Sealing devices
The present invention relates to sealing devices for sealing the gap between a tubular leg or a tubular piling can and a pile passing therethrough, for supporting permanent platforms at sea. 
     Permanent platforms at sea are used subsequent to drilling for oil or gas to support equipment used for delivering the oil or gas to ships or to a shore. 
     Such platforms are supported by tubular legs sometimes hundreds of feet long, and piling cans are affixed to the lower extremity of all or some of the legs. Piles are driven through the tubular legs and the piling cans into the sea bed. 
     When the piles are driven into the sea bed to the extent required, grouting cement is pumped into the annular space between each pile and its surrounding leg or can. On solidifying, the grouting cement firmly secures each leg or piling can to the pile passing therethrough, so providing a firm anchorage for the premanent platform. To prevent the grouting cement from spilling onto the sea bed before it solidifies, sealing devices are provided to seal the annular gap between each pile and its surrounding leg or can. 
     It is known to provide a sealing device for this purpose in the form of an annular pressure chamber of which the radially inner wall is constituted by a flexible cylindrical member provided with seals at its upper and lower edges to seal it to the upper and lower walls respectively of the chamber. Fluid (usually water) is pumped into the pressure chamber to bulge the flexible member radially inwardly into sealing engagement with the pile. 
     Such sealing devices have, however, not been entirely satisfactory and have suffered from the disadvantage that the seals between the flexible member and the upper or lower wall or both of the pressure chambers have failed whereby the seal with the pile has been lost and the grouting cement has leaked directly onto the sea bed. 
     It is an object of the present invention to provide an improved sealing device for sealing the gap between a tubular leg or a tubular piling can and a pile passing therethrough for supporting a permanent platform at sea. 
     According to the present invention, there is provided a sealing device for sealing the gap between a tubular leg or a tubular piling can and a pile passing therethrough for supporting a permanent platform at sea, the sealing device comprising a first part in the form of an annular sealing element and a second part, through which the pile can pass, in the form of an annular protective guard for the sealing element, both parts being coaxial with the leg or can, the guard, before a seal is made with the pile, lying between the sealing element and the pile, there being means provided which, in use, enable such relative movement in an axial direction between the guard and the sealing element, that the guard no longer protects the sealing element which is thus free to make sealing contact between the pile and the leg or can. 
     The sealing element can have a form or associated means such that it automatically makes sealing contact with the pile when the said relative movement is effected, or means can be provided whereby after the said relative movement has been effected the sealing element can then be urged into sealing contact with the pile. 
     In a preferred embodiment of the invention, the sealing element is in the form of an annular trough of which at least its inner wall diverges from the vertical so that the trough is wider at its open end that at its base, is resilient, and tends to make sealing contact with the pile, the guard, when located between the inner wall of the sealing element and the pile also serving as a constraint which distorts the said inner wall to or towards the vertical, whereby when the said relative movement is effected the said resilient inner wall springs into sealing contact with the pile. It will be appreciated that the base and the outer wall of the sealing element can also be resilient, with the outer wall, proceeding from the base, also diverging from the vertical. In order to strengthen the sealing element, an internal reinforcement of relatively stiff material, such as wire mesh, or a reinforcement as conventionally used in motor car tyres, can be provided therein. The internal reinforcement helps to prevent axial forces acting on the sealing element from the space between the pile and the leg or can from so distorting the inner wall of the sealing element that sealing contact with the pile is broken. 
     The said means for enabling relative movement between the guard and the sealing element can comprise an annular longitudinally expandable pressure chamber, located on either the axially outward side or the axially inward side of the sealing element. The outer wall of the pressure chamber is preferably coaxial with the leg or can and, advantageously, the guard, as well as protecting the sealing element, can extend axially beyond the sealing element to form the inner wall of the expandable pressure chamber. An annular ledge to which the sealing element is affixed can form one end of the pressure chamber and a similarly shaped surface affixed to the guard can form the other end. Thus by pumping a suitable medium, such as water or a cement and water slurry, into the pressure chamber, the guard, which is slidable relative to the sealing element, is made to move in an axial direction, thereby premitting the sealing element to spring into sealing contact with the pile. To assist the sealing contact between the guard and the ledge which it slides past, and between the end of the pressure chamber and the outer wall, seals in the form of two annular skirts can be provided on the inside of each end of the pressure chamber. When the air or water is pumped into the pressure chamber, the skirts are, respectively, compressed against the guard and the outer wall, so preventing the medium from leaking out of the pressure chamber. It will be appreciated that in this arrangement the guard must be imperforate along that part of its length which constitutes the inner wall of the pressure chamber. 
     As an alternative to moving the guard relative to the leg or can to free the sealing element, it would also be possible to fix the guard and move the sealing element. In this arrangement, the ledge to which the sealing element is affixed is slidable relative to the leg or can, and is attached, by means of connecting rods, to an annular piston in the pressure chamber, the walls of which are now formed by the outer wall, the guard, and an annular surface joining the guard to the outer wall. Thus by pumping the medium into the pressure chamber, the piston causes the sealing element to slide past the guard until it passes the end thereof when it then becomes free to spring into sealing contact with the pile. 
     Permanent platforms at sea, such as those used subsequent to drilling operations, are substantial structures, and the legs supporting the platforms are, as aforementioned, sometimes hundreds of feet long. Pipes running from the platform to the lower ends of its supporting legs and to the piling cans are used for pumping water or a cement and water slurry to activate the sealing devices. Also pumped through pipes is the grouting cement for filling up the annular space between each pile and its surrounding leg or can. Thus a considerable quantity of piping is necessary, there being usually six legs supporting each platform together with a larger number of piling cans. 
     According to a feature of the invention, when using a sealing device with a sealing element in the form of an annular trough, means are included in the device, for example apertures, which when the longitudinally-expandable pressure chamber is expanded such that the sealing element is free to make sealing contact with a pile located therethrough, provide fluid communication between the chamber and the annular space between the pile and its surrounding leg or can. Preferably, the apertures are provided at one end of the protective guard, being that end which prior to activation of the sealing device, covers the sealing element. 
     The sealing fluid such as grouting cement thus not only fills up the annular space, but also activates the sealing device. Only the pipe is therefore required for both operations, so halving the amount of piping necessary. 
     In another embodiment of the invention, the sealing element of the sealing device is in the form of an annular inflatable tube, and is located before a seal is made in the space between the annular protective guard and the leg or can, the arrangement being such that once the longitudinally expandable pressure chamber has been activated to remove from the sealing element the protective guard, the tube, or inflation, bulges radially inwardly forming sealing contact with the leg or can and the pile passing therethrough. The tube can be made, for example, somewhat in the form of a rubber inner tube for a pneumatic type. To inflate the tube, water, or a cement and water slurry, is pumped through a pipe connecting the tube to the permanent platform. The longitudinally expandable pressure chamber can be located, as in the sealing device using a trough-like sealing element, on either the axially inward or the axially outward side of the sealing element. 
     When using such a sealing device with a sealing element in the form of an annular inflatable tube, two pipes running from the permanent platform to the sealing device can be used; one of these carries the water or cement and water slurry to activate the pressure chamber and the other serves to inflate the tube. Alternatively a single pipe can be made to suffice for both functions. Such a single pipe is connected directly to the pressure chamber and through a check-valve to the inflatable tube. The check-valve is initially held closed by a shear-pin which is sheared and permits inflation of the tube only when the guard has been removed and further pressure builds up in the pressure chamber. The check-valve prevents subsequent deflation of the tube. A further pipe is required in both cases to carry grouting cement to the annular space between the pile and its surrounding leg or can. 
    
    
     The invention will not be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 shows scehmatically, and in elevation, part of a permanent platform at sea, used subsequent to drilling operations for oil or gas, 
     FIG. 2 shows schematically a plan view of the permanent platform of FIG. 1, 
     FIG. 3 shows a cross-sectional view to an enlarged scale of a sealing device of the type using a sealing element in the form of an annular trough, located at the lower extremity of a tubular leg of FIG. 1, 
     FIG. 4 corresponds to FIG. 3 after the sealing device has been activated to provide a seal, 
     FIGS. 5 and 6 show in corresponding inactivated and activated states an alternative arrangement of the sealing device of FIGS. 3 and 4, 
     FIG. 7 shows to an enlarged scale the sealing element of the sealing device of FIGS. 3 and 5, 
     FIG. 8 shows a cross-sectional view of a sealing device using an inflatable tube as the sealing element, and 
     FIG. 9 corresponds to FIG. 8 after the sealing device has been activated to provide a seal. 
    
    
     Referring to FIG. 1, a permanent platform 10 is supported on legs of which two are shown at 11 and 12. Attached to the lower ends of the legs are tubular piling cans 13 and 14. Piles 15, 16, 17 and 18 are driven through the piling cans and the legs into the sea bed 19 and a cement and water slurry is pumped into the spaces 20 and 21 between each pile and its surrounding leg or can. The platforms are substantial structures, for instance the distance between the platform 10 and sea level 22 can be one hundred feet or more, and the distance between sea level and the sea bed can be over five hundred feet. A pipe meeting the leg or can just above the lower extremity thereof can be used to pump grouting cement from the platform into the space between the pile and its surrounding can or leg, displacing water from the space as it is filled thereby. Sealing devices 24 are provided at the upper and lower extremities of the piling cans and at the lower extremities of the legs, to prevent the grouting cement from spilling onto the sea bed. 
     Referring to FIG. 2, which is a schematic plan view of the permanent platform 10, in practice several cans 13 are attached to the lower end of each leg 11, and piles are driven through each can into the sea bed so providing a strong anchorage for the platform. 
     Referring to FIG. 3, the sealing device 24 comprises an annular housing 25 joined to the lower extremity of a tubular leg 11. An annular protective guard 26 extends beyond the leg 11, and together with the housing 25 forms a pressure chamber 27. An annular resilient sealing element 28 is located in the chamber and is affixed at its base to an annular ledge 29. The ledge is slidable relative to the chamber and is attached to an annular piston 30 by means of connecting rods, one of which is shown at 31. The sealing element is manufactured in the form of an annular trough with its opposite walls diverging from the vertical, as shown in FIG. 7, and its inner diameter is arranged to be less than that of the pile with which it is to make sealing contact. Thus, the walls thereof, as shown in FIG. 3, are distorted substantially to a vertical position, the outer wall pressing against the housing 25 and the inner wall against the guard 26. 
     To achieve a seal between the leg and the pile, a suitable medium, such as water or a cement and water slurry, is pumped through a port 32 in the side of the housing into the pressure chamber 27 (see FIG. 4). The port is connected to the permanent platform by a pipe 33. The piston is thus forced axially outwardly moving, by means of the connecting rods, the sealing element past the protective guard. As soon as the sealing element is clear of the guard, it springs, due to the inbuilt resilience thereof, through the aperture 34 and makes sealing contact with the pile. An annular skirt 35 is provided on the piston to aid the sealing contact between it and the pressure chamber. 
     To prevent the sealing element from premature movement, a shear pin 36 (FIG. 3) is provided at the underside of the ledge 29. When the medium pumped into the pressure chamber exerts sufficient pressure, the shear pin shears and permits the sealing element to move axially outwards. 
     In accordance with a feature of the invention, circumferentially-spaced apertures 37 are provided around the lower end of the protective guard 26. As soon as the sealing element 28 makes sealing contact with the pile located therethrough, and the piston 30 reaches the end of its travel, the apertures provide fluid communication between the pressure chamber and the annular space 38 between the pile and its surrounding leg (see FIG. 4). Thus only one pipe from the permanent platform to the lower extremity of the tubular leg to which the housing 25 is attached is necessary, the grouting cement both activating the sealing device and filling the annular space. It will be appreciated that the circumferentially spaced apertures enable the grouting cement to pass itno the annular space 38 at several points. Thus the annular space is filled evenly, once the chamber has freed the sealing element from the protective guard. 
     When the tubular legs and piling cans of permanent platforms are submerged, considerable pressure is exerted on the pipe 33 and the pressure chamber. Sea water can leak past the walls of the sealing element and also past the skirt 35 to equalise the pressure within the chamber, and so fill the pipe. If this leakage should be insufficient, a one-way check valve can be provided on the pipe to allow sea water to fill it more quickly. 
     In the sealing device shown in FIGS. 3 and 4 relative movement between the sealing element and the protective guard is effected by fixing the guard and moving the sealing element. FIGS. 5 and 6 show a sealing device in which the sealing element is fixed and the guard is moved. 
     Referring to FIGS. 5 and 6, the annular pressure chamber 27 is formed by the housing 25, a fixed annular ledge 39 and the protective guard 26, there being an annular surface 40 similar in shape to the ledge 39 affixed to the upper end of the guard. The chamber is again shown on the axially inward side of the sealing element 28. The sealing element is affixed to an annular ledge 41 protruding radially inwardly from the lower end of the housing 25. The protective guard 26 is slidable, in this arrangement, relative to the housing 25 and is held centrally therein by virtue of the surface 40. 
     To operate the sealing device, water or a cement and water slurry is pumped, as before, through a port 32 into the pressure chamber 27. The chamber expands and, as it does so, it draws the guard 26 past the sealing element which thus becomes free to spring into sealing contact with the pile 15. Annular skirts 35 are provided to assist in the sealing contact between the ledge 39 and the guard 26 and between the annular surface 40 and the housing 25. Apertures 37 circumferentially-spaced around the guard enable, in similar fashion to before, grouting cement to pass directly into the annular space 38 once the chamber has been expanded. 
     It will be appreciated that in the sealing devices shown in FIGS. 3 and 5, the annular longitudinally expandable pressure chamber is shown on the axially inward side of the sealing element. This arrangement has the advantage that by means of the provision of apertures in the protective guard, only one pipe is required. However, by using two pipes, one to operate the sealing device and the other to fill the annular space between a pile and its surrounding leg or can, it would be possible for the chamber to expand when on the axially outward side of the sealing element. In such an arrangement, referring to the sealing device shown in FIG. 3, the sealing element would be moved axially inwardly past the protective guard which would be affixed to the lower end of the housing. Alternatively, referring to the sealing device shown in FIG. 5, the sealing element would be affixed to an annular ledge protruding radially inwardly from the housing, and the guard would be made to slide axially outwardly past the sealing element. In either arrangement, the principle of operation would be the same as for the previously described sealing devices. 
     Referring to FIG. 7, the sealing element of the sealing devices described is shown, to an enlarged scale, with an internal reinforcement of wire mesh 42 or any other suitable reinforcement therein. This helps to prevent axial forces acting on the sealing element, once it has made a seal with a pile passing therethrough, from so distorting the inner wall of the sealing element that sealing contact with the pile is broken. Such axial forces can be due to the pressure of grouting cement pumped into the space between the pile and its surrounding leg or piling can, especially in the case of piling cans where sealing devices are provided at each end (one being inverted relative to the other) and cement is pumped under pressure into the space confined between the two devices. 
     Referring now to FIGS. 8 and 9, according to an alternative embodiment of the invention, the sealing devices shown use a sealing element in the form of an annular inflatable tube, 43. This is located in the space below the annular pressure chamber 27. 
     To achieve a seal, water or a cement and water slurry is pumped into the pressure chamber, which is of similar construction to that shown in FIGS. 5 and 6, causing it to draw the protective guard 26 upwardly and away from the sealing element. The sealing element is then inflated by means of a suitable medium pumped through a pipe 44, thereby causing the element to bulge radially inwardly into sealing contact with the pile (see FIG. 9). Grouting cement can then be pumped into the annular space 38 through a pipe 45 and is prevented by the inflated tube from leaking onto the sea bed. 
     In a somewhat simplified form (not shown) of FIGS. 8 and 9 the pipe 33 is dispensed with and the pipe 44 is taken to the pressure chamber 27 as well as to the tube 43. A one-way check-valve is included in the entry to the tube 43 and is normally held closed by a shear pin. When, by pressure in the chamber 27, the guard has been removed, further pressure builds up in the pipe 44 causing the shear pin to break. The water or slurry then passes through the check-valve into the tube and inflates it to effect the seal. Deflation of the tube is subsequently prevented by the check-valve.