Pipeline inspection device and method using shear waves generated by EMAT
The method uses EMAT-generated shear waves with varying polarizations to analyze wave anisotropy for reliable crack detection and classification in pipelines, addressing the limitations of existing tools by enhancing crack detection and classification accuracy.
Patent Information
- Application Number
- IR140050140003006662
- Authority / Receiving Office
- IR · IR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-11-20
- Publication Date
- 2025-10-03
- Estimated Expiration
- 2041-11-20
AI Technical Summary
Existing EMAT pipeline inspection tools are unreliable in detecting and classifying cracks in different directions, particularly longitudinal, axial, and spiral cracks, and are sensitive to other pipeline defects, limiting their commercial acceptance.
A method and apparatus using first and second shear waves, polarized in different directions, to analyze wave anisotropy for crack detection and classification, employing EMATs to generate and receive waves without a coupling medium, allowing simultaneous detection and classification of cracks while being insensitive to other defects.
The method provides reliable detection and classification of cracks, including longitudinal, axial, and spiral cracks, with high sensitivity and specificity, while minimizing interference from other pipeline defects.
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Abstract
Description
Pipeline inspection device and method using shear waves generated by EMAT Field of invention The present application relates to a method for detecting and classifying cracks in a liquid or gas pipeline. The present application further relates to an apparatus for inspecting a pipeline for cracks. Background of the invention There are approximately 4,000,000 kilometers of pipelines transporting liquids and gases worldwide. Operators maintain a program of inspection and rehabilitation to assess the integrity of these pipelines to ensure safe operation within established economic parameters. The most widely used method for pipeline inspection in long-distance underground pipelines is by using so-called "smart pigging" or "in-line inspection" using smart pigs. Smart pigs are instruments equipped with sensors that collect information about the geometry and defects of the pipeline, which may include deformation of pipeline cracks, corrosion, and detached coatings. These instruments are self-contained and generally consist of a computer board, power supply, and sensors. The image data obtained by these instruments is generally downloaded for analysis upon the instrument's return. For short pipelines such as loading pipes or risers, connected pigs are generally used. Known techniques for performing smart pigging are based on magnetic flux leakage (MFL) and ultrasonic transducers (UT). MFL instruments use magnetism to detect most types of corrosion defects in pipelines. The detection of such defects is based on measuring the thickness of the pipeline wall. However, cracks in pipeline walls caused by stress corrosion cannot be reliably detected by MFL instruments. A crack or a group of cracks usually starts at the surface of the inner or outer wall of the pipeline and penetrates to a certain depth. Cracks in pipelines and welds are a serious concern because cracks can lead to leakage problems or even sudden bursting of high-pressure liquid or gas, which can lead to a dangerous situation and significant damage. UT instruments produce an acoustic wave that is transmitted to the wall of a pipeline. By directing the acoustic wave in a specific direction, the wave can be used to make wall thickness measurements to detect corrosion defects. UT instruments may also be used to inspect pipelines for cracks. However, UT instruments have limited application for gas pipeline inspection because the acoustic wave generated by a UT instrument generally requires a liquid as a coupling medium between the emitter and the substrate. Techniques using electromagnetic acoustic transducers (EMATs) have been proposed that allow the detection of cracks in liquid and gas pipelines. An EMAT produces an acoustic wave that interacts with pipeline defects, if any. The transmitted or reflected wave is measured and analyzed to detect the defect. Known techniques using EMAT technology are disclosed, for example, in US Patent No. US 2011 / 0167914 (US'914), US Patent No. US 7,819,010 (US'010) and US Patent No. US 2011 / 041612 (US'612). Pipeline inspection tools according to US'914 and US'010 use EMATs that generate guided waves. However, the use of guided waves results in image data that has relatively limited spatial resolution. The proposed method of US'612 uses horizontal shear waves and Lamb waves and can be used to detect and diagnose a variety of pipeline defects, but is not highly sensitive to cracks. Furthermore, pipeline inspection tools such as US'914, US'010 cannot simultaneously detect cracks that are located in different directions, for example in the lateral and axial directions of the pipeline. However, early and reliable detection of all types of cracks is desirable.In addition, known EMAT pipeline inspection tools may be sensitive to waves reflected from the inner layers of the pipe wall and at locations where the outer coating separates from the pipe wall. Such signals may be difficult to detect, thereby hindering the classification of cracks in the acquired image data. Therefore, the above techniques that use EMAT technology to detect and classify cracks in pipelines are not reliable, which is one of the main reasons why commercial EMAT tools have so far met with little acceptance in the market. Another pipeline inspection tool is disclosed in U.S. Patent No. US 2014 / 028300 A1. However, the tool according to this disclosure is not configured for crack classification, but is designed to detect a wide range of defects that would otherwise require a combination of different inspection methods using several different tools. Accordingly, multiple EMAT signals are sampled and analyzed separately and independently to detect a wide range of defects. United States Patent No. US 7,697,375 B2 relates to a tool that uses EMAT technology to inspect cemented joints in wellbore holes. However, the tool is not configured to detect and classify cracks. Purpose of the invention The present invention relates to pipeline inspection tools capable of reliably identifying and classifying cracks in different directions in a pipeline. Summary of the invention According to the teachings of the present disclosure, it is possible to simultaneously detect and classify different types of cracks in pipelines, in particular longitudinal, axial and spiral cracks. Furthermore, the present teachings lead to a method and apparatus for detecting and classifying cracks of any type, while being insensitive or only to a limited extent sensitive to other types of pipeline defects. The present training is applicable to pipelines over long distances as well as pipelines with short distances. Generally, such detection and classification is achieved using a measurement protocol in which a first shear wave is generated and propagated along a region of interest in the pipeline. Said region may include a crack located in any direction, such as an axial or lateral direction of the pipeline. The first shear wave is polarized in a first direction, such as a direction parallel to the direction of the crack of interest (e.g., axial or lateral direction). A second shear wave is generated which is polarized in a direction at least about 10 degrees different from the first direction, preferably at an angle of about 30 degrees or more, preferably at an angle of about 45 degrees or more, even more preferably at an angle of about 60 degrees or more, and preferably at an angle of about 90 degrees. The first and second shear waves are received for analysis, in which the anisotropy of the received waves is examined by comparing the wave characteristics (amplitude, wavelength, frequency, phase) of said received waves. Such a comparison can be obtained by calculating the wave attenuation anisotropy coefficient.In other words, the anisotropy of the first and second received shear waves is examined by comparing at least one wave characteristic of the first and second received shear waves, thereby enabling the detection and classification of cracks in the pipeline under investigation. The first and second emitted shear waves can have frequencies between 0.5 and 5 MHz. For example, shear waves can be generated using an EMAT. The first and second shear waves can be generated and detected by a single EMAT. Alternatively, multiple different EMATs can be used to generate and detect the first and second shear waves. According to the first embodiment, the first and second shear waves are emitted in a direction strictly perpendicular to the inner wall surface of the pipeline. When EMAT technology is used to generate and detect shear waves, one EMAT can be used to generate and detect the first and second shear waves. Alternatively, different EMATs can be used. For example, a first EMAT generates and detects the first shear wave, while a second EMAT generates and detects the second shear wave. When an EMAT is used to generate and detect the first and second shear waves, the EMAT rotates spatially after generating and detecting the first shear wave, so that the second shear wave can be generated and detected. According to the second embodiment, the first shear wave propagates in the axial direction of the pipeline and the second shear wave propagates in the lateral direction substantially circumferentially with the wall of the pipeline. Each shear wave can be generated by a separate emitting EMAT and each shear wave can be detected by a separate receiving EMAT that is different from the emitting EMATs. In accordance with the teachings of the present disclosure, an apparatus for detecting and classifying cracks in a pipeline is provided, the apparatus comprising: a first emitting EMAT for emitting a first shear wave along an inspection area, the first shear wave polarized in a first direction; a first receiving EMAT for receiving the first shear wave; a second emitting EMAT for emitting a second shear wave along the inspection area, the second shear wave polarized in a second direction at a minimum angle of about 10 degrees different from the first direction; a second receiving EMAT for receiving the second shear wave; an on-board or off-board processing unit for processing data from the first and second receiving EMATs, including examining the anisotropy of the first and second received shear waves by comparing at least one wave characteristic of the first and second received shear waves to detect and classify cracks in the inspection area. Such a device can be adapted to perform methods in accordance with the teachings of the present disclosure. In accordance with the teachings of the present disclosure, a pipeline inspection tool is provided comprising a pipeline carrier; a sensor module mountable on the pipeline carrier, which comprises at least one device in accordance with the teachings of the present disclosure; and at least one power supply unit, for supplying power to at least one sensor module. The pipeline inspection tool mentioned can be adjusted to move in the pipeline along the axial direction of the pipeline, preferably at a speed of about 0.1-4 meters per second. It is understood that the principles and teachings of the present disclosure can be used to detect and classify cracks. In particular, it is possible to simultaneously detect and classify longitudinal, axial, and helical cracks. It is understood that, in the context of this document, the term "crack detection" includes determining the presence of cracks based on the data obtained. It is noted that, in the context of this document, the term "crack classification" includes determining the type of crack (including size, direction) based on the data obtained. It is further explained that, according to the embodiments disclosed herein, horizontally polarized shear waves (also called “horizontal shear waves” or “SH waves”) are used, and are referred to herein as “shear wave(s). That is, particles in the lattice of a material under investigation are disturbed to oscillate in a plane parallel to the surface of the material under investigation, for example, the surface of the pipeline wall, while the disturbance propagates as a wave in a direction perpendicular to said plane. Furthermore, although the disclosed exemplary embodiments utilize EMAT technology, those skilled in the art will recognize that the teachings of the present disclosure are not limited to such technology. That is, any (future) generator capable of generating shear waves in (gas) pipelines is suitable for implementing the measurement protocol disclosed herein. Furthermore, the teachings of the present disclosure are not limited to examining pipelines that transport water, oil, or gas over long or short distances, but may be applied to other applications where metallic pipes are used, including drilling wells. Brief description of the attached maps The present invention has been described with reference to exemplary embodiments thereof, and reference is made accordingly to the drawings in which: Figure A1 shows an example visualization of EMAT; Figure A2 illustrates a coordinate system that is adapted in other exemplary embodiments disclosed herein. Figure B2 shows an example of a circumferential crack in a pipeline. Figure C2 shows an example of an axial crack in a pipeline. Figure D2 shows an example of a peripheral crack and a crack colony of peripheral cracks in a pipeline. Figure E2 shows an example of an axial crack and a cluster of axial cracks in a pipeline. Figure F2 shows an example of a spiral crack in a pipeline. Figures A3 and B3 relate to the first embodiment disclosed herein. Figures A4 and B4 relate to the second embodiment disclosed herein. Figures C4 and D4 correspond to an image of the emitted shear waves polarized in different directions. Figure 5 schematically shows a pipeline inspection tool moving through a pipeline at a certain speed. Description and description with details It is understood that for simplicity and clarity of illustration, reference numerals may be repeated throughout the figures to indicate corresponding or similar steps or components, as appropriate. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be apparent to those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. Furthermore, this description is not to be construed as limiting the scope of the embodiments described herein, but rather as merely describing the implementation of various embodiments described herein. Furthermore, it is noted that references to similar features may be indicated by different reference numerals in different figures disclosed herein. Figure 1 shows a material 101 that is the subject of the study. The material 101 may be a conductive material and / or a ferromagnetic material. According to the embodiments disclosed herein, the material 101 may be a material from which a pipeline wall is typically made, such as metal, steel, carbon steel, or iron. Figure 1 shows most of the major components of an exemplary electromagnetic acoustic transducer (EMAT) 102 in proximity to but not in contact with material 101. Generally, an EMAT 102 includes at least one electric coil 104 and at least one magnetic source 103. In the example of Figure 1, the magnetic source 103 includes a single permanent magnet having a south pole A103 and a north pole B103. Alternatively, the magnetic source 103 may include, for example, an electromagnet. In addition, Figure 1 shows two helical electric coils 104, although one skilled in the art will recognize that an EMAT may have more or less coils and other types of coils, for example, a coil having a helical or zigzag pattern depending on the particular application. The coils 104 are typically RF coils through which a pulsed or smooth oscillating AC current is transmitted. According to the present invention, the ultrasonic waves are preferably in the range of about 20 kHz to about 50 kHz, preferably in the range of about 0.2 kHz to about 20 kHz, even more preferably in the range of 0.5 kHz to about 5 kHz. Although Figure 1 shows a 102EMAT having a single permanent magnet, one skilled in the art will recognize that an EMAT may include additional permanent magnets in an adjacent portion, for example a sequence of six magnets with alternating magnetic pole directions. Alternatively, the 102EMAT may include multiple electromagnets. Furthermore, one skilled in the art will recognize that, depending on the particular application, different types of waves may be generated using different combinations of coils and magnetic sources. For example, an EMAT may generate different types of ultrasound waves, including shear waves, surface waves such as so-called Rayleigh waves, and guided waves such as so-called Lamb waves. In accordance with the present invention, EMATs are designed to generate shear waves. EMATs may be used to generate ultrasound waves in conductive and / or ferromagnetic materials such as pipelines made of carbon steel. The advantage of using EMATs to generate ultrasound is that EMATs do not require a coupling medium, e.g., a liquid. EMATs therefore allow the inspection of liquid and gas pipelines. In contrast, when using e.g. piezoelectric ultrasound transducers to generate ultrasound, physical contact (often through a liquid layer) of the transducer with the material under investigation is generally required. Referring to FIG. 1 , if the material 101 is a conductive material, the generation of a shear wave 105 in the material 101 may rely on the following: An EMAT is brought close to the surface A101 of the material 101. An RF current is sent through coils 104, which induces eddy currents in the material 101 at and near the surface A101. The eddy current electrons experience a Lorentz force due to the magnetic field from the magnetic source 103. This results in a magnetic field direction that is substantially perpendicular to the surface A101. At a macroscopic level, particles at and near the surface A101 begin to oscillate in the direction B105 (positive and negative y directions), thereby causing the surrounding particles to begin to oscillate in the direction B105 in the bulk. In this way, a deflection is created in the lattice which propagates as an elastic wave 105 through the conductive material 101, for example, in the direction A105 (negative x direction). Detection of the ultrasonic wave 105 may be achieved using a reverse process. For example, the generated ultrasonic wave may be propagated to a nearby area within a second and receive an EMAT (not shown), which induces eddy currents and thus an induced current that the EMAT receives. Alternatively, the first emitting EMAT is also the receiving EMAT. For example, the detected ultrasonic wave may be a reflection from a defect in the material 101 or a reflection from a wall of the material 101. The ultrasonic wave 105 will interact with defects in the conductive material 101 , for example, cracks 106 . Thus, analysis of the received ultrasonic wave can indicate the presence of defects in the conductive material 101 . In the case of material 101 being a ferromagnetic material, ultrasonic waves are generated via a magnetic mechanism. That is, an RF current is sent through coils 104, causing magnetic contraction at the ultrasonic frequency in material 101. This generates an ultrasonic wave 105 through the bulk of material 101. Detection of the ultrasonic wave 105 can be achieved using an inverse process. Ferromagnetic materials are usually also conductive. Steel is an example of a conductive ferromagnetic material. The skilled person will recognize that the generation of ultrasonic waves in such materials usually results in the generation of an enhanced signal. Referring now to Figures A2, B2 and C2. Figure A2 schematically shows a pipeline 201 with a diameter D, a wall thickness t and an outer boundary 202, in which a circumferential direction and an axial direction are shown. The pipeline 201 has an inner wall A203 and an outer wall B203. The directions will be referred to in the embodiments shown herein with respect to the aforementioned coordinate system. Figures B2 and C2 show a cross-section of a pipeline 203, where the pipeline 203 has an inner wall A203 and an outer wall B203. Figure B2 shows an example of a circumferential crack 204 in a plane A204 aligned in the circumferential direction. Figure C2 shows an example of an axial crack 204' in a plane 204'A aligned in the axial direction. It is noted that pipelines often exhibit axial cracks, while welded joints within the pipeline may exhibit circumferential cracks. Referring to Figure D-F2, a pipeline 203 is shown. Figure 2D shows another example of a circumferential crack 204. Such cracks are commonly found in welded joints. Furthermore, circumferential cracks are commonly observed in bundles of multiple cracks with a circumferential orientation 204-1. Figure 2E shows another example of an axial crack 204'. Axial cracks are commonly found in pipeline materials and may start at the outer boundary of the pipeline and penetrate to a certain depth. Furthermore, such cracks are commonly observed in multiple sets of axial cracks 204-2. Figure 2F shows a 204” spiral welded pipe and illustrates another type of crack that is sometimes found in pipelines. This type of crack is known as a spiral crack. A spiral crack propagates in the axial direction while changing direction in the circumferential direction. Spiral cracks can occur in pipes formed by spiral welds. Such pipes are known as spiral pipes or spiral welded pipes. Reference is made to Figures 3A and 3B, which relate to the detection and classification of cracks in pipeline 308. A first emitting EMAT (not shown) such as 101EMAT as described in FIG. 1 is positioned within the pipeline 308 such that a first shear wave 304 polarized in a plane 301 parallel to the plane of interest has an area of interest A303. That is, the shear wave 304 is polarized in the direction B304. The shear wave 304 propagates in the direction A304 toward the plane of interest, forming an area of interest A303. In the present case, the area of interest A303 includes a crack 303 that is parallel to the plane of interest. Due to this orientation, the shear wave 304 will not interact with the crack 303 or will not interact to a large extent. The shear wave is further propagated and received by a first receiving EMAT such as 101EMAT as shown in FIG. 1. The first receiving EMAT is located in the plane 302. Accordingly, a non-destructive shear wave will be measured. The plates 301 and 302 may be spaced apart by a distance d1, which may be in the range of 2 cm to 250 cm and preferably in the range of about 5 cm to 50 cm. As will be explained in more detail later, by examining the anisotropy of the received waves, the 303 crack can be identified and classified. Hence, the presence of the crack as well as information about the crack size and the crack direction (and therefore the type of crack, e.g. axial crack, longitudinal crack or spiral crack) can be determined. A second emitting EMAT (not shown) such as 101EMAT as described in FIG. 1 is located within the pipeline 308 such that it generates a second shear wave 307 polarized in a plane 305 parallel to the plane of interest which includes an area of interest A303. That is, the shear wave 307 is polarized in the direction B307. The shear wave 307 propagates in the direction A307 towards the plane of interest which constitutes the area of interest A303. Depending on the orientation of the crack 303, the shear wave 307 will interact with the crack 303, for example by converting (partially) into other wave modes. The damped shear wave is further propagated and received by a second receiving EMAT such as 101EMAT as shown in FIG. 1. The second receiving EMAT is located in the plane 306. Accordingly, a damped shear wave will be measurable. The plates 305 and 306 may be spaced apart by a distance d2 which may be in the range of 2 cm to 250 cm, preferably between 5 and 50 cm. In the present example, crack 303 is a circumferential crack, and plates 301 and 302 are spaced apart in the axial direction relative to each other, while plates 305 and 306 are spaced apart in the circumferential direction relative to each other. Additionally, the first shear wave 304 can be generated first, followed by the second shear wave 307. However, the first and second shear waves may also be generated substantially simultaneously, as long as interference can be avoided. Finally, it was noted that the sample visualization measurement protocol according to Figures A-B3 is very sensitive to the detection and classification of only cracks (of all types, e.g. circumferential, axial, helical), while it is not sensitive to other pipeline defects, such as delaminations. Reference is made to Figures 4A and 4B, which also relate to the detection and classification of cracks in pipeline 308. Accordingly, a first emitting EMAT such as EMAT 101 shown in FIG. 1 is located within a pipeline 308 such that a first shear wave 403 is generated polarized in a plane 401 parallel to the plane of interest including a region of interest A303. That is, the shear wave 403 is polarized in the direction B403. The shear wave 403 propagates in the direction A403 toward the plane of interest, which forms the region of interest A303. In the present case, the region of interest A303 includes a crack 303 that is parallel to the plane of interest. Due to this orientation, the shear wave 403 will not interact with the crack 303 or will interact to a lesser extent. The shear wave is further propagated, reflected off the outer wall 404 of the pipeline 308, and received as a reflected signal by a first receiving EMAT (not shown) such as the EMAT 101 described in FIG. 1. The first receiving EMAT is also located on the plate 401. Accordingly, a shear wave that is substantially indeterminate will be measured. Alternatively, the reflected signal may be received by the first emitting EMAT. A second emitting EMAT, such as an EMAT 101 shown in FIG. 1, is located within the pipeline 308 such that a second shear wave 403' is generated, polarized in the plane 401 parallel to the plane of interest having the area of interest 303A. That is, the shear wave 403' is polarized in the direction 403B'. The shear wave 403' propagates in the direction 403A' towards the plane of interest, which forms the area of interest 303A'. In the present case, the area of interest A304 comprises a crack 303 that is oriented parallel to the plane of interest. Given this orientation, the shear wave 403' will interact with the crack 303, for example by (partially) converting to other wave modes. The damped shear wave is further propagated, reflected at the outer wall 404 of the pipeline 308, further damped due to further interaction with the crack 303, and finally received as a reflected signal by a first EMAT receiver (not shown) such as EMAT 101 described in Figure 1. The first EMAT receiver is also located on the plate 401. Accordingly, a substantially damped shear wave will be measured.Alternatively, the reflected signal may be received by the first emitting EMAT. In the present example, crack 303 is a circumferential crack and plates 401 and 402 are spaced apart in the circumferential direction. Therefore, shear waves 403 and 403' propagate in a direction perpendicular to the wall of the pipeline 404. Additionally, the first shear wave 403 can be generated first, followed by the second shear wave 403'. However, the first and second shear waves may also be generated substantially simultaneously. It is also noted that the measurement protocol according to this exemplary embodiment may use only one EMAT to generate and receive the first shear wave 403 and the second shear wave 403'. In this case, the EMAT changes its spatial orientation after generating the first shear wave 403. For example, the EMAT is preferably rotated by an angle of about 90 degrees (vertical). Smaller or larger angles may also be used, as will be explained later with reference to Figures C4 and D4 of the present disclosure. The two received shear waves as obtained according to the exemplary embodiments of Figures A-B3 or Figures A4-B4 may be analyzed to determine whether the region of interest 303A contains a crack. In addition, if a crack is actually present, the type of crack may also be determined. Accordingly, by comparing the received shear waves, the presence of cracks can be determined. More specifically, if cracks are found, the cracks can be classified by size and direction. The analysis can be performed by calculating the wave attenuation anisotropy factor ("WAAF"). For example, such an analysis may be obtained by taking the difference in the measured amplitudes of the received waves. Alternatively, the WAAF can be calculated by dividing the amplitude of the first received wave by the second received wave. In addition, the skilled person will recognize that, in general, other wave characteristics (e.g., frequency, wavelength, phase) may be used to calculate the WAAF. In the following, an example of WAAF calculations is discussed, in which WAAF is calculated as the ratio of the measured amplitudes of the first and second received shear waves. For example, in the position of Figures A-B3, the first shear wave 304 is polarized in the direction B304, which is parallel to the direction of the crack 303. Here, the crack 303 is a circumferential crack. As previously discussed, the first wave 304 is not damped or at least damped by such a defect. Therefore, the attenuation of wave A from the first wave 304 detected by EMAT on page 302 is small. Conversely, the second shear wave 307 is polarized in a direction perpendicular to the direction of the said crack, and as explained above, interacts with the crack 303. Therefore, the attenuation of wave B from the second wave 307 detected by EMAT on page 306 is large. Therefore, the ratio as WAAF may be relatively small, for example, much smaller than 1. If there is no crack in the investigated area A303, the WAAF will be equal to or close to 1. Furthermore, the skilled person will recognize that if crack 303 is in fact an axial crack, the attenuation of wave A is relatively large compared to the attenuation of wave B, and a WAAF much larger than 1 is obtained. Furthermore, the larger the absolute value of WAAF, the larger the crack size.Therefore, the measurement protocol as shown in the exemplary embodiment of Figures A-B3 is simultaneously sensitive to all types of cracks. The same principles apply to the measurement protocol of Figures A-B4. Here, the first shear wave 403 is polarized in the direction B403, which is parallel to the crack direction of crack 303 (a circumferential crack). As discussed earlier, the wave is not damped or at least damped by such a defect. The attenuation of wave A' in the first wave 403, detected by EMAT on page 401, is therefore small. Conversely, the second shear wave 403' is polarized in a direction perpendicular to the said crack direction and interacts with crack 303, as explained above. The attenuation of wave B' of the second wave 403', detected by EMAT on page 306, is therefore large. The ratio as WAAF may be much smaller than 1. If there is no crack in the investigated area 303A, the WAAF will be equal to or close to 1. Furthermore, the skilled person will recognize that if crack 303 is in fact an axial crack, the attenuation of wave A' is relatively large compared to the attenuation of wave B' and a WAAF much larger than 1 is obtained. Furthermore, the larger the absolute value of WAAF, the larger the crack size.Therefore, the measurement protocol as described in accordance with the exemplary embodiment of Figures A-B4 is simultaneously sensitive to all types of cracks. Therefore, the above indicates that some WAAF provides the user with reliable information regarding crack detection and classification. Furthermore, it is noted that the same teachings also provide for the detection of helical cracks, even if these cracks are close to 45 degrees. In that case, the wave amplitude ratio as WAAF may be equal to or close to 1, but the attenuation of waves A and B or A' and B' is not small. On the other hand, if the EMATs are oriented at an angle to each other (thus not circumferentially or axially aligned, but oriented in the range of 20 degrees to 70 degrees, preferably in the range of 30 degrees to 60 degrees) a WAAF as calculated in the similar manner discussed above is relatively small, if the first emitted shear wave is polarized substantially parallel to the helical crack, while the second emitted shear wave is polarized substantially perpendicular to the helical crack. It is also noted that in the above examples the terms "small" and "large" are used with respect to wave attenuation. However, the skilled person will understand that such terms are relative to the amplitude of the initial wave emitted from the shear waves, or the situation where the wave experiences minimal attenuation due to the absence of defects. Furthermore, the inventors of the present disclosure have found that the WAAF calculated based on the measured shear waves according to the examples of Figures A-B3 or A-B4 is a very sensitive criterion for crack detection, while it is not sensitive to other pipeline defects, such as laminations inside the pipeline or coating that has separated from the pipeline wall. Therefore, the WAAF is related to reliable information about the presence and type of cracks in pipelines. As discussed above, a WAAF is a sensitive tool for simultaneously detecting different types of cracks, such as axial cracks, circumferential cracks, and spiral cracks. For example, if the A303 inspection area contains an axial crack, the WAAF will be much larger than 1. This means that a first shear wave is used that is essentially parallel to the desired crack direction and a second shear wave is generated at an angle to the desired crack orientation, preferably about 90 degrees (perpendicular). It is also noted that pipelines often exhibit axial cracks, while welded joints in the pipeline may exhibit circumferential cracks. Therefore, these types of cracks are considered to be the most relevant crack types. In addition, the above disclosed examples assume the first and second emitted waves are oriented substantially perpendicular to each other. However, one skilled in the art may appreciate that the first and second emitted waves may be polarized at an angle other than about 90 degrees relative to each other. This is illustrated in Figures C4 and D4. Accordingly, two shear waves are shown emitted in direction 408, where a first shear wave is polarized in direction A407 and a second shear wave is polarized in direction B407. Here, the first shear wave is polarized in plane 405, which is parallel to plane 406 (e.g., a plane having a slit that is parallel to plane 406). In the present example, planes 405 and 406 are parallel to the xy planes. The second shear wave is polarized in plane 409 perpendicular to plane 405 and further forms an angle with said plane 405 as shown in Figure C4. For clarity, shear waves in the xy plane are shown in Figure B4. The angle α will generally be at least about 10 degrees. Preferably, the angle α is greater than about 30 degrees.Preferably, the angle α is greater than about 45 degrees. However, preferably, the angle α is about 90 degrees. Furthermore, it is possible to use more emitted waves, such as the third and fourth waves. All waves can be polarized in a different direction. For example, in the case of 3 emitted waves, the first and second waves can be polarized as shown in Figures C4 and D4. The third wave can be polarized in the same plane as the first and second emitted waves, but at a different angle from α, for example α2. In another preferred embodiment, three waves with an angle of about 60 degrees are used. Thus, all cracks can be analyzed using WAAF. However, it can be seen that the use of 2 emitted waves that are substantially perpendicular to each other is more preferred. Referring to Figure 5, a pipeline inspection tool 601 is shown in a pipeline 602 with a diameter D, a wall thickness t and an inner wall A602. The pipeline 602 may be a pipeline with a diameter of about 5 cm to about 5 m, preferably about 8 cm to about 1.5 m and a thickness t of about 1 to about 100 mm, preferably about 2 mm to about 60 mm, even more preferably about 5 mm to about 30 mm. However, the skilled person will appreciate that the diameter D and the wall thickness t may be smaller or larger. Furthermore, the pipeline may be a short-distance pipeline (pipelines of a few 100 m such as loading or lifting pipes, e.g. as used offshore pipelines) or a long-distance pipeline (pipelines of kilometers in length). The instrument 601 includes a sensor module 603 that includes a plurality of EMATs, such as an EMAT 102 illustrated in FIG. 1 . Each EMAT is configured to generate ultrasonic waves in the pipeline 602 in accordance with any of the teachings described above. Preferably, the sensor module 603 includes a sufficient number of EMATs such that the pipeline 602 may be adequately measured. Alternatively, the sensor module 603 includes at least one EMAT that scans the pipeline circumferentially. However, such a scanning configuration acquires data at a much slower rate. Therefore, such a scanning configuration may be used to inspect pipelines over short distances. The sensor module 603 is capable of measuring wall coverage of at least about 45% in a passage, preferably 80% or more, even more preferably about 90% or more, even more preferably about 95% or more, and preferably about 100%. The tool 601 includes guiding means 605, such as disks, wheels, brushes, or electromagnetic guiding means, such that the tool 601 may scan the pipeline for cracks while moving in a direction 609 (axial direction, here: the z direction is positive). Additionally, the device 601 includes one or more processing units 606 for processing data from the sensor module 603 and a data storage unit 606' for at least storing processed data, although unprocessed data may also be stored. The device 601 may include cooling means 607 to prevent the one or more processing units 606 from overheating. One or more processor units 606 are configured to perform anisotropy analysis of the measured signals using a WAAF computational algorithm. The processor units 606 may also employ noise reduction algorithms. Furthermore, it is understood that the one or more processor units 606 and the data storage 606' may not be integrated into the instrument 601, but may be off-board elements. That is, the instrument 601 may be connected to the off-board processor and data storage, for example, via a suitable data cable. In particular, such an embodiment may be useful in the inspection of pipelines with small spacings. The instrument 601 may be powered by one or more power supply units 608 , such as batteries, so that, for example, the sensor module 603 is supplied with sufficient power during execution. During operation, the tool 601 moves along the inner walls of the pipeline 602 in the direction 609 at a relatively high constant speed, preferably about 0.1 m to about 4 m / s. However, one skilled in the art will recognize that the tool 601 may move at faster speeds (preferably about 5 m / s to about 20 m / s) or slower speeds (preferably about 0.01 m / s to about 0.09 m / s). The speed of the tool 601 may depend on the type of application. That is, the speed of the tool 601 for short pipelines may be about 100 m / s in 10 hours. The speed of the tool 601 for long-distance pipelines may be much higher, preferably about 0.1 m / s to about 10 m / s. The speed of the tool 601 may be adjusted using a speed control unit 610. In addition, the distance traveled by the instrument 601 can be measured using the odometer 611. The RF signal transmitted through the electrical coils is preferably in the range of 0.5 MHz to about 5 MHz. The RF signals may be applied for a period of about 100 ns to about 300 ns, although shorter (e.g., about 50 ns) or longer periods may also be possible, but not more than about 1 µs. In addition, the RF pulse repetition is preferably provided at a frequency of about 100 Hz to about 2 kHz. However, one skilled in the art will recognize that such parameters of the sensor module 603 may be adapted to the scan rate of the instrument 601, such that the entire pipeline 602 can be inspected for cracks. By describing the exemplary embodiments, it can be seen that the specific embodiments above are illustrative, and that variations in these embodiments can be introduced without departing from the spirit of the disclosure or the scope of the appended claims.
Claims
1. A method for detecting and classifying cracks in a pipeline, the method comprising the steps of: emitting a first shear wave along a region of inspection, the first shear wave being polarized in a first direction; receiving the first shear wave; emitting a second shear wave along the region of inspection, the second shear wave being polarized in a second direction at a minimal angle of about 10° different from the first direction, preferably at an angle of about 30° or more; receiving the second shear wave; examining the anisotropy of the first and second received shear waves by comparing at least one wave property of said first and second received shear waves for detecting and classifying cracks in the region of inspection.
2. The method of claim 1, wherein the first shear wave is emitted using a first emitting EMAT, wherein the first shear wave is received using a first receiving EMAT, wherein the second shear wave is emitted using a second emitting EMAT, and wherein the second shear wave is received using a second receiving EMAT.
3. The method according to any one of claims 1 or 2, wherein the first and second emitted shear waves are emitted in a direction substantially orthogonal to an inner wall surface of the pipeline.
4. The method according to any one of claims 2 or 3, wherein the first receiving EMAT is the same EMAT as the first emitting EMAT, and / or wherein the second receiving EMAT is the same EMAT as the second emitting EMAT.
5. The method according to any one of claims 2 or 3, wherein the first and second emitting EMAT, and the first and second receiving EMAT are all the same EMAT, and wherein the EMAT is rotated after the first shear wave is received, such that the second shear wave can be emitted.
6. The method according to any one of claims 1 or 2, wherein the first shear wave is emitted in an axial direction ( of the pipeline, and the second shear wave is emitted in a direction substantially circumferential to a wall of the pipeline.
7. The method according to any one of the preceding claims, wherein the first direction is substantially parallel to an axial direction of the pipeline, and wherein the second direction is substantially parallel to the circumferential direction of the pipeline.
8. The method according to any one of the preceding claims, wherein the step of examining the anisotropy of the first and second received shear waves includes the computation of a wave attenuation anisotropy factor.
9. The method according to any one of the preceding claims, wherein the first and second emitted shear waves have a frequency between about 0.5 and 5 MHz, and preferably are applied for a period of 100 ns to 300 ns, preferably with a pulse repetition at a frequency within 100 Hz to 2 kHz.
10. The method according to any one of the preceding claims, wherein the second direction is substantially orthogonal to the first direction.
11. The method according to any one of the preceding claims, wherein the pipeline has a diameter of 8 cm to 1.5 m, and a wall thickness of 5 mm to 30 mm.
12. An apparatus for detecting and classifying cracks in a pipeline, the apparatus comprising: a first emitting EMAT for emitting a first shear wave along a region of inspection, the first shear wave being polarized in a first direction; a first receiving EMAT, for receiving the first shear wave; a second emitting EMAT, for emitting a second shear wave along the region of inspection, the second shear wave being polarized in a second direction at a minimal angle of about 10° different from the first direction, preferably at an angle of about 30° or more; a second receiving EMAT, for receiving the second shear wave; an on-board or off-board processor unit for processing data from the first and second receiving EMATs, including examining the anisotropy of the first and second received shear waves by comparing at least one wave property of said first and second received shear wave for detecting and classifying cracks in the region of inspection.
13. The apparatus of claim 12, wherein the apparatus is adapted to carry out the method according to any of the claims 1-11.
14. A pipeline inspection tool comprising: a pipeline vehicle; a sensor module mountable on the pipeline vehicle, comprising at least one apparatus according to any one of claims 12-13; at least one power source unit, for supplying energy to at least the sensor module.
15. The pipeline inspection tool of claim 14, wherein the pipeline inspection tool further comprises guiding means (605) such that the pipeline inspection may move in the pipeline along an axial direction of the pipeline, at a speed of about 0.1-4 meter per second.