SYSTEM FOR NON-DESTRUCTIVE ULTRASONIC TESTING OF COMPONENTS

Description

[0001] The invention relates to a system for non-destructive testing (NDT) of components. It can be used particularly advantageously for testing large-format components or in hard-to-reach locations.

[0002] Weld seam testing has previously been performed using shear wave cuff solutions. There is currently no ready-made technology for these to remain attached to the component. However, especially in offshore applications for the testing of foundation structures, divers cannot wear cuffs several meters in diameter for every test. Therefore, a sensor cuff was developed into which special piezoelectric shear wave transducers are laminated. This can be done in such a way that a waterproof system solution is created that can remain permanently attached to the respective test object (even underwater).

[0003] Offshore foundation structures are currently monitored using visual inspection by divers. Each structure must be inspected visually or using approved non-destructive testing methods every four years. Vegetation, in particular, makes it difficult to reliably detect fine cracks using visual inspection. Currently, only visual inspection and the Alternating Current Focusing Technique (ACFM) are approved for non-destructive testing. ACFM involves magnetic crack detection by divers. This method is very time-consuming, as the coil sensor must be manually moved over all weld seams. Interpretation of the measured values ​​obtained in this way is only possible by specialist personnel and cannot be performed by the divers. Acute fillet welds are excluded from testing due to their geometry. Root welds cannot be inspected using the aforementioned NDT methods due to their location inside the pipe.Remote Operated Vehicles (ROVs) have developed rapidly in recent years and are now state-of-the-art for the inspection of underwater support structures, particularly in the oil and gas industry. The market for offshore wind turbines is developing only slowly. ROVs are used for classic NDT inspections, for example, to inspect weld seams. For this purpose, the area to be inspected is cleaned (sandblasting, brushing and / or high-pressure cleaning) and then inspected, e.g., visually, using ultrasonic measuring technology or ACFM. For the latter two methods, the sensor head must be placed directly on the area to be inspected, which is not possible, especially in fillet welds. The large number of required measuring points leads to a long inspection time.

[0004] There are also specific testing requirements for pipeline and vessel inspections. These typically vary from industry to industry and are performed as part of inspections. A continuous monitoring solution could replace expensive inspections (e.g., approximately €1 million per day in a coal-fired power plant) with data collection and testing during operation.

[0005] A number of shear wave testing systems are available for NDT measurements, but they cannot currently be used for permanent monitoring (the measurement system remains attached to the component). These systems are sensor sleeves with shear wave transducers, but they were not designed to remain attached to the test object as a structural health monitoring (SHM) solution and are therefore not suitable for this purpose. By remaining attached to the structure under investigation, recurring testing can be eliminated.

[0006] For example, DE 101 04 610 A1 describes an ultrasonic sensor arrangement for horizontally polarized transverse waves.

[0007] It is therefore an object of the invention to provide possibilities for the non-destructive testing of components with which a test for defects can be achieved under difficult conditions, with sufficient measuring accuracy and, if necessary, also permanently.

[0008] According to the invention, this object is achieved with a system having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in subordinate claims.

[0009] In the system, two ultrasonic transducers, which form a pair and each have a piezoelectric ceramic plate-shaped element with a rectangular geometry, which is formed on two opposite surfaces each with an electrode, can be attached to a surface of a component.

[0010] The ultrasonic transducers of the pair are arranged at a distance from each other so that there is no direct mechanical contact. According to the invention, the ultrasonic transducers of the pair can be arranged side by side with their central longitudinal axes aligned parallel, with the central longitudinal axes being aligned along a common axis.

[0011] In one alternative, the two piezoelectric ceramic plate-shaped elements exhibit different polarizations along their width b. The two ultrasonic transducers of the pair are connected to a pulsed electrical voltage source with the same polarity.

[0012] In a second alternative, the two piezoelectric ceramic plate-shaped elements have the same polarization along their width b. Both ultrasonic transducers of the pair are connected to a pulsed electrical voltage source with opposite polarity.

[0013] The width b is understood to be the longer edge length of one side of the piezoelectric ceramic plate-shaped elements.

[0014] The electrical voltage source is designed to apply electrical voltages in the frequency range from 10 kHz to 1 MHz to the two ultrasonic transducers.

[0015] At least one of the two ultrasonic transducers in the pair, or at least one additional ultrasonic transducer arranged at a known distance from the two ultrasonic transducers, is / are configured to detect ultrasonic waves reflected from defects in the component and / or shear waves emitted simultaneously by the two ultrasonic transducers in the pair, and to transmit the detected ultrasonic waves to an electronic evaluation and control unit. The electronic evaluation unit is configured to evaluate the detected ultrasonic waves with regard to their amplitude and / or their temporal progression.

[0016] The invention provides novel shear wave transducers for testing structures with guided shear waves. Unlike existing solutions, they offer the following advantages: This allows for cost-effective and automated production. This opens up potential for long-term monitoring technologies.

[0017] With appropriately designed and arranged ultrasonic transducers, higher amplitudes of the emitted guided shear waves can be achieved, which leads to improved efficiency and an expansion of the possible application spectrum.

[0018] The ultrasonic transducers in the pair can be designed very flat. The maximum thickness of the piezoelectric ceramic plate-shaped elements (dp ) can be kept ≤ 1 mm. The electrodes used also only increase the overall thickness insignificantly. Due to the small thickness of the ceramic material, adaptation to the respective component surface can be achieved through elastic bending, so that the ultrasonic transducers in the pair can be in close contact with the surface even on non-flat surfaces, thus enabling more efficient coupling of the emitted shear waves into the component along its surface as guided shear waves.

[0019] The ratio between width b and length I of the piezoelectric ceramic plate-shaped elements b to I should be at least 3 to 1.

[0020] The center-of-mass distance of the piezoelectric ceramic plate-shaped elements of the ultrasonic transducers of the pair should be an odd integer multiple of half the wavelength λ of the emitted ultrasonic waves.

[0021] When both ultrasonic transducers of a pair are activated, shear waves are emitted in a direction perpendicular to the central longitudinal axis of the ultrasonic transducers. They propagate divergently in this direction.

[0022] The ultrasonic transducers used in the invention are suitable due to their low component height, yet they still generate sufficiently high amplitudes to enable testing even at distances of several meters. A fundamental advantage is their small installation space requirement and flexibility. This opens up the possibility of applying grids with many distributed ultrasonic transducers to the component surface without having to make structural changes. The system can also include more than one pair of ultrasonic transducers for shear wave emission.

[0023] The invention also enables the retrofitting of existing components, which is a great advantage, for example, in applications where unexpected vulnerabilities or fault accumulations occur. Combining a larger number of such sensors and actuators into complex networks is also advantageous.

[0024] The ultrasonic transducer pairs overlap their effects during emission, allowing the amplitudes of the emitted shear waves to be increased without the need for complex electronic circuitry for each transducer. The distance between the two ultrasonic transducers should be chosen such that no direct force transmission can occur between them.

[0025] The advantage of this invention is that NDT methods can now be used cost-effectively for monitoring purposes. This increases the safety of the components being examined.

[0026] The ultrasonic transducers can be fixed to the component surface using an elastically deformable material.

[0027] For this purpose, the ultrasonic transducers can be embedded or laminated into an elastically deformable material. The ultrasonic transducers can be attached to the respective component using elastically deformable material in the form of a sleeve, which, for example, reduces wave resistance in offshore applications when permanently attached to the respective structure. Furthermore, they can also be installed under insulation / covers / enclosures for pipeline monitoring without requiring any geometry adjustments.

[0028] The invention can be used, for example, in the offshore monitoring of underwater welds (crack detection), pipeline monitoring (crack detection, even below an insulation / cover / enclosure), in container monitoring for cracks and corrosion, even below an insulation / cover / enclosure.

[0029] When using the system, either pulse-echo measurements can be performed with at least one pair of ultrasonic transducers, or transmit-receive measurements can be performed between at least one pair of ultrasonic transducers and another ultrasonic transducer arranged at a known distance from the respective pair. To determine damage, the wave components scattered at a defect can be detected and evaluated in reflection or transmission.

[0030] For the emission of shear waves, short burst signals are usually used. These have a limited duration and a relatively narrow frequency spectrum. The duration should be kept in the range of 5 µs to 1 ms. Detection can occur in the pauses between bursts when no shear waves are emitted.

[0031] The invention will be explained in more detail below by way of example. Features can be combined independently of the respective example or representation.

[0032] Showing: Figure 1 an example of a pair of ultrasonic transducers usable in the invention in two views; Figure 2 another example of a pair of ultrasonic transducers usable in the invention in two views; Figure 3 the direction of action of emitted shear waves (top view); Figure 4 an example of transmit functions that can be implemented as a broadband transmit signal (Sinc, above) or as a bandwidth-limited transmit signal (RC4); Figure 5A diagram of the frequency-dependent achievable vibration velocity of the SH0 mode in comparison; excitation by a single ultrasonic transducer 40 mm x 10 mm (black curve) vs. two pairs of ultrasonic transducers (grey curve), as used in the invention, 40 mm x 5 mm (x2). (Recorded by laser vibrometry at a distance of 200 mm from the center of the ultrasonic transducers, and Figure 6 a typical phase velocity diagram of the shear wave modes for the material steel

[0033] In Figure 1 A sectional view and a perspective view of an example of two ultrasonic transducers 1 and 2 arranged side by side are shown. Their central longitudinal axes are aligned parallel to each other, with the two central longitudinal axes also each aligned parallel to the edges of length b. The two ultrasonic transducers 1 and 2 form a pair.

[0034] How to Figure 2 As can be seen, an electrode 1.2 and 2.2 are located on each of the two opposite surfaces of the piezoelectric ceramic elements 1.1 and 2.1, which are connected to an electrical voltage source (not shown). The electrical voltage source can be operated directly or in pulsed mode via a frequency generator and controlled by an electronic evaluation and control unit (also not shown). This allows the electrical power and frequency at which shear waves are emitted to be influenced in a defined manner.

[0035] The distance a between the centroids of the two piezoelectric ceramic plate-shaped elements 1.1 and 2.1 is chosen as mentioned in the general part of the description. The distance a is chosen such that there is no direct mechanical contact, thus preventing direct mechanical influence during operation.

[0036] The actual detection of defects can be carried out as described in the general part of the description or as is known in principle from the prior art.

[0037] The two ultrasonic transducers 1 and 2, which form a pair, can be laminated into an elastically deformable material 3.

[0038] The one in Figure 4 The diagrams shown for emitted shear waves, which are designated as a broadband transmission signal (sinc function, windowed) or a bandwidth-limited transmission signal (RC4), show the detectable amplitudes in a time-resolved manner or as a function of the respective frequency. These are a broadband transmission signal up to 200 kHz (sinc) and a band-limited transmission signal (RC4 at 100 kHz).

[0039] The speed of shear waves is defined as follows: c ω = c s 1 − ηd 2 c s ωd 2 c s = G ρ with G ··· shear modulus, ρ ... density ω = 2 πf ηd = k π 2 , k = 0 , 1 , 2,3 , … d ··· half structure thickness f ··· frequency

[0040] Here, k describes the order of the wave mode (SH0, SH1, SH2, ...). For the fundamental shear wave mode (k=0), the formula reduces to the pure transverse wave velocity. The wavelength can be calculated from the known propagation velocity cs and the frequency f of the transmitted signal. λ = c s f

[0041] Laboratory measurements showed that the efficiency of the two ultrasonic transducers 1 and 2 can be increased by the two opposing piezoelectric ceramic plate-shaped elements 1.1 and 2.1 compared to a simple arrangement, ie the proportion of energy in the intended propagation direction of the emitted shear waves increases for the same volume of piezoelectric ceramic material.

[0042] The one in Figure 5The diagram shown shows the frequency-dependent achievable amplitudes in comparison with simple ultrasonic transducers 40 mm x 10 mm (black curve) in comparison with those with two ultrasonic transducers forming a pair, as can be used in the invention 40 mm x 5 mm (x2) (grey curve).

Claims

1. System for the non-destructive testing of components, in which two ultrasonic transducers (1, 2), which form a pair and each have a piezoelectric ceramic plate-shaped element (1.1, 2.1) with a rectangular geometry, which are formed on two opposite surfaces each with an electrode (1.2, 2.2), can be fastened to a surface of a component, wherein the two ultrasonic transducers (1, 2) in the pair are arranged at a distance from one another such that there is no direct mechanical contact and the two ultrasonic transducers (1, 2) in the pair are arranged beside one another with a parallel orientation of their central longitudinal axes, wherein each of the central longitudinal axes are also parallel to the edges of the piezoelectric ceramic plate-shaped elements (1.1, 2.1) having a width b, and the two piezoelectric ceramic plate-shaped elements (1.1, 2.1) have a different polarization along their width b, wherein the width b corresponds to a longer edge length of the rectangular geometry of the piezoelectric ceramic plate-shaped elements (1.1, 2.1) and the two ultrasonic transducers (1, 2) in the pair are connected in this case with the same polarity to an electrical voltage source which can be operated in a pulsed manner, or the two piezoelectric ceramic plate-shaped elements (1.1, 2.1) have an identical polarization along their width b, and the two ultrasonic transducers (1, 2) in the pair are connected in this case with opposite polarity to an electrical voltage source which can be operated in a pulsed manner, and the electrical voltage source is designed to apply electrical voltages in the frequency range of 10 kHz to 1 MHz to the two ultrasonic transducers (1, 2), and at least one of the two ultrasonic transducers (1, 2) in the pair and / or at least one further ultrasonic transducer arranged at a known distance from the two ultrasonic transducers (1, 2) in the pair is / are designed to detect ultrasonic waves reflected by defects on the component and / or shear waves simultaneously emitted by the two ultrasonic transducers (1, 2) in the pair, and the detected ultrasonic waves can be transmitted to an electronic evaluation and control unit, wherein the electronic evaluation unit is designed to evaluate the detected ultrasonic waves with respect to their amplitude and / or their temporal sequence.

2. System according to Claim 1, characterized in that the centre or area centroid spacing of the piezoelectric ceramic plate-shaped elements (1.1, 2.1) of the ultrasonic transducers (1, 2) in the pair is an odd integer multiple of half the wavelength of the emitted ultrasonic waves.

3. System according to one of the preceding claims, characterized in that the ratio of width b to length I of the piezoelectric ceramic plate-shaped elements (1.1, 2.1) of at least 3 to 1 is complied with.

4. System according to one of the preceding claims, characterized in that the piezoelectric ceramic plate-shaped elements (1.1, 2.1) have a maximum thickness dp of 1 mm.

5. System according to one of the preceding claims, characterized in that the ultrasonic transducers (1, 2) in the pair can be fastened to the respective component by means of an elastically deformable material (3).

6. System according to one of the preceding claims, characterized in that the at least two ultrasonic transducers (1, 2) in the pair are embedded or laminated in an elastically deformable material (3).

7. System according to one of the preceding claims, characterized in that a sleeve is formed with the elastically deformable material (3) and can be used to fasten the ultrasonic transducers (1, 2) in the pair to the surface of the respective component such that the ultrasonic transducers rest on the respective component surface in a flat manner.