Patent Publication Number: US-2017356161-A1

Title: System and method of concurrently trenching, laying and burying underwater pipeline

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority of U.S. provisional application No. 62/347,226, filed Jun. 8, 2016, the contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to laying underwater pipelines and, more particularly, to a system and method of concurrently trenching, laying and burying underwater pipeline. 
     Underwater pipelines often must be buried in the sea floor in order to protect them from icebergs, anchors, nets, currents, thermal instability and the like. The present state of the art is to either dig or plow a trench before laying the pipe, lay the pipe and then back fill the trench. Alternatively, the pipe is laid first and then either using jets, mechanical cutting machines or plows, the sea floor is cut underneath the pipe and allowing the pipe to settle in the trench. Both methods are very expensive. 
     Dredging or plowing in sand or loose material which is frequently experienced on continental shelves often results in slope sluffing and very high dredge quantities. Mechanical dredging from the surface is uneconomical over 100 meters and requires dredging from the seabed which means very low production and high costs. Plowing from the seabed has resulted in many bad experiences with many shut downs, high maintenance and therefore high cost. 
     Burying the pipe after it is laid is also very expensive because of the low production equipment involved. The large jetting barges and jetting machines require several passes because they have to work around the pipe. Both methods involve two different operations. To date, there are no successful systems or methods for concurrently trenching, laying rigid steel pipe and burying it all in one operation for large scale pipe (8″ to 72″) from either J lay or S Lay pipe laying ships. 
     As can be seen, there is a need for a system/method for concurrently trenching and burying while laying the underwater pipe. The present invention utilizes the resources of the pipe laying ship to create a high pressure seawater jetting system that trenches the pipe without slowing the pipe laying speed of the ship. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a system for laying an underwater pipeline comprises: a plurality of pipe support rings connected together by tension cables, wherein the tension cables are securable to a ship by a winch and the plurality of pipe support rings form a pipe channel sized to guide the underwater pipeline; and a sea water pipe comprising a distal portion and a proximal end, wherein the sea water pipe is disposed underneath the plurality of pipe support rings, the proximal end is fluidly connected with a pump and the distal end comprises a plurality of nozzles. 
     In another aspect of the present invention, a method of laying underwater pipeline from a ship comprises: providing a plurality of pipe support rings connected together by tension cables, wherein the tension cables are secured to a ship by a winch and a sea water pipe comprising a distal portion and a proximal end, wherein the sea water pipe is disposed underneath the plurality of pipe support rings, the proximal end is fluidly connected with a pump and the distal end comprises a plurality of nozzles; running the underwater pipeline over a stinger disposed at a rear end of the ship and through the plurality of pipe support rings via a tensioner secured to the ship; and pumping pressurized fluid from the pump and through the sea water pipe, wherein the plurality of nozzles blast a sea floor forming a trench, wherein the underwater pipeline rests within the trench. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an embodiment of the present invention; 
         FIG. 2  is an elevation view of an embodiment of the present invention; 
         FIG. 3  is a schematic view of an embodiment of the present invention; 
         FIG. 4  is a section view of an embodiment of the present invention taken along line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a section view of an embodiment of the present invention taken along line  5 - 5  in  FIG. 3 ; 
         FIG. 6  is a section view of an embodiment of the present invention taken along line  6 - 6  in  FIG. 5 ; 
         FIG. 7  is an elevation view of an embodiment of the plug of the present invention; and 
         FIG. 8  is a section detail view of an embodiment of the plug of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     The present invention is directed to a system that allows a pipe laying ship (S Lay or J Lay) to trench and bury large pipe concurrently while the ship is laying the pipe. The trenching technique is a combination of eroding the soil and moving it and decreasing the in situ density of the soil so appropriate settlement will take place. A large pump which generates high pressure and a large volume of sea water is located on the ship or adjacent to it. The sea water discharge pipe from this pump is fixed to the stinger and then to the larger pipe being laid by the ship on the sea floor. When the two pipes get to the sea floor the sea water pipe splits into two pipes which run alongside the larger pipe. The two sea water pipes may include four movable nozzles located on rings spaced along the large pipe. Those nozzles decrease the density of soil below the large pipe and they also erode the soil along the side of the large pipe. The large pipe has a marginally negative force when it is empty and being laid. Sea water is maintained inside the large pipe in the laying area so that settlement of the pipe is easily and quickly achieved. This sea water may be maintained in the pipe by a remotely operated pipe plug located on the horizontal portion of the large pipe. This pipe plug will be tethered to the pipe lay ship with power and controls. The plug may move with the within the large pipe. A control system may operate on the ship which varies the location of the plug and the rotating speed of the pump impeller to synchronize the speed and depth of the trenching with the laying speed of the ship. 
     Referring to  FIGS. 1 through 8 , the present invention includes a system and method for laying an underwater pipeline  18 . The present invention includes a plurality of pipe support rings  22  connected together by tension cables  26 . The tension cables  26  are secured to a S or J laying ship  10  by a winch. The plurality of pipe support rings  22  form a pipe channel sized to guide the underwater pipeline  18 . The present invention further includes a sea water pipe  20  having a distal portion and a proximal end. The proximal end is fluidly connected with a pump  12  on board the ship  10 . The distal end includes a plurality of nozzles  36 ,  38 . The sea water pipe  20  is disposed underneath the plurality of pipe support rings  22 . The underwater pipeline  18  is fed through the plurality of pipe support rings  22  while the nozzles  36 ,  38  form a trench  74  on a sea bed  72 . Therefore, the ship  10  is able to maintain a constant speed while the underwater pipeline  18  is being laid and buried on the sea bed  72 . 
     The underwater pipeline  18  may include a steel sea water gas pipe  70  with a surrounding concrete ballast  68 . As mentioned above, the underwater pipeline  18  is delivered from a rear end of the ship  10 . A stinger  14  may be attached to the rear end of the ship  10  and guides the underwater pipeline  18  from the ship  10  through the pipe support rings  22  and into the water  60  along an overbend  16 . A tensioner  32  is secured to the ship  10 . The tensioner  32  grips and releases the underwater pipeline  18  at a controlled pace. 
     As mentioned above, the plurality of pipe support rings  22  support the underwater pipeline  18  as it is being laid on the sea bed  72 . In certain embodiments, a plurality of rollers  24 , such as TEFLON® roller bearings, may be secured to an inner surface of each of the plurality of pipe support rings  22 . The underwater pipeline  18  slideably engages with the rollers  24  as it runs through the pipe channel. Each of the plurality of pipe support rings  22  may further include an elevation sensor  62  capturing data and sending the data to a main computer system in control of the tensioner  32 . 
     In certain embodiments, the sea water pipe  20  diverts from a single pipe to a first pipe and a second pipe at the distal portion. The first pipe and the second pipe each include the plurality of nozzles  36 ,  38 . The first pipe and the second pipe are disposed along opposing sides of a bottom half of the plurality of pipe support rings  22 . For example, the first pipe may be at about 7 o&#39;clock to 8 o&#39;clock positions and the second pipe may be at about 4 o&#39;clock to 5 o&#39;clock positions. The plurality of nozzles  36 ,  38  may include a plurality of horizontal nozzles  36  disposed on an inner side of each of the first pipe and the second pipe and a plurality of vertical nozzles  38  disposed on an outer side of each of the first pipe and the second pipe. The horizontal nozzles  36  may blast the sea bed  72  forming a trench  74  and the vertical nozzles  38  may blast the uprooted sediment away from the underwater pipeline  18 , thereby allowing the underwater pipeline  18  to embed within the formed trench  74 . 
     In certain embodiments, sea water  64  may be disposed within a portion of the underwater pipeline  18  to provide additional weight to the pipeline  18  as it sinks into the trench  74 . The pipe plug  44  may also be used as a block for the intermittent pressure testing of the completed gas pipeline  18 . In such embodiments, the present invention may include a pipe plug  44  disposed within the underwater pipeline  18  to contain the sea water  64  within the proper portion of the underwater pipeline  18 . The pipe plug  44  is mechanically operable to move along the inside of the underwater pipeline  18  as the pipeline  18  is being laid to continuously shift the weight to the portion that is being laid within the trench  74 . The pipe plug  44  includes a front surface  46  and a rear surface  46 . Disposed in between the surfaces  46  is an upper portion and a lower portion with a shaft  48  in between the upper and lower portions. The upper portion may include a pair of vertical shoe flanges  54  each having a horizontal collar  50  at a proximal end engaging the shaft  48  and a horizontal foot  52  at a distal end engaging the inside of the pipeline  18  wall. The lower portion may also include a pair of vertical shoe flanges  54  each having a horizontal collar  50  at a proximal end engaging the shaft  48  and a horizontal foot  52  at a distal end engaging the inside of the pipeline  18  wall. Each of the shoe flanges  54  includes a vertical jack  56 . The pair of shoe flanges  54  of the upper portion are connected by a horizontal jack  58  and the pair of shoe flanges  54  of the lower portion are connected by a horizontal jack  58 . When moving along the inside of the pipeline  18 , the vertical jacks  56  may retract a rear pair of shoes  52  from engaging the inside of the pipeline  18  and press the rear collars  50  against the shaft  48 . The vertical jacks  56  may press the front pair of shoes  52  against the inside of the pipeline  18  and retract the front collars  50  away from the shaft  48 . The horizontal jack  58  then pulls the front pair of shoe flanges  54  towards the rear pair of shoe flanges  54 . The front collars  50  then grip the shaft  48  via the vertical jacks  56  and the rear collars  50  retract from the shaft via the vertical jacks  56 . The horizontal jacks  58  then push the shaft  48  forward with the front pair of shoe flanges  54 , thereby moving the plug  44  forward. 
     During operation, the trenching zone  40  should be as long as possible so that the jetting system has time to do its job. This can be achieved by making sure the sea bend  28  has the largest radius possible. The sea bend  28  radius is determined by the amount of tension the tensioners  32  provide to the pipeline  18 . The trench C  40  is longer when the tension is higher. The over bend  16  is formed by the stinger  14  and the stinger  14  protects the pipeline  18  from crushing due to an over bend with a radius that is too small. However, when the system is in physical equilibrium the over bend  16  equals the sea bend  28 . 
     The method and system of the present invention enables S Lay pipe laying ships to lay large pipes under water and concurrently trench and bury them during the laying procedure. The S Lay ships can lay large pipes at the rate of 2.5 miles per day or 10 feet per minute. The concurrent burying system matches that laying speed. The present invention is primarily, but not exclusively intended for laying large (12″ to 72″) gas, oil, or fresh water pipelines on sea, ocean bay, lake or river bottoms by any of the many S Lay or J Lay vessels anywhere in the world. The system takes cost advantage of the ship deck space to mount very large powerful pump/motor units that will develop high volume high pressure sea water for jetting. The pumps have variable speed motors and controls to vary the volume and pressure when signaled to do so by the elevation sensing devices on all of the aluminum rings located in the trenching zone. The discharge of the pumps are through a large flexible stainless steel pipe which attaches to the bottom of the stinger and proceeds down the stinger to its end. The pipe is fixed to the first aluminum ring which surrounds the pipe. The rings support the sea water pipes from this point through to the end of the trenching zone  16 . The spacing of the rings is closer in the trenching zone because of the turbulence of the jetting action. 
     The gas pipe provides the structural support for the sea water pipe with its unused (at this time) structural strength. Just before reaching the sea bottom the sea water pipe splits into two sea water pipes and are mounted on the bottom of the gas pipe. The pipe is supported on the ring by TEFLON® roller bearings. The aluminum rings are at a fixed distance from the S Lay ship by virtue of the galvanized steel cables at the ring quarters. The four cables are fixed to the ship on winches and there is a friction stop at each ring. There may be spare rings stored around the pipe near the stinger to allow for flexibility in depth during laying major changes in depth may require shutdown and ring refitting. In the trenching zone, water jet nozzles may be included on rings spaced at every two feet along the length of the two sea water pipes. The horizontal flood nozzles disturb the soil particles, put them in suspension, and lower the comprehensive strength of the soil so settlement can occur. The vertical transportation nozzles disturb the soil, reduce its strength and then move the soil upwards. Simultaneously sea water is injected into the gas pipeline and this pipe contains the mobile plug. The purpose of the plug is to restrain the ballast sea water in the pipe. The plug with its membrane or sidewall seals the water within the pipeline. The plug moves in both directions in the pipe at the rate of about 10 feet per minute. The A unit within the plug closes its shoes against the pipe with its vertical jacks. The B unit releases its vertical jacks and move away from the A unit with its horizontal jacks. The B unit then closes its shoes against the pipeline with its vertical jacks. The A unit then releases its vertical jacks and moves toward B with its horizontal jacks. The sea water that is loaded in the pipeline is used to enhance the settlement process. The empty pipe is heavier than the displaced water and when the sea water is in the pipe the latter is much heavier than the displaced water, thereby accelerating the settlement. The plug and the retained sea water move as required to regulate the settlement process. If the settlement is occurring too quickly the plug and sea water move in the gas pipe away from the ship to lessen its effect on settlement. The plug may be controlled automatically from controls on the ship. 
     The present invention is applicable to a variety of soil conditions. The S Lay ship is outfitted for the concurrent trenching laying and burying method, preferably with such as with a large (as much as 10000 HP capacity) pump motor capacity on the deck of the ship. This redundancy is used so the jetting can continue when the pipe laying is shut down. The pump/motor may have variable speed controls so the pressure and volume to the jets can be varied at the central control room. Additional jets may be required for tougher soil and the jets may be movable and remotely operated. The rings in the trenching area may be galvanized steel to decrease the profile and to give added strength when pulling through the trenching zone. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.