RU2614186C1 - Method for non-destructive inspection for degree of damage of metal containers - Google Patents

Abstract

FIELD: nuclear energy.

SUBSTANCE: invention can be used for a nondestructive inspection for the degree of damage of metal containers with spent nuclear fuel. Core of the invention is that onto the surface of the container installed are ultrasound radiators and signal receivers in equal proportions, which generate rectangular pulses with appropriate width, length and frequency. Measured is initial speed of US signals propagation in a non-uniform medium to calculate the value of sensors displacement along the container wall and across it. Matrix of signals coming from all the receivers is formed. With the help of the matrix a scan sector is created with the ultrasonic wave travel time from each sensor to each point of the volume with due allowance for conversion of ultrasonic waves at their reflection and refraction at the media interfaces. Obtained signals by a computer program are formed into sector images. Then the sector images are formed into a composite V-image, basing on which a volume model of the defect from different measurement points is created. As per the change of the volume image over time the container wall degradation is determined.

EFFECT: technical result is creation of a portable method of measuring the degree of damage of metal containers with the inspection results quality exceeding refinement achieved by radiographic inspection.

1 cl, 2 tbl, 9 dwg

Description

The invention relates to the field of measuring technology, to methods of research or analysis of materials using acoustic waves and can be used to determine the damage to metals of the walls of containers containing spent nuclear fuel (SNF). In addition, the measurement of acoustic waves propagating in structural products is of particular importance for the technology of newly created materials.

Common defects in containers containing spent nuclear fuel are pores, cavities, and cold junctions arising from electron beam welding. The pore size is usually less than 3 mm. The main reasons for their appearance are poor cleaning and oxidation of the surface of the materials being welded. In some cases, defects of this kind can only be detected by destructive methods. Of particular importance is hydrogen, which dissolves in the metal being melted during welding. It enters the metal from air containing water vapor, from the moisture of the electrode coating; from rust located on the surface of the metal of the product and electrodes. At high temperatures, moisture turns into steam and dissociates with heat absorption. Hydrogen is also found in electrode coatings and in the metal itself. In small amounts, hydrogen is soluble in the metal even at room temperature, however, with increasing temperature, its solubility increases and when the metal passes from solid to liquid, it increases from 0.0007% (8 cm ³ per 100 g of metal) to 0.0025% (28 cm ³ per 100 g). The amount of hydrogen in the weld metal and the heat affected zone depends on the quality of the welding materials and the welding method. According to the ISO 2560 standard (ISO 2560: 2002, Covered electrodes forma nu al arc welding of mild steel and low alloy steel - Code of symbols for identification) on the hydrogen content in the deposited metal, the electrodes used give a hydrogen content in the deposited metal of 5 cm ³ / 100 g to 15 ^cm3 / 100g in a large concentration of hydrogen in the welds wall steel becomes brittle, which leads to loss of stability of the containers and their destruction [V. Poles. Disasters of large diameter pipelines. The role of hydrogen fields. Strength problems. 1995. - No. 1. - S. 137-146].

The following methods are known for non-destructive analysis of materials using acoustic waves propagating in metals. Non-destructive testing of the physical and mechanical properties of materials and products is carried out to determine the attenuation coefficient from the ratio of the amplitudes of the signals resulting from the addition of oscillations of the leading and trailing edges of the echo pulses with multiple reflected pulses [Patent RU 2047171, publ. 10/27/1995].

Non-destructive testing of the degree of damage to metals of operated elements of thermal power equipment is carried out by measuring the delay of a surface wave of ultrasonic vibrations on the surface of a previously non-working product from this metal, in the zone of emergency destruction of the metal of the element, and on the metal surface in the controlled zone of the element in operation. [Patent RU 2231057, publ. 06/20/2004].

A known method of non-destructive ultrasonic testing of welded joints of railway rails [patent RU 2309402, publ. October 27, 2007], which consists in the fact that an ultrasonic measuring unit containing several measuring elements is mounted on the rail surface. When sounding, the amplitudes and temporary position of the reflected signals are measured, the spatial position of the defect is calculated, the results of all soundings are combined and displayed, according to which the quality of the welded joint is evaluated.

A known method of monitoring an ultrasound tomograph, including N ultrasonic emitters and receivers, a multiplexer emitting and receiving matrices on N channels with the connection of one of the emitters to a digital-to-analog converter microcontroller. The microcontroller is connected to the information processing and visualization unit, which has the ability to restore a three-dimensional image of a controlled defect [RU patent for utility model No. 144100, publ. 08/10/2014]. Assessment of the depth of defects using ultrasound is carried out on the basis of amplitude measurements of the signal and by estimating the wave propagation time [RU 2532606, publ. 11/10/2014].

There is a method of visualizing ultrasonic flaw detection of a three-dimensional product, which consists in the fact that the ultrasonic transducers (SPD) of the antenna array are located at a distance of more than half the length of the ultrasound wave, produce cyclic irradiation of the object and the simultaneous reception of echo signals in the local areas of the control object. The signals from each local area are digitized and used for image reconstruction and visualization [RU 2532597, publ. 11/10/2014]. The disadvantage of this method is the loss of image accuracy due to the division of the zone into local areas. As a result of the conversion of signals from each of them into an aggregate signal, the quality of information about defects is lost.

The closest analogue, selected as a prototype, is a method of ultrasonic testing [patent US 8839673, publ. 09/23/2014], where a phased array is used, which emits pulses separately or complete with a variable pulse repetition rate (PRF). Defects in an object are identified by analyzing the reflected echo. The size of the defect and its location in the controlled object is correlated with the equivalent reflector size (ERS) using the Distance Gain-Size (DGS) method. The time division of ultrasonic pulses emitted by the radiation source (transducer) over the entire depth (distance) of the pulse following is used. Those. the subsequent impulse starts after the previous impulse has passed the entire distance to the defect or the full size of the part wall. A multichannel array is used, with which the front of the acoustic waves is formed, then the defect is reconstructed and visualized.

The disadvantage of this method is that this solution (like all others) cannot be applied for ultrasound tomography of spent nuclear fuel canisters due to the specificity of the control conditions and types of defects, as well as the lack of opportunities for realizing three-dimensional visualization of defects in real time. The specificity is that during storage, hydrogenation of the wall occurs. As a result, the speed of passage of the ultrasonic signal changes. Accordingly, it is necessary to change the repetition rate of ultrasound pulses. In turn, this leads to a distortion of the generated signal matrix, which serves as a data bank for three-dimensional visualization of objects. All of these shortcomings can be eliminated by measuring the velocity of propagation of the ultrasonic ultrasound, the magnitude of which change the location of the emitters and receivers in the array, and select the frequency of the emitters and receivers in the desired frequency range.

Theoretically, the problem of using a phased array is described in many works. The grating is a pulsed multi-element emitter of elementary ultrasonic waves. The first element of the array is turned on, which sends a signal at a certain speed in the direction of the diagnostic object, the remaining elements of the array receive reflected signals. These signals are stored in the database. For example, during the measurement process emits the i-th element of the lattice. Lattice elements 1 through N receive signals reflected from the defect. From these signals, the matrix Aij is formed. (Fig. 1). After all N elements are connected in series and reflected signals are received, the matrix is completely filled. It contains temporary signals of all emitter-receiver combinations at a given time for a given size and defect state. If the size and condition of the defect are not comparable with the distance over which the emitter moves, then the resulting image of the defect is eroded. The summed signals on the resulting artificial A-scan correspond to the travel time of the sound wave from the sensor to a point in the volume of the material, i.e. equivalent to times obtained using traditional emitters. This method is called DFA (lattice with digital focusing) - reconstruction of an object in the form of a sector scan. With an increase in the number of sensors of the multi-element grating and the speed of their movement on the reconstructed sector-scan, the defect in the material becomes more clearly visible. The travel time of the sound wave (at a known propagation velocity of the ultrasound) of each prism element for each volume point is calculated and entered in the corresponding table. The physically feasible focusing area and the resolving power of the phased array is limited by the thickness of the parts, and accuracy is achieved: 1) the speed of processing the results of measuring the propagation of ultrasonic scanning; 2) the speed of imaging. The size of the area for measuring defects is determined by the frequency of obtaining information (i.e., depends on the speed of propagation of the ultrasound) and the speed of image processing on a computer and is equal to 1 kilohertz, which corresponds to a speed of about a meter per second, if the measurements are automated by recording and recording. The described reconstruction of the image consists in the fact that in such an algorithm separate time signals are added, which quickly decay with increasing wall thickness of the controlled object. Thus, the focal space is insufficient to clearly detect the object. At the same time, the problem of fixing the defect change over time is not solved (for example, during the hydrogenation of the detection area). Therefore, it is necessary to improve the accuracy of measuring the size of the defect and its position in the material, the quality of visualization of a three-dimensional image, the resolution of the image of the defect of the metal of the container.

The task is to create a method for determining the degree of damage to metals of containers with spent nuclear fuel.

The technical result of the invention is the creation of a portable method for measuring the degree of damage to metal containers, with the quality of the inspection results exceeding the detail achieved with x-ray inspection.

The specified technical result is achieved by the fact that, as in the prototype, the method of non-destructive testing of the degree of damage to the metals of the containers includes the placement of phased array antenna sensors at the test object, moving the sensors along the selected direction, measuring the velocity of ultrasonic waves (USW) in the metal, converting to digital codes of received electrical signals, their storage, processing of digital codes, image reconstruction. Unlike the prototype, the ultrasonic wave lengths are preliminarily calculated based on the measured speeds and frequency of the sensor taking into account the conversion of ultrasonic waves when they are reflected and refracted at the media interfaces, divide each of the obtained ultrasonic wave lengths into two, compare these X values with a unit pixel size equal to 1 mm, changing the frequency of the sensor’s radiation, choose the value of X that is most suitable for the pixel size, the piezoelectric elements of the sensor are set in the lattice at a distance of not more than the found value of X, then ayut sensor along a selected direction with a step X, and transversely with 2X pitch signals from the sensor through each step is recorded in a table of run time of the ultrasonic wave from each probe to each point of the volume, and used for image reconstruction and visualization.

In FIG. 1 shows the appearance of ultrasonic arrays (sensors). Nominal parameters of ultrasonic sensors are given in table 1.

In FIG. 2 shows the appearance of the location of the phased array on the container wall, 1 — the container wall, 2 — the seam, 3 — the phased array sensor, 4 — the sensor holder connected to the manipulator, 5 — the data transmission cable to the data collection unit.

In FIG. 3 shows a diagram of measuring the velocity of propagation of ultrasonic ultrasonic waves in different directions relative to the wall of the container, 1 — the wall of the container, 3 — the phased array sensor, 6 — the directions of propagation of the ultrasonic vibrations, 7 — the scan field of the wave reflected on the computer screen.

In FIG. Figure 4 shows a general block diagram of the transmission of signals from a phased array to a programming unit and a data acquisition matrix

In FIG. 5 shows the blocks of the data collection circuit.

In FIG. 6 shows a diagram of the movement of sensors along the container wall, 1 - wall, 2 - seam, 3 - multi-element phased array sensor, 8 - the distance between the measurement positions (step), 9 - the distance between the measurement lines.

In FIG. 7 is a view of a sector scan showing on the computer screen defects in the walls of the container, 1 — the wall, 10 — defects in the walls of the container.

In FIG. Figure 8 shows artificial defects in the form of cutouts in a 32 mm thick container wall sample. The numbers indicate the size of the slots in the container wall.

In FIG. Figure 9 shows the reconstructed images of defects artificially prepared in the wall.

Table 1. Parameters of ultrasonic sensors.

Table 2. Technical parameters of the electronics unit.

The phased array sensors (Fig. 1) are located on the surface of the container (Fig. 2). Phased array sensors (Fig. 3) send ultrasonic signals in various directions. The directions of signal propagation are sequentially selected by the computer program for controlling the sensors. The phased array sensors measure the speed of sound propagation in the container wall in various directions relative to the position of the container wall (Fig. 3). For this purpose, the transit time of the ultrasonic wave by measuring the distance from the wall or defect and vice versa is measured. From the measured speeds and frequency of the phased array sensor, ultrasound wavelengths are calculated in different directions 6, etc. (Fig 3). Divide each of the obtained wavelengths into two. This value is denoted as X. Then, these values of X are compared with the size of a single pixel of the digital field of the computer program equal to 1 mm, and the value of X is selected that corresponds to a maximum value of 1 mm equal to the size of the pixel. The piezoelectric elements of the sensor are placed in the lattice at a distance equal to the found value of X. Install the phased array sensors along the selected direction relative to the container wall and move the sensor along the selected direction with step X and across with step 2X. The signals from the sensor through each step are recorded in a table of travel times of the ultrasonic wave from each sensor of the phased array to each point in the volume (Fig. 4). Based on these signals, a composite B-image is formed, on the basis of which a volumetric image (visualize) of the defect is created in magnitude and its position in the container wall.

Blocks of a computer program (Fig. 5) allows you to reconstruct B-scans and step-by-step fill the three-dimensional matrix (Fig. 4). The matrix data is then used to obtain a three-dimensional image of the object. Each phased array sensor is simultaneously an emitter and receiver of an acoustic signal. Switching sensors on and off is carried out automatically using a control program and a computer (Fig. 5). The lattice sensors are moved along the surface of the SNF container using a three-axis manipulator. The manipulator provides three-dimensional movement of the phased array sensors along the X, Y, and Z axes. Information about the specific position of the object during monitoring is recorded automatically by the coordinate determination unit and transmitted to the electronics unit for further processing and reconstruction of images.

In anisotropic inhomogeneous material (including hydrogenated), where acoustic waves propagate in a non-linear fashion, the form of the wave front, as well as the wave propagation velocity, depends on the structure of the material. In the case of welds, this means that the distance between the position of the sensor and the seam affects the values of the signals in the generated data table that determine the size and position of the defect. For the analysis of austenitic compounds in real time, to improve the quality of control, measurements are made of the propagation of sound in the material for all intended measurement positions. The obtained auxiliary tables are stored along with the coordinate data of the sensor for reconstruction of two-dimensional and three-dimensional images in real time. Ultrasonic signals from defects, measured by phased array sensors, are transmitted to a software unit for automatic data processing (Figs. 4, 5). Ultrasound signals are recorded from each sensor, the position of which relative to the product is recorded using the coordinate determination unit. All ultrasound data is stored together with the coordinates of the location of the sensor. This allows you to create two-dimensional and three-dimensional images. Those. the sensors of the antenna array measure the speed of sound propagation in the seam area of the container with SNF or its wall (Fig. 6). Ultrasound data is recorded in accordance with the DFA principle. The scanning step is selected based on the properties of the material of the container wall. The scan step is equal to X = 1 mm (the direction perpendicular to the seam is the scan direction), and the distance between the tracks is 2 mm (parallel to the seam is the index direction perpendicular to the scan direction) (Fig. 6). The size of 1 mm corresponds to the size of a pixel for reconstruction using a sector-scan computer program. The position of each sensor (and, accordingly, the travel time of the signal) is recorded in an auxiliary table. A sector scan is shown in FIG. 3 and indicated by the number 7. An image of a sector scan is formed into a composite B-image. Using a B-image, a three-dimensional defect model is created from various measurement points. Ultrasound signals are recorded from each phased array sensor, taking into account the correction for the signal propagation velocity, which varies depending on the properties of the material of the container wall (for example, hydrogen saturation of the metal). Those. The ultrasound signal received from the sensor is converted by a focusing method with a synthesized aperture lattice with digital focus (DFA - lattice with digital focusing). Such a transformation is necessary to build a tomographic image in real time. At the same time, the lattice, using a computer program, provides reception (formation) of echo signals (reflected from signal defects) in the control object, taking into account the dispersion of the acoustic properties of the material of the object. The program provides and takes into account the relationship between the sets of echo signals reflected from the boundaries of parts, and defects of various shapes, sizes and locations. All acoustic signals are automatically recorded over the entire volume of the monitored object. Based on the measured acoustic signals in total, the volumetric configuration of the object of analysis is restored (the wall of the container with SNF) containing defective structures.

The processing system of the data (Fig. 5) received from the sensors includes a computational module, a manipulator control unit (a device integrated into the measurement and data acquisition system), a coordinate determination unit that ensures the correct operation of the electronics and data acquisition, and an ultrasonic electronics unit. The ultrasonic electronics unit is a stand-alone 64-channel ultrasound device with the function of working in the phased array method and the digital focus array method. The technical characteristics of the ultrasonic electronics unit are given in table 2. The computer has the following configuration: 1000 W power supply; IntelXeon processor (R) 2.5 GHz, Quadcore; 16 GB RAM (on Windows XP64 Bit); NVidia GeForce 8800; DVD drive; OS Windows XP Professional 64-Bit.

The method of non-destructive testing of the degree of damage to the metals of containers is carried out according to the following algorithm: a phased array sensor is placed on the surface of the container wall (for example, in the area of the weld, as the most vulnerable). The phased array sensor measures the speed of sound propagation in the container wall in all directions relative to the axis of the container, taking into account the boundary of the change in the properties of the medium. The ultrasonic wavelength is calculated from the measured ultrasound speed and the sensor frequency, and half the wavelength X is compared with the pixel value of the computer image-building program. If X does not match the pixel size, pick up the frequency of the sensor radiation so that X is equal to the size of the pixel. The phased array sensors are mounted at distance X. The sensors are moved at a selected frequency along and across the axis of the container, as shown in FIG. 6. Moving the sensor automatically using a computer program is carried out by the manipulator. Ultrasound signals are recorded from each sensor, the position of which relative to the product is recorded using the coordinate determination unit. All ultrasonic signals are stored in the matrix (Fig. 4) together with the coordinates of the location of the sensor to create a two-dimensional and three-dimensional image of the defect. Ultrasound data is recorded in accordance with the DFA principle with a scanning step along the length of the sample equal to the pixel size and doubled the distance between the tracks (direction perpendicular to the scanning direction) (Fig. 6). The computer program generates the received signals into sector images. Sector images are transformed into a composite B-image. A sector scan is shown in FIG. 7. An image of a sector scan is formed into a composite B-image. On the basis of the B-image, a volumetric image (visualize) of the defect is created in magnitude and in the place of its position in the container wall (Fig. 7).

Thus, to implement the method of non-destructive testing of the degree of damage to the metals of the containers, phased array sensors 3 are placed on the wall surface of the container 1 (for example, in the region of the weld 2). Measure the phased array sensor 3 the speed of sound propagation in the container wall in all directions 6 (Fig. 3). Using the measured speed V and the frequency of the sensor ν, the ultrasound wavelength λ is calculated using the formula λ = V / ν. Divide the obtained value by two and find the value X = λ / 2. In the program for constructing an image on a computer, a unit pixel value of 1.02 ± 0.02 mm is fixed. The found value of X is compared with a unit pixel size of 1 mm. If X does not correspond to a value of 1 mm, pick up the radiation frequency of the sensor so that X with an accuracy of 0.02 mm is equal to a pixel size of 1 mm. Install sensors 3 phased array at a distance of 1 mm. The sensors 3 are moved with the selected frequency along and across the axis of the container, as shown in Fig. 6. The sensor with the holder 4 moves automatically using a computer program using the manipulator (Fig. 2). Ultrasound signals are recorded from each sensor to each defect (D1-D2 ... DN, Fig. 4). The position of the sensors relative to the product is recorded using the coordinate determination unit. All ultrasonic signals are stored in the matrix A _ij (Fig. 4) together with the coordinates of the location of the sensor to create a two-dimensional and three-dimensional image of the defect. Ultrasonic data is recorded in accordance with the DFA principle with a scan step of 8 along the length of the sample 1 mm and a distance of 9 between the tracks 2 mm (direction perpendicular to the direction of scanning) (Fig. 6). The computer program generates the received signals into sector images. Sector images are transformed into a composite B-image. A sector scan is shown in FIG. 7. An image of a sector scan is formed into a composite B-image. On the basis of the B-image, a volumetric image (visualize) of the defect is created in terms of the size and place of its position in the container wall (Fig. 8).

To implement the method in a container metal (steel grade 12X18H10T, 32 mm thick), artificial defects were prepared in the form of inclined cutouts with three different depths located along the entire width of the sample with inclination angles of 50 °, 40 °, 30 °, 20 °, and 10 ° with dimensions of cuts along the length of 10 mm, 4 mm, 2 mm. Created cutouts model defects (cracks) of various directions (Fig. 8, cutouts 10, 4, 2). Steel samples contain 3 cutouts (10, 4, 2 mm deep, with tilt angles of 0, 10, 20, 30, 40, and 50 degrees) (Fig. 8). The depth of the cutouts and their angular position were reconstructed into B-scans (Fig. 9).

A specific example of a method for non-destructive testing of the degree of damage to metals of spent nuclear fuel containers. An Olympus 5L16-A3 multi-element sensor consisting of 16 piezoelectric sensors (Fig. 3, 6) was placed on the wall 1 of the container (Fig. 2) made of steel grade 12X18H10T with artificial cutouts (Fig. 7). Measured by the phased array sensor 3, the speed of sound propagation in the container wall in all directions (Fig. 3). The measurement directions are shown in FIG. 3 in figures 6. The speed was measured by the value of the propagation time of the ultrasonic ultrasound from the sensor and back in all directions. For this, the ultrasound travel time from each sensor to each defect and container wall was recorded. Travel time was recorded in an auxiliary table (matrix). The speed of sound propagation was calculated for all positions of the sensors (Fig. 4). Using the measured velocity V and the sensor frequency ν, the lengths λ of the ultrasonic waves propagating in the indicated directions were calculated using the formula λ = V / ν. The frequency of the sensor is 3 MHz. The speed of sound is 5900 m / s. The wavelength is 1.966 mm. The obtained value was divided by two and the value X = λ / 2 was found. X = 0.986 mm. The obtained value was compared with the pixel size to restore the volumetric image and the position of the defect. In the program for constructing an image on a computer, a unit pixel value of 1.02 ± 0.02 mm is fixed. The found value of X was compared with a unit pixel size of 1 mm. If X does not correspond to a value of 1 mm, the radiation frequency of the sensor was selected so that X with an accuracy of 0.02 mm was equal to a pixel size of 1 mm. Sensors 3 of the phased array 3 were also installed at a distance of 1 mm. The sensors 3 were moved with a selected frequency along and across the axis of the container, as shown in FIG. 6. The sensor was automatically moved using a computer program by the manipulator 4 (Fig. 2). Ultrasound signals were recorded from each sensor, the position of which relative to the product is recorded using the coordinate determination unit. All ultrasonic signals were stored in the matrix (Fig. 4) together with the coordinates of the location of the sensor to create a two-dimensional and three-dimensional image of the defect. Ultrasound data was recorded in accordance with the DFA principle with a scanning step along the length of the sample of 1 mm and a distance between tracks of 2 mm (direction perpendicular to the direction of scanning) (Fig. 6). The computer program generates the received signals into sector images. Sector images are transformed into a composite B-image. A sector scan is shown in FIG. 7. An image of a sector scan is formed into a composite B-image. On the basis of the B-image, a volumetric image (visualize) of the defect is created by the size and place of its position in the wall of the container. The B-scan of sample 1 (Fig. 8). The configuration of the computer program is presented in table. 2.

As a rule, the best result is obtained using phased arrays from Sonaxis and Olympus NDT. For prismatic radiation, special prisms are used for both longitudinal and transverse waves with refractive angles of 45 and 60 degrees.

The method of non-destructive testing of the degree of damage to metal of containers based on the proposed method (phase grating with digital focus) is highly informative, allows tomographic reconstruction of defects in a controlled object in real time, provides high reliability, reliability, reproducibility and high performance of ultrasonic non-destructive testing .

Claims (1)

A method of non-destructive testing of the degree of damage to container metals, including the placement of sensors of a phased antenna array at a test object, moving sensors along a selected direction, measuring the propagation speed of ultrasonic waves (ultrasonic waves) in a metal, converting received electrical signals to digital codes, storing them, processing digital codes, image reconstruction, characterized in that the ultrasound lengths are preliminarily calculated based on the measured speeds and sensor frequency taking into account the conversion ultrasonic waves during their reflection and refraction at the interface, divide each of the obtained values of the ultrasound length by two, compare these values of X with a unit pixel size of 1 mm, changing the frequency of the sensor’s radiation, choose the value of X that most closely matches the size of the pixel , the piezoelectric elements of the sensor are installed in the grating at a distance of no more than the found value of X, then the sensor is moved along the selected direction with step X, and across with step 2X, the signals from the sensor through each step are recorded in the table zu run time of the ultrasonic wave from each probe to each point of the volume, and used for image reconstruction and visualization.

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