The invention relates to a method for detecting a crack in a pipeline from an inside of the pipeline, wherein, with the aid of at least one ultrasonic transmitter in the pipeline, successively ultrasonic pulses can be transmitted in a direction of an inner wall of the pipeline and wherein, with the aid of at least one ultrasonic receiver in the pipeline, reflections of the ultrasonic pulses on the pipeline are received.
The invention further relates to an assembly of a pipeline and a system for detecting a crack in the pipeline from an inside of the pipeline wherein the system is provided with a carriage which is operatively transported inside the pipeline in a longitudinal direction of the pipeline coinciding with a driving direction of the carriage and wherein the system is further provided with at least one ultrasonic transmitter and at least one ultrasonic receiver mounted on the carriage. In addition, the invention relates to a system of the assembly.
Such a method, assembly and system are known per se.
In pipelines such as for instance gas pipelines, the problem of cracking can occur. Such cracking has recently been observed in pipelines which had been rolled up before being laid. These pipelines were, in addition, provided with zinc anodes attached on the pipeline on an outside of the pipeline by means of welding in order to prevent oxidation of the pipeline. Now it appears that particularly in areas of the pipeline where the pipeline is provided with the anode, cracking can take place. These cracks particularly extend from an outer wall of the pipeline in radial direction to an inner wall of the pipeline. In addition, these cracks particularly extend in tangential direction of the pipeline.
It is of the utmost importance that these cracks in such gas lines can be detected quickly and accurately so that repair can be done. Because these pipelines are usually underground or on a seabed, it is not practicable to carry out an inspection from an outside of the pipeline. A drawback of the known methods, assemblies and systems for detecting cracks in a pipeline from an inside of the pipeline is that this detection takes up very much time. With the known detections, the ultrasonic transmitter and the ultrasonic receiver are moved in contact with and along an inner wall of the pipeline in order to thus scan the wall of the pipeline. This scanning movement takes up very much time.
The invention contemplates providing a method whereby cracks in a pipeline can quickly and adequately be detected from an inside of the pipeline.
To this end, the method according to the invention is characterized in that the ultrasonic transmitter and the ultrasonic receiver are mutually separated at a distance from each other, while the ultrasonic transmitter and the ultrasonic receiver are moved together along the inner wall in tangential direction of the pipeline and at a distance from the inner wall for scanning the pipeline, while the pipeline is filled with a liquid such as water for obtaining an immersion between the ultrasonic transmitter, the ultrasonic receiver and the inner wall of the pipeline for the purpose of scanning, while the presence of a crack is detected on the basis of points in time at which reflections of the successive ultrasonic pulses are received.
Because the pipeline is filled with water for obtaining an immersion between the ultrasonic transmitter, the ultrasonic receiver and the inner wall of the pipeline, a scanning movement can be carried out relatively fast.
When such a scanning movement is carried out, for instance the point in time at which a reflection of an inner wall is detected and a reflection of an outer wall is detected is registered. Further, it is the case that a diffraction occurs on the edges of a crack, if any. Any diffraction, which is in fact a reflection of an ultrasonic pulse, can also be detected. The point in time at which these reflections occur can also be registered. If, therefore, in addition to the expected reflections on the inner wall and the outer wall, other reflections occur, this is a strong indication of cracking. If, in addition to the reflections on the inner and outer wall, two additional reflections are detected, these will often indicate a starting point and an end point of a crack, viewed in radial direction of a wall of the pipeline. In the case of cracking from an outside of the pipeline, as indicated hereinabove, no separate reflection can be detected of the origin of the crack since it coincides with the outer wall of the pipeline which already generates a reflection. What can be detected then is a reflection of an end point of the crack, viewed in radial direction. The point in time at which this reflection is registered with respect to the reflections of the inner wall and/or the outer wall is a measure for a position of the end of such a crack. In particular, these cracks extending from an outer wall of the pipeline in radial direction to an inner wall of the pipeline can thus be detected. More generally, other cracks in the interior of the wall of the pipeline, which cracks do not extend to the outer wall and/or to the inner wall, can thus be detected as well.
It particularly holds true that the ultrasonic transmitter and the ultrasonic receiver are separated from each other in a longitudinal direction of the pipeline for detecting cracks of which at least a part extends in a tangential direction of the pipe. Here, it preferably holds true that the beam width of a wave transmitted by the ultrasonic transmitter in a direction in which the ultrasonic transmitter and the ultrasonic receiver are separated from each other is larger than a beam width in a direction perpendicular to the direction in which the ultrasonic transmitter and the ultrasonic receiver are separated from each other. Thus, in tangential direction of the pipeline, a scanning movement can be carried out whereby a high resolution is obtained in the tangential direction for determining the starting point and the end point of a crack extending in tangential direction (and in radial direction as described hereinabove).
This scanning movement in tangential direction can be carried out relatively fast due to the use of water so that there is no direct contact between the ultrasonic transmitter and the ultrasonic receiver on the one hand and the inner wall of the pipeline on the other hand. Further, it preferably holds true that the ultrasonic transmitter and the ultrasonic receiver are also moved in a longitudinal direction of the pipeline. The movement in radial direction and the movement in longitudinal direction can be carried out alternately. However, preferably these movements are carried out simultaneously. The result is that the ultrasonic transmitter and the ultrasonic receiver move along a helix extending in the longitudinal direction of the pipeline. Here, it particularly holds true that a width of a transmitted ultrasonic pulse near the inner wall of the pipeline in a direction from the ultrasonic transmitter to the ultrasonic receiver is larger than the distance between neighboring positions in which the ultrasonic transmitter and the ultrasonic receiver are located when they always take up a same tangential position during scanning. In the case that the ultrasonic transmitter and the ultrasonic receiver move along the helix, this in fact means that a beam width of a transmitted ultrasonic pulse near the inner wall of a pipeline in a direction from the ultrasonic transmitter to the ultrasonic receiver is larger than the pitch of the helix. In successive rotations, then overlap will occur of successively scanned areas of the pipeline.
It particularly holds true that the ultrasonic transmitter and the ultrasonic receiver are transported in the pipeline at a relatively high transport speed to predetermined areas where cracks are expected, while, during scanning of the areas, the ultrasonic transmitter and the ultrasonic receiver are moved in the longitudinal direction of the pipeline at an average scanning speed which is lower than the transport speed. Here, these areas can be determined by the positions of the anodes. Because the cracking takes place near the anodes, thus just areas where the cracking can be expected can be scanned. The result is that that the pipeline can be analyzed for cracking at a still higher speed. It particularly holds true that use is made of a carriage which is transported inside the pipeline in a longitudinal direction of the pipeline, which carriage is provided with a rotor which is rotated about a rotational axis extending in the longitudinal direction of the pipeline, while the ultrasonic transmitter and the ultrasonic receiver are mounted on the rotor. Here, it preferably holds true that further a first ultrasonic transmitter/receiver is mounted on the rotor whereby, with the aid of the first ultrasonic transmitter/receiver, ultrasonic pulses are transmitted in a radial direction of the pipeline and where, on the basis of reflections on the pipeline of the ultrasonic pulses transmitted by the first ultrasonic transmitter/receiver, which reflections are received with the first ultrasonic transmitter/receiver, it is determined whether the rotational axis is in a center of the pipeline. It further preferably holds true in that case that, on the basis of reflections on the pipeline of the ultrasonic pulses transmitted by the first ultrasonic transmitter/receiver, which reflections are received with the first ultrasonic transmitter/receiver, it is checked whether an area is scanned where an anode is present by detecting the presence of welds whereby the anode is attached on the pipeline.
The invention will now be explained in more detail with reference to the drawing, in which:
a shows an image of a pipeline according to
b shows a top plan view of the anode of the pipeline according to
c shows a view of the anode of the pipeline according to
a shows a cross section of in a longitudinal direction of a pipeline of a rotor of a carriage according to
b shows a possible receiving signal obtained with the apparatus according to
a shows a cross section in radial direction of the pipeline of a rotor of the carriage according to
b schematically shows a possible receiving signal;
c schematically shows a number of successive receiving signals obtained on the basis of successive transmitted ultrasonic pulses;
d shows a graphic representation which can be obtained on the basis of the signals according to
a shows a cross section in a tangential direction of the pipeline of an alternative embodiment of a carriage according to
b shows a number of successive receiving signals which can be obtained on the basis of successive transmitted ultrasonic pulses with the aid of the apparatus according to
In
In
In order to be able to detect the cracks, use is made of a system 20 as shown in
As
With the aid of the assembly described up to this point, the following method can be carried out.
With the aid of the ultrasonic transmitter, successive ultrasonic pulses are performed. In this example, the ultrasonic transmitter and the ultrasonic receiver are separated from each other in the driving direction V of the carriage, that is, in this example in a longitudinal direction A of the pipeline.
It will be clear that, on the basis of the points in time at which the reflections of an ultrasonic pulse are received, the presence of a crack can be detected since, in
Because the rotor 26 rotates, the ultrasonic transmitter and the ultrasonic receiver will be moved at a distance from the inner wall and in tangential direction of the pipeline for scanning the inner wall. This means that, at the moment that a next ultrasonic pulse is transmitted, the rotor has rotated over an angle Δφ (see
It particularly holds true that the beam width of a wave transmitted by the ultrasonic transmitter in a direction in which the ultrasonic transmitter and the ultrasonic receiver are separated from each other is larger than a beam width in a direction perpendicular to the direction in which the ultrasonic transmitter and the ultrasonic receiver are separated from each other. In the present example, this means that a beam width of a pulse transmitted by the ultrasonic transmitter in a longitudinal direction of the pipeline is larger than a width of the beam in tangential direction of the pipeline. In other words, it holds true in this example that a beam width of a wave transmitted by the ultrasonic transmitter in a driving direction of the carriage is larger than the beam width perpendicular to the driving direction of the carriage.
The result is that, in this example, the length of the crack in tangential direction as well as the depth of the crack can accurately be determined. The length of the crack in tangential direction is determined by the number of successive times that a crack is detected when the ultrasonic transmitter successively transmits the pulses. As said, then the number of times times Δφ is an indication of the length of the crack in tangential direction. The length of the crack in radial direction can be determined on the basis of the points in time mentioned.
In
Now the carriage, and thereby the ultrasonic transmitter and the ultrasonic receiver, is also moved in a longitudinal direction of the pipeline. This may, for instance, be carried out by having the carriage form a seal with an inside of the pipeline. By now generating pressure on one side of the carriage, for instance with the aid of the water, which pressure is larger than the pressure on the other side of the carriage, the carriage will start to drive in the driving direction under the influence of the pressure difference. In this example, the rotation of the rotor and the driving of the carriage in the driving direction take place simultaneously so that the ultrasonic transmitter and the ultrasonic receiver are moved together along a helix extending in the longitudinal direction of the pipe. Here, it particularly holds true that a width of a transmitted ultrasonic pulse near the inner wall of the pipeline in a direction from the ultrasonic transmitter to the ultrasonic receiver is larger than the distance between neighboring positions in which the ultrasonic transmitter and the ultrasonic receiver are located when they always take up the same tangential position during scanning. In other words: in this example, it holds true that a width of a transmitted ultrasonic pulse near the inner wall of the pipeline in a direction from the ultrasonic transmitter to the ultrasonic receiver is larger than the pitch of the helix. The result is that the area that is scanned with the aid of a rotating movement of the rotor partly overlaps with the area that is scanned by a next rotating movement of the rotor. In this manner, one knows for sure that the complete relevant part of the pipeline can be scanned.
Further, it particularly holds true that, with the aid of the carriage, the ultrasonic transmitter and the ultrasonic receiver can be transported in the pipeline at a relatively high transport speed to predetermined areas where cracks are expected, while, during scanning of the respective areas, the ultrasonic transmitter and the ultrasonic receiver are moved in the longitudinal direction of the pipeline at an average scanning speed which is lower than the transport speed. In this example, this average scanning speed is the pitch of the helix divided by the time needed to let the rotor rotate over 360°. In this example, the areas are determined by the positions of the anodes. It is thus possible to move the carriage at a relatively high speed to an area where an anode is present. This is exactly the area where a crack can be expected. Once the carriage has arrived in the area, its speed in the longitudinal direction of the pipeline is reduced so that it propagates in the longitudinal direction at a speed equal to the transport speed.
As discussed hereinabove, it holds true that the size and the position of at least a part of the crack in radial direction of the pipeline can be determined on the basis of the points in time mentioned. Here, it holds true that the point in time of the reflection on the inner wall can be taken as a reference point in time, while the points in time of the other reflections are determined with respect to the reference point in time for further processing. It is also possible that the point in time of the reflection on the outer wall is taken as a reference point in time, while the points in time of the other reflections are determined with respect to the reference point in time for further processing. All this has been discussed with reference to
It further holds true that the position and/or the size of at least a part of the crack in tangential and/or longitudinal direction of the pipeline is determined on the basis of momentary positions of the ultrasonic transmitter and the ultrasonic receiver in the pipeline in which they are located inside the pipeline when the ultrasonic reflections of the crack are received. In the foregoing, it has been set forth that, particularly in tangential direction, the length of the crack can be determined accurately given the beam widths used. In this example, the length and position of a crack in the longitudinal direction of a pipeline can be determined with a resolution no larger than the beam width in the longitudinal direction or the pitch D of the helix (the largest determines the resolution).
The signal processing means 36 may for instance be provided with a screen for delivering an image as shown in
It particularly holds true in this example that, on the rotor, further a first ultrasonic transmitter/receiver 44 is mounted whereby, with the aid of the first ultrasonic transmitter/receiver 44, ultrasonic pulses can be transmitted in radial direction of the pipeline while, on the basis of reflections, on the pipeline of the ultrasonic pulses transmitted by the first ultrasonic transmitter/receiver, which reflections were received with the first ultrasonic transmitter/receiver 44, it is determined whether the rotational axis is in the center of the pipeline. In this example, the first ultrasonic transmitter/receiver 44 is a zero-degree scanner known per se. The frequency at which the pulses are transmitted by the ultrasonic transmitter/receiver 44 may, for instance, be equal to but also smaller than the frequency at which pulses are transmitted with the aid of the ultrasonic transmitter 30. If the rotational axis of the rotor is in the center of the pipeline, the period of time after transmitting a pulse until a reflection on the inner wall is received will not vary with the rotating movement of the rotor. If the rotational axis is not in the center of the pipeline, then this point in time, which is the measure for the distance from the ultrasonic transmitter/receiver 44 to the inner wall 14, will vary according to a sinus, the period of the sinus coinciding with one rotating movement of the rotor.
In this example, the signal processing means 36 are arranged for being able to determine whether the rotational axis is in the center of the pipeline on the basis of reflections on the pipeline of the ultrasonic pulses transmitted by the first ultrasonic transmitter/receiver 44, which reflections are received with the first ultrasonic transmitter/receiver 44. If this point in time varies, then an alarm can be delivered by the signal processing means 36. It further holds true in this example that signal processing means are arranged for being able to check, on the basis of reflections on the pipeline of the ultrasonic pulses transmitted by the first ultrasonic transmitter/receiver, which reflections are received with the first ultrasonic transmitter/receiver, whether an area is scanned in which an anode is present by detecting the presence of welds whereby the anode is attached on the pipeline. To this end, with the aid of the signal processing means, for instance an image can be generated as shown in
In
The invention is by no means limited to the above-described embodiments. For instance, as already briefly indicated hereinabove, the ultrasonic transmitter and the ultrasonic receiver may also be separated from each other in a tangential direction of the rotor. All this is shown in
Number | Date | Country | Kind |
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1026538 | Jul 2004 | NL | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NL2005/000467 | 7/1/2005 | WO | 00 | 1/9/2008 |