GB2308082A - Pipe straightener - Google Patents

Description

PIPE STRAIGHTENER The invention relates to a pipe straightener for removing the residual curvature (elastic spring back) of a pipe which is unwound from a reel on which the pipe has been coiled into plastic deformation, and is particularly concerned with such a pipe straightener for use on an offshore pipe laying vessel to straighten a continuous length of coated steel pipe which is unwound under tension from a large diameter storage reel prior to being guided overboard to be laid as a pipeline on the seabed.

Generally, such straighteners comprise a fixed frame which is rigidly mounted on the vessel, and a succession of grooved rollers or sheaves which are mounted on the frame and are designed to guide and act on the pipe as it is drawn through the straightener so as to exert a reverse bending moment on the pipe sufficient to cancel out the residual curvature possessed by the pipe as a result of having been coiled into plastic deformation on the storage reel. Such straighteners are usually purpose built for a specific pipe laying operation, and therefore tend not to be very adaptable.

According to the invention there is provided a pipe straightener for removing the residual curvature of a pipe which is unwound from a reel on which the pipe has been coiled into plastic deformation, comprising at least three substantially identical modules, each module having a support frame on which at least one sheave is mounted so that it is adjustable in position between opposite ends of the frame in a linear direction substantially perpendicular to the rotational axis of the sheave the modules being mounted side by side so that their frames are rigidly fixed relative to each other and the median planes of their sheaves lie substantially in a common plane perpendicular to the rotational axes of the sheaves.

In use, the sheave or sheaves of each module is adjusted in position relative to the ends of the frame so that the sheaves of successive modules will act on a pipe on opposite sides of its axis so as to exert a desired reverse bending moment on the pipe as it is drawn through the straightener.

Preferably the modules will be mounted so that an intermediate module between two other modules is inverted with respect to the two other modules.

The modular construction of the pipe straightener in accordance with the invention enables the spacing between the modules, and hence the spacing between the sheaves of successive modules in the direction of movement of a pipe through the straightener, to be adjusted and set as desired in order to reduce and achieve a better balance of the sheave contact pressure so as not to damage the surface of the plastic or other material coating the pipe.

Also, since the sheaves are adjustable in position on each module in a direction substantially perpendicular to the direction of pipe movement the straightener can readily be set up for use with a variety of different pipe diameters and bends without having to make the straightener unduly complex. Furthermore, as will become clearer later, the straightener can also be set up for pipes which are unwound from either the top or the bottom of a vertically mounted storage reel (i.e. a storage reel mounted for rotation about a horizontal axis).

By way of example, one embodiment of a pipe straightener in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of the pipe straightener arranged for removing residual curvature from a pipe which is unwound from the top of a vertically mounted storage reel; Figure 2 is a view similar to Figure 1 but showing the pipe straightener arranged for removing residual curvature from a pipe unwound from the bottom of a vertically mounted storage reel; Figure 3 is a front view of one of the modules of the straightener; Figure 4 is a vertical section through the module taken on the line A-A in Figure 3; and, Figure 5 is a horizontal section through the module taken on the line B-B in Figure 3.

The pipe straightener shown in Figures 1 and 2 comprises three identical modules 1 which are mounted in an upright condition and side by side in the direction which the pipe 2 to be straightened is drawn through the straightener.

As shown in Figures 3 to 5, each module 1 comprises a rectangular support frame 3 formed by two similar, horizontal H-shaped sub frames 4,5 at opposite ends forming the base and the head of the upright module, a pair of upright rear frame members 6,7 interconnecting the two H-shaped sub-frames 4,5 at the rear end of each leg thereof, and a pair of cross-members 8,9 interconnecting the legs of each H-shaped sub-frame 4,5 at their rear ends and extending parallel to the central cross-bars 4a, 5a of the sub-frames. The frame 3 is thus open at the front and at each side in front of the upright rear frame members 6,7.

Attached to the front of each rear frame member 6,7 is a respective member 10,11 which forms, with the rear frame member, a guide channel 12, 13 which opens laterally inwards and extends from the end sub-frame 4 to a position just over half way along the rear frame member 6,7 towards the other end sub-frame 5.

Each module 1 also comprises a pair of sheaves 14,15 for engaging the periphery of a pipe 2 to be straightened, the sheaves being rotatably mounted in a rectangular sheave cage 16 which is mounted substantially horizontally on the support frame 3 and is adjustable in position between the two end sub-frames 4,5 in a direction substantially parallel to the upright rear frame members 6,7. The sheave cage 16 is open at the top and bottom, and has a mounting pin 17 extending perpendicularly between the front and rear sides of the cage at a position mid-way between the ends of the cage and near the top. The mounting pin 17 is pivotally connected to the upper end of a jack 18 which has its lower end pivotally mounted centrally on the central cross-bar 4a of the end sub-frame 4.The jack 18 serves to adjust the vertical position of the sheave cage 16, and hence the sheaves 14,15, and the cage 16 is guided and steadied relative to the support frame by means of flanges 19,20 which extend from the opposite ends of the cage at the rear thereof and are received in the guide channels 12,13. In addition, each flange 19,20 carries a pin l9a,20a which is slidably received in a vertical slot 10a,11a in the respective channel forming member 10,11.

The two sheaves 14,15 are identical and are mounted in the cage 16 for rotation in a common plane about parallel axles 14a,15a which extend perpendicularly between the front and rear sides of the cage 16 at positions substantially mid-way between the central jack 18 and the opposite ends of the cage. The peripheries of the sheaves project from the open top and bottom of the cage 16 and are preferably shaped to match the pipe to be straightened and to engage a 120 arc of the circumference of the pipe. For this purpose, each sheave 14,15 may be provided with a replaceable tyre which can be changed to suit different diameter pipes.

In the pipe straightener arrangement shown in Figure 1, the two outer modules 1 are mounted with the end sub-frame 4 as the base, so that their sheaves 14,15 are arranged to contact the underside of the pipe 2 as it is drawn through the straightener, and the central module 1 is inverted so that it is mounted with its end sub-frame 5 as the base and its sheaves 14,15 are arranged to engage the upper side of the pipe 2. The modules 1 are rigidly fixed to the deck of the laying vessel and possibly also to each other, with the spacing between the modules and the positions of their sheave cages 16 relative to the respective end sub-frames 4 being adjusted to suit the dimensions and characteristics of the pipe 2 and its coating and the residual curvature which is to be removed from the pipe.

The positioning of the sheave cage on each module is critical to the operation of the pipe straightener and a high degree of accuracy (preferably to within 1 mm) in the setting and maintenance of the position is necessary. Accordingly, the jack 18 is preferably a screw jack, which can rest on its self-locking threads when the required setting is reached. The jack 18 may be mechanically, electrically or hydraulically operated.

Furthermore, each module 1 is preferably provided with position indicating means which shows the vertical setting of the cage 16.

For example, this may be provided by means of a scale on the members 10,11 adjacent the slots lOa,lla, and a position marker on the pins 19a,20a which are located in the slots.

The use of two sheaves instead of one on each module serves further to reduce stresses in the wall and coating of the pipe being straightened, and the pivotal mounting of the cage 16 on the jack 18 ensures equal load distribution to the two sheaves 14,15. Each sheave may be permitted a degree of lateral play on its axle to accommodate horizontal pipe deformations and installation tolerances.

The open front and sides of the frame 3 of each module allows easy access of the pipe to the straightener and allows the pipe line end terminations to be brought through the straightener.

The pipe straightener arrangement shown in Figure 2 is simply the inverse of the arrangement in Figure 1, the two outer modules being mounted with the end sub-frame 5 as the base so that their sheaves 14,15 are arranged to contact the upper side of the pipe 2 as it is drawn through the straightener, and the central module being mounted with its sub-frame 4 as the base so that its sheaves 14,15 are arranged to contact the underside of the pipe 2.

As mentioned earlier, the pipe straightener shown in Figures 1 and 2 is arranged to remove the residual curvature from a pipe unwound from a vertically mounted storage reel, but it will readily be appreciated that it can also be used to straighten a pipe unwound from a horizontally mounted storage reel (which rotates about a vertical axis) simply by turning the modules 1 through 900 so that the rear frame members 6 and 7 form the base.

Claims (11)

1. A pipe straightener for removing the residual curvature of a pipe which is unwound from a reel on which the pipe has been coiled into plastic deformation, comprising at least three substantially identical modules, each module having a support frame on which at least one sheave is mounted so that it is adjustable in position between opposite ends of the frame in a linear direction perpendicular to the rotational axis of the sheave, the modules being mounted side by side so that their frames are rigidly fixed relative to each other and the median planes of their sheaves lie substantially in a common plane perpendicular to the rotational axes of the sheaves.

2. A pipe straightener according to claim 1, comprising three modules in which the central module is inverted with respect to the other two.

3. A pipe straightener according to claim 1 or claim 2, in which the sheave or sheaves of each module is or are rotatably mounted in a sheave cage which is adjustable in position in the linear direction and is guided by guide means on the support frame.

4. A pipe straightener according to claim 3, in which the sheave cage is adjusted in position by means of a jack acting between the cage and one end of the support frame.

5. A pipe straightener according to claim 4, in which the sheave cage carries two sheaves and is pivotally connected to the jack so as to equalise the load distribution to the sheaves.

6. A pipe straightener according to claim 4 or claim 5, in which the jack is a screw jack.

7. A pipe straightener according to any one of the preceding claims, in which each module includes means for indicating the position of the sheave or sheaves between the ends of the frame.

8. A pipe straightener according to any one of the preceding claims, in which the support frame of each module comprises a pair of sub-frames at opposite ends by which the module can be mounted in an upright position on either end, and frame members interconnecting the two end sub-frames at one edge thereof so that when the module is upright and the frame members are at the rear, the module is open at the front and at each side.

9. An invertable pipe straightener module comprising a support frame which comprises a pair of sub-frames at opposite ends by which the module can be mounted in an upright position on either end, and frame members interconnecting the two end sub-frames at one edge thereof so that when the module is upright and the frame members are at the rear, the module is open at the front and at each side, and at least one sheave which is mounted on the support frame so that it is adjustable in position between the opposite ends of the frame in a linear direction perpendicular to the rotational axis of the sheave.

10. A pipe straightener module according to claim 9, substantially as described with reference to Figures 3 to 5 of the accompanying drawings.

11. A pipe straightener according to claim 1, substantially as described with reference to the accompanying drawings.