Abstract:
A system and method for measuring loads on a pipe, including a pair of collars that can be secured around the outer surface of the pipe to be monitored in an axially spaced relationship; and a connecting element having a strain gauge is fixed to the collars such that when the collars are secured to the pipe, the connecting element is arranged to measure distortion of the pipe due to applied loads, wherein the ends of the connecting element are attached to the collars such that when the collars are secured to the pipe, the ends of the connecting element are fixed against axial and circumferential movement relative to the pipe. The system includes the apparatus mounted on a pipe, such as a flexible pipe, in a subsea oil or gas installation.

Description:
CROSS REFERENCE TO RELATED DOCUMENTS 
       [0001]    We claim benefit of priority to Great Britain Patent Application Serial No. 0801499.5 of ROBERTS et al., entitled “STRUCTURAL LOAD MONITORING USING COLLARS AND CONNECTING ELEMENTS WITH STRAIN SENSORS,” filed on Jan. 28, 2008, the entire content of which is hereby incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to systems and methods for monitoring loads on pipes, and more particularly to a system and method for monitoring loads on pipes used in the subsea oil and gas industry. 
         [0004]    2. Discussion of the Background 
         [0005]    Flexible pipes are increasingly used in systems for the subsea oil and gas industry. There are considerable advantages in the cost and ease of deployment that can be obtained by using such systems. However, the movement allowed by such flexible systems also can create potential for failure of the flexible pipes, which can be both costly and dangerous. To date, there is little historical experience that the industry can use to evaluate such risks in advance and because of the serious nature of the consequences of failure, it is desirable to monitor such pipes frequently or continuously. 
         [0006]    Some systems have been proposed for detecting damage or failure in aspects of a pipe structure that could lead to catastrophic failure of the pipe if left unattended. An example of this can be found in U.S. Pat. No. 7,296,480. In this case, a strain gauge attached to a connecting structure in the form of a rod is mounted on the side of a flexible pipe so as to measure the twist in the pipe near an end-fitting resulting from failure of one or more reinforcing plies in the pipe. A fiber optic sensor is held in place circumferentially on the pipe at various locations but is free to slide axially. In this way, twist can be measured, which is the result of ply failure. This measurement, which may be combined with gas detection, can be used to detect failure. However, such a system is limited in that it only measures twist at an end-fitting resulting from the failure or one or more plies. 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, there is a need for a method and apparatus (e.g., which also can be referred to herein as a “system”) that addresses the above and other problems. The above and other needs and problems are addressed by the exemplary embodiments of the present invention, which provide a method and apparatus for measurement and detection of pipe deformation arising from the loads imposed upon the pipe in use. It is also an object to provide a system that can be used to discriminate between the deformations in various sections of the pipe. The invention achieves these objectives by using pairs of collars to locate the ends of connecting elements, which include strain gauges and so as to provide a reference for different types of deformation measurement and load determination, advantageously, without the need to wait for failure to occur. 
         [0008]    Accordingly, in a first exemplary aspect of the present invention there is provided an apparatus for measuring loads on a pipe, including a pair of collars that can be secured around the outer surface of the pipe to be monitored in an axially spaced relationship; and a connecting element fixed to the collars such that when the collars are secured to the pipe, distortion of the pipe due to applied loads causes distortion of the connecting element. The ends of the connecting element are attached to the collars, such that when the collars are secured to the pipe, the ends of the connecting element are fixed against axial and circumferential movement relative to the pipe; and a strain gauge is fixed to or included in the connecting element so as to measure distortion of the connecting element. The strain gauge can be a fiber optic device, e.g., a Bragg grating device. However, any suitable strain gauges or extensometers, such as optical strain gauges and extensometers, electrical strain gauges and extensometers, and the like, can be employed. 
         [0009]    The connecting element may have different shapes, including a cross section that can be round, oval, square, or rectangular, for example. The cross section of the connecting element can also vary in shape or dimensions with length. The mechanical properties of the connecting element can also vary with length. These variations with length can be used to optimize the performance of the measurements. For example, they can vary in such way that the stiffness of the connecting element is reduced at locations where the sensing elements are placed. 
         [0010]    The attachment points on the collars for connecting elements can be aligned axially, or offset circumferentially relative to the surface of the pipe so that the connecting element lies at an angle to the pipe axis. The attachment points can also be offset radially from the surface of the pipe. Multiple connecting elements can be fixed between the collars, in which case the strain gauges can be mounted so as to have different alignment between the collars. In another example, more than two collars are provided, the connecting elements being connected between, i.e., with, two or more of the collars. 
         [0011]    In a second exemplary aspect of the invention there is provided an installation for measuring loads on a pipe, including an apparatus according to the first aspect of the invention mounted on a pipe to be monitored. The installation can also include a data acquisition and analysis unit, and means for passing data back to the unit from the strain gauge or gauges. A number of apparatus installations can be provided, spaced apart along the pipe to be monitored. The pipe can be rigid, semi-rigid or flexible. Such pipes can advantageously be used in subsea oil and gas installations. 
         [0012]    In a third exemplary aspect of the invention there is provided a method of monitoring loads on a pipe, including providing a pair of collars having one or more connecting elements fixed therebetween; securing the collars in an axially spaced relationship around the outer surface of the pipe to be monitored, such that when the collars are secured to the pipe, the ends of the one or more connecting elements are fixed against axial and circumferential movement relative to the pipe, such that distortion of the pipe due to applied loads causes distortion of the connecting elements; providing a strain gauge fixed to the one or more connecting elements so as to measure distortion of the one or more connecting elements; and measuring distortion of the pipe due to applied loads. The method can be performed using an apparatus according to the first aspect of the invention. It is advantageous to provide multiple apparatus located at different locations on the pipe to be measured. 
         [0013]    Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and implementations. The present invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0015]      FIG. 1  illustrates schematically an exemplary subsea system in which the present invention is applicable; 
           [0016]      FIG. 2  illustrates an exemplary matrix of collars and connecting elements with strain gauges for monitoring of a pipe structure; 
           [0017]      FIG. 3  illustrates an exemplary matrix of collars and connecting elements with strain gauges in a crisscross pattern for monitoring of a pipe structure; 
           [0018]      FIG. 4  illustrates an exemplary matrix of collars and connecting elements with strain gauges with radial extensions for monitoring of a pipe structure; 
           [0019]      FIG. 5  illustrates an exemplary matrix of collars and connecting elements with strain gauges of varied thickness for monitoring of a pipe structure 
           [0020]      FIG. 6  illustrates an exemplary plurality of matrices of collars and connecting elements with strain gauges for monitoring of a pipe structure; 
           [0021]      FIG. 7  illustrates another exemplary plurality of matrices of collars and connecting elements with strain gauges with varied orientations and arrangements for monitoring of a pipe structure; 
           [0022]      FIG. 8A  illustrates exemplary collar and connecting elements with strain gauge installations coupled to a data acquisition and analysis unit; and 
           [0023]      FIG. 8B  illustrates an exemplary collar and connecting elements with strain gauge installations having a memory and a processor coupled to a reader unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Various embodiments and aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and implementations. The invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited. Likewise, the term “comprising” is considered synonymous with the terms “including” or “containing” at least for purposes of Australian or the U.S.A. law. 
         [0025]    In this disclosure, whenever a composition, an element or a group of elements&#39; is preceded with the transitional phrase “comprising”, “including” or an equivalent thereof, it is understood that we also contemplate the same composition, element or group of elements with transitional phrases “consisting essentially of”, “consisting”, “selected from the group of consisting of”, or “is” preceding the recitation of the composition, element or group of elements and vice versa. 
         [0026]    All numerical values in this disclosure are understood as being modified by “about”. All singular forms of elements, such as collars or connecting elements, or any other components described herein including (without limitations) components of the systems or methods of the invention are understood to include plural forms thereof and vice versa. 
         [0027]    The present invention provides, systems, installations and methods that allow structural monitoring of pipes, such as a rigid, semi-rigid or flexible pipe, particularly of the types used in the subsea oil and gas industry. However, the exemplary systems, installations and methods can also be used in any suitable structure where structural monitoring is desirable. For example, the invention may also be used in extensometry in civil engineering, public works and geotechnical engineering, e.g., to monitor road or railway bridges or viaducts, dams for hydroelectric power stations, nuclear reactor buildings and cooling towers associated with these reactors, miscellaneous buildings, tunnels and mines, rock movements and ground movements, or to check land or submarine seismic areas, buried pipes, pipelines, riser pipes, which may be flexible riser pipes, dikes and offshore platforms. 
         [0028]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to  FIG. 1  thereof, there is illustrated a subsea system, including a Floating Production Storage and Offloading (FPSO) vessel  10 , which is anchored to the sea bed by anchor chains  12 . A tanker offloading buoy  14  is connected to the FPSO  10  by means of a flexible offloading pipeline  16 . Further flexible flowlines  18  connect the FPSO  10  to nearby platforms  20  to allow direct production to the FPSO. Also, existing subsea wells  22  have connections to subsea manifolds  24  from which flexible flowlines and risers  26  lead to connect to the FPSO  10 . Advantageously, the methods and systems of the exemplary embodiments allow for monitoring of pipelines  16 , flowlines  18  and risers  26  through which fluids flow, as well as structural pipes, such as those used in the support structures of the platform(s)  20 . Accordingly, with the exemplary embodiments the monitoring of loads on flexible pipes, structures, and the like, is possible and useful for predicting or detecting damage and/or failure of such pipes and structures in subsea installations. 
         [0029]    In an exemplary embodiment, a matrix of collars, and connecting elements each of which includes one or more strain gauges is provided and configured to detect distortion of the pipe to which it is attached.  FIG. 2  illustrates an exemplary embodiment, including a pair of collars  30   a  and  30   b  clamped around a pipe  32 . The collars  30   a  and  30   b  are formed from two semi-circular rings joined by means of a hinge  34  on one side (e.g., shown for collar  30   a ), a flange  36   a  and connectors  36   b  (e.g., nuts and bolts, shown for collar  30   b ). By unfastening the connectors  36   b  and the flange  36   a,  the collars  30   a  and  30   b  can be opened and placed around the pipe  32 . The flange  36   a  and the connector  36   b  can then be closed and the connectors  36   b  tightened until the collars  30   a  and  30   b  are securely clamped around the pipe  32 . Each of the collars  30   a  and  30   b  also includes end fittings for one or more connecting elements  38 . For example, two connecting elements  38  are shown, disposed on opposite sides of the pipe  32 , each of which carries a strain gauge  37  on or in its structure. In further exemplary embodiments, the number and arrangement of the connecting elements and collars can be selected according to operational requirements. An advantageous form of the strain gauge is a fiber optic sensor, such as a Bragg grating device, and the like. 
         [0030]    By securing the collars  30   a  and  30   b  to the pipe  32 , and fixing the ends of the connecting elements  38  to the collars  30   a  and  30   b,  the connecting elements  38  are effectively linked to the outer surface of the pipe  32 . Therefore, any deformation of the pipe  32  in the region between the collars  30   a  and  30   b  will cause a corresponding deformation in the connecting elements  38 , which can be detected by the attached strain gauge  37  and analyzed. For example, if the pipe  32  is bent in the plane of the drawing so that the ends move downwards (shown as arrows D in  FIG. 2 ) and the middle upwards (shown as arrow U in  FIG. 2 ), the upper connecting element  38  will be stretched and the lower connecting element  38  compressed. Different effects will also be found if the pipe is subjected to axial compression or extension, shear, or torque depending on the loads applied. 
         [0031]      FIG. 3  illustrates a further exemplary embodiment in which several connecting elements having strain gauges (not shown) are provided. In  FIG. 3 , a pair of connecting elements  40   a  and  40   b  is aligned with the axis of the pipe  32 , and another pair of connecting elements  42   a  and  42   b  has connection points on the collars  30   a  and  30   b  that are circumferentially offset, so that the connecting elements  42   a  and  42   b  lie at an angle to axis of the pipe  32 . Advantageously, the number and arrangement of connecting elements can be selected according to the loads and deformations to be monitored. 
         [0032]      FIG. 4  illustrates a further exemplary embodiment in which the sensitivity to deformation is amplified. In  FIG. 4 , the connecting elements  38 , which include strain gauges (not shown) are fixed to the collars  30  by means of radial extensions  44 . The effect of the radial extensions  44  is to amplify mechanically any bending or shear deformation at the surface of the pipe  32 . The greater the distance a given connecting element is offset from the surface of the pipe  32 , the greater the amplification of the deformation. Radial offset is one way in which the response of the system can be tuned. Other ways to tune the system include the separation of the collars or varying thickness of the connecting elements. 
         [0033]      FIG. 5  illustrates a further exemplary embodiment in which the thickness of the connecting elements is varied. In  FIG. 5 , the connecting elements, having strain gauges (not shown), include thick end portions  46   a  and  46   b  connected to the collars  30  and center sections  48  that are of reduced diameter. The effect of the reduced diameter is that the connecting element is much more sensitive to deformation. Advantageously, this embodiment can be combined with the other embodiments discussed herein to obtain the desired sensitivity of the system. It is also possible to alter the stiffness of the connecting elements structure by modifying the mechanical parameters of the material used instead or in addition to the variation in shape. Composite materials could be used for this purpose, as their mechanical parameters can be designed to vary with length. 
         [0034]    Because the system of the invention can be retroactively retrofitted onto a pipe, which is already placed in service or is ready to be placed in service, it can be fixed in any location where load deformation may be an issue. Furthermore, multiple installations can be provided on any given pipe, as is shown in  FIG. 6 . In  FIG. 6 , two sets of collars  50  and  52  and at least two connecting elements  54   a  and  54   b  having strain gauges (not shown) are provided on the pipe  32  in different locations. Advantageously, this approach can assist in cases where it is not possible to instrument directly a region of the pipe  32 , wherein outputs from the offset installations can be used to interpolate or extrapolate parameters to the inaccessible regions. In addition, it is possible to monitor different parts of the pipe  32  having different load strengths and crossreference readings from other locations. 
         [0035]      FIG. 7  shows an exemplary embodiment with multiple collars and connecting elements having strain gauges (not shown). It is possible to “daisy-chain” the system to measure different parameters at different positions and/or directions. In  FIG. 7 , four collars  60   a - 60   d  are mounted on the pipe  32 . In some cases, simple connecting elements  62   a  and  62   b,  for example, as described in relation to  FIG. 2 , connect adjacent collars  60   a  and  60   b,    60   c  and  60   d,  respectively. Other connecting elements, such as connecting element  64 , can connect three collars  60   b,    60   c  and  60   d.  Further a connecting element  66  can be arranged at an angle, for example, as shown in  FIG. 3 . The number of collars, and the number and arrangement of connecting elements can be selected according to the pipe and the type of load to be evaluated. Advantageously, it is possible to monitor different parts of the pipe  32  having different load strengths and cross-reference readings from other locations to obtain the desired sensitivity of the system. 
         [0036]    As shown in  FIG. 8A , each collar and connecting element with strain gauge installation  802  of the exemplary embodiments of  FIGS. 2-7  is effectively a stand-alone measurement sub-system and can feed back its readings to a data acquisition and analysis unit  804  (e.g., a personal computer, laptop computer, etc.) located at the surface or at any other suitable location, e.g., a remote location. In addition, as shown in  FIG. 8B , a memory and processor  806  can be provided in each collar and connecting element with strain gauge installation  802 , and which can accumulate data that in turn can be downloaded by a reader unit  808  that is brought into close proximity to the respective collar and connecting element with strain gauge installation  802 . 
         [0037]    The data acquisition and analysis unit  804  can be used to compare the data received from the strain gauges with a given threshold, thereby making it possible to detect an abnormal twist of the pipe  32  and the unit  804  can generate information or an alarm that allows the operator to anticipate the malfunction or breakage of the flexible pipe, and therefore to take an appropriate action. 
         [0038]    While monitoring load deformation of flexible pipes is of particular interest, similar effects can also be monitored in rigid and semi-rigid pipes. However, in flexible pipe applications, the particular design and configuration of the monitoring installation can itself affect the flexibility of the pipe in that specific region. It is generally considered preferable that the installation provides the least possible resistance to the load structure. Where possible, it is preferable not to add significantly to the pipe stiffness, as this in turn may affect the sensitivity to the parameter being measured. One resulting advantage is that the clamping force of the collars and the friction force do not need to be very high to retain the collars in place on the pipe. 
         [0039]    All or a portion of the devices and subsystems of the exemplary embodiments can be conveniently implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be appreciated by those skilled in the electrical art(s). Thus, the exemplary embodiments are not limited to any specific combination of hardware circuitry and/or software. In addition, one or more general purpose computer systems, microprocessors, digital signal processors, microcontrollers, and the like, can be employed and programmed according to the teachings of the exemplary embodiments of the present inventions, as will be appreciated by those skilled in the computer and software arts. Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as will be appreciated by those skilled in the software art(s). 
         [0040]    While the inventions have been described in connection with a number of exemplary embodiments, and implementations, the inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of the appended claims.