Key information

Title
Method and device for non-destructive testing of a plate material
Application number
20190133
Case type
National
Status
22.12.2025 Patent meddelt (B1)
Filed
31.01.2019
Effective date
31.01.2019
Publicly available
03.08.2020
Next annual fee due
31.01.2027
Applicant
HALFWAVE AS (NO)
Owner
HALFWAVE AS (NO)
Inventor
Petter Norli (NO)
Agent
AWA NORWAY AS (NO)
Granted
22.12.2025
Patent number
349352
Expiry date
31.01.2039

Abstract and drawing

Disclaimer: This text has been machine-scanned and may contain errors – please refer to "Publications" for legally binding content.
It is disclosed a method and device for testing a layered structure (1) for the presence of pits and holes (3), said method including the steps of: transmitting an acoustical signal from a transmitting transducer (2) facing the structure (1) and positioned in a distance from the structure, the frequency of the transmitted signal and the angle of incidence of the signal towards the structure being adapted to promote the formation of Lamb signals in the structure, receiving an acoustical signal returned from the structure in a receiving transducer (4) also facing the structure at a distance from the structure, the receiving transducer (4) being located in a distance from said transmitting transducer (2) along the direction of the structure, time gating the received signal identifying a tail part (8) carrying information from Lamb signals travelling in the structure, and determining the energy content in said Lamb mode part of the signal.

Publications

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Date
 Date Doc. No. Process Case number In/Out Journal description To/from
 02.01.2026 23-01 Saksbehandling 20190133(349352) UT PT Registreringsbrev nasjonal patent (15) (PT20190133)
28.10.2025 22-01 Saksbehandling 20190133 UT Intention to grant AWA NORWAY AS
 25.09.2025 21-06 Saksbehandling 20190133 INN 20250925 173411 Letter of Reply AWA NORWAY AS
 25.09.2025 21-05 Saksbehandling 20190133 INN 20250925 173411 Krav Oversatt Norsk AWA NORWAY AS
 25.09.2025 21-04 Saksbehandling 20190133 INN 20250925 173411 Figures Amended AWA NORWAY AS
 25.09.2025 21-03 Saksbehandling 20190133 INN 20250925 173411 Description amended AWA NORWAY AS
 25.09.2025 21-02 Saksbehandling 20190133 INN 20250925 173411 Description amended - marked AWA NORWAY AS
 25.09.2025 21-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 07.08.2025 20-01 Saksbehandling 20190133 UT Substantive examination AWA NORWAY AS
 01.07.2025 19-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 08.05.2025 18-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) HILDEBJØRG VARTDAL
 29.10.2024 17-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 30.04.2024 16-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 31.10.2023 11-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 08.05.2023 12-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 31.10.2022 13-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) AWA NORWAY AS
 17.03.2022 14-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 13.09.2021 15-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 12.03.2021 10-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 11.09.2020 09-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 02.03.2020 08-03 Saksbehandling 20190133 INN Hovedbrev OSLO PATENTKONTOR AS
 02.03.2020 08-02 Saksbehandling 20190133 INN Krav OSLO PATENTKONTOR AS
 02.03.2020 08-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 22.01.2020 07-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 30.08.2019 06-02 Saksbehandling 20190133 UT PT_report 01:36:21
30.08.2019 06-01 Saksbehandling 20190133 UT Realitet patent OSLO PATENTKONTOR AS
 25.03.2019 05-01 Saksbehandling 20190133 INN Ang ITS
22.02.2019 04-01 Saksbehandling 20190133 UT Infobrev til oppfinner OSLO PATENTKONTOR AS
 18.02.2019 03-02 Saksbehandling 20190133 INN Erklæring Søkers rett til oppfinnelse OSLO PATENTKONTOR AS
 18.02.2019 03-01 Saksbehandling 20190133 INN Korrespondanse (Hovedbrev inn) OSLO PATENTKONTOR AS
 05.02.2019 02-01 Saksbehandling 20190133 UT Formal Examination 1 OSLO PATENTKONTOR AS
 31.01.2019 01-06 Saksbehandling 20190133 INN Beskrivelse OSLO PATENTKONTOR AS
 31.01.2019 01-05 Saksbehandling 20190133 INN Krav OSLO PATENTKONTOR AS
 31.01.2019 01-04 Saksbehandling 20190133 INN Sammendrag OSLO PATENTKONTOR AS
 31.01.2019 01-03 Saksbehandling 20190133 INN Fullmakt OSLO PATENTKONTOR AS
 31.01.2019 01-02 Saksbehandling 20190133 INN Figurer OSLO PATENTKONTOR AS
 31.01.2019 01-01 Saksbehandling 20190133 INN Søknadsskjema Patent OSLO PATENTKONTOR AS

Description, claims and drawings

Disclaimer: This text has been machine-scanned and may contain errors – please refer to "Publications" for legally binding content. Description
Field of the InventionThe present invention relates to the field of non-destructive testing, and more specifically to a method and device for testing the integrity of layered structures such as the walls of oil and gas pipelines using acoustical transducers.BackgroundIn the oil and gas industry, there is a need for efficient testing of pipelines. The structural integrity of pipelines may be tested using inspection pigs which travel inside the pipelines measuring the condition of the pipe wall. There have been devised several methods for measuring the condition of pipeline walls. Here we will mention methods using magnetic flux leakage and ultrasonic testing. Methods using magnetic flux leakage are mainly effective only for detecting metal loss (thinning of the pipeline wall) caused by corrosion. Ultrasonic testing methods are used for detecting corrosion and cracks in pipeline walls, even though there is some overlap between the technologies. However, conventional ultrasonic testing methods, e.g. using pulse-echo based scanning of the pipe wall, have limitations relating to the need for a liquid couplant.Summary of the InventionIt is an object of the present invention to provide a device and method for acoustical testing of pipelines able to detect the presence of defects such as small holes or pits in the wall, pits and holes having diameters of 1.5 to 8.0 mm.The scope of the invention is defined in the appended claims.According to a first aspect, the invention relates to a method for testing a layered structure for the presence of pits and holes, said method including the steps of: transmitting an acoustical signal from a transducer facing the structure and positioned in a distance from the structure, the frequency of the transmitted signal and the angle of incidence of the signal towards the structure being adapted to promote the formation of Lamb signals in the structure,receiving an acoustical signal returned from the structure in a receiving transducer also facing the structure at a distance from the structure, the receiving transducer being located in a distance from said transmitting transducer,time gating the received signal identifying a tail part carrying information from Lamb signals travelling in the structure, anddetermining the energy content in said Lamb mode part of the signal. This method aims to extract information from Lamb waves travelling as refracted waves in the wall. By lowering the frequency of the acoustic signals, the number of excited wave modes is reduced. Compared to common pulse echo methods, this is a method opposite of what normally would be expected.According to a preferred embodiment of the invention, the frequency of the transmitted signal is in the range 0 - f.According to a more preferred embodiment, the frequency of the transmitted signal is in the range 0 - ½f.In order to achieving a proper coupling to the structure, overcoming the large difference acoustical impedance between e.g. gas and steel, one would normally prefer to use a transmitting frequency hitting and exciting a thickness resonance of the structure. By lowering the frequency, one will not obtain this beneficial effect. However, by lowering the frequency fewer Lamb modes will be activated concentrating the available energy into the remaining modes.According to a particular embodiment of the invention, the transmitting transducer is emitting a signal spanning an angle promoting the formation of the S0 Lamb mode.According to an embodiment of the invention, the acoustical signal emitted from the transmitting transducer is spanning an angle of two times the angle of incidence φ, where φ is determined from:where C0 is the longitudinal velocity of the medium between the transmitter and the plate and Cp is the phase velocity in the structure.This enhances the effect mentioned above. By tailoring the width of the signal lobe from the transducer, the number of excited wave modes may be reduced and the available signal energy concentrated into the most desired wave modes. The width of the signal lobe defines the maximum incident angle of the wave hitting the structure.According to another aspect, the invention also relates to a device for performing the above mentioned method, the device including:a signal generator adapted to provide a signal to a transmitting transducer facing the structure and positioned in a distance from the structure, wherein the transmitting transducer is adapted to transmit an acoustic signal towards said structure, a receiving transducer also facing the structure at a distance from the structure, the receiving transducer being located in a distance from said transmitting transducer, the receiving transducer being adapted to receive an acoustic signal received from the structure. According to the invention the transmitting transducer is adapted to transmit an acoustic signal wherein the frequency of the transmitted signal and the angle of incidence of the signal towards the structure is adapted to promote the formation of Lamb signals in the structure, the device further including a processing means adapted to time gate the received signal identifying a tail part carrying information from Lamb signals travelling in the wall, and to determine the energy content in said Lamb mode part of the signal. According to a preferred embodiment of the device, the signal generator is adapted to generate a signal in the range 0 - ½f.According to a further preferred embodiment, the signal generator is adapted to generate a signal in the range 0 - ½f, wherein f is the fundamental thickness resonance of the wall.According to an embodiment of the invention the transmitting transducer is adapted to emit the acoustic signal spanning an angle promoting the formation of the S0 Lamb mode.According to an embodiment the transmitting transducer is adapted to emit a signal spanning an angle of two times the angle of incidence φ, where φ is determined from:where C0 is the longitudinal velocity of the medium between the transmitter and the plate and Cp is the phase velocity in the structure.This transducer design is used to provide a closely defined width of the transmitted acoustical signal.According to another embodiment, the transmitting transducer has a curved front surface determining the angular extent of the emitted signal.This design of the transducer allows more acoustical energy to be emitted by the transducer compared with the previous embodiment.According to another embodiment, the transmitting transducer includes an annular piezoelectric element. This design aims to reduce the acoustical energy emitted in the central part of the signal lobe, wherein more energy may be made available in the outer parts which excite the Lamb waves.Brief Description of the DrawingsFurther aspects of the invention will appear from the following detailed description when read in connection with the appended drawings, in which:Fig. 1 is a schematic illustration of the inventive device and the electronics circuits of the device,Fig. 2 is a diagram showing the transmission coefficient as a function of frequency and angle of incidence,Fig 3a-c is schematic sectional drawings of acoustical transducers that may be used in the invention,Fig. 4 is an amplitude-versus-time diagram of a typical signal as received in said inventive device,Fig. 5a is a two-dimensional plot showing the energy content in the leading part of the received signal, andFig 5b shows the energy content in a later part of the signal.Detailed descriptionFig. 1 shows the setup for detecting faults in the way of small holes and pits 3 in a layered structure 1, such as the wall of a pipe. The setup includes a transmitting transducer 2 transmitting acoustical signal bursts towards the structure 1 and a receiving transducer 4, the receiving transducer 4 being mounted a short distance in the longitudinal direction from the transmitting transducer 2. The transducers are mounted directly facing the structure. This will waste some acoustical energy, but provides the ability to look for pits and holes in any direction, a feature not offered by a setup using transducers mounted with an angle towards the structure.The instrument setup includes electronic circuits for exciting the transducers, receive response signals from the transducers, and store the received signals. The setup includes a signal generator 10 providing the driver signal to the transmitting transducer 2, the receiving transducer 4, an amplifier 11, a preamplifier 12 and means for processing the received signal. The means will normally include a processor 13, a storage medium 16, communication interface 15 and a position detector 14. The processor 13 may also control other functions in the setup, such as the signal generator 10. The transmitting transducer will emit signals in a conical lobe 17 in front of the transducer.The setup also includes means for displacing the transducer, not shown, allowing the transducer to scan the structure. The normal operating setup will include a number of transducers mounted in a grid on the cylindrical outer surface of a pig adapted to travel inside a pipeline while inspecting the wall from the inside.However, the invention may also find other applications, such as inspecting flat plates or even inspecting tubular bodies from the outside, when this is accessible. The signal from the transmitting transducer 2 will travel in the fluid inside the pipe as a compressional wave and hit the pipe wall. The incoming compressional wave will set up a corresponding acoustical signal in the wall, the signal consisting of a compressional wave part and a part of the incoming signal that is converted into various wave modes at the fluid-steel interface, such as shear and Lamb waves, both at their fundamental frequencies and their harmonics.When leaving the structure the various wave signals will be converted back to compressional waves travelling in the fluid to the receiving transducer 4.Even though the received signal only includes compressional mode energy, several techniques may be used to resolve which parts of the received signal that is produced by different wave modes, i.e. when travelling in the pipe wall.It has been found that certain wave modes are more effective in displaying defects present in the structure. Effective signals for detecting pits and holes in the wall are the Lamb waves, and in particular the fundamental or first symmetric Lamb mode, here called S0, but also its harmonics.When injecting a signal into a layered structure, resonance peaks are found at frequencies where the structure thickness is an integer number of half wavelengths. The frequency f of a thickness resonance is defined as f=nc/2D, where c is the acoustical compression velocity of the structure material, D its thickness and n denoting the harmonic. Injecting the signal at a thickness resonance frequency will enhance the coupling to the structure.Below said fundamental thickness resonance, the Lamb modes A0, S0 and A1 may occur, depending on the angle of incidence. At even lower frequencies, below half of the fundamental thickness resonance, only the fundamental Lamb modes A0 and S0 will occur. It is of course an advantage to limit the transmitted signal to this frequency range, to concentrate the injected energy into these two modes only.However, the incident angle of the transmitted wave will also determine which modes that are activated. This is illustrated in Fig.2 as a diagram showing the transmission coefficient as a function of frequency and angle of incidence. In the case shown in Fig.2, an acoustical signal is transmitted in water towards a steel plate. With a wave transmitted in the range 0 – ½ f, f being the first or fundamental thickness resonance, and the transmitted wave is hitting the plate at an incident angle in the range from 17° to about 40°, only the S0 mode will be present. In the large end, this is dependent on the frequency, as illustrated in Fig. 2. At larger incident angles, also the A0 mode may occur. It is preferred to limit the incident angle to a small area around 17° to maximize the acoustical energy injected as S0 mode waves, as a broader wave lobe will spread the energy. This angle of incidence is dependent on the relationship between the acoustical velocities in the bordering media. The acoustical velocity in steel is fairly constant. However, the acoustical velocity in a gas is very different from the acoustical velocity in a liquid. The optimum incident angle of 17° mentioned above relates to water only. In nitrogen (at atmospheric pressure) it will be close to 4° and in oil about 18°. In the present case, it is preferred to make the investigation of the pipeline in a homogeneous environment only involving gas, water or oil. Thus, the instrument setup has to be tailored to provide the correct angle of incidence with the fluid present in the pipeline. This angle may have to be found by measurements in the fluid concerned, or by solving the below Rayleigh-Lamb equations, and identifying the S0 mode:and where ω is the angular frequency, k the wave number, Cl and Ct are the longitudinal and shear wave velocities respectively, and d is the thickness of the plate.The first equation relates to the propagation of symmetrical Lamb waves in a plate, while the second inverted equation relates to the propagation of asymmetrical Lamb waves in a plate.If the longitudinal velocity of the medium between the transmitter and the plate is C0, the incidence angle φ required for the excitation of the desired mode is found to be:where Cp is the phase velocity in the structure (Cp=ω/k).Thus, for the purpose of exciting the fundamental symmetrical Lamb mode, the optimum conditions will be to inject an acoustical signal at a frequency of half the fundamental thickness resonance and at an angle of incidence in the range φ to 2φ. The incident angle in question is defined by the outer rim of the transmitter lobe 17 shown in Fig.1, the lobe width spanning two times the incident angle. A defined lobe width may be achieved by either using a transducer with a small aperture, providing the transducer with a curved (convex) front surface, or by placing an acoustic lens in front of the transducer.Fig. 3a shows a conventional piezoelectric transducer consisting of a stack of piezoelectric elements 31 terminated in a transition element 32 improving the acoustical coupling to the outside medium. The aperture of the transducer, defined as the angle between the -6dB points of the main signal lobe is given by where k=w/c0, w being the angular frequency, c0 is the soundvelocity in the surrounding medium and a is the radius of the transducer.Fig. 3b shows an optional transducer for use in the inventive setup. Here, the stack of piezoelectric elements 31 is somewhat wider than in the version shown in Fig. 3a, and the adaption of the lobe width to the desired incident angle is achieved by providing the transition element 32 with a curved outer surface. The larger dimensions of the piezoelectric elements allow the transducer to emit a stronger signal. The transducer designs shown in Fig.3a and 3b limits the width of the signal lobe to avoid exciting unnecessary acoustical modes. This means that the signal energy is concentrated into the desired Lamb modes, and most preferably into the S0 mode only. However, the energy emitted in the central part of the lobe will hit the wall at smaller incident angles (i.e. normal or near normal to the structure) and will not contribute to the formation of Lamb signals and is in fact a waste of energy. In Fig. 3c there is shown a toroidal (annular, ring shaped) transmitting transducer designed to emit less energy in the central part of the lobe. This transducer includes a stack of piezoelectric elements 31 and a transition element 32 as in the previous embodiments, but here there has been drilled a hole 33 through the central part of the stack. However, the formula for the lobe width given above does not apply here. In this case one has to exploit the side lobes from the transducer. The central lobe will be less predominant, and side lobes will appear stronger. The position of these side lobes may be determined by careful design of the transducer. The received signal shown in Fig.4 consists of a signal onset part 7 including the part of the compressional wave that has been reflected from the surface of the layered structure (echo). The signal also includes a tail 8 that includes the part of the signal that has travelled in the structure.Then, if a time gating (window) is applied to the received signal extracting the part of the signal occurring in the tail 8, the signal will predominantly be influenced by the S0 Lamb wave, considering the above conditions with regard to frequency and incident angle of the impinging signal.Fig. 5a, b illustrates the magnitudes of signals returned from a rectangular flat plate, 26 mm thick, which is immersed in water. The transducer is placed 90 mm above the plate and excites the plate with a chirp signal of 20 μS duration. In the plate there are four holes of 8.0, 2.0, 1.5 and 4.0 mm diameter, respectively, as seen from the top end of the plate to the bottom.Fig. 5a shows the energy in the signal from the leading (echo) part. Only the largest hole may be discerned, using a suboptimal transducer lobe.Fig. 5b shows the energy in the tail part. The 8.0 and 4.0 mm holes “suck” energy providing a large contrast to the surrounding plate. The smaller holes of 2.0 and 1.5 mm diameter provide a much lower contrast, but are nevertheless clearly visible.
Claims
C l a i m s1. A method for testing a layered structure (1) for the presence of pits and holes (3), said method including the steps of:transmitting an acoustical signal from a transmitting transducer (2) facing the structure (1) and positioned in a distance from the structure, the frequency of the transmitted signal and the angle of incidence of the signal towards the structure being adapted to promote the formation of Lamb signals in the structure,receiving an acoustical signal returned from the structure in a receiving transducer (4) also facing the structure at a distance from the structure, the receiving transducer (4) being located in a distance from said transmitting transducer (2),time gating the received signal identifying a tail part (8) carrying information from Lamb signals travelling in the structure, anddetermining the energy content in said Lamb mode part of the signal.2. A method according to claim 1, wherein the frequency of the transmitted signal is in the range 0 – f, wherein f is the fundamental thickness resonance of the structure.3. A method according to claim 1, wherein the frequency of the transmitted signal is in the range 0 - ½f.4. A method according to claim 1-3, wherein the transmitting transducer (2) is emitting a signal spanning an angle promoting the formation of the S0 Lamb mode.5. A method according to claim 4, wherein the acoustical signal emitted from the transmitting transducer (2) is spanning an angle of two times the angle of incidence φ, where φ is determined from:where C0 is the longitudinal velocity of the medium between the transmitter and the plate and Cp is the phase velocity in the structure.6. A device for testing a layered structure (1) for the presence of pits and holes (3), the device including:a signal generator (10) adapted to provide a signal to a transmitting transducer (2) facing the structure (1) and positioned in a distance from the structure, wherein the transmitting transducer (2) is adapted to transmit an acoustic signal towards said structure,a receiving transducer (4) also facing the structure at a distance from the structure, the receiving transducer (4) being located in a distance from said transmitting transducer (2), the receiving transducer (4) being adapted to receive an acoustic signal received from the structure,c h a r a c t e r i z e d i n that the transmitting transducer (2) is adapted to transmit an acoustic signal wherein the frequency of the transmitted signal and the angle of incidence of the signal towards the structure is adapted to promote the formation of Lamb signals in the structure, the device further including a processing means (13) adapted to time gate the received signal identifying a tail part (8) carrying information from Lamb signals travelling in the structure, and to determine the energy content in said Lamb mode part of the signal.7. A device according to claim 6, wherein the frequency of the transmitted signal is in the range 0 – f, wherein f is the fundamental thickness resonance of the structure.8. A device according to claim 6, wherein the signal generator (10) is adapted to generate a signal in the range 0 - ½f, wherein f is the fundamental thickness resonance of the structure.9. A device according to claim 6-8, wherein the transmitting transducer (2) is adapted to emit the acoustic signal spanning an angle promoting the formation of the S0 Lamb mode.10. A device according to claim 9, wherein transmitting transducer (2) is adapted to emit a signal spanning an angle of two times the angle of incidence φ, where φ is determined from:where C0 is the longitudinal velocity of the medium between the transmitter and the plate and Cp is the phase velocity in the structure.11. A device according to claim 9 or 10, wherein the transmitting transducer has an aperture determining the angular extent of the emitted signal.12. A device according to claim 9 or 10, wherein the transmitting transducer has a curved front surface determining the angular extent of the emitted signal.13. A device according to claim 9 or 10, wherein the transmitting transducer includes an annular piezoelectric element.
Drawings

Priority

No priority

Patent classes

IPC classesG01N 29/04G01N 29/38CPC classesG01N 29/041G01N 29/38

Citations

US 2009/0078049 A1 (A1)US 2018/0017533 A1 (A1)

Applicants, owners and inventors

Owners
HALFWAVE AS
Fjordveien 1 1363 HØVIK NO (BÆRUM Municipality, Akershus county)Org. number: 897067382Inventors
Petter Norli
Holtegata 16 A 0259 OSLO NO (OSLO Municipality, Oslo county)

Agent

AWA NORWAY AS
AWA NORWAY AS

Org. number: 925400262

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Postboks 1052 Hoff 0218 OSLO NO (OSLO Municipality, Oslo county)
Org. number: 925400262
Reference: 173411-DAMR/HIVL

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