Patent Publication Number: US-6659226-B2

Title: Scaffolding system for volumes of various shapes

Description:
The present invention relates to a scaffolding system for volumes of various shapes, and particularly but not exclusively for use in lagging the tanks of liquefied gas tanker ships. 
     BACKGROUND OF THE INVENTION 
     More generally, the invention relates to scaffolding systems that can be put in place inside enclosures whose walls can present a wide variety of shapes, and in particular can be spherical, cylindrical, of polygonal vertical section, or indeed a combination of such shapes. 
     This problem is to be found in particular when applying the thermal insulation or “lagging” to tanks in ships used for transporting liquefied gas. 
     Accompanying FIGS. 1A and 1B are a longitudinal section and a cross-section through a ship for transporting liquefied gas. The ship  10  has a plurality of tanks  12 ,  14 ,  16 , and  18  disposed along the length of its hull. When the ship is being built and after the tanks have been made, at least once the main walls  20  thereof have been made, it is necessary to lag these walls  20  with an insulating structure, possibly constituted by a plurality of layers of material. FIG. 1B is a cross-section through a typical shape for such a tank  14 . It comprises a floor or bottom  20 , a ceiling  26  having an access opening  30 , and vertical side walls  22  and  24 . The floor  20  is connected to the side walls via bottom sloping walls  32  and  34 , while the ceiling  26  is connected to the side walls via top sloping walls  36  and  38 . The tank also has a vertical front wall  35  and a vertical rear wall  37 . 
     It will be understood that with such tanks, or more generally with similar enclosures, the problem when making scaffolding consists firstly in the difficulty of gaining access to the enclosure and secondly in the unusual and irregular shape of the walls which the scaffolding is to face once it has been erected. 
     It will also be understood that when building a ship for transporting liquefied gas, the time required for building is a parameter that is economically decisive. It is therefore very desirable for shipyards to have scaffolding systems for putting into place, in particular inside tanks, which systems should be suitable for being put into place and then dismantled relatively quickly and should be suitable for use with the particular shape of the walls to which the scaffolding system is intended to give access. 
     Furthermore, in order to obtain a better understanding of the problem posed, it needs to be recalled that the width of the tank can be about 30 meters (m), that the length of the tank can be about 40 m and that the height of the tank is likewise about 30 m. It can thus be seen that the area of the walls to which the scaffolding system is to give access is very large. 
     Accompanying FIG. 1C is a cross-section through another volume shape which also requires scaffolding to be put into place for lagging its walls. This tank comprises a wall  11  and a coffer  13 . In right section, the wall comprises a bottom  21 , side walls  23  and  25 , and a ceiling  27  pierced by an access opening  28 . Top sloping walls  29  and  31  and bottom sloping walls  33  and  39  interconnect the side walls with the ceiling and the bottom. 
     It will be understood that installing scaffolding inside such a tank raises special problems. 
     In patent application WO 93/20307, scaffolding is described for working inside the tank of a methane tanker, which scaffolding comprises a carrier structure made up of two legs interconnected by cross-members forming a gantry, and by a large number of modular platforms mounted at various heights and cantilevered out from the outside face of said legs. 
     Such a structure requires erection time that is lengthy insofar as it must be made along the entire length of the tank and insofar as it requires a very large amount of scaffolding material, in particular for making the modular platforms. 
     Document U.S. Pat. No. 4,057,943 also describes a scaffolding structure, in particular for the tanks of a methane tanker, in which a carrier structure is assembled inside the tank, the structure standing on the bottom of the tank and carrying a set of platforms including adjustable ends for giving access to the different portions of the inside wall of the tank. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to form a scaffolding system for volumes of various shapes and in particular for tanks for storing or transporting liquefied gas, enabling the scaffolding to be put into place quickly inside the volume and making the scaffolding easy to use without requiring a large quantity of scaffolding elements to be involved. 
     The invention achieves this object by means of a scaffolding system for volumes of various shapes presenting a bottom and end walls, the system being characterized in that it comprises at least a first scaffolding structure comprising: 
     a gantry-forming structure comprising at least two vertical poles interconnected to form a gantry, each of said poles having a bottom end; 
     means secured to said bottom of the volume to guide said bottom ends of the poles in rectilinear displacement in a longitudinal direction on said bottom; 
     means forming a horizontal main platform and means for guiding said main platform-forming means in vertical translation along said poles, said platform-forming means having two end edges in a direction orthogonal to the displacement direction of said gantry; 
     at least two horizontal auxiliary platforms mounted to move in horizontal translation relative to said main platform, each platform having an outer edge; and 
     means for displacing each auxiliary platform separately relative to the main platform between a retracted position in which the outer edge of the auxiliary platform is retracted relative to the outer edge of the main platform, and an extended position in which the outer edge of the auxiliary platform is substantially vertically in register with the outer edge of the main platform. 
     It will be understood that this scaffolding system has three degrees of freedom to give access to all of the portions of the wall of the volume in which the scaffolding is erected. Longitudinal displacement of the gantry-forming structure constitutes one degree of freedom in the length direction of the volume, vertical displacement of the main platform relative to the gantry constitutes a second degree of freedom in the height direction of the volume, and the ability of the two auxiliary platforms to be displaced relative to the main platform enable the outline of the scaffolding to be matched to the different portions of the wall of the volume at different levels. 
     In a preferred embodiment, the scaffolding system further comprises at least second and third scaffolding structures very similar to said first scaffolding structure. These two scaffolding structures make it possible to work on the extreme front and rear walls of the tank, the moving first scaffolding structure making it possible to work on the side walls between the two end structures. 
     Preferably, the edges of the end scaffolding structures facing the end wall have respective telescopic extensions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will appear better on reading the following description of a preferred embodiment of the invention given by way of non-limiting example. The description refers to the accompanying figures, in which: 
     FIG. 1A, described above, is a longitudinal section through a ship for transporting liquefied gas; 
     FIG. 1B, described above, is a section on line B—B of FIG. 1A; 
     FIG. 1C is a cross-section through another kind of volume; 
     FIG. 2 is a cross-section view showing the carrier structure of the scaffolding system; 
     FIG. 3 is a cross-section view showing the entire scaffolding structure, the main platform being at an intermediate position; 
     FIG. 3A is a cross-section view showing the main platform in its low position; 
     FIG. 4 is a view similar to FIG. 3 showing the main platform in its high position; and 
     FIG. 5 is a plan view showing the entire scaffolding system made up of three scaffolding structures. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference initially to FIG. 5, it can be seen that in a preferred embodiment, the scaffolding system for use inside the tank  12  is constituted by three scaffolding structures There are two end structures having respective references  40  and  42  disposed respectively in the vicinity of the front wall  25  and of the rear wall  27  of the tank  12 . The scaffolding system has a third scaffolding structure  44  disposed between the structures  40  and  42 , and it could optionally have a plurality of intermediate structures. These structures  40 ,  42 , and  44  are displaceable in the direction of arrow F, i.e. in the long direction of the tank  12 , between the front and rear walls  25  and  27  thereof. For this purpose, longitudinal rails or running elements  50  and  52  are placed on the bottom  20  of the tank. These rails can be lifted to enable the bottom of the tank to be lagged. 
     Since the scaffolding structures  40 ,  42 , and  44  are substantially identical, the description below goes into greater detail for the intermediate structure  44 . 
     In shorter tanks, the scaffolding system could comprise a single scaffolding structure  44  on its own. The rails  50  and  52  must allow the gantry of said structure to be displaced along the entire length of the tank. 
     In contrast, in longer tanks, or more generally in longer volumes, a plurality of intermediate scaffolding structures identical to the structure  44  can be provided so as to reduce the total time required to take action inside the volume. 
     FIG. 2 shows the carrier portion of the scaffolding structure  44 . This is in the form of a gantry that is preferably constituted by four vertical poles, with only the poles  54  and  56  being visible. The vertical poles are interconnected close to their bottom portions by a set of horizontal beams  56 , and close to their top portions by a set of horizontal beams  58 , the assembly thus constituting a rigid gantry. The top end of the gantry is preferably fitted with a working floor  59  giving access to the ceiling  28  of the tank. 
     The width L of the gantry is slightly less than the smallest width L′ of the tank wall. In the particular case shown in FIG. 2, this smallest width L′ of the tank corresponds to the ceiling thereof. 
     As already mentioned, the bottom ends  54   a ,  56   a  of the poles are fitted with running elements for cooperating with the rails  50  and  52  and to allow the gantry to be displaced in the long direction of the tank. 
     The scaffolding structure has a main horizontal platform  60  which can be displaced vertically while being guided by the vertical poles of the gantry. The central portion of the platform  60  is constituted by a lattice structure  62  having guide elements such as  64  fixed thereto for guiding the main platform  60  in translation up and down the poles  54 ,  56 . Motor means (not shown) serve to control displacement of the main platform  60  up and down the poles  54 ,  56 . Each guide element  64  is preferably fitted with its own motor means, with all four motor means naturally being mutually synchronized so as to ensure that the main platform is displaced perfectly horizontally. It would not go beyond the ambit of the invention if only some of the guide elements  64  were to be fitted with motor means, while the other guide elements merely act as guides only. 
     Working floors are fixed to the central structure  62  of the main platform  60  and outside the zone defined by the four poles  54 . Two working floors  66  and  68  are preferably provided defining two vertically separated working levels. Top and bottom auxiliary platforms  70  and  72  are mounted on each of the working floors  66  and  68  of the main platform  60 . These auxiliary platforms can be moved horizontally relative to the working floors  66  and  68  between a retracted position in which the platforms are adjacent to the vertical poles, and an extended position in which the platforms can be as far out as the edges  66   a  and  68   a  of the working floors  66  and  68 . It will be understood that at each end of the main platform, there are two working levels  66  and  68  that are stationary and two working levels that are movable in a horizontal direction and constituted by the top and bottom platforms  70  and  72 , each of which has its own working floor. 
     Each working floor  66 ,  68 ,  70 , and  72  is preferably fitted with a telescopic extension  74  that can be moved in a horizontal direction and that is suitable for projecting beyond the outer edges of the working floors. These extensions  74  give access to the vertical walls and to the top and bottom sloping walls and they enable the positions of the working zones to be matched to the shape of the walls of the volume and to installing successive different layers of coating that are to be put into place on the walls. 
     The vertical poles  54  and  56  can be fitted with service ladders or stairways  80  and a lift or elevator  82  is provided between the top platform  60 ,  69  of the gantry and the bottom  20  of the tank. 
     The way in which such a scaffolding system is used can be seen clearly from the above description. When the main platform  60  is facing a vertical wall, the top and bottom auxiliary platforms  70  and  72  occupy positions that correspond to the outer edges of the main platform  60 . Four working levels are thus made available. When the main platform is close to the ceiling of the tank, the top auxiliary platforms  70  occupy a retracted position relative to the outer edges of the main platform, as shown in FIG.  4 . the top auxiliary platform provides a working zone for reaching the top sloping walls. In contrast, the bottom auxiliary platform  72  is naturally in alignment with the outer edge of the main platform. 
     It will be understood that when the main platform  60  is in a low position it is the bottom auxiliary platforms  72  which occupy a retracted position so as to give access to the bottom sloping walls. In contrast, the top auxiliary platform  70  is in alignment with the edge of the main platform. 
     It will be understood that because the gantry is longitudinally movable and because the main platform is vertically movable, in combination with the auxiliary platforms being horizontally movable relative to the main platform, it is possible to reach each zone of the wall of the volume by means of a working floor regardless of the shape of the wall of the volume. 
     As already mentioned, the end scaffolding structures  40  and  42  have exactly the same general structure as the scaffolding structure  44  described above with reference to FIGS. 2 to  4 . In other words, each scaffolding structure  40 ,  42  likewise comprises a gantry, a main platform, and two top auxiliary platforms together with two bottom auxiliary platforms identical to those of the structure  44 . On its side facing the adjacent end wall  25  or  27  each of them also has a telescopic extension  75 . They can also have corner extensions  77  that are telescopically mounted on a direction at about 45° relative to the displacement direction of the extensions  75 . 
     It will be understood that the scaffolding structure makes it possible to reach any zone of the wall of the volume regardless of the shape of the volume. It can also be seen clearly that the relatively small number of working floors makes it easy to handle lagging elements of large dimensions, which corresponds to the techniques now in use, in particular for the tanks of ships that transport liquefied gas.