Abstract:
Clamping die ( 15 ) in a device for engagement with a cylindrical body ( 4 ), which clamping die ( 15 ) includes a gripping surface ( 153 ) that is arranged to be able to extend in parallel with the center axis of the cylindrical body ( 4 ), wherein a groove ( 154 ) is provided in each of two side surfaces ( 151 ) adjacent to the gripping surface ( 153 ) and in close proximity to the gripping surface ( 153 ), said groove ( 154 ) extending substantially in parallel with the gripping surface ( 153 ).

Description:
BACKGROUND 
     The invention relates to a clamping device for temporary suspending a drill or casing string from a drill floor, in which a wedge device forms a substantially circular releasable attachment in an opening in the drill floor and is provided with a series of clamping dies having an engagement surface with variable curvature for engagement with the cylindrical tubular, and a spherical seat for support of the clamping device in the drill floor. 
     In drilling operations, e.g. exploration and production drilling for oil and gas, clamping devices are used in many situations to engage a cylindrical body, for example a pipe, in particular to suspend a drill pipe within circumscribing structures. One example of this is slips or slips means within a rotary table on a drill floor. 
     Since tubulars with different pipe diameters are used, a technique is used today where clamping dies, slips and other components that engage with the external pipe surface to retain the tubular in a firm grip, need to be replaced when changes in the external pipe diameter occurs. This is time consuming and costly, and it implies that several sets of clamping devices need to be available at a location that often suffers from lack of space. 
     When the drilling operations take place from a floating installation, e.g. a floating drill rig or a drill ship, the installation will be moved due to waves and currents in the body of water, and these motions can by a rigid connection between the clamping device and the drill floor result in that the drill string is subjected to bending loads from the clamping device. 
     The object of the invention is to assist or reduce at least one of the disadvantages of the prior art technology. 
     The object is achieved by the features that are presented in the description to follow and in the appended claims. 
     SUMMARY 
     The invention relates in one aspect to a slips means having one or more clamping dies arranged for engagement with a cylindrical body, in which each clamping die includes a clamping face with a curved form where each lateral portion of the clamping face forms a lip having preferably tapering thickness, wherein within each of the adjacent lateral surfaces are formed a groove provided in parallel with the clamping face and extend inwardly towards a central plane through the clamping die. The grooves are filled with a flexible material, e.g. polyurethane, which provides for that the rigidity of the lips increases. When the clamping face is forced against a cylindrical body having larger radius than the radius of curvature of the clamping face, the lips are forced outwardly such that the engagement surface between the cylindrical body and the clamping face increases. Thus adequate clamping force is achieved without the spot load on the cylindrical body gets unnecessary heavy. The flexibility of the lips is determined by their thickness, the material composition and type of material that is used in the grooves. 
     In a second aspect the invention relates to a spherical seat arrangement for the wedge device, where the wedge device is a slips means arranged within a rotary table associated with a drill floor. 
     In a third aspect the invention relates to a slips means which comprises a plurality of auxiliary wedges, each being arranged for slidable support of a clamping die, and where at least one of the auxiliary wedges is provided with an actuator which is arranged for displacement of the auxiliary wedge along an inclined plane. 
     The invention relates in particular to an arrangement in a clamping die for engagement with a cylindrical body, where the clamping die includes a clamping face that is arranged to be able to extend in parallel with the centre axis of the cylindrical body, wherein a groove is provided in each of two side surfaces adjacent to the clamping face and in close proximity to the clamping face, said groove extending substantially in parallel with the clamping face. 
     The clamping face is preferably curved having a centre axis in parallel with the centre axis of the cylindrical body. 
     Each of the grooves and the clamping face forms preferably a lip having substantially gradually tapering thickness from the bottom to the opening of the groove. 
     The groove is preferably filled with a flexible material different from the material of the surrounding clamping die portions of the groove. 
     The groove is preferably filled with polyurethane. 
     The clamping die is preferably arranged in a slips means, a support tong, a power tong or a back-up tong. 
     The slips means is preferably provided in a spherical seat within a rotary table of a drill floor. 
     The spherical turning surface centre of the seat is preferably arranged within or in close proximity to the rotary axis of the rotary table. 
     The slips means preferably comprises a plurality of auxiliary wedges, each being arranged for sliding support of a clamping die. 
     Preferably at least one of the auxiliary wedges is provided with an actuator which is arranged for displacement of the auxiliary wedge along an inclined plane. 
     Each of the auxiliary wedges is preferably connected to the adjacent auxiliary wedges by means of one or more carriers for synchronous motion of the auxiliary wedges. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following an example of a preferred embodiment, which is illustrated in the appended drawings, will be described, where: 
         FIG. 1  shows a perspective cross section through a rotary table that comprises a slips means according to the invention, 
         FIG. 2  shows a section through a rotary table having the slips means according to the invention; 
         FIG. 3   a  shows in a smaller scale a corresponding section as in  FIG. 2 , where a centre axis of the pipe string is coincident with the rotary axis of the rotary table; 
         FIGS. 3   b  and  3   c  shows the pipe string suspended inclined in respect of the rotary axis of the rotary table; 
         FIG. 3   d  shows the same situation as in  FIG. 3   a , but with the pipe string having smaller diameter; 
         FIG. 4   a  shows in larger scale a top view of the rotary table having a pipe string freely movable in the slips means, the wedges being retracted; 
         FIG. 4   b  is a detail view of a carrier connecting adjacent wedges in  FIG. 4   a;    
         FIG. 4   c  shows a top view of the rotary table having a pipe string suspended in the slips means, said wedges being engaged against the pipe wall; 
         FIG. 4   d  is a detail view of the carrier shown in  FIG. 4   c  with the wedges engaged against the pipe wall; 
         FIG. 5   a  shows in larger scale a cross section through the slips means when it grips around a pipe having small diameter; 
         FIG. 5   b  is a detail view of longitudinal grooves in lateral surfaces of wedges depicted in  FIG. 5   a;    
         FIG. 5   c  shows what corresponds to  FIG. 5   a , but where a pipe having larger diameter is retained by the slips means; and 
         FIG. 5   d  is a detail view of a portion of  FIG. 5   c  and generally shows flexing of lips formed by the longitudinal grooves in the lateral surfaces of the wedges when the wedges engage the larger diameter pipe. 
     
    
    
     DETAILED DESCRIPTION 
     A slips means  1  is in a per se known way arranged in a per se known rotary table  2  in a drill floor  3 , e.g. on a drill rig that is used during exploration and production drilling for oil and gas. The slips means  1  is arranged to releasably retain a cylindrical body  4 , e.g. a drill pipe or a casing. 
     The slips means  1  is provided with an annular base sleeve  11  that is secured to the rotary table  2 . The base sleeve  11  is provided with a spherical seat face  111  having radius R and with its centre located in the centre axis of the rotary table and in close proximity to the upper level of the rotary table  2 . 
     A carrying sleeve  12  is arranged internally of the base sleeve  11 , and a spherical support surface  121  is complementary to the seat face  111  of the base sleeve  11 . The carrying sleeve  12  has an outer diameter that is slightly smaller than the internal diameter of the base sleeve  11 , so that the carrying sleeve  12  thereby can be turned about the centre for the spherical seat face  111  with the consequence that the centre axis of the carrying sleeve  12  is not coincident with the centre axis of the base sleeve  11  and the rotary table  2 . 
     The carrying sleeve  12  is internally provided with totally six inclined first sliding surfaces  122  having centralized first dove tail grooves  122   a . The sliding surfaces  122  are in the position of use of the slips means  1  inclined from top to bottom in the direction inwardly toward the centre axis of the carrying sleeve and with a centre line that is coincident with the first centre line of the dove tail groove  122   a  and is placed in a plane coincident with said centre axis. 
     Each sliding surface is arranged for receipt of an auxiliary wedge  13  having lateral surfaces  131  and a first bottom surface  132  and a top surface  133  which converge in the direction downwards and towards the centre axis of the carrying sleeve  12 . The lateral surfaces  131  converge towards the top surface  133 . The first bottom surface  132  is provided with an elongated first dove tail  132   a  complementary to the first dove tail groove  122   a.    
     Every second auxiliary wedge is connected to the base sleeve  11  by means of an actuator  14 , here shown as a hydraulic cylinder. Each auxiliary wedge  13  is connected to their adjacent auxiliary wedges  13  by a carrier  134  in the form of a pin  134   a  that projects from a lateral surface  131  of the auxiliary wedge  13  and engages slidable into a complementary recess  134   b  in opposing lateral surface  131  of the adjacent auxiliary wedge  13 . Thus a direct displacement of an auxiliary wedge  13  along the sliding surface  122 , by operating the actuator  14 , results in that the adjacent auxiliary wedges  13  that are not directly connected with an actuator  14 , move synchronous with the actuator  14 . The operation of all the actuators  14  takes place simultaneously and at the same speed, and thus all the auxiliary wedges  13  move synchronous. 
     In the top surface  133  of the auxiliary wedge  13  a second dove tail groove  133   a  having a centre line is provided, which is located in a plane coincident with the centre axis of the carrying sleeve  12 . 
     A wedge shaped clamping die  15  is provided with two lateral surfaces  151  and a second bottom surface  152  and an opposing clamping face  153  which together converge in the direction downwardly and towards the centre axis of the carrying sleeve  12 . The lateral surfaces  151  converge towards the clamping face  153 . The second bottom surface  152  is provided with an elongated second dove tail  152   a  complementary to the second dove tail groove  133   a  in the top surface  133  of the auxiliary wedge  13 . 
     The clamping face  153  of the clamping die  15  is concavely curved having axis direction coincident with the centre axis direction of the carrying sleeve  12 . In each of the two lateral surfaces  151  and in close proximity to the clamping face  153 , a groove  154  is provided that extends substantially in parallel with the clamping face  153  in the entire longitudinal extension of the clamping die  15 . Each of the grooves  154  and the clamping face  153  thus defines a lip  155 . The width of the groove  154  is decreasing towards the bottom of the groove. 
     Each of the grooves  154  is filled with a flexible material  156 , typically polyurethane, having elasticity considerably different from the material of the clamping die parts surrounding the grooves  154 . 
     When the slips means  1  is inactive, the auxiliary wedges  13  are retracted, i.e. all the way up into the carrying sleeve  12  and within the central opening of the rotary table  2  a cylindrical body  4 , e.g. a drill pipe, can freely be installed or displaced. When the drill pipe  4  is to be retained, the auxiliary wedges  13  are displaced by means of the actuators  14  downwardly and inwardly until the clamping face  153  of the clamping dies  15  engage the drill pipe  4 . By the sliding motion of the clamping die  15  against the inclined top surface  133  of the auxiliary wedge  13 , a pipe that is suspended in the rotary table  2  will pull the clamping dies downwardly, such that the grip or engagement with the drill pipe  4  is enhanced. 
     The spherical seat face  111  in the base sleeve  11  and the corresponding support surface  121  that the carrying sleeve  12  abuts the base sleeve  11  with, results in that the centre axis of the slips means and thus the centre axis of the retained cylindrical body  4  can adopt a direction that deviate from the centre axis of the rotary table  2  without adding a bending load to the body  4 , for example when a drilling vessel is rolling due to waves. 
     The lips  155  of the clamping dies that define the clamping face  153  in axial direction form flexible lateral portions in the clamping faces. When the clamping die abuts a cylindrically designed body  4  having larger diameter than the diameter of curvature of the clamping face  153 , the lips  155  will yield or give away, and the engaging surface between the clamping die  15  and the cylindrically formed body  4  increases and results in less surface pressure and thus less risk for deformation of the body  4  than if clamping dies according to the prior art that have less diameter of curvature than the diameter of the body  4  is used. 
     The flexible material  156  provides for that the rigidity of the lips  155  increases. Thus the depth of the grooves  154  can be increased, and the lip  155  can be made larger in order to further improve the properties of the clamping faces  153 .