Abstract:
An in-line inspection tool comprising primary and secondary sensor suites is disclosed. The primary sensor suite may detect both interior and exterior defects. The secondary sensor suite may comprise a plurality of housings distributed in the circumferential direction around the body of the tool. Each housing may contain at least one flux sensor and at least one flux concentrator. The flux concentrator may increase the flux delivered to the flux sensor, thereby increasing the sensitivity of the secondary sensor suite while reducing the number of flux sensors required. The secondary sensor suite may detect substantially exclusively interior defects. By comparing the outputs of the primary and secondary sensor suites, a user may determine whether a defect is located on the interior or exterior of a pipeline being inspected.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/269,875 filed Nov. 12, 2008. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to pipeline inspection tools, and more particularly to apparatus and methods for determining whether a defect resides on the interior or exterior surface of a pipeline. 
     2. Background of the Invention 
     Oil, petroleum products, natural gas, hazardous liquids, and the like are often transported using pipelines. The majority of these pipelines are constructed from steel pipe. Once installed, a pipeline will inevitably corrode or otherwise degrade. Proper pipeline management requires identification, monitoring, and repair of defects and vulnerabilities of the pipeline. For example, information collected about the condition of a pipeline may be used to determine safe operating pressures, facilitate repair, schedule replacement, and the like. 
     Typical defects of a pipeline may include corrosion, gouges, dents, and the like. Corrosion may cause pitting or general wall loss, thereby lowering the maximum operating pressure of the pipeline. Vulnerabilities may also include curvature and bending anomalies, which may lead to buckling, and combined stress and chemical or biological action such as stress corrosion cracking. Without detection and preemptive action, all such defects and vulnerabilities may lead to pipeline failure. 
     Information on the condition of a pipeline is often collected using an in-line inspection tool. An in-line inspection tool typically uses sensors to collect information about a pipeline as it travels therethrough. In the past, in-line inspection tools have used magnetic flux leakage to determine the condition of a pipeline wall. Flaws in ferromagnetic pipe can be detected by the perturbations they cause in a magnetic field applied to the wall of a pipeline. 
     Some in-line inspection tools include primary sensors suitable to identify defects that occur in ferromagnetic pipe both on the inner diameter (ID) or interior surface and on the outer diameter (OD) or exterior surface of the pipe. However, the primary sensors may be unable to determine which are interior defects (i.e., located on the inner diameter) and which are exterior defects (i.e., located on the outer diameter). Accordingly, some in-line inspection tools include secondary sensors tasked with discriminating between interior and exterior defects. 
     Current technologies require numerous secondary sensors, usually about half the number of primary sensors. Accordingly, current systems are hampered by the cost, power consumption, space consumption, data storage consumption of all those secondary sensors. Thus, what is needed is a new apparatus and method for reducing the number of secondary sensors without reducing the ability to discriminate between interior and exterior defects. 
     SUMMARY 
     An in-line inspection tool and associated methods in accordance with the present invention may comprise or utilize various components including a plurality of inspection assemblies. The inspection assemblies may be distributed circumferentially about the tool. Inspection assemblies may move in a radial direction with respect to the main body of an in-line inspection tool. This freedom of motion may accommodate general and local changes in the pipeline being inspected. 
     In selected embodiments, an inspection assembly may include a sensor assembly and a mount. A mount may extend to connect a sensor assembly to the rest of an in-line inspection tool. A mount may enable a sensor assembly to move in a radial direction with respect to the rest of an in-line inspection tool. In certain embodiments, a mount may comprise a four bar linkage (e.g., a parallelogram linkage). A mount may hold a sensor assembly in a proper orientation against the interior surface of the pipeline being inspected. 
     A sensor assembly may include a housing, circuit board assembly, back bar, two magnets, one or more sensors (e.g., flux sensors), one or more flux concentrators, two fillers, and a wear plate. The housing may contain and protect other components of a sensor assembly from the pressure and chemicals found in a pipeline environment. A circuit board assembly may include whatever electronic components or connections are necessary to support proper operation of the one or more sensors connected thereto. 
     A back bar may be formed of a magnetic material and form a link in the magnetic circuit of a sensor assembly. The two magnets may have opposite polarity and be positioned on a back bar, one opposite the other. The magnets may generate a magnetic field thereabout. Two fillers, one for each magnet, may be formed of a material (e.g., low carbon steel) suitable for passing or conducting the magnetic field from the magnets to the face of the sensor assembly. Accordingly, with the face of the sensor assembly positioned directly against the interior surface of a pipeline, the interior surface, fillers, magnets, and back bar may combine to form a magnetic circuit. 
     Extending between the two magnets to effectively form a small short in the magnetic circuit may be a combination of one or more sensors and one or more flux concentrators. Accordingly, when a defect in the wall of a pipeline perturbs the magnetic field applied thereto by a sensor assembly, that perturbation may be directed by one or more of the flux concentrators to one or more corresponding sensors. Accordingly, defects (i.e., interior defects) in the pipe wall anywhere across the width of the sensor assembly (and slightly therebeyond) may be detected. 
     In operation, a primary sensor suite may detect both interior and exterior defects. In contrast, due to the size or type of the magnets involved, the magnetic field induced into the wall of a pipe by the secondary sensor suite may be weak. This weak magnetic field may not penetrate to the outside of the pipeline being inspected. Thus, the magnetic field generated by a secondary sensor suite may be altered (i.e., perturbed) by interior defects, but not by exterior defects. 
     By so limiting a secondary sensor suite, an inference may be made that if the primary sensor suite detects a defect, but the secondary sensor suite does not, then the defect must be located on the exterior of the pipeline being inspected. Conversely, if both the primary and secondary sensor suites detect a defect, then the defect must be located on the interior of the pipeline being inspected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which: 
         FIG. 1  is an elevation view of one embodiment of an in-line inspection tool in accordance with the present invention; 
         FIG. 2  is a perspective view of selected inspection assemblies positioned with respect to one another as they would be when installed on an in-line inspection tool in accordance with the present invention; 
         FIG. 3  is a cross-sectional view of one embodiment of an inspection assembly in accordance with the present invention; 
         FIG. 4  is an exploded perspective view of the inspection assembly of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of one embodiment of a sensor assembly in accordance with the present invention; 
         FIG. 6  is a cross-sectional view of the sensor assembly of  FIG. 5 ; 
         FIG. 7  is a schematic perspective view of a sensor, flux concentrator pair, magnet pair, and back bar in accordance with the present invention; 
         FIG. 8  is a schematic top plan view of one embodiment of a flux concentrator in accordance with the present invention; 
         FIG. 9  is a perspective view of selected internals of a multi-sensor embodiment of a sensor assembly in accordance with the present invention; and 
         FIG. 10  is a perspective view of selected internals of a single-sensor embodiment of a sensor assembly in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the drawings herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in the drawings, is not intended to limit the scope of the invention as claimed, but is merely representative of various embodiments of the invention. The illustrated embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
     Referring to  FIG. 1 , an in-line inspection tool  10  or vehicle  10  in accordance with the present invention may comprise various components including inspection sensors  12   a ,  12   b , canisters  14 , driving cups  16 , couplers  18 , position sensors  20 , and the like. Depending on the configuration of the in-line inspection tool  10  and the size of the pipeline to be inspected, the arrangement and number of components (e.g., the number of canisters  14 ) may vary. 
     Canisters  14  may house equipment such as one or more processors, memory devices, and batteries. The driving cups  16  may center the tool  10  within the pipeline and enable fluid traveling within a pipeline to engage the tool  10 , thereby pushing the tool  10  through the pipeline. In selected embodiments, driving cups  16  may be formed of a somewhat flexible polyurethane or similar material. Couplers  18  may support bending of the tool  10 , enabling the tool  10  to accommodate bends in the pipeline. Like the driving cups  16 , in selected embodiments the couplers  18  may be formed of somewhat flexible polyurethane or similar material. Alternatively, the couplers  18  may be formed of a mechanical pivoting device. 
     An in-line inspection tool  10  may extend in a longitudinal direction  22  from a head end  24  to a tail end  26 . The various components  12 ,  14 ,  16 ,  18 ,  20  of an in-line inspection tool  10  may be arranged in series. For example, in the illustrated embodiment, the head end  24  of a tool  10  may comprise a head section  28  comprising one or more driving cups  16 . Following the head section  28  may be a primary sensor suite  30 . In selected embodiments, a primary sensor suite  30  may comprise an array of magnets  32  and sensors  12   a . A coupler  18   a  may extend to connect the head section  28  to the primary sensor suite  30 . 
     Following the primary sensor suite  30  may be a first canister  14   a . In one embodiment, the first canister  14   a  may house the hardware providing the processing and memory storage for the in-line inspection tool  10 . A coupler  18   b  may extend to connect the primary sensor suite  30  to the first canister  14   a.    
     The first canister  14   a  may be followed by another driving cup  16  and a secondary sensor suite  34 . A coupler  18   c  may engage the second sensor suite  34  and extend rearwardly to engage a second canister  14   b . In one embodiment, the second canister  14   b  may house the batteries providing the power for the in-line inspection tool  10 . 
     In selected embodiments, a driving cup  16  may connect to the second canister  14   b . One or more position sensors  20  may then engage the second canister  14   b , driving cup  16 , or some combination thereof to form the tail end  26  of the in-line inspection tool  10 . In one embodiment, the position sensors  20  may comprise one or more odometers  20  positioned to roll along the interior surface of the pipeline and measure the distance traveled by the in-line inspection tool  10 . 
     Referring to  FIG. 2 , in selected embodiments, a secondary sensor suite  34  may include a plurality of inspection assemblies  36  distributed circumferentially (i.e., in a circumferential direction  38 ) about a central axis  40  of an in-line inspection tool  10 . Each inspection assembly  36  may include a sensor assembly  42  and a mount  44 . A mount  44  may extend to connect a sensor assembly  42  to the rest of an in-line inspection tool  10 . For example, a mount  44  may extend to connect corresponding sensor assembly  42  to an interior cylinder (not shown) forming the back bone of the secondary sensor suite  34 . Accordingly, inspection assemblies  36  may encircle the interior cylinder. 
     In selected embodiments, sensor assemblies  42  may be staggered in the axial direction  40 . Accordingly, as adjacent sensor assemblies  42  move inward in a radial direction, they may do so without structural interference therebetween. This stagger may be accomplished by shortening the length of every other mount  44 . Alternatively, the stagger may be accomplished by alternating in the axial direction  40  the position of securement between the mounts  44  and the rest of an in-line inspection tool  10 . 
     In certain alternative embodiments, sensor assemblies  42  may be shaped and secured in the manner described in U.S. patent application Ser. No. 12/403,754 filed Mar. 13, 2009, which is hereby incorporated by reference. Accordingly, sensor assemblies  42  in accordance with the present invention may be held adjacent to one another with the first end of one sensor assembly  42  circumferentially overlapping the second end of an adjacent sensor assembly  42 . For example, a first end of each sensor assembly  42  may be tapered toward the leading edge of the sensor assembly  42 . The second end of each sensor assembly  42  may be tapered toward the trailing edge thereof. 
     As adjacent sensor assemblies  42  move inward in a radial direction, they may be urged closer to one another. The force urging the two sensor assemblies  42  closer together may increase the overlap thereof. In selected embodiments, the abutting surfaces may be specifically designed to permit or even facilitate this additional overlap. 
     With additional overlap of adjacent sensor assemblies  42 , each sensor assembly  42  may tend to rotate about an axis extending in the radial direction. That is, for sensor assemblies  42  to slide past one another, each sensor assembly  42  may rotate to vacate space into which an adjacent sensor assembly  42  may extend. The corresponding angles or tapers of adjacent contacting ends may ensure that each sensor assembly  42  rotates in the same direction. While overlap of sensor assemblies  42  may result in multiple sensors tracking the same portion of pipe, this redundancy in constricted spaces may ensure that sensor coverage in non-constricted spaces is uniformly distributed and complete. 
     In selected embodiments, a mount  44  may be sufficiently flexible or provide a pivoting mechanism to permit a sensor assembly  42  held thereby to rotate about an axis extending in the radial direction in the manner described hereinabove. A mount  44  may also be sufficiently biased so that after the constriction in the pipe has passed, the mount  44  may return the sensor assembly  42  held thereby to its original alignment. 
     Referring to  FIGS. 3 and 4 , inspection assemblies  36  may move with respect to the interior cylinder or main body of an in-line inspection tool  10 . For example, a mount  44  of an inspection assembly  36  may enable a sensor assembly  42  to move in a radial direction  46  with respect to the rest of an in-line inspection tool  10 . This freedom of motion may accommodate changes in the pipe being inspected. For example, features such as bends, constrictions, changes in the thickness of the wall of the pipe, circumferential welds, dents, and damaged pipe walls may all affect the interior diameter of a pipeline. Movement of mounts  44  may permit corresponding sensor assemblies  42  to closely track the interior surface of a pipeline in spite of changes in the interior diameter thereof. 
     In selected embodiments, a mount  44  in accordance with the present invention may include a base  48 , first link  50 , second link  52 , interface  54 , wear plate  56 , and biasing member  58 . A base  48  may include one or more apertures  60  for receiving fasteners  62 . The fasteners  62  may provide the connection between a corresponding inspection assembly  36  and the rest of an in-line inspection tool  10 . 
     In operation, a base  48 , first link  50 , second link  52 , and interface  54  may operate as a four bar linkage. For example, a base  48 , first link  50 , second link  52 , and interface  54  may form a parallelogram linkage. Accordingly, the base  48 , first link  50 , second link  52 , and interface  54  may hold a sensor assembly  42  in the correct location against the interior surface of the pipeline being inspected, restrict movement of the sensor assembly  42  to a single radial plane (i.e., a plane containing the central axis  40 ), and support movement of the sensor assembly  42  within the radial plane to pass bends, changes in diameter, pipeline features, and damaged pipe walls without impeding movement of the in-inspection tool  10 . In selected embodiments, various pins  66  may pivotably connect the base  48 , first link  50 , second link  52 , and interface  54  to another. 
     A biasing member  58  may urge or bias a mount  44  to a particular location within its range of motion. For example, a biasing member  58  may urge a parallelogram linkage formed by a base  48 , first link  50 , second link  52 , and interface  54  radially outward to one extreme of its range of motion. Accordingly, a biasing member  58  may hold a sensor assembly  42  against the interior surface of the pipeline being inspected, despite gravitational forces, magnetic forces, and the like that may urge the sensor assembly  42  toward the central axis  40  of the in-line inspection tool  10 . 
     In selected embodiments, a biasing member  58  may be configured as a torsion spring. For example, in the illustrated embodiment, a biasing member  58  is configured as a torsion spring and held in place about a pivot pin  66  by a spring spacer  68 . The torsion spring has a first end engaging a base  48  and a second end engaging a second link  52 . Accordingly, pivoting of the second link  52  with respect to the base  48  may respectively load and unload the torsion spring. If desired or necessary, a torsion spring may be preloaded such that there is an immediate and significant resistance to inward deflection of a corresponding sensor assembly  42 . 
     An interface  54  may provide a location for securing a wear plate  56  to the rest of a mount  44 . In certain embodiments, an interface  54  may include various fasteners  70  securing a wear plate  56  thereto. In selected embodiments, the various fasteners  70  may include two threaded fasteners  70  welded to extend from the underside of a wear plate  56  (e.g., below one of the wear surfaces  74 ). Washers  72  and the like may be included as needed or desired to effect a proper and secure connection between an interface  54  and a wear plate  56 . In certain alternative embodiments, an interface  54  may support pivoting of a sensor assembly  42  about an axis extending in a radial direction  46 , facilitating the overlap described hereinabove. 
     A wear plate  56  may include various wear surfaces  74 . The wear surfaces  74  may be positioned to slide along the interior surface of a pipeline during inspection. Accordingly, a wear plate  56  may be configured to withstand such use. Moreover, a wear plate  56  may prevent other components of an inspection assembly  36  from being exposed to such wear. 
     In selected embodiments, a wear plate  56  may include a cradle  76 . A cradle  76  may be sized and shaped to receive a sensor assembly  42  therewithin. A cradle  76  may also be configured to retain a sensor assembly  42  therewithin. For example, in certain embodiments, a cradle  76  may include one or more apertures  78  for receiving fasteners  80 . Accordingly, the fasteners  78  may pass through the apertures  78  and engage a sensor assembly  42 , thereby securing the sensor assembly  42  to the wear plate  56  and to the rest of the inspection assembly  36 . 
     Referring to  FIGS. 5 and 6 , in certain embodiments, a sensor assembly  42  in accordance with the present invention may include a housing  82 , circuit board assembly  84 , back bar  86 , two magnets  88   a ,  88   b , one or more sensors  90  (e.g., flux sensors  90 ), one or more flux concentrators  92 , two fillers  94   a ,  94   b , and a wear plate  96 . A housing  82  may contain and protect other components of a sensor assembly  42  from the pressure and chemicals found in a pipeline environment. In selected embodiments, one or more of the components within a housing  82  may be potted in chemical and pressure resistant materials (e.g., selected polymers). 
     A housing  82  may include various apertures  98 ,  100 ,  102 . One or more such apertures  98  may receive fasteners  80  for securing a sensor assembly  42  in place. Another aperture  100  may provide a location for wires to exit or enter the housing  82 . Yet another aperture  102  may provide the opening into which the other components of a sensor assembly  42  are inserted during a manufacturing or installation process. 
     A circuit board assembly  84  in accordance with the present invention may include whatever electronic components or connections are necessary to support proper operation of the one or more sensors  90  connected thereto. A back bar  86  may be formed of a magnetic material and form a link in the magnetic circuit of a sensor assembly  42 . In selected embodiments, a back bar  88  may include one or more apertures  104  extending therethrough. The apertures  104  may enable sensors  90  positioned on one side of a back bar  86  to connect to a circuit board assembly  84  positioned on an opposite side of the back bar  86 . 
     In selected embodiments, two magnets  88   a ,  88   b  of opposite polarity may be positioned on a back bar  86 , one opposite the other. In such embodiments, the magnets  88   a ,  88   b  may generate a magnetic field thereabout. Fillers  94   a ,  94   b , one for each magnet  88   a ,  88   b , may be formed of a material (e.g., low carbon steel) suitable for passing or conducting the magnetic field from the magnets  88  to the face  64  of the sensor assembly  42 . Accordingly, with the face  64  of the sensor assembly  42  positioned directly against the interior surface of a pipeline, the interior surface, the fillers  94 , magnets  88 , and back bar  86  may combine to form a magnetic circuit. 
     Extending between the two magnets  88   a ,  88   b  to effectively form a small short in the magnetic circuit may be a combination of one or more sensors  90  and one or more flux concentrators  92 . The one or more sensors  90  may monitor the magnetic circuit or field for perturbations thereof. 
     In operation, a primary sensor suite  30  may detect both interior and exterior defects. In contrast, due to the size or type of the magnets  88  involved, the magnetic field induced into the wall of a pipe by the secondary sensor suite  34  may be weak. This weak magnetic field may not penetrate to the outside of the pipeline being inspected. Thus, the magnetic field generated by a secondary sensor suite  34  may be altered (i.e., perturbed) by interior defects, but not by exterior defects. 
     By so limiting a secondary sensor suite  34 , an inference may be made that if the primary sensor suite  30  detects a defect, but the secondary sensor suite  34  does not, then the defect must be located on the exterior of the pipeline being inspected. Conversely, if both the primary and secondary sensor suites  30 ,  34  detect a defect, then the defect must be located on the interior of the pipeline being inspected. 
     Capping a housing  82  may be a wear plate  96 . A wear plate  96  may be formed of a non-magnetic, wear-resistant material. For example, a wear plate  96  may be formed of a non-magnetic alloy of select metals. In selected embodiments, a wear plate  96  may be arced to match the curvature of the interior surface of a pipeline to be inspected. The fillers  94  may be similarly arced. Accordingly, a sensor assembly  42  may be configured at its face  64  to support intimate contact with the interior surface of the pipeline. 
     Select components of an inspection assembly  36  may be formed of non-magnetic, minimally magnetic, or magnetically permeable materials. For example, certain components may be formed of non-magnetic stainless steel. This may preclude or limit the undesirable interference of such components with the magnetic field induced in the wall of the pipe being inspected. 
     Referring to  FIGS. 7 and 8 , flux concentrators  92  in accordance with the present invention may strengthen the magnetic flux  106  delivered to a sensor  90  (e.g., flux sensor  90 ). In selected embodiments, a flux concentrator  92  may be formed of a material with higher magnetic permeability than the surrounding matter (e.g., air, potting material, or the like). A flux concentrator  92  may have a relatively wide distal end  108  or edge  108  and a relatively narrow proximal end  110  or edge  110 . A flux concentrator  92  may further include a gradual taper creating a smooth transition from the distal end  108  to the proximal end  110 . 
     In operation, due to its higher magnetic permeability, a flux concentrator  92  or pair of flux concentrators  92   a ,  92   b  may create a short in the magnetic circuit or field generated by corresponding, adjacent magnets  88   a ,  88   b . Accordingly, flux  106  may be routed in a first concentrator  92   b  and concentrated at the narrow end  110  thereof, proximate a flux sensor  90 . The flux sensor  90  may measure the strength of the concentrated magnetic field more readily than the strength of the lower level ambient field 
     As flux  106  passes through a sensor  90 , it may exit adjacent a narrow edge  110  of a second flux concentrator  92   a . The second flux concentrator  92   a  may provide continuity to the concentrated flux field and return the concentrated field to the normal level in the ambient background field. Accordingly, one flux concentrator  92   b  may fulfill the concentration role, while the other  92   a  guides the concentrated flux field through the flux sensor  90 , receives the concentrated flux field, and distributes the flux field back to its original dimensions. 
     Referring to  FIG. 9 , in selected embodiments, a sensor assembly  42  may include more than one sensor  90 . For example, in the illustrated embodiment, a sensor assembly  42  includes three flux sensors  90   a ,  90   b ,  90   c . Each flux sensor  90  may be positioned between two flux concentrators  92 , each positioned as a minor image of the other. For example, a first flux sensor  90   a  may be positioned between first and second flux concentrators  92   a ,  92   b , a second flux sensor  90   b  may be positioned between third and fourth flux concentrators  92   c ,  92   d , and a third flux sensor  90   c  may be positioned between fifth and sixth flux concentrators  92   e ,  92   f.    
     When an interior defect in the wall of a pipe perturbs the magnetic field applied thereto by a sensor assembly  42 , that perturbation may be directed by one or more of the flux concentrators  92  to one or more of the flux sensors  90 . Accordingly, defects in the pipe wall anywhere across the width of the sensor assembly  42  (and slightly therebeyond) may be detected. In certain embodiments comprising a sensor assembly  42  with multiple sensors  90 , those multiple sensors  90  may be connected in series on a single circuit. Accordingly, in such embodiments, any change in the magnetic field caused by a defect anywhere across the width of the sensor assembly  42  may be passed along a single data line and a single recording channel. Thus, a sensor assembly  42  may be very sensitive, yet conserve data storage space. 
     Referring to  FIG. 10 , in selected embodiments, a sensor assembly  42  may include only one sensor  90 . For example, in the illustrated embodiment, a sensor assembly  42  includes one flux sensor  90 . This one flux sensor  90  may be positioned between two flux concentrators  92   a ,  92   b , each positioned as a mirror image of the other. Accordingly, when an interior defect in the wall of a pipe perturbs the magnetic field applied thereto by a corresponding sensor assembly  42 , that perturbation may be directed by a flux concentrator  92  to the flux sensor  90 . Accordingly, defects in the pipe wall anywhere across the width of the sensor assembly (and slightly therebeyond) may be detected. Thus, a sensor assembly  42  may be sufficiently sensitive, yet save the cost of additional sensors and conserve electrical power. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.