|Publication number||US3566609 A|
|Publication date||Mar 2, 1971|
|Filing date||May 15, 1969|
|Priority date||May 15, 1969|
|Publication number||US 3566609 A, US 3566609A, US-A-3566609, US3566609 A, US3566609A|
|Inventors||Leif H Smith|
|Original Assignee||Brown & Root|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (11), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
March 2, 1971 L. H. SMITH 3,566,609
METHOD AND APPARATUS FOR LAYING PIPELINES March 2, 1971 l H SMH-H A 3,566,609
METHOD AND APPARATUS FOR LAYING PIPELINES Filed May l5, 1969 4 Sheets-Sheet 2 March 2, 1971 L H, SMITH' 3,566,609
METHOD AND APPARATUS FOR LAYING PIPELINES March 2, 1971 Filed May l5, 1969 FIGB L. H. SMITH 3,566,609
lMETHOD AND APPARATUS FOR LAYING PIPELINES 4 Sheets-Sheet L United States Patent O U.S. Cl. 61-72.3 26 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for laying pipelines or other elongate flexible means on a submerged surface using a variable buoyancy, articulated ramp, pivotally connected to a tioating vessel means. The articulated ramp is formed by a string of buoys pivotally interconnected by flexible or rigid spacers. The pivotal connections may provide for horizontal, vertical, or universal movement of the buoys. Each of the buoys is provided with a depending cradle for slidably supporting the pipeline. The buoys are at least partially Hooded in response to stripping-out of the pipeline from the cradles so that the buoyancy of the ramp is adjusted in response to changes in the supported pipe weight, whereby desirable stress conditions on the pipeline leaving the ramp are maintained.
BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for laying elongate flexible means on a submerged surface.
In pipelaying techniques it has been common in the past to olset stress conditions in the pipe by using buoyant ramps such as those described in U.S. Pat. No. 3,280,571 to Hauber et al. and U.S. Pat. No. 3,390,532 to Lawrence, both assigned to the assignee of this application.
These buoyant ramps are often pivotally connected to iioating vessel means and are operable to slidably support portions of pipeline being laid therefrom.
Means for selectively and remotely controlling the ramp buoyancy are employed so as to maintain desirable stress conditions on the pipeline.
Although the methods and apparatus disclosed in the above-identified patents constitute significant improvements in the pipelaying art, they may be susceptible of improvement. For example, it may be highly desirable to maintain automatic, continuous control of ramp buoyancy in response to changes of the Weight of pipeline supported by the ramp. Insofar as manual intervention to compensate for changes in supported pipeline weight is substantially eliminated, such a control is beneficial whether or not employed with the controls disclosed in those patents.
Furthermore, the provision for such weight compensation in an articulated support ramp would be particularly desirable. Although articulated ramps have been proposed in the past, they have not been provided with the weight compensation feature. An articulated ramp with this feature would not only accommodate for current changes because of its articulated nature, and be amenable to the substitution of ramp sections for either repair purposes or for providing increased iiexibility in weight accommodation design, but would also automatically accommodate for changes in the weight of a pipeline supported by the ramp. Thus, a great degree of control over pipeline stress conditions is enhanced, and the design flexibility obtained by means of the articulated feature enables the use of the variable buoyancy ramp of the present invention in various depths of waters and permits variations in ramp profiles.
3,566,609 Patented Mar. 2, 1971 ice OBJECTS AND SUMMARY OF THE INVENTION Recognizing the need for methods and apparatus for laying elongate liexible means with eicient stress control, it is an object of the present invention to provide such methods and apparatus which substantially satisfy the criteria heretofore noted.
It is a particular object of the invention to provide a method and apparatus for laying elongate flexible means on a submerged surface characterized by the adjustment of the buoyancy of a supporting ramp in response to changes in yweight supported by the ramp.
Another object of the invention is to provide an articulated ramp means, the buoyancy of which is adjusted in response to changes in supported weight of elongate ilexible means.
It is a further object of the invention to provide an articulated ramp means wherein pivotal connections between the ramp sections provide for horizontal, vertical or universal relative movement between these sections.
It is still another object of the invention to provide a method and apparatus for laying pipeline in which the buoyancy of a supporting ramp is adjusted in response to stripping out of the pipeline beyond pipeline sensing stations on the ramp.
It is a related object of the invention to provide a method and apparatus for laying pipelines, in which the prole of a supporting ramp is adjustable in response to cooperation between the pipeline and pipeline sensing stations on the ramp.
It is another related object of the invention to provide a variable buoyancy float for slidably supporting a pipeline, and means on the float for varying the buoyancy thereof in response to changes in pipeline weight supported thereby.
It is likewise an object of the invention to provide such a float with means, responsive to stripping out of supported pipeline, for liooding the float.
It is a still further object of the invention to provide a method and apparatus employing a weight change responsive, variable buoyancy ramp compatible with other known pipe stress control systems.
One aspect of the present invention designed to accomplish at least some of the foregoing objects entails apparatus for laying pipeline on a submerged surface, which apparatus includes a variable buoyancy ramp means pivotally or flexibly lattached to a tloating vessel means and slidably supporting a portion of the pipeline. A plurality of sensing elements, possibly such as rollers, are biased into engagement with the pipeline. These sensing elements control ood and/or air-bleed valves of the ramp means. As the pipeline is stripped out from engagement with the sensing elements, the ramp means is progressively ooded to decrease its buoyancy.
Another independently significant facet of the invention involves the fact that the ramp may be constructed as an articulated string by pivotally interconnecting a plurality of variable buoyancy oat means. The float means, as well as their spacing, may be identical or may be varied to satisfy design criteria.
Other aspects of the invention will appear from the description of the preferred embodiments and methods as illustrated in the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic side elevational view of an overall apparatus employed in laying a pipeline, including a floating vessel and one preferred embodiment of an at least partially submerged, -articulated ramp pivotally attached thereto;
FIG. 2 is an enlarged, partially broken, side elevational view illustrating the floats and one form of rigid float spacers forming the articulated ramp of FIG. 1;
FIG. 3 is a top plan view of the rigid float spacers shown in FIG. 2, taken along line 3-3 therein;
FIG. 4 is an enlarged, top plan detail of another form of rigid oat spacer of an articulated ramp;
FIG. 5 is an enlarged, top plan detail of still another form of rigid spacer;
FIG. 6 is a front elevational View of a oat means illustr-ated in FIG. 1;
FIG. 7 is a partially broken away side elevational view of a iloat means illustrated in FIG. 6;
FIG. 8 is a schematic side elevational View similar to that of FIG. 1, but showing another preferred embodiment of the articulated ramp;
FIG. 9 is a side view of a drag sled shown in FIG. 8;
FIG. 10 is an end elevational view of the drag sled shown in FIG. 9;
FIG. 11 is a schematic side elevational view illustrating a procedure for installing the oat means of the present invention on a previously laid portion of pipeline;
FIG. 12 is a schematic side elevational View illustrating a procedure for installing the float means during commencement of a pipelaying operation.
DESCRIPTION yOF PREFERRED BUOY SYSTEM APPARATUS AND METHOD General summary FIGS. 1 and 8 schematically illustrate arrangements for laying a flexible pipeline 10 on a surface 12 submerged beneath a body of water 14. The illustration of FIGS. 1 and 8 is representative of offshore locations where pipelines are being laid, such as those in the Gulf of Mexico or offshore California.
The depth of the water body 14, represented by the distance d between the submerged surface 12 and the water surface 16 may be as much as several hundred feet.
The apparatus includes a floating, bargelike vessel 18 and a variably buoyant and substantially submerged, articulated ramp 20 for slidably supporting the pipeline 10. This ramp is pivotally connected to barge 18, as indicated at 22, and includes a plurality of pivotally interconnected float means 24.
A feeder-tensioner may control the payout of the pipeline 10. This tensioner may be of the torqued wheel type which accommodates for wave action to prevent stresses of the pipe, as is more particularly described in the previously mentioned Lawrence Pat. N0. 3,390,532,
the disclosure of which is hereby incorporated by reference.
A deck mounted ramp 25a supports the portion of the pipeline 10 on the barge 18. This ramp in many instances is situated on the starboard side of the barge 18, but m-ay be located on the port side, as shown, or at an intermediate position. Spaced roller assemblies 25h (of the type more particularly described in the Lawrence Pat. No. 3,390,532 or the Hauber Pat. No. 3,280,571) may support the pipeline along the ramp 25a.
Each of the float means includes a depending pipe support cradle 26 (FIGS. 6 and 7) and a pipe sensing means 28, which may be in the form of a roller 28a for controlling the buoyancy of the iloat. As the pipeline is stripped out from the cradles, by slidably moving the ramp 20 with respect to the line, the rollers 28a cause the llooding of the float means by successively activating ood valves 30 and vent valves 82 (in a manner hereinafter more fully described), whereby the buoyancy of the ramp is changed in response to variation of the weight of pipe supported thereby.
As used herein the term stripping out refers to the passage of a pipeline section through a sensing station, thereby resulting in either the absence of pipeline at the Station or in the presence of pipeline section having a different sectional configuration or one having a camming projection to activate the sensing means. Since different sectional conigurations of the pipeline are ordinarily representative of a dilerence in the weight of supported pipeline, the sensing means at the sensing station will normally be employed to sense such weight changes. However, it will also be apparent that additional sensing means may be activated by cam means provided on the pipeline so as to produce various curved profiles of an articulated ramp means (and therefore the pipeline supported thereby) without regard to a change in weight of the supported pipeline, as hereinafter more fully described.
It will also be appreciated that control of ramp means buoyancy by stripping out and sensing according to the present invention may be employed while laying of cable or other elongate flexible means. Furthermore, without departing from the inventive concept, a rigid ramp means rather than an articulated ramp means may be employed, at least where buoyancy control relating primarily to weight or pipeline character compensation is involved. Moreover, sensing means other than the spring biased rollers 28a may be employed to sense increases or decreases in weight of the exible means or to sense cam means provided thereon.
In the case of an automatic byouancy adjustment to compensate for an increase in weight, it would Ibe necessary to provide at least some of the float means 24 with automatically actuatable blowing out or venting means (not shown) for increasing their buoyancy. Such venting means would also be desirable in situations wherein the pipeline is to be laid in discrete sections with spacing between sections.
However, for the purpose of simplicity of understanding, the ldetailed description of the buoy system is primarily related to the complete stripping out of the terminal portion of a pipeline being laid, whereby only the absence of pipeline section (proportional to decrease in weight) is sensed, thereby obviating the need for venting means.
Detailed description The interconnection of and the procedure for installing the float means-In the embodiment of FIG. 1, the cradles 26 of the previously identified float means 24 are pivotally interconnected, to form the string of articulated ramp 20, by means of rigid spacers 32 of uniform,
selected, or adjustable lengths. These spacers may be pivotally attached to the iloat cradles 26 by generally horizontal pivot pin and tongue assemblies 33 as shown in FIGS. 2 and 3. This particular pivotal connection permits, and constrains, relative angular movement between the oat means 24 to movement about generally horizontal axes, indicated at 34.
If desired, the pivotal interconnection between some or all of the float means 24 may include the horizontal pivot pin and tongue assembly 33 at one end of the rigid spacer 32 and a vertical pin and tongue assembly 36 at the other end as illustrated in FIG. "4. With this type of connection, relative vertical and horizontal motion between separate float means 24 of the string 20I is permitted. Alternatively, the spacers 32 may interconnect the cradles 26 by means of ball and socket or universal joints, indicated at 38 in FIG. 5, whereby universal or torsional relative movement is permitted between the float means 24.
It will be appreciated that other variations of nonrotatable connections (not shown), ball and socket or universal joints 38, horizontal pin and tongue assemblies 33, and Vertical pin and tongue assemblies 36, may be selectively employed in the same string 20 or on the same rigid spacer 32 to provide the desired degree of flexibility or restraint of string movement.
In any case, it is apparent that the use of removably attached rigid spacers 32, as illustrated, permits a variety of designs for different desired buoy separation distances,
in accordance with weight support and water depth requirements, while still enabling the use of the same major ramp components (the fioat means 24).
In another preferred embodiment illustrated in FIG. 8, the float means 24 are pivotally interconnected by universally flexible, cable or chainlike spacers 40 to form the string 20. These flexible spacers may be secured to adjacent float means by conventional connectors such as clevis and pin units, or by mere cable defined eyes When such flexible interconnection is contemplated, a drag sled 42, hereinafter more fully described, is attached to the terminal float means 24 remote from the vessel 18. This sled 42 is designed to yieldably anchor the lower end of the ramp means 20 on the submerged surface 12 and prevent the individual fioat means 24 from riding up the pipe string i.
The procedure for installing the float means 24 on the pipeline 10 may now be described with reference to FIGS. 1l and 12.
In operations entailing the commencement of a pipelaying operation in a direction away from an underwater installation, such as a platform 44 (FIG. 12) the pipeline may first be provided with a welded end cap 46, often termed a bull plug.
One end of a pulley cable 47 may be attached to a suitable clevis or projection 48 on the end cap 46, while the pipeline 10 is on the lay barge. The other end of the cable 47 may be associated with a winch 5() on the platform `44 above the water surface. A diver may be employed to pass the cable around a sheave 52 and extend it to the winch 50` at the water surface. This sheave 52 may be conveniently mounted on the external portion of a generally J-shaped conduit 54, termed a riser, fixed to the platform 44.
When tension is applied to the cable 47 for a limited time, the pipeline 10 will begin to project beyond the lay barge. After suicient pipe projection has been accomplished, a first float means 24 may be installed on the pipeline. This fioat means 24 is then anchored to the pipeline 10 to prevent it from moving up the pipeline due to its permanently buoyant condition hereinafter described. Although other acceptable anchoring means will suffice, the first float means 24 may be conveniently anchored by a fiexible line 56 attached to the cradle 26 of the first float means and to a second projection 58 on the end cap 46.
The winch 50, which may be alternatively mounted on the lay barge or a nearby work barge (not shown) rather than on the platform v44 is next employed to pull the pipeline 10 off the stationary lay barge by a given amount sufficient to permit installation of a second fioat means 24. This second float means is connected to the first fioat means 24 by a rigid spacer 32 or a exible spacer 40. The procedure is repeated on a cyclic basis until the end cap 46 reaches the vicinity of submerged surface 12 and a coupling Zone such as the lower end 54a of a riser 54. The last oat means is pivotally connected to the lay barge at 22 (by either a rigid spacer 32 or a iiexible connector 40 depending on whether the FIG. 1 or FIG. 8 embodiment is utilized) for pivotal movement about a generally horizontal axis.
It will be appreciated that the pulling cable 47 may be threaded through the riser 54, rather than externally associated therewith. Such an arrangement is described in the United States patent application Ser. No. 817,495, of I oe C. Lochridge and William R. Rochelle, filed Apr. 18, 1969, for Pipeline Connections With Underwater Work Chamber, and assigned to the assignee of the present invention. In the manner described in this application, the end cap 46l may be telescoped into an alignment funnel (not shown) on the riser end 54a to thereby align the pipeline 10 with the riser terminus.
In any case, the first installed float means should be located on the pipeline 10 at a suicient distance from the terminus thereof to permit the terminus to be manipulated, without interference, when connecting it to the riser.
When rigid spacers 32 are employed, the connecting line S6 between the first installed oat means 24 and the end cap 46 may be subsequently removed by a diver upon completion of the ramp installation, without danger of the ramp means 20 riding up the pipeline. However, in the case of the iiexible interconnectors 40, the sled 42 is connected, prior to removal 0f the connecting line 56, to the last oat means, in a manner subsequently described, to prevent such upward riding of the ramp means 20.
As the laying operation is continued while maintaining desired tension on the pipeline 10 with the tensioner 2-5, float means 24 may be added or removed as the depth of the water body 14 increases or decreases so as to maintain the desired profile of supported pipeline.
In the event of bad weather, it may be necessary to discontinue the pipelaying operation. In such instances, it may be desirable to lay the end portion of the pipeline on the submerged surface 12, without removing the installed fioat means. A procedure (not illustrated) for accomplishing this result may include the welding of a second end cap (substantially identical to the end cap 46 on the initial pipeline portion) to the end of the pipeline on the lay barge 18.
A cable attached to this second end cap may be tensioned by a suitable deck mounted winch 25C (FIGS. 1 and 8) located at the bow 18b of the barge 18, and the tension applied by the tensioner 25 may be discontinued. It will be appreciated that this cable and Winch are generally aligned with the axis of the pipeline on the ramp so that the correct direction of the tensile forces on the pipeline will be maintained. As the lay barge 1\8 is moved in the laying direction, the second end cap will reach the stern 18a (FIGS. 1 and 8) of the barge. The connector, either fiexible or rigid as the case may be, between the last fioat means and the barge 18 is then disconnected from the barge and attached to a suitable projection on the second end cap. Also, a suitable removable sheave (not shown) may be positioned at the stern 18a so that the tensioning cable may be passed about the sheave to prevent fouling of the cable in the spaced roller assemblies 25b of the deck mounted ramp 25a.
After an anchor is connected to the second end cap, the barge 18 is moved ahead in the laying direction and the pipeline 10 is lowered while maintaining constant tension on the pipeline by the cable attached to the second end cap and the deck mounted winch. When the pipeline 10 is completely lowered, a second anchor may be attached to the end of the tensioning cable and this anchor may be provided with a marker buoy.
The procedure may be substantially reversed to pick up the pipeline and oat means when the laying operation is to be continued. First, the tensioning cable is retrieved with a suitable hoist apparatus (not shown) and then it is attached to the winch 25C. After removal of the second anchor (by using the hoist apparatus) the cable is tensioned by the winch to lift the pipeline. The first anchor is then removed from the end cap (again using the hoist apparatus) and the last oat means is next connected to the lay barge 18. After removal of the removable sheave at the stern 18a, further tension may be applied to the cable to pull the pipeline to the bow 18h, or another section of pipeline may be placed on the roller assemblies 25b and this section may be connected to the lifted pipeline at the stern 18a. Tension control may then be transferred back to the tensioner 25, after which the cable and end cap are removed. Care should be taken to insure maintenance of continuous tension on the pipeline as it is being lifted from the submerged surface 12. It will be appreciated that the pipeline 10 may be flooded during the previously described lowering operation, in which case it should be dewatered before continuing the laying operation.
Referring now to FIG. 1l, a procedure for installing the float means 24 on a pipeline 10 which has been previously laid on the submerged surface 12 is there shown. Such installation may be required where the pipelaying operation has been discontinued due to bad weather and the float means 24 were not lowered together with the pipeline terminus as above described.
This procedure entails the attachment of davit lines 60 to spaced portions of the pipeline 10. These lines 60 extend from davits 62 on the lay barge 18. The pipeline is raised by the davit lines 60 and subsequently dewatered, if necessary. It will be appreciated the davit lines 60 are properly positioned to maintain the raised pipeline in a desired profile wth the terminus adjacent the bow 18b of the lay barge 18.
An end cap 63 may be welded or otherwise fastened to this terminus and connected by a cable 64 to a deck mounted winch 66 adjacent the bow 18h. The cable 64 may be passed about a deck mounted sheave 67 and tension may then be applied to the cable 64.
A second cable 68 may be installed between a second winch 70 (adjacent the stern 18a of the lay barge 18), and a second sheave 72 (clamped or otherwise suitably secured to the portion of the pipeline 10 resting on the submerged surface 12). This second sheave 72 may be installed by a diver after which the end of the second cable 68 may be passed about the sheave and carried by a diver to the raised terminus of the pipeline adjacent the bow 18b of the barge 18.
Upon installation of a first float means 24 and a rigid or flexible interconnector 32 or 40, the raised end of the second cable 68 is attached to this rst iloat means 24 in any suitable manner. The second cable 681 is then repeatedly pulled a desired distance to pull the float means 24 downwardly and permit continued installation of more iloat means 24 on the pipeline 10. The last lloat means 24 is attached by a rigid or flexible interconnector, to a suitable projection (not shown) on the upper end cap 63 of the raised pipeline.
As the first installed float means is moved toward each of the davit lines 60, the davit lines may be consecutively released. When all the davit lines are removed and the required number of float means 24 have been installed, the lay barge 18 is moved forward relative to the pipeline to lay the pipeline 10 on the submerged surface 12. It will be appreciated that tension is maintained on the pipeline 10 by the cable 64 during this barge movement. Next, the pipeline is picked up and the last float means 24 is connected to the lay barge in the same manner as that previously described in connection with the picking up of a pipeline having float means installed thereon.
Of course, when flexible interconnections are employed, the sled 42 is attached to the first float means after the pipeline has been lowered to the submerged surface and prior to picking up the pipeline.
The float means.-Each individual iloat means 24 of the strings of FIGS. 1 and 8 are comprised of the previously identified cradle 26 and sensing means 28, as well as buoy means 74, as best viewed in FIGS. 6 and 7.
The buoys or body members 74 of the float means 24 are generally cylindrical and are closed by end caps 74a and 74h. Each buoy 74 is provided with concentric, inner and outer buoyancy chambers 76 and 78. In the preferred embodiment, the inner chamber 76 is permanently void so as to provide the float means 24 with a positive buoyancy, regardless of the condition of the outer chamber 78.
On diametrically opposite portions of the buoy adjacent the front end 80 of the body member, the previously identified flood valve .30 and air bleed valve 82 are located in pockets 83 and 83a provided in the body member 74. These valves control the buoyancy condition of outer buoy chamber 78. For simplicity of illustration the valve structure and the associated control linkage (described below) for the valves are omitted from FIG. 2.
Each of the valves includes a fluid passage 84 and 86, communicating with the outer chamber 78. These passages are normally blocked from communication with the water body 14 by means of rotatable valve means schematically shown at 88 and 90. These valve means may be of the conventional plug variety, as exemplified in U.S. Pat. No. 2,813,695, the disclosure of which is hereby incorporated by reference. It will be appreciated that a suitable ball valve would also be an acceptable form of the rotatable valve means 88 and 90.
The rotational movement of valve means 88 and 90 is controlled by the sensing means 28. In the preferred and illustrated embodiment, the sensing means comprises the roller 28a, rotatably mounted in a generally C-shaped, downwardly facing bracket 92 by a pivot bolt 94.
Pivotally attached to the ends of the pivot bolt 94, which ends project through the legs of the bracket 92, are the first or outer ends of two elongated levers 96. The other ends of these levers 96 are pivotally supported on pins 98 mounted on spaced support flanges 100 projecting downwardly from the buoy 74. These ilanges may be secured to the buoy 74 in any suitable manner such as by welding or the like.
The ends of the levers 96 adjacent the roller 28a are provided with laterally outwardly projecting arms 102. Coil compression springs 104, each having one end attached to one of these arms 102 and the other end attached to a respective one of two spring support brackets 106, bias the levers 96 (and therefore the roller 28a) toward the bottom of the cradles 26.
It will be appreciated that the two spring support brackets 106 may be attached to the front end 80 of the buoy 74, in any suitable manner, in positions wherein they are generally superposed above the projecting arms 102 of the levers 96.
The connection between the sensing means 28 and the flood valve 30 includes a link 108 provided with a central, generally longitudinal slot 110. This link 108 is xed to a top leg of the roller support bracket 92 at one end, as shown in FIG. 6.
Slidably and rotatably received within the slot 110 of the link 108 is a pin 112. This pin 112 extends through the slot 110 into opposite legs of a generally U-shaped yoke 114 to which it' is fixed. This yoke 114 in turn fixedly supports a stern 116 rigidly attached to the rotatable valve means 88 of the flood valve assembly 30.
A yoke handle 117 projects outwardly of the yoke 114 to provide a handle for manual control of the flood valve assembly. Downward movement of this handle (to a valve-open position) is permitted even when the roller 28a and roller support bracket 92 are in their uppermost positions, since the yoke pin 112 is slidable in the link slot 108 and since the roller support bracket 92 (and therefore the link 108 fixedly attached thereto) is rotatable about the roller pivot means 94. However, it will be apparent that the friction of the rotatable valve means 88 and will normally maintain the stem 116 in its upper (valve closed) position absent either deliberate activation of handle 117 or downward movement of the sensing roller 28a under the action of the springs 104.
This spring activated movement of the roller 28a also results in rotation of the valve means 88 to cause opening of the flood valve assembly 30 since the upper end of the slot of the link 108 drags the yoke pin 112 downwardly to rotate the stem 116. It will be appreciated that the rotatable connection between the roller bracket 92 and the elongated links '96, together with the permissible relative rotation between the slot 110 and the yoke pin 112, permits such downward movement.
When the ilood valve means 88 is rotated to its open position, it is necessary to provide forrescape of air from the outer buoy chamber 78, by rotating the bleed valve means 90. This rotatable bleed valve means is rigidly connected to a rotatable stem 118 which is fixed to a yoke 120 in a manner similar to the attachment of the stem 116 and yoke 114. The bleed valve connected yoke 120 is rotatably connected, by a pin 122 to one end of a link 124. The other end of this link 124 is rotatably connected to the pin 112 of the yoke 114 associated with the flood valve means 88.
Thus, pivotal movement of the flood valve yoke 114, either manually by means of the handle 117, or in response to the downward movement of sensing means 28, results in a concurrent pivotal movement of the bleed valve means 90 by movement of the link 124 and the stern 118 associated therewith.
As Will be apparent, the slot 110 is sufficiently elongated so that slight upward and downward movement of the sensing means 28 resulting from slight irregularities in the pipeline will neither break the valve stem 116 or 118 nor effect a rotation of the valve means 88 and 90 prematurely. As previously mentioned, the valve means are normally frictionally maintained in position. However, significant downward movement of the sensing means 28 toward the bottom of the cradle 26, as the pipeline 10 is stripped out therefrom, results in actuation of the valve means 88 and 90.
Normally, after installation of the float means 24 on the pipeline 10, the pipeline is continuously supported on the ramp means by spaced rollers 124. These rollers are mounted on the bottom of spaced, generally J-shaped crossover members 126. In the preferred and illustrated embodiment, the roller axes 124a are downwardly inclined toward one another to provide a generally V-shaped, slidable supporting surface for the pipe 10.
The rollers 124 may be rotatably supported in any suitable manner to provide this slidable supporting surface, such as by brackets 126a attached to the crossover member 126.
Two crossover members 126 (and roller assemblies) are pivotally attached to each buoy 74, adjacent the bottom thereof for movement about an axis generally parallel with the buoy axis, as indicated at 128. The pivot connection may be by means of pinning the illustrated tongues 130 provided on the upper end of each of the crossover members 126, to projections 132 welded or otherwise secured to external plates 134 provided on the buoy 74. Of course, any other suitable pivot connection would suffice.
Pivotally but releasably attached (such as by a suitable removable pin) to the shorter leg of each crossover member 126, as shown at 136, is one end of a swing leg 138. The other end of this leg is pivotally fixed to the float 74, as illustrated at 140, in a manner similar to the attachment of the upper ends of the crossover members 126 of the float. With the swing legs 138 in their illustrated positions, the cradle 26 is generally U-shaped. It will be apparent that to install a float means 24 or to disconnect it from the pipeline 10, it is only necessary to disconnect and move the swing legs 138 counterclockwise, as viewed in FIG. 6, about pivot 140, and if necessary because of pipeline diameter, to swing the crossover members 126 outwardly about the axes 128.
As previously described, the float means 24 may be interconnected by the rigid spacers 32. For this purpose, connecting legs 142 may be inserted in spaced and registered apertures 144 in the crossover members 126. These connecting legs 142 are permanently fitted, as by welding, in the apertures 144 and the ends 146 thereof are structured to pivotally couple with the selected end structures of the rigid spacers described in connection with FIGS. 3, 4 and 5.
Although the connecting legs 142 and rigid spacers 32 have been illustrated as being located on only one side of the cradles 26, it will be appreciated that they may be provided on both sides thereof. In the latter case, it may be desirable to shorten the swing legs 138 as well as lengthen the shorter legs 12612 of the crossover members 10 126 and provide these lengthened legs with additional connecting legs 142. In this event, the additional member 142 would be disposed beneath the disconnectable joints 136 on the right side of the FIG. 6 assembly.
When the flexible spacers of FIG. 8 are employed, the interconnection between the installed oat means 24 and between the last float means in the barge may be accomplished, as previously mentioned, by conventional clevis and pin units or the like.
The sled-Referring now to FIGS. 9 and l0,- it Will be seen that the previously identified sled 42, used in connection with the flexibly interconnected ramp means 20 of FIG. 8, may comprise two generally parallel tubular legs 148 interconnected, in fluid communication, by transverse conduits 150 to form a generally U-shaped member.
The spacing between the legs 148 is sufcient to accommodate the pipeline 10. The ends of each of the legs 148 may be angled upwardly and be each provided with a clevis 152. Two flexible lines may be respectively connected to these clevises 152 and joined to another line to form a bridle which may be connected to the first installed oat means of the ramp means 20 after ramp means 20 has been connected to the barge 18.
The sled 42 is positively buoyant when filled with an air or gas medium so that it may be floated into position over the laid pipeline 10. After superposing the sled 42 over the pipeline, it may be flooded to a desirable extent and then lowered to a submerged position straddling the pipeline. This lowering may be accomplished in any suitable manner, such as by controlling the descent of the sled with a hoist cable (not shown) extending from a winch on a service boat (not shown). This cable could be connected to one or more of the transverse conduits 150.
The flooding of the sled may be controlled by divers operating suitable flood and bleed valves 154 and 156. Upon lowering of the sled, the last float means 24 may be disconnected from the end cap 46 on the pipeline terminus (FIG. l2) and then connected to the sled 42.
T he negative buoyancy of the lowered sled should be sufficient to develop a friction force to offset the sum of the horizontal forces developed by all the float means 24 in order to prevent these float means from riding up the pipeline. However, the sled should not develop more friction with the submerged surface than required above, in order to prevent interference with the advancement of the lay barge 18 during the pipelaying operation.
It will be appreciated that the sled 42 may be provided with a compressed gas container 158 to facilitate recovery of the sled after completion of the laying operation. This container 158 may be connected to one of the transverse conduits 150 by a fluid line schematically illustrated at 160. A valve 162 may be provided on a portion of this line, externally of the sled, and may be diveroperated to dewater the sled to a desired degree, with the bleed valve 156 closed and flood valve 154 open.
Operation of the buoy systenL-It will be apparent that subsequent to the installation of the oat means 24 on the pipeline 10 and the provision of the requisite exible or rigid connections between the float means, the pipeline 10 is cradled between the crossover mounted rollers 124 and the spring biased sensing rollers 28a. During laying, the ramp means 20 is slidably moved with respect to the pipeline, i.e., the lay barge 18 (and therefore the ramp means 20) is moved in a direction away from the submerged portion of the pipeline while the pipeline is continuously laid under the control of the tensioning unit 25.
So long as supported pipeline occupies a cradle 26, the flood and bleed valves 30` and 82 of the associated buoy 74 remain closed. However, at the end of the laying operation, when the terminal portion of a pipeline passes through the rearmost cradle of the first float means 24 (probably located a sucient distance from the lay barge 18 to be totally submerged), the spring biased roller 28a moves downwardly toward the bottom of the cradle y26. The flood and bleed valves 30 and 82 are thereby opened as previously described.
Progressive stripping of the pipeline from the cradles results in successive flooding of the float means 24. Thus, the buoyancy of the string is decreased in direct response to the degree of stripping of the pipeline because the number of unooded float means 24 remains proportional to the length of supported pipeline. This change in buoyancy minimizes the addition of stress to the pipeline since the string Ztl does not pivot upward in the Water body 14 as it would in the absence of a buoyancy adjustment. f
Prior to stripping, tension on the pipeline may be transferred to the tensioning cable associated with the winch 25e located at the bow 1811 of the barge (FIGS. l and 8). After the pipeline end is payed out to the stern 18h, the previously mentioned removable sheave (not shown) may be installed at the stern to prevent fouling of the cable in the roller assemblies 25b on the ramp 25a or in the rollers 124 on the cradles 26. It will be appreciated that the removable sheave should be elevated above the deck of the barge by an amount sufficient to prevent fouling of the cable but not great enough to maintain the portion of the cable passing through the cradles 26 during stripping at an elevation which would interfere with movement of the sensing means 28 upon stripping of the pipeline from the cradles.
It will be apparent that buoyancy adjustments other than those accomplished during final paying out of the pipeline may be practiced with the ramp means of the present invention without departing from the scope thereof. For example, some or all of the float means 24 may be provided with other sensing means (not shown) in addition to the main sensing means 28` that comes into play at the end of a laying operation. These other sensing means may be activated by suitable cam fingers provided on the pipeline to selectively change the buoyancy of the individual float means of the ramp means 20 so as to alter the profile thereof during the laying operation,
Of course, these additional sensing means would be suitably connected to additional flood and bleed valve means. Moreover, blow-out means (which may be in the form of compressed gas containers such as the container 158 described in connection with the sled 42) may be provided to be actuable by pipeline camming fingers, or remote or diver operable control means. This blow-out means would enable an increase of buoyancy of a partially or totally flooded float means 24 so as to bring the prole of the ramp means 20* back to its original form or to a new form wherein a change in buoyancy of one or more float means would be required.
The additional sensing means provided on the float means for changing the profile of the ramp means by flooding or bleeding individual float means may be readily programmed by any suitable pipeline mounted camming fingers.
It will be appreciated that if spring biased sensing means are employed for this profile changing purpose, the linkage connecting the sensing means to their associated ood and bleed valve means would provide for activation of these valve means upon upward rather than downward movement of the sensing means as is the case with the main sensing means 28. This could be readily accomplished by using flood and bleed valve means similar to those illustrated in FIGS. 6 and 7 but set to be opened rather than closed in an upwardly pivoted position. Movement to this position may be accomplished by the bottom rather than the top of a slot in a link similar to the link 108.
Finally, it will be apparent that partial or full ooding of some or all of the float means 24 may be accomplished prior to installation thereof in order to set the ramp means 20 at an initially desirable prole. This l2 flooding would, of course, be correlated with the weight of pipeline to be supported.
After the pipeline 10 has been completely stripped from al1 cradles 26 of the ramp means, the individual float means 24 may be retrieved in numerous Ways. Since the buoys 74 are always positively buoyant due to the permanently void chamber 76, the float means will eventually surface after complete stripping. After surfacing of the float means, they may be retrieved by suitable hoisting apparatus on the barge.
SUMMARY yOF ADVANTAGES AND SCOPE OF INVENTION With the structure and mode of operation of the overall invention having been described, the principal advantages of various aspects of the invention have been demonstrated.
The flexible, articulated buoyant ramp for supporting a straight inclined and submerged section of pipeline, when provided with means for varying the ramp buoyancy in response to weight change of supported pipeline provides a uniquely effective mechanism and method for minimizing pipe stress, Moreover, optimum and continuously effective pipe support along the length of the inclined and submerged straight pipe section, regardless of the total pipe weight supported by the ramp, is provided.
When the articulated form of ramp is employed, it is particularly adaptable to accommodate for design variations in profile and for implementation in the crabbing method. Furthermore, joints between the buoy sections, or the configurations of the sections themselves, may be varied. to permit or constrain the relative motion between the float means to a degree commensurate with anticipated undersurface currents or wave action.
'It will be appreciated that variations in the disclosed structure of the oats, rollers, valves, valve actuating means, and means for attaching the floats may be constructed without departing from the spirit of the invention.
Although the invention has been described with reference to particular preferred embodiments and methods, it will be further appreciated by those skilled in the art that modifications such as those suggested, in addition to others, as well as additions, deletions, or substitutions and other changes not specilically described may be made which fall within the spirit of the invention as defined in the following claims.
What is claimed is: 1. Apparatus for laying pipeline on a submerged surface, the apparatus comprising,
a plurality of variable buoyancy oat means for buoyantly and slidably supporting a section of pipeline,
means for interconnecting said float means, said interconnecting means including means for pivotally connecting at least some of said oat means, thereby to form a variable buoyancy pipeline support ramp in which at least some of said float means are pivotally movable relative to one another, and
at least some of said variable buoyancy oat means including means responsive to a change of pipeline weight supported by said support ramp, for changing the buoyancy of said ramp.
2. Apparatus according to claim 1 including,
floating vessel means and means for pivotally connecting said support ramp to said floating vessel means.
3. Apparatus according to claim 1 wherein:
said interconnecting means includes rigid spacer means extending between and connected to adjacent ones of said float means,
at least some of said rigid spacer means comprising said means for pivotally connecting at least some of said float means.
4. Apparatus according to claim 3 wherein:
said interconnecting means includes means for constraining relative pivotal movement between said oat means to movement about generally horizontal axes.
5. Apparatus according to claim 3 wherein:
said means for pivotally connecting at least some of said oat means comprises swivel joint means for permitting universal relative pivotal movement between said at least some of said float means.
6. Apparatus according to claim 3` wherein:
said rigid spacer means are releasably connected to said adjacent ones of said float means.
7. Apparatus according to claim 1 including:
drag means to create a friction force with the submerged surface which will oppose the sum of the horizontal components of the buoyancy forces of said float means. 8. Apparatus according to claim 7 wherein: said interconnecting means comprises flexible spacer means for interconnecting said float means, said exible spacer means comprising said means for pivotally interconnecting at least some of said float means,
said drag means being connected to said one terminal portion of said support ramp, and comprising a generally U-shaped, adjustably buoyant, member adapted to overlie a portion of pipeline and frictionally engage the submerged surface.
9. Apparatus according to claim 1 wherein:
each of said float means comprises cradle means for slidably supporting pipeline, and
each of said responsive means is operative responsive to a change of the cross-sectional dimension of a pipeline section supported by said cradle means.
10. Apparatus according to claim 1 wherein:
each of said oat means comprises a lloodable body member,
valve means for controlling the flooding of said body member, and
generally U-shaped cradle means depending from said body member for slidably supporting pipeline, and
each of said responsive means comprises sensing means, pivotally attached -to said body member, and biased toward engagement with pipeline passing through said cradle means,
means connecting said sensing means to said valve means,
said sensing means being operative to control the operation of said valve means in relation to the position of said sensing means with respect to said body member.
11. Apparatus according to claim 10 wherein:
each of said sensing means is operative to cause said valve means to flood said body member upon stripping out of pipeline from the associated one of said cradle means.
12. Apparatus for laying pipeline on a submerged surface from a floating vessel means, the apparatus comprising,
elongate variable buoyancy ramp means for slidably supporting pipeline,
means pivotally connecting said ramp means to said oating vessel means,
said ramp means including longitudinally spaced sensing stations through which said supported pipeline passes,
means responsive to stripping out of pipeline beyond selected ones of said sensing stations for changing the buoyancy of said ramp means.
13. Apparatus according to claim 12 wherein:
said ramp means comprises an articulated string of variable buoyancy float means pivotally interconnected,
one of said sensing stations being associated with each one of said oat means, and
said responsive means being operable to sequentially flood said iloat means.
14. A variable buoyancy oat comprising,
a oodable body member,
generally U-shaped cradle support means depending from said body member,
valve means for controlling the ooding of said body member,
sensing means pivotally depending from and connected to said body member and biased toward the bottom of said cradle means, and
means connecting said sensing means to said valve means.
15.` A variable buoyant float according to claim 14 including:
connecting means, associated with one of said body member or said cradle support means, and adapted to be connected to another of said floats.
16. A variable buoyancy oat according to claim 14 wherein:
said floodable body is constructed to provide the float with a positive buoyancy in both flooded and nonflooded conditions of said oodable body member.
17. A variable buoyancy oat according to claim 14 wherein:
said sensing means comprises a spring biased roller.
18. A variable buoyancy float according to claim 14 wherein:
at least one of the legs of said cradle means is pivotally attached to the base of said cradle means.
19. Apparatus for laying elongated exible means on a submerged surface from a floating vessel means, the apparatus comprising:
elongated, articulated, variable buoyancy ramp means for slidably supporting the elongated flexible means depending from said floating vessel means,
connecting means pivotally attaching said ramp means to said oating vessel means, and
' buoyancy adjustment means responsive to a sensed change in structural condition of the elongated flexible means supported by said ramp means, for varying the buoyancy of said ramp means.
20. Apparatus according to claim 19 wherein said condition of said elongated flexible means is representative of the weight of said elongated flexible means supported by said ramp means and wherein:
said ramp means includes a rigid means defining a buoyancy control reference,
said buoyancy adjustment means including sensing means on said ramp means and movable with respect to said reference, said sensing means being biased toward engagement with the slidably supported elongate flexible means and being adapted to control the variations of buoyancy of said ramp means in accordance with movement of said sensing means with respect to said reference.
21. Apparatus for laying elongated flexible means, which depends from oating vessel means, on a submerged surface, the apparatus comprising,
elongate, variable buoyancy, ramp means for slidably supporting the elongate flexible means,
connecting means adapted to pivotally attach said ramp means to the oating vessel means, and
buoyancy adjustment means responsive to a change in the weight of the elongated flexible means supported by said ramp means, for varying the buoyancy of said ramp means.
22. Apparatus according to claim 21 wherein:
said ramp means includes a rigid means defining a buoyancy control reference,
said buoyancy adjustment means including sensing means on said ramp means and movable with respect to said reference, said sensing means being biased toward engagement with slidably supported elongate flexible means and being adapted to control the variations of buoyancy of said ramp means in accordance with the relative position of said sensing means with respect to said reference.
23. A method of laying elongate flexible means on a submerged surface, the method comprising:
buoyancy, and generally axially slidably supporting a portion of elongate, exible means on a variably buoyant supporting ramp,
slidably moving the portion of elongate, exible means off the ramp,
Varying, while the elongate flexible means is supported by the ramp, the buoyancy of the supporting ramp in response to a sensed change of weight of the elongate flexible means supported by the ramp.
24. A method of laying pipeline on a submerged surface, the method comprising:
buoyantly, and generally axially slidably supporting the pipeline by a variable buoyant supporting ramp having spaced pipeline sensing stations,
slidably moving the pipeline relative to the ramp,
adjusting, While the pipeline issupported by the ramp, the buoyancy of the ramp in response to sensed changes of pipeline section at the sensing stations.
25. A method of laying pipeline on a submerged surface, the method comprising:
buoyantly, and generally axially slidably supporting the pipeline by a variable buoyant supporting ramp having spaced pipeline sensing stations,
slidably moving the pipeline relative to the ramp,
decreasing, while the pipeline is supported by the ramp, the buoyancy of the ramp as the pipeline is stripped beyond the sensing stations.
26. A method of laying pipeline on a submerged surface from a floating vessel means, the method comprising:
buoyantly and slidably supporting a portion of the pipeline depending from the oating vessel means on an elongated, articulated, variably buoyant supporting ramp,
slidably moving the portion of the pipeline off the ramp,
varying, while the pipeline is supported by the ramp, the buoyancy of portions of the articulated ramp in response to a change sensed by means on the ramp in structural condition of the pipeline supported by the ramp.
References Cited UNITED STATES PATENTS 3,214,921 11/1965 Goepfert et al. 61-72.3 3,472,035 10/1969 Broussard et al. 61-72.3
FOREIGN PATENTS 661,070 3/1964 Italy 6172.3 128,713 1960 USSR 61-72.3
JACOB SHAPIRO, Primary Examiner
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|U.S. Classification||405/167, 405/171|
|International Classification||B63B35/04, F16L1/225|
|Cooperative Classification||F16L1/225, B63B35/03|
|European Classification||B63B35/03, F16L1/225|