Patent Publication Number: US-6705029-B2

Title: Trenching machine

Description:
This invention relates to an apparatus for forming a trench along the bed of a body of water and more particularly to a machine for forming a trench for burying a pipeline or cable lying along a seabed. 
     BACKGROUND OF THE INVENTION 
     In the energy, telecommunications and other industries, it has been a common practice to lay pipelines, cables and other types of conduits along seabeds for conveying fluids such as oil and gas and communications data from offshore rigs to a mainland and between mainlands. Typically, such conduits are first laid along the seabed and then are buried so as to avoid any damage thereto resulting in a loss of fluid conveyed or disruption of data transmitted therethrough. 
     In the prior art, there has been developed a number of machines for forming a trench for burying such conduits. Typically, such machines have consisted of a frame adapted to straddle a conduit lying along a seabed, means mounted on a machine frame and engageable with the conduit for propelling the machine along the conduit, means mounted on the machine for ejecting high velocity streams of water to dislodge the seabed along the conduit and thus form a trench into which the conduit is caused to fall as the machine is propelled along the conduit, and often means also mounted on the machine for educting spoils produced by the high velocity streams injected by the machine and thus facilitating the formation of the trench. Examples of such machines are illustrated and described in U.S. Pat. Nos. 3,751,927 to Joseph C. Perot, Jr., 4,087,981 to Robert M. Norman, 4,112,695 to Mike M. Chang et al and 4,117,689 to Charles F. Martin. 
     The conventional means for propelling such prior art trenching machines along a conduit to be buried has consisted of a set of rollers, one or more of which are adapted to be driven, usually by a hydraulic motor mounted on the machine frame. Such means of propulsion, however, has been found not to be entirely effective in providing uninterrupted and consistent travel of the trenching machine along the conduit. The use of rollers as a propulsion means has been found to be ineffective in providing sufficient traction with the conduit for propelling the machine along the conduit, particularly when the conduit is formed of a material with a smooth surface such as a plastic coating, causing damage to the conduit when the traction force is excessive and fractures the conduit often consisting of a concrete pipeline, and in negotiating projections on the conduits such as anodes commonly provided on underwater pipelines. 
     In a typical operation for burying a conduit lying along a seabed, there is provided a service barge, a submersible trenching machine adapted to be launched from the service barge and attached to the conduit and an umbilical line interconnecting pumps and compressors provided on the barge and the trenching machine. Operators of such barges and machines commonly are compensated by the linear footage of conduit buried. Interruptions of the trenching operations of such machines are very costly to such operators not only because of the loss of revenue in operation of the trenching machine but also because of the cost of operating the service barge and the equipment on board. 
     Accordingly, the principal object of the present invention is to provide an improved trenching machine of the type described which is operable to readily and positively grip a conduit lying along a seabed, propel the machine along such conduit at a steady and consistent rate of travel and easily negotiate any obstruction on the conduit without interrupting the travel of the machine. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved apparatus for forming a trench in the bed of a body of water for burying a conduit lying therealong which generally consists of a main frame, at least one buoyancy tank mounted on the main frame, a pair of endless track assemblies, each engageable with a side of the conduit being buried, in gripping relation, for propelling the frame along the conduit, and means mounted on the main frame and communicable with a source of fluid under pressure, for ejecting high velocity streams of fluid to dislodge portions of the bed lying below the conduit when the track assemblies grip and propel the main frame of the machine along the conduit to form a trench and allow the conduit to fall therein. Preferably, the fluid injecting means consists of a pair of jet legs mounted on the front end of the machine frame, provided with a plurality of forwardly and laterally directed nozzles for ejecting water under pressure for dislodging material from the seabed along the path of the conduit, and there further is provided a pair of eductors mounted at the rear end of the machine frame, having inlets for drawing spoils produced by the jet legs and ejecting such spoils laterally as the machine moves forwardly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a service barge afloat on a body of water, a pipeline lying along the bed of such body of water, a trenching machine embodying the present invention operatively connected to such pipeline and a service line extending from the barge to the trenching machine; 
     FIG. 2 is an enlarged, perspective view of the trenching machine shown in FIG. 1; 
     FIG. 3 is a side elevational view of the machine shown in FIG. 2; 
     FIG. 4A is a cross-sectional view taken along line  4 — 4  in FIG. 3, illustrating the traction assemblies of the machine gripping a pipeline as when in an operational mode; 
     FIG. 4B is a view similar to the view shown in FIG. 4A, illustrating the traction assemblies disengaged from the pipeline in a nonoperational mode; 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  in FIG. 3; 
     FIG. 6 is an enlarged, perspective view of a traction assembly used in the machine shown in FIGS. 2 and 3; 
     FIG. 7 is an enlarged, top plan view of the traction assembly shown in FIG. 6, having an upper plate portion thereof removed; 
     FIG. 8 is an enlarged, perspective view of a tensioning assembly used in the traction assembly shown in FIGS. 6 and 7; and 
     FIG. 9 is a schematic of the hydraulic system utilized with the machine shown in FIGS. 2 through 7 for operating the traction assemblies. 
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
     Referring to FIG. 1 of the drawings, there is shown a body of water  10 , a pipeline  11  lying along the bed  12  of the body of water, a service barge  13  stationed on the body of water above or adjacent the pipeline, a trenching machine  14  embodying the present invention, and a service line  15  commonly referred to as an umbilical cord interconnecting the service barge and the trenching machine for conveying water, air and hydraulic fluid under pressure from pumps and compressors and on the barge to the trenching machine. Generally, the machine includes a main support frame  16  adapted to straddle pipeline  11 , a buoyancy assembly  17  mounted on the main support frame, a propulsion unit  18  mounted on the main support frame and operatively engageable with pipeline  11 , an excavating assembly  19  mounted on the front end of the main support frame and an eductor assembly  20  mounted on the rear end of the main support frame. 
     Support frame  16  consists of a plurality of steel members welded together, having sufficient strength to support the various components of the machine yet small in cross sectional configuration to facilitate its travel through the water. It includes a substantially rectangularly configured upper section  16   a  having a set of corner members  16   b  through  16   e  extending below section  16   a  to provide a longitudinal opening in the support frame for receiving pipeline  11  therethrough. Disposed at the front and rear areas of frame section  16   a  is a set of transverse members  21  and  22  provided with depending brackets supporting a pair of longitudinally spaced rollers  21   a  and  22   a . Such rollers are adapted to seat on pipeline  11  when the machine is mounted thereon in straddling relation as shown in FIGS. 2 and 3, to align the propulsion assembly vertically with the pipeline. The diameter and configuration of each of such rollers is selected to accommodate pipelines of different diameters. They further are formed of a material sufficiently compressible and/or are displaceable to allow them to negotiate past any protrusion on the pipeline so as not to interfere with the travel of the machine along the pipeline. Similarly mounted on the depending leg portions of frame section  16   a  is a first set of brackets supporting a first set of rollers  23 ,  23 , and a second set of brackets supporting a set of transversely spaced rollers  24 ,  24 . The sets of rollers  23 ,  24  are adapted to engage the side portions of a pipeline segment extending through the longitudinal opening of the support frame to align the propulsion assembly transversely relative to the pipeline. Such rollers of different diameters are used to accommodate pipelines of different diameters. They also are formed of a material or mounted to permit them to pass over any protrusions on the pipeline as the machine is propelled along the pipeline. The function of longitudinally spaced rollers  21   a  and  22   a  and transversely spaced rollers  23  and  24  is merely to align the propulsion unit on the pipeline vertically and transversely when the machine is mounted on the pipeline as shown in FIGS. 2 and 3. 
     Frame section  16   a  further is provided with a pair of longitudinally disposed, transversely spaced rod members  25  and  26  disposed above the lower end thereof, which support propulsion assembly  18 , and a platform portion  27  on the upper end thereof which supports buoyancy assembly  17 . 
     Buoyancy assembly  17  consists of a pair longitudinally disposed, transversely spaced tanks  28  and  29  rigidly mounted on platform portion  27  of the support frame. Such tanks are symmetrically positioned relative to a centerline of the support frame. Each of the tanks is substantially cylindrical in configuration having conically configured front-end portions to facilitate their travel through the water. Mounted on and depending from platform portion  27  is an air manifold  30  adapted to service the buoyancy tanks and the eductor assembly. The manifold is connected through an air hose forming part of the umbilical cord, to a compressor provided on the service barge. In the conventional manner, compressed air may be supplied to or vented from the buoyancy tanks to control the buoyancy effect of the tanks. 
     Propulsion assembly  18  is supported on main frame  16  and is adapted to engage pipeline  17  when the machine is mounted on the pipeline in straddling relation as shown in FIGS. 2 and 3 for propelling the machine along the pipeline. The assembly consists of a pair of substantially identical track assemblies  18   a  and  18   b  which are pivotal about the longitudinal axes of members  25  and  26 , into and out of engagement with pipeline  11 , when the machine is mounted on the pipeline as shown in FIGS. 2 and 3. As best shown in FIGS. 3,  4 A and  4 B, track assembly  18   a  includes a set of bushings  31  and  32  mounted on rod member  25 , a pair of depending arm members  33  and  34  rigidly connected to bushings  31  and  32 , respectively, and a track housing  35  mounted on the lower ends of such arm members. Similarly, track assembly  18   b  includes a set of bushings  36  and  37 , a pair of depending arms  38  and  39  rigidly connected at their upper ends on bushings  36  and  37  and a track housing  40  pivotally mounted on the lower ends of depending arm members  38  and  39 . Track housings  35  and  40  are substantially identical in construction and operation. The track assemblies are adapted to be displaced relative to each other about the axes of rod members  25  and  26 , into and out of engagement with a segment of pipeline  11 , when the machine is mounted on the pipeline, by means of a first fluid actuated cylinder assembly  41  operatively interconnecting arm members  34  and  39  and a similar fluid actuated cylinder assembly  42  operatively interconnecting arm members  33  and  38 . 
     As best seen in FIGS. 6,  7  and  8 , track housing  40  includes upper and lower plate members  43  and  44  and a pair of end plate members  45  and  46 . Mounted along one side of the upper and lower plate members are sets of bearings  47  in which there are journaled a plurality of shafts  48 . Each of such shafts is provided with a pair of axially spaced sprockets  47   a  and  47   b . On the inner side of track housing  40 , adjacent end wall  45 , is a tensioning assembly  49 , and also mounted on the outer side of track housing  40 , adjacent end wall  46 , is a drive assembly  50 . 
     Referring to FIG. 8, tensioning assembly  49  includes a stationary base member  51  rigidly secured at its upper and lower ends to upper and lower plate members  43  and  44 , a pair of vertically spaced rod members  52  and  53  rigidly secured at one set of ends thereof to base member  51 , a carrier member  54  having openings therein receiving rod members  52  and  53  therethrough to permit carrier member  54  to displace on rod members  52  and  53  relative to base member  51 , a first set of springs  55  and  56  disposed on rod members  52  and  53 , respectively, between members  51  and  54 , and a second set of springs  57  and  58  also disposed between members  51  and  54  for biasing carrier member  54  away from base member  51 . Mounted on the ends of carrier member  54  is a set of bearing blocks  59  and  60  in which there is journaled an idler shaft  61 . Formed on the intermediate portion of shaft  61  is a pair of axially spaced sprocket portions  62  and  63  which lie in the same planes as sprockets  47   a  and  47   b  of idler shafts  47 . 
     Drive assembly  50  consists of a hydraulic fluid motor  64  mounted on upper plate member  43 , having a drive shaft provided with a set of sprocket portions disposed in the same planes as sprocket portions  62  and  63  of assembly  49  and sprocket portions  47   a  and  47   b  of idler shafts  47 . 
     Trained about the sets of sprockets of the drive and idler shafts is a set of endless chains  65 ,  65 . Such chains are provided on the outer sides thereof with a plurality of pads  66 . As best shown in FIGS. 6 and 7, idler shafts  47  are disposed sufficiently close to the inner sides of plate members  43  and  44  so that the pads along the inner flight of the endless track will project inwardly, beyond the inner edges of plate members  43  and  44  to engage a side portion of a pipeline segment without interference from plate members  43  and  44 . Pads  66  are formed of a compressible material, preferably Neoprene, and are adapted to grip a segment of the pipeline when urged against it to provide a traction force between the track assembly and the pipeline for propelling the machine along the pipeline as motor  50  is operated to drive the endless track. Slack in the endless track is compensated for by tensioning assembly  49 . 
     The displacement of the track assemblies into and out of engagement with a segment of the pipeline disposed within the support frame, and the operation of fluid motor  50  is controlled by a hydraulic fluid system  70  shown in FIG.  9 . The system includes a hydraulic fluid reservoir  71 , a hydraulic fluid pump  72  and a pair of selector valves  73  and  74  mounted on the surface barge, cylinder assemblies  33  and  34  and hydraulic fluid motors  50  and  50   a  mounted on track assemblies  18   a  and  18   b  and interconnecting hoses forming part of the umbilical cord. A pair of supply and return lines  75  and  76  including selector valve  74  and suitable branch lines interconnect the pump and reservoir and drive motors  50  and  50   a . Supply and return lines  77  and  78  including selector valve  73  and suitable branch lines interconnect the pump and reservoir and fluid cylinders  33  and  34 . Provided in branch line  78   a  communicating with the rod end of fluid cylinder  33  is an accumulator  79  and a relief valve  80  responsive to a predetermined pressure in branch line  77   a  communicating with the base end of cylinder assembly  33 . Similarly, branch line  78   b  communicating with the rod end of cylinder assembly  34  includes an accumulator  81  and a relief valve  82  responsive to a predetermined pressure in a branch line  77   b  communicating with the base end of cylinder assembly  34 . 
     In the use of control system  70  to operate the machine, it will be appreciated that selector valve  73  may be operated to extend and retract cylinder assemblies  33  and  34  to correspondingly cause track assemblies  18   a  and  18   b  to displace into and out of engagement with a pipeline segment extending through the machine, and selector valve  74  may be operated when the track assemblies engage the pipeline to cause the machine to be propelled in either forward or rearward directions along the pipeline. Whenever the track assemblies encounter an obstacle on the pipeline such as an anode, accumulators  79  and  81  function to allow the cylinder assemblies to extend and thus allow the track assemblies to ride over the obstacle. The system allows the machine to firmly grip and provide suitable traction on the pipeline, propel the machine along the pipeline in either the forward or rearward direction and overcome any obstacle on the pipeline while continuing to grip the pipeline and be propelled therealong. 
     Excavating assembly  19  consists of a pair of L-shaped tubular members  90  and  91  or what are commonly referred to as jet legs, mounted on the front end of the support frame and spaced transversely. Each of such members is provided with an elongated, vertical section having a segment along a rear side thereof received in a channel provided on a corner member of the main frame which permits the entire member to be displaced relative to the main frame, a rearwardly extending section formed substantially at a right angle to the elongated section and a section interconnecting the elongated and lower sections. Pins or bolts may be inserted in registered openings in such channel member and protruding segment to secure the leg at a desired position relative to the main frame. Each member is tubular and is supplied with water under pressure through a hose connected to a pump on the service barge, which forms part of the umbilical cord. The forwardly facing portion of the elongated section of each member  90  and  91  is provided with a plurality of nozzles communicating with the interior of the section for directing high velocity streams of water forwardly and laterally for dislodging seabed material along and below the pipeline to form a trench into which the pipeline is caused to fall and be buried as the machine is propelled along the pipeline. Preferably, such nozzles are spaced along the elongated section of each member  90  and  91 . Some of such nozzles are positioned to direct jets of water directly ahead in a vertical plane and other jets are positioned to direct jets of water laterally in planes displaced at an angle in the range of 15 to 25 degrees relative to the plane of the first set of jets. Such nozzles also may be positioned in horizontal planes or in planes angularly displaced from horizontal planes. As best shown in FIG. 3, the bottom side of the lower section of each member  90  and  91  also is provided with a set of nozzles for directing streams of high pressure water in a downward direction, and each interconnecting section is provided with a set of nozzles positioned to direct jets of water in a rearward direction. 
     As best shown in FIGS. 2 and 3, eductor assembly  20  consists of a pair of tubular members  100  and  101  mounted on the rear end of the support frame and spaced transversely. Tubular member  100  includes an elongated section  100   a  disposed in longitudinal alignment with the elongated section of member  90 , and an upper, laterally angled section  100   b . The forwardly facing portion of section  100   a  is provided with an elongated segment received within a channel shaped portion of a corner component of the support frame to permit tubular member  100  to be adjusted vertically relative to the support frame. The position of each of such members also may be secured relative to pins or bolts inserted in registered holes in such channel member and segment. The lower end of member  100  is provided with a forwardly opening inlet  102  disposed substantially in longitudinal alignment with the lower section of member  90 , and the upper end of such member is provided with a laterally opening outlet  103 . Eductor member  101  is similar in construction to eductor member  100 . It includes an elongated section disposed in longitudinal alignment with the elongated section of member  91 , and forwardly opening inlet  104  at the lower end thereof disposed in longitudinal alignment with the lower section of tubular member  91  and a laterally opening outlet  105 . 
     A pair of air hoses interconnect air manifold  30  and the lower ends of the eductor members for injecting high velocity streams of air up through each of the eductor members which function to draw mixtures of water and spoils produced by jet legs  90  and  91  therethrough, and discharge such mixtures of water and spoils laterally through outlets  103  and  105  to clean the trench formed by the jet legs and allow the pipeline to fall and position on the bottom of the trench. 
     When it is desired to use the trenching machine as described to bury a pipeline laid along a seabed such as from an offshore drilling rig to a facility on shore, the machine will be loaded on a barge and transported to a point along and above the pipeline such as pipeline  11  shown in FIG.  1 . Before the machine is placed in the water, the jet legs and eductor tubes are positioned relative to the main frame, properly sized rollers  21   a ,  22   a ,  23  and  24  are mounted on the main frame and the control system is operated to displace the track assemblies apart. The amount of displacement of the jet legs and eductor tubes relative to the support frame will determine the depth of the trench to be formed. The sizes and configurations of the positioning rollers will depend on the diameter of the pipeline to be buried and possibly the nature of the material of the pipeline. The track assemblies are spread apart to permit the machine to be positioned on the pipeline with a segment of the pipeline extending through the longitudinal opening in the lower end of the main frame. 
     When the machine is thus properly adjusted, a crane on the service barge may be used to place it in the water. Once placed in the water in a vicinity near the selected starting point of the pipeline to which the machine is to be connected, air in buoyancy tanks  28  and  29  may be vented to permit the machine to descend into the water as the umbilical cord connected to the machine is paid out. As the machine descends toward the starting point of the pipeline, divers may or may not be sent down to guide the machine down to the seabed so that the jet legs and eductor tubes rest on the seabed straddling the pipeline. With the divers then clear of the machine and preferably having returned to the barge, suitable controls on the barge are operated to supply water under pressure to the jet legs and air under pressure to the air manifold and then to the eductor tubes. Under such conditions, the nozzles positioned on the lower sections of the jet legs will begin to dislodge seabed below the machine to eventually cause the machine to descend positioning rollers  21   a  and  22   a  to seat on the pipeline and positioning rollers  23  and  24  to align the machine transversely. Spoils generated by the jet streams produced by the jet legs will be drawn through the lower inlets of the eductor tubes and directed laterally clear of the cavity into which the machine settles. 
     Once the machine is thus properly positioned on the pipeline, selector valve  73  may be operated to displace track assemblies  18   a  and  18   b  inwardly into gripping engagement with the pipeline. The machine then is in condition to begin forming a trench and burying the pipeline. This may be accomplished simply by operating selector valve  74  to cause the track assemblies to operate and thus cause the machine to crawl along the pipeline. As the machine moves forwardly, the jet legs will eject streams of high velocity water toward the seabed to dislodge the seabed material and thus form a trench into which the pipeline will be caused to fall and eventually become buried. Spoils produced by the jet legs will be drawn through the lower inlets of the eductor tubes to thus assure a clean bottom of the trench formed to further assure laying the pipeline at a desired depth below the seabed surface. If for any reason it is desired to reverse the direction of the machine, selector valve  74  simply may be operated to reverse the directions of fluid motors  50  and  50   a.    
     As the machine advances along the pipeline and incurs an obstacle such as an anode, the positioning rollers will compress and/or displace sufficiently to permit them to override the obstacle. When the inner flights of the track assemblies encounter such an obstacle they will continue to exert a traction force on the sides of the pipeline but will be permitted to displace outwardly, in the order of a few inches, and override such obstacles as permitted by fluid in the rod ends of cylinder assemblies  33  and  34  being permitted to flow into accumulators  79  and  81 . 
     When the pipeline operation has been completed and it is desired to retrieve the machine, selector valve  74  may be operated to discontinue the operation of drive motors  50  and  50   a , and selector valve  73  may be operated to displace the track assemblies from engagement with the pipeline. The supply of pressurized water and air to the jet legs and eductor tubes may then be discontinued and air may be supplied to the buoyancy tanks to cause the machine to ascend to the surface. The crane aboard the barge may then be used to hoist the machine onto the deck of the barge. As the machine ascends, the umbilical cord connected to the machine correspondingly would be taken up and stored on the barge. 
     The main support frame may consist of a galvanized, carbon steel weldment. Because of the harsh and often corrosive environment in which the machine is used, suitable measures are required to be taken to avoid deterioration and dysfunction of the machine. The positioning rollers mounted on the main frame for locating the machine on a pipeline may be displaceable or spring loaded to allow them to accommodate anodes and other protrusions provided on the pipeline. The buoyancy tanks also are formed of galvanized carbon steel and are configured to allow the machine to travel freely along the pipeline. They are sized to provide a positive buoyancy. The propulsion assembly is intended to accommodate fluid pipelines and data transmission cables having outside diameters in the range of 4″ to 20″. The drive motor of each of the track assemblies preferably is a gear motor with an integral drain case. Since the chains of the track assemblies also will be operating in a harsh environment, they preferably are nickel coated. In addition, they would be provided with ears for bolting the pads thereon. The pads are intended to be compressible and vary in length, width and material. It further is contemplated that each of the track assemblies be provided with means for injecting water under pressure into the interior thereof to purge the areas around the sprockets and chains of spoils having migrated into the interiors of the assemblies. Such purging has the effect of prolonging the service lives of the sprockets and chains. Periodically, however, such chains will become worn and would have to be replaced. 
     The jet legs are intended to be displaced vertically relative to the main support frame in order to vary the depth of the trench to be formed. It is contemplated that the jet legs be sized to provide a 3′ to 4′ trench on each pass. It further is contemplated that instead of a single tubular conduit for each jet leg, a pair of such conduits may be provided. The drive system is designed to provide the track assemblies with a clamping pressure of 2,500 psi, supply the jet legs with 3000+ gpm of water at 1000 psi and further supply the eductors with 1600 cfm of air at 120 psi. The umbilical cord essential consists of a sheathed cluster of lines for conveying air, water and hydraulic fluid from the service barge to the trenching machine. 
     The invention as described provides a simple, compact and efficient machine which may be transported on a service barge to a suitable location at a pipeline lying along a seabed to be buried, placed in the water and lowered to a position astride the pipeline, operated to firmly grip the pipeline, advance along the pipeline and form a trench in which the pipeline is caused to fall into to be buried and easily detached and retrieved. It may be utilized to bury fluid pipelines normally used to transport oil and gas or cables normally used for electronic data transmissions. It further may be easily adjusted to vary the depth of the trench formed and to accommodate conduits of different diameters. 
     From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those persons having ordinary skill in the art to which the aforementioned invention pertains. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.