WO2008010712A1

WO2008010712A1 - System for measuring on a wall of a pipeline with phased array

Info

Publication number: WO2008010712A1
Application number: PCT/NL2007/050354
Authority: WO
Inventors: Reinier Antonius Parie; Thomas Theodorus Arnoldus Van Overbeek; Herman Jozef Moolenaar; Paul André de Jong
Original assignee: Röntgen Technische Dienst B.V.
Priority date: 2006-07-17
Filing date: 2007-07-17
Publication date: 2008-01-24
Also published as: NL1032186C2

Abstract

A system for performing measurements, with the aid of at least one ultrasonic beam, on a wall of a pipeline from a position in the pipeline. The system is provided with a measuring body, which measuring body is provided with a transmitting and receiving device for transmitting ultrasonic beams and for receiving reflections of the beams on the wall of the pipeline. The transmitting and receiving device comprises at least one element array, of which each element is arranged for transmitting an ultrasonic wave. The elements of the element array are arranged with respect to each other such that in combination they extend at least distributed over a path, this path extending at least for a part in tangential direction around an axial axis of the transport device extending in axial direction. The system is further provided with a control device for controlling the elements according to a phased array for forming the beams.

Description

Title: System for measuring on a wall of a pipeline with phased array

This invention relates to a system for performing measurements, with the aid of at least one ultrasonic beam, on a wall of a pipeline from a position in the pipeline, wherein the system is provided with a transport device which is arranged to be positioned in the pipeline, which transport device is provided with a measuring body, which measuring body is provided with a transmitting and receiving device for transmitting ultrasonic beams and for receiving reflections of the beams on the wall of the pipeline, wherein the transport device, in use, comprises a radial, axial and tangential direction which coincides with a radial, axial and tangential direction of the pipeline and wherein the at least one beam has a propagation direction with a radial component in the direction of the wall of the pipeline.

Further, the invention relates to a method for performing measurements, with the aid of ultrasonic beams, on a wall of a pipeline from a position in the pipeline utilizing such a system.

Such a system and such a method are known per se and are used for tracing defects in metal parts of the pipe wall of a pipeline, such as cracks and corrosion. Normally, the transmitting and receiving device has a limited number of transmitting and receiving elements in the form of a limited number of transmitting and receiving transducers, a transducer being capable of transmitting a beam and typically also of receiving ultrasonic waves. Here, the system can utilize techniques to obtain information on the basis of received reflections (including diffractions) of the ultrasonic beam on the wall. These reflections can be measured with the same transducers as those with which the ultrasonic waves were transmitted. Also, the transmitting and receiving device can utilize the time-of- flight diffraction (TOFD) and/or tandem technique known per se. Such techniques are described inter alia in the European norm ENV 583-6, January 2000 (TOFD) and "Ultrasonic Testing of Materials", J. & H. Krautkramer, ISBN 3-540-07716-2, New York, 1977 (Tandem). Here, responses are mostly received with other transducers than the transducers with which the beams were transmitted. The transport device is typically designed to be transported through the pipeline for scanning the pipeline. In order to be able to perform measurements in as many directions as possible, the measuring body is often designed to be rotatable relative to the pipeline, i.e. rotatable relative to the remainder of the transport device.

In use, the transport device is introduced into the pipeline. Then, the measuring body is rotated, so that each of the transducers transmits the beam each time in a modified direction. Thus, a ring-shaped zone is scanned. After scanning of the zone, the transport device can be transported further in the pipeline for subsequently scanning a next ring-shaped zone. Also, transportation through the pipeline and rotation can be carried out simultaneously, so that the pipe wall is scanned according to a helix.

A drawback of the known transport device is that measuring through rotation of the measuring body in the pipeline takes relatively much time.

The necessity of rotating the measuring body can constitute a considerable limitation on the speed of movement of the transport device in axial direction, since the rotation speed is limited by technical possibilities and/or a measuring speed.

Also, rotation requires much energy, which can present problems especially if the system involves a battery-supplied apparatus.

To reduce the necessity for rotation, according to the invention, the system is characterized in that the transmitting and receiving device comprises at least one element array, of which each element is arranged for transmitting an ultrasonic wave, wherein the elements of the element array are arranged with respect to each other such that in combination they extend at least distributed over a path, this path extending at least for a part in tangential direction around an axial axis of the transport device extending in axial direction, wherein the system is further provided with a control device for controlling the transmitting and receiving device, wherein the control device is arranged for each time causing ultrasonic waves to be transmitted with the aid of at least one selected subset of elements of a set of elements formed by the element array, wherein the subset comprises a plurality of elements, and wherein the control device is further arranged for controlling the elements of the subset as a phased array for forming and directing the at least one beam with the aid of the elements of the subset, the beam being formed from the ultrasonic waves, and for selecting mutually different subsets for generating mutually different beams.

The method according to the invention has the characterizing feature of each time transmitting at least one beam with the aid of at least one selected subset of elements, wherein different subsets are selected for transmitting different beams and wherein measurements on the wall are performed with the aid of the beams.

Due to a plurality of elements transmitting waves simultaneously for forming the beam, elements can be used that are smaller than the transducers in the known systems. Because the desired direction of the beam can be chosen by means of selection of the subset of elements, and moreover by the manner of controlling the phased array formed by these selected elements, in many cases rotation of the measuring body relative to the housing can be at least partly or wholly avoided. In this way, therefore, embodiments of the system are possible whereby the measuring body in use does not rotate relative to the pipeline or relative to the remainder of the transport device, which can be beneficial to the accuracy of the measurements. Furthermore, the phased array of elements affords the possibility of transmitting and receiving ultrasound beams in a direction which in unequal to the tangential direction, and also of compensating for divergence that arises upon formation of the beam as a result of possible mutually different orientation directions of each of the selected elements. A preferred embodiment of the system according to the invention has the feature that the control device is arranged, in use, to control successively mutually different subsets of elements of the at least one element array for successively transmitting mutually different beams for scanning the wall.

Thus, spread in time, different beams can be generated for scanning the wall. Also, a preferred embodiment has as a feature that the control device is arranged for controlling the elements such that simultaneously a plurality of different beams are generated, with each of the beams being formed using one subset of elements. Thus, simultaneously, a plurality of beams can be generated. This can be done in particular in combination with the above-discussed preferred embodiment, so that then simultaneously and consecutively, different beams are generated.

Furthermore, an embodiment of the system according to the invention has the feature that the subset of elements comprises at least three elements. If the subset controlled as a phased array comprises at least three elements which are separated with respect to each other for instance in tangential direction, the formation of a beam diverging in tangential direction can be avoided. The fact is that this diverging beam may be formed because the elements of the beam-forming subset have a mutually different position. With the use of the three elements, the phased array can be controlled for causing the ultrasonic beam generated by the elements of the subset to substantially converge in tangential direction. Also, it is possible that the phased array can be controlled such that the beam has an at least virtually flat wave front.

An advanced embodiment of the system according to the invention has the feature that the transmitting and receiving device comprises a plurality of element arrays. Here, it is possible that the control device is furthermore arranged for causing, each time with the aid of a modified subset of elements of each of the element arrays, at least one ultrasonic beam to be transmitted per element array. In this way, also, multiple beams can be formed simultaneously and the measuring speed can be raised further.

It is possible that the transmitting and receiving device is provided with at least one element array of a first type which makes use of pulse echo. Also, the transmitting and receiving device may be provided with at least two element arrays of a second type which are separated from each other at a distance and which utilize time-of-flight diffraction (TOFD) or tandem technique. An advantage of this is that a better imaging can be created, since strong properties of both types of measurement can be exploited.

The at least one element array can be one-dimensional, in which case it is possible to have the beam converge in a direction perpendicular to the array with the aid of an acoustic lens and in a direction of the array through a chosen phase control. The at least one element array may also be of two- dimensional design, with the dimensions of the element array extending in the tangential and axial directions. In that case, the beam can, without acoustic lens, converge in axial and tangential direction through an appropriate phase control of the subset of elements if this subset is also two- dimensional. A preferred embodiment of the system according to the invention has the feature that the control device is reprogrammable. An advantage of this is that properties of the beam can be determined as desired, optionally beforehand.

Also, an embodiment of the system according to the invention has the feature that the elements are provided with piezo crystals for generating the ultrasonic waves. It has been found that piezo crystals are very suitable for generating ultrasonic waves.

Especially if piezo crystals are used for generating the ultrasonic waves, it is preferred that the control device is further provided with electronic components, for instance components which jointly form a microprocessor, for controlling the transmitting and receiving device. Electronic components are in many case simply programmable, and in many cases even reprogrammable. Further, they are particularly suitable for controlling the piezo crystals, since piezo crystals are eminently suitable for converting an electrical signal into an acoustic vibration.

A preferred embodiment of the system according to the invention is characterized in that the at least one element array extends over a loop closed upon itself. When the at least one element array extends over a loop closed upon itself, a scan at least substantially closed upon itself can be performed on the wall without necessitating displacement of a part of the transport device in axial or tangential direction during the scan. Moreover, the loop closed upon itself affords possibilities of a compact design of the transport device. Preferably, such a loop is contained within a plane perpendicular to the axial direction. More particularly, the path extends over a circle in tangential direction. Such a setup has the advantage that use can be made of the rotation symmetry that is often present in a pipeline. If the element array extends over a circle, the elements of the element array have substantially a same distance to the inner and/or outer surface of the pipeline. Below, the invention will be further elucidated with reference to the drawing, wherein:

Fig. 1 shows in perspective view a first embodiment of a system according to the invention;

Fig. 2 shows a cross section of the transport device of the system from Fig. 1;

Figs. 3a-c show detailed views of the portion delineated in Fig. 2 with a broken line;

Fig. 3d shows a cross section of the transport device from Fig. 1;

Fig. 4a shows in perspective view a second embodiment of a system according to the invention; Fig. 4b shows in perspective view a third embodiment of a system according to the invention;

Fig. 5 shows a detailed view of the portion delineated in Fig. 4a with a broken line; Fig. 6 shows in perspective view a fourth embodiment of a system according to the invention; and

Fig. 7 shows a detailed view of the longitudinal section of the transport device adjacent the arrows PP'.

Fig. 1 shows a first embodiment of a system S according to the invention. The system S comprises a transport device 1 which is shown in perspective view in Fig. 1. The transport device 1 is provided with a housing 2 which, at least in this first embodiment, comprises a cylinder-shaped measuring body 4 and at the two ends 6, 8 thereof a frame, in this example in the form of a suspension 10. In the embodiment shown in Fig. 1, the suspensions 10 are so arranged and mounted on the measuring body 4 that the measuring body 4 can be introduced in a centered manner into a pipeline 13 with an axial axis A. To that end, each of the suspensions 10 is provided with three arms 11, with each of the arms 11 having at an end remote from an axial axis A' of the cylinder-shaped body 4 a little wheel 12 and a springing element (not shown in the drawing) situated between the axial axis A' and the wheel 12. The axial axis A of the pipeline coincides in use, when the transport device 1 is in the pipeline 13 to be inspected, with the axial axis A' of the transport device 1. Further, a radial direction B' of the transport device 1 is defined to coincide with a radial direction B of the pipeline 13 when the transport device 1 is in the pipeline 13 (see Fig. 2). Also, a tangential direction C of the transport device 1 is defined as coinciding with a tangential direction C of the pipeline when the transport device 1 is in the pipeline (see Fig. 2). The three arms 11 are separated at an angular distance of approximately 120° with respect to each other by means of bent bars 14. Further, one suspension 10 at one end 6 is staggered approximately 60° with respect to the other suspension 10 at the other end 8. The suspension being arranged in this way allows the transport device 1 to move in axial direction of the pipeline 13 with a favorable speed of, for instance, 0.5 to 1 m/second, while the measuring body 4 remains properly centered.

The cylinder-shaped measuring body 4 is provided with a transmitting and receiving device 15 for transmitting ultrasonic beams and for receiving reflections of the beams on the wall. A reflection on the wall is understood to mean reflections on the inner wall 24 (see Fig. 3a), the outer wall 26 (see Fig. 3a) and/or reflections and/or diffractions in the wall. The transmitting and receiving device 15 comprises a number of elements 16 which in the first embodiment in combination all form one element array 18, in the form of a row 19 extending along a circle on and around the cylinder-shaped measuring body 4, as can also be seen in Fig. 1. It holds here that the elements of the element array are so arranged with respect to each other that in combination they extend distributed over a path, this path extending at least for a part in tangential direction around an axial axis of the transport device extending in axial direction. It holds furthermore that the path extends over a loop closed upon itself, in this example over a circle in tangential direction. Further, it holds in this example that the elements are arranged mutually at equal distances from each other in tangential direction. The number of elements 16 as shown in the drawing is only intended by way of illustration. The number of elements 16 depends on the number of measurements desired per length unit and hence varies per embodiment. The elements 16 are known per se and, at least in this embodiment, are arranged for transmitting and receiving ultrasonic waves. To this end, the elements are mostly provided with piezo crystal.

Further, the system S is provided with a control device 20, represented schematically in the drawing, for causing, with the aid of a subset of the element array 18, the ultrasonic waves to be transmitted, which waves form an ultrasonic beam. In this example, the control device is connected mechanically with the transport device 1. However, this is not requisite; the control device may also be placed at a distance from the transport device 1, for instance outside the pipeline 13 to be inspected. In this first embodiment, the control device 20 is provided with electronic components, such as for instance an electronic microprocessor, electronic memory components, transistors, diodes and the like (not shown in the drawing). It is also possible, however, that optical components (not shown in the drawings either) form part of the control device 20.

Further, the control device in this embodiment is furthermore arranged for forwarding signals to signal processing means 21. Connection between the signal processing means 21 and the control device 20 may proceed via a cable, but may also be wireless. Fig. 2 shows a cross section of the transport device 1 from Fig. 1 adjacent the elements 16. The transport device 1 is in the pipeline 13 provided with a wall 23 having an inner and an outer surface 24, 26. In this first embodiment, each element 16 is arranged to transmit and to receive a wave. In this first embodiment, the transport device is designed such that the distance between the elements on the one hand and an axial axis A" of the transport device 1 on the other is always the same. In use, the axial axis of the transport device 1 coincides with an axial axis of the pipeline 13. Here, this means that in use a distance d from the elements 16 to the inner surface of the pipeline is at least virtually the same for each element 16. The elements 16 in this example form an element array 18. In this example, this is a one-dimensional element array 18. The elements of the element array 18 are positioned with respect to each other such that in combination they extend distributed over a path P which path P extends at least for a part in tangential direction around the axial axis A" of the transport device 1. In this example, the path P forms a circle. The relative positioning of the elements 16, as can be seen in Fig. 2, has as a consequence that a beam E that is formed by the ultrasonic waves transmitted by a subset D of elements of the set of elements formed by the element array 18, the elements of the subset D in this example being neighboring elements, will be a divergent beam Z, if no phase difference between waves transmitted by the elements 16 is present. To compensate for this divergence, however, the control device is arranged to control the subset of elements as a phased array, in this example a one-dimensional phased array. Furthermore, it is possible with the aid of the control device to control the subset for forming and directing the beam. In this example, the subset is provided with at least three elements 16. The cylinder-shaped measuring body 4 is further provided, at its circumference, with an acoustic lens (not shown in the drawing). In the first embodiment, the lens serves for focusing waves coming from the elements 16, so that the beam obtained converges in axial direction.

The operation of the system S is further explained with reference to Figs. 3a-c. Figs. 3a-c show on an enlarged scale the portion of Fig. 2 framed with the broken line I. A first step is shown in Fig. 3a. In the first step, the control device 20 causes a subset D of the element array to transmit a beam Z. The subset D of the element array 18 by means of which the beam is formed are the elements 16i-5 and here forms a one-dimensional subset which extends in tangential direction. The elements 16i-g in Fig. 3a each transmit waves and in this way form a beam whose propagation direction has virtually exclusively a radial component. The, control device 20 controls for instance the elements I61-I65 such that the phase of the elements I61, I65 leads the phase of the elements I62-4 and that the phase of the elements I62, I64 leads the phase of the element I63. In this way, a beam is obtained which converges in tangential direction. The beam also converges in axial direction by the use of an acoustic lens. In this example, the focus of the beam is thus directed at the inner surface 24, which is normally favorable for the performance of measurements on the wall of the pipeline 13. If desired, the focus of the beam Z may also be directed at a different location by controlling the elements with the aid of the control device in a manner differently phase-shifted with respect to each other. After transmitting of the beam and receiving of a response of this beam on the wall 23 by the transmitting and receiving device 15, the received response can be passed on via the control unit to the signal processing means 21, such as a computer or other calculating unit (not shown in the drawing). These signal processing means can be set up outside the pipeline 13. In this example, reflections of the beam on the wall are received with the aid of the same elements as those with which the beam was generated. However, this is not requisite. For instance, reflections could moreover be also received by neighboring elements of the elements with which the respective beam was transmitted. A second step is shown in Fig. 3b. In Fig. 3b it can be seen that thereupon in the same manner again a beam is formed. Now, however, it is the subset D' of the elements by means of which the beam Tl is formed, modified by the control device 20 to the elements I62-I66. As the control device 20 controls the elements I62-I66 such that the phase of these elements I62, 16β leads the phase of the elements I63-5 and the phase of the elements I63, I65 leads the phase of the element I64, the beam Tl diverging in tangential direction is formed. The beam also converges in axial direction by the use of an acoustic lens. Because other elements are being used now, the beam is directed at a different location. Reflections of the beam Tl in this example are received with the aid of the elements 162-166- Here, also, reflections could moreover be also received by neighboring elements of the elements with which the respective beam was transmitted.

A third step is shown in Fig. 3c. In Fig. 3c, again a beam Z" is formed, but now by the subset D" which comprises the elements I63-7. Reflections of the beam Z" in this example are received with the aid of the elements I63- 16₇. Here, also, reflections could moreover be also received by neighboring elements of the elements with which the respective beam was transmitted.

In the above-mentioned manner, thus, each time the subset D, D', D", etc. of the element array by means of which the beam is formed, is modified. Thus, the inner surface adjacent the element array can be scanned without the measuring body 4 needing to be rotated relative to the suspension 10 (or, relative to the remainder of the transport device) or relative to the pipeline 13. Thus, in each case, a subset of the element array 18 is selected for forming a suitable beam for measuring on a particular zone of the wall of the pipeline 13. Thus a scan which is closed upon itself, in this example a ring-shaped scan, can be performed on the wall. Also, the transport device 1 can be transported in axial direction through the pipeline 13 for thus scanning the wall along a helical pattern.

It therefore holds in this example that the control device is arranged for controlling the elements of the element array such that alternately with different subsets of elements different beams are generated. It further holds here that mutually different subsets of elements of the element array are shifted with respect to each other in tangential direction for transmitting beams shifted with respect to each other in tangential direction. Thus, by consecutive beams transmitted with the aid of the element array a scan in tangential direction can be carried out. It preferably holds here that neighboring beams adjoin or partially overlap in the wall of the pipeline 13 so that the complete wall can be scanned. It may also be that the subset of Fig. 2b is not transmitted, in other words, that the subset in each case moves up in tangential direction by more than one element, while, for instance, the beams Z and Z" still adjoin or overlap in the wall. Also, the generated waves may be pulsed waves. The pulse repetition time of the beams transmitted with the aid of the element array can then have a value such that during the selection of a subset at least one pulse is transmitted.

In Fig. 3d it is shown that the control device 20 is furthermore arranged for controlling the elements of the element array such that simultaneously by a plurality of subsets Dl, D2, D3 and D4 of the elements, respectively, a plurality of different beams Zl, Z2, Z3 and Z4 are generated.

It is here assumed that the element array 18 in circumferential direction is provided with two hundred elements. In this example, in the first step, each of the subsets Dl, D2, D3 and D4 of the element array comprises five elements, respectively indicated by 16i-5, I651-55, lβioi-ios and 16i5i-i55. In the same manner as described above, the subset Dl is modified in the second step into the subset Dl' which comprises the elements I62-6, for forming the beam Zl'. In the second step, also the subset D2' is formed by the elements I652-56, the subset D3' is formed by elements I6102-106 and the subset D4' is formed by the elements 16₁52-i56- In subsequent steps, corresponding changes are carried out, so that the wall of the pipeline 13 adjacent the element array 18 is scanned. Thus, a scan which is closed upon itself, in this example a ring-shaped scan, can be performed on the wall in 50 steps. Also, the transport device 1 can be transported in axial direction through the pipeline 13 for thus performing such scans, which scans are shifted with respect to each other in axial direction and preferably adjoin or which scans partly overlap. In that example, four scans are then involved, each along a helix.

In Fig. 4a, a second embodiment of the system S is shown. The second embodiment substantially corresponds to the first embodiment. However, the second embodiment is not provided with an acoustic lens for converging the beam in axial direction. Further, the elements 16 in the second embodiment form a two-dimensional element array, which is possible in that the element array 18 has been designed in the form of seven juxtaposed rows 19i.-7 of elements which have been positioned at a distance from each other in axial direction. Here, also, it holds that the elements of the element array are arranged with respect to each other such that in combination they extend distributed over a path which path extends at least for a part in tangential direction around an axial axis A' of the transport device extending in axial direction. Here, the path again involves a partial surface of an outside of the measuring body where the elements are arranged.

The operation of the second embodiment is described with reference to Fig. 5. The operation of the second embodiment of the transport device 1 corresponds to the operation of the first embodiment. The control device 20 effects for instance the following. For instance for obtaining a convergent or flat beam, the subset D comprises the elements 16ij, with i=l-5 and j=l-7. Here, the subset is hence a two-dimensional subset which extends in tangential and axial direction. The phase of the elements lβy and I65J leads the phase of the elements 162,j and 164,j (j=l-7). Also, the phases of the elements I62_J and I64J in turn lead the phase of the elements I63_J (J=I-T). Further, the phase of the elements 16i,i and 16i,7 leads the phase of the elements 16i,2 and 16i,β (i=l-5). The phase of the elements 16i,2 and 16i,β in turn leads the phase of the elements 161,3 and 161,5 (i=l-5). Also, the phase of 16i,3 and 16i,5 leads the phase of the elements 16i,4 (i=l-5). Thus, the beam formed with the aid of the two-dimensional subset of the two-dimensional element array is a beam converging in tangential and axial direction. In this example, reflections of the beam on the wall are received with the aid of the same elements as those with which the beam was generated. However, this is not requisite. For instance, reflections could moreover be also received by neighboring elements of the elements with which the respective beam was transmitted.

Because the selected subset of elements here also comprises elements spread in two dimensions, a two-dimensional phased array is involved. If in each case the selected subset were to comprise a number of element arrays spread over one dimension, as in the example of Fig. 2, then a plurality of one-dimensional phased arrays would be involved. Hence, with a two- dimensional element array also one-dimensional subsets can be selected, in principle in any one-dimensional direction.

As described with reference to Fig. 3d for the first embodiment, in this embodiment, also, it is possible that with the control device simultaneously by a plurality of subsets of the elements a plurality of different beams are generated. These simultaneously transmitted beams are then shifted relative to each other in tangential direction. Also, simultaneously beams can be formed which are shifted relative to each other in axial direction and are possibly shifted relative to each other also in tangential direction. A first beam is then for instance formed by the elements lβy with j=l,2,3 and a second beam is then for instance formed by IGr.j with j=5,6,7, where for instance i=i' when the beams are not staggered relative to each other in tangential direction. Preferably, the element array is then provided with (many) more than 7 elements in tangential direction.

In Fig. 4b, a third embodiment of the system S is shown. The system according to Fig. 4b corresponds to a large extent with the system according to Fig. 4a. The difference is that in the system according to Fig. 4b the two- dimensional element array 18, viewed in axial direction, comprises many more than seven elements 16ij. The control device 20 is arranged to control a subset of elements of the element array as a two-dimensional phased array for generating at least one beam and for determining the tangential and axial direction of the at least one beam as well as for determining the convergence or divergence of the at least one beam. Such a subset of elements comprises for instance nine elements which are arranged with respect to each other in a manner spread in axial and tangential direction. In Fig. 4b such a possible subset D of three by three elements is shown. This subset D of elements can be controlled as a two-dimensional phased array with which, by varying the phase difference with which the respective elements are controlled, the tangential and axial direction of the beam can be determined. Also, in this way, the convergence or divergence of the respective beam can be determined. This is understood to encompass, besides a diverging or converging beam, a beam that does not diverge or converge, i.e. a pencil beam. The control device 20 is here furthermore arranged for controlling a plurality of subsets of elements for generating a plurality of such different beams. Thus, for instance, also a subset D' can be controlled as shown in Fig. 4b. Thus it is possible, when consecutively different subsets of elements are controlled, to consecutively generate beams having in each case a different tangential or axial direction. Thus, scanning can be done both in tangential and/or in axial direction. Also, it holds in this example that the control device is arranged for controlling a plurality of subset elements of the element array, so that a plurality of such beams are generated simultaneously. In the example, therefore, simultaneously in Fig. 4b two beams could be generated: the first beam with the aid of the subset D and the second beam with the aid of the subset D'. Naturally, also other subsets of elements can be controlled. Here, it is also conceivable that instead of a subset with 3x3 elements (three rows of elements which are staggered relative to each other in tangential direction x three rows of elements which are staggered relative to each other in axial direction), also, a different subset can be chosen, such as subsets with 4x4, 5x5, 6x6, 4x7, 7x4 elements. Such variants are each understood to fall within the framework of the invention.

Reflections of the beams can be received by the elements as discussed above. Naturally, with the system according to Fig. 4b, also a measurement on the wall of a pipeline can be carried out with the known Time -of- Flight Diffraction (TOFD) and/or tandem technique.

In Figs. 6 and 7, a fourth embodiment of the transport device is shown. The fourth embodiment, like the second embodiment, substantially corresponds to the first embodiment. In this embodiment, the cylinder- shaped measuring body 4 is provided with five element arrays 18 which are positioned spaced-apart in axial direction. The elements of the central element array I83 form a first type of element array, whose elements are arranged (in this example ordinarily directed), under the control of the control device 20, as a phased array to transmit, each time with the aid of a modified subset of the elements, a beam which has at least substantially a radial direction. Responses of the beam on the wall in this example are also received by the elements of the element array I83. A single element from the first-type element array is of a type that transmits a wave in radial direction. The operation may be as discussed with reference to Fig. 3.

The elements of an outermost element array 18i form a second type of element array whose elements are arranged (in this example ordinarily directed), under the control of the control device 20, as a phased array, to generate with different subsets of elements different beams which have at least substantially a radial and axial component. The axial component is in the direction of the element array I82 and is obtained through a choice of the type of element. The element array is here so directed that a normal N to the surface of a single element (which level coincides with the direction of a beam transmitted by one element) includes an angle with the axial axis which is equal to (90°-16.9°). A normal N to a surface of the elements to this end has a radial and axial component. The axial and radial component of the beam is thus determined by the type of element and the tangential component (including the absence thereof) of the beam by the mutual phase differences with which the elements of the subset are controlled. Any convergence in tangential direction can again be determined by the phase control and any convergence in axial and radial direction (i.e. in the direction of said normal N) by a possible acoustic lens. A single element from the outer element array 181 is of a type which transmits a wave which has at least substantially a radial component and an axial component (in the direction of the element array I82). The direction of the beam is such that the beam after refraction on the inner surface 24 of the pipeline 13 includes for instance an angle between 20° and 70°, preferably an angle between 30° and 60° and more preferably between 40° and 50° with a radial direction of the transport device. In this example, the angle after refraction is approximately 45°. Responses of the beam on the wall in this example are also received by the elements of the element array 18i.

The elements of an outer element array I85 form a second type of element array whose elements are arranged (in this example ordinarily directed), under control of the control device 20, as a phased array, to generate with different subsets of elements different beams which have at least substantially a radial and axial component, all this as discussed for the element array I81. The axial component is in the direction of the element array I84 and again is obtained through a choice of the type of element. The radial and axial component of the beam is determined by the type of element and the tangential component, if any, of the beam by the mutual phase differences with which the elements of the subset are controlled. A single element from the outer element array I85 is of a type which transmits a wave which has at least substantially a radial component and axial component (in the direction of the element array I84). The element array is then directed such that a normal N to the surface of a single element (which level coincides with the direction of a beam transmitted by one element) includes an angle with the axial axis which is equal to (90°- 16.9°). The direction of the beam is such that the beam after refraction on the inner surface 24 of the pipeline 13 includes for instance an angle between 20° and 70°, preferably an angle between 30° and 60° and more preferably between 40° and 50° with a radial direction of the transport device. In this example, the angle after refraction is approximately 45°. Responses of the beam on the wall in this example are also received by the elements of the element array 18g. The elements of the central and the two outermost element arrays 18i, I83 and I85 are provided with elements for both transmitting the ultrasonic waves and receiving ultrasonic waves.

The intermediate element arrays I82 and I84 are used for carrying out so-called time-of-flight diffraction (TOFD), which is described in more detail inter alia in Dutch patent application 1026538 (not published). The element array is then so directed that a normal N' to the surface of a single element (which level coincides with the direction of a beam transmitted by one element) includes an angle with the axial axis which is equal to (90°-11.2°). In this embodiment, by an element of the element array I82, a beam is transmitted of which a response on the wall of the pipeline 13 is received with an associated element of the element array I84. Each of the elements of the receiving section is arranged and positioned for receiving ultrasonic beam coming from a corresponding element of the element array I82. Each of the elements of the receiving section is placed at some distance from the corresponding element of the transmitting section, which can be seen in Fig. 7 for a single element pair. In this example, a beam is transmitted in each case by one of the elements of the element array I82. Here, there is no beam generated with the aid of simultaneously transmitting of a subset of elements of the element array I82 according to a phased array, although it is possible. The beam to be generated can be formed as discussed with reference to Fig. 1 where the elements are then directed as shown for the element array I82 in Fig. 7 to obtain a beam in a direction with an axial component. For TOFD, however, the beam must diverge in the direction of the normal N' to the plane of an element, i.e. diverge in axial and radial direction, so that then the acoustic lens is omitted. Also, the beam may be formed as discussed with reference to Fig. 4, in which case the elements are then arranged and directed as shown in Fig. 4 and the elements are controlled in phase by the control device, such that a beam is obtained in the direction of the normal N', i.e. in a direction with a radial and axial component while the beam moreover diverges in the direction of the normal N', i.e. in axial and radial direction. In any case, if desired, a response of the beam can be received with a corresponding number of elements of the element array 184. Then, too, TOFD is involved. Entirely analogously as discussed for the element array I82, a beam can be transmitted with the element array I84 (by an element or by a subset) and a response of which is received with the element array I82.

The invention is not limited to the exemplary embodiments outlined. To prevent divergence of the beams in axial direction, it is possible, as for instance discussed with reference to Fig. 3, that each of the element arrays is provided with an acoustic lens. Such an acoustic lens can for instance run fully around the associated element array. If a two- dimensional element array is used as discussed with reference to Fig. 4, with a proper phase control a beam can be obtained which converges not only in tangential direction but also in axial direction, without making use of an acoustic lens.

By performing measurements at different angles, a better image of any cracks or defects present in the pipeline 13 can be obtained. If a beam is transmitted by the element array I81, then, with the aid of the element array I85 reflection of the beam on the outer wall 26 can be received. If such reflection proves not to be there, this is an indication of a fault at the outer wall 26. The reflection on this fault is then for instance received by element array I81. Also, a beam transmitted by the element array 18i can first reflect on the inner wall and then reflect on a fault in the wall so that the reflections are received by another element array 18n (n=2,3,4,5). What is involved then is a tandem technique, known per se. In this known tandem technique, however, the multihead rotated and use was made of transducers each generating a beam, instead of an element array (one- or two- dimensional) according to the invention. It is observed that by the word 'axis' in this description primarily an imaginary line is meant, which does not necessarily need to be embodied by a tangible body.

It will be clear to those skilled in the art that many variants on the embodiments of the invention shown here are possible. Thus, it is possible to provide an adjusted embodiment of the third embodiment in which each of the element arrays are provided with at least two rows, for instance three rows, to enable convergence in axial direction. What is then involved again is a two-dimensional phased array. In the examples where, with a subset of elements of an element array according to a phased array, a beam was transmitted, and with the same element array a response of the beam on the wall was received, the same subset of elements was used for receiving. However, the invention is not limited thereto. Thus, use can be made of a supplemental number of elements (which may or may not be of the same element array as the one with which the beam was transmitted) for receiving, or of other elements for receiving (which may or may not be of the same element array as the one with which the beam was transmitted). In this example, the control device is mechanically connected with the transport device. However, the control device can also be arranged outside the pipeline 13 and for instance be wired to the elements. Also, the connection between the signal processing means 21 and the control device 20 may be wired or wireless. Also, an element array may extend along a segment of a circle instead of a full circle. Also, the element array can extend along a loop closed upon itself that has a different shape, such as, for instance, a circle, oval, square, hexagon, etc.

Claims

1. A system for performing measurements, with the aid of at least one ultrasonic beam, on a wall of a pipeline (13) from a position in the pipeline (13), wherein the system is provided with a transport device (1) which is arranged to be positioned in the pipeline, which transport device is provided with a measuring body (4), which measuring body (4) is provided with a transmitting and receiving device (15) for transmitting ultrasonic beams and for receiving reflections of the beams on the wall of the pipeline, wherein the transport device, in use, comprises a radial, axial and tangential direction which coincides with a radial, axial and tangential direction of the pipeline and wherein the at least one beam has a propagation direction with a radial component in the direction of the wall of the pipeline, characterized in that the transmitting and receiving device (15) comprises at least one element array (18), of which each element (16) is arranged for transmitting an ultrasonic wave, wherein the elements (16) of the element array (18) are arranged with respect to each other such that in combination they extend at least distributed over a path, this path extending at least for a part in tangential direction around an axial axis of the transport device extending in axial direction, wherein the system is further provided with a control device (20) for controlling the transmitting and receiving device (15), wherein the control device is arranged for each time causing ultrasonic waves to be transmitted with the aid of at least one selected subset (D, D', D", Dl, D2, D3, D4) of elements of a set of elements (18, 16n) formed by the element array, wherein the subset comprises a plurality of elements, and wherein the control device (20) is further arranged for controlling the elements of the subset (D) as a phased array for forming and directing, with the aid of the elements (16) of the subset, the at least one beam (Z, TI, Z", Zl, Z2, Z3, Z4), which beam is formed from the ultrasonic waves, and for selecting mutually different subsets for generating mutually different beams.

2. A system according to claim 1, characterized in that the elements of a subset are neighboring elements.

3. A system according to claim 1 or 2, characterized in that the control device is arranged for controlling the elements of the element array, such that consecutively with different subsets of elements different beams are generated.

4. A system according to claim 1, 2 or 3, characterized in that the control device (20) is further arranged for controlling the elements of the element array, such that simultaneously by a plurality of subsets of the elements a plurality of different beams are generated.

5. A system according to any one of claims 3 or 4, characterized in that mutually different subsets of elements of the element array are shifted relative to each other in tangential direction for transmitting beams shifted relative to each other in tangential direction.

6. A system according to claim 4 or 5, characterized in that the control device effects, in use, that with consecutive beams transmitted with the aid of the element array a scan in tangential direction is carried out.

7. A system according to claim 6, characterized in that a plurality of and in particular all tangentially neighboring beams transmitted with the aid of the element array adjoin or overlap each other at least partly at the wall of the pipeline.

8. A system according to any one of the preceding claims, characterized in that the at least one subset comprises at least three elements (16, 16i,

16y).

9. A system according to any one of the preceding claims, characterized in that the transmitting and receiving device comprises a plurality of element arrays.

10. A system according to any one of the preceding claims, characterized in that the transmitting and receiving device comprises at least one first type element array which, in use, is controlled as a phased array for transmitting at least one first beam and for receiving reflections i of the at least one first beam on the wall, wherein in particular the direction of the at least first beam of the first type element array is directed at least substantially in radial direction.

11. A system according to any one of the preceding claims, characterized in that the transmitting and receiving device comprises at least one second type element array which, in use, is controlled as a phased array for transmitting at least one second beam and for receiving reflections of the at least one second beam on the wall, wherein the direction of the at least one second beam has at least substantially exclusively a radial and axial component.

12. A system according to claim 11, characterized in that the direction of the at least one beam includes an angle between 5° and 40°, preferably an angle between 10° and 30° and more preferably between 14° and 20° with a radial direction of the transport device.

13. A system according to claim 10, characterized in that the transmitting and receiving device comprises at least one first type element array and at least two second type element arrays, wherein the at least one first-type element array is situated between the at least two second type element arrays.

14. A system according to any one of the preceding claims, characterized in that the transmitting and receiving device comprises at least one third type element array for transmitting at least one third beam, wherein the direction of the at least one third beam has at least substantially a radial and axial component and wherein, in use, the third-type element array is possibly controlled as a phased array and wherein the elements furthermore form at least a fourth type element array which is separated in axial direction from the third type element arrays for receiving reflections of the at least one third beam.

15. A system according to claim 14, characterized in that the at least one third beam has a direction with an axial component in the direction of the fourth type element array and wherein preferably the direction of the beam includes an angle between 4° and 30°, more preferably an angle between 7° and 14° with a radial direction of the transport device.

16. A system according to claims 13 and 14, characterized in that the at least one first type element array is situated between respectively the at least one third type element array and the at least one fourth type element array, while preferably the at least one third type element array and the at least one fourth type element array are situated between the second type element arrays.

17. A system according to any one of the preceding claims, characterized in that the path extends along a segment of a circle in tangential direction.

18. A system according to any one of the preceding claims, characterized in that the path extends over a loop closed upon itself, more particularly over a circle in tangential direction, while preferably the elements are arranged at an equal distance with respect to each other in tangential direction.

19. A system according to any one of the preceding claims, characterized in that a number of the elements comprise elements adjoining each other and/or that all elements adjoin each other.

20. A system according to any one of the preceding claims, characterized in that the measuring body comprises a cylinder-shaped body, wherein the elements are arranged spread over the cylinder-shaped body.

21. A system according to any one of the preceding claims, characterized in that the elements of the at least one element array have at least substantially a same distance to the axial axis of the transport device, which axial axis in use coincides with the axial axis of the pipeline.

22. A system according to any one of the preceding claims, characterized in that a subset of elements extends at least in tangential direction.

23. A system according to claim 22, characterized in that elements of the subset are controllable, such that the beam formed with this subset converges at least in tangential direction.

24. A system according to claim 23, characterized in that the control device controls the subset, such that the beam formed converges at least in tangential direction.

25. A system according to any one of the preceding claims, characterized in that a phased array formed by the subset is of one-dimensional design and whose dimension extends in tangential direction.

26. A system according to claim 25, characterized in that elements of the one-dimensional subset are controllable, such that the beam formed with this subset converges in tangential direction.

27. A system according to claim 26, characterized in that the control device controls the subset, such that the beam formed converges in tangential direction.

28. A system according to any one of the preceding claims, characterized in that the element array is a one-dimensional element array extending in tangential direction.

29. A system according to any one of the preceding claims, characterized in that the measuring body is furthermore provided with at least one acoustic lens for converging the at least one beam in axial direction.

30. A system according to any one of the preceding claims 1-27 or 29, characterized in that a phased array formed by a subset is of two- dimensional design and whose dimensions extend in tangential and axial direction.

31. A system according to claim 30, characterized in that the elements of the two-dimensional subset are controllable, such that the beam formed with this subset converges in tangential and axial direction.

32. A system according to claim 31, characterized in that the control device controls the subset, such that the beam formed converges in tangential and axial direction.

33. A system according to any one of the preceding claims 1-27 or 29-32, characterized in that the element array is a two-dimensional element array extending in tangential and axial direction.

34. A system according to claim 33, characterized in that the control device is arranged for controlling a subset of elements of the element array as a two-dimensional phased array for generating at least one beam and for determining the tangential and axial direction of the at least one beam as well as for determining the convergence or divergence of the at least one beam, wherein the subset comprises elements which are arranged spread relative to each other in axial and tangential direction.

35. A system according to claim 33 or 34, characterized in that the control device is arranged for controlling a plurality of different subsets of the element array for generating a plurality of such different beams.

36. A system according to claim 35, characterized in that the control device is arranged for simultaneously controlling a plurality of subsets of elements of the element array so that a plurality of such different beams are generated simultaneously.

37. A system according to any one of the preceding claims, characterized in that the elements of the at least one subset are controllable by the control device, such that the at least one transmitted ultrasonic beam has an at least substantially flat wave front.

38. A system according to any one of the preceding claims, characterized in that the transport device is arranged for moving through the pipeline in axial direction of the pipeline.

39. A system according to any one of the preceding claims, characterized in that the control device is provided with electronic components for controlling the transmitting and receiving device.

40. A system according to any one of the preceding claims, characterized in that the control device is provided with optical components for controlling the transmitting and receiving device.

41. A system according to any one of the preceding claims, characterized in that the control device is of reprogrammable design.

42. A system according to any one of the preceding claims, characterized in that at least one of the elements is provided with piezo crystals for generating the at least one ultrasonic wave.

43. A system according to any one of the preceding claims, characterized in that the measuring body in use does not rotate relative to the remainder of the transport device.

44. A system according to any one of the preceding claims, characterized in that at least a part of the control device is mechanically connected with the transport device.

45. A system according to any one of the preceding claims, characterized in that at least a portion of the elements is further arranged for receiving the reflections of the at least one beam on the wall.

46. A system according to any one of the preceding claims 1-34 or 37-45, characterized in that the control device is arranged for controlling the elements, such that simultaneously a plurality of different beams are generated, while each of the beams has been formed with the aid of one subset.

47. A system according to any one of the preceding claims 1-34 or 37-46, characterized in that the control device is arranged, in use, to control successively mutually different subsets of elements of the at least one element array for successively transmitting mutually different beams for scanning the wall.

48. A system according to claim 47, characterized in that the control device is arranged, in use, to control in each case simultaneously a plurality of mutually different subsets of elements of the at least one element array for simultaneously transmitting mutually different beams in mutually different directions.

49. A system according to claim 48, characterized in that the control device is arranged, in use, to control successively mutually different pluralities of subsets of elements for successively transmitting mutually different pluralities of beams for scanning the wall.

50. A method for performing measurements, with the aid of ultrasonic beams, on a wall of a pipeline from a position in the pipeline utilizing a system according to any one of the preceding claims, wherein the method comprises transmitting in each case with the aid of at least one selected subset of elements at least one beam, wherein different subsets are selected for transmitting different beams and wherein with the aid of the beams measurements on the wall are performed.

51. A method according to claim 50, characterized in that the method comprises successively transmitting, with the aid of modified selected subsets of the elements, different ultrasonic beams for performing a scan of the wall of the pipeline.

52. A method according to claim 50 or 51, characterized in that scanning is performed such that a scanned portion of the wall forms a loop closed upon itself.

53. A method according to claim 50, 51, or 52, characterized in that the method comprises, in each case simultaneously with the aid of a plurality of selected subsets of elements, in each case simultaneously transmitting a plurality of mutually different ultrasonic beams, so that measurements are performed simultaneously on different parts of the wall of the pipeline.

54. A method according to claim 53, characterized in that by successively selecting different pluralities of subsets of elements, mutually different pluralities of ultrasonic beams are transmitted for scanning the pipeline.

55. A method according to claim 54, characterized in that the scan forms at least one loop closed upon itself and hence a circumferential scan on the wall.