Field of the invention

The present invention relates to a gripping device for pipes according to the introduction to patent claim 1. Prior art

There are a number of antiskid attachment devices for pipes, pipe strings or other elongated objects, the purpose of which is to prevent the object from sliding in the attachment device and possibly being lost. The process of drilling for petroleum or recovering petroleum involves pushing a pipe string through a slips and a gripping device in the drill floor. The slips and the gripping device are arranged to secure the drill string in the vertical direction while pipe sections are screwed on to or unscrewed from the pipe string. If the pipe string begins to slide, the gripping device will be pulled downwards together with the pipe string, causing the slips to squeeze even harder round the pipe string. Such devices are known, for example, from Norwegian patent 315336 and the publication WO 02/075101.

A number of drawbacks have been found in the known devices. If the pipe string has a very low weight, the gripping device does not work satisfactorily, and the pipe string also slides therein. Furthermore, the gripping or friction surface against the pipe string will be subject to wear over time, and replacing this gripping surface today is a costly and time-consuming operation.

The object of the present invention is to provide a gripping device which avoids the above-mentioned drawbacks.

Summary of the invention

The present invention will become apparent from the characterising part of patent claim 1. Further preferred embodiments will be apparent in the dependent patent claims.

Detailed description

A preferred embodiment of the present invention will now be described with reference to the attached drawings, in which: Fig. 1 is a perspective view of an attachment device with a gripping device according to the invention, where the attachment device assumes a first, activated position;

Fig. 2 is a side view of the attachment device in fig. 1 ;

Fig. 3 is a side view of the attachment device in fig. 1 in a second, deactivated position;

Fig. 4a is a perspective view of a gripping arm in the gripping device according to the invention; Fig. 4b is a side view of the gripping arm in fig. 4a;

Fig. 4c is a view from above of the gripping arm in fig. 4a;

Fig. 5a is a view from above of the gripping arm where the insert is in a first extreme position;

Fig. 5b is a view from above of the gripping arm where the insert is in a second extreme position;

Fig. 6a illustrates the gripping insert viewed in the direction of the friction surface; Fig. 6b is a perspective view of the gripping insert; and Fig. 6c is a view from above of the gripping insert.

We refer to figs. 1-3 where an attachment device 1 is illustrated comprising a slips 2, a foundation plate 3 for attaching to the drill floor 4 and a guide device 5 with a gripping device 10.

The guide device 5 comprises a number of pivot joints and actuators which control the function of the attachment device 1. In a first, activated position illustrated in figs. 1 and 2, the slips is arranged grippingly round a pipe string 6 which is passed through an opening in the drill floor 4. The gripping device 10 is also arranged grippingly around the pipe string 6. If the pipe string 6 now begins to slide downwards, the gripping device 10 will be pushed in the same direction as the pipe string. This in turn causes the load transmission elements 12 in the gripping device 10 to press against the slips, pushing the wedges in the slips 2 radially inwards towards the pipe string. The engagement of the slips with the pipe string is consequently reinforced, and the sliding movement of the pipe string will cease.

The guide device 5 can also guide the attachment device 1 to a second deactivated position illustrated in fig. 3. In this position the pipe string will pass freely through the opening in the well deck. The guide device 5 can guide the gripping device 10 by means of two actuators. A first actuator 7 guides the gripping device (horizontally in figs. 1 and 2) towards and away from the pipe string 6 respectively. A second actuator 8 guides the releasable gripping movement of the gripping device 10, i.e. the movement of respective gripping arms towards and away from each other respectively.

The gripping device 10 according to the invention will now be described in detail with reference to figs. 4a-c. A gripping arm 14 is shown here with a first end 16 comprising an attachment device 18 for attaching to the second actuator 8. At an opposite end 20 the gripping arm preferably comprises a substantially cylindrical bore 22 with a gripping insert 24, which will be further described in detail below. The term "substantially cylindrical" here means that the bore 22 is cylindrical, but an opening of a certain width is provided in the bore. The function of this opening will become apparent from the description below.

At the other end 20 there is also provided a load transmission element 12, whose function is mentioned above. The load transmission element 12 protrudes downwards from the gripping arm 14 towards the slips 2. A reinforcing body 17 is preferably also provided for reinforcing the load transmission element 12.

The gripping arm 14 further comprises an opening 26 for rotatable attachment thereof to the gripping device 10. The centre axis of the opening 26 thus constitutes the axis of rotation for the gripping movement of the gripping device 10.

The gripping insert 24 comprises a cylinder 30 with an external diameter equal to the internal diameter of the substantially cylindrical bore 22, thus enabling the cylinder 30 to be mounted rotatably in the bore 22 (see fig. 6b). The cylinder 30 further comprises a slot 32, preferably in the cylinder's longitudinal direction, as illustrated in figs. 4c and 6b-c. The slot 32 is preferably of a dovetail shape designed for mounting an insert 34. It should be noted that the slot may be of other suitable shapes, such as T-shaped, or other suitable attachment devices between the cylinder 30 and the gripping insert 24 may also be employed, or they may be produced as a unit. The insert 34 is preferably made of a hard metal such as ASTM 8620 modified. The insert 34 comprises a friction surface with grooves 36 as illustrated in fig. 6. The friction surface with grooves 36 is preferably curved to match the outer shape of the pipe string 6 and radially facing the external surface of the pipe string (as illustrated in figs. 1 and 4a). The insert 34 further extends a distance from the outer periphery of the cylinder 30, forming on each side a stop 38 for the gripping insert's 24 rotating motion in the bore 22, which will be described below. It should be noted that the width of the opening in the bore 22 is greater than the width of the insert 24.

We now refer to fig. 5a where the gripping insert 24 is shown in a first extreme position, where one side of the insert 34 abuts against the edge of the opening in the bore 22. In fig. 5b the second extreme position of the gripping insert 24 is illustrated, where the second side of the insert 34 abuts against the second edge of the opening in the bore 22.

The gripping arm 14 further comprises an upper cover plate 15 (illustrated in fig. 1) which forms an enclosure of the gripping insert 24 in the gripping arm 22, with the result that the gripping insert 24 is substantially immovable in the longitudinal direction of the bore 22. Furthermore, a lubricant is applied in order to ensure the rotational movement described with reference to figs. 5a and 5b.

With the attachment device 1 with the gripping device 10 according to the invention, a good grip is obtained on a pipe string, even though it is of low weight. The flexibility achieved through the ability to move or rotate the gripping insert 24 relative to the gripping arm 14 ensures that the friction surface is at an optimal angle in relation to the pipe string, i.e. the friction surface's contact with the pipe string is as great as possible even when the pipe string is in motion or is off-centre relative to the slips. Moreover, easy replacement of the gripping insert 24 is achieved, since only the cover plate 15 requires to be removed.