MX2007008986A - Pipeline inspection tool and method based on rotating magnet-induced eddy currents - Google Patents

Abstract

Disclosed are an apparatus and method for integrity monitoring of tubular components and, in particular, pipe walls. The apparatus comprises a configuration of permanent magnets (22, 24) arranged to rotate circumf erentially within the pipe, whereby uniform low-frequency currents are generated within the pipe wall which, in turn, generate fields detectable with, for example, conventional Hall Effect sensors (60, 62). The method comprises steps to rotate the apparatus within the pipeline and sense disruptions caused by anomalies in the pipe wall.

Description

TOOL AND METHOD FOR INSPECTION OF PIPES THROUGH CURRENTS INDUCED BY ROTARY MAGNETS Background of the Invention Field of the Invention This invention relates, in general, to an apparatus designed and operated to inspect conductive objects, including electrically conductive objects and magnetically permeable objects, tubing (whether for gas or oil pipelines), tubing Heat exchange and pit lining walls, for example, due to corrosion and mechanical damage as well as other anomalies and defects, such as fissures and pitting. More particularly, this invention relates to a pipe inspection apparatus, which "slips" into the interior of the pipe independently of the fluid flow therein using rotating permanent magnets to generate uniform electric currents of low frequency inside the walls, which in turn create magnetic fields that can be detected with conventional Hall Effect sensors.

Description of Related Art Essential liquids and gases, which include water, chemicals and fossil fuels, flow through piping systems. Large volumes of products as diverse as oil and liquid hydrocarbons, natural gas, propane and suspensions of solids such as granulated carbon and minerals, such as copper and iron, are transported constantly between the extraction and processing sites and the consumption sites over great distances. In general, these pipes range from a few inches to 15.24 meters (60 inches) in diameter and extend thousands of miles in length. Pipes that are normally constructed of metal, particularly ferrous metals, are also susceptible to damage and other defects that can affect the integrity of the system. The result can be a failure that threatens life and property, serious environmental damage, disturbances both in the local economy and in the distant one and the losses of the product that is being transported. The additional result may be the reduction of public confidence in this efficient and economic means of transportation of materials with the possible opposition of the public to the growth or development of these means of transport. To minimize the risk of failure, the pipes are closely monitored and inspected. In general, inspection methods involve the injection of a uniform energy into an object, whereby an anomaly or defect disturbs this uniformity. Next, the sensors detect changes in the uniformity and in this way, they detect the anomaly or defect. These methods use pipe inspection devices that are introduced into the pipeline and move through it, generally but not exclusively, through the material flowing in the pipe. For example, on an x-ray the anomalies are detected when a portion of an incident X-ray energy passes through the material. A film or charge coupled device that is located on the opposite side of the source material can be used to detect this change in absorption. A pipe inspection apparatus could also comprise magnetic components to induce magnetic flux within the wall of the pipe. Naturally, the magnetic flux enters the metal wall of the pipe and is distributed evenly in order to produce a full volumetric inspection. Abnormalities or defects in the pipe wall tend to disturb the uniform flow of fluid and create an escape of magnetic flux that can later be detected by sensors, generally, within the apparatus itself. This inspection methodology is known as Magnetic Flow Escape ("MFL"). Nevertheless, the MFL can be difficult to implement in autonomous drag or slide systems because the devices are large and heavy. In addition, MFL-based devices are not capable of detecting all types of defects and have almost the same shape factor as the tube, making it difficult to pass diameter restrictions. Among the alternative procedures, small and light devices have shown promising attempts except implementations that have been blocked by light speed and long distance requirements, factors that are not as restrictive for slip-based inspection systems. Other methods of inspection include, for example, the induction of electric currents in the pipe by means of the positioning of an auxiliary magnetic pole and the relative movement of the inspection apparatus and the wall of the pipe. See, for example, U.S. Patent No. 5,751,144 to Weischedel ("eischedel"). These methods generate circumferential currents that are better used when trying to detect cracks or axial cracks. As described in Weischedel, one of the "necessary conditions" for reliable detection is the induction of "substantial parasitic currents, so that parasitic current changes that are representative of structural faults can be easily detected." To conveniently induce these eddy currents, the inspection apparatus must first include a small "auxiliary pole", relative to the two main poles, "having the same magnetic polarity as one of the main poles" and the apparatus must be moving at an excess speed, generally, approximately 6.44 kilometers (4 miles) per hour in relation to the wall of the pipes to generate stray current signals that can be measured and are reliable. In this way, these methods depend on the linear movement of the magnets through the inside of the tube. In addition, the parasitic currents and the resulting signals are still generally weak and therefore require more sophisticated sensors to detect anomalies. The methods using the distant field technique (RFT) or the distant field parasitic current technique (RFEC) are also known. This technique uses a sinusoidal current flowing in an excitation coil (for example, electric coils) to induce current in the tube wall and a remote receiving coil through two tube diameters in order to detect such defects like the loss of metal and stress corrosion cracks. However, the resulting signals are very small, which requires sensitive and expensive amplifiers to detect these signals. These traditional RFEC techniques also use low frequency exciters, although the sensitivity of the coil sensors that are used to detect the signals of the anomalies decreases with the reduction of the frequency. In addition, these techniques use "indirect energy coupling" by sending the field outside the boundaries of the tube wall. See, for example, U.S. Patent No. 2, 573,799 to MacLean. The use of electric motor concepts (through fixed coils) has also been developed. See for example, Plamen Alexandrov Ivanov, Remote Field Eddy Current Probes for the Detection of Stress Corrosion Cracks In Transmission Pipelines (2002) (Unpublished dissertation Ph.D, Iowa State University). Further discussions of RFEC could be found in T. R. Schmidt, History of the Remote-Field Eddy Current Inspection Technique, 47 Materials Evaluation 14 (1989).

Summary of the Invention Recent development efforts in the field of internal pipeline inspection include a new generation of motorized inspection platforms that "slide or drag" slowly inside a pipeline and are capable of maneuvering through of physical barriers that can limit inspection. The present invention provides an electromagnetic inspection system for pipe slippers or draggers that can be used to evaluate a wide range of pipe anomalies including corrosion, mechanical damage and cracks or cracks. A rotating excitation assembly based on a permanent magnet produces strong, low frequency, uniform electrical currents in the tube wall. These currents disperse on the wall outside the magnets and generate magnetic fields inside and outside the wall. At distances generally of a pipe diameter or more, the currents flow in the circumferential direction and the current and the resulting magnetic fields are deflected by the defects of the pipe, such as corrosion and fissures aligned in axial position. The conventional Hall Effect sensors are used to detect these changes. In one embodiment, a device is provided that detects an anomaly in an electrically conductive cylindrical structure, the device comprises a first and a second pole, the poles have opposite polarities, means of rotation of the poles about an axis of rotation, the axis The rotation is coaxial with the long axis of the structure, by means of which, the currents are induced within the structure and at least one current flow sensor, the current flow sensor is separated from the first and second poles magnetic along the axis of rotation. The device of the invention could also include the separation of the sensor from the magnetic poles according to the relationship expressed later in Equation 1. The sensor of the invention could also include sensors adapted to detect the axial magnetic flux and the radial magnetic flux . In a preferred embodiment of the invention, the sensor is placed outside of a near field and within a far field. In a further preferred embodiment, each of the first magnetic pole and the second magnetic pole comprises a greater or equal intensity of 25 megaGauss-Oersted. The device of the invention could also include a magnetically permeable bar in which the first and second magnetic poles are joined. In a further embodiment, the bar is adapted to include means that allow the bar to operate telescopically in the extension of its long axis, thereby allowing the bar to slide over the obstructions in the interior wall of the structure. Alternatively or in combination, the bar could be articulated in order to provide the same capacity. In a method of detecting an anomaly in an electrically conductive wall of a tubular structure such as a pipe, the device of the invention could be placed within the structure and the bar could be rotated about its axis of rotation approximately in 1- 10 Hz. Next, the device is pushed through the structure. Induced currents, which by themselves induce magnetic fields, are detected for example, through Hall Effect sensors.

Brief Description of the Figures Figure 1 is an isometric view of an embodiment according to the present invention and illustrates the induced current lines. Figure 2 is an isometric view of another embodiment according to the present invention. Figure 3a is a graphical representation of the coaxial signals close to the rotating magnets according to the present invention. Figure 3b is a graphic representation of the coaxial signals far from the magnets rotating according to the present invention. Figure 4 is a graphical representation of the axial decrease of the induced magnetic field flowing in the tube wall according to the present invention. Figure 5 is a graphical representation of the decrease of the three configurations of the magnetizer according to the present invention. Figure 6 is a graphic representation of a common output signal for detecting an anomaly according to the present invention. Figures 7a-7d are graphical representations of the signals on the inner surface of the tube wall at varying coaxial distances according to the present invention. Figures 8a-8d are graphical representations of the signals on the inner surface of the tube wall at varying coaxial distances according to the present invention. Figure 9 is a graphical representation of the corrosion anomaly signals of 77 percent depth and 5.08 centimeters (2 inches) in length according to the present invention. Figure 10 is a graphical representation of the signals of a corrosion anomaly of 72 percent depth and 3.56 centimeters (1.4 inches) in length according to the present invention. Figure 11 are elevational views of a telescopic structure according to the present invention. Figure 12 are elevational views of an articulation structure in accordance with the present invention.Detailed Description of the Invention Reference Numbers 10 Inspection Apparatus 11 Inspection Apparatus 20 Magnet Assembly 22 Magnet 24 Magnet 26 Fastener 28 Rod 30 Swing Arrow 35 Movement Transmission Mechanism 40 Connection Connection 42 Alignment Plate 44 Alignment Wheel 50 Axis 60 Series of sensors 62 Sensor 70 Tube, cylinder or other tubular structure 80 Power lines 90 Telescopic mechanism 92 Articulation mechanism. Beginning with Figure 1, in one embodiment of the present invention 10, rotating permanent magnets 22, 24 (shown with spinning arrow 30) produce an alternating electrical current 80 that moves in a generally elliptical pattern. (As discussed more fully below, a plurality of pairs of magnets 22, 24 could be used to produce electric current 80). Figure 1 shows the positioning inside the tube of the rotating permanent magnet excitation assembly 20 which induces the strong currents 80 in the tube wall 70. This procedure uses alternating poles N and S, 22, 24 that rotate about an axis 50. In a preferred embodiment, the magnets 22, 24 are magnetically connected to a magnetically permeable bar 28 and are connected to the bar 28 with the fasteners 26 to form a magnet assembly 20. Because the tube 70 is conductive and the magnets 22, 24 are moving, the current 80 is generated in the tube wall 70. The direction of the current is orthogonal to the magnetization direction and the direction of movement. Because the direction of motion is circumferential 30 and the direction of the magnetization is radial, initially the current flow is in the axial direction. However, the Cargo Conservation Law states that there is no increase or accumulation of cargo. Therefore, the current flows in the circuits 80, not in segments. The basic flow of these circuits 80 is illustrated in Figure 1. The number of pairs of magnetic poles 22, 24 is an important variable together with the diameter of the tube 70, its electrical conductivity and its magnetic permeability. Operably connected to the shaft 50 is a series of sensors 60, which are preferably comprised of the Hall Effect sensors 62. Preferably, the shaft 50 comprises a connecting link means 40 which is widely known in the art. , which allows the assembly of magnets 20 to rotate 30 while also allowing the series of sensors 60 to remain fixed in a rotating manner. Furthermore, it is preferred that the connecting connection means 40 be adapted in order to provide a universal connection shape joint between the sensor series 60 and the magnet assembly 20. Figure 2 shows another embodiment of the invention. In addition to the assembly of magnets 20, the shaft 50 and the connection junction 40, the inspection apparatus 11 comprises a drive mechanism or motion transmission 35 that rotates the magnet assembly 20 and a plurality of alignment plates 42 and wheels of alignment 44 which center the apparatus 11 within the tube 70. There are many choices for the drive mechanism 35. Applicants have found, for example, that a DC motor (ie, a direct current motor) works well. For pipes with high flow velocities, a pneumatic motion transmission could be used. The inspection apparatus 11 could also be introduced and located using a directional drilling rig with the rod supplying the necessary rotational power. Next, with reference to Figures 3a and 3b, the magnetic field in the tube has two general parts, each with different properties and effects. One part is the direct magnetic field that comes from the strong permanent magnets 22, 24. The second field is due to the current 80 flowing in the tube 70. Figures 3a and 3b are illustrative of the results of a magnet assembly. comprising two magnets 22, 24 that rotate in five Hz in a welded tube of electrical resistance (ERW) 70 of 30.48 centimeters (12 inches) of internal diameter (ID) with a wall thickness of 0.91 centimeters (0.358 inches). The magnet assembly 20 is comprised of two poles 22, 24 with permanent NdFeB magnets of 35 megaGauss-Oersted. The dimensions of the magnets 22, 24 were 5.08 centimeters (2 inches) in the axial direction, 2.54 centimeters (1 inch) in the circumferential direction and 1.27 centimeters (0.5 inches) in thickness in the axial direction. The air gap was nominally 0.84 centimeters (0.33 inches). Next to the rotating assembly of magnets (for example, a sixth part of the tube diameter) 20, the magnetic field of the magnets 22, 24 (the near field) is dominant and produces an alternating signal in the shape of a chair (Figure 3a). Further (for example, the diameter of a tube) of the assembly of magnets 20, they dominate the magnetic fields caused by the currents 80 flowing in the tube 70 (the far field) (Figure 3b). The current 80 in the tube 70 induces a magnetic field that can be detected by a coil or sensor 62 / series of Hall Effect sensors 60. In this way, the placement of the series of sensors 60 is important. In this example, when the separation of the sensor series 60 and the magnet assembly 20 is approximately the diameter of the pipe, the direct fields of the magnetizer would be imperceptible. Likewise, the stream 80 in the tube 70 is nominally sinusoidal. The separation distance that is required to achieve a sinusoidal signal is a function of the diameter of the tube 70 and the number of pairs of magnets NS 22, 24. Next, with reference to Equation 1 below, the amplitude of the magnetic field (Bpjc) which is produced by the current 80 decreases as the coaxial separation distance (Z) between the magnet assembly 20 and the series of sensors 60 increases. In a first order approximation, the decrease ratio is nominally exponential and proportional to the ratio of the number (n) of magnet pairs NS 22, 24 divided by the radius (r) of 170. Equation 1 where r = Cylinder radius d2 = 2 /? s μ (classic blade depth) n = Number of Pairs Poles ß = Coupling Factor? = Rotational Frequency s = Conductivity μ = Magnetic Permeability MQ = Magnetization Intensity of the Magnetizer Part Z = Length along the Rotation Axis. Equation 1 implies that the current 80 in the cylinder 70 decreases faster for cylinders of smaller diameter 70 and assemblies of magnets 20 with more poles 22, 24. The physical explanation is that a few poles 22, 24 in a large cylinder 70 they allow the establishment of large current circuits 80 that extend a significant distance from the magnet assembly 20. On the contrary, many poles 22, 24 on small cylinders 70 produce many small circuits 80 which are opposite each other and do not extend far of the assembly of magnets 20. The initial magnitude of the current 80 (in Z = 0) is proportional to many variables; the amplitude increases with increasing diameter, magnet intensity, magnet coupling, conductivity, permeability and rotational frequency and decreases with increasing number of pole pairs. From the examination, both in terms of amplitude and decrease, the signal is more intense for larger diameter tubes with some poles. Figure 4 shows in graphic form the calculated axial decrease of the axial component and the radial component that is compared with the experimental results. The calculated results were obtained using the magnetic finite element analysis (FEA) procedure. The solution was obtained using a three-dimensional rotational analysis problem solver that was able to calculate the current generated by a permanent magnet passing through a conductor. (Opera-3d® by Vector Fields, Ltd, Aurora, Illinois). For the experimental results, the rotating assembly of magnets 20 was in an axial location while the sensor 62 was moved along the inner surface of the tube 70. At discrete locations along the tube, the amplitude was measured with a sensor Hall Effect 62. The density of the measurements was larger in the near field than in the far field due to the nature of the changes in amplitude. As illustrated in Figure 4, the calculations and experiments showed that the decrease or fall of the magnetic field is exponential. The decrease ratio in the 30.48 centimeter (12 inch) tube is nominally of the order of magnitude per tube diameter. The experimental verification is superimposed on the modeling results.

Figure 5 shows how the decrease ratio is related to both the diameter of the tube and the number of poles. Three configurations were verified: (1) a tube with a diameter of 155mm (six inches) and two pole magnetizers; (2) a tube with a diameter of 310mm (twelve inches) and two pole magnetizers; and (3) a tube with a diameter of 310mm (twelve inches) and four pole magnetizers. The wall thickness of both tube samples was nominally 9mm (0.37 inches) and it was assumed that the magnetic permeability and electrical conductivity of both samples were equal. The rotational frequency was five Hertz. The rotational speed for the four-pole unit was cut in half to keep the frequency of the inspection current equal to the other two configurations. The graphs in Figure 5 show that the drop or decrease ratio is similar for the magnetizer of 15.24 centimeters (6 inches) with two poles and the magnetizer of 30.48 centimeters (12 inches) with four poles; only the initial amplitude of the smallest diameter magnetizer is lower. The magnetizer decrease ratio of 30.48 centimeters (12 inches) with two poles is nominally half of the other two. For the configuration of four poles in the 30.48 centimeter (12 inch) tube, two bars 28 were added to the two pole magnet assembly 20 and the polarity of the magnets was assigned appropriately.

A common test result of an anomaly is shown in Figure 6. A prototype system was pulled through a tube with a diameter of 30.48 centimeters (12 inches) and a nominal thickness of 0.94 centimeters (0.37 inches) with defects machined of loss of metal. The axial and radial Hall Effect sensor data were recorded continuously as the tool was pulled smoothly through the tube without stopping. The Hall Effect sensors were of a commercially available linear radiometric type widely available. The field levels were expanded by a factor of 100 using an operation amplifier once the displacement of the Q-point was removed using a resistance voltage divider. A 10-turn, 1000-ohm potentiometer was used to adjust the variation between the sensors. The two sensors were placed for the measurement of the axial and radial component of the magnetic field. The axial speed of the tool was nominally 7.62 centimeters (3 inches) per second. The rotation of the magnets was 300 rpm (5 Hz). The upper graph shows the unprocessed sinusoidal signals. The lower graph shows a trace through the peak values. The axial component of the magnetic field increases in the area of metal loss. The radial component increases before the metal loss zone and subsequently decreases. While common variations in tube conductivity and permeability can affect the amplitude by detecting the axial and radial signal, detection can be simplified. A combination of modeling and prototype was used to improve the inspection of the propagation of the current intensity along the tube 70 that was used to detect the anomalies of the pipe. After examination of various configurations, the best performance was achieved using a two pole exciter 20. A prototype for a 30.48 centimeter (12 inch) diameter pipe is shown in Figure 2. A pair of NdFeB magnets 22, 24, each with a length of 5.08 centimeters (2 inches), a width of 2.54 centimeters (1 inch) and a thickness of 1.27 centimeters (0.5 inches), and which has an intensity of 38 megaGauss-Oersted, was placed in a soul of steel 28. The central part or core 28 was machined from a steel 1008. While the magnets 22, 24 have a strong attraction to the steel core 28, the aluminum guide rails 26 place the magnets 22, 24 with precision on the soul 28. The air gap between the magnets 22, 24 and the test tube with a nominal thickness of 0.94 centimeters (0.37 inches) was 1.27 centimeters (0.5 inches). The support plates 42 with wheels 44 kept the magnet assembly 20 centered in the tube and a variable speed direct current motor 36 was used to rotate the magnet assembly 20.

Figures 7a-7d illustrate the magnetic field on the inner surface of the tube wall at distances ranging from near the series of magnets (one sixth of the diameter of the tube) to 2.5 tube diameters for a two-pole system that rotates at 5 Hz in a tube with a diameter of 30.48 centimeters (12 inches). The signals radial (solid lines) and axial (dotted lines) are indicated. Figure 7a is in one sixth part of the pipe diameter, Figure 7b is in one half, Figure 7c is in a pipe diameter and Figure 7d is 2.5 pipe diameters. As shown, the field due to direct field effects is imperceptible at distances greater than a tube diameter and the measured signal is almost sinusoidal. The field is also strong, being of the order of a Gauss. Currents can be detected at distances beyond two tube diameters. Similarly, Figures 8a-8d illustrate the magnetic field on the inner surface of the tube wall at fluctuating distances of one sixth of the tube diameter (Figure 8a)HEM , at one half of the tube diameter (Figure 8b), at a tube diameter (Figure 8c), up to 1.5 tube diameters (Figure 8d) for a four pole system that rotates at 2.5 Hz in a tube diameter of 30.48 centimeters (12 inches). As indicated, the levels of the signal at similar distances are not as strong and contain more noise. Figures 9 and 10 show the results of the tests carried out with the prototype described above for particular corrosion anomalies. Figure 9 illustrates the signals for an anomaly with a depth of 77 percent and a length of 5.08 centimeters (2 inches) (characterized as depth and length). Figure 10 illustrates the signals for a depth anomaly of 72 percent and a length of 3.56 centimeters (1.4 inches) (depth and length). In both cases, 1 axial sensor and 1 radial sensor were directly aligned in radial position with the anomaly, 2 sensors were displaced by five nominal degrees and 3 sensors were displaced nominally by five additional degrees in the same circumferential direction. In another embodiment of the present invention, the magnet configuration comprises a shape factor that allows the tool to pass the obstructions within the pipe. For example, Figure 11 shows a telescopic structure 90 that allows the bars with which the magnets are attached to shorten as they pass through the obstructions. Alternately, Figure 12 shows an articulated structure 92 that allows the bars to be folded to pass through the obstructions. Other folding arrangements, such as spring-loaded universal joints or combinations, could also be employed. For the telescopic structure 90, simple mechanical devices such as spindles can be used to move the magnets to the proper position for inspection. However, the maximum range of the telescopic magnetizer 90 in the collapsed position is larger than the range of the articulation configuration 92. For the articulation configuration 92, the magnetizer could be designed to be placed through obstructions that are smaller than one third of the diameter of the tube. However, in the collapsed position the force of attraction of the magnets could be strong and the mechanism that could return the magnets to the inspection position could require considerable force. Following the foregoing description and summary of the invention, it will be appreciated by those skilled in the art that, while the apparatus and methods described and illustrated herein constitute exemplary embodiments of the present invention, the invention is not limited to these precise embodiments and that changes and modifications may be made thereto without departing from the scope of the invention as defined by the claims. Likewise, it will be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein be incorporated in the claims unless explicitly stated in the claims by telves. Finally, it will be understood that it is not necessary to comply with any or all of the advantages or stated objectives of the invention described herein in order to fall within the scope of any claim, because the invention is defined by the claims and because the inherent and / or unforeseen advantages of the present invention could exist even when they have not been discussed explicitly herein.

Claims (32)

1. CLAIMS 1. A device that helps in the detection of an anomaly in an electrically conductive wall of a pipe, characterized in that it comprises: a magnetically permeable bar, the bar is adapted to be placed diametrally inside the pipe and is constituted by: a first end, the first end includes: a first permanent magnet, the first permanent magnet in turn includes: a first magnetic polarity; and a magnetic intensity greater than or equal to 25 mega-Gauss-Oersted; a second end, the second end includes: a second permanent magnet, the second permanent magnet in turn includes: a second magnetic polarity; and a magnetic intensity greater than or equal to 25 mega-Gauss-Oersted; and an axis of rotation, the axis of rotation is equidistant from the first end and the second end and is adapted to be coaxial with the long axis of the pipe; and means of rotating the bar about the axis of rotation, whereby, the currents are induced within the wall. The device according to claim 1, further characterized in that it comprises: a series of sensors, the series is separated from the bar along the axis of rotation. The device according to claim 2, characterized in that: the sensor series comprises at least one Hall Effect sensor. 4. The device according to claim 3, characterized in that: at least one Hall Effect sensor is adapted to detect the axial magnetic flux. The device according to claim 3, characterized in that: at least one Hall Effect sensor is adapted to detect the radial magnetic flux. The device according to claim 3, characterized in that: at least one Hall Effect sensor is adapted to detect the circumferential magnetic flux. The device according to claim 2, characterized in that: the series is outside a near field. 8. The device according to claim 2, characterized in that: the series is located in a far field. The device according to claim 2, characterized in that: the series is separated from the bar by at least one third of the diameter of the pipe. The device according to claim 2, characterized in that: the series is separated from the bar according to the relation: 11. The device according to claim 2, further characterized in that it comprises: the means that transmits the output of the series of sensors; and the medium that records the output of the series. 12. A method of detecting an anomaly in an electrically conductive wall of a pipe, characterized in that it comprises the steps of: (a) placing the device of claim 2 in a coaxial position within the pipe; (b) rotating the bar, whereby far-field currents are induced within the wall; (c) pushing the device through the pipe; and (d) detecting the current flow within the wall within the far field. The method according to claim 12, further characterized in that it comprises the step of: (e) rotating the bar at a speed greater than or equal to one Hertz. The method according to claim 12, further characterized in that it comprises the steps of: (e) transmitting an output of the series of sensors; and (f) record the output of the series. 15. A device for detecting an anomaly in an electrically conductive cylindrical structure, characterized in that it comprises: a first and a second magnetic poles, the first and second magnetic poles are separated and have opposite polarities; the means rotating the first and second magnetic poles around an axis of rotation, the axis of rotation is coaxial with the long axis of the structure, by means of which, the currents are induced within the structure; and at least one current flow sensor, the current flow sensor is separated from the first and second magnetic poles along the axis of rotation. 16. The device according to claim 15, characterized in that: the sensor is separated a distance (Z) from the first and second magnetic poles according to the relation: 17. The device according to claim 15, characterized in that: at least one sensor comprises: a first sensor adapted to detect the axial magnetic flux; and a second sensor adapted to detect the radial magnetic flux. 18. The device according to claim 15, characterized in that: at least one sensor is outside a near field. 19. The device according to claim 15, characterized in that: at least one sensor is located in a far field. 20. The device according to claim 15, characterized in that: at least one sensor is separated by at least one third of the diameter of the structure. The device according to claim 15, characterized in that: at least one of the first magnetic pole and the second magnetic pole comprises a greater or equal intensity of 25 mega-Gauss-Oersted. 22. The device according to claim 15, characterized in that: the structure is tubular. 23. The device according to claim 22, characterized in that: the first magnetic pole and the second magnetic pole are operatively connected to a magnetically permeable rod, the rod is adapted to be positioned diametrally within the structure. 24. The device according to claim 23, characterized in that the bar is further adapted to move telescopically in the extension of a long axis of the bar. 25. The device according to claim 23, further characterized in that the bar comprises: at least one hinge, the hinge is adapted to allow a portion of the bar to rotate about the hinge. 26. The device according to claim 15, characterized in that at least one sensor comprises a Hall Effect sensor. 27. The device according to claim 23, further characterized in that it comprises: a frame, the frame has a generally cylindrical shape and is adapted to be placed coaxially within the tubular structure, the bar is rotatably coupled with the frame; and the means joined with the frame for the rotation of the bar in a circumferential direction relative to the interior of the tubular structure. 28. A method of detecting anomalies in an electrically conductive tubular structure, characterized in that it comprises the steps of: (a) placing the device of claim 27 within the tubular structure; and (b) rotating the bar about the axis of rotation, whereby, the currents are induced within the tubular structure. 29. The method according to claim 28, characterized in that the currents are substantially sinusoidal. 30. The method according to claim 28, further characterized in that it comprises the step of: (c) detecting the flow of current within the tubular structure. 31. The method according to claim 30, further characterized in that it comprises the steps of: (d) transmitting the results of the detection step; and (e) record the results. 32. The method of compliance with the claim 28, characterized in that the bar is rotated at a speed greater than or equal to one Hertz.