DEVICE AND METHOD FOR DETERMINING THE EXTENSION OF DEFECTS USING V-THROUGH SOUNDATION

Description

[0001] The invention relates to a method for determining the extent of defects, in particular crack depths, in a test specimen, preferably a pipeline wall. In the method, sound waves in the ultrasonic range are excited by at least one transmitting transducer, which propagate in the form of a sound beam, wherein the acoustic axis of the sound beam preferably forms an angle with the normal of a surface facing the transmitting transducer. The sound waves couple obliquely into the test specimen and are reflected, in particular in a V-shape, at a preferably outer boundary surface of the test specimen. The boundary surface can form the outer surface of the test specimen. In the case of test specimens constructed from several layers, in particular of different materials, the corresponding boundary surface can, however, also be arranged within the test specimen.This is the case, for example, with a pipeline with a metallic core encased in a concrete casing. The sound waves reflected at the interface of the test specimen are recorded by at least one receiving transducer spaced apart from the transmitting transducer. From a reduction in the amplitude of the sound waves recorded by the receiving transducer, an evaluation unit is used to determine the extent of a defect located within a sound path. The evaluation unit can be partially present in a device described below in the form of conventional electrical and / or electronic means used for the evaluation of ultrasonic transducers; these means can also be located at least partially remote from the device.

[0002] Furthermore, the invention comprises an arrangement for carrying out the method according to the invention, comprising a device for detecting signals based on defects in a test body and an evaluation unit for evaluating the signals based on defects in a test body recorded by the device according to the method according to the invention.

[0003] Such a method is known as V- or W-transmission from non-destructive materials testing using ultrasonic technology and is used, for example, to inspect weld seams. This method uses transmitting and receiving transducers in the form of probes that are placed directly on the test specimen.

[0004] US 2008 / 0148856 A1 discloses a measuring device with two ultrasonic transducers for examining a hollow structure, as well as a method for determining defects. One ultrasonic transducer emits a sound wave, and the system detects a defective area if the other ultrasonic transducer does not receive the wave or only receives it with a reduced amplitude. Furthermore, the use of a liquid or gel-like coupling medium is shown to more effectively couple the ultrasonic waves into and out of the structure under investigation.

[0005] US 2,893,239 discloses a measuring device with three ultrasonic transducers arranged in a liquid tank for detecting defects in metallic objects, particularly rails. The signals received by the ultrasonic transducers are displayed on a cathode ray tube, allowing an operator to determine the defect type, as well as the approximate orientation and location of a defect.

[0006] US Pat. No. 5,201,225 discloses a device and method for determining the thickness of coated panels using a dual-type ultrasonic probe comprising an ultrasonic transmitter and an ultrasonic receiver. The thickness of a coated panel is determined based on the propagation times or propagation time differences of ultrasonic signals.

[0007] DE 10 2012 110 917 A1 discloses an ultrasonic testing device for the non-destructive testing of a workpiece with an internal bore. The device comprises at least one test head in which at least one ultrasonic transducer is arranged. Information on a specific measurement method is not disclosed.

[0008] DE 102 02 432 A1 describes a method and a device for inspecting pipelines using ultrasound. The device comprises measuring sensors composed of a plurality of sensor elements arranged in series. The evaluation of the signals recorded by the measuring sensors is based on their transit times or transit time differences.

[0009] US 2,799,157 discloses a device with a transmitting transducer and a receiving transducer that can be moved along the surface of a test body. The evaluation or determination of any defects in the test body is carried out based on the intensity of the signals picked up by the receiving transducer.

[0010] JP 60 073 4560 discloses a method for determining defects using ultrasound. A transmitting transducer emits ultrasonic waves, which are picked up by a receiving transducer. A pattern resulting from the measured values is compared with previously determined patterns to determine any defect present and, if applicable, the defect type.

[0011] The publication "An Ultrasonic Angle Beam Method for in situ Sizing of Fastener Hole Cracks" by J.E. Michaels, T.E. Michaels, and Bao Mi discloses a method for determining fatigue cracks around fastener holes in aluminum structural components. Ultrasonic waves are transmitted to the fastener hole through a transmitting transducer, and the reduction in energy of the signal detected by a receiving transducer is determined. The measurements are performed under load and in a load-free state. The area of a defect can be determined from the ratio of the energies of the signals detected by the receiving transducer.

[0012] The object of the invention is to provide a method that enables the reliable determination of crack depths of any cracks in a test specimen over a larger range of crack depths.

[0013] In the method according to claim 1, the transmitting transducers and the receiving transducers are guided past the test specimen at an at least substantially constant distance from the test specimen. The sound waves couple into the test specimen via a liquid medium, a coupling medium, with a delay path. Because the transmitting transducers and the receiving transducers are arranged at a distance from the test specimen, they can be guided along the test specimen without contact. The test specimen can be tested while the transmitting transducer and the receiving transducer move past the test specimen. Due to the contact-free embodiment, the method can be carried out with a high degree of reliability even with very large test specimens, such as the walls of a pipeline. The receiving transducer and the transmitting transducer are not exposed to mechanical stress and the associated wear, or are exposed to only a greatly reduced extent.This means that the process can be carried out for long periods or for large test specimens with little or no interruption for maintenance and repairs.

[0014] According to the invention, a further receiving transducer records the sound waves reflected from a defect. This receiving transducer is preferably arranged adjacent to the transmitting transducer. The further receiving transducer records the portions of the sound wave reflected back from the defect. This echo can also be used to determine the crack depth. While the signal recorded by the receiving transducer from a V-shaped ultrasound transmission through the test specimen is particularly well suited to detecting crack depths from approximately 3 mm, preferably up to 10 mm, the evaluation of the echo recorded by the further receiving transducer is particularly well suited to detecting crack depths down to approximately 4 mm. By combining both methods and jointly evaluating them in the evaluation unit, crack depths of defects can be determined over a very wide depth range compared to the prior art.

[0015] The decrease in sensitivity of the V-wave transmission method at small crack depths is due to the fact that at small crack depths, there is hardly any attenuation of the amplitude of the sound waves received by the receiving transducer through a crack. The signal is thus saturated. A small change in crack depth causes only a marginal change in the signal.

[0016] With the echo method, based on the sound waves reflected from a defect toward the transmitting transducer, an increase in crack depth hardly results in an increase in the amplitude of the reflected sounds, the echo, for very large cracks. The echo signal picked up by the receiving transducer is saturated at large crack depths because the sound waves are already almost completely reflected.

[0017] Simulation tests have also surprisingly shown that evaluating the echo signal offers further advantages for inclined cracks or grooves. In previous methods, which measure an angle-beam echo, its amplitude depends heavily on the inclination of the defect. For example, the amplitude of a signal originating from a defect running perpendicular to the surface of the test object (inclination angle 0°) can be many times greater than the amplitude of a signal originating from a defect inclined by, for example, 10°. In contrast, the amplitude of the echo signal recorded using this method remains virtually unchanged at inclination angles of up to ± 10°, enabling reliable detection and identification even of inclined defects.

[0018] According to the invention, the crack depths are determined from the difference in the amplitudes recorded or recorded by the receiving transducer and the additional receiving transducer. By calculating the difference in the characteristic curves for the relationship between crack depth and amplitude of the respectively recorded sound waves, a relatively uniform common characteristic curve is generated, via which the crack depth can be determined from the correspondingly measured amplitudes.

[0019] The correlation between crack depth and amplitude of the sound waves picked up by the receiving transducer or between crack depth and amplitude of the sound waves picked up by the further receiving transducer and reflected at the defect can preferably be determined in the case of V-shaped transmission and / or in the case of the echo method by measurements on a defined reference body with known defect extent, in particular known defect depths.

[0020] Furthermore, when evaluating the difference in amplitudes, changes in amplitude caused by defects, which affect both the receiving transducer and the other receiving transducer equally, are excluded from the evaluation. When using the corresponding methods to inspect pipeline walls, for example, one should consider a reduction in amplitudes caused by deposits on the surface of the test specimen facing the transducers. By combining the signals, a reliable crack depth determination can be achieved regardless of such deposits.

[0021] The object is further achieved by an inventive arrangement according to claim 10.

[0022] Advantageous embodiments of the invention can be found in the subclaims which refer back to the independent claims and in the following description.

[0023] In a preferred embodiment, the transmitting transducer, in the form of a transmitting and receiving transducer, is used as an additional receiving transducer. This allows the method to be implemented with less material expenditure, since the combination of the transmitting transducer and the additional receiving transducer eliminates the need for a separate additional receiving transducer.

[0024] The use of a transmitting and receiving transducer in conjunction with pulsed excitation of sound waves is particularly advantageous. The transmitting transducer excites a short sound pulse. With a suitable test specimen thickness, the transmitting phase is completed when the echo—that is, the portion of the sound pulse reflected from a defect toward the transmitting transducer—reaches the transducer. The transmitting transducer can thus function as an additional receiving transducer without interference with the excitation of the transmitting transducer.

[0025] The body serving as the test specimen for the method according to the invention preferably has parallel, flat surfaces, disregarding any defects or welds, which are spaced apart by a small distance compared to the dimensions of the test specimen. The transmitting transducer and the receiving transducer can be designed as piezoelectric transducers. In this case, the piezoelectric elements of the transducer are deformed when a voltage is applied or generate a voltage when they are deformed. By exciting the piezoelectric element in a corresponding transmitting transducer with a sufficiently high frequency, the transmitting transducer excites sound waves in the medium surrounding the transmitting transducer. The transmitting transducer is connected to the test specimen via a liquid medium, so that the technology can be used particularly in pipelines carrying liquids during operation.The ultrasonic waves excited in the medium hit the surface of the test specimen at an angle to the surface normal and couple into the test specimen in such a way that the sound waves travel obliquely through the test specimen. The sound waves are reflected at a preferably outer boundary surface. The sound waves then pass through the thickness of the test specimen and exit again at the first boundary surface at a distance from the entry point. The exit location depends on the angle at which the sound waves couple into the test specimen and on the thickness of the test specimen. The sound waves emerging from the test specimen in turn couple into the medium and are picked up by a receiving transducer that is aligned with at least part of the exit point. Here the sound waves are converted back into an electrical signal.The receiving transducer is thus acoustically coupled to the test object via the coupling medium for the recording of sound waves. The distance between the transmitting and receiving transducers from the test object is preferably between 0.5 cm and 5 cm.

[0026] While the transmitting and receiving transducers are moved contactlessly past the test specimen at a constant distance from each other, defects result in the sound waves picked up by the receiving transducer exhibiting a reduced amplitude. From this, the extent of the defect is determined in an evaluation unit.

[0027] It is assumed that the reduction in the amplitude of the sound waves picked up by the receiving transducer is due to at least some of the sound waves being reflected from a defect located within the sound wave path through the test specimen from the entry point to the exit point in a direction different from the otherwise existing exit point. As the transmitting and receiving transducers pass the test specimen, the spatial extent of the defect can be determined along the direction of movement of the transmitting and receiving transducers.

[0028] Particularly preferably, the depth of the defect is determined from the reduction in the amplitude of the sound waves picked up by the receiving transducer. In addition to the longitudinal extent of defects within the test specimen, the depth of cracks is a particularly important parameter that must be recorded using non-destructive material testing. Such cracks represent a weakening of the material of the test specimen. Very deep cracks cause severe local weakening of the test specimen. If the test specimen is used as intended, for example, if a pipeline wall is pressurized to transport a fluid, there is a risk of material failure at the defects. If the crack depth is known, the load on the test specimen can be adjusted accordingly until repairs can be carried out, for example by reducing the pressure within a pipeline.Until the repair is carried out, failure of the test specimen and possible consequential damage, such as the leakage of a fluid from a pipeline, can be avoided.

[0029] The reduction in the amplitude of the sound waves picked up by the receiving transducer correlates with the crack depth. A deeper crack results in a larger portion of the sound wave being reflected by the crack and thus no longer reaching the receiving transducer via the intended sound path. The correlation between the reduction in amplitude and crack depth is usually determined in advance using a reference specimen similar to the test specimen, in which correspondingly defined defects of known extent, especially of known depth, have been machined. This correlation can be represented as a characteristic curve.

[0030] Surprisingly, it has been shown that cracks with a depth of up to 10 mm can be reliably detected, especially in pipelines.

[0031] Particularly preferably, the transmitting transducer generates sound waves in the form of sound pulses. This improves the signal-to-noise ratio. The extent of defects can be determined more reliably and accurately using this method.

[0032] Particularly preferably, the transmitting transducer excites sound pulses in the form of a rectangular pulse or a needle pulse, so that easily detectable pulses can be processed in the evaluation.

[0033] Preferably, the transmitting transducer excites sound waves at specific time intervals and / or at specific spatial positions, i.e. discretely, while the transmitting and receiving transducers are moved past the test specimen. This creates a measuring grid above the test specimen, with measurements being taken at specific points on the measuring grid. To test the wall of a pipeline, for example, measurements could be taken at intervals of one millimeter each in the longitudinal and circumferential directions. The measuring grid can be adapted depending on the required accuracy and available processing capacity or the planned feed rate. The time planned for testing the test specimen can also be taken into account. For example, a measurement in the feed direction can be taken only every 2 or 3 mm.

[0034] Preferably, the transmitter transducer excites sound waves in a frequency range between1 MHz und 10 MHz, besonders bevorzugt mit ca. 4 MHz, d. h. 4 MHz ± 0,2 MHz.

[0035] In In a preferred embodiment, the sound wave excited by the transmitting transducer forms a parallel wavefront. This ensures that the receiving transducer generates a clear and strong signal when picking up the sound wave reflected in a V-shape at the preferably outer boundary surface of the test specimen. Particularly preferably, the sound waves reflected at the boundary surface are picked up by a receiving transducer whose acoustic axis coincides with the acoustic axis of the transmitting transducer. The transmitting and receiving transducers are thus inclined to one another in a V-shape, corresponding to the direction of propagation of the sound waves. The acoustic axis of the transmitting transducer corresponds to the acoustic axis of the outgoing sound beam. The sound waves arriving at the receiving transducer are detected along its acoustic axis.

[0036] In In an alternative embodiment, the sound wave excited by the transmitting transducer forms a divergent wavefront. The sound wave, which is reflected in a V-shape at the preferably outer boundary surface, is partially picked up by receiving transducers arranged at a distance from one another in the direction of the main propagation of the sound wave, which in turn are each at different distances from the transmitting transducer. A defect located in the sound path does not necessarily result in an attenuation of the amplitude in a receiving transducer, but rather causes a corresponding amplitude to no longer be detectable at a receiving transducer or a group of receiving transducers. Based on the information as to which receiving transducers record a corresponding drop in amplitude or a corresponding lack of amplitude, the crack depth can be determined.

[0037] In In a preferred embodiment, the thickness of the test specimen is determined. The thickness can be determined by evaluating the time-of-flight information relating to the sound waves passing through the test specimen in a V-shape. Alternatively, the thickness of the test specimen can be determined using a dedicated ultrasonic depth sensor. To evaluate the recorded signals, different characteristic curves created using reference specimens of different thicknesses can be used for different test specimen thicknesses. This allows a reliable determination of the extent of defects, in particular crack depths, even in the case of local deviations in the thickness of the test specimen from the assumed thickness for which a device for performing measurements is designed.

[0038] The invention also relates to an arrangement for carrying out the method according to the invention, comprising a device for detecting signals based on defects in a test body, in particular an inspection pig for testing a pipeline, and an evaluation unit for evaluating the signals based on defects in a test body and recorded by the device according to the method according to the invention. The device has at least one transmitting transducer and at least one receiving transducer, wherein the transmitting transducer and the receiving transducer are arranged at a distance from one another and with their acoustic axes inclined towards one another in such a way that signals of a V-shaped transmission can be recorded.

[0039] Such a device for detecting defect-based signals in a test specimen is known from the prior art. It uses probes with a transmitting transducer and a receiving transducer, respectively, that are in direct contact with the test specimen or with a prismatic element in direct contact with the test specimen. A disadvantage here is potential wear on the transmitting and receiving transducers, or on the prismatic elements, as they are moved past the test specimen.

[0040] The above-mentioned disadvantages are avoided in a device of an arrangement according to the invention according to claim 10 in that the transmitting transducer and receiving transducer are arranged in a receptacle, wherein the receptacle is movable in the direction of the test body and the receptacle has a guide element that can be brought into contact with the test body, such that in an operating position, the transmitting transducer and the receiving transducer are arranged in the receptacle at a distance from the test body when the guide element is in contact with the test body. This prevents the transmitting transducer and / or receiving transducer from coming into contact with the test body and possibly being damaged in the process.On the other hand, the fact that the holder can be moved towards the test specimen into an operating position in which the guide element is in contact with the test specimen ensures that the transmitting transducer and / or receiving transducer are guided past the test specimen at a defined distance from the latter.

[0041] According to the invention, the device of the arrangement comprises several pairs of transmitting transducers and receiving transducers, which are offset from one another transversely to the feed direction and arranged one behind the other in the feed direction in a common receptacle. Due to the offset arrangement of the pairs of transmitting transducers and receiving transducers transversely to the feed direction, the device can scan a wider area of the test specimen in a single pass. This makes it possible to reduce the number of passes with which the test specimen is measured. Due to the offset arrangement, it is also possible to realize smaller offsets of the pairs of transmitting transducers and receiving transducers, where otherwise two transmitting transducers or two receiving transducers would interfere with each other due to their installation space.

[0042] Particularly preferably, the guide element is arranged in front of the transmitting transducer or the receiving transducer in the feed direction of the device during a test run. This can prevent damage to the transmitting transducer or the receiving transducer if the test specimen has an irregular surface or if deposits have accumulated on the surface of the test specimen facing the transmitting transducer or the receiving transducer. The guide element arranged in front of the transducers in the feed direction will cause the movable holder to lift off the surface of the test specimen upon contact with an irregularity protruding from the surface of the test specimen in the direction of the transmitting transducer or the receiving transducer. In this case, the transmitting transducer or the receiving transducer are also lifted off the surface along with the holder, thus protecting them from damage. This enables safe operation of the device.This is particularly advantageous when used in the form of an inspection pig, which is used over long distances within a pipeline that is not accessible or difficult to access from the outside.

[0043] In a preferred embodiment, the guide element is designed as a runner. Such a runner allows the support to slide along the surface of the test specimen and to lift off when the runner encounters an obstacle. The runner-shaped design largely prevents problems caused by jamming on a suddenly appearing obstacle on the surface of the test specimen.

[0044] Preferably, the guide element is formed by a protrusion of the receptacle that projects toward the test specimen. The guide element is thus formed integrally with the receptacle and reliably lifts the receptacle from the test specimen if the surface of the test specimen exhibits a protruding irregularity. Particularly preferably, the receptacle has a guide element arranged in front of and behind the transmitting transducer or receiving transducer. Particularly preferably, the receptacle has a circumferential guide element that encloses the transmitting transducers or receiving transducers arranged in the receptacle.A circumferential guide element can ensure that a short projection does not cause the holder to momentarily lift off the surface of the test specimen, whereby after passing the guide element the holder moves towards the test specimen and the transmitting transducer and / or receiving transducer is damaged by the projection if it is located behind the guide element or between two guide elements.

[0045] The guide element preferably has a wear pad, in particular a ceramic one. Since the guide element is in contact with the surface of the test specimen, a wear pad can prevent damage to the surface of the test specimen and improve the wear resistance of the guide element. This can improve the service life and thus the operational reliability of the device. Furthermore, friction between the test specimen and the guide element can be minimized by selecting a suitable material for the wear pad.

[0046] In In an alternative, preferred embodiment, the guide element is designed as a rotatable, cylindrical, wheel-shaped body. By using a wheel-shaped guide element, wear on the surface of the test specimen or the guide element can be minimized. The guide element does not slide along the surface of the test specimen, but rather rolls on it. Friction and the associated wear are largely minimized. This increases the reliability and operational safety of the device.

[0047] The device preferably has a return element that applies a force to the holder, moving it in the direction of the test specimen. Such a return element ensures that the holder or guide element is brought into contact with the surface of the test specimen. The return element is designed to allow for deflection of potentially protruding irregularities in the surface of the test specimen. The return element is particularly preferably designed as a spring. Alternatively, return elements, for example, as a hydraulic element or an electric motor, are also conceivable.

[0048] In a preferred embodiment, receiving transducers arranged at different distances from the transmitting transducer are assigned to a transmitting transducer. These receiving transducers are arranged at different locations on the test specimen to pick up sound waves emanating from the receiving transducer. This can, for example, increase the spatial resolution of the signals attributable to defects and improve the subsequent data analysis. Additionally or alternatively, by assigning multiple receiving transducers to a transmitting transducer, conclusions can be drawn about different sound paths of a signal in the test specimen, which can be attributed, for example, to different thicknesses of the test specimen at different points to be tested.

[0049] Particularly preferably, the acoustic axes of the transmitting transducer and receiving transducer are arranged in a common plane. This enables, in particular, the use of a divergent sound wave emitted by the transmitting transducer. The signal of the divergent sound wave is recorded at different exit points by different receiving transducers. This allows data to be recorded with improved spatial information.

[0050] In a preferred embodiment, the device is designed as an inspection pig, wherein the inspection pig has a central longitudinal axis and a plurality of receptacles with corresponding transmitting and receiving transducers are arranged circumferentially around the central longitudinal axis. This makes it possible to record signals based on defects at several locations distributed around the circumference of the test body or pipeline with a single pass of such an inspection pig through a test body in the form of a pipeline. Ideally, such an inspection pig has so many receptacles or transmitting and receiving transducers arranged that an inspection of the entire circumference of the pipeline can be carried out with sufficient spatial resolution in a single pass. This allows the number of necessary test passes to be reduced to preferably one pass.

[0051] Further advantageous embodiments can be found in the following description of the figures. They show: Fig. 1 a schematic representation of an arrangement according to the invention, Fig. 2 a characteristic curve for the correlation of measured amplitude and groove depth of a groove in a reference body for the signal of a V-transmission and for a pulse-echo signal, Fig. 3 characteristic curve of the difference of the Fig. 2 shown signals over the groove depth of a groove in a reference body, Fig. 4 a schematic representation of an alternative arrangement according to the invention for use with divergent sound waves, Fig. 5 characteristic curve for the correlation of groove depth in a reference body and position of a receiving transducer, at which the measured amplitude exceeds a predeterminable threshold value, relative to the transmitting transducer, Fig. 6 differences of amplitudes according to Fig. 2 and Fig. 3 with and without deposits on the test specimen, Fig. 7 Simulation results of the amplitudes of an angle mirror echo and a pulse echo signal when varying the inclination of a groove, Fig. 8 Device for detecting signals based on defects in a test specimen in the form of an inspection pig for carrying out the method according to the invention, Fig. 9 Arrangement of transmitting transducer and receiving transducer in a receptacle of an inspection pig according to Fig. 8 , Fig. 10Arrangement of transmitting transducer and receiving transducer with ultrasonic depth sensor according to a further embodiment of the invention.

[0052] In the following, equivalent elements of the invention are provided with a common reference number where appropriate. The features of the exemplary embodiments described below may also be the subject of the invention in other combinations of features than those shown, but at least in combination with the features of an independent main claim.

[0053] Fig. 1 shows a schematic diagram of an arrangement according to the invention for carrying out the method according to the invention with a transmitting transducer 2 and a receiving transducer 4. The transmitting transducer 2 and the receiving transducer 4 are arranged at a distance from the test specimen 10. Sound waves 5 excited by the transmitting transducer 2 propagate in a coupling medium until they couple into the test specimen 10. The transmitting transducer 2 forms an angle α with its acoustic axis 6 with a normal 3 to the surface 8 of a test specimen 10, preferably a wall or wall of a pipeline. The sound waves 5 excited by the transmitting transducer 2 couple into the test specimen 10 significantly at an angle β upon arrival at the test specimen 10 (cf. Fig. 4 ) and pass through it in a V-shape. The sound waves 5 are reflected at an outer boundary surface 11 of the test specimen 10. The receiving transducer 4 is aligned with its acoustic axis 6 to the exit point of these sound waves passing through the test specimen 10 in a V-shape. The acoustic axis 6 of the receiving transducer 4 also forms an angle α with a normal 3 of the surface 8 of the test specimen 10. As in Fig. 1 As can be seen, if a defect 12 exists within the test specimen 10, the sound waves 5 passing through the test specimen 10 do not completely reach the receiving transducer 4. The sound waves 5 incident on the defect 12 are at least partially reflected by it. In As a result, the amplitude recorded by the receiving transducer 4 is lower. From this, an evaluation unit 14 calculates the extent of the defect 12, and in particular, the depth. In Fig. 1 The transmitting transducer 2 is depicted in the form of a transmitting and receiving transducer. The transmitting and receiving transducer combines the transmitting transducer 2 with a further receiving transducer 16. The function of the further receiving transducer 16 can be achieved solely by electronically switching the transmitting transducer 2, so that the same hardware operates alternately as a transmitting and receiving transducer. This receives a portion of the sound waves 5 reflected at the defect 12 as an echo signal. To do this, the transmitting transducer 2 excites sound waves 5 in the form of a sound pulse. This sound pulse is preferably so short that the transmitting transducer 2 has finished exciting the sound waves 5 when the echo of the sound waves 5 reflected at a defect 12 reaches the transmitting transducer 2 or the further receiving transducer 16, which in this case are designed as a single component.

[0054] Fig. 2 shows the course of the amplitude, which the receiving transducer 4 (dashed line, V-transmission) or the further receiving transducer 16 records (solid line, pulse echo operation) as a function of the depth of a defect 12 arranged in the sound path. In Fig. 2 The characteristic curves for ideal defects in the form of grooves of known depth, machined into a reference body, are shown. It can be seen that the amplitude recorded by the additional receiving transducer 16 hardly increases with increasing groove depths greater than 4 mm. This is where signal saturation occurs. The range of groove depths greater than 4 mm is marked as range A. Likewise, the amplitude of the V-transmission signal recorded by the receiving transducer 4 shows only a slight decrease in amplitude in a range of groove depths up to 3 mm. Here, too, a saturation range can be seen (range B). Another saturation range can be seen at groove depths greater than 8 mm (range C). The reference body, which is shown in Fig. 2 has a thickness of 10 mm. Fig. 2 It can be seen that groove depths up to 4 mm can be accurately determined using the pulse-echo signal recorded by the additional receiving transducer 16. Groove depths between 3 mm and 8 mm, in contrast, can be accurately determined using the V-wave signal recorded by the receiving transducer 4. A combination of the two operating modes, i.e., transmitting transducer 2, receiving transducer 4, and the additional receiving transducer 16, thus enables crack depth determination in a range from 0 mm to 8 mm.

[0055] Fig. 3 shows one of the Fig. 2 The difference in amplitudes generated by the correlations shown. An approximately linear relationship between groove depth and amplitude attenuation on a logarithmic scale can be seen up to a groove depth of 8 mm. By using receiver transducer 4 and another receiver transducer 16, a point on this characteristic curve can be determined from the difference in the recorded amplitudes, and the depth of a defect 12 can be deduced from this. This occurs in the evaluation unit 14.

[0056] While Fig. 1 represents a transmitter transducer 2 which emits a sound wave 5 with a largely parallel wave front, Fig. 4 a transmitting transducer 2 that emits a sound wave 5 with a diverging wavefront. The dashed lines indicate the boundaries of the resulting sound cone, where a -6 dB attenuation occurs compared to the corresponding position in the central beam, while the dot-dash line shows the limits of a -12 dB attenuation. Again, the transmitting transducer 2 is designed as a combined transmitting and receiving transducer that integrates the further receiving transducer 16. Likewise, the transmitting transducer 2 is again aligned such that its acoustic axis 6 forms an angle α with the normal 3 of the surface 8 of the test specimen 10. In the Fig. 4 A plurality of receiving transducers 4 are arranged, which are spaced apart from the transmitting transducer 2 in the direction of propagation of the sound waves 5 in the test body 10 and each have a different distance from the transmitting transducer 2. A defect 12 in turn causes a shadowing of the sound waves 5, which this time has the consequence that only certain receiving transducers 4 pick up sound waves excited by the transmitting transducer 2. The transmitting transducer 2 and the receiving transducer 4 are arranged at a distance from the test body 10. Sound waves 5 excited by the transmitting transducer 2 propagate through a coupling medium arranged between the transmitting transducer 2 and the test body 10 until they couple into the test body 10. Likewise, sound waves 5 coupling out of the test body 10 propagate via the coupling medium until they are picked up by a receiving transducer 4 or the further receiving transducer 16.

[0057] Fig. 5 shows a representation in which the groove depth is shown in correlation with the distance of the receiving transducers 4, at which an amplitude of the sound waves 5 exceeding a certain threshold can be detected, from the transmitting transducer 2. The deeper the defect 12 is, the further the first receiving transducer 4, at which the specified threshold of the signal is exceeded, is from the transmitting transducer 2. Thus, the defect depth can be determined based on the distance of the first receiving transducer 4, at which an exceedance of the threshold is detected, from the transmitting transducer 2.

[0058] Here, too, a saturation range is shown up to groove depths of about 3 mm, in which a determination of the groove depth using this signal alone is hardly possible. Therefore, the system uses Fig. 4 also supplementary information from a pulse-echo signal which is received by the further receiving transducer 16 in order to be able to determine the depth of less deep defects 12.

[0059] Fig. 6 shows how the use of the difference in amplitudes recorded by the further receiving transducer 16 (solid line, pulse echo operation) and the receiving transducer(s) 4 (dashed line, V-transmission) can be used to determine the depth of defects 12 independently of any deposits that may be present on the surface 8 of the test specimen 10. Fig. 6a shows a V-transmission of a test specimen 10 without deposits. Fig. 6b shows the amplitudes recorded by the additional receiving transducer 16 and the receiving transducer 4 on a reference body with grooves of different depths. The grooves are machined and the groove depths are known. Fig. 6c shows a V-transmission of a 10 test specimen 10 with deposits arranged on the surface of the test specimen 10. The amplitudes recorded by the further receiving transducer 16 and the receiving transducer 4 are in Fig. 6d Due to the deposits, the amplitudes are lower than the amplitudes in Fig. 6b without deposits, since the sound waves 5 experience additional attenuation when passing through the deposit layer twice. Fig. 6e shows the difference between the amplitudes recorded by the further receiving transducer 16 and the receiving transducer 4. The amplitudes calculated from the amplitudes according to Fig. 6b The difference calculated agrees with the difference calculated from the amplitudes according to Fig. 6d calculated difference. Since both a V-transmission signal, which is picked up by the receiving transducer 4, and a pulse-echo signal, which is picked up by the further receiving transducer 16, must pass through the deposit layer, the attenuation of the amplitude caused by this deposit is eliminated when forming the difference between the two signals. The difference between the two signals results in a characteristic curve analogous to Fig. 3 , by means of which the groove depth can be reliably determined in an evaluation unit 14. This allows defect depths to be reliably determined despite deposits on the test specimen 10.

[0060] Fig. 7 illustrates a further advantage of the method according to the invention for inclined cracks or grooves. Fig. 7a shows a defect 12 running obliquely in the test specimen 10, which encloses an angle γ with a normal 3 to the surface 8 of a test specimen 10. Fig. 7b und 7c show simulation results of the amplitudes of a conventional angle mirror echo ( Fig. 7b ) and a pulse-echo signal according to the invention ( Fig. 7c ) when the inclination of the defect varies from 12 to 10°. The amplitude of the angle-beam echo depends strongly on the angle γ, so that, for example, at an inclination angle of -10°, an attenuation of approximately 15 dB already occurs. In contrast, the amplitude of the pulse-echo signal is almost constant in the range from -10° to +10°. Therefore, the use of the pulse-echo signal ensures reliable detection and determination even of inclined defects 12.

[0061] Fig. 8 shows a device 17 for detecting signals based on defects 12 in a test specimen 10 in the form of an inspection pig for testing pipelines. The transmitting transducer 2 and the receiving transducer 4 are each arranged in receptacles 18. The device 17 has a plurality of receptacles 18 with transmitting transducers 2 and receiving transducers 4, distributed around the circumference around a longitudinal central axis 20. The receptacles 18 are movable radially in the direction of a test specimen 10. The receptacles 18 each have at least one guide element 22, which can be brought into contact with the test specimen 10 and are designed such that the transmitting transducer 2 and the receiving transducer 4 are arranged at a distance from one another in the receptacle 18 when the guide element 22 comes into contact with the test specimen 10 on the test specimen 10.In the present case, the receptacles 18 each have guide elements 22 arranged in the feed direction of the device 17 within a pipeline before and after the transmitting transducer 2 and receiving transducer 4.

[0062] In Fig. 8 In a receptacle 18, several pairs of transmitting transducers 2 and receiving transducers 4 are arranged, which are spaced apart from each other in the feed direction and slightly offset from each other, as is also the case Fig. 9 As a result, a large portion of the circumference of a test specimen 10 to be tested, in the form of a pipeline, can be simultaneously scanned in one pass by the device 17. Such a device enables the recording of signals based on defects 12 in a test specimen 10 in a single pass.

[0063] Fig. 10shows an arrangement of transmitting transducer 2 and receiving transducer 4 with an ultrasonic depth sensor 24. The transmitting transducer 2 and receiving transducer 4 are arranged with their acoustic axes angled towards each other, so that a V-shaped transmission of sound through a test specimen 10 can occur. The ultrasonic depth sensor 24, on the other hand, is aligned with its acoustic axis perpendicular to the surface of a test specimen 10 and can thus determine the thickness of the test specimen 10. The thickness of the test specimen 10 or the deviation of the test specimen thickness from a nominal or assumed test specimen thickness can be used to correct the signals received from the transmitting transducer 2 and receiving transducer 4.

[0064] This correction can be achieved, for example, by storing different correlations for reference bodies of different thicknesses. Such an ultrasonic depth sensor 24 can also be used in the previously described configurations.

Claims

1. Method for determining the extent of crack depths in a test specimen (10), wherein at least one transmitting transducer (2) excites sound waves (5) in the ultrasonic range, the sound waves (5) propagate in the form of a sound beam, the acoustic axis (6) of which forms an angle (α) with the normal (3) to a surface of the test specimen (10) facing the transmitting transducer (2), the sound waves (5) couple into the test specimen (10) obliquely and are reflected at an interface (11) of the test specimen (10), and at least one receiving transducer (4) spaced apart from the transmitting transducer (2) receives the sound waves (5) reflected at the interface (11) of the test specimen (10), wherein, by means of an evaluation unit (14), an extent of a defect (12) arranged within a sound path is determined from a reduction of the amplitude of the sound waves (5) received by the receiving transducer (4), wherein the transmitting transducer (2) and the receiving transducer (4) are guided past the test specimen (10) at an at least substantially constant distance therefrom and the sound waves (5) are coupled into the test specimen (10) with an advance section via a liquid medium and wherein a further receiving transducer (16) receives sound waves (5) reflected at a defect (12), characterized in that the crack depth is determined from the difference between the amplitudes which the receiving transducer (4) and the further receiving transducer (16) have received.

2. Method according to Claim 1, characterized in that the transmitting transducer (2) excites sound waves (5) in the form of a rectangular pulse or needle pulse.

3. Method according to Claim 2, characterized in that the transmitting transducer (2) excites sound waves (5) at specific time intervals and / or at specific spatial positions while the transmitting transducer (2) and receiving transducer (4) are guided past the test specimen (10).

4. Method according to any of the preceding claims, characterized in that the transmitting transducer (2) excites sound waves (5) in a frequency range of between 1 and 10 MHz, in particular approximately 4 MHz.

5. Method according to any of the preceding claims, characterized in that the transmitting transducer (2) in the form of a transmitting and receiving transducer is used as further receiving transducer (16) that receives the sound waves (5) reflected at a defect (12).

6. Method according to any of the preceding claims, characterized in that the sound wave (5) excited by the transmitting transducer (2) forms a parallel wavefront.

7. Method according to any of Claims 1 to 5, characterized in that the sound wave (5) excited by the transmitting transducer (2) forms a divergent wavefront, the sound wave is reflected at the interface in a v-shaped manner and a plurality of receiving transducers (4) spaced apart from one another and from the transmitting transducer to different extents in the direction of propagation of the sound waves (5) in each case receive parts of the sound wave (5) reflected at the outer boundary surface in a V-shaped manner.

8. Method according to Claim 7, characterized in that the extent of a defect (12), in particular the depth of a crack, is determined on the basis of the amplitudes of the received sound waves (5), said amplitudes being registered by the spaced apart receiving transducers (4), and also known position data of the individual receiving transducers (4).

9. Method according to any of the preceding claims, characterized in that the thickness of the test specimen (10) is determined by means of a depth sensor (24).

10. Arrangement for carrying out a method according to any of Claims 1 to 9, comprising a device (17) for detecting signals based on defects (12) in a test specimen (10), comprising at least one transmitting transducer (2), at least one receiving transducer (4) and at least one further receiving transducer (16), wherein the transmitting transducer (2) and the receiving transducer (4) are arranged at a distance from one another and in a manner inclined towards one another with their acoustic axes (6) such that the signals of a V-shaped through-transmission can be received, wherein the transmitting transducer (2), the receiving transducer (4) and also the further receiving transducer (16) are arranged in a receptacle (18), wherein the receptacle (18) is movable in the direction of the test specimen (10) and the receptacle (18) has a guide element (22), which is able to be brought into contact with the test specimen (10), in such a way that when the guide element (22) makes contact with the test specimen (10), the transmitting transducer (2), the receiving transducer (4) and the further receiving transducer (16) are arranged at a distance from the test specimen (10) in the receptacle (18), characterized in that the device (17) has a plurality of pairings of transmitting transducers (2), receiving transducers (4) and further receiving transducers (16) arranged offset with respect to one another transversely with respect to the feed direction and one behind another in the feed direction in a common receptacle (18), and in that the arrangement has an evaluation unit (14) for evaluating the signals recorded by the device, said signals being based on defects (12) in a test specimen (10), according to the method according to any of Claims 1 to 9.

11. Arrangement according to Claim 10, characterized in that the device (17) has a restoring element that applies to the receptacle (18) a force that moves the latter in the direction of the test specimen (10).

12. Arrangement according to Claim 10 or 11, characterized in that a transmitting transducer (2) is assigned receiving transducers (4) arranged at different distances from the transmitting transducer (2).

13. Arrangement according to any of Claims 10 to 12, characterized in that the device (17) is embodied as an inspection pig having a centre longitudinal axis (20) and having a plurality of receptacles (18) distributed around the centre longitudinal axis (20) in the circumferential direction.