MXPA97003099A

MXPA97003099A - Magnetic flow tube inspection device for analyzing anomalies in a tube wall

Info

Publication number: MXPA97003099A
Application number: MXPA/A/1997/003099A
Authority: MX
Inventors: Laursen Poul
Original assignee: Pipetronix Ltd
Priority date: 1996-08-22
Filing date: 1997-04-28
Publication date: 1998-02-01

Abstract

The present invention relates to an apparatus for analyzing anomalies in a pipe wall comprising: a body of generally cylindrical shape, means for supporting the body in relation to the pipe wall, means for driving the body through the pipe; means for providing electrical power to the body, means for storing data, a plurality of bars arranged circumferentially around the body, each bar mounted flexibly on the body to allow it to move radially inwardly and radially outwardly to provide clearance to the apparatus in case of that you find obstructions while traveling through the pipe, means mounted on the bars to generate and transmit a magnetic field through the portions of the pipe wall adjacent to the body, means mounted on the bars adjacent to the body to measure the loss of Magnetic flow caused by anomalies in the pipe wall, means to transmit the m issues of magnetic flux loss to the data storage means and a plurality of wheels mounted on the bars adjacent to the magnetic field generating means to support movement of the body against the pipe wall through the pipe, to reduce the wear of the magnetic field generating means and the magnetic flux loss measuring means

Description

APPARATUS FOR ANALYZING ANOMALIES IN A WALL OF PIPES FIELD OF THE INVENTION This invention relates generally to apparatuses known as "intelligent pigs" used as diagnostic tools in oily and gas pipelines and, more specifically, to pigs that use magnetic fields to diagnose defects and other anomalies in pipe walls.

BACKGROUND OF THE INVENTION In maintaining the structural integrity of a pipe, it is important to be able to detect and repair anomalies in the walls of the pipe. For current purposes, anomalies include defects such as cracks, pitting, corrosion and dents. In particular, it is important to be able to determine the location of the anomaly, the type of anomaly and the geography of the anomaly (ie its shape and size).

When you want to test the structural integrity of a pipe, a pig can be placed in the pipeline where it is pushed through the pipeline by the product in the line, such as oil or gas. The pig typically engages urethane "cups" near its near end to seal the ring between the pig and the wall of the pipe, thus preventing fluid in the pipeline from flowing through the ring. The pressure behind the pig increases to the point where the pig begins to move. The differential pressure created through the front and back of the cups keeps the pig moving on the line.

As the pig moves through the pipeline, it can collect data concerning anomalies in the wall of the pipe. If this information can be measured by the pig, store it and retrieve it later, it can then be analyzed to allow remedial action to be taken.

It is known to use a pig in combination with magnetic flux leakage (MFL) technology to detect defects in the walls of the pipe, the principle of the mfl is based on magnetizing the pipe wall and using sensors to measure the leakage field generated for anomalies in the material of the tube wall. For example, if there are no anomalies present, the magnetic field will be continuous and there will be no leakage to be detected. If there is an anomaly such as a crack, the magnetic field in the pipeline will be interrupted and the loose fields generated will provide useful information concerning the anomaly.

Although there are pigs, including pigs manufactured by the assignee of the present application, who do an adequate job in detecting and measuring anomalies in pipe walls, said pigs have limitations that may impact the quality of the measurements obtained. The main disadvantage with the pigs of the prior art is that they are not capable of generating sufficient magnetic power for transmission through relatively thick pipe walls. In any situation, the required magnetic field is proportional to the thickness of the tube wall; that is, the thicker the wall, the stronger the field must be to penetrate the wall. The pigs of the prior art are, in most cases, limited to pipe walls of approximately 12 mm (approximately 1 inch) in thickness since these pigs are not designed to generate the magnetic field required for thicker pipe walls.

Another limitation of the pigs of the prior art is the space (and therefore the number) of sensor elements that are mounted around the circumference of the pig. For example, if the distance between the sensor elements is 15 mm, as in the case of the pigs of the previous generation manufactured by the assignee of the present application, then a defect could be up to 12 mm in diameter and would not always be detected in the correct way The placement of the sensors in relation to the wall of the pipe also limits the depth of the defect that can be felt. The methods of the prior art for mounting the sensor element, the element that actually measures the magnetic field, places limitations on how close the sensor element can be placed in relation to the wall of the pipe. The above results in a signal-to-noise ratio less than optimal and, therefore, a less than optimal MFL reading. For example, a defect with less than 10% loss of thickness material typically can not be picked up with these sensors.

Yet another limitation of the prior art is the length of the pipe that the pigs can inspect. This limitation is dictated not only by the amount of data that the recording units can collect and the amount of battery available to keep the readings working, but also by the fact that the mechanical components wear out during a prolonged period of time. against the wall of the tube, the components that transmit the magnetic field to the wall of the pipe and the sensors themselves are in direct contact with the wall of the pipe and therefore tend to wear out over time.

Therefore, the need for a pig capable of detecting and diagnosing anomalies in relatively thick pipe walls and capable of achieving a higher level than previously achieved in the accuracy of measuring the magnetic flux leakage has been developed. in any size of pipe wall. A need has also been developed for a pig in which the components that generate the magnetic field and the components that measure the MFL are less prone to wear than the pigs of the prior art so that the pigs may be more suitable for durable applications. or a series of rapid tests without the need for re-supplies between tests.

SUMMARY OF THE INVENTION In a first aspect, the present invention provides an apparatus for analyzing anomalies in a pipe wall comprising: a body of generally cylindrical shape; means for supporting the body in relation to the wall of the pipe; means to propel the body through the pipeline; means for providing electrical energy to the body; means to store the data; means mounted on the body for generating and transmitting a magnetic field through portions of the wall of the pipe adjacent to the body; means for measuring magnetic flow leaks adjacent to the body caused by anomalies in the wall of the pipe; means for transmitting leakage measurements in the magnetic flux to the data storage means; and a plurality of wheels mounted on the body adjacent to the magnetic field generating means to rotate against the wall of the pipe as the body moves through the pipe to reduce wear of the magnetic field generating means and the means to measure the leakage in the magnetic flux.

The apparatus may further comprise a plurality of bars, each bar mounted flexibly on the body to allow the bar to move radially inwardly and radially outwardly to provide room for the apparatus in case it encounters obstacles as it travels to through the pipeline; and wherein the means for generating and transmitting a magnetic field to the wall of the pipe, the means for measuring the leakage of the magnetic flux and the wheels for turning are mounted on the bars.

The means for measuring leaks in the magnetic flux may comprise: a sensor body; at least one sensing element, which is capable of sensing the absolute magnetic field, contained within the sensing body; and wherein the sensor body is flexible so that it can follow the contour of the wall of the pipe as the apparatus moves through the pipe and thereby keep the sensor element in a substantially constant orientation with respect to the wall of the pipe.

The apparatus may further comprise non-ferromagnetic means, mounted on the upper surface of the sensor body, to reduce wear on the sensor body and to protect the sensor element from damage.

The wear reducing means and the sensor element can be mixed to form an integral unit. The wear reducing means may comprise a wear pad and at least one wear pad. The wear pad may have the shape to generally follow the contour of the pipe wall.

The body of the sensor can have the shape of a parallelogram in its cross section. The sensor body can be a one-piece polymer that is petrochemical resistant, temperature resistant in the range of 0 ° C to 80 ° C and can withstand pressures of up to about 3700 pounds per square inch. For example, the sensor body could be constructed of polyurethane.

The means for generating and transmitting a magnetic field to the pipe wall will comprise: a first brush containing steel placed on top of a first magnet at one end of each bar; a second brush with steel placed on top of a second magnet of the polarity opposite the first magnet on the other end of the bar; and where the top surfaces of the brushes come into closed con with the wall of the pipe at all times.

The brushes may comprise a plurality of steel cables contained and joined in a plastic resin and mounted on a steel shell. For example, the plastic resin can be polyurethane.

In another aspect, the invention provides an apparatus for analyzing anomalies in a wall of the pipe comprising: a first section of generally cylindrical shape containing means for providing electrical power to the apparatus; a second section of generally cylindrical shape for storing data collected by the apparatus; a third section is generally cylindrical having means for generating and transmitting a magnetic field through portions of the wall of the pipe adjacent to the third section and means for sensing magnetic flow leaks adjacent to the third section caused by anomalies in the wall of the pipe; a plurality of wheels mounted on the third section to rotate against the wall of the pipe as the apparatus moves through the pipe to prevent wear of the generating and transmitting means of the magnetic field and the sensing means of the leaks in the pipe. the magnetic flux; means for supporting the sections in relation to the wall of the pipe; means for driving the sections through the pipeline; means for transmitting measurements of magnetic flux leakage to data storage media; a plurality of wheels mounted on the third section adjacent to the generating means of the magnetic field to rotate against the wall of the pipe as the apparatus moves through the pipe to reduce the wear of the magnetic field generating means and the magnetic flux sensing means; means for supporting the sections in relation to the wall of the pipe; means for driving the sections through the pipeline; means for transmitting measurements of magnetic flux leakage to data storage media; a plurality of wheels mounted on the third section adjacent to the generating means of the magnetic field to rotate against the wall of the pipe as the apparatus moves through the pipe to reduce wear on the magnetic field generating means and the means for measuring leakage of the magnetic flux; and wherein the adjacent sections are connected by flexible links to allow movement of the apparatus through curves and restrictions in the pipeline. The sections can be arranged in any order.

BRIEF DESCRIPTION OF THE DUCTS For a better understanding of the present invention and to clearly show how it can be carried out, reference will now be made by way of example to the accompanying drawings, which show an apparatus according to the preferred example of the present invention and in which. Figure 1 is a diagrammatic illustration of an apparatus for analyzing anomalies in a pipe wall according to the preferred example of the present invention; Figure 2 is a diagram illustrating the principle of magnetic flux leakage as measured by the present invention; Figure 3 is a side view of the magnetizing section of the apparatus illustrated in Figure 1; Figure 4 is an axonometric view of the magnet unit of the apparatus illustrated in Figure 1; Figure 5 is a cross-sectional view, taken along line 5-5 of Figure 1, showing the arrangement of the wheels and brushes in the magnetizing section of the apparatus of Figure 1; Figure 6 is a cross-sectional view taken along line 6-6 in Figure 1 showing the arrangement of the magnet units and the sensors in the magnetizing section; Figure 7 is a elevational view of a sensor; Figure 8 is a side view, partially in section, of a sensor; Figure 9 is a bottom view, partly in section, of a sensor; Figure 10 is a front view, partly in section, of a sensor; Figure 11 is a terminal view of a sensor; Figure 12 is a side cross-sectional view of a brush taken along line 12-12 of Figure 11.

DETAILED DESCRIPTION OF EXEMPLARS PREDD ECTOS Referring now to Figure 1, an apparatus 10 for analyzing anomalies in pipe walls or a "pig" as they are commonly known, comprises a first section 12, a second section 14 and a third section 16. In the exemplary illustrated, the first section 12 contains the batteries or other means for providing electrical power to the apparatus. Annular seals 20 or "cups" as they are commonly known, are mounted around the circumference of the first section to seal the ring between the first section and the wall of the pipe. According to the above, the flow of the pipeline fluid such as natural gas or oil is blocked by the annular seal, which results in the propulsion of the pig through the pipeline.

The second section 14 has on it mounted means for magnetizing the wall of the pipe 21 and means for detecting the resulting leakage of the magnetic flux. These means are described in more detail below. The third section 16 contains the data acquisition system for the pig. The data concerning the analysis of anomalies in the wall of the pipeline can be transmitted from the sensors to the data acquisition system, stored and subsequently recovered for analysis when removing the pig from the pipeline.

The adjacent sections are connected by a flexible link 22 as a universal joint to allow movement of the pig through curves and obstacles in the pipe.

The order of the three sections in the pipeline is not important. The only requirement is that the annular seal 20 must be mounted on the section farthest downstream when the pig is placed in the pipe.

Furthermore, it is not essential that the apparatus be formed of three sections. In fact, it is possible to place the electrical means, the magnetizing means and the data acquisition system all in a single section. It may be preferred, however, to place these systems in separate sections when building a pig for use in relatively thick pipes since it may be a little more difficult to place all the systems of the above elements in a single section for said applications.

The wheels of the suspension 26 are mounted around the circumference and at opposite ends of each section to rotate against the wall of the pipe so as to stabilize the pig within the pipe and facilitate the movement of the pig through the pipe. Other means to stabilize the pig inside the pipeline are possible. For example, cups can be used to stabilize the pig. Also, it is not essential that the stabilizing means are mounted in each section. It is enough if stabilizer means are mounted in the section that is farther ahead and in the section that is closest when the pig is inserted in the pipe.

With reference now to Figures 2 through 4, the principle of the MFL uses brushes 42 reinforced with magnet 27 to magnetize the wall of the pipe 25. The sensors 48 are mounted between brush arrays to detect the leaky field generated by anomalies in the material of the pipe wall. If the wall of the pipe has no anomalies or defects, the magnetic flux is not affected and the sensor does not detect fields (as illustrated in the top diagram of Figure 2). If, however, an abnormality 29 is present, the field is affected and the sensor detects this free field and sends a signal back to the registration unit (as illustrated in the lower scheme of Figure 2).

The strength of the MFL signal that results from an anomaly is affected by many parameters, such as the magnetic force, the magnetization of the tube pairs, anomalies in the geometry, anomalies in the type, etc. The problem is that not all of these parameters are known and controlled, which makes it difficult to obtain a measure of the exact anomaly.

Referring now to Figures 3 and 4, the magnetizing section (the second section 14 in Figure 1) is constructed from a central body 30, which is supported by a plurality of suspension wheels 26 mounted near opposite ends of the body. the magnetizing section. These wheels support the entire magnetizing section against the wall of the pipe for movement of the section through the pipe. A plurality of arrays of suspended magnet units 34 are mounted on the central part of the section and around the circumference of the section. Each of the magnet unit arrangements is suspended on directional means 36, such as springs or the like, so that they can travel to the center of the pig where necessary, thus reducing the diameter of the pig and allowing the pig to pass through restrictions. and curves of the pipe.

As best illustrated in Figure 4, the magnet unit arrangement 34 consists of a support bar 38 and two end groups containing a magnet or groups of magnets 40. The magnets in opposite end groups are of opposite polarities to induce a magnetic field in the wall of the pipe. Each end group has a series of brushes 42 mounted on top. The construction of these brushes is described in more detail below. For present purposes it is sufficient to note that these brushes contain steel cables or other arrangements of steel material in contact with a steel shell along the base of the brush to make contact with the magnet below and, therefore, to generate the necessary magnetic field.

For convenience of illustration, only half of five brushes is illustrated in each end group of Figure 4. Other numbers and shapes of brushes could be used without departing from the spirit of the present invention. When the pig travels through the pipe, the upper surfaces of these brushes are in substantial contact with the wall of the pipe during the journey and therefore transmit the necessary magnetic flux to the wall of the pipe.

As best illustrated in Figure 4, to reduce the amount of wear of these brushes during a trip, a rotating wheel 44 is mounted to each end of the magnet unit. An additional advantage is that these wheels maintain a substantially constant distance between the magnet units and the wall of the pipe so that a substantially constant magnetic field is produced during the pig's journey.

The sensors 48 that collect the anomalies in the wall of the pipe are placed in an arrangement placed between the two end groups of the magnet unit and thus between the brush arrangements.

The sensors can be a molded polyurethane unit. As best illustrated in Figures 7 to 9, the sensors contain a base platform 50 that mounts the sensor to the support bar, the sensor body 52, the upper platform 54, the wear platform 56, the cushions of wear 58 and the sensor elements 60. The sensor elements make the actual measurement of the MFL and therefore must be able to sense absolute magnetic field contrary to the sensor elements that are only able to detect changes in the magnetic field.

Preferably, these components are all joined in the molding process. By eliminating the need for a mechanical linkage of the sensor elements with the wear pad, the present invention is able to place the sensor element as close to the pipe wall as possible. This arrangement results in a better signal-to-noise ratio and, therefore, better device performance.

Although the sensor illustrated in Figures 7 to 9 illustrates an upper platform and a wear platform that are oriented perpendicular to the base platform, it is not necessary that this particular arrangement be used. For example, the upper platform and the wear platform could be arranged parallel to the base platform so that these platforms form the upper surface of the parallelogram shape of the sensor.

As best illustrated in Figures 4 and 9, however, there are certain advantages with the shape and arrangement of the sensors illustrated in these drawings. As illustrated in Figure 9, sensing elements 60 are equidistantly spaced apart in upper platform 54. By arranging the sensors as illustrated in Figure 4, with their upper platforms in quincunx, it is possible to place the sensor elements in a manner that are equidistantly separated around the circumference of the apparatus. It is also possible to place the sensor elements closer than would otherwise be possible. The advantage of being able to place the sensor elements more closely and, therefore, be able to place more sensor elements around the pig is that a higher degree of resolution can be achieved in the signal detected by the elements. The advantage of being able to position the sensor elements equidistantly around the pig is that a more constant signal will be detected by the sensor elements. For example, it has been found that a constant separation of 6 mm (about Vi of an inch) or less, measured between the centers of the adjacent sensor elements, provides an improved degree of resolution in the signal detected by the sensor elements. It will be appreciated that there are other arrangements of the sensors and sensor elements that will result in the sensing elements being positioned equidistantly, or nearly, around the circumference of the pig.

Preferably, the sensor body has the shape of a parallelogram. It has been found that this form is particularly useful in keeping sensor elements close to the wall of the pipe and in maintaining the orientation of the sensor elements in relation to the wall of the pipe.

According to the above, the parallelogram shape of the sensor body results in improved accuracy of the sensor signal and also results in consistency of the signal quality so that the differences in the signal at different positions in the pipeline can be interpreted as due to anomalies instead of being attributable to pipe curves or restrictions.

Preferably, the sensor body is a one-piece polyurethane polymer that is resistant to petrochemicals so that it will not break with chemicals in the pipeline. The sensor body is also preferably resistant to temperature in the range of 0 ° C to 80 ° C and can withstand pressures of up to about 3700 pounds per square inch.

A sensor such as that described in accordance with this preferred specimen has the advantages of being flexible enough to follow the contours of the pipe wall to keep the sensor elements in the same position in relation to the wall and yet they are durable enough to withstand long trips in the pipeline.

As best illustrated in Figure 10, the wear pad 56 is curved along its upper surface 65 to follow the curvature in the pipe. This design places the sensor elements closer to the surface of the pipe wall than previously possible. As a result, there is an improved signal-to-noise ratio and an improved reading is achieved. Wear pads, which may be constructed of ceramic material or similar, reduce the amount of wear on the sensors thus giving them a longer life. The means to reduce the wear on the sensors, such as the wear platform and the wear cushions, must be non-ferromagnetic so that they do not interfere with the signal that is registered by the sensor elements.

With reference now to Figures 11 and 12, the brushes comprise steel cables 70 contained in polyurethane 72 mounted on a steel shell 74. This composite has a much improved wear capacity with improved magnetic transmission properties to allow the magnetization of thicker pipe walls than the prior art pigs. This is due to the increased density achieved by packing the steel cables closest to each other, which in turn is achieved by linking the steel cables in polyurethane.

The pig of the present invention is now described by reference to its operation in a pipeline. The first step to get to the extent of the anomalies is to achieve even magnetization in the wall of the tube. The above is achieved by designing a high efficiency magnetizing unit that is capable of transmitting a high amount of magnetic flux within the tube wall.

The next step is to measure and store the signal leaks correctly. To do this, the pig of the present invention has higher resolution than known in the prior art due to the construction and separation of the sensors. It has been found that if the sensors of the present invention were placed closer together, they could detect smaller and less deep defects. A signal from the sensor is taken at predetermined intervals along the length of the pipe. All data is then stored in the data acquisition system for subsequent recovery and analysis by removing the pig from the pipeline.

The final step is the measurement of the anomalies to interpret the recorded signal with as many parameters as possible. The above is achieved by running the tool over a tube section with known defects and correlating the received signals with the current defect. In this way the size of an unknown defect can be determined through these calibration curves.

With a more efficient magnet unit design, higher levels of magnetization are achieved. The best brush design can transmit this magnetic field inside the tube wall more effectively.

Sensors placed closer together and better positioning of the sensors increase the sensitivity of the tool. This means that much smaller anomalies can be detected in tubes with thicker walls than previously possible.

The addition of rotating wheels to the magnet unit and the incorporation of wear cushions to the sensors greatly reduces the wear of brushes and sensors. This, in turn, makes the new design more appropriate for running long applications. Conversely, the tool can make many short trips with less time between them, since longer replenishments between trips are no longer required. This description is made with reference to the preferred specimen of the invention. However, it is possible to make other copies that employ the principles of the invention and that fall within the spirit and scope as defined by the following Claims.

Claims

CLAIMS: 1. An apparatus (10) for analyzing anomalies (29) in a pipe wall (25) comprising: A body (14) of generally cylindrical shape; means (26) for supporting the body in relation to the wall of the pipe; means (20) for driving the body through the pipe; means (12) for providing electrical energy to the body; means (16) for storing data; means (42) mounted on the body for generating and transmitting a magnetic field through portions of the wall of the pipe adjacent to the body; means (48) for measuring magnetic flow leaks adjacent to the body caused by anomalies in the wall of the pipe; means for transmitting measurements of magnetic flux leaks to data storage media; and a plurality of wheels (44) mounted on the body adjacent to the generating means of the magnetic field to rotate against the wall of the pipe as the body moves through the pipe to reduce wear on the generating means. di magnetic field and the means to measure the leakage in the magnetic flux.
2. The apparatus of Claim 1 further comprising: a plurality of bars (34), each bar mounted flexibly on the body to allow the bar to move radially inwardly and radially outwardly to provide space for the apparatus in case find obstacles as you travel through the pipe; and wherein the means for generating and transmitting a magnetic field to the wall of the pipe, the means for measuring the leakage in the magnetic flux and the rotating wheels are mounted on the bars.
3. The apparatus of Claim 2, wherein the means for measuring the leakage in the magnetic flux comprises: a sensor body (52); at least one sensor element 860), which is capable of feeling the absolute magnetic field, contained within the sensor body; and wherein the sensor body is flexible so that it can follow the contour of the pipe wall as the apparatus moves through the pipe and thus keeps the sensor element in a substantially constant orientation with respect to the wall of the pipe.
4. The apparatus of Claim 3, wherein the apparatus further comprises non-ferromagnetic means (56), mounted on the upper surface of the sensor body, to reduce wear of the sensor body and to protect the sensor element from damage.
5. The apparatus of Claim 4, wherein the wear reducing means and the sensing element are joined together to form an integral unit.
6. The apparatus of Claim 4, wherein the wear reducing means is generally formed to follow the contour of the pipe wall.
7. The apparatus of Claim 4, wherein the wear reducing means comprises a wear pad (56) and at least one wear pad (58).
8. The apparatus of Claim 3, wherein the sensing elements are generally positioned equidistantly around the circumference of the body.
9. The apparatus of Claim 8, wherein the distance between the centers of the adjacent sensor elements is less than 6 mm.
10. The apparatus of Claim 3, wherein the transverse shape of the sensor body is generally a parallelogram.
11. The apparatus of Claim 10, wherein the sensor body is a one-piece polymer that is resistant to petrochemicals, resistant to temperature in a range of from 0 ° C to 80 ° C and can withstand pressures of up to about 3700 pounds per square inch.
12. The apparatus of Claim 11, wherein the sensor body is constructed of polyurethane.
13. The apparatus of Claim 2, wherein the means for generating and transmitting a magnetic field to the wall of the pipe comprises: a first brush with steel (42) located above a first magnet (40) on one end of each bar; a second brush with steel placed on top of the second magnet of the polarity opposite the first magnet on the other end of the bar; and wherein the top surfaces of the brushes come into close contact with the wall of the pipe at all times.
14. The apparatus of Claim 13, wherein the brushes comprise a plurality of steel cables (70) contained and joined in a plastic resin (72) and mounted on a steel shell (74).
15. The apparatus of Claim 14, wherein the plastic resin is polyurethane.
16. An apparatus (10) for analyzing anomalies (29) in a pipe wall (52) comprising, in any order: a first section (12) of generally cylindrical shape containing means for providing electrical power to the apparatus; a second section (14) of generally cylindrical shape for storing data collected by the apparatus; a third section (16) of generally cylindrical shape having means (42) for generating and transmitting a magnetic field through portions of the pipe wall adjacent to the third section and means (48) for sensing the leakage in the magnetic flux adjacent to the third section caused by anomalies in the wall of the pipe; and further comprising: means (26) for supporting the sections in relation to the wall of the pipe; means (20) for driving the sections through the pipe; means for transmitting leakage measurements in the magnetic flux to the data storage means; a plurality of wheels (44) mounted on the third section adjacent to the generating means of the magnetic field to rotate against the wall of the pipe as the apparatus moves through the pipe to reduce wear on the field generating means magnetic and the means to measure the leakage in the magnetic flux; and wherein the adjacent sections are connected by flexible links (22) to allow the movement of the apparatus through curves and restrictions in the pipe. EXTRACT OF THE INVENTION An apparatus (10) for analyzing anomalies (29) in a pipe wall (25) is provided. The apparatus is formed of one or more cylindrical body sections (14). The magnetizing units (34) are mounted around the circumference of each section. Each magnetizing unit is formed by a support bar (34), brushes (42) that are capable of inducing a magnetic field, sensors (48) mounted between the brushes that are capable of measuring leaks in the magnetic flux caused by anomalies in the wall and castors 844) that reduce wear on the brushes and the sensor. Each sensor contains a sensor element (60) that is capable of feeling the absolute magnetic field. The support bar is flexibly mounted on the body so that it can follow the contour of the pipe wall as the apparatus moves through the pipe. The brushes are preferably formed by steel cables contained in polyurethane and mounted on a steel shell. The sensors preferably have a transverse parallelogram shape and are molded of polyurethane to be flexible enough to maintain the orientation of the sensor element relative to the wall of the pipe.