KR20060098385A - A method of constructing a semi-submersible vessel using dry dock mating - Google Patents

Abstract

A method of constructing a semi- submersible rig in a shipyard and completely assembling the rig at the shipyard. An upper hull (1) of the rig is constructed on land next to a dry dock, where the lower hull (2) is constructed in the dock where mating takes place. The upper hull is then skidded to a position above the lower hull. The lower hull is floated and lifted by flooding the dry dock, and position of the lower hull is adjusted using the ballast tanks of the lower hull. Once the upper hull and the lower hull are met and aligned, they are permanently welded together, completing the rig assembly in the dry dock.

Description

Semi-submersible vessel drying method using dry dock matching method {A METHOD OF CONSTRUCTING A SEMI-SUBMERSIBLE VESSEL USING DRY DOCK MATING}

FIELD OF THE INVENTION The present invention generally relates to the construction of offshore structures, and more particularly to methods of drying semi-submersible drilling rigs, vessels or structures (referred to as "leags") in shipyards. will be.

Market demand for semi-submersible leagues is increasing with the trend of exploring oil and gas reserves from sea floors of more than 150 meters in depth.

There are two conventional methods of building a semi-submersible rig. A first, so-called "sequential block stacking" method is provided for manufacturing a semi-submersible rig from bottom to top. According to this method, the lower hulls of the rig, pontoons, columns and associated bnracing, are first constructed in block-to-block using a land crane or a floating crane. The upper hull is then constructed and assembled in the same sequential manner on the lower hull. One disadvantage of this method is the use of expensive land and floating cranes. Often, the drying schedule depends on the availability of the floating crane. Moreover, large block joint welding results in a long drying schedule. On the one hand, the installation and purchase of enclosures, major equipment, should be carried out when the rig is mounted after the entire rig has been built. This in turn results in a long overall drying schedule and a late purchase of the equipment, in particular the drilling package located in the center of the upper hull.

The existing method of drying the second semi-submerged rig is to manufacture the upper and lower hulls simultaneously and subsequently connect the two halves together. According to this method, upon completion, the upper hull is carried in a barge and both the upper and lower hulls are dragged to an offshore position where the lower hull is constructed in deep sea. The lower hull is then sinked to the desired depth using ballast and counterweights and only the top of the column protrudes from the water. Temporary moorings, power pack systems and complex logistics are required for this type of work. The pants are positioned by carrying the upper hull on top of the lower hull. The pants shall be fixed in position with respect to the lower hull prior to mating. The floating pants then sink gradually by ballasting until the upper hull bottom meets the lower hull column. Welding at the connecting joint between the upper and lower hulls is finally carried out. The main drawback of this approach is often associated with very dangerous work in harsh and uncontrollable offshore environments. Moreover, the work can be very inaccurate. In this regard, the safety and quality of work has become a major concern.

Other methods of building offshore rigs are disclosed in published or published patent documents. For example, US Pat. No. 6,347,909, issued February 19, 2002, discloses a method of transporting decks by sea and installing decks on offshore structures. The deck is fully fabricated on one set of deep girder that supports the jacking unit. The deck and deep girder fixed to each other are stitched onto two pontoons. The finished assembly is led to an installation site where the girders are jacked up and at the same time ballon is ballasted down until the assembly is supported by the pontoons. The deck is then lowered onto the substructure and the pontoon is released.

Another example of a patented method is disclosed in US Pat. No. 6,340,272, issued January 22, 2002, which discloses a method for building an offshore platform by mating its own floating deck assembly and its own floating substructure. The self-floating deck structure can be a floating pier or pants, on which the desired equipment is mounted. Registration is achieved by sinking the substructure, positioning the peer or pants over the substructure, and deballasting the substructure to create a vertical support force between the substructure and the peer or pants.

Another patented method is disclosed in US Pat. No. 5,924,822, issued July 10, 1999, which discloses an apparatus and method for installing decks on offshore substructures. Two independent pontoons each have two pillars extending upward from the pontoons and spaced apart from each other. Each pontoon is provided with a ballast tank which is ballasted downward during transport. The pontoons allow the deck to be placed directly on the offshore substructure. For the floating substructures, the pontoons are ballasted and the floating substructures are simultaneously debalanced to transfer the deck to the floating substructures.

U.S. Patent No. 5,237,949, issued August 24, 1993, discloses a method for manufacturing and assembling an offshore platform where the normal draft exceeds the depth of the channel between the site of manufacture and use of the platform. The hull and deck of the platform are manufactured separately in a shallow grabbing dock. The deck is then raised and the grabbing dock is partially floated and the floated hull moves to the deck to mate.

Japanese Patent Application No. 56-154381, published November 28, 1981, discloses a semi-submersible rig consisting of a pair of pontoons, an upper deck and a column. The end of the connection member and the end of the deck on the column are fixed. The deck, pontoons, and posts are then ballasted to align the posts' alignment with the centers of the decks to adjust the inclination of the posts.

Although the patented method can operate under certain conditions, there has been a need to make the method of assembling a semi-submersible rig close to the shipyard, preferably at the shipyard, simpler, safer and more cost effective.

It is therefore an object of the present invention to provide a method of building a semi-submersible rig that is safer, more dangerous and less expensive than other methods.

Still another object of the present invention is to provide a method of drying a semi-submersible rig using a dry dock and land side of a conventional shipyard.

These and other objects of the present invention are achieved by providing a method in which the upper hull and the lower hull can be built simultaneously in a shipyard to shorten the overall construction schedule. The upper hull is completely dried on the land side on skiding truss and support towers, and the lower hull is dried in a dry dock adjacent to the skid truss. A support truss is installed in the dry dock to support a number of skiding beams that extend from the upper hull drying location to the mating position on the lower hull within the dry dock.

Once the upper hull and the lower hull are dry, the upper hull is loaded into the mating position by skiding on a skiding beam using a hydraulic jacking system. The mating operation is performed by subsequently floating the upper hull in the dry dock upwards until the lower hull meets and supports the upper hull. Joint welding of the upper and lower hulls is finally performed. In this way, the completed registration operation is performed in a controllable state to ensure the stability and quality of the operation.

BRIEF DESCRIPTION OF DRAWINGS To further understand the spirit and objects of the present invention, reference is made to the following detailed description in which the accompanying drawings are referred to by the same reference numerals.

1 and 2 are profiles and top views, respectively, of job layouts loaded and matched.

3 is a side view of the upper hull supported by the skiding truss and the drying tower.

4 illustrates the installation of a support truss in a dry dock.

5 shows the positioning of wedge-shaped members in the method of the present invention.

FIG. 6 shows the upper hull at the mating position on the lower hull in the dry dock. FIG.

7 shows the steps in the process when the upper hull is fully supported by the lower hull and the skid truss is removed after the mating operation.

8 shows the decomposition of the skiding beams before the rig is floating.

9 shows the completion of the matching operation.

Referring to the drawings in more detail, FIGS. 1 and 2 show a general layout of a shipyard area including a dry dock. In a dry dock, the semi-submersible rig of the present invention is dried and mated. As can be seen from FIGS. 1 and 2, the semi-submersible rig comprises an upper hull 1 and a lower hull 2. During construction, the upper hull is supported by skiding truss 3 located on land adjacent to the dry dock 4. The truss 3 is designed such that the finished upper hull on the skiding beam 6 is skided using skiding shoes 8 during the load-out operation. An auxiliary support structure 5 or support truss 5 is erected on the dry dock 4.

A skiding beam or connecting member 6 extends between the support truss 5 and the bottom of the skiding truss 3. The connecting member 6 is removed from the support truss after the mating operation is completed, as described in more detail below.

The cylinder of the hydraulic jacking system 7 is mounted to the first skiding shoe 8 and the fixing block 9 is attached to the distal end of the skiding beam 6. A strand wire 14 connects the fixing block 9 and the jacking system 7. Two bars 10 are located behind the support truss 5 on the dock floor. The pants 10 have a fully ballasted tank. The pants 10 are connected to the distal end of the beam 6 by a bar 11. The pants 10 act as counterweights to limit the upward movement of the skiding beam 6.

Before drying the upper hull 1, a temporary support tower 16 is erected around the skid truss 3 for supporting the upper hull 1 (FIG. 3). The working platform 19 is dried under the upper hull 1. The vertical staircase 17 and the horizontal workway 18 provide access from the ground to the upper hull 1 via the work platform 19. Such members are provided as safety and manufacturing protection features.

4 shows the installation of the support truss 5 in a dry dock. As can be seen in the figure, the support truss 5 has a top 5A and a bottom 5B. The lower part 5B has a connecting member 5C having an outwardly convex surface. The upper portion 5A has a connecting member 5D having an inwardly concave surface, which has a complementary radius to the radius of the connecting portion 5C. The lower part 5B is installed on the dry dock floor, and the upper part 5A is subsequently installed using the pants 10. The upper portion 5A of the trough 5 is simply lowered so as to lean against the lower portion 5B so that the concave surface 5D and the convex surface 5C are mated to match. Welding is not necessary, which results in rapid installation and disassembly of the support truss 5 and short dry dock occupancy time.

5 shows a feature of the invention with respect to the positioning of the friction reinforcing member between adjacent members of the drying process. A number of wedge shaped members, for example wood wedges 13, are used to minimize the welding requirements. In detail '1' of FIG. 5, two wedges 13 are assembled between the bottom of the upper hull 1 and the top of the skidding truss 3. Similarly, as shown in detail 'A' and detail '2' of FIG. 5, the support truss 5 and the skiding beam 6 are mounted on a wedge 13 assembled between the door floor and the support truss, respectively. Lies. High compressive strength wood, which transmits vertical rods and friction between the interfaces, limits lateral movement between adjacent members.

When the upper hull 1 and the lower hull 2 are dried, the upper hull 1 is jacked and aligned with the posts of the lower hull 2 and slides along the skiding beam 6 above the position above the lower hull 2. Lose. 6 shows the position of the upper hull 1 and the lower hull 2 after the upper hull has reached the mating position. Sufficient clearance of about 500 mm is allowed between the top of the lower hull column and the bottom of the upper hull.

The next step in the process involves floating above the lower hull. At this stage of the process, the dry dock is submerged. The desired floating state of the lower hull 2 is achieved by ballasting each water tank and delivering ballast water among the tanks, the alignment of the upper and lower hulls being adjusted by a flotation method. The upper part of the column of the lower hull 2 eventually contacts the bottom of the upper hull 1. Welding of temporary guide members in the upper and lower hull joints is carried out at this stage.

The lower hull 2 is continuously floated until the lower hull supports the weight of the upper hull 1 and the gap between the upper hull 1 and the lower hull 2 is closed. The upper hull 1 is then completely removed from the skidding truss 3. Sufficient welding at the upper and lower hull joints permanently attaches the upper hull 2 to the lower hull 1.

Subsequent to the mating step, the semi-submersible rig is removed from the auxiliary support structure 5. The skid truss 3 is withdrawn from the mating position back to the land side using the jacking system 7 mounted on the skid truss 3. The skiding beams 6 on the dry dock 4 are cut using the jacking systems 7, 9 mounted on the connecting member 6, pulled out and pulled into the pants 10. The connecting beam 6 is then removed from the dry dock 4 onto one or more conveyors or low bay trailers 12.

FIG. 8 shows that the hulls 1 and 2 float from the supporting truss 5 and the finished rig in the mating position of the dry dock 4.

9 is a plan view showing the step of removing the rig from the support truss 5 of the dry dock 4.

The process of the present invention provides several advantages over existing conventional rig drying methods. The overall drying period is shortened by making the upper and lower hulls simultaneously. High hazards and inaccuracies of matching are avoided under adverse water conditions, ensuring high safety and quality. As a result, useful alignment of the upper and lower hull structures and the quick purchase of equipment are possible.

The method provides for a suitable support structure for the upper hull while taking into account changes in the loading pattern during the complete installation of the upper hull. A safe work platform is erected under the upper hull to enhance the safety and manufacturing protection features of the present invention. The tower provides secure access in the vertical and horizontal directions from the ground to the work platform below the upper hull. In addition, an unobstructed slip of the upper hull to the mating position is provided.

The support truss element is easily installed, aligned and removed. There is no need to stack additional dry dock floors. Potential problems caused by different ground fixation during the skidding process are eliminated and interference between the cross tracing of the support truss and the lower hull is minimized or eliminated from each other.

Additional advantages of the method of the present invention relate to the removal of expensive ground fixation points to withstand high pulling forces during the skidding process, the use of a skid beam recovery method, truss support and preservation of the skid surface. Wood wedges allow for improved adjustment of structural level and limited lateral movement by interfacial friction.

The invention is described with reference to specific embodiments and this description is not intended to limit the invention. Various embodiments of the disclosed and other embodiments of the present invention are apparent to those skilled in the art with reference to this detailed description. Accordingly, it is contemplated that the appended claims cover any modification or embodiment within the scope of the invention.

Claims (26)

Providing means for supporting the upper hull on land and upper hull, Providing a lower hull in a dry dock adjacent said upper hull support means, Providing means, mounted to said upper hull support means, for moving said upper hull to a position above said lower hull, Transporting the upper hull to a position above the lower hull, Ballasting the lower hull such that the upper hull and the lower hull are aligned; Assembling the semi-submersible rig by matching the upper hull to the lower hull, and Removing the semi-submersible rig from the upper hull support means, Semi Submerged Rig Drying Method. The method of claim 1, Providing an auxiliary support structure for temporarily supporting the upper hull when the upper hull is positioned above the lower hull, wherein removing the semi-submersible rig from the upper hull support means comprises: Removing the semi-submersible rig from the support structure, Semi Submerged Rig Drying Method. The method of claim 1, Providing the upper hull support means may include the skating to maintain the upper hull in an elevated position on land prior to the construction of the skating truss and the multiple tower superstructures and to provide horizontal and vertical access to the upper hull. Establishing tris and said plurality of tower superstructures, Semi Submerged Rig Drying Method. The method of claim 3, wherein Providing means for limiting lateral movement of the upper hull relative to the skid truss without welding between the upper hull and the skidding truss, Semi Submerged Rig Drying Method. The method of claim 4, wherein The limiting means comprises a plurality of wedge-shaped members having at least an outer surface formed of a friction increasing material, the wedge-shaped members being assembled between the bottom surface of the upper hull and the contact surface of the skidding truss, Semi Submerged Rig Drying Method. The method of claim 2, The providing of the auxiliary support structure further comprises providing a connection beam extending from the auxiliary support structure and the upper hull support means to erect a support truss in the dry dock. Semi Submerged Rig Drying Method. The method of claim 6, Providing means for limiting lateral movement of the auxiliary support structure relative to the dry dock without welding and / or securing between the auxiliary support structure and the dry dock, Semi Submerged Rig Drying Method. The method of claim 7, wherein The limiting means comprises a plurality of wedge-shaped members having at least an outer surface formed of a friction increasing material, the wedge-shaped members being assembled between the bottom surface of the auxiliary support structure and the floor of the dry dock, Semi Submerged Rig Drying Method. The method of claim 6, Providing means for limiting lateral movement of the connection beam and the auxiliary support structure without welding between the auxiliary support structure and the connection beam, Semi Submerged Rig Drying Method. The method of claim 9, The limiting means comprises a plurality of wedge-shaped members having at least an outer surface formed of a friction increasing material, the wedge-shaped members being assembled between the bottom surface of the connecting beam and the contact surface of the auxiliary support structure, Semi Submerged Rig Drying Method. The method of claim 6, The means for transporting the upper hull comprises a jacking system mounted to the upper hull support means and the connecting beam, Semi Submerged Rig Drying Method. The method of claim 6, The connecting beam has a tip, the tip is fixed to the upper hull support, Semi Submerged Rig Drying Method. The method of claim 12, And removably securing the distal end of the connecting beam to a counterweight positioned behind the auxiliary support structure, Semi Submerged Rig Drying Method. The method of claim 1, Further comprising installing the auxiliary support structure on the floor of the dry dock, Semi Submerged Rig Drying Method. The method of claim 14, The auxiliary support structure includes a lower portion having an outwardly convex connection member and an upper portion having a correspondingly concave connection member inwardly, and the step of installing the auxiliary support structure on the dry dock floor includes: And mating the bottom in conformity, Semi Submerged Rig Drying Method. The method of claim 2, Removing the semi-submersible rig from the auxiliary support structure includes recovering the upper hull support means and the connection beam, Semi Submerged Rig Drying Method. The method of claim 16, Pulling the upper hull support means using a jacking system on the upper hull support means, Semi Submerged Rig Drying Method. The method of claim 16, And pulling out the connection beam using a jacking system mounted on the connection beam to a plurality of conveyors, Semi Submerged Rig Drying Method. As a semi submersible rig drying method, Providing a plurality of support towers and skidding truss on land, Drying the upper hull of the semi-submersible rig on the skid truss and the support tower, Providing a support truss in a dry dock adjacent to the skid truss, Drying the lower hull of the semi-submersible rig in the dry dock simultaneously with the drying of the upper hull, Securing the jacking system under the skiding truss, Providing a plurality of skiding beams fixed between the support truss and the bottom of the skiding truss, Jacking the upper hull to transfer the dried upper hull to a position above the dried lower hull along the skiding beam, Floating the upper hull in the dry dock, Ballasting the lower hull such that the upper hull and the lower hull are aligned; Mating the upper hull with the lower hull to assemble the semi-submersible rig in the dry dock, and Removing the semi-submersible rig from the skid truss and the support truss, Semi Submerged Rig Drying Method. The method of claim 19, Wherein the skiding beam has a distal end, the distal end being detachably connected to a counterweight to limit the elevation of the skiding beam during the transport of the upper hull, Semi Submerged Rig Drying Method. The method of claim 20, Installing the support truss on the floor of the dry dock, Semi Submerged Rig Drying Method. The method of claim 21, The support truss includes a lower portion having an outwardly convex connection member and an upper portion having a correspondingly concave connection member inwardly, and the step of installing the support truss on the dry dock floor includes: Including mating to match, Semi Submerged Rig Drying Method. The method of claim 20, Mounting a friction-enhancing wedge-shaped member between at least the upper hull and the skidding truss, the wedge-shaped member restricting lateral movement of the upper hull without welding between the upper hull and the skidding truss. doing, Semi Submerged Rig Drying Method. The method of claim 19, Removing the semi-submersible rig from the skid truss and the support truss includes recovering the skid truss and the skiding beams, Semi Submerged Rig Drying Method. The method of claim 24, Further comprising pulling the skid truss using a jacking system mounted on the skid truss, Semi Submerged Rig Drying Method. The method of claim 24, And pulling out the skid beam by using a jacking system mounted on the skid beam for a plurality of pants, Semi Submerged Rig Drying Method.

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