Acoustic Detection of Defects in a Pipeline

Abstract

The invention relates to an acoustic sensor system (1) for detecting a defect (2) of a pipeline wall (3), having: at least one transmitter unit (4) which is configured to emit ultrasound in the direction of a pipeline wall (3) and detect an ultrasound echo reflected by the pipeline wall (3); and a control unit (5) which is connected to the at least one transmitter unit (4) for signaling purposes and which is configured to detect a defect (2) of the pipeline wall (3) using a present change in he ultrasound echo. The invention additionally relates to an in-line inspection device comprising the sensor system (1), to a method for detecting a defect (2) in a pipeline wall (3), to a computer program, to a data carrier signal, and to a data storage unit.

Claims

1. An acoustic sensor system (1) for detecting a defect (2) of a pipeline wall (3), comprising: at least one transmitter unit (4) configured to emit ultrasound toward the pipeline wall (3) and to detect an ultrasound echo reflected from the pipeline wall (3); and a control unit (5) signally connected to the at least one transmitter unit (4) and configured to detect the defect (2) of the pipeline wall (3) based on an occurring change in the ultrasonic echo.

2. The acoustic sensor system according to claim 1, wherein a single transmitter unit (4) forms an immersion normal beam probe; or wherein a plurality of transmitter units (4) form an immersion normal beam probe.

3. The acoustic sensor system (1) according to claim 1, wherein the control unit (5) is configured to: drive at least a first transmitter unit (4) of the sensor system (1) for emitting ultrasound in the direction of the pipeline wall (3) and for detecting an ultrasound echo reflected by the pipeline wall (3); temporarily drive at least a second transmitter unit (4) of the sensor system (1) for detecting the ultrasonic echo reflected from the pipeline wall (3); and detect the defect (2) of the pipeline wall (3) based on an occurring change of the ultrasonic echo.

4. The acoustic sensor system (1) according to claim 1, wherein at least one transmitter unit (4) is configured for emitting and detecting low-frequency ultrasound, wherein an amount of a wavelength of the low-frequency ultrasound is greater than/equal to an amount of a wall thickness (WT) of the pipeline wall (3), wherein in particular the amount of the wavelength of the low-frequency ultrasound relates to the amount of the wall thickness (WT) of the pipeline wall (3) according to 2.Math.WT/n, wherein n is a natural number.

5. The acoustic sensor system (1) according to claim 1, wherein at least one transmitter unit (4) is configured to transmit and detect high-frequency ultrasound.

6. The acoustic sensor system (1) according to claim 1, wherein the control unit (5) is configured to evaluate the change in the ultrasonic echo corresponding to a change in an ultrasonic echo divergence generated by corrosion in order to detect corrosion.

7. The acoustic sensor system (1) according to claim 1, wherein the control unit (5) is configured to determine a wall thickness (WT) of the pipeline wall (3) based on a difference between an inner wall echo time (T.sub.FWE) and an outer wall echo time (T.sub.BWE).

8. The acoustic sensor system (1) according to claim 1, wherein the control unit (5) is configured to determine a wall thickness (WT) of the pipeline wall (3) based on at least two resonance frequencies (f1, f2, . . . fi) of the outer wall echo or based on at least one resonance frequency (f1, f2, . . . fi) of the outer wall echo and a duration of the at least one resonance frequency (f1, f2, . . . fi) of the outer wall echo.

9. The acoustic sensor system (1) according to claim 1, wherein the control unit (5) is configured to determine a wall thickness (WT) of the pipeline wall (3) on the basis of at least one outer wall echo time (T.sub.BWE) and at least one period duration (T1, T2, . . . Ti) of an outer wall echo at this at least one outer wall echo time (T.sub.BWE).

10. The acoustic sensor system (1) according to claim 1, wherein the control unit (5) is configured to carry out crack detection and a crack size determination based on at least one amplitude of at least one resonance frequency (f1, f2, . . . fi) and/or at least one amplitude of an outer wall echo.

11. The acoustic sensor system (1) according to claim 1, wherein an attenuation of the ultrasonic echo is proportional to a depth of the defect (2).

12. The acoustic sensor system (1) according to claim 1, comprising a single transmitter unit (4) configured to detect reflected ultrasound; and a plurality of transmitter units (4) arranged around the single transmitter unit (4) and each configured to emit ultrasound.

13. The acoustic sensor system (1) according to claim 1, comprising exactly two transmitter units (4), of which the first transmitter unit (4) is configured to detect reflected ultrasound, and the second transmitter unit (4) is configured to emit ultrasound.

14. The acoustic sensor system (1) according to claim 13, wherein the second transmitter unit (4) is formed by a one-piece ring at its ultrasound exit surface and an ultrasound entrance surface of the first transmitter unit (4) is arranged, preferably concentrically, inside the ring.

15. The acoustic sensor system (1) according to claim 1, comprising a plurality of transmitter units (4), wherein ultrasonic exit and entrance surfaces of the transmitter units (4) are arranged circularly.

16. An inline inspection device, ILI, for inspecting a pipeline wall (3), comprising one or more acoustic sensor system(s) (1) according to claim 1.

17. A method for detecting a defect (2) of a pipeline wall (3), comprising the following steps: operating (S100) at least one transmitter unit (4) to emit ultrasound in the direction of the pipeline wall (3) and to detect an ultrasound echo reflected from the pipeline wall (3); and operating (S200) a control unit (5) signally connected to the at least one transmitter unit (4) to detect the defect (2) of the pipeline wall (3) on the basis of an occurring change in the ultrasound echo.

18. (canceled)

19. The method for detecting a defect (2) of a pipeline wall (3) according to claim 17, further comprising the step of transmitting a computer program with a data carrier signal.

20. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In the following, the invention is explained in more detail with reference to the accompanying drawings based on preferred exemplary embodiments. The term Figure is abbreviated in the drawings as Fig; In the drawings:

[0057] FIG. 1a is a schematic view of a sensor system according to a first embodiment;

[0058] FIG. 1b is a schematic view of a sensor system according to a second embodiment;

[0059] FIG. 2a is a schematic top view of an ultrasonic entrance/exit surface of a physical unit of a sensor system according to a third embodiment;

[0060] FIG. 2b is a schematic top view of an ultrasonic entrance/exit surface of a physical unit of a sensor system according to a fourth embodiment;

[0061] FIG. 2c is a schematic top view of an ultrasonic entrance/exit surface of a physical unit of a sensor system according to a fifth embodiment; and

[0062] FIG. 3 is a flow chart of a method according to an embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0063] The described exemplary embodiments are merely examples that can be modified and/or supplemented in a variety of ways within the scope of the claims. Each feature described for a particular exemplary embodiment can be used independently or in combination with other features in any other exemplary embodiment. Any feature described for an exemplary embodiment of a particular claim category may also be used in a corresponding manner in an exemplary embodiment of another claim category.

[0064] FIG. 1 a shows a schematic view of a sensor system 1 according to a first embodiment. The sensor system 1 is suitable for detecting defects 2 of a pipeline wall 3. The pipeline wall 3 is made of metal, for example of steel. The sensor system 1 comprises a transmitter unit 4 and a control unit 5. The transmitter unit 4 and the control unit 5 are integrated in a common physical unit 10. The transmitter unit 4 is configured to emit ultrasound and receive ultrasound, which is reflected in the form of ultrasonic echoes from a pipeline wall 3.

[0065] The transmitter unit 4 is configured to emit and detect high-frequency ultrasound. Here, the transmitter unit 4 emits high-frequency ultrasound with a frequency in a range from 3 to 5 MHz. Thus, the sensor system 1 detects, for example, corrosion or detachment of coatings in liquid-carrying pipelines, which are, for example, oil-carrying or water-carrying.

[0066] Alternatively, the transmitter unit 4 is designed to emit and detect low-frequency ultra-sound. Here, the transmitter unit 4 emits low-frequency ultrasound with a frequency in a range from 500 to 600 KHz. Thus, the sensor system 1 detects, for example, corrosion or detachment of coatings in gas- or liquid-carrying pipelines. For example, gas with a pressure of 10.sup.7 Pa may be present in the pipeline.

[0067] In the following, the reference signs 4A, 4B, 4a, 4b are also assigned for the transmitter unit 4. The latter reference signs refer to a structural form of the transmitter units 4, 4A, 4B, 4a, 4b, wherein all transmitter units 4, 4A, 4B, 4a, 4b can be driven as a first or as a second transmitter unit.

[0068] FIG. 1b shows a schematic view of a sensor system 1 according to a second embodiment. The sensor system 1 of the exemplary embodiment of FIG. 1b is suitable for detecting corrosion, cracks and detachments of coatings at or in a pipeline wall 3, which is liquid-carrying.

[0069] The sensor system 1 comprises two physical units 10, which are spatially separated from each other. The physical units 10 can be fixed to each other at a distance of, for example, 5 cm, or be designed to be movable relative to each other. The physical units 10 of the sensor system 1 each comprise a control unit 5 and a transmitter unit 4A, 4B. Alternatively, according to an embodiment not shown, a common control unit 5 may be provided for both transmitter units 4A, 4B. The control unit 5 needs not be integrated within one of the physical units 10 of the sensor system 1. In the embodiment two physical units 10 respectively comprising a transmitter unit 4A, 4B are shown. However, more than these two physical units 10 comprising a respective transmitter unit can be provided.

[0070] The transmitter units 4A, 4B are driven differently by the control unit 5: The first transmitter unit 4A is driven to operate in a pulse echo mode (PE mode), and to operate in a pitch catch mode (PC mode). In addition, the first transmitter unit can be driven simultaneously in the pitch catch mode and in the PE mode (see also explanations with respect to the flow chart in FIG. 3). The PC mode is also abbreviated as “PC” below and the PE mode is also abbreviated as “PE” below. In both modes PE, PC described above, the first transmitter unit 4A emits ultrasound towards the pipeline wall 3 and detects ultrasonic echoes reflected from the pipeline wall 3. The second transmitter unit 4B is driven in the PC mode (see also explanations with respect to FIG. 3) to detect the ultrasonic echo reflected from the pipeline wall 3.

[0071] The control unit 5 is operated in both modes PE and PC. The control unit 5 evaluates signals corresponding to the ultrasonic echoes in order to detect a defect 2 of the pipeline wall 3 based on a change in the ultrasonic echo occurring in the PE, PC mode.

[0072] When the pipeline wall 3 is intact, the first transmitter unit 4A detects in the PE mode the majority of the ultrasound emitted normally onto the pipeline wall surface, which is reflected as an echo. A minor portion of the ultrasonic echo is detected by the second transmitter unit 4B in the PC mode. In the case of corrosion, the first transmitter unit 4A detects a significant change in the ultrasonic echo in the PE mode. The second transmiller unit 4B, too, detects a change in the ultrasonic echo in the PC mode. The detected signal changes in the PE and PC modes are each sufficient to determine that corrosion is present. In the case of a crack in the pipeline wall 3, for example in the form of a linear defect, a change in the ultrasonic echo is detected in the PC mode. In detecting the change in the ultrasonic echo, it is taken into account that an ultrasonic echo generated by ultrasound emitted from the transmitter unit(s) is partially suppressed by the crack, and is partially generated by ultrasound reflected at the crack. In the case where the crack is located between the transmitter unit 4 emitting the ultrasound and the transmitter unit 4 detecting the ultrasound, the detected signal of the ultrasonic echo is reduced. In the case where the emitting and detecting transmitter units 4 together approach the crack, a detected ultrasonic echo signal increases compared to an ultrasonic echo signal generated at an intact pipeline wall surface. The transmitter units 4, 4A, 4B may include a low noise, high gain amplifier (not shown). This can be used in both modes PE, PC.

[0073] The transmitter units 4, 4A, 4B of the embodiments described above and below are piezoelectric broadband transmitters. The physical units 10 of the sensor system 1 may, as an alternative to an embodiment comprising one transmitter unit 4A, 4B per physical unit 10, each be configured in accordance with one of the exemplary embodiments of FIGS. 2a to 2c. FIGS. 2a to 2c each show a schematic top view of an ultrasonic entrance/exit surface of a physical unit 10 of a sensor system 1 according to a third to fifth embodiment. In these exemplary embodiments, ultrasound emitting and ultrasound detecting transmitter units 4a, 4b are integrated in the physical unit 10. The transmitter units 4a, 4b can operate as a first or a second transmitter unit 4 depending on the operation mode in the PE mode or PC mode.

[0074] According to the embodiment shown in FIG. 2a, the physical unit 10 comprises an emitting transmitter unit 4b and a detecting transmitter unit 4a.

[0075] According to an exemplary embodiment of FIG. 2b, the physical unit 10 comprises a plurality of ultrasound emitting transmitter units 4b and an ultrasound echoes detecting transmitter unit 4a arranged centrally with respect to the ultrasound emitting transmitter units 4b.

[0076] According to an exemplary embodiment shown in FIG. 2c, a physical unit 10 comprises a detecting transmitter unit 4a and an emitting transmitter unit 4b annularly surrounding the detecting transmitter unit 4a. In other words, the second transmitter unit 4b is formed by a one-piece ring at its ultrasound exit surface, and an ultrasound entrance surface of the first transmitter unit 4a is disposed inside the ring.

[0077] Alternatively or additionally, physical units 10 according to the exemplary embodiment of FIG. 2a or 2c are arranged to each other (circularly) in a configuration as shown in FIG. 2b. The number of detecting transmitter units 4a arranged in the center and/or of emitting transmitter units 4b arranged in the circle is adaptable as required according to a signal-to-noise ratio to be achieved, the characteristics of the pipeline and a size of the sensor system 1. The emitting transmitter units 4b may also be arranged in a plurality of circles of different diameters around the detecting transmitter unit(s) 4a. Alternatively to the above exemplary embodiments, the detecting transmitter units 4a are arranged in circles around one or more ultrasound emitting transmitter unit(s) 4b. This may be realized in one physical unit 10 or in multiple physical units 10 according to the principles described above.

[0078] According to one exemplary embodiment, the transmitter units 4, 4a, 4A, 4B, 4b emit or detect ultrasound in the high frequency range. According to an alternative exemplary embodiment, the transmitter units 4, 4a, 4A, 4B, 4b emit or detect ultrasound in the low-frequency range. Alternatively, the sensor system 1 comprises physical units 10 which emit or detect ultrasound in the high-frequency range and physical units 10 which emit or detect ultrasound in the low-frequency range.

[0079] A flow chart of a method for detecting a defect 2 and for characterizing a wall thickness WT of the pipeline wall 3 is shown in FIG. 3. The method comprises the following steps: According to a step “S100”, operating at least one transmitter unit 4, 4a, 4A, 4b, 4B is implemented to emit ultrasound toward the pipeline wall 3 and detect an ultrasound echo reflected from the pipeline wall 3. According to a step “S200”, operating of a control unit 5 signally connected to the at least one transmitter unit 4, 4a, 4A, 4b, 4B is implemented to detect a defect 2 of the pipeline wall 3 based on an occurring change of the ultrasonic echo.

[0080] Operating (S100) the transmitter unit 4, 4a, 4A, 4b, 4B may include both the PE mode and the PC mode. The PE mode is advantageous for detecting corrosion by use of one physical unit 10, see FIG. 1a, or when only one physical unit 10 is used in the sensor system 1 of the exemplary embodiment of FIG. 1b. In the PE mode, one of the transmitter units 4a, 4b of the exemplary embodiments of FIGS. 2a to 2c or the combinations of physical units described in this context can be operated, too.

[0081] The PC mode occurs in the context of operating at least two transmitter units 4a, 4A, 4b, 4B. These may, for example, be operated in separate physical units 10 (see FIG. 1b) or in one physical unit 10 (see FIGS. 2a and 2c and the explanations in this context) in the PC mode. As an example, the following method comprising the following steps may be used:

[0082] Step “S100” comprises operating at least a first transmitter unit 4, 4a, 4A, 4b, 4B according to the PE mode and according to the PC mode to emit ultrasound toward a pipeline wall 3 and to detect an ultrasound echo reflected from the pipeline wall 3. Further, operating at least one second transmitter unit 4, 4a, 4A, 4b, 4B in the PC mode is provided to detect the ultrasonic echo reflected from the pipeline wall 3.

[0083] Step “S200” comprises operating a control unit 5 signally connected to the transmitter units 4, 4a, 4A, 4b, 4B to detect a defect 2 of the pipeline wall 3 based on an occurring change in the ultrasonic echo.

[0084] In determining the wall thickness WT and characteristics of defects 2 of the pipeline wall 3, the control unit 5 utilizes the time course of a frequency signal which is output to the control unit 5 by the transmitter units 4, 4a, 4A, 4b, 4B. The frequency signal is evaluated either directly or after applying a Fourier transformation several times (either in a frequency domain or in a time domain).

[0085] When operating the control unit 5 (S200) to detect defects 2, various methods may be used:

[0086] The control unit 5 may use a method for detecting corrosion (indicated by “K”). To this end, the control unit 5 is configured to evaluate the change in the ultrasonic echo corresponding to a change in an ultrasonic echo divergence generated by corrosion in order to detect corrosion.

[0087] Alternatively or additionally, the control unit 5 is configured to carry out a method for determining the wall thickness WT (indicated by “WT1” in the flow chart). The method WT1 is carried out by the control unit 5 to evaluate data obtained from measurements by use of one/more transmitter units 4, 4a, 4A, 4b, 4B which emit high frequency ultrasound. The control unit 5 determines the wall thickness WT (see FIGS. 1a and 1b) of the pipeline wall 3 based on a difference between an inner wall echo time (T.sub.FWE) and an outer wall echo time (T.sub.BWE). The inner wall FW (see FIGS. 1a and 1b) is a surface of the pipeline wall 3 facing the transmitter unit 4, 4a, 4A, 4b, 4B. The outer wall BW (see FIGS. 1a and 1b) is a surface of the pipeline wall 3 facing away from the transmitter unit 4, 4a, 4A, 4b, 4B, which is outside the pipeline. A first detected inner wall echo may be used in determining the wall thickness WT. The wall thickness WT may alternatively or additionally be determined by use of a second or further detected inner wall echo.

[0088] The wall thickness WT can then be derived from the following formula:

“WT” (“C”, “L2” “(““T”, “BWE” “-” “T”, “FWE”))/“2”

[0089] Here, C.sub.L2 is the speed of sound in the pipeline wall.

[0090] Alternatively or additionally, the control unit 5 is configured to carry out a method for determining the wall thickness WT (indicated by “WT2” in the flow chart). The method WT2 is carried out by the control unit 5 to evaluate data obtained from measurements by use of one/a plurality of transmitter units 4, 4a, 4A, 4b, 4B emitting low frequency ultrasound. Here, the control unit 5 is configured to determine a wall thickness WT of the pipeline wall 3 based on resonance frequencies f1, f2, . . . fi of the outer wall echo. Here, the control unit 5 determines resonance frequencies f1, f2, . . . , fi of the outer wall echo in a frequency domain. The wall thickness WT then results from

[00001]$\mathrm{WT}=\frac{C_{L2}}{2\left(f2-f1\right)}$

[0091] Here, C.sub.L2 is the speed of sound in the pipeline wall. The resonance frequency f2 of the outer wall echo is the resonance frequency following in time the resonance frequency f1 of the outer wall echo. Alternatively or in addition to the frequencies f1 and f2, other resonance frequencies fi obtained from the Fourier transform can be used to determine the wall thickness WT.

[0092] The method of the control unit 5 described below is denoted by “WT3” in the flow chart. Accordingly, a signal-to-noise ratio may be improved by carrying out a second degree Fourier transform on the detected signal. Such a Fourier transform may be carried out for signals from transmitter units 4, 4a, 4b, 4A, 4B operated both at high-frequency and at low-frequency. Here, a wall thickness WT is determined on the basis of a period duration T1, T2, . . . , Ti of the outer wall echo time T.sub.BWE of an ultrasonic signal transformed by means of a second degree Fast Fourier transform (FFT). Here, preferably a maximum amplitude of the signal of the outer wall echo is used for determining the wall thickness. The wall thickness WT is then obtained, for example, taking into account a period duration T1 of the maximum amplitude of the outer wall echo signal:

[00002]$\mathrm{WT}=\frac{C_{L2}T1}{2}$

[0093] Alternatively or additionally, the control unit 5 is configured to carry out a method for determining crack characteristics (“crack detection”, abbreviated as “CD” in the flow chart). The method CD is carried out by the control unit 5 to evaluate data obtained from measurements by use of one/a plurality of transmitter units 4, 4a, 4A, 4b, 4B which emit low-frequency or high-frequency ultrasound. Here, the control unit 5 is configured to carry out crack detection and a crack size determination based on amplitudes from the resonance frequencies f1, f2, . . . fi and (an) amplitude(s) of an outer wall echo. In particular, the control unit 5 is configured to carry out crack detection and a crack size determination based on amplitudes of resonance frequencies f1, f2, . . . fi in a frequency domain and (an) amplitude(s) of an outer wall echo of an ultrasonic signal transformed by second degree FFT. In the aforementioned method of investigating crack characteristics, an attenuation of the ultrasound echo is proportional to a depth of the defect 2.

[0094] The aforementioned exemplary embodiments are suitable for wall thickness determination of pipelines with thicknesses from 6 mm to 30 mm. Other wall thicknesses WT are also conceivable.

LIST OF REFERENCE SYMBOLS

[0095] 1 sensor system

[0096] 2 defect

[0097] 3 pipeline wall

[0098] 4, 4a, 4b, 4A, 4B transmitter unit

[0099] 5 control unit

[0100] 10 physical unit

[0101] BW outer pipeline wall

[0102] CD crack characterization method

[0103] FW inner pipeline wall

[0104] PC PC mode

[0105] PE PE mode

[0106] WT wall thickness

[0107] WT1 first method for wall thickness determination

[0108] WT2 second method for wall thickness determination

[0109] WT3 third method for wall thickness determination

[0110] S100 operating at least one transmitter unit

[0111] S200 operating at least one control unit