There is a significant displacement of the reflection exit point from the beam cladding boundary compared to its geometric coordinates and a change in the speed of transverse waves in the transition zone.

Taking these features into account, the technology for monitoring welded joints of clad pipelines requires preliminary mandatory measurement of the thickness of the pearlite part.

Better detection of planar defects (cracks and lack of fusion) is achieved by using a probe with an input angle of 45° and a frequency of 4 MHz. The better detection of vertically oriented defects at an input angle of 45° compared to angles of 60 and 70° is due to the fact that when the latter are sounded, the angle at which the beam meets the defect is close to the 3rd critical angle, at which the shear wave reflection coefficient is the smallest.

At a frequency of 2 MHz, when sounded outside the pipe, echoes from defects are shielded by an intense and long-lasting noise signal. The noise immunity of the probe at a frequency of 4 MHz is on average 12 dB higher, which means the useful signal from a defect located in the immediate vicinity of the surfacing boundary will be better resolved against the background noise.

When sounding from inside the pipe through the surfacing, maximum noise immunity is established when the probe is set to a frequency of 2 MHz.

The method of monitoring pipeline welds with surfacing is regulated by the Gosatomnadzor guideline RFPNAEG-7-030-91.

Manual ultrasonic testing (UT) of welded joints of vessels and pipelines made of pearlitic and martensitic-ferritic steels

Date of publication: 09.24.2015

Annotation: This article is devoted to the issue of the scope of application of manual ultrasonic testing (UT) of welded joints of vessels and pipelines made of pearlitic and martensitic-ferritic steels, except for cast parts.

Keywords: ultrasonic testing, non-destructive testing, echo method, electronic scanning, linear scanning, sector scanning.

Manual ultrasonic testing (UT) of welded joints, discussed in this article, can be used in the diagnosis of vessels and pipelines made of pearlitic and martensitic-ferritic steels, except for cast parts.

Ultrasonic testing provides detection and assessment of the admissibility of discontinuities with an equivalent area provided for by the standards regulated by Rostechnadzor.

The testing technique described in this article can be applied when performing ultrasonic testing of base metal equipment and welded joints of technical devices used at a hazardous production facility.

In welded joints, the metal of the weld and the heat-affected zone is subject to control and the same quality assessment. The width of the controlled heat-affected zone of the base metal is determined in accordance with the requirements of Table 1.

Table 1 - Size of the heat-affected zone of the base metal, assessed according to the standards for welded joints

The width of the controlled sections of the heat-affected zone is determined from the boundary surface of its cutting specified in the design documentation.

In welded joints of parts of different thicknesses, the width of the specified zone is determined separately for each of the welded parts.

Ultrasonic testing is carried out after correction of defects detected during visual and measuring inspection, at ambient air and product surface temperatures at the inspection site from + 5 to + 40 °C. The surfaces of welded joints, including heat-affected zones and probe movement zones, must be cleaned of welding beads, dust, dirt, scale, and rust. The nicks and flaking scale along the entire length of the controlled area must be removed from them. When preparing the scanning surface, its roughness should be no worse than Rz=40 µm.

The width of the area prepared for control must be at least:

Htgb + A + B- when monitoring with a combined direct beam probe;

2 Htgb + A + B- when monitoring with a once reflected beam and according to the “tandem” scheme;

H + A + B- when monitoring PC probes of chord type, where A is the length of the contact surface of the probe (width for PC probes).

Carrying out control involves the use of the following equipment, materials and tools:

• pulsed ultrasonic flaw detectors with sets of transducers and connecting high-frequency cables;
• CO, OSO, SOP, auxiliary devices, including means for determining surface roughness (roughness samples, profilometers);
• ARD and SKH diagrams, nomograms;
• auxiliary devices, materials and tools.

When testing, flaw detectors are used with an adjustment range of the measuring attenuator of at least 60 dB and a step step of no more than 2 dB (the dynamic range of the flaw detector screen is at least 20 dB). The speed of propagation of ultrasound in materials should be 2500-6500 m/s for longitudinal waves and 1200-3300 m/s for transverse ones. The range of sounding on steel when working with a direct combined probe in echo-pulse mode is at least 3000 mm, and when working with an inclined probe - at least 200 mm (along the beam). The range of measurements of defect depths using a depth-measuring device in echo-pulse mode is not less than 1000 mm for steel when working with a straight probe, and not less than 100 mm in both coordinates when working with an inclined probe.

The selection of inclined combined transducers and direct transducers is carried out taking into account the thickness of the controlled welded joint according to Tables 2 and 3.

Table 2 - Selection of combined inclined transducers

Table 3 - Selection of direct converters

The ultrasonic testing procedure includes the following operations:

• setting the scanning speed and depth gauge of the flaw detector;
• setting the search, control and rejection sensitivity levels, TCR parameters (if necessary);
• scanning;
• when an echo signal appears from a possible discontinuity: determining its maximum and identifying the discontinuity (selecting a useful signal from the background of false signals);
• determining the limit values ​​of discontinuity characteristics and comparing them with standard values;
• measurement and recording of discontinuity characteristics if its equivalent area is equal to or exceeds the control level;
• preparation of documentation based on control results.

The control results are assessed from the point of view of compliance of the measured characteristics with the maximum permissible values ​​​​established in regulatory documents. The quality of the heat-affected zone, the dimensions of which are indicated in Table 1, is assessed by the same standards.

Quality standards based on the results of ultrasonic inspection are determined according to the governing normative and technical documentation in force at the time of inspection (RD, PKD, TU, PC). If there are no special standards for a specific controlled welded unit, it is permissible to be guided by the standards given in Table 4.

Table 4 - Maximum permissible values ​​of characteristics of discontinuities detected during inspection

The quality of welded joints is assessed using a two-point system:

• point 1 - unsatisfactory quality: welded joints with discontinuities, the measured characteristics or quantity of which exceed the maximum permissible values ​​​​according to current standards;
• point 2 - satisfactory quality: welded joints with discontinuities, the measured characteristics or quantity of which do not exceed established standards. In this case, welded joints are considered to be of limited suitability (score 2a) if discontinuities with A to<А<А бр; ∆L <∆L 0 ; n< n 0 , and absolutely suitable (score 2b), if no discontinuities with A ≥ A k are detected in them, where A is the measured amplitude of the echo signal from the discontinuity; Ak and Abr are the amplitudes of the control and rejection sensitivity levels at the depth of the discontinuity; ∆L and ∆L 0 - measured conditional length of discontinuity and its maximum permissible value; n and n 0 - measured number of discontinuities with A to ≤ A ≤ A br and DL ≤ DL 0 per unit length of the welded joint (specific quantity) and the maximum permissible quantity.

The main measured characteristics of the identified discontinuity are:

• the ratio of the amplitude and/or time characteristics of the received signal and the corresponding characteristics of the reference signal;
• equivalent discontinuity area;
• coordinates of the discontinuity in the welded joint;
• conventional dimensions of discontinuity;
• conditional distance between discontinuities;
• the number of discontinuities at a certain length of the connection.

The measured characteristics used to assess the quality of specific compounds must be regulated by technological control documentation.

A discontinuity is considered transverse (type “T” according to GOST R 55724-2013, Appendix D) if the amplitude of the echo signal from it when sounded by an inclined combined probe along the seam (regardless of the conditional length) Apop is no less than 9 dB greater than when voicing across the seam Aprod. In this case, only echo signals with an amplitude equal to or greater than the control sensitivity level Ak for the depth of a given discontinuity are considered.

If the difference in amplitudes of echo signals in the indicated directions of sounding is less than 9 dB, the discontinuity is considered longitudinal.

When measuring the orientation of a discontinuity, the weld reinforcement at the measurement location must be removed and smoothed flush with the base metal.

Discontinuity is considered either volumetric or planar depending on the measured values ​​of identification characteristics (features) according to GOST R 55724-2013, section 10.

Identification of the shape of a discontinuity can be carried out using flaw detectors with visualization of defects.

When inspecting welded joints with a groove for the backing ring, defects are assessed for the nominal thickness of the welded elements (in the groove zone).

During expert or duplicate inspection, the inspection results of two flaw detectors should be considered comparable if the equivalent areas of the same discontinuity differ by no more than 1.4 times (3 dB).

Deviations from the standards for assessing detected discontinuities are allowed in accordance with the procedure provided for by the Rostechnadzor Rules, as well as by special technical solutions agreed upon in the prescribed manner.

List of information sources:

1. GOST R 55724-2013 “Non-destructive testing. Welded connections. Ultrasonic methods".
2. GOST 12.1.001 “Ultrasound General Safety Requirements”.
3. GOST 12.3.019 “Electrical tests and measurements. General safety requirements."
4. GOST 26266-90 “Non-destructive testing. Ultrasonic transducers. General technical requirements".
5. PB 03-440-02 “Rules for certification of non-destructive testing specialists”.
6. RD 34.10.133-97 “Instructions for adjusting the sensitivity of an ultrasonic flaw detector.”
7. SP 53-101-98 “Manufacture and quality control of steel structures.”

S.A. Shevchenko, N.L. Mikhailova, A.A. Shestakov, S.G. Tsareva, E.V. Shishkov