Abstract:
An obstacle detecting pig for preliminary inspection of a section of a pipeline travels through the section and determines if there are any restrictions that exceed industry guidelines or that might damage other pigs that require the full bore of the pipe. In a first embodiment, a disk-shaped segmented resilient member ( 14 ) is mounted in the body of the pig. Its outside diameter is smaller by a spacing ( 21 ) than the inside diameter of the pipeline ( 15 ). The spacing is set at the maximum tolerable size of the obstacle encountered. The deformation of the member ( 14 ) is transmitted by a linkage ( 22 ) to a slider ( 16 ) activating a switch system signaling that an obstacle has been encountered. A non-resiliently deformable checkup disk ( 19 ) may be provided at the rear end of the pig, to double check that a no-signal passage through the pipe is not due to failure of the switching system. In a particularly preferred embodiment, the resilient member is a disc-shaped detector ( 46 ) made from an elastomer and provided at its leading surface with a scratch recording layer ( 51 ), for instance a layer of lead which is thin enough to follow resilient deformations of the elastomeric ring ( 50 ) as it encounters an obstacle, and return of the ring back to its regular, shape. The scratches caused on the recording layer are evaluated after the passage of the pig through the examined pipeline section. The detector is mounted directly on a slider ( 44 ) or the like operating device designed to produce electric signal when an anomaly is encountered. Preferably, the detector ( 46 ) is a replaceable element of the pig. In another embodiment described and claimed, the detector is comprised of a pair of flexible discs having embedded therein pairs of electronic signal providing means such as a magnet and a magnetic switch or sensor.  
     The device is structurally simple thus providing low manufacturing and operation costs and simple operation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an obstacle monitoring pipeline pig used in checking the interior of a pipeline for obstacles which might impede the movement of subsequently used pipeline inspecting devices or which exceed industry guidelines.  
           [0002]    A number of caliper pigs are on the market that provide detection of anomalies inside pipelines. They are usually expensive to produce and operate. These existing pigs monitor all restrictions along a pipeline regardless of the size of the anomalies. They normally collect a significant amount of data that requires interpretation by a technician or computer programs. This type of caliper pigs is represented, for instance, by the disclosure of U.S. Pat. Nos. 4,953,412 and 5,088,336 (both Rosenberg et al.) and also by U.S. Pat. Nos. 3,755,908 (VerNooy). The disclosures of the above patents are incorporated herein by reference.  
           [0003]    U.S. Pat. No. 4,481,816 (Prentice) describes a caliper pig provided with a monitoring arrangement comprising a substantially circular array of detecting portions which deform upon contact with the interior surface of the pipeline and remain deformed to provide an indication that the minimum radial distance has been exceeded. Viewed from the standpoint of the present invention, the device disclosed is of a relatively complex structure and allows only a single use of the detecting portions. Also, if a relatively large deformity is encountered prior to reaching a somewhat smaller deformity, the latter may be undetected.  
           [0004]    U.S. Pat. No. 4,227,309 (Jones) describes a pipeline pig which includes a flexible disc at a foremost part of the body. The disc is fixedly secured to the body of the pig and is provided with strain gauges which transmit deformations of the disc to electrical impulses to show which portion of the disc has been deformed by an abnormality within the pipeline. The use of the strain gauges renders the overall structure of the flexible disc complex thus increasing the cost of replacement of a damaged disc. Furthermore, the strain gauges are too sensible for the rough working environment of a damaged pipeline and may therefore produce false readings. The piezo electric strip was found working as a microphone; it recorded all vibrations and one could not differentiate between the vibrations and restrictions. Vibrations of the body and thus of the disc are often encountered in use of the pig. There is no backup system which would indicate, at least roughly, the location of an abnormality in case of failure of the electronic system. The location of the disc at the foremost end of the body is disadvantageous as distorted readings of the deformation of the disc by an abnormality occur at a straight portion of the pipeline and in bends of the pipeline. Also, the disc being fixedly secured to the body, it cannot maintain the same angular clock position as it inevitably changes such position with the rotation of the pig about its longitudinal axis. Such rotation may occur when an abnormality is encountered by the guiding cups. The device therefore is not capable of showing the clock position of an abnormality instantly recorded.  
           [0005]    U.S. Pat. No. 4,299,033 (Kiley et al.) presents a calipering tool for oil wells or the like applications. It operates with a plurality of feelers which are in a constant contact with the pipe of a well. The tool is of a complex structure. While it may be useful in calipering wells, it is not suitable for applications where only major deformities of the pipe are required to be discovered to avoid damage to a subsequently used caliper pig. Also, the tool of this reference is raised and lowered by means of a suspension cable which cannot be used in pipeline calipers as they often have to travel long distances of tens of miles.  
           [0006]    U.S. Pat. No. 4,443,948 (Reeves) describes a pig for monitoring the internal surface profile of a pipeline. It is provided with a plurality of sensors which are in constant contact with the inner surface of the monitored pipeline. A complex system is required to compare output signals from the sensors with an expected value and reference signal generated when they differ by more than a predetermined amount.  
           [0007]    U.S. Pat. No. 4,457,073 (Payne) shows a pipeline pig with sensing means capable of monitoring small changes in the internal configuration of a pipeline. A complex mechanism is used to monitor dragging effect to which an elastomeric cap is submitted upon encountering an obstacle. A major obstacle would most likely destroy or at least damage the mechanism used to record the deformities, as the radial cup is in a constant contact with the interior of the monitored pipeline.  
           [0008]    U.S. Pat. No. 4,098,126 (Howard) is provided with a plurality of sensors disposed about the circumference of a resilient holding cup. A spring system forces the sensors against the inside of the pipeline. The device is suitable for monitoring relatively small deformities but would become damaged if a major or sharp deformity is encountered. It is of relatively complex structure with a number of flat spring elements constantly pressing the sensors against the pipeline.  
           [0009]    U.S. Pat. No. 4,091,678 (Potter) shows a device for detecting dents or out of round conditions of a buried pipeline. The pig contains two concentric rings. The outer ring is sized to accurately fit the inspected pipeline. It carries on its inner surface electrical contacts adapted to co-operate with contacts provided on the outer surface of the inner ring to close an electric circuit when the outer ring is deformed radially inwardly. The device may be suitable for detecting minor anomalies of the cross-section of the pipeline. Larger deformities would destroy or at least damage the system of coaxial rings.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to provide an obstacle monitoring or caliper pig which would be of a simple structure permitting relatively low manufacturing costs, monitoring only major obstacles of a predetermined minimum magnitude and providing a simple operation.  
           [0011]    In general terms the invention provides a caliper pig for detecting an obstruction in a pipeline, having an elongated body including a front end and a rear end and comprising carrying guide rings at said front and rear ends for supporting the body in a coaxial sliding engagement with the interior of the pipeline and driving the body through the pipeline, the front end first, using the flow of fluid in the pipeline, said body further carrying a coaxial, generally disc-shaped, detector operatively associated with transfer mechanism including a converting member movable relative to the body responsive to a generally axial force to transmit a mechanical impulse developed at the detector to activate and to deactivate an electrical signal producing device housed in said body, wherein  
           [0012]    (i) said detector has an outer diameter smaller than the inside diameter of the pipeline to define therewith a generally annular void having a predetermined radial clearance;  
           [0013]    (ii) said transfer mechanism is operatively disposed between a flexing portion of the detector and said converting member to transmit changes in the form of the deflector to said axial force.  
           [0014]    In a particularly preferred embodiment, the detector comprises a resilient disc shaped member mounted on said slider and having a scratch recording layer bonded to a front face of the member turned toward said front end of the pig bonded to a scratch recording layer. The scratch recording layer possesses resiliency sufficient for the layer to follow deformation of the resilient detector and return of the detector to a non-deformed state. Furthermore, the scratch recording layer it has smoothness and softness sufficient for the layer to become and remain scratched when the detector engages an anomaly of a predetermined minimum radial magnitude and when the detector returns to said non-deformed state. Thus, after passage of the pig through the pipeline, the front face of the disc indicates the nature and magnitude of anomaly or anomalies encountered during the passage by way of scratched portions of the recording layer.  
           [0015]    In another aspect, the invention provides, for use in a pipeline caliper pig including a body provided with support and drive members for sliding engagement with the interior of the pipeline to drive the body coaxially through the pipeline by the flow of fluid in the pipeline:  
           [0016]    an elastomeric, generally disc-shaped detector compatible with said body for securement thereto, said ring comprising;  
           [0017]    (a) a first face, an axially opposed second face, and a circular circumferential edge portion having a predetermined diameter smaller than the inside diameter of the pipeline;  
           [0018]    (b) said first face having a forward surface possessing:  
           [0019]    (i) resiliency sufficient to follow resilient deformations of the ring and to return, with the ring, from a deformed to a non-deformed state;  
           [0020]    (ii) smoothness and softness sufficient to become and remain scratched by obstacles in the pipeline as the detector, secured to said body, advances through the pipeline.  
           [0021]    Yet another embodiment of the present invention is generally characterized by a combination, wherein a detector, particularly for use in a caliper pig for detecting an obstruction in a pipeline, is provided. It comprises, in general terms, a resiliently deformable body including a securement portion adapted to be secured to a support, and a flexing portion spaced from the securement portion and adapted to flex relative to said support when subjected to a force in a predetermined direction;  
           [0022]    said body comprising  
           [0023]    a resiliently deformable first member having a leading face and a trailing face and  
           [0024]    a resiliently deformable second member having a leading face and a trailing face;  
           [0025]    the trailing face of said first member being turned toward the leading face of said second member;  
           [0026]    the distance between the trailing face of said first member and the leading face of said second member being at a predetermined minimum when the body is in a relaxed state;  
           [0027]    signal generating means disposed in said flexing portion of the body and remote from said securement portion thereof,  
           [0028]    said signal generating means comprising:  
           [0029]    a first generating element secured to said first member; and  
           [0030]    a second generating element secured to said second member in an alignment with the first generating element when the body is in a relaxed state;  
           [0031]    said first and second generating elements being adapted to co-operate to emit a first signal when the elements are close to each other, and a second signal, distinct from said first signal, when the elements are remote from each other due to a difference between the degree of flexing between the first and second deformable members. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    The invention is described in greater detail with reference to the attached simplified, diagrammatic, not-to-scale drawings, it being understood that while these are presently preferred embodiments, they may be modified to a substantial degree without departing from the gist of the present invention. In the drawings:  
         [0033]    [0033]FIG. 1 is a simplified section view of the pig of the present invention shown as it passes through a section of a pipeline; and  
         [0034]    [0034]FIG. 2 is a simplified sectional view taken along the section line II-II of FIG. 1.  
         [0035]    [0035]FIG. 3 is a view similar to that of FIG. 1 but showing another, preferred, embodiment of the pig of the present invention;  
         [0036]    [0036]FIG. 4 is a diagrammatic sectional view of a detector as a replaceable part of the pig shown in FIG. 3;  
         [0037]    [0037]FIG. 5 is a partial section view similar to FIG. 3 but showing only a detail of an alternative structure of the detector attachment to the body of the caliper pig;  
         [0038]    [0038]FIG. 6 is a section view similar to FIG. 4 but showing the alternative structure of the detector used in the embodiment of FIG. 5;  
         [0039]    [0039]FIG. 7 is a simplified section view of yet another embodiment of the pig of the present invention;  
         [0040]    [0040]FIG. 8 is a simplified, diagrammatic view taken in the direction of arrows VIII-VIII of FIG. 7;  
         [0041]    [0041]FIG. 9 is a diagrammatic view of mutual arrangement of a sensor spring relative to the detector surface;  
         [0042]    [0042]FIG. 10 is a diagrammatic, out-of-scale view of an exemplary embodiment of the structure of a sensor spring of the present invention;  
         [0043]    [0043]FIG. 11 is a diagrammatic, out-of-scale side view of yet another embodiment of the present invention;  
         [0044]    [0044]FIG. 12 is a detail of the embodiment of FIG. 11 showing the sensor in an operative position when encountering a relatively small irregularity of the pipeline;  
         [0045]    [0045]FIG. 13 is a view similar to that of FIG. 13 showing the sensor at the initial stage of encountering a larger irregularity than that shown in FIG. 12; and  
         [0046]    [0046]FIG. 14 is a view similar to that of FIG. 13 at the stage following the initial contact of FIG. 13, with the sensor in an actuated state. 
     
    
     DETAILED DESCRIPTION  
       [0047]    The first embodiment of the inventive caliper pig is provided with supporting elastomeric rings  10 ,  11 ,  12  connected to a centrally disposed cylindric body one after the other and comprised of a front ring  10 , an intermediate ring  11  and a rear ring at the back end of the pig.  
         [0048]    A segmented, generally disk-shaped resilient member has a number of segments separated from each other along a generally radial line of separation  14   b . The member  14  is concentric with the support or guide rings  10 - 12 . It is fixedly secured to the body  20  between the front support ring  10  and the intermediate support or guide ring  11 . The resilient member  14  has a smaller outside diameter than the inside diameter of the pipeline  15 . The member  14  thus defines an annular void between its outer surface and the inner surface of the pipeline wall. The member  14  may be provided with a scratch recording leading face not shown in FIGS. 1 and 2 but described later with reference to FIGS. 3 and 4.  
         [0049]    The radial width of the void  21  is predetermined and depends on the operational requirements of particular application. It generally correspond to the maximum tolerable size, usually specified by the operator of the pipeline, of restrictions at the inner surface of the pipeline  15 . As a rule, the width of the void  21  presents about 10% of the inner diameter of the pipeline. A number of links  22  are pivotally connected with their rear ends to front faces of the segments  14   a  of the resilient member  14  at its flexing portion which is radially beyond the flanges or the like members securing the disc  14  to the body  20 . The front ends of the same links  22  are pivotally connected to a slider  16  which is slidable in axial direction on the body  20 . When the resilient member is relaxed (as shown in FIG. 1), it holds the slider  16  at a predetermined resting position relative to the body  20  such that the first and second switches  17 ,  18  are inactive.  
         [0050]    The pig is propelled through the pipeline by a pressure differential at the front and rear ends of the pig, driving the pig from the left to the right of FIG. 1. If an obstacle is encountered at the wall of the pipeline  15 , which is radially in excess of the width of the void  21 , the respective segment  14   a  of the resilient member  14  is deflected by a force which is proportional to the size of the obstacle. Since the pig continues its movement, the segment  14   a  of the resilient member  14  pulls the slider  16 , via the respective link  22 , to the left of FIG. 1. The slider  16  is displaced a predetermined distance which is sufficient to activate the mechanism (not shown in detail) of the first switch  17 . As a result, emission of an appropriate signal takes place indicating that a relatively small obstacle, for instance, a dent in the wall of pipeline  15  has been encountered. Eventually, the resilient member runs over the obstacle and returns back to the relaxed state thus returning the slider  16  back to the resting position where both switches  17 ,  18  are again inactive.  
         [0051]    If the obstacle encountered is more substantial, e.g. a partly closed valve, the resilient member  14  is displaced along the body  20  to a greater axial distance, activating the second switch  18  to provide a signal of the more substantial anomaly having been encountered.  
         [0052]    A deformable barrier ring  19  made, for instance, of a malleable, relatively thin sheet metal, has the same diameter as the resilient member  14 . It is mounted at the rear end of the pig. Its purpose is to double check the function of the switches  17 ,  18 . If any of the switches malfunctions and fails to indicate an anomaly, then such anomaly inevitably deforms the ring  19  thus providing information that the switch triggering mechanism malfunctioned. If no signal of an obstacle is received and after the completed run of the pig C the check ring  19  is not deformed, then indeed no obstacle was encountered in the inspected section.  
         [0053]    Whenever the pig detects a restriction, time may be recorded and saved for analysis at the end of the run. Information recorded may be fed to a computer that will correlate the time the restrictions were encountered with other tracking information and pipeline geographic position. The positioning will only provide the operator with an approximation of the restriction location. This, however, is a sufficient information as the state of any given pipeline section is normally monitored and anomalies recorded by the pipeline owner or user.  
         [0054]    As the pig is designed to only detect large restrictions that are associated with partially closed valves or some other fitting problems, or exceed industry guidelines, the limited accuracy will still provide the operator with sufficient information to determine if there are any excessive restrictions and, if a restriction has been identified, to eliminate it before running other, more sensitive caliper pigs, and ensure that the pipeline is maintained within the industry guidelines.  
         [0055]    Turning now to the embodiment of FIG. 3, an improved and particularly preferred embodiment of the pig is shown in an operative position, received in a pipeline  30 . The pig comprises two resilient guide rings  31 ,  31  a, one at the front, the other at the rear of the pig body  32  which has a generally tubular configuration. The front guide ring  31  is secured to the body  32  by a holder plate  33  pressed against the ring  31  by an end cap  34 . The rear guide ring  31   a  is secured to the body  32  by holder plates  35 ,  36  pressed against the rear end of the body  32  by an end cap  37 . As is well known, at least the front guide ring  31  engages the pipeline  30  in a sealing fashion to provide a pressure differential caused by the flow of a fluid through the pipeline  30 , driving the pig from the left to the right of FIG. 3.  
         [0056]    The front end cap  34  is provided with a threaded inner portion  38  which is engaged in a tubular sleeve  39  fixedly secured, for instance by welding or adhesively, to the body  32  near the front end thereof. The inner portion  38  of the end cap abuts against a plug  40  provided with a front O-ring  41  and a rear O-ring  42 , to seal the hollow tubular interior  43 . The tubular interior  43  houses a switch mechanism or the like electromechanical device.  
         [0057]    The slider  44  of the embodiment shown has a cylindric surface integrally formed with a radially outwardly projecting rear flange or shoulder portion  45 . A resilient disc shaped detector  46  abuts with its back end against the flange portion  45 . The detector  46  is retained generally in abutment with the flange portion  45  on the slider  44  by a retainer clip  47  received in an appropriate groove machined in the surface of the slider  44 . As in the first embodiment described, the portion of the disc  46  radially outwardly of the shoulder portion  45  is generally referred to as a flexing portion of the detector. The slider comprises a known switch mechanism. Such switch mechanism would typically have a magnet or magnets on the inside of the slider  44  and detector switch or switches secured to the body  32 . Many obvious modifications of the electric signal producing arrangement can be used without departing from the invention. Therefore, the sleeves  44  or  16  are to be considered merely as preferred embodiment of what is generally referred to as a transfer mechanism including a converting member (e.g. the sleeve) movable relative to the body  32  or  20  responsive to a generally axial force to transmit a mechanical impulse developed at the detector  46  to activate or deactivate an electrical signal producing device.  
         [0058]    The outer diameter (OD) of the detector  46  is about 20% smaller than the inside diameter (ID) of the pipeline  30 . For instance, if the ID of the pipeline  30  is 10″, then the OD of the detector  46  is about 8″. The detector  46  is composed of a resilient disc, in the embodiment shown a polyurethane disc  50 . The front face of the disc  50  is provided with a scratch recording layer, in the embodiment shown, a lead layer  51  which is bonded to the disc  50  so that the two form a generally integrally formed structure. According to the present invention, the thickness of the lead layer  51  is selected such that it has flexibility sufficient to follow deformation of the disc  50  when the detector  46  encounters an anomaly in the pipeline. At the same time, the flexibility of the layer  51  provides that once the anomaly is cleared, the layer  51  follows the disc  50  bouncing back to the original, relaxed position. The lead layer  51  is preferred in the present invention as it can be easily scratched by obstacles encountered during the passage of the pig through the pipeline  30 . By the same token, the flexibility of layer  51 , which is mainly due to the selected thickness thereof, permits the return back to the relaxed position while the scratches on the surface of the layer  51  remain recorded ready to be interpreted upon passage of the pig through the examined section of the pipeline  30 .  
         [0059]    The desired thickness of the layer  51  is easy to determine, for instance by a simple trial-and-error method. As an example, it has been established that in case of the above example of a diameter of the detector being about 8″, the preferred thickness of the polyurethane disc  50  is about {fraction (3/4)}″ and the thickness of the lead layer  51  meeting the above resiliency conditions is about {fraction (1/16)}″. These figures, of course, are optional.  
         [0060]    While, at the present time, lead has provided best results in resiliency and retaining the scratch marks on the face of the detector  46 , those skilled in the art will appreciate that other materials can be used to substitute the lead layer  51 . A vast number of different materials including paints applied to the leading face of the disc  50  would also provide satisfactory results both from the standpoint of flexibility and retaining the scratches made during the passage through a the pipeline  30 .  
         [0061]    Turning now back to FIG. 3, the rear end portion of the body  32  carries a compression spring  52 . The front end of the spring  52  presses against the rear surface of the flange  45 , while the rear end of the spring  52  engages the surface of the holder plate  35 . The rear guide ring  31  a may be provided with passages (not shown) for the fluid to flow through the pipeline  30  and generate the required propelling force at the front ring  31 .  
         [0062]    The spring  52  holds the slider  44  in a relaxed position shown in FIG. 3. When an obstacle is encountered, the detector  46  deflects and at the same time exerts axial force upon the slider  44  displacing it to the left of FIG. 3, thus triggering the not shown switch mechanism provided within the cavity  43 .  
         [0063]    It is advantageous to provide the detector  46  as an easily exchangeable replacement part for the pig. One embodiment of such spare or replacement detector  46  is shown in FIG. 4. The disc-shaped detector  46  has an outer circumference  56  having a predetermined diameter, for instance 8″, as discussed above. The inner central opening  57   a  in a sleeve  57  bonded to the disc  50  is compatible with the outer surface of the slider  44  and, in the exemplary size discussed above is about 2″.  
         [0064]    An alternative embodiment of the detector  46  is shown in FIG. 6. Here the detector is again a laminate of a resilient disc  50  with a scratch recording lead face  51 . The laminate is held between opposed flanges  48 ,  49  by a series of bolts and nuts  48   a ,  49   a . FIG. 5 shows that the assembly of FIG. 6 is again retained on the body  32  between the shoulder portion  45  and the retainer clip  47 .  
         [0065]    The detector laminate  50 ,  51  shown was produced by first preparing a lead plate having the above thickness of about {fraction (1/16)}″ and major and minor diameters of about 8″ and 2″, respectively. The surface facing the resilient disc  50  was cleaned and roughened. The lead plate was then placed in a compatible form and the desired volume of polyurethane poured into the form over the lead plate. With the polyurethane cured, sufficient bond was obtained between the polyurethane disc and the lead layer.  
         [0066]    Embodiments of the present invention have also been produced, where the detector was simply bonded to the slider  44  thus eliminating the need for the shoulder  45  clip  47  arrangement. A vast number of other obvious, notoriously known methods of mechanical securement of the detector to the body exist and can be used to secure the detector  46  in operative position.  
         [0067]    While the embodiments described above have worked satisfactorily, it was realized that a further improvement may be provided which would not only detect an anomaly but also its general position relative to the periphery of the pipeline.  
         [0068]    [0068]FIGS. 7 and 8 show such additional improvement  
         [0069]    As is the embodiment of FIG. 3, the improved pig comprises a pair of front and rear resilient guide rings  60 ,  61 . The front ring  60  is secured to a tubular body  62  having an axis L of elongation, by way of a front end cap  63  threadably engaging a threaded portion  64  projecting from a plug  65  which is fixedly secured, by welding or adhesively, to the inside of the tubular body  62  at the front end thereof. The front end cap  63  holds the front ring  60  between an inner front flange  66  and an outer front flange  67 . The inner front flange  66  is fixedly secured to the front end of the tubular body  62 . Thus, the outer front flange  67 , the front ring  60  and the cap  63  are all fixedly secured relative to the tubular body  62 .  
         [0070]    Similarly, the ring  61  is secured to the tubular body  62  by way of a rear end cap  68  threadably engaging a threaded portion  69  projecting from a rear plug  70  which is fixedly secured, by welding or adhesively, to the inside of the tubular body  62  at the rear end thereof. The rear end cap  68  holds the rear ring  61  between an inner rear flange  71  and an outer rear flange  72 . The inner rear flange  71  is fixedly secured to the rear end of the tubular body  62 . The outer rear flange  72 , the rear ring  61  and the cap  68  are thus all fixedly secured relative to the tubular body  62 .  
         [0071]    A tubular mandrel  73  is mounted for a free rotation on the body  62 . The mandrel  73  rotates on bushings  74 ,  75 . The bushings also prevent axial displacement of the mandrel  73  relative to the body  73 . The mandrel  73  is also freely rotatable relative to the inner front flange  66  and the inner rear flange  71  and their associated assemblies of the front and rear rings  60 ,  61 .  
         [0072]    Welded to the lower exterior of the mandrel  73  is a tubular member  76  with screwed sealed cap  77 . The tubular member  76  has two functions: it houses a recording system and at the same time provides ballast which maintains the freely rotatable mandrel  73  in a position shown in FIG. 7, regardless of the actual instant position of the discs  60 ,  61  and the tubular body  62  fixedly secured to them. The weight of the tubular member  76  will thus maintain the member at a downward, essentially 6 o&#39;clock position when viewed axially relative to the mandrel  73 . As a result, all portions of the face of a disk-shaped sensor  78  are maintained at all times at a generally constant position with respect to a fictitious vertical reference plane P. See FIG. 8.  
         [0073]    The resilient disc-shaped detector  78  abuts against a plate or shoulder portion  79  which is fixedly secured relative to the mandrel  73  by a weld  80  to the mandrel  73 . The rear surface of the plate detector  78  abuts a circular plate  81  which, in turn, abuts an annular spacer member  82 . At the opposite end of the spacer member  82 , a plate  83  sealingly encloses the interior of an annular cylindric chamber  83   a  disposed between the radially outer surface of the spacer member  82  and an outer annular wall  83   b . The entire chamber  83   a , the spacer member  82 , the rear annular plate  81 , the plate detector  78  and the front annular plate  79  welded to the mandrel  73  are fixedly secured to each other and thus to the mandrel  73  by a series of bolts  84 . The bolts  84  are disposed at, a uniform circumferential spacing about the above members and pass through bolt passages  84   a  (FIG. 8).  
         [0074]    As in the first embodiment described, the portion of the disc  78  radially outwardly of the plates  79 ,  81  is generally referred to as a flexing portion of the detector  78 .  
         [0075]    L-shaped springs  86  made of a commercially available spring steel of about {fraction (1/16)}″ have each an axial arm  87  and a radial arm  88  adjoining each other at a coiled central section  89  at an angle, in the embodiment shown, a right angle. The central section  94  has about 3-4 coils. The axial arm  88  is provided at its free end with a coiled support section  95 . Both arms are resiliently flexible.  
         [0076]    Each spring  86  is pivotable, at the central section  89 , relative to the plate  81  about an associated pivot pin  94  passing through the central section  89  and projecting to both sides thereof. Each pivot pin  94  is held in place by a short, tangential groove  96  (FIG. 9) machined in the face of the annular rear plate  81  turned towards the disc detector  78 . The opposed ends  94   a ,  94   b  of each pin are pressed against the resilient surface of the detector  78  and are thus held in place. In other words, each spring can swing within a respective plane defined by the L-shape, i.e. a plane parallel with (in the embodiment shown, generally coincident with) the axis-L of the mandrel  73 . The springs  86  are evenly peripherally spaced with respect to the disc  78  as best seen in FIG. 8. It will be appreciated that the coincident arrangement with axis-L is not absolutely necessary even though it is preferred.  
         [0077]    Each axial arm  87  is provided at its free end with a permanent magnet  90  held in place by the respective support section  95 . Assigned to each magnet  90  is a magnetic position switch  91 . In the embodiment of FIGS. 7 and 8, a magnetic position switch commercially available under the trade name Hamlin has been proposed. As is known, the magnetic position switch  91  is located in a nonmagnetic envelope fixedly secured to the surface of the annular spacer  82 . The non-magnetic envelope can be made from a number of suitable materials for instance from stainless steel, aluminum or a thermoplastic material. In many applications, the magnetic sensors are grouped depending on the accuracy of indication of the pipeline anomaly is required.  
         [0078]    [0078]FIGS. 8 and 9 show that the radial arms  88  of springs  86  are evenly spaced around the detector  78 . The radial arms  88  are each located in an associated groove  92  milled into the face of the disc  78 . The grooves  92  terminate short of the edge of the disc  78 . The remaining portion from the radially outer end of grove  92  to the edge on disc  78  contains a radial hole  97  (FIG. 9). Free end portions  93  of the radial arms  88  of the springs  86  are each inserted into a respective hole  97 . The holes co-operate with the pivots  94  to keep the radial arms  88  of springs  86  secured to and generally flush with the surface of the disk  78  at all times.  
         [0079]    [0079]FIG. 8 further shows that, in the embodiment described, the grooves  92  or the free end portions  93  divide the entire circumference of the disc  78  into twelve segments. They have each a predetermined arc and length of its chord. In the embodiment of FIG. 8, the arc and thus the length of the chord is the same in each segment.  
         [0080]    While this arrangement is preferred in most applications, it can be modified to two or more different arcs of the segments.  
         [0081]    As shown in FIG. 8, there are twelve switches disposed about the periphery at slightly counter-clock wise offset location in which the XII o&#39;clock point is offset counterclockwise by 15° so that the uppermost point of the circle is between the XII o&#39;clock and I o&#39;clock position.  
         [0082]    If it is desired to find out only whether a particular obstacle is in the upper or lower part of the pipeline, then only two groups of the signal developing switches are required of the usual twelve switches. In case of twelve switches disposed about the periphery of plate  81  and offset as described, a group of switches at the offset X, XI, XII, I, II and III o&#39;clock positions would serve in determining an anomaly in the upper part of the pipeline, while switches in those in the IV, V, VI, VII, VIII and IX &#39;o clock position would transmit a signal corresponding to the anomaly in the lower part of the pipeline. If a more detailed indication is required, more groups, each having a fewer number of switches, would be grouped or each switch would indicate anomaly at its position about the periphery of the pipeline. Customers normally specify their requirements concerning the accuracy required.  
         [0083]    In operation, the pig is propelled through an associated pipeline in a fashion as already described. When an obstacle is encountered, a segment of the disc  78  becomes deflected in the direction D shown at the bottom of FIG. 7. Assuming that the detected obstruction is at the lower part of the pipeline, the radial arms  88  follow the local deflection of the disc raising the axial arms  87  of the lower springs  86  at the offset 6 and 7 o&#39;clock positions to bring the associated magnets  90  into contact with the magnetic sensor switch  91 . The sensing switches  91  then transmit electric signal to a conventional electronic recording device located within the tubular member  76 . This is effected by leads, not shown; passing through passages  98  in the disks  81 ,  78  and  79 .  
         [0084]    The springs  88 , holding each a magnet and the annular spacer  82  holding a plurality of magnetic switches can also be generally referred to as transmission devices comprised of a first transmission member and a second transmission member. In the embodiment described the spring  86  functions as the first transmission member. The spacer  82  of the embodiment described is an example of a second transmission member. It will be understood that the particular embodiment described is not the only one readily conceivable and that the functions can be easily reversed. The designation of the transmission members as first and second is therefore to be understood as a general definition of the two and does not necessarily refer to which of the members carries the magnet  90  and which carries the switch  91 . For the same reason, the term “first support portion” of the embodiment shown is designated as the one carrying permanent magnet while the “second support portion” of the second transmission member carries the switch, it being understood that this function can readily be reversed. Therefore the above general terms must be interpreted in their general meaning and not to be limited to their meaning with respect to the embodiment disclosed.  
         [0085]    The sensing switches, their leads (not shown) passing through one or more passages  95  to the recording device in the tubular body  62  and the recording device itself do not form a part of the present invention and are therefore not described in detail. They are comprised of commercially available components.  
         [0086]    [0086]FIG. 11 shows an improvement of the previously described embodiment of FIG. 7. The improved embodiment presents a substantially simpler and thus less expensive structure and an improved reliability in operation.  
         [0087]    The front and rear carrying guide rings  60 ,  61 , the mandrel  73  rotatable on the elongated body or carrier  62 , and the tubular member  76  secured to the lower portion of the mandrel  73 , are identical in structure and function with the embodiment of FIG. 7 and are therefore referred to with the same reference numbers.  
         [0088]    In FIG. 11, the resilient, disc-shaped detector body  178  has a different, substantially simplified structure. The detector is provided with two coaxially arranged, resiliently flexible discs  179 ,  180 , each having a resiliently flexible outer portion and, preferably, with an intermediate scratch indicating layer  181 . The disc  179  presents an embodiment referred to as “a first member,” the disc  180  as “a second member” or vice-versa. In the embodiment shown the layer  181  is a thin sheet of plastic material cut into a disc-like configuration having the same diameter as the rear or trailing disc  180 , as viewed from the standpoint of direction D in which the pig advances through the pipeline. The diameter of the trailing disc  180  is, preferably, but not necessarily, larger than that of the leading disc  179 . The layer  181  is sandwiched between the leading disc  179  and the trailing disc  180 .  
         [0089]    The assembly of discs  179 ,  180 ,  181  is fixedly secured to the mandrel  73  by a pair of opposed flanges  182 ,  183  presenting and embodiment of what can generally be referred to as “a support of a securement portion.” The flanges are welded or otherwise fixedly secured to the mandrel  73 , generally as in the previously described embodiment. The bolts  184 , disposed at a uniform circumferential spacing, secure the discs much in the same fashion as in the previously described embodiment.  
         [0090]    Thus, the assembly of discs  179 ,  180  and  181  is freely rotatable about the axis L by virtue of its securement to the freely rotatable mandrel  73 . Viewed from the standpoint of direction D, each disc  179 ,  180 , has a leading face qnd a trailing face.  
         [0091]    Embedded in the leading disc  179  near its trailing face  185  is a series of equidistantly circumferentially spaced apart permanent magnets  186 . Similarly, there are embedded in the trailing disc  180  near its leading face  187 , equidistantly circumferentially spaced apart magnetic switches or sensors  188  which are aligned each with one of the magnets  186 . Each pair of the magnet  186  and sensor  188  presents an embodiment of an electronic signal generating means, wherein the magnet and the sensor forms a first and a second electronic signal generating element or vice-versa.  
         [0092]    The switches or sensors  188  co-operate with the magnets  186  in a fashion similar to that of the previously described embodiment of FIG. 7. That is to say, when a respective magnet  186  is at a close proximity to its associated sensor  188 , the sensor  188  is activated to emit a first signal communicated by the respective lead  189  to a conventional recording device located in the tubular member  76 . The close proximity between the magnets and the sensors  188  exists when the two discs  179 ,  180  are in a relaxed state shown in FIG. 11.  
         [0093]    As shown in FIGS.  12 - 14 , when an obstruction is encountered, as the body  62  advances in the direction D, the close proximity of one or more of the sensors  188  with their associated magnets  186  is disturbed causing a change in the electronic signal.  
         [0094]    The sensors  188 , the magnets  186  and the recording device located in the tubular member  76  are all commercially available items. Their particular design does not form a part of the present invention and therefore is not described in detail.  
         [0095]    Turning now to FIG. 12, a situation is depicted where a relatively small obstruction  190  has been encountered by the pig traveling in the direction D. At a position shown, the obstruction  190  protrudes into the inside of the pipeline at a radius (measured from the axis L) which is larger than the radius of the leading disc  179  but smaller than that of the trailing disc  180 . Therefore, the leading disc  179  passes by the obstruction  190  maintaining its relaxed state. As a flexing part of the trailing disc  180  encounters the obstruction  190 , it is subjected to an axial force directed opposite to the direction D. The opposite force is also referred to as “a force in a predetermined axial direction.” The flexing part of the trailing disc  180  flexes rearwards as shown in the drawing. This flexing causes disturbance of the relationship between the respective pair comprised of the magnet  186  and the associate sensor  188 . As a result, a second electronic signal, different from the first signal, is communicated to the recording device in tube  76 . The position of the disturbed arrangement is also recorded since the ballast, formed by or secured to the tube  76  maintains a position of the tube  76 , vertically aligned with the axis L.  
         [0096]    In FIG. 13 a larger abnormality  190  has been encountered which reaches into the pipeline at a radius smaller than either of the two discs  179 ,  180 . At the outset, both discs flex rearwards as shown. The magnet or magnets  186  remain at a close spacing from the associated sensor  188 . However, as shown in FIG. 14, as soon as the leading disc  179  passes the obstruction, it springs forwards to a relaxed state while the trailing disc  180  remains flexed thus disturbing the close arrangement between the magnet  186  and the associated sensor  188  again resulting in a change of the electronic signal.  
         [0097]    The presence and radial position of the abnormality  190  can be double checked upon eventual examination of the scratches caused by the abnormality  190  on the leading surface of the scratch disc  181  which, preferably, is a thin, separate disk from plastic polyethylene.  
         [0098]    In an exemplary embodiment suitable for a pipeline having a 20″ ID, the outside diameter of the large, (in the embodiment shown, trailing) disc  180  would be about 19½″ and that of the small diameter, leading disc  179  would be about 19″. The thickness of each disc is about {fraction (3/4)}″. The discs  179 ,  180  are preferably integrally formed but an embodiment wherein they would be subdivided into a plurality of independently flexing segments with aligned pairs of signal generating devices may also be feasible under certain circumstances.  
         [0099]    Those skilled in the art will readily appreciate that many equivalent arrangements to those described may exist. For instance, the disposition of the magnets  186  and the sensors  188  can be reversed and does not even have to be uniform but may alternate within one of the two discs with an appropriate modification of the other disc. While it is preferred that the trailing disc  180  have a diameter larger than that of the leading disc, the arrangement is optional. The two discs may also have generally the same diameter. In an extreme, not recommended, the disk  179  could even have a larger diameter than of the trailing disc  180 .  
         [0100]    The flexing portion described is a disc. However, an equivalent arrangement could be made in an embodiment where the disc would be replaced by a plate or a strip where the checkup of a generally planar surface is required. Even in a pipeline monitoring arrangement, a system of several independent strips, each having a leading flexing portion and a trailing flexing portion, could be used, while, obviously, the disc-shaped arrangement is preferred for its simplicity.  
         [0101]    Those skilled in the art are aware that other equivalent, commercially available systems producing electronic signal suitable for utilizing the mechanism of the present invention are available.  
         [0102]    Accordingly, many different modifications of the overall arrangement of the monitoring pig of the kind disclosed can be made which may depart from the embodiments described without departing from the gist of the present invention.