The present invention relates to a method for constructing and assembling huge modules, and in particular steel truss¬ work modules for oil rigs operating at sea, and a module fabricated by said method. The completed module is defines by a surrounding module frame comprising truss frames for side walls and a roof, as well as one or more deck structures located within and fixed to the module frame.

In the past construction of huge steel modules has been limited, inter alia, by technical conditions, as limitations in the lifting capacity in the constructing yards, and limitations in the lifting capacity on crane barges for lifting the completed modules at sea. The typical lifting capacity on larger Norwegian yards is 200 - 300 tons. Special equipment may, however, be provided for particularly heavy lifting operations, etiher in the form of mobile cranes, floating cranes, or encompassing lifting mast systems. Among these, only the mentioned is practical for constructing in an assembling hall. For lifting completed modules at sea, the limitation has been approximately 3000 -4000 tons, thus limiting the module weight to approximately 2500 - 3000 tons.

Thus, constructing modules by the traditional way, is developed from the limitations set by the lifting equipment. This, indeed, also goes for the constructing sequence and degree of completion of prefabricated deck structures and module members.

It is essential to be aware of the fact that the modules have huge dimensions, and may appear at a width of more than 20 meters, and a length of 50 meters or more. Previously, module weights have not exceeded 2500 tons.

The constructing technique commonly used has been some kind of prefabrication of trusswork structures in the form of truss frames. Initially, such a frame is erected and consti¬ tutes a central vertical frame in the completed module. A lower deck half is then mounted onto the central frame, and a second deck half is mounted onto, the other side of the central frame. Thereafter, auxiliary supports are erected at each corner of the lower deck, as well as one or more auxiliary supports between each corner to support the next deck half which is, in turn, mounted onto the central frame. A corresponding deck half is mounted onto the other side of the central frame. Another set of auxiliary supports is erected and placed on the latter deck, whereafter another deck half is provided on the supports and is fixed to the central frame. In this manner the module is assembled until the predetermined number of deck structures has been mounted. Finally, the prefabricated truss structures that will form side walls are erected and secured to the deck edges, and the auxiliary supports can be removed. Thus, the completed module is comprised of trusswork frames in the side walls and the central wall, and any desired number of deck structures. Installation of equipment, including pipeworks and cableworks may be carried out during deck construction.

The trend of developments now seem to be that lifting capacity at sea will increase to approximately 12000 tons. This is reflected by the interest of oil companies to construct larger and more complete modules on shore, which will provide time savings, weight savings, and be less expensive. There is reason to believe that module weights of future oil rigs will be between 4000 and 10000 tons.

There exist a demand from oil companies of constantly decreasing total project time . This means a reduced period of time from the decision that an oil field is to be deve¬ loped until production is a fact. There is also a need to

reduce the steel weights on the rigs, i.e. a desire for low spesific weight of the modules. Furthermore, a high degree of prefabrication on shore would be advantageous, i.e. low requirement for completion at sea. All demands are based on the desire for reduced developing costs.

As to the demands of the companies, the desire to be co pe- tive as regards prices, i.e. high productivity, is decisive. There is a demand for good utilization of the production facilities, i.e. for short throughput at the yard, and optimal utilization of equipment and staff. Furhtermore, it is desireable to find a design and constructing methods furthering production.

Those constructing techniques conventionally employd cannot fully utilize the possibilities of savings in construction time and the improvements of productivity which are present when dimensions and weights are no longer limited.

By the method according to the present Invention time savings is achieved compared with conventional constructing methods due to the fact that all deck structures may be erected simultaneously, and simultaneously with the construction of the module frame, and that equipment can be installed on the deck structures before the latter are introduced into the module. In addition time savings are achieved due to the fact that dates for ordering equipment for det decks are lesss critical, since equipment with long delivery periodes may enter into the building process at later dates than conven¬ tional. This is further emphasized by the fact that the uppermost deck, which is the first to be installed, normally has the least complicated equipment with the shortest period for delivery, whereas the lowermost deck has equipment conventionally requiring long delivery periods. It is also possible to save time by having the deck structures or portions of them built by subcontractors to a high degree of completion. Concequently, the constructing yard will experi-

ence more flexibility in managing staff and equipment. Additionally, time savings are achieved by an essential increase in productivity as a consequence of having decks manufactured and equipment installed on ground. There will be far more convenient access with cranes, simplified transport of equipment, reduced demands for temporary platforms and scaffolding, and a considerably larger working area will be accessible, so that a larger total labour force can be put on the project.

10

A construction period for a module of 20 -22 months is not unusual, and it is considered possible to save 6 - 8 months of the construction time relative to the previous construct¬ ing method. Improvements of productivity are not included in

15 this assessment.

As regards saving weights, the present method will normally not have a weight saving effect per se, but indirectely, weights per unit of volume of the module will be reduced,

20. because it is possible to build modules efficiently with a very large volume. Indirectly, the number and size of modules will also influence the total weight of the rig.

With the present method it will be easier to achieve a higher

25 degree of completion. Again, this is partly a consequence of the assembling procedure and partly the module size. The module size permits more work to be done and tested within the systems of the module. Connections with other modules are considerably reduced, and thus the demand for completion at

30 sea. This is substantiously reflected by reduction of costs and time savings.

The above mentioned is acchieved according to the invention by a method of the kind set forth in the introduction that is

35 characterized by the fact that a first, separately built, deck structure is introduced at floor leven into the module frame through a temporary lower opening in one of the side

wall frames, and is properly positioned inside the module frame, and is then controllably elevated inside the module frame to the desired level. Said deck structure is then fixed to the module frame, and this sequence is, if desired, repeated for a second separately built deck structure to be introduced into said module frame, positioned, and elevated to a desired level below the first deck structure, and then fixed to the module frame. This sequence is repeated until the desired number of deck structures is installed, and the lower opening In the side wall frame(s) is then closed by insertion of truss braces. It will also be possible to construct the module frame excluding the opening, i.e. with all side walls being closed. The frame then has to be elevated to a suitable level above floor level to permit the deck structure to be introduced from the underneath of the module frame before they are elevated inside the frame.

Advantageously, two or more cross beams may temporarily be provided and secured on top of the module frame, and hoisting means including wires can be provided on said cross beams with the wire ends fastened to a temporary lifting frame located at floor level inside said module frame for elevating or lifting the deck structure to the desired level.

Alternatively, said deck structure may be elevated in the module frame by means of hydraulic jacks provided at floor level, or by lifting mast structures or the like provided external of the module frame.

Suitably, the module frame may be assembled by erecting the side wall frames and securing them in pairs at their adjacent ends to make said adjacent ends form corners, and by provid¬ ing a roof frame on top of the upper end rim of the side wall frames, and secure the roof frame to the side wall frames in order to form a rigid defined module frame.

The module frame is adopted to be enlarged without serious problems by providing the module frame with one or more approximately vertical inner frames to define two or more smaller module frames with adjacent or common partitions (inner frames) having mutually equal or different dimensions, and separate deck structures may be inserted independently into each new module fram, each separate deck structure being elevated to a level independently of the deck levels in the adjacent module frame(s).

Advantageously the deck structures may be constructed simultaneously, and be completely or partly provided with equipment and components before they are inserted into the module frame.

The deck structures can, suitably be conveyed from the constructing site to and into the module frame(s) by means of rigid, removable transport frames running on rails, said frames being adapted to the opening in the module frame.

The fixing or attachment between separate members of the module frame and between decks and the module frame is preferably achieved by welding, but other connections, e.g. bolted or riveted unions are feasible.

By the above disclosed method according to the invention a module is achieved which is characterized by a module frame comprising side wall frames and a roof frame, and one or more deck structures provided inside said module frame at desired levels, with said deck structure(s) secured to said module frame in such manner that together they form a reinforced integrated truss module.

Till now no limitations worth mentioning of the method have been observed. Lifting gears of particularly suited usage is linear winches, e.g. as those produced by Freyssinet (Centre Hole Jacks) having a lifting capacity of up to 930 tons per unit. The number of lifting units may be up to 6 or 8, i.e.

permitting decks weighting 7000 tons to be lifted with excisting equipment. Decks weighting between 800 and 2000 tons are most common today.

The present method will not be limited by the strength of the frame of the module, which is constructed to absorb such loads statically and dynamically with safety factors added.

Other and further objects, features, and advantages will appear from the following description of an embodiment of the invention, presently preferred, with reference to the enclosed drawings, where

figures 1- 5 present constructing steps according to the previously used method for constructing huge trusswork modules; figures 6-11 diagrammatically present the constructing steps for constructing huge trusswork modules according to the present inven¬ tion; figure 12 presents the separate members necessary for constructing the module frame; figure 13 presents the module fram with hoisting gears and lifting frames, as well as rails for displacement of the module; and figure 14 is a sectional view through the module of figure 13, where a removable transport frame running on rails is diagrammatically shown.

As mentioned , figures 1 - 5 present the constructing steps according to the method for constructing huge trusswork modules previously employed.

Figures 6 - 11 diagrammatically present the separate con¬ structing steps of a method for constructing and assembling huge modules (1), especially trusswork modules of steel for

oil rigs operating at sea. Construction may, advantageously, be carried out in a constructing hall, but constructing outdoor, naturally, may also be an alternative. In the figures the deck structures 3 are presented in the form of exposed frames in order to illustrate the constructing method, but during constructing operations the deck structu¬ res will be completely or partly provided with equipment, including pipeworks and cableworks which conventionally belong to the module.

10

Figure 6 presents separate module frame members, e.g. side walls 6, 7, 8, and a roof frame 4 located on a yard floor in an assembly plant. When the module frame (2) is to be constructed, the side walls 6, 7, 8 are erected and secured

15 to each other adjacent end portions, said portions thus forming corners. In the figure two longitudinal walls 7, 8, and an end wall 6 are shown, but all side walls may, natural¬ ly, be of equal length thus forming a square base. It is, of course, also feasible that one or a number of the side walls

20" have a more irregular shape than those plane side wall frames shown.

Figure 7 presents the assembled module frame 2 without front side wall 5.The roof frame 4 is provided on top of the end

25. portions of side wall frames 6, 7, 8 and is secured to the frames. Process equipment 11 having an extension which in the completed module will extend through serveral deck structures 3 is indicated to be mounted to roof 4 of module frame 2 before the first deck is introduced.

30

In figure 8 truss braces 9 are shown, which are secured to vertical members 16 of side wall frames 7, 8 and to roof frame 4 to form end wall 5 with an opening 12. This figure shows the step in which a first deck structure 3 is intro¬

35 duced into the module frame 2. Two further deck structures ready for installation are also shown. Subsequent the deck structure 3 has been moved completely inside the module

frame 2 it is properly positioned relative to the module frame 2 and relative to the process equipment 11, and is elevated inside the module frame to a desired level. Figure 9 shows a first and a second deck structure 3 secured to the module frame 2, and a third deck structure is shown being moved into the module frame.

Figure 10 presents the last deck structure 3 ready to be introduced in the module frame.

Figure 11 presents the module 1 constructed and assembled, and with the last truss braces 9 secured to the vertical end members 16 of the side wall frame and to deck structures 3. Thus the end wall 5 forms an end wall similar to the end wall 6.

Figure 12 presents another constructing procedure differing from that shown in figure 6 -11. Two of the side walls lack their vertical end member, and the module frame 2 is built by erecting side walls 5, 6 and 7, 8 in pairs, after which they are fixed together in pairs adjacent end portions, said portions forming corners. Then roof frame 4 is mounted, as disclosed above, on top of the end surfaces of the side wall frames 5, 6, 7, 8. There is still a lower opening 12 in one side wall frame 5 for inserting deck structures 3.

Figure 13 presents the module frame 2 provided with wheel sets 36 for movement along rails 35. Cross beams 20 are temporarily provided ontop of the module frame 2, and to said cross beams hoisting equipment 14, e.g. linear winches, are secured. From the hoisting equipment wires 15 are suspended and are at their lower ends fastened to a lifting beam or a lifting frame 21. In the figure a deck structure 3 is shown while it is lifted by means of the hoisting equipment to a predetermined level. When the desired number of deck structu¬ res is secured said cross beams 20, the hoisting equipment 14, and the lifting frame 21 are removed. Truss braces 9 are

provided in the opening 12 and are secured to the deck structure and side wall 5 to close the opening 12 and for additional stiffening of the module.

Figure 14 Is a diagrammatical section through the module frame 2 according to figure 13 during lifting operations of a deck structure 3. In addition to hoisting equipment 14, and cross beam 20, rigid and removable transport beams, if desired, transport frames 30 running on wheels are illustra¬ ted for conveying the deck structures 3 from the building site and into the module frame.

As disclosed above, the method comprises a constructing sequence permitting maximum completion of decks and inter- mediate-decks of the module before they are installed in the module frame 2. All decks are built at floor level or on supports at a low level, and are completely or partly equipped with associated equipment. Simultaneously to building the decks the module frame is completed, apart fromthe lower opening 12 for later insertion of the deck structures.

By the hoisting equipment in the form of linear winches the transmission of loads to the deck is achieved by means of wires, cables, rods, or chains in addition to the lifting frame or lifting beams which are located underneath the deck structures to be lifted in order to distribute the load. The forces from the hoisting equipment is absorbed by the module frame.

Another lifting procedure implies lifting from the underside of the deck by a jacking up operation. Jacking up may be carried out in different manners by transmitting load to the module frame or by transmitting load to the floor leven on which the module rests. Hydraullcal or mechanical jacks may be used.

Yet another lifting method comprises lifting by means of masts or lifting mast structures (Resmast systemer) that are provided external or internal of the module frame and serve as transmission means for the lifting forces. Lifting may be carried out by means of winches, hydraulics or mechanically.