Abstract:
Sensors, including fiber optic sensors and their umbilicals, are mounted on support structures designed to be retro-fitted to in-place structures, including subsea structures. The sensor support structures are designed to monitor structure conditions, including strain, temperature, and in the instance of pipelines, the existence of production slugs. Moreover the support structures are designed for installation in harsh environments, such as deep water conditions using remotely operated vehicles.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority to the co-pending provisional application having Ser. No. 60/624,736, which was filed on Nov. 3, 2004. The provisional application having Ser. No. 60/624,736 is herein incorporated by reference in its entirety.  
         [0002]     The application is also related to the subject matter disclosed in U.S. application Ser. No. 10/228,385, filed 26 Aug. 2002, the subject matter of which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0003]     The present invention relates to apparatus and methods for monitoring fatigue, structural response and operational limits in structural components. More particularly the present invention relates to apparatus and methods for installation of monitoring systems on marine and land structural members.  
       DESCRIPTION OF THE RELATED ART  
       [0004]     All structures respond in some way to loading, either in compression, tension, or combinations of various loading modes. While most structures and systems are designed to accommodate planned loading, it is well known that loads exceeding design limits or continued cyclical loading may induce fatigue in the structure. While some structures may be readily monitored for signs of fatigue, others are not easily monitored. Examples include subsea structures, such as pipelines, risers, wellheads, etc.  
         [0005]     In most instances, monitoring systems are installed when the structure is installed or constructed. However, there exists a system of subsea risers, pipelines and other structures that have already been installed without the benefit of monitoring systems. These subsea components are subject not only to normal planned current or wave loading, but met ocean events, such as hurricanes, or sustained cyclical loading from vortex induced vibration (VIV) loading.  
         [0006]     A major concern in all offshore operations is the operational life of subsea components. A fatigue-induced failure can result in a substantial economic loss as well as an environmental disaster should produced hydrocarbons be released into the sea. When a subsea production structure is nearing the end of its serviceable life or has suffered substantial fatigue, producing companies are likely to shut-in production rather than run the risk of a catastrophic failure. This can result in substantial financial losses to the producing company.  
         [0007]     Currently, most subsea structures, such as risers and pipelines, including steel catenary risers, are not monitored. Structural integrity of such bodies is modeled, based on known loading factors, sea state data, and boundary conditions. Because there is no direct measurement of strain or fatigue in these structures, high safety factors, on the order of 10 to 20, are factored into these models. It will be appreciated that as the models indicate that a structure is nearing the end of its serviceable life or has undergone unacceptable fatigue, the choice for the production company is to repair or replace the structure or to shut-in production. In some instances, the structural integrity is far better than the models may predict. This means that the producing companies may be incurring substantial expense in repairing or replacing the structures or losses from shutting in production. The alternative, a loss of containment of produced hydrocarbons, would, however, subject any producing company to far greater liability costs when compared to repair, replacement or shut-in.  
         [0008]     Recently efforts have been made to develop monitoring systems for subsea structures. U.S. Patent Publication 2004/0035216, published 26 Feb. 2004, U.S. Application 10/228,385, entitled Apparatuses and Methods for Monitoring Stress in Steel Catenary Risers, which is herein incorporated by reference in its entirety, describes an apparatus and method for monitoring subsea structures utilizing a series of fiber optic Bragg grating (FBG) sensors to measure strain in several directions on a subsea structure. The design and use of FBG sensors is discussed within the &#39;385 application. Multiple fiber optic strands from a centralized fiber bundle have a Bragg grating applied to them and are attached to the subsea structure. Small gratings are etched on the fibers where attached to the structure. As a light is applied to the fiber a return signal is received. As a strain is applied to the structure, the grating is likewise strained and the returned signal undergoes a frequency shift that is proportional to the strain. The aforementioned application discloses the performance of the FBG sensors and a means for attaching them to the structure. It will be appreciated that by obtaining actual strain data, the models used to determine serviceable life are more accurate and the safety factors can be reduced to manageable levels. As, such, producing companies are more likely to reduce repair/replacement costs or shut-in losses without substantially increasing environmental risk.  
         [0009]     Thus, there exists a need for an improved method and apparatus to permit retrofit of an FBG or other sensor monitoring system that can be adapted to structures already in place.  
       SUMMARY OF THE PRESENT INVENTION  
       [0010]     The present invention is directed to a means of retrofitting sensors to installed marine elements. More particularly, the present invention utilizes a set of collars that may be remotely installed on subsea structures. One or more fiber optic sensors and umbilicals leading to a system are affixed to the structure by means of multipart collars. The collars may be hingeable for ease of installation or may be assembled as separate items. The umbilical acts as a protective sleeve for the fiber optic sensor and its fiber optic communication line. The sensors may be bonded internal to the the umbilical. Moreover, the fiber optic sensors may be of the FBG type previously disclosed, or may be of the Fabry Perot (FP) interferometer type. The nature of FP sensors is well known to those of ordinary skill in the art. In a Fabry Perot sensor, light is reflected between two partially silvered surfaces. As the light is reflected, part of the light is transmitted each time it reaches the surface, resulting in multiple offset beams that set up an interference. The performance of FP sensors is similar in that relative movement between the two silvered surfaces will result in a change of wavelength of the light.  
         [0011]     The present invention contemplates that the fiber optic sensors and their umbilicals are secured to the collars or other support structures. The support structure is then deployed subsea and installed on an existing subsea structure. The umbilicals may be removably attached to the support structure. This permits subsequent replacement of a sensor/umbilical in the event of failure. Alternatively, it permits installation of the sensor/umbilical following attachment of the support structure to the structure. In the present invention, multiple sensor/umbilical pairs may be attached to a single support structure. When the support structure is attached to the subsea structure, the sensors are fixed in position relative to the subsea structure. It will be appreciated that multiple support structures/umbilical/sensor assemblies may be attached to the subsea structure, thereby permitting strain monitoring along the length of the subsea structure. The flexibility of support structure design and attachment scheme of the sensor/umbilical pairs permits the user to design a custom monitoring system for the subsea structure.  
         [0012]     In one application, the present invention may provide a large and dense array of sensors over a relatively small portion of the structure. In the case of a subsea pipeline or a riser, this type of deployment could be used to determine not only strain from physical forces (physical loading and current forces) but may be used to detect large volumes of denser production (slugs) as they pass through the monitored section. As the slugs pass through a pipeline, the internal pressure within the pipe increases, resulting in detectable strain in the pipe internal and external walls. This strain may be detected by the sensors arrayed to measure hoop strain and may be recorded by the monitoring system. As the slug passes down a pipeline, it will be detected by subsequent sensors. The design of a sensor array and its placement along a pipeline section may be used to characterize the slug velocity and size.  
         [0013]     In another application, the present invention may provide for multiple support structures over long spans of the structure. In the case of SCRs, it would permit monitoring strain across the touch down zone. This type of application would also permit monitoring of the effects of temperatures on a subsea element. It will be appreciated that high temperature/high pressure well production may have hydrocarbon production temperatures in the range of 200° to 350° F. This production may be rapidly cooled as it passes through subsea flow lines to production risers. The effect of this rapid temperature change on subsea equipment is poorly documented. It will be appreciated that the failure of a piece of subsea equipment due to temperature failure would have a disastrous effect on the environment.  
         [0014]     While the foregoing and following discussion focuses on the use of fiber optic FBG and FP sensors, it will be appreciated that the sensors described herein may include hybrid sensors, i.e., fiber optic sensors in combination with other types of transducers including a means for converting the transducer signal for transmission through a fiber optic medium.  
         [0015]     The foregoing summary has outlined rather broadly the features and technical advantages of the present invention so that the detailed description of the preferred embodiment that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed might be readily used as a basis for modifying or designing other apparatuses and methods for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth and claimed herein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments and applications of the present invention, and, together with the detailed description, serve to explain the invention. In the drawings:  
         [0017]      Figs. 1A and 1B  are side and top views, respectively, of a cutaway section of a tubular showing one embodiment of the present invention;  
         [0018]      FIGS. 2A and 2B  are side and top views, respectively, of a cutaway section of a tubular showing another embodiment of the present invention;  
         [0019]      FIG. 3  is a perspective view of an application of the present invention showing spaced collars having multiple sensors on each fiber optic cable on an SCR;  
         [0020]      FIG. 4  is a side view of another application of the present invention is which the sensor umbilical is wound helically between the collars so as to sense vortex induced vibration;  
         [0021]      FIGS. 5A and 5B  are side and top views of another embodiment of the present invention utilizing two locking collars;  
         [0022]      FIGS. 6A and 6B  are side and top views of another two collar embodiment of the present invention;  
         [0023]      FIGS. 7A and 7B  are top and side views of another embodiment of the present invention utilizing a bladder contact system;  
         [0024]      FIGS. 8A-8C  are detailed views of the bladder and sensor contact system of  FIGS. 7A and 7B ;  
         [0025]      FIGS. 9A-9C  are top, cross-sectional and detailed views of another embodiment of the present invention;  
         [0026]      FIGS. 10A and 10B  are side and cross-sectional views of another embodiment of the present invention; and  
         [0027]      FIGS. 11A and 11B  are cross-sectional and detailed views of another embodiment of the present invention as applied to concrete or cement coated structures; and  
         [0028]      FIGS. 12A and 12B  are side and cross-sectional views of the present invention as applied to a tubular connection. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     In one embodiment the structure to which the monitoring system is attached is discussed in terms of a tubular subsea element. However, it will be appreciated that the structure need not be tubular. The specific geometry of the support structure and the means of securing it about the structure may be readily varied to the geometry of the structure. Moreover, the structure need not be limited to a subsea element, as the same principles would operate with a horizontal or vertical structure, subsea or on the land.  
         [0030]     In  FIGS. 1A and 1B , a cutaway of a subsea element  10  is shown with one embodiment of the monitoring system of the present invention mounted thereon. A collar  20  is shown comprised of two collar sections  22 A and  22 B. The collar sections  22 A and  22 B each have a hinge portion built therein and are pinned together by pin  24 , thus allowing the collar sections  22 A and  22 B to open and close tightly about the vertical element  10 . It will be appreciated that a deformable material such as rubber or plastic may be placed on the internal surfaces of collar sections  22 A and  22 B. The material is deformed against the outer surface of the subsea element  10  when the collar  20  is closed thereabout, thereby further securing the collar  20  against movement relative to the subsea element  10 . The pin  24  may be secured by any number of means known to those skilled in the art, including, but not limited to cotter pins, snap rings, etc. In  Fig. 1B , a collar latch  26  is depicted as holding collar sections  22 A and  22 B in a closed position about the vertical element  10 . The collar latch  26  may be readily selected by those skilled in the art from any number of latch designs that are capable of being operated underwater, either manually or by remotely operated vehicle (ROV). Collar sections  22 A and  22 B are provided with at least one groove or notch section  28 , which will serve to provide a placement point for the fiber optic umbilical, to be discussed below. It will be appreciated that the collar sections  22 A,  22 B, the pin  24  and latch  26  may be readily fabricated from metal, fiberglass, thermoplastic or other material suitable for the marine environment. Moreover, the collars may be coated with copper or other anti-fouling coating to prevent marine growth on the collars.  
         [0031]     Multiple fiber optic umbilicals  40  are shown as being installed in collar  20 . The fiber optic umbilical  40  provides an appropriate shield for the one or more fiber optic fibers  42  within each umbilical  40 . The umbilical  40  may be constructed from an appropriate material, such as thermoplastic or other material. Each of the fibers  42  has at least one sensor  44  integrated therein and secured to the inner wall of the umbilical  40  by epoxy or some other suitable means. As noted above, the sensor  44  may be of the FBG or FP type. While fiber optic fibers  42  of  FIG. 1A  are shown with a single sensor  44 , multiple sensors may be placed on a single fiber. This may be achieved by designing the FBG or FP sensor  44  to have an initial different wavelength response to the same light source as other FBG or FP sensors  44 . Accordingly, any measurement of strain from the multiple sensors could be distinguished one from the other. The sensor umbilicals  40  are depicted as being within grooves  28  within the collar sections  22 A and  22 B. The umbilicals  40  are secured within the grooves  28  and to the collar sections  22 A and  22 B by means of umbilical latches  50 . The latch  50  may be readily selected by those skilled in the art from any number of latch designs that are capable of being operated underwater, either manually or by ROV. It will be appreciated that the number of umbilicals  40  that may be deployed on collar  20  and may be a simple matter of engineering design. The sensor umbilicals  40  are then connected to a system (not shown) designed to monitor and record strains on the element  10 . Moreover, the umbilical  40  may be used to shield multiple fibers  42 , each having multiple sensors  44  thereon.  
         [0032]     The collar  20  with umbilicals  40  already installed thereon may be lowered on a heave-resistant line from an appropriate work vessel. At the selected depth, the collar  20  and umbilicals  40  may be maneuvered into position about structure  10 . The collars  20  may then be opened and closed about the structure  10  by means of divers or ROVs, depending upon the depth of installation. Further, installation of the collar or other support structure may be achieved utilizing an ROV together with a special installation system designed to permit the installation of multiple support structures in a single trip. U.S. Pat. No. 6,659,539, incorporated herein by reference in its entirety, describes a method and apparatus for installing multiple clamshell devices, such as collar  20 , using Shell&#39;s RIVET™ system, commercially available from one or more Shell Companies. Utilizing the RIVET™, the collars  20  and umbilicals  40  would be loaded into the RIVET™, lowered to the desired position next to the structure  10  and RIVET™ arms would be activated to close the collar  20  sections about the marine element  10 . An ROV can be used to activate the RIVET™ structure or it may be remotely activated. The ROV may also be used to close the collar latch  26 , if required. Alternatively, a self-closing latch  26  may be used on collar sections  22 A and  22 B.  
         [0033]     The monitoring system may be located on a structure or vessel above the water line. However, in many instances, the sensors may not be readily adjacent to a surface structure, making it impractical to have umbilicals  40  lead back to the surface structure for connection to the monitoring system. It is contemplated with respect to the present invention that the monitoring system may further include a subsea-based system. The subsea system would analyze and record the strain information much like a surface system. The information could be stored for periodic transmission from the subsea system to a surface based system or retrieval of data from the subsea system. This may be accomplished by means of short range electromagnetic transmission, acoustic transmission via transponders and receivers or simple data retrieval utilizing an ROV system. Alternatively, the monitoring and recording system could be based in a surface buoy tethered to the marine element. The surface buoy could be battery and/or solar powered to provide power for the monitoring system. Further, the surface buoy system could transmit information to a remote station. Thus, it would be possible to support a remote monitoring system away from a structure. It will be appreciated that the remote monitoring system disclosed therein could be utilized with any of the embodiments discussed herein.  
         [0034]      FIGS. 2A and 2B  depict side and vertical cutaways of another embodiment of the present invention. A collar  20 , comprised of collar sections  22 A and  22 B, each having a mating hinge section incorporated therein are secured about marine element  10  by means of hinge pin  24  and latch  26 . In the embodiment depicted in  FIGS. 2A and 2B , a single groove  28  is incorporated into collar  20 . An umbilical  40  is shown as being placed in groove  28  and secured within the collar  20  by means of a suitable latch  50 . Whereas the umbilical  40  of  FIGS. 1A and 1B  had but a single fiber therein, the embodiment shown in  FIGS. 2A and 2B  depict multiple fiber optic fibers  42  therein, each having a sensor  44  bonded to the inside wall of the umbilical  40 . The embodiment shown in  FIGS. 2A and 2B  depict each of the sensors  44  at approximately the same axial position within the umbilical  40 . It will be appreciated that each fiber optic fiber  42  need not have its sensor bonded to the inside of the umbilical  40  wall in the same axial position. Moreover, more than one sensor  44  may be placed on a single fiber optic cable  42 , as discussed above. The sensors  44  may be spaced azimuthally inside umbilical  40 . Motion by marine element  10  in a specific direction will affect each sensor  FIG. 3 . is a perspective view of a marine element  60 , in this case an SCR, on which a plurality of collars  20  and umbilicals  40  have been mounted in the touch down zone (TDZ), i.e., that portion of the riser where it comes into contact with the seabed  70 . The implementation depicted in  FIG. 3  utilizes multiple sensors  44  on a single fiber optic fiber  42  within umbilical  40 . It will be appreciated, however, that the ability to detect a frequency shift created by FBGs, and therefore the strain seen by a particular sensor  44 , will decrease as the number of sensors on a single fiber optic fiber increases. As a result, it may be desirable as the number of collars  20  installed on a structure increases, to have separate umbilicals  40  and/or fibers  42  on the collars  20 .  
         [0035]      FIG. 4  depicts a series of collars  20  placed on a vertical element  10 . Unlike the alignment in shown in  FIG. 1A , the umbilicals  40  are shown as being deployed in a helical manner by indexing each umbilical  40  over to the adjacent groove  28  in collar sections  22 A and  22 B. As noted previously, the umbilicals  40  are secured to the collar  20  by means of an umbilical latch  50 . The umbilicals  40  may then be installed on collars  20  in a helical manner as shown in  FIG. 4  using ROVs to place the umbilical  40  and close latch  50  to secure them to the collar  20 . It is well known to those skilled in art that the installation of helical bodies about a larger body will have the result of suppressing VIV. At the same time, it will be appreciated that a single umbilical  40 /sensor  44  combination that has failed during its operational life may be replaced by sending down an ROV to open the appropriate latch  50  on each collar to remove the defective umbilical  40 /sensor  44  and replace it with an operational one.  
         [0036]     Another embodiment of the present invention is depicted in  FIGS. 5A and 5B , in which a dual collar system utilizing spacer members placed between the collars. A marine element  70  is shown having two collars  101  placed at two different locations along the longitudinal axis of the tubular  70 . Each of the collars  101  are comprised of collar halves  100 A and  100 B and are free to rotate about pin  102 . Each collar  101  is also equipped with a latch  104  to secure the collar halves  100 A and  100 B together. Strips of spacers  109  are show as being affixed to and connecting collars  101 . The spacers  109  depicted in  FIGS. 5A and 5B  are shown as rectangular strips in compression between the collars  101 . The spacers may also have other geometric configurations and may made from ABS plastic, PVC plastic, or other thermo plastics, soft metals, fiberglass or other materials that would permit the spacers  109  to flex sufficiently to place them in compression between collars  101 . A fiber optic umbilical  110  attached to a surface monitoring system (not shown) is shown as being connected to fiber optic junction  112 . Junction  112  may be affixed to one of the collars  100 A or  100 B or may be affixed to the spacer  109 . The junction  112  shown in  FIG. 5A  is shown as being “daisy-chained” through fiber optic umbilical  113  to other similar junctions  112  mounted on the spacers  109 . Each junction  112  further has a fiber optic sensor lead  114  leading away from the junction  112  and terminating in a FBG or FP sensor  116 .  FIG. 5A  shows the sensor  116  as being mounted on the inside of spacer  109  to protect it from current borne objects. The sensor  116  may further be protected by means of epoxy, plastic or other suitable marine resistant coating. With the spacers  109  being under compression, any strain seen by marine element  70  will result in a change in the compression of the spacers  109 . These changes may be detected by the sensors  116  and transmitted to the monitoring system. While  FIG. 5A  shows multiple junctions  112 , it will be appreciated that a single fiber optic junction having multiple fiber optic sensor leads  114  may be used to place multiple sensors  116  on the spacers  109 .  
         [0037]     A variation of this spacer system for monitoring is shown in  FIGS. 6A and 6B . Instead of flexible spacers  109  as used in  FIGS. 5A and 5B , multiple spacer bars  120  are used as spacers between collars  100 A and  100 B secured about marine element  70 . The spacer bars  120  may be placed in tension, compression or an unloaded condition between collars  100 A and  100 B. A fiber optic umbilical  110 , attached to a surface monitoring system (not shown) is shown as being connected to a single fiber optic junction  112 . Multiple fiber optic sensor leads  114  lead away from junction  112  and terminate in FBG or FP sensors  116  placed on the inside of spacer bars  120 . Alternatively, multiple junctions  112  may be used similar to those depicted in  FIGS. 5A and 5B . Strain seen by the marine element  70  will be transmitted via collars  100 A and  100 B to the spacer bars  120 . The strain may be detected by the sensors  116 , transmitted through junction  112 , and fiber optic cable  110  to the surface system or another system, where it may be recorded. It will be appreciated that implementations depicted in  FIGS. 5A, 5B  and  6 A,  6 B may be installed utilizing the aforementioned RIVET™ system.  
         [0038]     An alternative to mounting sensors on intermediate objects attached to a marine element is to mount the sensor directly on the marine element. However, retrofitting sensors directly to an installed marine element is generally difficult in assuring (a) placement and (b) contact between the sensor and marine element.  FIGS. 7A and 7B  depict the design of a collar system that permits a sensor to be directly in contact with an installed marine element. A single collar  200  is comprised of collar halves  202 A and  202 B pivoting about pin  206 . The collar halves  202 A and  202 B are secured about the marine element utilizing a latch  204 , for example a self-locking latch. Each collar half  202 A and  202 B may have at least one recess  212  therein for the mounting of an inflatable bladder  210 A and  210 B which is placed between the inside of the collar halves  202 A and  202  B and the marine element  70 . Each of the collar halves  202 A and  202 B is provided with an injection port  208 A and  208 B which are depicted in greater detail in  FIGS. 9A-9C .  
         [0039]     Collar  202 B is shown in section and detail in  FIGS. 8A-8C . It will be appreciated that collar  202 A has similar detail but is not shown for the sake of brevity. Collar  202 B has an annular chamber  212  machined azimuthally about the interior of the collar  202 B. Inflatable bladder  210 B is mounted in the recess  212  and is in fluid communication with port  208 B. It will be appreciated that a check valve (not shown) may be placed in the fluid passage between bladder  210 B and port  208 B. A fiber optic umbilical  214  is depicted passing through access port  216  in collar  202 B. The access port  216  may be sealed to the marine environment by means of epoxy, potting compound or other suitable substance. Chamber  212 B further includes a flexible, non-corrosive carrier plate  220 B bearing fiber optic strand  215 B which terminates in a FBG or FP sensor  222 B. As depicted in  FIGS. 8A-8C , the carrier plate  220 B is retained within the chamber by placing part of the plate within relief grooves  218  formed in the chamber  212 . Other methods for retaining the carrier plate  220 B may used such as leaf springs or other suitable retaining systems. A vent port  224 B is further drilled in collar  202 B and may further be provided with a check valve (not shown) to permit the flow of water from chamber  212 B to the marine environment but prevent water from the marine environment from flowing back into the chamber  212 B.  
         [0040]     In operation, the collar  200  may be installed about a marine element  70  by a diver, ROV or ROV and RIVET™ system. As noted above, the latch  204  is designed to be self-locking to tightly fit collar  200  about the marine element  70 . Following securing the collar  200  about the marine element  70 , a diver or ROV may be sent down to the collar  200 . An epoxy may be pumped into port  208 B, which is in fluid communication with the bladder  210 B. As can be seen in  FIG. 8B , as the epoxy  240  enters the bladder  210 B, the bladder  210 B expands and starts to deflect towards the marine element  70 , pulling the carrier plate  220 B out of grooves  218 B. Alternatively, the carrier plate  220 B may be scored adjacent to where it is affixed to chamber, rendering it frangible across the scoring allowing it to part and move toward the marine element  70  as the bladder  210 B is inflated by pumping in the epoxy  240 . In  FIG. 8C , the bladder  210 B is shown as fully inflated with the sensor  220 B in contact with the marine element  70 . It will be appreciated that as bladder  210 B is inflated, that it will displace water originally in annulus between chamber  212 B and marine element  70 . Accordingly vent port  224 B is provided to permit the displacement of the water and the addition of a check valve can prevent the return of water back into the annulus through port  224 . The pump is disconnected from port  208 B and the epoxy  240  is allowed to cure. With fiber optic cable  214  in communication with a surface monitoring system, this embodiment provides for a direct contact between the marine element  70  and the sensor  222 B. It will be appreciated that multiple carrier plates  220  and sensors  222  may be installed in the chamber  212 B, either utilizing multiple cables  214  or a single cable and a fiber optic junction that leads to multiple sensors. While  FIGS. 7A, 7B  and  8 A- 8 C depict two azimuthal bladders  210 A and  210 B, it will be appreciated that small individual bladders may be used for one or more sensors. This type of arrangement would require additional pumping ports or a flow system that permits selection and inflation of the individual bladders without over-pressurizing other bladders that could result in damage to the sensor. Other systems may be readily designed to advance the sensor  222  into contact with the marine element upon injection of epoxy or some other bonding fluid. For example, sensor  222  may be mounted on a rod recessed in a sleeve in port  208 . Upon injection of epoxy through port  208 , the rod bearing the sensor is advanced into contact with the marine element as epoxy continues to fill cavity  212  displacing any water through port  224 . It will be appreciated that the embodiments depicted in  FIGS. 1, 2  and  7 - 8  are designed to be secured around an existing marine element in a hinged or clamshell fashion that may use the RIVET™ tool for installation.  
         [0041]     In other instances, a marine element may be horizontal or lying at or along the ocean bottom or partially embedded in the ocean bottom. It will be appreciated that it would be difficult, if not impossible, to install a fully encircling collar of the types disclosed above. Accordingly, there exists yet another embodiment to permit retro-fitting to horizontal and/or partially embedded marine elements. An embodiment for monitoring a partially embedded marine element  70  is depicted in  FIGS. 9A-9C .  FIG. 9A  is a top view of the marine element having a shroud  300  disposed over the top of the marine element  70 . The shroud  300  may be fabricated from fiberglass, thermoplastic, metal or other materials suitable for a marine environment. The shroud  300  may be lowered onto the marine element  70  from a surface vessel with the assistance of a diver or an ROV. The shroud  300  is secured to the marine element  70  by at least one spring-loaded (springs not shown), locking balls  302  installed in the interior of the shroud. As the shroud  300  lowered over the marine element  70 , the spring loaded balls  302  are pushed back into shroud  300 . As the shroud  300  is further lowered, the locking balls  302  pass the diameter of the marine element  70  and are then biased outwardly by the springs, thereby affixing the shroud  300  to the marine element  70 . It will be appreciated that other retaining methods may be used to secure the shroud  300  to the marine element, including screws passing through shroud  300  that may be tightened about the marine element by a diver or an ROV. Alternatively, spring-loaded or screw-activated locking dogs may be used to secure the shroud  300  to the marine element  70 . A sensor assembly  304 , including fiber optic umbilical  310 , is mounted atop the shroud  300 . The fiber optic umbilical  310  is connected to an instrumentation system (either surface or subsurface) that is used to monitor and record the data.  
         [0042]     The sensor assembly is shown in greater detail in  FIG. 9C , which is a cross sectional view of the sensor assembly  304  and marine element  70 . The shroud  300  is provided with a slotted hole  320 , having slot portion  322  therein. A slotted sensor module  308  is designed to fit within threaded slotted hole  320 . The module  308  has a key  306  manufactured therein and cooperates with slot  322  to align and limit the module  308  movement toward the marine element  70 . The module  308  may be comprised of a potted epoxy thermoplastic, metal or other marine resistant material. The fiber optic umbilical  310  may be potted as part of the module and terminates in a FBG or FP sensor  312  mounted at the end of the module. Alternatively, a hole in the sensor module  308  or shroud  300  may be provided for passing the fiber optic cable  310  to the end of the sensor module. The sensor assembly  304  may further be provided with a grommet  324  or protective other means to protect sensor  312 . The sensor module  308  is secured in slotted hole  320  by a lock down screw or bolt  314  that mates with the threads in slotted hole  320 . The module  308  and grommet  324  may be designed to bring the grommet  324  into contact with the marine element  70  and thus permit the sensor  312  to directly monitor strain. Alternatively, if the sensor  312  is not in direct contact with the marine element  70 , it will still be capable of monitoring the marine element  70  as large mechanical strains placed on the marine element will be passed to the sensor  312  through shroud  300 . The illustrated embodiment thereby provides for a means for monitoring strains in elements that are horizontally situated or partially embedded.  
         [0043]     In other instances, it may be desirable to monitor the strain placed on a tubular or other connection. A system for carrying out monitoring is depicted in  FIGS. 10A and 10B , which are side and cross-sectional views of such a system. Two tubular elements  70  are joined in a pin and box connection  400  in which the male threaded end of one of the tubulars is screwed into sealing engagement with the box end of the other tubular. In this embodiment collar halves  402 A and  402 B rotate about pin  404 . In this instance, the assembly is made up of two collar sets, each disposed on one side of the connection  400 . The respective collars may be secured by latches, bolts, machine screws  406  or other suitable retaining mechanism. A sensor support connection  408  is attached to each of the collars  402  by epoxy or other suitable means. The connections  408  are aligned to permit the attachment of a sensor support  410  prior to deployment. A fiber optic umbilical (not shown) is introduced such that a sensor  420  may be disposed in between the sensor support  410  and pin and box connection  400 . This permits sensor  420  to directly monitor strain incurred by pin and box connection  400 . While a single sensor is depicted in  FIGS. 10A and 10B , it will be appreciated that multiple sensor supports  410  and sensors may be deployed using junction boxes and shown in  FIGS. 5A and 5B .  
         [0044]     In some instances, a marine element  70 , such as a pipeline, is coated with concrete to add extra weight and to prevent the pipeline from moving in response to near bottom currents. The present invention contemplates yet another embodiment to permit monitoring of concrete coated marine elements. In cross-sectional view  FIG. 11A , a marine element  70  having a concrete coating  72  thereabout is shown in a horizontal position partially embedded in the surface. A sensor assembly  340  is depicted in  FIG. 11A  and shown in greater detail in  FIG. 11B . A hole  342  is drilled and/or milled through the concrete coating  72 . This may be accomplished by a diver or by using a work ROV equipped with a drill. It will be appreciated that a masonry drill and/or mill that is less capable of cutting into the steel of the marine element  70  may be used to prevent damaging marine element  70 . Upon completion of drilling, a threaded, slotted sensor housing  344  may be inserted in the hole  342 . The slotted sensor housing  344  is designed to receive a sensor module  346  having keyed portion  350  designed to mate with the slotted sensor housing  344  to align and position the sensor module  344 . As with the embodiment of  FIGS. 10A and 10B , the module  346  may be made of any suitable marine resistant material. The module  346  provides a pass-through or potted fiber optic cable  348  that terminates in a FBG or FP sensor  352  on the bottom of module  346 . The module  346  is retained in the housing  344  utilizing a set screw  354  or other suitable means. The module  346  itself is retained within the concrete coating  72  by a quick setting epoxy  356  that is pumped into the annulus between the housing  344  and hole  342 . Alternatively, a tapered sleeve or other friction retaining means may be used to retain the housing  344  within the hole  342 . As will be noted in  FIG. 11B , as illustrated, the sensor  352  is not in direct contact with the marine body  70 . Rather, any strains will be transmitted through the cement coating  72 , to the housing  344  and to the sensor module  346  and sensor  352 .  
         [0045]      FIGS. 12A and 12B  are cross-sectional and detailed views, respectively, of another single collar embodiment of the present invention. Two collar halves  80  and  82  pivot about pin  83 . The collar halves  80  and  82  may be made of metal, thermoplastic or other materials suited to long term marine exposure. They are positioned about marine element  70  closed and secured by a suitable latch  84 . A sensor base  86  is affixed to one of the collar ( 80  or  82 ) halves. The base  86  may be attached utilizing adhesives, resins, or may be welded to the selected collar half. One or more fiber optic cable grooves  92  are formed or machined in the sensor base  86 . A locking latch arm  90  pivots about pin  86 , which is in turn connected to sensor base  86 . The locking latch arm  90  is drilled and threaded to receive contact pin  94 . The contact pin  94  is used to insure that the fiber umbilical optic  94  having fiber optic cable  95  and FBG or FP sensor (not shown) remain in contact with the sensor base  86 . In this instance, the collar may be installed on the tubular  70  prior to being installed in its location. The fiber optic umbilical  94  may be installed after the marine element  70  has been installed.  
         [0046]     The present application has disclosed a number of different support structures that may be used to retrofit existing, in place marine structures with fiber optic monitoring equipment. As noted above, the fiber optic sensors may be used for the purpose of strain measurement, slug detection and temperature measurement. Various modifications in the apparatus and techniques described herein may be made without departing from the scope of the present invention. It should be understood that the embodiments and techniques described in the foregoing are illustrative and are not intended to operate as a limitation on the scope of the invention.