Abstract:
A gauge for measuring the thickness of a piece of steel or other ferromagnetic substrate. The gauge may be used to measure the wall thickness of tubing, a pipe, a shim, a plate, etc, given that it&#39;s made from a material that a magnet might be attracted to. The gauge uses a force sensor to measure the force between a magnet and the tubing, pipe, shim, plate, etc. Because different thicknesses correspond to a different magnitude of force, the gauge may be used to find flaws and variations in the material. The gauge may use a force sensor that is approved for use in or near flammable environments.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present application relates generally to the inspection and measurement of substrates made of steel or other ferromagnetic material. Substrates may be used in load bearing applications where a departure from a specified material thickness may be undesirable. Such departures might occur over a small area, as may be caused by a corrosion pit, or over a large area, as may be caused by manufacturing variation or error. 
         [0003]    2. Description of the Related Art 
         [0004]    Commonly in industry, where it may be difficult to access both sides of a substrate, the thickness of the substrate may be measured by an inspection instrument located proximal to the substrate. For example, it may be difficult to measure the thickness of a substrate (e.g. pipe, tubing, coiled tubing, strip, plate, etc.) that has an extended length. The inspection instrument may be moved substantially continuously along the substrate, or vice versa. Inspection instruments may operate on ultrasonic or magnetic principles, and may require electricity, which may make the inspection instruments unsuitable for use in some environments. 
         [0005]    For example, inspection instruments may be desired for use in an environment where flammable gases may be encountered, such as on or around oil refineries, oil wells and/or gas wells. Thus, it may be desirable for electrical equipment to be constructed such that an electrical fault is incapable of igniting flammable gases. Equipment designed toward overcoming inadvertent gas ignition is generally required to be certified by an approving authority, such as Underwriters Laboratories, OSHA, FM Global, Nationally Recognised Testing Laboratories, ETL, NSF International, the Canadian Standards Association, The TÜV Rheinland Group, and those approving authorities cooperating with the ATEX directive. 
         [0006]    Some types of electrical sensing instruments (e.g. pressure sensors, temperature sensors, force sensors, etc.) are available for purchase, with certification from the approving authority, for use in flammable atmospheres. However, instruments that inspect the thickness of a ferromagnetic substrate are not readily available with certification, creating difficulties when it is desired to conduct an inspection in an environment having a potentially explosive atmosphere. 
         [0007]    It would be beneficial to provide a method and/or apparatus for adapting available, certified sensors to effect an inspection of a ferromagnetic substrate, while maintaining safety from accidental ignition in a flammable atmosphere. 
         [0008]    The present invention is directed toward overcoming, or at least reducing the effects of one or more of the issues set forth above. 
       SUMMARY 
       [0009]    One embodiment of the invention is a gauge for measuring the thickness of a ferromagnetic substrate, the gauge comprising at least one first magnet with a first polarity, the first magnet having a first polarity, a force measurement means operatively connected to the at least one first magnet, wherein the force measurement means is configured to measure the force between the at least one first magnet and a substrate, the substrate comprising ferromagnetic material, and wherein the at least one magnet is configured to magnetically saturate the substrate. 
         [0010]    The gauge may further comprise at least one second magnet, having a second polarity. The at least one second magnet is oriented such that the second polarity is opposite the first polarity. The gauge may further comprise a yoke, comprising ferromagnetic material, connected to the at least one first magnet and the at least one second magnet, wherein the at least one first magnet is in substantially a same plane as the at least one second magnet, and wherein the force measurement means is operatively connected to the at least one first magnet and the at least one second magnet. 
         [0011]    The gauge may further comprise a standoff means connected to the force measurement means which is configured to hold the at least one first magnet at a standoff distance from the substrate. The gauge may further comprise a distance measurement means, wherein the distance measurement means is configured to measure the distance between the at least one first magnet and the substrate. The substrate may comprise a pipe, a tube, coiled tubing, a strip, a shim, or a plate. The first magnet and the second magnet may be contoured to substantially match a contour of the substrate. The standoff distance may be configured to be about equal to or greater than the greatest expected thickness of the substrate. The force measurement means may comprise a mechanical scale, an accelerometer, a transducer, a load cell, a fiber optic strain sensor, hydrostatic load cell, spring balance gauge, or other suitable means. The force measurement means may be configured to prevent accidental ignition of flammable matter. The force measurement means may be certified by an approving authority for use in environments comprising flammable matter. The standoff means may comprise an arch and a movement means. The movement means may comprise a sliding member or a rotatable roller. The gauge may further comprise a frame, the frame may comprise a first frame member and a second frame member, the first frame member and the second frame member may be pivotally connected together, and a portion of the frame may be connected to the standoff means. 
         [0012]    Another embodiment of the invention is an apparatus for inspecting the thickness of a substrate. The apparatus may comprise a frame, having a first frame member and a second frame member. The first frame member and the second frame member may be pivotally connected together. The apparatus includes at least one thickness measurement gauge. The at least one thickness measurement gauge may include a first magnet with a first polarity, a second magnet having a second polarity, the second magnet being oriented such that the second polarity is opposite the first polarity, and a yoke connecting the at least one first magnet and the at least one second magnet. The apparatus includes a force measurement means that may be connected to the yoke, and a standoff means operatively connected to the force measurement means. An aperture is formed in the middle of the frame and may be configured to accommodate a substrate that comprises ferromagnetic material. The force measurement means of the at least one thickness measurement gauge is configured to measure the force between the substrate and the at least one first magnet and the at least one second magnet. 
         [0013]    The force measurement means may be configured to connect to a computer. The apparatus may include a speed sensor that may be configured to measure the speed of the substrate relative to the apparatus. The apparatus may include a temperature sensor, that may be configured to measure a temperature substantially proximate to the apparatus. The apparatus may include a tilt angle sensor that may be configured to measure a tilt of the apparatus with respect to the Earth. 
         [0014]    An embodiment of the invention is a method for measuring the thickness of a substrate comprising holding at least one magnet at a standoff distance from a substrate, the substrate comprising ferromagnetic material, moving the substrate with respect to the magnet, measuring the force between the substrate and the magnet using a force measurement means, outputting the measured force between the substrate and the magnet from the force measurement means, and comparing the measured force at a first point along the substrate to the measured force at a second point along the substrate to find variation in the substrate. 
         [0015]    The method may include using the measurement of the force between the substrate and the magnet to calculate a thickness of the substrate. The method may include calculating a difference in thickness between the first point and the second point. The substrate may comprise a pipe, tube, coiled tubing, strip, or plate. The force measurement means may be may comprise a mechanical scale, an accelerometer, a transducer, a load cell, a fiber optic strain sensor, hydrostatic load cell, spring balance gauge, or other suitable means. The force measurement means may be certified by an approving authority to be used in a flammable environment. The method may include displaying an output based at least partially on the outputted measured force. 
         [0016]    These and other embodiments of the present application will be discussed more fully in the description. The features, functions, and advantages can be achieved independently in various embodiments of the claimed invention, or may be combined in yet other embodiments. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0017]      FIG. 1  is a cutaway side view of an embodiment of a thickness measurement gauge; 
           [0018]      FIG. 2  is a cutaway side view of the thickness measurement gauge of  FIG. 1  with magnetic flux density lines added; 
           [0019]      FIG. 3  is a cutaway side view of the thickness measurement gauge of  FIG. 1  with magnetic flux density lines; 
           [0020]      FIG. 4  is a cutaway perspective view of another embodiment of a thickness measurement gauge; 
           [0021]      FIG. 5  is a perspective view of yet another embodiment of a thickness measurement gauge; 
           [0022]      FIG. 6  is a graph of a magnetization curve of a mild steel; 
           [0023]      FIG. 7  is a side view of a coiled tubing reel; 
           [0024]      FIG. 8  is a block diagram of an embodiment of a thickness measurement gauge. 
       
    
    
       [0025]    Like reference numbers and designations in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0026]    In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that modifications to the various disclosed embodiments may be made, and other embodiments may be utilized, without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0027]      FIG. 1  is a cutaway side view of an embodiment of a thickness measurement gauge  100  that may measure the thickness of ferromagnetic material. The gauge  100  comprises a first magnet  120 , polarized in a first direction, and a second magnet  130  polarized in a second direction that is opposite the first direction. The first magnet  120  and the second magnet  130  are connected by a connecting member (“yoke”)  110 , which is comprised of a ferromagnetic material. Ferromagnetic material may include Iron (e.g. iron, steel, stainless steel, steel alloys), Nickel, Manganese, Chromium, or Cobalt, as well as alloys and rare earth metals, and ceramic materials, such as ferrites. The first magnet  120  and the second magnet  130  are connected to one side of the yoke  110 , which may hold the magnets  120 ,  130  substantially within the same plane. The magnets  120 ,  130  generate a magnetic field that propagates through the yoke  110  (as shown in  FIG. 2 ). Other configurations of the magnets  120 ,  130  and the yoke  110 , such as swapping and/or reversing the magnets, would be apparent to one of ordinary skill in the art given the benefit of this disclosure. 
         [0028]    Referring again to  FIG. 1 , a target substrate  140  is held at a standoff distance, sd, relative to the magnets  120 , 130  of the gauge  100 . The target substrate  140  comprises ferromagnetic material, which may be attracted to the magnets  120 ,  130 . When a magnet, such as the magnets  120 ,  130  of the gauge  100 , is near ferromagnetic material, such as the target substrate  140 , a force is seen between the two components and can be measured by a force measurement means  160 . The magnitude of the force is affected by a number of variables. For example, the magnitude of the force is affected by the distance between the magnets  120 ,  130  to the target substrate  140 ; a greater distance corresponds to a smaller force. Also, the physical size of the magnets  120 ,  130 , as well as the strength and direction (orientation) of the magnetic field generated by the magnets  120 ,  130 , may affect the force. The shape of the magnets  120 ,  130  or the shape of the target substrate  140  may affect the force as well. For example, if the magnets  120 ,  130  are substantially planar and the target substrate  140  is not, then the magnetic field would be conducted more strongly by portions of the target substrate  140  that are closer to the magnets  120 ,  130 , which may result in a different force than would be seen with complementarily shaped components. 
         [0029]    The material of the target substrate  140  may also affect the magnitude of the force between the substrate  140  and the magnets  120 ,  130 . Generally, materials that have a greater permeability have a greater attraction to a magnet, resulting in a greater force seen between the magnet and the material. It may be said that a material with greater permeability may accommodate a greater magnetic flux density or may have a greater ability to conduct magnetic flux through itself than materials with lesser permeability. Additionally, a greater amount of a material may conduct more magnetic flux which will result in a greater force between the material and the source of the magnetic flux. For example, the target substrate  140  will generally produce a weaker force than a relatively thicker target substrate  141  (shown in  FIG. 3 ) when near a magnet. The correspondence between force and thickness may be advantageously used for calculating the thickness of ferromagnetic material, such as the target substrate  140  without directly measuring the thickness. For example, if all other variables are held at substantially the same value, a change in the force between the target substrate  140  and the magnets  120 ,  130  will be attributable to a change in thickness of the target substrate  140 . Because the thickness of the target substrate  140  and the force are related, if the force is known, the thickness may be predicted to an industrially useful degree of accuracy, such as within a hundredth of a inch, given that all other variables are held substantially constant, and that the target substrate  140  is in saturation, as will be further discussed later. 
         [0030]      FIG. 2  is another side view of the gauge  100  of  FIG. 1 , comprising the first magnet  120 , the second magnet  130 , and the yoke  110 , as well as the target substrate  140 .  FIG. 2  also illustrates magnetic flux lines. Magnetic flux lines can be used to represent the magnetic flux density, B, of a magnetic system, such as the system of  FIG. 2 . The magnetic flux lines form continuous, closed loops. Each magnetic flux line represents a linkage (“flux linkage”) between the magnets  120 ,  130  and the target substrate  140 . The flux linkages correspond to the magnetic force between the magnets  120 ,  130  and the target substrate  140 . More flux lines travelling through the target substrate  140  represents a greater force between the target substrate  140  and the magnets  120 ,  130 . 
         [0031]    As illustrated by  FIG. 2 , internal gauge flux lines  150  represent portions of magnetic flux that are inside the magnets  120 ,  130  and the yoke  110 , whereas external gauge flux lines  151  represent portions of magnetic flux that have propagated out of the gauge  100 . Additionally, magnetic flux lines may propagate within the target substrate  140 , as illustrated by internal target flux lines  152 , as well as through the target substrate  140 , as illustrated by external target flux lines  153 . The presence of external target flux lines  153  indicate that the target substrate  140  is in saturation, and may not accommodate additional flux linkages, as will be further discussed later. 
         [0032]      FIG. 6  shows a magnetization curve of steel, with Magnetic Induction or Magnetic Flux Density, B, (induced in target ferromagnetic material) on the Y-axis, and Magnetic Intensity, H, (radiated from a magnetic source) on the X-axis. As shown in  FIG. 6 , when H is small (less than about 7,000 Amps/Meter), B scales approximately linearly. However, as H gets larger, B begins to increase more slowly, until, at increasingly large H values (greater then about 12,000 Amps/Meter), B grows very slowly by comparison, seeming to approach a value asymptotically. The region of the graph in which B grows slowly compared to the growth of H is called the “saturation region”. When the target substrate  140  (shown in  FIG. 1 ) is in the saturation region or “in saturation,” a greater Magnetic Intensity, H, may increase the total magnetic flux density, B, a very small (substantially negligible) amount. Alternatively, when the target substrate  140  is near the non-saturation portion of the magnetization curve, a variation in the target substrate  140 , such as a thick region, may take the target substrate  140  out of saturation, which may result in unexpected force readings, such as a smaller increase in force than would be expected if the material were in saturation. 
         [0033]    Further, the force between the magnets  120 ,  130  and the target substrate  140  may not vary with the thickness of the target substrate  140  if the target substrate  140  is not saturated. A non-saturated target substrate  140  indicates that all of the available magnetic flux radiating from the magnets  120 ,  130  is propagating through the target substrate  140  and that all possible flux linkages have been formed between the target substrate  140  and the magnets  120 ,  130  and that none have propagated through and beyond the target substrate  140 . Therefore, if a variation in the target substrate  140 , such as a thick region, is seen by the magnet, additional linkages will not form, which will result in the same magnitude of force as was seen between the magnets  120 ,  130  and the target substrate  140  at the thinner region. By contrast, when the target substrate  140  is in saturation, magnetic flux will propagate through the target substrate  140  and will appear on the other side of the target substrate  140 , indicating that the magnets  120 ,  130  are radiating more magnetic flux than the target substrate  140  can conduct. When a thicker region in the target substrate  140  is seen by the magnets  120 ,  130 , some of this extra magnetic flux will be conducted by the additional material, increasing the magnetic force between the target substrate  140  and the magnets  120 ,  130 . 
         [0034]      FIG. 3  illustrates the gauge  100  of  FIGS. 1 and 2  interacting with a target substrate  141  that is thick, relative to the target substrate  140  (shown in  FIGS. 1 and 2 ). The target substrate  141  comprises the same ferromagnetic material as the target substrate  140 , and is held at the same standoff distance, sd, from the magnets  120 ,  130  to the closest surface of the target substrates  140 ,  141 . 
         [0035]      FIG. 3  also shows magnetic flux lines  150 ,  151 ,  152 , and  153 . As illustrated in  FIG. 3 , due to greater thickness, the target substrate  141  is able to accommodate a greater number of internal target flux lines  152  (flux linkages) than the target substrate  140  of  FIGS. 1 and 2 . This is also indicated by fewer external target flux line  153  propagating out of the target substrate  141 , relative to the target substrate  140 . The larger number of flux linkages translates into a greater force between the target substrate  141  and the magnets  120 ,  130 , relative to the force between the target substrate  140  and the magnets  120 ,  130 . Given that all other relevant variables are known or measurable, and that the target substrates  140 ,  141  are in saturation, the difference in force will correspond to the difference in thickness. Thus, the difference in force may be used to calculate the difference in thickness between the target substrate  140  and the target substrate  141 . 
         [0036]    In another embodiment, the gauge  100  may include only a single magnet  120  with a force measurement means  160  that is configured to measure the force between the magnet  120  and a target substrate  140 , as shown in  FIG. 8 . 
         [0037]    The gauge  100  may further comprise other suitable components, such as sensors to correct for non-ideal conditions that the gauge  100  may encounter. For example, if the temperature of the gauge  100  and/or the target substrate  140  (shown in  FIG. 1 ) changes, the Magnetic Flux Density, B, in the target substrate  140  may also change. A change in the Magnetic Flux Density, B, may result in a variation of the measured force, which may cause an undesired change in the apparent measured thickness of the target substrate  140 . The change can be compensated for by operatively connecting a temperature measurement means  176  to the gauge  100 . The temperature reading from the temperature measurement means  176  may be used to correct the measured thickness of the target substrate  140 , as would be understood by one of ordinary skill in the art, given the benefit of this disclosure. The temperature measurement means  176  may be placed on or near the gauge  100 , or may be placed in a separate location, given that the separate location is maintained at substantially the same temperature as the gauge  100 . Alternatively, the temperature may be input into the system, or corrected for, manually. 
         [0038]    Another suitable component may be a speed measurement means  174 . The speed measurement means  174  may be added to correct for eddy currents created by movement from the gauge  100  and/or the target substrate  140  with respect to each other. Movement in the axial direction will result in eddy currents being created in the target substrate  140 . Such eddy currents create opposing magnetic forces, which may change the measured force, and thus the apparent thickness of the target substrate  140 . The eddy currents may be compensated for by factoring in the speed of the target substrate  140  with respect to the gauge  100 . The speed measurement means  174  may be connected to and/or located on or near the gauge  100 . Alternatively, the speed may be measured or calculated through other means and may be input into the system, such as, for example, manually or another suitable input means. 
         [0039]    Additionally, a change in the orientation of the gauge  100  with respect to the ground may change the output of the force measurement means  160 ; the force of gravity may add or subtract from the force seen by the force measurement means  160 . The force of gravity can be accounted for by operatively connecting a tilt angle measurement means  178  to the gauge  100 , and using measurements from the tilt-angle sensor to adjust the thickness measurement of the target substrate  140 . Alternatively, the gauge  100  may be held at a substantially constant angle and/or the tilt angle of the gauge  100  may be manually input into and/or compensated for in the system. 
         [0040]    The gauge  100  may be operatively connected to a computer  180  that may interface with the force measurement means  160 , the speed measurement means  174 , the temperature measurement means  176 , and/or the tilt angle measurement means  178 , 
         [0041]    The gauge  100  may further comprise other suitable components that may correct for non-ideal conditions that may be encountered by the gauge  100 , as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. 
         [0042]      FIG. 4  illustrates another embodiment of a thickness measurement gauge  400  comprising a first magnet  420  having a surface  425  and a second magnet  430  having a surface  435 . The magnets  420 ,  430  are connected by a yoke  410 , the yoke  410  comprising ferromagnetic material. A target substrate  440  comprising ferromagnetic material is also shown in  FIG. 4 . The surfaces  425 ,  435  have been contoured to complement the target substrate  440 . This contouring may ensure that a flaw or variation in the target substrate  440  that is not centered with the magnets  120 ,  130  may be measured substantially accurately. The target substrate  440  of  FIG. 4  may comprise a portion of a pipe, a tube, coiled tubing, a strip, a bar, or other suitable object. Other target substrates  440  would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. 
         [0043]    The embodiment of  FIG. 4  further comprises a force measurement means  470  connected to the yoke  410  and to a support arch  460 . As shown in  FIG. 4 , the support arch  460  is generally U-shaped and comprises a movement means, such as a sliding member or a first roller  481  connected to the support arch  460  at one end through a first rotatable axle  482 , and a second rotatable roller  483  connected to the support arch  460  at the other end through a second axle  484 . Movement means may comprise other suitable components, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. 
         [0044]    The support arch  460  is substantially rigid and may provide a substantially uniform and constant standoff distance, sd, between the magnets  420 ,  430  and the target substrate  440 . The first rotatable roller  481  and the second rotatable roller  483  may roll smoothly along the outer surface of the target substrate  440  enabling the gauge  400  and the target substrate  440  to be moved smoothly in relation to each other while keeping the standoff distance substantially the same. 
         [0045]    Though the support arch  460  will ideally keep the magnets  420 ,  430  at a substantially constant standoff distance, sd, it is recognized that variation in the standoff distance, sd, may be present. To minimize the effects of this potential variation, the standoff distance, sd, may be set at about equal to the greatest expected thickness of the target substrate  440 . Greater standoff distances, sd, such as two or three times the greatest expected thickness of the target substrate  440 , may further minimize the effect of variation in the standoff distance, sd. Alternatively, a distance measurement means  172  (shown in  FIG. 1 ) may be used to measure the distance between the target substrate  440  and the magnets  420 ,  430 . Measurements from the distance measurement means  172  may be used to correct for variations in the standoff distance. The distance measurement means  172  may interface with the computer  180  (shown in  FIG. 1 ). 
         [0046]    The gauge  400  may be used to measure the absolute thickness of the target substrate  440  or may be used to measure relative variations and/or flaws in the thickness of the target substrate  440 . For example, given that the relevant variables of the system illustrated by  FIG. 4 , such as the characteristics of the target substrate  440  and the characteristics of the gauge  400  are known, the target substrate  440  may be placed at the standoff distance, sd, a force measurement may be taken, and the thickness of the target substrate  440  may be calculated. 
         [0047]    In another example, the gauge may be used to calculate the relative thickness of the target substrate  440 . A sample force measurement may be taken at a reference point on the target substrate  440 , such as at one end of the target substrate  440  or at another suitable point that may be measured independently to verify that the force measurement is representative of the thickness of the target substrate  440 . The sample force measurement may be compared against other measurements to show variation in the target substrate  440 . Alternatively, the gauge  400  may be used to take dynamic measurements along the target substrate  440 , outputting the measurements to be analyzed in substantially real time or as a whole or in parts, at a later time. 
         [0048]    The force measurement means  470  may be any device that can measure force. For example, the force measurement means  470  may be a mechanical scale, an accelerometer, a transducer, a load cell, a fiber optic strain sensor, hydrostatic load cell, spring balance gauge, or other suitable means. Some sensors that may potentially be used with the gauge  400  are among the Honeywell, Sensotec line of load cells, such as, for example, the Model 41 Precision Low Profile Load Cell. The force measurement means  470  may have an interface that may be used in a larger system, such as with a system that comprises one or more cables, connectors, in-line amplifiers, display units, power supplies, chart recorders, alarm panels, or data acquisition computers, as would be apparent to one of ordinary skill in the art given the benefit of this disclosure. For example, the force measurement means  470  may be operatively connected to a device, such as a computer  180  (shown in  FIG. 1 ), that may monitor, record, and/or compare the measurements taken by the force measurement means  470  and may output a signal or alarm, based at least partially on the measurements outputted by the force measurement means. The signal or alarm may indicate that a flaw or a violation of a specified variance in the target substrate has been detected. Further, the computer may output a comparison of two measurements, and absolute measurement, a running output of a measurement, or another suitable measurement, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. The output of the computer  180  and/or the force measurement means  470  may be displayed on a display (not shown) that is operatively connected to the computer  180  and/or the force measurement means  470 . 
         [0049]    The gauge  400  may be used in an environment where flammable gases may be encountered, such as on or around oil refineries, oil wells and/or gas wells. In such environments, it may be desirable for electrical equipment to be constructed such that an electrical fault is incapable of igniting flammable gases. Equipment constructed toward overcoming accidental gas ignition is generally required to be certified by an approving authority, such as Underwriters Laboratories, OSHA, FM Global, Nationally Recognised Testing Laboratories, ETL, NSF International, the Canadian Standards Association, The TÜV Rheinland Group, and those approving authorities cooperating with the ATEX directive. Currently, some types of electrical sensing instruments such as pressure, temperature, and force measurement means are available for purchase with certification from the approving authority for use in such environments. A gauge  400  comprising a force measurement means  470  that is certified by the approving authority may be suitable for use in an environment where flammable gases may be encountered. 
         [0050]    The gauge  400  may further comprise other suitable components, such as sensors to correct for non-ideal conditions that the gauge  400  may encounter, as described previously. 
         [0051]      FIG. 5  is a perspective view of yet another embodiment of a thickness measurement gauge  500 . The gauge  500  comprises a gauge frame  510 , a first, second, third, and fourth gauge section  520 ,  540 ,  560 , and  580  respectively. Each of the gauge sections  520 ,  540 ,  560 , and  580  comprise a support arch  526 ,  546 ,  566 , and  586 , a force measurement means  527 ,  547 ,  567 , and  587 , a yoke  521 ,  541 ,  561 , and  581 , a first magnet  522 ,  542 ,  562 , and  582 , and a second magnet (not shown). The support arches  526 ,  546 ,  566 , and  586  further comprise rollers  523 ,  543 ,  563 , and  583  and axles  524 ,  544 ,  564 , and  584 , and may act as a movement means, and may keep the magnets at a substantially constant standoff distance from a target substrate  530 . Other movement means and standoff means would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. 
         [0052]    The gauge frame  510  further comprises a first frame member  514  and a second frame member  515 , pivotally connected at one end by a hinge  516  and connected at the other end by a connecting means  550 . The connecting means  550  illustrated in  FIG. 5  comprises a first tab  552 , a second tab  554 , and a securing means (not shown). The first frame member  514  and the second frame member  515  of the gauge frame  510  may be connected with other suitable components, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. 
         [0053]      FIG. 5  further illustrates the target substrate  530 . The target substrate  530  may comprise a portion of a pipe, a tube, coiled tubing, a strip, a bar, or other suitable substrate. The target substrate  530  is positioned within an aperture  570  formed at the convergence of the four gauge sections  520 ,  540 ,  560 , and  580 . The magnets may be contoured to substantially match the outer surface  534  of the target substrate  530 . To position the target substrate  530  within the gauge  500  illustrated in  FIG. 5 , the connecting means  550  may be disengaged, allowing the gauge frame  510  to open at the hinge  516 , separating the first and second frame members  514 ,  515  and allowing the target substrate  530  to be place into or taken out of the aperture  570 . Alternatively, the connecting means  550  may be disengaged, allowing the gauge  500  to be opened at the hinge  516  and removed from around the target substrate  530 . Additionally, the target substrate  530  may be fed through the aperture  570  from one end of the target substrate  530 , which may reduce or eliminate the need for the first frame member  514  and the second frame member  515  to be disconnected from each other. 
         [0054]    In the embodiment illustrated in  FIG. 5 , the magnets are contoured to substantially match the contour of the target substrate  530 , which may maintain the standoff distance, sd, at substantially the same distance from the outer surface of the target substrate  530  across the outer surface of the magnets. The gauge  500  may be configured such that the magnets may be replaceable, for example, with differently shaped or contoured magnets which may allow the contours a of differently shaped the target substrate  530  to be substantially matched. 
         [0055]    As previously described, the gauge  500  may measure the thickness of the target substrate  530 . As configured in  FIG. 5 , the gauge  500  may take four measurements simultaneously, in the areas of the four gauge sections  520 ,  540 ,  560 , and  580 . The four measurements may substantially measure the absolute or relative thickness of a full cross-section of the target substrate  530 . 
         [0056]    The gauge  500  may be configured such that it may be moved relative to the target substrate  530 , or such that the target substrate  530  is moved relative the gauge  500 . By moving the gauge  500  and/or the target substrate  530  relative to each other, the relative or absolute thickness of the target substrate  530  may be measured. As configured, the gauge  500  may measure substantially all the variations and/or flaws in the target substrate  530  with a single pass along the length of the target substrate  530 . 
         [0057]    The gauge  500  may be used advantageously in an environment where a large amount of pipe or coiled tubing, comprising ferromagnetic material, is being installed. For long term reliability, it may be desirable to measure the thickness of the pipe or coiled tubing, monitoring changes in thickness for flaws and/or manufacturing variation. The pipe or tubing may be moved through the aperture  570  of the gauge  500 . The gauge  500  may continually measure the absolute and/or relative thickness of the pipe or coiled tubing as it moves through the aperture, outputting measurements that may be compared and/or interpreted by a person and/or computer. 
         [0058]    The gauge  500  may be used in an environment where flammable gases may be encountered, such as on or around oil refineries, oil wells and/or gas wells. A gauge  500  comprising force measurement means  527 ,  547 ,  567 , and  587  that are certified by an approving authority, such as Underwriters Laboratories, OSHA, FM Global, Nationally Recognised Testing Laboratories, ETL, NSF International, the Canadian Standards Association, the TÜV Rheinland Group, and those approving authorities cooperating with the ATEX directive, may be suitable for use in an environment where flammable gases may be encountered, as described previously. 
         [0059]    The gauge  500  may further comprise other suitable components, such as sensors to correct for non-ideal conditions that the gauge  500  may encounter, as described previously. 
         [0060]      FIG. 7  illustrates a coiled tubing reel  700  that may be used in an environment where a large amount of coiled tubing, comprising ferromagnetic material, may be installed, such as, for example, on or around oil wells and/or gas wells. The coiled tubing reel  700  includes an embodiment of a thickness measurement gauge  780 , such as, for example, a previously described embodiment of a thickness measurement gauge  100 ,  400 ,  500 . The coiled tubing reel  700  illustrated in  FIG. 7  comprises ferromagnetic tubing  740  that may be wound around a reel  770 , which is rotatably connected to a frame  750  with a connecting means, such as a reel axle  760 . The gauge  780  is connected to the frame  750  though one or more connecting means, such as an articulated connector  710  and a support member  720 , which may be rotatably connected to the frame  750  by a connecting means, such as an axle  730 . The tubing  740  may pass to a side of the gauge  780  or through an aperture formed in the gauge  780 , as it is withdrawn from or rewound upon the reel  770 . As illustrated in  FIG. 7 , the gauge  780  is configured to measure the wall thickness of the tubing  740  by measuring the force between a magnet and the tubing. The coiled tubing reel  700  may be used in an environment where flammable gases may be encountered, such as on or around oil refineries, oil wells and/or gas wells. 
         [0061]    While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. 
         [0062]    For example, equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and the number and configuration of various vehicle components described above may be altered, all without departing from the spirit or scope of the invention as defined in the appended claims. 
         [0063]    Such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed exemplary embodiments. It is to be understood that the phraseology of terminology employed herein is for the purpose of description and not of limitation. Accordingly, the foregoing description of the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes, modifications, and/or adaptations may be made without departing from the spirit and scope of this invention.