Abstract:
An underwater trenching system is mountable on a side of a barge to be propelled by the barge along a waterway, the bed of which contains a trench with a laid pipeline. To remove the excess sediment from the trench the trenching unit delivers pressurized water and air to the trench. A sparge assembly with jet nozzles directs jets of water, breaking up the formation that has built up around the pipeline. The airlift assembly creates a turbulent flow to lift the disturbed sediment and remove it from the created trench.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of my co-pending application Ser. No. 12/150,826 filed on Apr. 30, 2008, entitled “Underwater Trenching Device” the full disclosures of which are incorporated by reference herein and priority of which is hereby claimed. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an underwater trenching system, and more particularly, to a trench making equipment that enlarges an underwater trench for burying a pipeline. 
         [0003]    Many oil and gas production sites require installation of miles of pipelines for delivery of the produced material to a refinery or other destination. Often times, the pipelines are laid underwater, especially in shallow coastal waters. The pipes are usually buried at the bottom of a waterway, such as a river, marsh, or sea. In some locations, the pipes are simply laid along the bottom of a waterway and left exposed, to be buried by the action of the currents. In other uses, a trenching tool, such as a water jet, a cutter head, or a scoop, or clam shell digger digs a trench around the pipe, which then settles into the trench. 
         [0004]    The bottom sediment eventually settles around the pipe although a large portion of it is carried to other areas of the waterway. The time when the sediment remain in suspension varies although it is known to have a potential for creating serious environmental damage to plants, animals, marine life, and the water. Over time, the sediment has a tendency to shift the pipeline, which causes it to rise from the bottom or from the trench. Current governmental regulations prohibit disturbing the waterway bottom for the second time, such that digging out the original trench for adjusting position of the pipeline is not a viable option. As a consequence, the only viable alternative is to excavate the side of the trench near the bottom and cause the pipeline to drop into the new indentation in the soil. 
         [0005]    In short, all currently known equipment and methods for underwater trenching create large clouds of silt and debris that remain in suspension for a long time and seriously disrupt the ecology of the waterway. Reforming the trench by additional excavation of the bottom is not allowed. 
         [0006]    There exists therefore a need for an underwater trenching system that avoids bottom trenching, while achieving the goal of lowering the pipeline into a trench without excavating the bottom of the trench. 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore an object of the present invention to provide an underwater trenching system that is capable of evacuating sediment from a side of the trench without substantially disturbing the soil. 
         [0008]    It is another object of the invention to provide an underwater trenching system that allows the pipe to settle back into the trench. 
         [0009]    It is a further object of the present invention to reduce the time and cost of trenching by omitting the necessity to employ underwater divers. 
         [0010]    These and other objects of the invention are achieved through a provision of an underwater trenching apparatus for repairing a trench formed in a bed of a waterway, within which a pipeline is located. The trenching apparatus comprises an elongated boom assembly having a proximate end configured for hingedly securing to a side of a floating vessel, such as a barge. A trenching unit is secured to a distal end of the boom assembly and moves between an above-water position and an underwater position with the help of a lifting means positioned on the deck of the barge, such for instance a lifting crane, a cable of which is detachably secured to the boom assembly. 
         [0011]    The trenching unit comprises a pair of spaced-apart opposing sparge assemblies that deliver water and air under pressure to the trench where the pipeline is located. The water and air disturb the underwater formation and move the disturbed sediment or loose formation away from the pipeline in the trench. An elongated conduit admits the sediment through a bottom inlet opening and discharges the sediment through an upper outlet opening. An airlift unit mounted inside the tubular member is connected to an above-water air supply. The airlift unit creates turbulence inside the tubular member, causing sucking of the sediment into the tubular member and lifting the sediment and water toward the discharge opening. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Reference will now be made to the drawings, wherein like parts are designated by like numerals, and wherein 
           [0013]      FIG. 1  is a schematic view illustrating the underwater trenching apparatus of the instant invention in operation. 
           [0014]      FIG. 2  illustrates the underwater trenching apparatus of the instant invention in transit or storage position. 
           [0015]      FIG. 3  is a detail view showing the trenching unit connected to a single manifold. 
           [0016]      FIG. 4  is a detail view showing the trenching unit with its pair of sparge assemblies. 
           [0017]      FIG. 5  is detail, partially cut-away view showing one of the sparge assemblies and the airlift insert. 
           [0018]      FIG. 6  is a detail view showing the airlift assembly mounted in the inlet portion of the tubular conduit. 
           [0019]      FIG. 7  is detail view of the bottom of the sparge assembly illustrating the direction of intake flow entering the inlet portion of the tubular conduit. 
           [0020]      FIG. 8  is a detail view of the nozzle of the sparge conduit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Turning now to the drawings in more detail, the system of the present invention is designated by numeral  10 . The system  10  comprises an elongated boom assembly  12 , a proximate end  14  of which is secured to a barge  16  or other suitable vessel. Conventional trenching equipment is usually centered on the barge. The system  10 , in contrast, is positioned on a side of the barge, with the boom assembly  12  secured to the starboard  20  of the barge  16 . Of course, the boom assembly  12  may be also secured to the port of the barge hull, depending on the location of the pipeline in the waterway. In  FIG. 1 , the trenching system  10  is mounted on the barge  16  that moves in the direction of arrow  17 . 
         [0022]    The proximate end  14  boom assembly  12  is hinged to a hinge plate  18 , which can be formed from a length of an I-beam, attached to the starboard  20 . The hinge plate  18  extends substantially horizontally, transversely to the starboard  20  and suspends the boom assembly  12  off the side of the barge  16 . The boom assembly  12  can move up and down in relation to the hinge plate  18 . A support bracket  22  supports the hinge plate  18  from below and absorbs some of the vertical and horizontal forces applied to the hinge plate  18  when the boom assembly  12  moves between a transport position shown in  FIG. 2  to an operating position shown in  FIG. 1 . A second reinforcing bracket  24  may be secured to the hinge plate  18  to further reinforce the position of the hinge plate  18  on the side of the barge  16 . 
         [0023]    A distal end  26  of the boom assembly  12  is selectively secured to a lifting means  30 , which can be a deck crane, positioned on the deck  32  of the barge  16 . A lifting cable  34  detachably secures the boom assembly  12  to the lifting crane  30  to raise and lower the boom assembly  12 . The distal end  26  of the boom assembly  12  carries a trenching unit  40  that is lowered below the waterline  42  to reach the mud line  46 . 
         [0024]    The boom assembly  12  comprises a pair of elongated beams  48 ,  50  which are spaced from each other and are retained in a substantially parallel relationship by a plurality of transverse braces  54  and diagonal braces  56 . A mesh walkway  60  is secured between the beams  48 ,  50 , allowing operators to access the trenching unit  40  and to measure the depth, at which the pipeline  62  extends below the mud line  46 . The depth measuring can be conducted using conventional devices that are well known in the industry and are not part of the instant invention. 
         [0025]    Mounted on the deck  32  of the barge  16  is water and air supply units that deliver water under pressure and pressurized air to the trenching unit  40 . As can be seen in  FIG. 3 , an air compressor  64  is positioned on the deck  32  and is connected to the trenching unit  40  by air supply conduits  68 ,  69 . Water to the trenching unit  40  is supplied by a pair of jet pumps  70 ,  72  that deliver water to the trenching unit  40  via water conduits  74 ,  76 , respectively. The jet pumps  70 ,  72  can produce 300 p.s.i. of pressure to the trenching unit  40 . The jet pumps are self-contained with fuel tanks, powered generator and an air compressor. 
         [0026]    The trenching unit  40  comprises a pair of sparge units  80 ,  82  that are connected to a single manifold  84  that supplies water under pressure through manifold connectors  86 ,  88 ,  90 , and  92 . Only two manifold connectors are active at a particular time during operation of the trenching unit  40 . Depending on the diameter of the pipeline  46  and the width of the desired trench, the trenching unit can be connected, through the manifold connectors to either two adjacent manifold connectors or to a pair of further spaced-apart manifold connectors. In the example illustrated in  FIG. 3 , manifold connector  88  and  92  are used to supplying the pressurized water to the sparge units  80 ,  82 . 
         [0027]    The sparge units  80  and  82  are mirror images of each other. Each of the sparge units comprises a tubular conduit  94  that has a first inlet portion  96 ,  98 , respectively, and a second discharge portion  102 ,  104 , respectively. The discharge portions  102 ,  104  are oriented at an angle to longitudinal axes of the first inlet portions  96 ,  98 . The outlet openings of the second discharge portions  102 ,  104  are oriented in opposite directions so that effluent is discharged away from the pipeline  46 . 
         [0028]    The air supply conduit  68  is secured to the side of the first inlet portion  98  for delivering pressurized air to the interior of the first inlet portion  96 . Mounted inside the first inlet portion is an airlift insert  106  that has exterior dimensions slightly smaller than the interior of the first inlet portion conduit  98 . The insert  106  is secured inside the conduit defined by the first inlet portion and has a flared inlet opening  108 . 
         [0029]    A plurality of openings  110  is formed in the walls of the insert  106  allowing air delivered through the air conduit  68  to enter the interior of the insert  106  and create turbulence inside the insert  106 . The turbulent flow carries the sediment, as will be explained in more detail hereinafter, toward the second discharge portion  102  and ultimately—to the discharge opening  112  of the second discharge portion  102 . As shown in  FIG. 5 , the air supply conduit  68  is connected to the interior of the first inlet portion  98  at a level where the openings  110  in the insert  106  are located. 
         [0030]    The openings  110  are preferably formed at an angle to the longitudinal axis of the insert  106 , as shown in  FIG. 5 . The inclined openings  110 , which can be inclined at about 45 degrees in relation to the longitudinal axis, force the air upward into the first inlet portion  98  and create a turbulent flow therein. The flared bottom of the insert  106  and a reduced size of the remainder of the insert body  106  also facilitate the creation of a sucking force by creating a venturi effect and drop in pressure as the flow moves through the tubular portions  96 ,  102  ( 98 ,  104 ). 
         [0031]    Each sparge unit  80 ,  82  is provided with a sparge conduit  120 ,  122 , respectively. The sparge conduits  120 ,  122  are connected to the manifold  84  through manifold connector flanges  124 ,  126 . Each sparge conduit  120 ,  122  is provided with a plurality of discharge nozzles  128 ,  130  that jet pressurized water/air mixture into the waterway bed  140  in the area adjacent the pipeline  46 . The nozzles  128 ,  130  are detachably mounted in the corresponding openings formed in the wall of the sparge conduits  120 ,  122 . 
         [0032]    Each nozzle has exterior threads  131  that allow the nozzle to be threaded into the opening in the wall of the sparge conduit. An inlet opening  132  of the nozzle  128  (or  130 ) has a generally conical configuration, as can be seen in more detail in  FIG. 8 . An outlet opening  134  has a diameter smaller than the diameter of the inlet opening  132 , such that the velocity of the fluid exiting the nozzle  128  ( 130 ) is increased causing a jetting effect. The water and air exiting the outlet opening  134  blast away sediment from the bottom of the waterway enlarging the trench  142  surrounding the pipeline  46 . 
         [0033]    The disturbed sediment is sucked into the bottom opening  146  of the first inlet portion  98  and moves through the insert  106  under the force of the flow created by the incoming air flow. Some of the water moving through the sparge conduit  120  is diverted to the first inlet portion  98  below the airlift insert  106  by a pair of water hoses, or pipes  148 ,  150  to facilitate movement of the sediment through the trenching unit  40 . The sediment can be discharged to the waterway bed  140  above the mud line  46  or, if the trench is shallow—even to the banks of the waterway. 
         [0034]    To ensure alignment of the trenching unit  40  with the pipeline  46 , the trenching unit  40  is provided with a guiding means, which comprises a plurality of rotating guiding rollers. A transverse roller  152  is secured between the sparge conduits  120 ,  122  at a position downstream from the inlets openings of the sparge conduits  12 ,  122 . In the embodiment shown in  FIG. 4 , the transverse roller  152  is positioned at an approximate level above an anticipated depth of the pipeline  46 . 
         [0035]    A pair of vertical guiding rollers  154 ,  156  is positioned in a general vertical alignment with the first inlet portion  96 , and a similar pair of vertical guiding rollers  158 ,  160  is positioned in a general vertical alignment with the first inlet portion  98 . The rollers  154 ,  156 ,  158 , and  160  prevent the trenching unit  40  from significantly deviating from the dimensions created by the sides of the trench, where the pipeline  46  is located. The distance between the rollers  154 ,  156  and  158 ,  160  is selected to conserve energy and enlarge the trench  142  only as necessary for the pipeline  46 . 
         [0036]    The barge  16  can be propelled by a tug boat  170  shown in phantom line in  FIG. 1 , or by other suitable means that allow the trenching unit  40  to move along the pipeline and enlarge or form a trench. If desired, the roller guides  154 ,  156 ,  158  and  160  can be distanced to straddle the pipe  46  and keep the trenching unit  40  aligned with the pipeline  46 . The rollers are also important in protecting the conduits from contact with rocky trench walls. 
         [0037]    If desired the nozzles  128 ,  130  can be strategically spaced along the length of the inlet portions such that the majority of the nozzles are located closer to the bottom of the trench, while fewer nozzles are located in an area that would be approximately above the pipeline  46 . The depth of the pipeline  46  embedment can be measured prior to lowering the trenching unit  40  into water. 
         [0038]    The barge  16  is propelled along the waterway at a desired speed, allowing the sparge units  80 ,  82  to disturb underwater sediment and for the airlift force to lift the disturbed sediment away from the trench. The actual speed of travel depends on the condition of the waterway bed. Naturally, slower speed will be necessary where there exists clay bottom than where the bed is sandy. It is envisioned that a land vehicle may be employed for transporting the trenching apparatus of the present invention. Depending on several factors, such as the width of the waterway, the location of the pipeline and the depth, at which the pipeline is buried the land vehicle with the boom assembly mounted thereon may be employed. 
         [0039]    Many changes and modifications can be made in the design of the present invention without departing from the spirit thereof. I therefore pray that my rights to the present invention be limited only by the scope of the appended claims.