Abstract:
A method of forming a field joint for a subsea pipeline includes the steps of positioning an end of a first pipe adjacent to an end of a second pipe, welding the end of the first pipe to an end of the second pipe, and applying a coating material over an exterior surface of the first pipe, over the welding, and over an exterior surface of second pipe such that the coating material is in sealing relationship therewith. The coating material has air-filled glass spheres therein. A mold is placed over the adjacent pipe sections and the coating material is injected under pressure into the mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and apparatus for forming a subsea pipeline. More particularly, the present invention relates to methods for forming a joint in a subsea pipeline. Additionally, the present invention relates to methods of laying and positioning the subsea pipeline. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     Offshore pipelines have normally been laid on the seabed by using a pipe laying barge. Pipe sections, typically 40 feet long, are welded to the end of the assembled pipeline on the barge and the pipe is launched over the stern of the barge as the vessel moves forward. 
     The part of the pipe between the vessel and the seabed adopts an S-shaped configuration or a J-shaped configuration having an upper curve called an “overbend” and a lower curve called a “sagbend”. It is important to ensure that there is not excess curvature in the overbend and the sagbend, or else the resulting high stress in the pipe can cause ovalization, buckling or fracture. Such buckles can be extremely expensive to repair. Typically, a supporting structure is employed to support the pipe in the overbend region so as to prevent excess curvature. Stingers are well known for this purpose and typically employ a buoyant structure for supporting the pipe. However, instead of a buoyant stringer, a fixed and rigid stern ramp is also known for supporting the pipe in the overbend. Such a stern ramp comprises a rigid structure extending from the stern of the pipe laying barge and remains fixed during pipe laying operations. The ramp is fitted with rollers along its length late which are positioned along an arcuate path for supporting pipe launched from the barge as it curves downwardly into the water in the overbend. 
     During these normal pipe laying operations, fresh pipe sections are welded to the end of the assembled pipeline on the barge, with the barge remaining stationary relative to the seabed, and similarly, the assembled pipe remaining stationary relative to the barge. When a fresh pipe length has been welded on and the joint finished as required, a length of pipe corresponding to the freshly added-on length is launched from the barge by moving the barge forward under the pipe and allowing the pipe to slide off the stern of the barge over the stern ramp or stinger. 
     During such pipe laying operations, it is very important to determine the touchdown point of the pipeline. The touchdown point is the point of which the pipeline contacts the seabed. In the past, ROVs have been employed for the purpose of determining this touchdown point. If the touchdown point is too close to the vessel, then there is a risk of buckling and/or overstressing. If the touchdown point is too far from the vessel, then there is a risk of the buckling of the pipe. As such, it is desirable to always ascertain the touchdown point of the pipe as the pipe laying operation continues. 
     ROVs have been employed for the purposes of determining this touchdown point. The ROV can utilize cameras in order to visually see the touchdown of the pipeline with the seabed. Unfortunately, the ROVs must be tethered to the vessel. In certain circumstances, the touchdown point may be nearly a mile from the vessel. As such, the length of the tether that is available may not be sufficient to cover such as distance. Under these circumstances, a second vessel, along with a second ROV, would be required. This significantly increases the expense of the pipe laying operation. 
     The efficiency of the pipe laying operation is largely determined by the efficiency with which the pipe can be welded end-to-end aboard the vessel. In the past, the pipes are welded in end-to-end relationship. Another section of pipe is placed over this welded joint and then welded to the pipe. This extra section of pipe can simply be placed over the pipeline in semi-cylindrical sections. These edges of the cylindrical sections are then welded together at the joint so that the pipe over lies the weld joint. This is a very time-consuming and inefficient operation. 
     Offshore hydrocarbon recovery operations are increasingly moving into deeper water and more remote locations. Often satellite welds are completed at the sea floor and are tied to remote platforms or other facilities through extended subsea pipelines. These pipelines extend through water that is thousands of feet deep, where temperatures of the water near the sea floor are in the range of 40° F. The hydrocarbon fluids, usually produced along with some water, reach the sea floor at much higher temperatures, characteristic of depths thousands of feet below the sea floor. When the hydrocarbons flow, any water present begin to cool, a phenomena that may significantly affect flow of the fluids through the pipelines. Some crude oils become very viscous or deposit paraffin when the temperature of the oil drops, making the oil practically not flowable. Hydrocarbon gas under pressure combines water at reduced temperatures so as to form a solid material, called a “hydrate”. Hydrates can plug pipeline. These plugs are very difficult to remove. 
     Typically, so as to avoid the effect of such low temperatures, the pipeline can be surrounded by an insulating material, such as concrete, insulating foam or electrical heating pipes. Since the insulating material extends along the pipeline, the section of the insulating material must be removed from the pipe so that the welding operation can occur at the pipe joint. As such, there will be a space, adjacent to the weld, that is free of the insulating material. There is a need to be able to suitably cover this exposed area after the welding operation has been completed. In certain circumstances, in the past, an insulating material is placed over the space. The application of this insulation material, in the past, has been very time-consuming. It often takes a great deal of time for the insulating material, such as epoxy, to effectively cure in this space. 
     In the past, various patents have issued relating to the forming of field joints for a subsea pipelines and relating to the method of laying and positioning a subsea pipeline. For example U.S. Pat. No. 3,690,111 issued on Sep. 12, 1972 to J. F. Matthews, Jr., describes an offshore pipeline installation method. The underwater pipeline is installed by lowering it to the bottom of the water from the stern of a lay barge as the barge advances along a long preassembled pipeline section which floats near the surface of the water and is held in tension by a second vessel positioned in front of the lay barge. An additional floating section is connected in place when the lay barge reaches the end of the initial section. This additional section is held in tension by the second vessel. Laying of the line is continued as the lay barge advances. 
     U.S. Pat. No. 4,120,167, issued on Oct. 17, 1978 to Denman et al., teaches offshore pipe laying in which a forward movement of a pipe-laying vessel is controlled to maintain the position of the pipe as laid on the sea bed. The position of the touchdown point on the sea bed of the pipeline suspended from the vessel is measured at periodic intervals by driving a survey vessel fitted with an echo location device along the already laid line. The measured position of a touchdown point is compared with the desired track and any deviation is computed. Further movements of the pipe-laying vessel are adapted to minimize this deviation. 
     U.S. Pat. No. 4,124,991, issued on Nov. 14, 1978 to W. M. Adler, provides an offshore pipe laying method which employs a pipe laying vessel with a fixed stern ramp and includes repeated steps of launching pipe while allowing pipe tension to drop within safe limits. Fresh pipe sections are welded on during the forward movements of the vessel. 
     U.S. Pat. No. 4,226,444, issued on Oct. 7, 1980 T. W. Bunyan, discloses a method of joining pipes in which a sleeve is placed over the adjacent ends of the pipes so as to overlap each pipe. The sleeve fits with clearance around the pipe ends. The ends of the clearance space are closed by inflating hollow sealing rings and then epoxy resin is injected into the clearance space to fill the space. The pressure of the epoxy resin composition is then raised to a pressure substantially greater than atmospheric and the pressure is maintained until the resin composition is set. 
     U.S. Pat. No. 5,328,648, issued on Jul. 12, 1994 to McBrien et al., shows a method of using a composite joint infill system. A pair of concrete coated pipe joints are welded together end-to-end with a gap between the concrete coatings. The gap is filled with a fast setting elastomeric polymeric infill material, either solid or foamed, and a particulate filler material. A mold is used for molding the infill material. The mold is filled with filler material before the polymer components are injected. 
     U.S. Pat. No. 6,058,979, issued on May 9, 2000 to L. W. Watkins, shows a deep sea insulated pipeline that has an inner pipe which is encased lengthwise by an insulating core. The insulating core comprises macrospheres surrounded by syntactic foam that includes a semi-rigid resin binder and microspheres. The semi-rigid resin binder reinforces the macrospheres to provide sufficient strength to withstand the hydrostatic pressure at depths in excess of several thousand feet of water, and is yet flexible enough to accommodate bending associated with deep sea pipe laying operations. The deep sea insulated pipeline may also include a protective outer casing. The inner pipe extends through and cooperates with the outer casing to define an annulus chamber containing the insulating core. 
     U.S. Pat. No. 6,641,330, issued on Nov. 4, 2003 to Andersen et al., discloses a method and apparatus for laying elongated articles. Fiber-reinforced flexible adhesive tape is used to bind an elongate article or bundle of articles during subsea laying operations. The apparatus includes at least one carrier for a tape spool arranged to rotate while moving bodily around the axis of the article during laying. 
     U.S. Pat. No. 6,739,803, issued on May 25, 2004 to Bass et al., teaches a method of insulating an electrically-heated pipe-in-pipe subsea pipeline Inner and outer pipe segments are formed and the inner pipe is coated and insulated. The coating may include sprayed polyurethane foam and insulating half-shells that are placed around welds. Epoxy is preferably coated on the inner pipe before other coatings. The segments are loaded on a lay barge and water stops are preferably installed in the annulus as the pipeline is formed. Water stops may be formed by placing a liquid polymer in the annulus and allowing it to cure. 
     It is an object of the present invention to provide a method that facilitates the accurate determination of a touchdown point of the pipeline from a remote distance. 
     It is another object of the present invention to provide a method that avoid buckling and overstressing of the pipeline. 
     It is another object of the present invention to provide a method which minimizes the ROV requirements. 
     It is still another object of the present invention to provide a method which minimizes the time required for forming field joints. 
     It is still another object of the present invention to provide a method that enhances the ability to monitor pipes and pipe joints. 
     It is still a further object of the present invention to provide a method which improves the buoyancy of the pipeline at the joints. 
     It is still another object of the present invention to provide a method that improves the insulating quality at the joints. 
     These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a method of forming a field joint for a subsea pipeline. This method includes the steps of: (1) positioning an end of a first pipe adjacent to the end of a second pipe; (2) welding the end of the first pipe to an end of the second pipe; and (3) applying a coating material over the exterior surface of the first pipe and over the welding and over an exterior surface of the second pipe such that the second coating material is in sealing relationship therewith. 
     The coating material of the present invention is formed with air-filled glass spheres therein. The coating material is of an epoxy material. 
     The first pipe has an insulator material extending therearound and radially outwardly thereof a distance from the exterior surface of the pipe. This insulator material has an end spaced from the end of the first pipe. The second pipe has an insulator material extending therearound and radially outwardly of the exterior surface of the second pipe. This insulator material of the second pipe has an end spaced from an end of the second pipe. The coating material extends between the ends of the insulator material of the first and second pipes. 
     The method of the present invention further includes the step of wrapping a wrap material around the exterior surfaces of the first and second pipes at the ends thereof. This step of wrapping occurs prior to the step of applying the coating material. The wrap material is of a honeycomb configuration. The coating material is applied into spaces of this honeycomb material. 
     In the present invention, an RFID tag is applied adjacent to the ends of the first and second pipes. The RFID tag can be incorporated into the coating material or applied to the coating material. 
     The step of applying the coating material includes the steps of: (1) placing a mold around the exterior surface of the first pipe and over the welding and over the exterior surface of the second pipe; (2) injecting the coating material under pressure into the mold; and (3) curing the coating material such that the coating material is bonded to the exterior surfaces of the first and second pipes. 
     The present invention is also a method of laying and positioning a subsea pipeline that comprises the steps of: (1) forming a pipeline of a plurality of pipe sections joined together in end-to-end relationship such that a joint is formed between adjacent pipe sections; (2) discharging the plurality of pipe sections sequentially outwardly of a ship and into the water; (3) positioning an ROV in the water in an area adjacent to the pipeline; and (4) sending and receiving sonar signals toward and from the pipeline by the ROV so as to ascertain the touchdown point. The joint has coating material extending thereover. This coating material has air-filled glass spheres therein. 
     The step of sending and receiving the sonar signals includes directing the sonar signals towards the coating material at the joints of the plurality of pipe sections of the pipeline. The step of forming includes affixing an RFID tag onto or into the coating material at each of the joints. The ROV will have an RFID tag reader therein. An ROV can then fly along the pipeline so as to receive data from the RFID tags at the joints of the pipeline. 
     The step of forming includes positioning a mold over the adjacent pipe sections at the joint thereof, injecting an epoxy material having the glass spheres therein under pressure and into an interior of the mold and over the joint, and curing the epoxy material such that the coating material is in sealing relationship over the joint. A honeycomb material can be wrapped over an exterior surface of the pipe sections at the joint. The epoxy material is injected into the spaces within the honeycomb material. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagrammic illustration of a prior art technique for laying of a subsea pipeline and for the determining of the touchdown point of the pipeline. 
         FIG. 2  is a cross-sectional view showing the ends of the pipe prior to welding. 
         FIG. 3  is a plan view showing the honeycomb shape of the wrap material. 
         FIG. 4  shows the joining of the ends of the pipe together by welding and the application of the wrap material over the ends of the pipe. 
         FIG. 5  is an end view showing the application of a mold over the joint in the pipeline. 
         FIG. 6  is a cross-sectional view showing the application of the glass spheres and epoxy material into the wrap material at the joint. 
         FIG. 7  is a diagrammatic illustration of the sonar reading of the location of the pipe joints. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is shown a method of laying pipe in accordance with the prior art. As can be seen, there is a vessel  12  that moves along the surface  14  of the body of water  16 . The pipeline  18  is laid such that the pipeline will reside against the floor  20  of the sea bed. The pipeline  18  extends in a generally S-shaped pattern from the vessel  12  downwardly so as to have a touchdown point  22  at the floor  20 . 
     In  FIG. 1 , it can be seen the pipeline  18  will be assembled in an assembly-line fashion onboard the ship. In this manner, the various sections of pipeline are joined in end-to-end relationship by welding. Various types of insulating material can be applied over the exterior surface of the pipeline so as to provide the necessary insulation so as to protect the contents of the pipeline from the near-freezing temperatures at the floor  20  of the body of water  16 . 
     In  FIG. 1 , it can be seen that there is an ROV  24  that is connected by a tether  26  to the vessel  12 . The ROV  24  (illustrated in  FIG. 1  in an exaggerated fashion) is configured so as to travel through the water  16  to a position adjacent the touchdown point  22 . The ROV  24  can include suitable cameras so that an observer aboard the vessel  12  will be able to visually determine the touchdown point  22  and the determine the distance of the touchdown point from the vessel  12 . As such, the operator of the vessel  12  will make the necessary calculation so as to avoid any buckling or overstressing of the pipeline  18 . 
     Unfortunately, in conventional operations, the ROV  24  will need a suitable tether  26  having a length that allows the ROV  24  to move to a position adjacent to the touchdown point  22 . In very deep water, this touchdown point may be as far as a mile from the vessel  12 . Under these circumstances, it may be necessary for another vessel to move into position and launch an ROV so that a touchdown point can be determined. This is a very complicated and expensive procedure. As such, a need has developed whereby the touchdown point  22  can be determined in an efficient and effective manner with an ROV, such as ROV  24 , from a location remote from a touchdown point. 
       FIG. 2  shows a prior art technique whereby a first pipe  30  is positioned so as to be welded to a second pipe  32 . The first pipe  30  has an insulating material  34  extending thereover. Similarly, the second pipe  32  has an insulating material  36  extending thereover. The pipe  30  has an end  38  adjacent to an end  40  of the second pipe  32 . It can be see that the insulating material  34  terminates a distance from the end  38  of pipe  30 . Similarly, the insulating material  36  terminates a distance from the end  40  of the pipe  32 . The insulating materials  34  and  36  are removed adjacent to the ends  38  and  40  so as to allow proper welding of the ends  38  and  40  to occur. As a result, the pipes  30  and  32  will be generally uninsulated in the space between the ends of the insulation  34  and  36  at the point of welding. In order to enhance the ability to insulate this space, various techniques have been employed in the past so as to cover this space (as described in the Background herein). 
       FIG. 3  illustrates a wrap  42  as used in the method of the present invention. The wrap material  42  has a width dimension and a length dimension. In particular, the wrap material  42  has a generally honeycomb configuration. The honeycomb material  42  should have a width suitable for extending between the ends of the insulation  34  and  36  of the pipes  30  and  32  and over the welding between the ends  38  and  40 . The wrap  42  can be formed of any suitable polymeric material. Suitable clips, or other fasteners, can be applied to the wrap material  42  so as to facilitate the ability to fix the wrap material over the joint of the pipes  30  and  32 . 
       FIG. 4  is a detailed view showing the placement of the wrap material  42  in the space between the ends  44  of the insulation  34  of pipe  30  and the end  46  of the insulating material  36  of pipe  32 . Prior to the placement of the wrap material  42  into the space between ends  44  and  46 , the respective ends  38  and  40  of the pipes  30  and  32  are fixed by weld  50 . Weld  50  will extend circumferentially around the respective ends  38  and  40  of the pipes  30  and  32  so as to effectively secure the ends of the pipes together. 
     The wrap material  42  is then wrapped around the exposed ends of the pipes  30  and  32  and over the weld  50 . It can be seen in  FIG. 4  that several layers of the wrap material  42  are created by this wrapping process. Ultimately, the wrap material  42  is wrapped until the outer periphery of the wrap material resides adjacent to the outer surface of the insulation  34  and  36  of pipes  30  and  32 . An RFID tag  52  can be affixed to the outer surface of the wrapped material  42  or, alternatively, can be placed within the wrap material  42 , as desired. 
       FIG. 5  illustrates that a mold  60  is positioned over the pipes  30  and  32  in the area of the welding  40 . The mold  60  has a clamshell construction. There is a first section  62  that is pivotally connected at  64  to a second section  66 . An inlet nozzle  68  passes through the wall of the mold  60  so as to communicate with the interior of the mold  60 . A hose  70  can then be used so as to deliver a coating material under pressure into the interior of the mold  60 . 
     In this step of the process, the sections  62  and  64  are initially pivoted outwardly away from the pipe  30 . The pipe  30  can then pass through the space  72  at the edges of the sections  62  and  66 . Mold  60  can then have the sections  62  and  64  closed and locked together. The coating material can then be injected through hose  70  and through inlet  68  into the interior thereof. As such, the coating material can be effectively formed under pressure and under high temperatures in the space between the ends  44  and  46  of the respective insulations  34  and  36  of pipes  30  and  32 . After injection, the sections  62  and  66  of the mold  60  can then be opened and moved to the next joint. 
       FIG. 6  shows the injection of the coating material into the space between the insulations  34  and  36  of pipes  30  and  32 . It can be seen that this coating material will fill the spaces of the honeycomb pattern of the wrap material  42 . The coating can also cover the RFID tag  52 , if desired. The coating material  54  will also extend over the weld  50  of the ends  38  and  40  of pipes  30  and  32 . 
     Importantly, within the concept of the present invention, the coating material  54  is preferably an epoxy material. Significantly, the present invention contemplates the use of air-filled glass spheres that are mixed with the epoxy material prior to injection. As such, the epoxy material and the glass spheres will be injected and formed into the space between the insulations  34  and  36  of pipes  30  and  32 . 
     The glass spheres  80  will fill a significant volume of the coating material  54 . Since the glass spheres are filled with air, they will have increased buoyancy. The air within these glass spheres is a very good acoustic reflector. Additionally, the glass spheres have excellent insulation qualities. As such, the pipes  30  and  32  are effectively insulated by this construction at the area of the welding  50 . 
     The RFID tag  52  can be incorporated in a variety of ways. The RFID tag  52  can be adhesively mounted to the coating material  54  on the exterior surface thereof. The RFID tag  52  can also be embedded into the coating material. The RFID tag  52  is embedded into the field joint and can contain information that is specific to the field joint. For example, the RFID tag can include information such as the date welded, the position of the RFID tag on the sea bed, the type and quality of the pipe, the type and quality of the weld, inspection information and vendor or supplier information. As such, the RFID tag  52  can provide an detailed record as to the assembly of the pipeline. 
       FIG. 7  shows that there is a vessel  100  that has an ROV  102  connected by a tether  104  to the vessel  100 . The pipeline  106  is illustrated as extending through the water  108  so as to have a touchdown point  110  at the floor  112  of the sea bed. The various joints  114  will occur along the pipeline  106  at regular intervals. 
     The ROV  102  is equipped with sonar equipment for sending and receiving sonar signals to and from the joints  114 . Importantly, in the present invention, since the glass spheres are air-filled, they are an extremely good sonar reflector. With high-powered sonar equipment, the ROV  102  is able to effectively determine the position of the each of the joints  114  relative to the sea floor  112 . Ultimately, the joint  116  at the touchdown point  110  can easily be determined, at a great distance, by the ROV  102 . As a result, the present invention is able to avoid the additional vessels and/or ROVs that would be required in order to determine the touchdown point  106 . The various locations of the joints  114  and  116  can be mathematically calculated so as to determine the shape and orientation of the pipeline  116  as it is laid upon the sea floor. As a result, by incorporating such air-filled glass spheres into the joints of the pipeline  106 , the present invention is able to rely upon sonar to determine location, rather than visual observation. There is no need for the ROV to be in such close proximity to each of the joints in order to determine location. As such, the ROV  102  can be more efficiently and effectively used so as to lay and position the pipeline  106 . 
     Since each of the joints  114  and  116  has an RFID tag thereon, the ROV  102  can be utilized so as to “fly by” each of these joints so as to receive information from each of the RFID tag. The RFID tag used communication through the use of the radio waves to exchange data between a reader on the ROV  102  and the tag for the purposes of identification and tracking. As such, through the use of these RFID tags, the ROV  102 , along with the associated processing equipment on the vessel  100 , is able to provide a complete record of the pipeline installation. 
     The process of the present invention greatly improves the time for completing the formation of the pipeline joints on the vessel  100 . The injection molding of the coating material onto the joint has a cure time of approximately two minutes. As such, it is possible to establish this coating material in a quick and convenient manner. Welding operations, such as those that are used to place pipe segments over the joints, are effectively avoided. Additionally, the coating material, along with the glass beads therein, is flexible and very buoyant. As such, the ability to lower the pipe into the water  108  is enhanced. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.