US3051113A

US3051113A - Apparatus for supporting floating load

Info

Publication number: US3051113A
Application number: US699772A
Authority: US
Inventors: William F Swiger
Original assignee: Superior Oil Co; Union Oil Company of California
Current assignee: Superior Oil Co; Union Oil Company of California
Priority date: 1957-11-29
Filing date: 1957-11-29
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28

Description

Aug. 28, 1962 w. F. SWIGER APPARATUS FOR SUPPORTING FLOATING LOAD 4 Sheets-Sheet 1 Filed Nov. 29, 1957 m u N\ N\ G w o F o G N NM 2 E .ww W QM w w r Iv gwk k F k 5* Q QM \N N\ P til):

Aug. 28, 1962 w. F; SWIGER 3,051,113

APPARATUS FOR SUPPORTING FLOATING LOAD Filed Nov. 29, 1957 4 Sheets-Sheet 2 S unl INVENTOR Mil/AM E SW/6'67? Arm/24mm APPARATUS FOR SUPPORTING FLOATING LOAD Filed Nov. 29, 1957 4 Sheets-Sheet 3 5 ENT OR.

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Aug. 28, 1962 w. F. SWIGER APPARATUS FOR SUPPORTING FLOATING 1.01m

4 Sheets-Sheet 4 Filed Nov. 29, 1957 INVENTOR.

wk hwm 3,051,113 Patented Aug. 28, 1962 APPARATUS FOR SUPPGRTING FLGATING LOAD William F. Swiger, Scituate, Mass, assignor to Shell Oil Company and Continental Oil Company, both corporations of Delaware, and The Superior Oil Company and Union Oil Company of California, both corporations of California, all of Los Angeles, Calif.

Filed Nov. 29, 1957, Ser. No. 699,772 8 Claims. (Cl. 114-.5)

This invention relates to apparatus for drilling in underwater formations.

Although the apparatus of this invention may be used indrilling underwater formations for a variety of purposes, it is particularly well suited for offshore oil exploration, and it is described in detail with respect to that activity.

At the present time, the oil industry is actively conducting offshore exploration by drilling from floating vessels with equipment such as that described in US. Patent 2,808,229.

In a typical floating drilling vessel, a drilling derrick is mounted on a truss over a central opening or well in the vessel and drilling operations are conducted through the opening. Due to wave action on the floating vessel when in the open ocean, large deforming shock forces are imposed on the hull of the vessel. If these forces are uncompensated, they are fully transmitted from the vessel bull to the derrick truss and derrick proper, with the re suit that repeated strains are imposed which produce fatigue of the structural members of the derrick and the truss. One solution to the problem is to build the vessel, derrick and truss of such strength and rigidity that the forces are overcome. However, such a solution would greatly increase the size and cost of the floating drilling equipment.

This invention provides a derrick truss or mounting in which the deformations imparted by wave action to the hull are prevented from being fully transmitted to the derrick and its truss, thus permitting the use of more lightweight and inexpensive construction than would otherwise be possible. 7

In the presently preferred form of the invention, a derrick is disposed on an arched structure or truss which in turn is supported on the vessel. One end of the truss in cludes a footing rigidly attached to the vessel. The other end of the truss includes a movable footing disposed to move with respect to the vessel. Thus, as the vessel is subjected to deforming forces by wave action, the movable footing of the truss moves with respect to the vessel .to avoid the transmission of hull deformations to the truss and derrick proper.

In the preferred form of the invention, the movable footing of the truss is slidable and has means for preventing it from moving in a direction transverse to that in which it is adapted to slide. A longitudinal tying mem her is connected to opposite ends of the lower ends of the truss for additional strength. Also in the preferred form of the invention, each of the footings are pivotally connected to the truss.

These and other aspects of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a fragmentary side elevation of a floating vessel on which a drilling derrick is mounted in accordance with the invention;

FIG. 2 is a view taken on line 22 of FIG. 1;

FIG. 3 is an enlarged view taken on line 33 of FIG. 2;

FIG. 4 is a view taken on line 44 of FIG. 3;

FIG. 5 is an enlarged view taken on line 5-5 of FIG.

1; and

PEG. 6 is a view taken on line 66 of FIG. 2.

Referring to FIG. 1, a floating drilling vessel or barge it} is anchored by a plurality of anchor lines 12 in a body of water 14 over an underwater formation 15 in which an underwater well 16 is being drilled from the floating vessel. A rotary drilling derrick 13 which includes the usual rotary table 2%, drill string 23 and other associated equipment, which is not shown because it may be conventional, is mounted on a derrick support or truss 22 which in turn is mounted on the main deck 23 of the floating vessel. As can be seen most clearly from FIGS. 1 and 2, the derrick truss includes a pair of laterally spaced, longitudinal and parallel arched structures 24 mounted on opposite sides of a central opening or well 25 in the floating vessel. For the purpose of reference, the right-hand ends of FIGS. 1 and 2 are considered the forward end of the vessel, thus making the lower arched structure in FIG. 2 the starboard arched structure. The port arched structure is identical with that of the starboard arch, and therefore for brevity, only the latter is described in detail below.

The starboard arch includes a longitudinal and horizontal main brace or upper chord 26 welded at its forward end to a downwardly and forwardly extending starboard forward leg 28. A downwardly and rearwardly extending starboard aft leg 30 is welded to the aft end of the starboard main brace. Preferably, both legs and main brace of the starboard arched structure are heavy I-beams with their webs lying in a common vertical plane. A starboard aft footing 32 (see FIGS. 1 and 3) is attached to the lower portion of the starboard aft leg and rests on the main deck so that it is slidable longitudinally but not laterally. The footing for the starboard aft leg is identical with the footing for the port aft leg and similar to that of the footings for the port and starboard forward legs of the truss, and therefore, only port aft footing is described in detail. The differences in structure between the forward and aft footings are pointed out below.

Referring to FIG. 3, the port aft footing includes a pair of vertical gusset plates 34 welded to opposite sides or" the flanges of the lower end of the port aft leg, which is cut off at a slight angle shown most clearly by the dotted lines in FIG. 3. Going counterclockwise (as viewed in FIG. 3), each gusset plate has a horizontal top edge 34A, a forwardly and downwardly extending diagonal edge 343, a relatively short vertical forward edge 34C, a downwardly and rearwardly sloping lower edges 34D, a convex trailing edge 34B, and a vertical rear edge 34F. A separate transverse stiffener plate 35 is welded between each gusset plate and the center of the web of the port aft leg. Each stiffener plate is parallel to the flange-s of the leg and perpendicular to the web and gussets, and extends from the lower end of the web to the diagonal edge of the gusset plates. A relatively largetransverse and horizontal pin 36 is disposed at its opposite ends in a separate bore 37 in each gusset plate and is welded to the rear edges of the stiffener plates of the port aft leg and rests in a semi-cylindrical cradle 35 formed in the upper horizontal surface of a block 40 welded to the upper surface of a sl-idable pad 42 which rests on a lubricated horizontal plate 43 mounted on the main deck. The upper surface of the lubricated plate provides a surface of low coefiicient of friction so the pad can slide freely longitudinally. The lubricated plate can be of any suitable material such as a porous bronze plate impregnated with graphite and sold by the Merriinam Brothers, inc. under the trade name Lulbrite. This type plate was used and had a maximum coeflicient of friction of 0.1 at 1,000 pounds per square inch, and a minimum tensile strength of 40,000 pounds per square inch. A downwardly projecting external shear lug 44 on the large pin extends down into a semi-annular slot 46 formed in the center of the cradle so the pin and leg are prevented from moving laterally with respect to A 3 a the block. The lower edge of each gusset plate is disposed between a respective pair of laterally spaced vertical side plates 48 welded to opposite sides of the top of the pad. The outer side plates are higher than the two inner side plates, and the two inner plates are also welded to the ends of the block. In addition, a pair of longitudinal reinforcing plates 56 are welded to the center of the forward and rear ends of the block and to the upper surface of the pad.

A longer and smaller pin 52 makes a slip fit through a longitudinal bore 54 in the larger pin and at each end projects through a respective hole 56 in each of the outer side plates 48. The ends of the smaller pin are of reduced diameter and externally threaded so a separate nut 58 threaded thereon outside each of the outer side plates holds the pin in the footing. Thus, the slidable' footing is free to pivot with respect to the port aft leg about the longitudinal axes of the pins in a vertical longitudinal plane. The hull is reinforced underneath the footing below the main deck and includes a pair of vertically spaced horizontal upper and lower foundation plates 62, 63, respectively. A horizontal cover plate 64 is welded across the top edges of the gussets and an aft pair of laterally spaced long bolts 66 extend down opposite sides of the web in the leg through aligned bores 67, 68, 69, 7d, 71, and 72 in the cover plate, top flange of the leg, slidable pad, lubricated plate, and upper and lower foundation plates, respectively. The aft pair of bolts make a loose fit in the cover plate bores, and the bores in the top flange of the leg and the slidable pad are elongated in a longitudinal direction to accommodate the relative movement of the vessel deck as described below. A forward pair of laterally spaced long bolts extend down opposite sides of the leg web through a loose fitting bore 73 in the cover plate, a longitudinal slot 74in the upper fiange of the port aft leg, through a longitudinal slot 76 in each of the transverse stiifener plates 35, through a longitudinal slot 77 in the pad, and close fitting bores 73, 79, and 80 in the lubricated plate and upper and lower foundation plates, respectively.

As can be seen most clearly in FIG. 3, the bolts make a relatively close fit through the bores in the lubricated and foundation plates so that the bolts are substantially immobile with respect to .the deck and hull of the vessel. However, the bores permit the bolts, deck, and lubricated pad tomove longitudinally with respect to the footing. The bolts are held in place by nuts 80 at each end. Spherical washers 82 are disposed between the nuts and the cover plate at the upper ends of .the bolt-s and between the nuts and lowerfoundation plate at the lower end of the bolts. The long bolts in both the starboard and port footings are tightened'barely hand-tight, and the nuts are tack-welded to the bolts to maintain their position. Thus, the pad can slidewith respect to the deckalong a longitudinal axis, but is restrained by the bolts from lateral movement. I

The starboard aft legand footing of the starboard 7 arched structure is identical with that of the port arrangement just described and therefore is not repeated.

The lower ends of the starboard and port forward legs of the starboard and port arched structures are each 'rnounted in footings identical with that described for the port aft leg, except thatthe Lubrite plate is omitted (the forward pads being of increased thickness to compensate 'for the missing lubricated plates) and the holes for the bolts through the pads and gusset cover plates are of the same diameter as the holes through the foundation plates so that each forward footing is rigidly anchored to the deck of the vessel. vAlso, the washers used'on the bolts v for the forward footings are fiat since there is no relative movement ofthe forward footings with respect to the. vessel, and the nuts on the boltsin the forward footings are made up tight to anchor the footings rigidly to the main deck. Nevertheless, each of the forward legs are free to pivot with respect to their respectivefooting in a longitudinal vertical plane about the transverse pins in each of their individual footings.

A star-board longitudinal arch-tying member or lower chord 84- is bolted at its forward end between the rear portions of the gusset plates of the starboard forward leg, and bolted at its rear end between the inside forward portions of the gussets for the starboard aft leg footing. Preferably, the longitudinal tying member is made up of three collinear I-beams tied together by two splices 86. As shown in FIG. 1, the flanges of the I-beams are vertical. Referring to FIG. 5, adjacent ends of the I-beams of the tying member are spliced by a pair of side plates 89 attached by bolts 91 to the flanges at the abutting ends of the individual I-beam sections, and upper and lower plates 92 are attached by bolts 94 to the webs at the abutting ends of the I-beam sections by bolts 94. The web of the central portion of the tying member rests on a pair of longitudinally spaced supports 96 mounted on the main deck. Preferably, the longitudinal arched tying member is assembled after the mounting of the respective footings on the deck, and the plates at the left-hand end of the left-hand splice are not bored and bolted until the setting of the footings is completed. The lower ends of the legs of the port arched structure are similarly tied together by a port longitudinal arch-tying member 97.

A horizontal forward lateral brace 93 is bolted at its ends to the forward ends of the horizontal main braces of each of the two arched structures. A horizontal aft lateral brace 1% is bolted at its opposite ends to the aft ends of the horizontal main braces of each of'the two arched supports. An upwardly and rearwardly extending starboard forward diagonal brace 191 is bolted at its lower end to the lower portion of the starboard forward leg and is bolted at its upper end to a bracket 102 bolted portion of the starboard forward diagonal brace and is bolted at its rear end to the starboard end of the forward lateral brace. The port forward leg is similarly provided with. a port forward diagonal brace 106 and a port forward stiffener brace 108. The starboard aft leg has a similarly mounted starboard aft diagonal brace 110 bolted at its lower end to the leg and bolted at its upper end to a bracket 112 bolted to the center of the aft lateral brace. The lower end of a starboard aft-stiffener brace 114 is bolted to the central portion of the starboard aft diagonal brace and the upper end of the stiifener brace 114 is bolted to the starboardend of the aft lateral brace. The diagonal braces just described are I-beams with their webs disposed in vertical planes, and the respective stiffener braces are T-beams. 1

A port aft diagonal brace 116 is bolted at its lower end to the port aft leg and at its upper end to the aft bracket on the aft lateral brace. The port a-ft diagonal brace is also an l-beam with its web in a vertical plane, but instead of a stifiener brace, it has a pair of T -bearns 118 welded to the opposite sides of the center of its web as shown in FIGS. 2 and 6.

In the operation of the equipment shown in the draw ings, the vessel is subjected to a considerable load in its central portion due to the heavy drill string carried by the derrick. As waves act on the vessel to exert a moment which tends to deform the upper surface of the main deck, the movement of the deck is not transmitted into the truss or derrick, because the deck under the slidable footings moves with respect to the footing; In addition, as the angle of the deck with respect to the truss legschanges, the footings pivotto avoid transmitting this movement into the truss. Also, as the deck of the vessel is deformed to cause pivoting of the footing and relative sliding movement between the movable footings and the deck, the slight movement imparted to the relatively loose bolts in the aft footings is accommodated by the spherical washers and the longitudinal slots through whichthe'bolts extend.

chored to the deck, the deck does not slide with respect to them. However, the forward footings are free to pivot to accommodate any change in angle of the deck with respect to the forward legs. Thus, bending moments'imposed on the hull of the floating vessel by wave action are not transmitted to the truss or derrick, thereby permitting the use of lighter construction and reducing the possibility of premature fatigue due to repeated stresses.

I claim:

1. Apparatus for supporting a load on a body of water comprising a deformable floating vessel, a unitary loadbearing structure comprising a pair of upwardly extending load-bearing legs mounted with their lower ends supported by the vessel at spaced locations, an elongated upper chord rigidly connected at longitudinally spaced locations to respective upper portions of the legs, an elongated lower chord rigidly connected at longitudinally spaced locations to the legs below the upper chord to resist any tendency for the lower portions of the legs to move toward and away from each other, means on the vessel providing a lubricated surface for the structure, the lower end of one of the legs being disposed on the lubricated surface and being free to slide with respect to the vessel, and means holding the lower end of the other leg against sliding with respect to the vessel.

2. Apparatus for supporting a load on a body of water comprising a deformable floating vessel, a unitary load-bearing structure comprising a pair of upwardly extending load-bearing legs mounted with their lower ends supported by the vessel at spaced locations, an elongated upper chord rigidly connected at longitudinally spaced locations to respective upper portions of the legs, an elongated lower chord rigidly connected at longitudinally spaced locations to the legs below the upper chord to resist any tendency for the lower portions of the legs to move toward and away from each other, a slidable footing for one of the structure legs adapted to slide with respect to the vessel, and pivot means holding the lower end of the other structure leg against sliding with respect to the vessel.

3. Apparatus for supporting a load on a body of Water comprising a deformable floating vessel, a unitary loadbearing structure, a pair of upwardly extending loadbearing legs mounted with their lower ends supported by the vessel at spaced locations, an elongated upper chord rigidly connected at longitudinally spaced locations to respective upper portions of the legs, an elongated lower chord rigidly connected at longitudinally spaced locations to the legs below the upper chord to resist any tendency for the lower portions of the legs to move toward and away from each other, a movable footing for one of the structure legs adapted to move with respect to the vessel, pivot means connecting one of the legs to the movable footing, a fixed footing for the other structure leg immobile with respect to the vessel, and pivot means connecting the other leg to the fixed footing.

4. Deformation isolation apparatus for supporting a load on a body of water comprising a deformable floating vessel, a substantially rigid unitary load-bearing structure comprising a first pair of upwardly extending legs mounted with their lower ends supported by the vessel at spaced locations, a first elongated load-bearing upper chord rigidly attached at longitudinally spaced locations to respective upper portions of the first pair of legs, a first elongated lower chord rigidly connected at longitudinally spaced locations to the first pair of legs below the first upper chord to resist any tendency of the legs to move toward or away from each other and to form a first rigid arched structure component, a second pair of upwardly extending legs mounted with their lower ends supported by the vessel at spaced locations, a second elongated load-bearing upper chord rigidly attached at longitudinally spaced locations to respective upper portions of the second pair of legs, a second elongated lower chord rigidly connected at longitudinally spaced locations to the second pair of legs below the second upper chord to resist any tendency of the legs to move toward or away from each other and to form a second rigid arched structure component disposed beside the first, and cross bracing connecting the arched components together, one pair of adjacent leg ends of the structure components being free to slide with respect to the vessel, and means holding the other pair of adjacent leg ends against sliding with respect to the vessel.

5. Deformation isolation apparatus for supporting a load on a body of water comprising a deformable floating vessel, a substantially rigid unitary load-bearing structure comprising a first pair of upwardly extending legs mounted with their lower ends supported by the vessel at spaced locations, a first elongated load-bearing upper chord rigidly attached at longitudinally spaced locationsto' respective upper portions of the first pair of legs, a first elongated lower chord rigidly connected at longitudinally spaced locations to the first pair of legs below the first upper chord to resist any tendency of the legs to move toward or away from each other and to form a first rigid arched structure component, a second pair of upwardly extending legs mounted with their lower ends supported by the vessel at spaced locations, a second elongated load-bearing upper chord rigidly attached at longitudinally spaced locations to respective upper portions of the second pair of legs, a second elongated lower chord rigidly connected at longitudinally spaced locations to the second pair of legs below the second upper chord to resist any tendency of the legs to move toward or away from eachother and to form a second rigid arched structure component disposed beside the first, and cross bracing connecting the arched components together, fixed footing means for one pair of adjacent leg ends of the structure rigidly attached to the vessel to be immobile with respect to it, pivot means connecting the said one pair of adjacent leg ends of the structure to the fixed footing means, slidable footing means for the other pair of adjacent leg ends of the structure mounted on the vessel to be slidable with respect to it, and pivot means connecting the said other pair of adjacent leg ends of the structure to the slidable footing means.

6; Apparatus for supporting a load on a body of water comprising a deformable floating vessel, a pair of upwardly extending legs mounted with their lower ends supported by the vessel at spaced locations, an elongated load-bearing upper cord rigidly connected at longitudinally spaced locations to respective upper portions of the legs, an elongated lower cord separate from the upper cord rigidly connected at longitudinally spaced locations to the legs below the upper cord to resist any tendency of the lower portions of the legs to move toward and away from each other, the lower end of one of the legs being free to slide with respect to the vessel and means holding the lower end of the other leg against sliding with respect to the vessel.

7. Deformation isolation apparatus for supporting a load on a deformable base floating on a body of water comprising a pair of upwardly extending legs'mounted with their lower ends supported by the base at spaced locations, a load-bearing upper cord rigidly connected at longitudinally spaced locations to respective upper portions of the legs, a lower cord separate from the upper cord rigidly connected at longitudinally spaced locations to the legs below the upper cord to resist racking of the legs relative to each other, the lower end of one of the legs being pivotally mounted and free to slide with respect to the base, and pivotal means holding the lower End of the other leg against sliding with respect to the ase.

8. Base deformation isolation apparatus for supporting a load on a deformable base floating on a body of water comprising a substantially rigid unitary load-bearing structure including a forward pair of upwardly extending legs supported by the base at spaced locations, an

7 aft pair of upwardly extending legs supported by the base at corresponding spaced locations, first elongated load-bearing upper cord members extending fore and aft connected rigidly to the upper ends of corresponding forward and aft legs, second elongated lower cord members separate from the first cordmembers rigidly connected to corresponding forward and aft legs below the cord members to resist racking of the fore and aft pairs of legs relative to each other and relative to the upper cord members, and transverse cross-bracing between the forward pair of legs and between the aft pair of legs,

7 whereby a load platform is supportable on the loadbearing cord members above the deformable base; pivot means securing one of the pair of legs of the structure to the base, slidable footing means for the other pair of structure legs mounted on the vessel, means pivoted to the other pair of legs for cooperation with the slidable footing means, and means for limiting the slidable cooperation between the slidable footing means and the pivoted means on the other pair of legs.

References Cited in the file of this patent UNITED s'rATEs PATENTS Schroeder Oct. 27, Wichert Jan. 19, Maddock Feb. 11, Rhodes Mar. 19, Crites et al. Apr. 8, Cormier May 12, Cuthrell Ian. 12, Cohen Mar. 14, Tobin May 20, Woolslayer et al Oct. 14, Woolslziyer et al. July 12, Woolslayer et al. July 25, Milk June 8, Bauer et al. Oct. 1, Crake Oct. 6, Marsh Oct. 13,