Abstract:
An apparatus and method for detecting magnetic flux leakage in an object. The apparatus includes a frame assembly, a sensor bar and a U shaped magnetic circuit consisting of first and second magnet and steel pieces  44, 46  and  42  connecting the magnets. The sensor bar is connected to the frame assembly and includes a plurality of coils and at least one sensor operatively connected to at least one of the plurality of coils. The first magnet and the second magnets are connected steel pieces and to the frame assembly. They form a U shaped magnetic circuit which is completed by the steel plate being inspected. The sensor bar is placed between the tips of the U shaped magnetic circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/928,849, filed Jan. 17, 2014, which is hereby expressly incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Magnetic flux leakage (MFL) is a magnetic method of testing that is used to detect corrosion, erosion and pitting in steel structures, such as pipelines and storage tanks. A u-shaped magnetic circuit is used to magnetize the steel. The magnetic field “leaks” from the steel at areas where there is corrosion or missing metal. In an MFL device, a magnetic field sensor is placed between the poles of the magnetic circuit to detect the leakage field. 
     MFL inspection devices have been used for many years with only coils, or coil pairs, as sensors. Wire coils sense changes in magnetic field (AC component). Coils are useful, in that, the interface uses simple low-power electronics, they can be very sensitive, they are somewhat temperature stable, they sense fields inside the coil so a single coil can cover a large area, mechanically rugged, and multiple sensors can be manufactured to be very similar. However, coils only respond to changes in magnetic fields, and the size of the output signal is related to the size of the magnetic field, number of coil turns and the rate of change of the magnetic field (Faradays Law). 
     More recently, MFL inspection devices have used magnetoresistors (e.g., Hall effect devices), rather than coils. Magnetoresistive sensors sense absolute magnetic field levels (DC component). Magnetoresistors respond to steady state and changing magnetic fields. However, magnetoresistors interface needs are somewhat complex electronics, multiple sensors are all different and need individual calibration, sensor output changes with temperature and mechanical stress, are not sensitive to tiny magnetic fields, and require power to operate. 
     The inspection tools are used to find metal loss flaws for things like: railroad rails, pipelines, spherical liquid natural gas (LNG) tanks and above-ground storage tank floors and walls and the like. For example, typically, the floor of a storage tank is made by welding rectangular steel plates together. The floor is sometimes coated with fiberglass or a tar-like substance. The MFL inspection device rides over a bumpy surface on the tank floor. Most of the time, the bumps cause false signals to be seen by the magnetic field sensors. When there are many bumps, it is hard to see the signals from metal loss flaws. The operator of the MFL inspection device has to move the device back and forth over a short distance that doesn&#39;t have any bumps to see if the signal is from the flaw. 
     To this end, although MFL devices exist, there is a need for an improved MFL detection apparatus with improved accuracy, repeatibility and one that filters out false signals. It is to such an MFL detection apparatus and methods of making and using such apparatus and components of the apparatus that the present disclosure is directed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG. 1  is a side view of an apparatus for detecting magnetic flux leakage constructed in accordance with one embodiment of the present disclosure, the apparatus being positioned on a steel plate. 
         FIG. 2  is a perspective view of the apparatus of  FIG. 1 . 
         FIG. 3  is a bottom view of one embodiment of a magnet portion of the magnetic flux assembly of the apparatus of  FIG. 1  constructed in accordance with the present disclosure. 
         FIG. 4  is a cross-sectional view of a sensor bar of the apparatus of  FIG. 1  constructed in accordance with one embodiment of the present disclosure. 
         FIG. 5  is a top cross-sectional view of one embodiment of an array pattern of a pair of coils of the sensor bar of  FIG. 4 . 
         FIG. 6  is a top cross-sectional view of another embodiment of an array pattern of a triad of coils of the sensor bar of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to a MFL detection apparatus/scanner, and more particularly, but not by way of limitation, to an improved MFL detection apparatus and methods for making and using same. One embodiment of this disclosure is directed to sensor systems that are more accurate than previous systems, are better able to filter out false signals, and are easier to calibrate. The multi-sensor approach measures the MFL signals along with the signal environment. Various embodiment(s) of this disclosure combines a unique group of sensors to accurately measure MFL. 
     Referring now to the drawings, and more particularly to  FIGS. 1 and 2 , one embodiment of an apparatus for detecting magnetic flux leakage  10  is shown positioned over a portion of a steel plate  12  of an above ground storage tank. It should be understood that although the apparatus  10  disclosed herein is discussed in use on the steel floor of an above-ground storage tank, the apparatus  10 , as disclosed herein, may be utilized for detecting flaws in railroad rails, pipelines, LNG tanks, walls, and the like. Further, it should be understood by one of ordinary skill in the art that the apparatus  10  may be used on any magnetizable material. 
     Broadly, the apparatus  10  includes a frame assembly  14 , a handle assembly  16  and a magnetic flux assembly  18  which supports instrumentation for performing the magnetic flux leakage measurements. The frame assembly  14  includes a pair of spatially disposed substantially u-shaped members  20  and  22 . The frame assembly  14  is mounted on a plurality of wheels  25 ,  26 ,  27  and  28  so that the apparatus  10  may be movable over the steel plate  12  being inspected. 
     The handle assembly  16  is connected to the u-shaped members  20  and  22  of the frame assembly and is configured for an operator to steer and manipulate the apparatus  10  over the surface of the steel plate  12 . A computer and command module  30  is mounted on the handle assembly  16  for controlling the electronic and/or other powered operation of the apparatus  10 . The module  30  is provided with a display screen (not shown) for displaying detection/inspection results and instructions for communicating with the operator. Further, module  30  stores and transmits the magnetic flux leakage detection information via a signal path  32  from the magnetic flux assembly  18 . Once magnetic flux leakage is detected, the information will reflect on the module  30 . The signal path can be either manual signal paths, or electronic communication signal paths. The electronic communication signal paths can be logical and/or physical links between various software and/or hardware utilized to implement the present invention. The physical links could be air-way or cable communication links. When the apparatus is implemented, the signal paths may not be separate signal paths but may be a single signal path or multiple signal paths. In addition, it should be understood that the various information does not always have to flow between the components of the present invention in the exact manner shown provided the information is generated and received to accomplish the purposes set forth herein. 
     A power source  34 , such as a battery, is shown for providing power to the apparatus  10  by way of a cable  35 . The power source  34  is positioned on the handle assembly  16 . However, it will be understood by one of ordinary skill in the art that the power source may be positioned any place on the apparatus  10  and power may be provided to the apparatus in various ways. Further, any known power source used for providing power to an object can be utilized herein, so long as the power source functions in accordance with the present disclosure. 
     The magnetic flux assembly  18  includes a pair of magnet assemblies  36  and  38  and a sensor bar  40 . The pair of magnet assemblies  36  and  38  and sensor bar  40  are operably connected to a steel support member  42  positioned in and operably connected to the u-shaped members  20  and  22  of the frame assembly  14 . Each of the magnet assemblies  36  and  38  are positioned on opposite sides of the sensor bar  40 . Each of the magnet assemblies  36  and  38  are provided with a steel portion  44  and  46 , respectively, and a magnet portion  48  and  50 , respectively. The steel portions  44  and  46  are operably connected to the steel support member  42  and the magnet portion  48  and  50  are operably connected to the steel portions  44  and  46 , respectively. This forms a magnetic circuit that is completed when sitting on the steel plate  12 . 
     Referring to  FIG. 3 , each magnet portion  48  and  50  (not shown) are configured to provide two rows of permanent magnets forming rows of north and south pole faces  52  and  54 , respectively. When the pole faces of the magnets are magnetically coupled to the steel plate  12 , a continuous magnetic circuit is formed. In one preferred embodiment, Neodymium iron boron magnets produced by K&amp;J Magnetics, Inc. may be utilized (2″×2″×½″, Nickel plated N42 material). However, it should be understood that any size or type of magnet may be utilized in the apparatus  10  so long as the magnet functions in accordance with the present disclosure. 
     Referring to  FIGS. 1-2 and 4 , the sensor bar  40  includes a pair of coils  60  ( 60   a  and  60   b ), a plurality of magnetic field sensors (magnetoresistor)  62 , a temperature sensor  64 , and an accelerometer  66 . In one embodiment, the coils  60  are arranged perpendicular to the steel plate  12  being inspected to measure the tangential magnetic field changes and the magnetic field sensors  62  are arranged parallel to the steel plate  12  being inspected to measure the normal component of the magnetic field. There are a plurality of coil pairs and sensors positioned and/or stacked end to end along the length of the sensor bar  40  to examine a wide area of the steel plate  12 . The length of the sensor bar  40  may vary and thus the number of coils pairs and magnetic field sensors will vary. Referring to  FIG. 5 , by way of example, the coils  60  are shown in twelve pairs of one inch coils ( 1 A- 12 A and  1 B- 12 B) that can inspect twelve inches of the steel plate at one time. As shown, there is a slight shift between the coils so as to cover any gap between the coil pairs. If the coil pairs are not shifted, there is a small gap between coil pairs that is not sensitive to magnetic field changes. Thus, when one of the coils in a pair is shifted there is no area that is not sensitive to magnetic field changes. 
     Referring to  FIG. 6 , in another embodiment, the pair of coils  60  may be provide in group of three coils  70  ( 70   a ,  70   b ,  70   c ) in a triad configuration. The triad configuration consists of three coils  70  perpendicular to the steel plate to be inspected. The center coil  70   c  has twice as many windings as the two outer coils  70   a  and  70   b . The coils  70  are wired to subtract the outer coils  70   a  and  70   c  from the central coil  70   c . The output of the triad coil  70  is sent into an amplifier (not shown). The arrangement of the triad coil  70  makes it sensitive to MFL “flaw shaped” signals and not sensitive to background noise. A single pair of coils effectively subtracts common mode noise (noise induced in both coils). A typical MFL flaw signal from sensor coils rises to a peak above a reference line, then falls below the reference line and finally returns to the reference line. The triad configuration has two sets of coils wired to look for the point where the flaw signal goes from positive to negative (that is the center of a flaw). Two signals from each coil pair in the triad configuration could also be made and let the computer make better flaw decision with the extra flaw signal data. 
     Referring back to  FIG. 4 , the temperature sensor  64  is positioned in the sensor bar  40  and helps to compensate the sensor and magnet variations related to temperature. Various temperature sensors may be utilized in apparatus  10 , for example, in one preferred embodiment, analog devices ADT7301, 13 bit±1° C. digital temperature sensor are used. 
     The accelerometer  66  is positioned in the sensor bar  40  and used to compensate the output of the coils  60  and  70  since the output varies with speed. Most MFL systems attempt to get a constant velocity so they do not have to compensate for changes in velocity. The accelerometer  66  also communicates to the module  30  when the apparatus  10  is sensing, sitting still, or being transported so battery power  34  can be maximized. One example of an accelerometer that may be utilized in the apparatus  10  are analog devices ADXL 362, 3 axis±2g MEMS accelerometer. Although shown positioned in the sensor bar  40 , in another embodiment, the accelerometer may be positioned in the module  30 . It should be understood that the accelerometer may be positioned at various locations on the apparatus  10 , so long as the accelerometer functions in accordance with the present disclosure as described herein. 
     A thin non-magnetic stainless steel wear surface portion  80  is provided on a bottom surface  82  of the sensor bar  40  so as to engage the surface of the steel plate  12  ( FIGS. 1 and 2 ) and protect the coils  60  and magnetic field sensors  62 . 
     The apparatus  10  reduces sensor outputs that are not related to metal loss flaws (false calls), gives a better size indication of the metal loss flaw by compensating for temperature, instrument speed and distance between the metal being inspected and the sensor assembly, and saves battery power by knowing when the apparatus  10  is being used as a sensor. 
     The construction and arrangement of the apparatus  10 , as shown in the various exemplary embodiments, is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed of multiple parts or elements, and elements shown as multiple parts may be constructed to be integrally formed, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present embodiments. 
     From the above description, it is clear that the present disclosure is well adapted to carry out the objects and to attain the advantages mentioned herein as well as those inherent in the invention. While embodiments of the invention have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the invention disclosed.