Abstract:
An instrument pig and method of operation thereof for determining the characteristics of a ferromagnetic pipeline through which it passes, including a pig body, first and second coaxial circumferential, spaced apart magnets of opposed polarities supported to the pig body and providing substantially complete magnetic saturation of an area of the pipeline between the magnets, first instruments between the magnets and arranged to generate signals that are responsive to flux leakage servicing to provide first information as to anomalies in the pipeline interior and/or exterior surfaces, second instruments supported by the pig body between said magnets and arranged to generate signals that are responsive to eddy currents induced in the pipeline interior surface servicing to provide second information as to anomalies in the pipeline interior surface, signal processing circuitry combining the first and second signals and wherein the second instruments are energized only in response to signals generated by said signal processing circuitry.

Description:
REFERENCE TO PENDING APPLICATIONS 
   This application is not based upon any pending domestic or international patent applications. 
   REFERENCE TO MICROFICHE APPENDIX 
   This application is not referenced in any microfiche appendix. 
   FIELD OF THE INVENTION 
   Disclosed herein is a pipeline inspection instrument pig having ID-OD discrimination. The instrument pig functions by flux leakage detection coupled with an eddy current system providing means for discriminating between anomalies in the pipeline exterior and interior surfaces. ID-OD discrimination is accomplished employing an eddy current pulser coil and an eddy current detection coil to provide a signal used to indicate whether a detected flux leakage anomaly is in the pipeline interior surface. 
   BACKGROUND OF THE INVENTION 
   The Prior Art 
   The use of magnetic flux leakage inspection tools in pipelines is an established technology. Flaws in ferromagnetic pipes have been detected by establishing a magnetic field in the wall of the pipe and detecting flux leakage caused by anomalies in the pipe wall. Distortion of the magnetic field caused by anomalies such as corrosion, pits, or changes in the structure of the pipe wall, some of which can be caused by couplings, welds, collars, or so forth, can be found, measured, and identified in recorded information. Flux leakage pipeline inspection tools therefore provide an established method of determining the characteristics of a pipeline through which an inspection pig passes. 
   One problem which has existed with reference to flux leakage inspection tools is that of identifying whether a detected flux leakage is occasioned by anomalies, such as corrosion, on the interior or exterior pipe wall surface. When making an inspection of a pipeline it is important to record the location and size of anomalies in the pipe wall as well as of the anomaly identified as to whether it exists on the pipe interior surface or the pipe exterior surface. 
   A known means of measuring flux leakage is by the use of a Hall-effect device. 
   Flux leakage inspection instrument pigs typically include the use of a plurality of armatures, each having at one end a positive magnetic pole and at the other end a negative magnetic pole. The magnets are constructed and dimensioned so as to substantially magnetically saturate a short circumferential length of the pipe as the inspection pig moves through the pipe. 
   For background information relating to instrument pig used for pipeline inspection and particularly pigs that detect anomalies by measuring flux leakage, reference can be made to the following previously issued United States Patents: 
   
     
       
             
             
             
           
         
             
                 
             
             
               PATENT 
               DATE OF 
                 
             
             
               NUMBER 
               ISSUE 
               TITLE  
             
             
                 
             
           
           
             
               3,949,292 
               Apr. 6, 1976 
               Pipeline Inspection Device with Pivotal Sup- 
             
             
                 
                 
               port Structure 
             
             
               4,769,598 
               Sep. 6, 1988 
               Apparatus for Electromagnetically Testing 
             
             
                 
                 
               the Walls of Pipelines 
             
             
               4,945,306 
               Jul. 31, 1990 
               Coil and Hall Device Circuit for Sensing 
             
             
                 
                 
               Magnetic Fields 
             
             
               4,964,059 
               Oct. 16, 1990 
               Apparatus for Inspecting A Pipeline 
             
             
               5,283,520 
               Feb. 1, 1994 
               Method of Determining Thickness of 
             
             
                 
                 
               Magnetic Pipe by Measuring the Time It 
             
             
                 
                 
               Takes the Pipe To Reach Magnetic 
             
             
                 
                 
               Saturation 
             
             
               5,293,117 
               Mar. 8, 1994 
               Magnetic Flaw Detector for Use with Ferro- 
             
             
                 
                 
               magnetic Small Diameter Tubular Goods 
             
             
                 
                 
               Using A Second Magnetic Field To Confine 
             
             
                 
                 
               A First Magnetic Field 
             
             
               5,506,505 
               Apr. 9, 1996 
               Apparatus for Remotely Indicating Pipeline 
             
             
                 
                 
               Pig Including A Sensor Housing Having Sur- 
             
             
                 
                 
               face Engaging Orthogonally Disposed Para- 
             
             
                 
                 
               magnetic Materials A Solid State Sensor and 
             
             
                 
                 
               A Flag 
             
             
               5,565,633 
               Oct. 15, 1996 
               Spiral Tractor Apparatus and Method 
             
             
               5,864,232 
               Jan. 26, 1999 
               Magnetic Flux Pipe Inspection Apparatus for 
             
             
                 
                 
               Analyzing Anomalies In A Pipeline Wall 
             
             
               6,023,986 
               Feb. 15, 2000 
               Magnetic Flux Leakage Inspection Tool for 
             
             
                 
                 
               Pipelines 
             
             
               6,640,655 
               Nov. 4, 2003 
               Self Tracking Sensor Suspension Mechanism 
             
             
               6,683,452 
               Jan. 27, 2004 
               Magnetic Flux Density Apparatus for, e.g., 
             
             
                 
                 
               Detecting An Internal Crack of A Metal or A 
             
             
                 
                 
               Shape of the Metal 
             
             
                 
             
           
        
       
     
   
   In addition to the above-listed patents, a relevant reference is an article published in the Society of Petroleum Engineers in May 1991 entitled “Full-Signature Multiple-Channel Vertilog,” G. W. Adams and W. D. Moffat, authors. 
   BRIEF SUMMARY OF THE INVENTION 
   The instrument pig of this invention is used for determining the characteristics of a ferromagnetic pipeline through which it passes. The essential features of the instrument pig include a pig body that is coaxially supported within a pipeline and is configured with cups to cause the pig body to move within the pipeline in response to fluid flow. “Fluid” as used herein includes liquids, gases or combinations thereof. 
   Supported to the pig body are a plurality of first and second coaxial, circumferential spaced apart magnets of opposed polarities. The pairs of magnets are arranged circumferentially around the pig body with the magnetic poles spaced close to the pipeline interior circumferential wall. The spaced apart magnets of opposed polarities are configured for providing substantially complete magnetic saturation of a circumferential area of the pipeline between the magnets, the fully magnetized area of the pipeline constantly moving with the pipeline pig body as it moves through the pipeline. 
   Affixed to the pig body are first instruments that are supported between the magnetic poles and arranged to generate signals that are responsive to flux leakage. Flux leak from the fully magnetized section of the pipeline occurs as a consequence of anomalies appearing in the interior or exterior circumferential surfaces of the pipeline wall. 
   A second instrument is supported by the pig body between the poles of the magnets and arranged to generate signals that are responsive to eddy currents induced in the pipeline interior surface. By measuring induced eddy currents, indication can be obtained of whether a detected anomaly exists in the interior surface. If an anomaly is detected that occurs as a consequence of flux leakage and if the eddy current instruments indicate that the pipeline interior circumferential wall is free of anomalies, then by logic it is concluded that the detected anomaly is in the pipeline exterior surface. If an anomaly is detected and simultaneously the eddy current instrumentation indicates the existence of an anomaly in the interior pipeline surface, then the logic system provides an indication that the detected anomaly is on the pipeline interior surface. 
   Determining whether a detected anomaly is on the interior or exterior surface is thereby obtained by combining the first and second signals to indicate both the magnitude and the interior or exterior location of the pipeline anomalies. 
   Energy is required to induce eddy currents into the interior surface of a pipeline, and typical eddy current sensing systems can consume substantial amounts of energy for continuous operation. It is necessary to introduce and then measure eddy currents only when measurements need to be recorded. For this reason, in the instrument pig herein, the eddy current instruments are energized only when requested by a signal processing circuit. 
   While flux leakage can be detected in various ways, a very successful and a preferred system for practicing the invention herein includes the use of Hall-effect devices. 
   The invention herein can be further summarized as a method of determining the characteristics of the interior and exterior surfaces of a metal pipeline, including the steps of (a) moving an axially supported pig body through a pipeline; (b) by means carried by the pig body, magnetically saturating a circumferential zone of the pipeline that moves with the instrument pig; (c) continuously measuring changes of reluctance in the moving circumferential magnetized zone of the pipeline to provide indications of the presence and size of anomalies in the pipeline interior or exterior surfaces; (d) electrically actuating a plurality of pulse coils to induce eddy currents in the internal surface of the moving circumferential zone of the pipeline; (e) by means of a plurality of sensing coils, each paired with a pulse coil, measuring the eddy currents to determine the presence or absence of an anomaly in the pipeline interior surface; (f) comparing the results of steps in (c) and (e) to determine whether an anomaly detected in step (c) is on the interior or exterior of the surface of the pipeline; (g) recording the results of steps (c) and (f) to provide information as to the anomaly&#39;s size and interior/exterior location with respect to the pipeline wall; and (h) energizing said plurality of pulse coils in step (d) only generated by said signal processing circuitry. 
   A better and more complete understanding of the invention will be obtained from the following detailed description of the preferred embodiments, and the claims, taken in conjunction with the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view of a pipeline pig assembly of a type that can be employed in practicing the invention. The pipeline pig in  FIG. 1  includes cups for contacting the interior surface of a pipeline wall and for causing the pig to move by fluid flow, either liquid or gas, through the pipeline. 
       FIG. 2  is an elevational view of the instrument portion of the pipeline pig of  FIG. 1  showing a plurality of paralleled, closely spaced apart armatures with permanent magnets. The armatures are attached by link arms to the pig body. 
       FIG. 3  is an elevational cross-sectional view of  FIG. 2  showing only a top and bottom positioned armature with its magnets, spacers, linkages, and instruments employed in this invention. 
       FIG. 4  is a partial isometric view showing a typical pipeline pig body and representative armatures with associated magnets, instruments, spacers, and linkages as employed in the invention. 
       FIG. 5  is a diagrammatic elevational, cross-sectional view showing a portion of a pipeline wall and showing the basic instruments employed in the invention including a Hall-effect sensor assembly and in combination an eddy current sensor. 
       FIG. 6  is a diagrammatic elevational view of a portion of an instrument pig used to practice the invention. This view illustrates a pig body with one armature with its attached magnets and instrumentation positioned between the magnets. By block diagram, the basic electronics used to practice the invention are illustrated. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   It is to be understood that this invention is not limited to the details of construction and arrangement of components illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. Further, the phraseology and terminology employed herein are for purposes of description and not of limitation. 
   Elements employed in illustrating the practice of the instrument pig and the methods of determining the characteristics of the interior and exterior surfaces of a metal pipeline, as illustrated in the attached drawings, will be identified by numbers indicated hereinbelow: 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               10 
               instrument pig 
             
             
               12 
               instrumentation section 
             
             
               14 
               elastomeric cups 
             
             
               16 
               instrument support package 
             
             
               18 
               odometers 
             
             
               20 
               pig body 
             
             
               22 
               A&amp;B end plates 
             
             
               24 
               armatures 
             
             
               26 
               positive pole magnet 
             
             
               29 
               negative pole magnet 
             
             
               30 
               forward link arm 
             
             
               32 
               rearward link arm 
             
             
               34 
               pin 
             
             
               36 
               slot 
             
             
               38 
               spacers 
             
             
               40 
               Hall-effect sensor 
             
             
               42 
               interior circumferential surface 
             
             
               44 
               pipeline 
             
             
               46 
               exterior circumferential surface 
             
             
               48 
               range of measurement 
             
             
               50 
               eddy current sensor system 
             
             
               54 
               induced eddy currents 
             
             
               56 
               head assembly 
             
             
               58 
               sensed eddy current 
             
             
               60 
               Hall-effect process circuitry 
             
             
               62 
               62A-D 
             
             
               64 
               eddy current pulser circuit 
             
             
               66 
               eddy current process circuit 
             
             
               68 
               output signal 
             
             
               70 
               signal processing and output circuit 
             
             
               72 
               Hall-effect instrumentation 
             
             
               74 
               eddy current instrumentation 
             
             
               76 
               conductor 
             
             
               78 
               conductor 
             
             
               80 
               conductor 
             
             
               82 
               conductor 
             
             
               84 
               conductor 
             
             
               86 
               odometer wheel 
             
             
               88 
               odometer circuit 
             
             
               90 
               positioning signal 
             
             
               92 
               conductor 
             
             
               94 
               recorder 
             
             
                 
             
           
        
       
     
   
   Referring to  FIG. 1 , a typical instrument pipeline pig of the type that can employ the principals of this invention is illustrated. The overall pipeline instrument pig is indicated generally by the numeral  10  and includes an instrumentation section  12  to which this invention is specifically directed. The typical instrument pipeline pig  10  includes the use of a plurality ( 5  being shown) of elastomeric cups  14  that have two basic functions. First, the cups  14  support the pipeline pig centrally within the pipeline, and second, they have circumferential edges or lips that engage a pipeline interior wall, forming a piston-like relationship so that fluid flowing through the pipeline causes a force against the cups that moves the instrument pipe  10  through the pipeline. 
   In addition to the instrumentation section  12 , a typical pipeline pig  10  includes as illustrated, an instrument support package  16  that typically contains batteries by which electrical energy is supplied to the instrumentation section  12 , and recording instruments. Instrument support package  16  is connected to the instrumentation section  12  by means of an internal cable (not shown). 
   Further, the typical pipeline pig includes an odometer  18  that is in the form of a wheel that engages the pipeline interior wall surface to provide electrical signals by which the location of detected anomalies in the pipeline wall are recorded. 
   It must be understood that the instrument pig  10  is illustrated by way of example only and not by limitation. The invention herein lies exclusively within the arrangement of the instrumentation section  12  and such instrument section can be used in conjunction with other instrument pig systems. 
   The instrumentation section  12  is illustrated in greater detail in  FIGS. 2-6 . Referring to  FIGS. 2 and 3 , a basic structural arrangement of an instrumentation system by which this invention can be practiced is illustrated. The instrumentation section  12  includes a pig body  20  having spaced apart end plates  22 A and  22 B. Supported between the end plates are a plurality of elongated armatures  24  that are in closely spaced parallel arrangement and positioned circumferentially around the pig body  20 . Each armature  24  supports at one end a positive pole magnet  26  and at the other end a negative pole magnet  28 . Rather than being called “negative” and “positive” pole magnets, they are frequently referred to as north pole and south pole magnets. Magnets  26  and  28  mounted on associated armatures  24  are closely spaced and of magnetic intensity so that the circumferential portion of the length of the pipe between magnets  26  and  28  is at least substantially fully magnetically saturated. 
   Each armature  24  is supported between plates  22 A and  22 B by a forward link-arm  30  and a rearward link-arm  32 . Each of the forward link-arms  30  is pivoted at one end to plate  22 A and at the rearward end to an armature  24 . The rearward link-arms  32  are each pivoted to an armature  24  at one end and the rearward end has a pin  34  received in a slot  36 . The link arms  30  and  32  thereby allow flexible radial position of each armature  24  with respect to the pig body  20 —that is, each armature can be deflected inwardly and outwardly as required to conform to the internal cylindrical surface of the pipe wall through which the instrument pig travels. 
   To maintain the magnets  26  and  28  in close proximity to the interior pipeline wall but at the same time prevent the magnets from being worn by engagement with the pipeline wall, spacers  38  are employed. Spacers  38  may be wheels as illustrated in the drawings or may be pads arranged to slide against the internal wall of the pipeline to thereby space the magnets  26  and  28  in close proximity to the pipeline wall but without touching the wall. The use of wheels functioning as spacers is a known technology and not a part of this invention. 
   The essence of the invention is best illustrated by referring to  FIGS. 5 and 6 .  FIG. 5  diagrammatically illustrates the basic concepts. The instrument pig  10  as generally indicated in  FIG. 5  carries with it instrumentation that includes essentially a Hall-effect sensor  40  supported by the instrument in close proximity to the interior circumferential surface  42  of a cylindrical pipeline  44  that has a corresponding exterior circumferential surface  46 . The use of Hall-effect sensors  40  is known technique for detecting flux leakage in a magnetically saturated pipe wall. The range of detection of anomalies obtained by Hall-effect sensor  40  is indicated by the dotted lines  48  in FIG.  5 . 
   If the instrument pig  10  of this invention included instrumentation that contained only Hall-effect sensors, it would function to provide a record indicative of anomalies in the pipe wall but such record would not provide information as to whether the detected anomalies are on the pipe interior circumferential surface  42  or the exterior circumferential surface  46 . To provide this lacking information, the instrument package of the instrument pig of this invention includes the use of eddy current sensor systems  50 . An “eddy current” is, generally speaking, an induced electric current in an electrically conductive object that typically causes a loss of energy. Eddy currents are sometimes also called “Foucault currents.” Eddy currents move contrary to the direction of a main current and usually in a circular motion. A unique characteristic of eddy currents is that when induced into a conductive object, they typically are confined to a shallow depth of the skin surface of the object. This characteristic is taken advantage of in the present invention in that, as illustrated in  FIG. 5 , each eddy current sensor system  50  functions by inducing an eddy current indicated by the dotted lines  54  into the interior circumferential surface  42  of pipeline wall  44 . The eddy currents  54  are induced by pulsing a coil carried by the eddy currents sensor system  54 . 
   Eddy current sensors are often employed to measure the proximity of electrically conductive materials. They exploit the “skin depth” effects that result from exposing a conductive material to a high-frequency magnetic field. As such, their effective field of view into the material is limited to a few thousandths of an inch. Additionally, they are able to operate inside a strong low-frequency magnetic field with little effect on performance. 
   The sensor concept disclosed in  FIG. 5  incorporates both the Hall-effect sensor  40  and the eddy current sensor system  50  that are supported in the same head assembly, such head assemblies  56  being seen best in  FIGS. 3 ,  4  and  6 . The system of this invention employs Hall-effect sensors  40  as primary quantitative indicators of metal loss and therefore the existence of anomalies in the pipe wall interior and exterior circumferential surfaces  42  and  46 . This is so since the field of view, that is the range of measurement  48  seen in  FIG. 5 , includes the entire pipe wall  44 . However the eddy current sensors see only a short depth into the interior pipe wall  42  and responds to metal loss that is localized to the inside wall of the pipe. 
   The eddy current sensor systems  50  employ the use of a pulse coil design to minimize the power required. This is illustrated in  FIG. 5  by an induced eddy current  54  and a sensed eddy current represented by the dotted lines of  58 . The quantitative extent of sensed eddy currents indicate the presence or absence of anomalies, that is missing metal, from the interior circumferential surface  42  of pipe  44 . 
   An important feature of the present invention is that the eddy current sensor system  50  is energized or excited to produce the induced eddy current  54  only as requested from the instrument electronics. This is schematically represented in  FIG. 6  which shows Hall-effect process circuitry  60  that responds to detected anomalies  62 A through  62 D in the wall of pipeline  44 . When requested by the signal processing circuit  70 , eddy current pulser circuit  64  is activated to stimulate the eddy current sensor system  50  to initiate induced eddy current represented by  54  in FIG.  5 . An eddy current process circuit  66  responds sensed eddy current  58  ( FIG. 5 ) and provides an output signal on conductor  68  to signal processing output circuit  70 . 
     FIG. 6  indicates schematically a portion of the instrument pig  10  of this invention showing the pig body  20 , an armature  24 , positive and negative magnets  26  and  28  as supported on the armature and a head assembly  56  positioned between the magnets that contain Hall-effect instrumentation  72  and eddy current instrumentation  74 . Eddy current instrumentation  74  responds to eddy current pulser circuit  64  to cause induced eddy currents  54  as seen in FIG.  5  and for detecting and measuring resultant sensed eddy current flow indicated by the numeral  58  in FIG.  5 . As shown in  FIG. 6 , the eddy current pulser signal is carried by conductor  76  to eddy current instrument  74  while the sensed eddy current is carried by conductor  78  to eddy current processing circuit  66 . The conductor  80  carries the signal from Hall-effect instrumentation  72  to the Hall-effect processing circuitry  60 . Initiating signals from processing circuit  70  to actuate eddy current pulser  64  are carried by conductor  82  while the quantitative process signal generated by the Hall-effect instrument  72  is passed by conductor  84  to signal processing and output circuit  70 . 
     FIG. 6  shows the use of an odometer wheel  86  supplying signals to an odometer circuit  88  which provides a positioning signal  90  to signal processing and output circuit  70 . 
   While ID/OD discrimination sensors have conventionally been arranged in a second array of heads located somewhere away from the magnetizer systems of an instrument pig, in the invention herein the Hall-effect sensor  72  and eddy current instrumentation  74  are in the same head assembly  56  positioned between magnetic poles  26  and  28 . This system eliminates the need for a secondary sensor array located elsewhere on a tool and subsequently reduces the number of connectors and cables required to pass signals from the sensor heads to the data logging electronics. 
   In summary, first instrumentation Hall-effect instrumentation  72  that is included in head assembly  56  and positioned between magnetic pole  26  and  28  is arranged to generate signals by way of conductor  80  that are responsive to flux leakage and thereby serves to provide first information as to anomalies  62 A through  62 D in the pipeline interior or exterior surfaces  42  and  46 . Second instrumentation, that is, eddy current instrumentation  74 , is supported by head assembly  56  between magnets  26  and  28  and arranged to generate signals that are responsive to eddy currents  54  and  58  as seen in  FIG. 5  that are induced in the pipeline interior surface  42  that provides second information as to anomalies in the interior wall  42  of the pipeline  44 . An important feature of the invention herein as illustrated in the schematic circuit diagram of  FIG. 6  is that the second eddy current instrumentation is energized only in response to signals generated by signal processing circuit  70 . In this way the energy required to operate eddy current instrumentation  74  is employed only when data is required and thus substantial energy saving is obtained. 
   The invention described herein is not limited to the specific illustrations contained in the drawings which are representative only of one embodiment of the invention which are presented to be a preferred embodiment at the time of the preparation of this application, but it is understood that the invention is limited only by the scope of the attached claim or claims including the full range of equivalency to which each element or step thereof is entitled.