GB2448919A

GB2448919A - Cutting Apparatus

Info

Publication number: GB2448919A
Application number: GB0708570A
Authority: GB
Inventors: George Silk
Original assignee: Mirage Machines Ltd
Current assignee: Mirage Machines Ltd
Priority date: 2007-05-03
Filing date: 2007-05-03
Publication date: 2008-11-05
Also published as: WO2008135747A2; WO2008135747A3; GB0708570D0

Abstract

Apparatus for cutting through a pipe wall under water, as in decommissioning an offshore structure, has a body 16 which can be lowered down the pipe 10 and then locked in position, and a cutting head 20 at the bottom of the body with a toothed disc-like blade 52 which can be advanced radially into contact with the pipe wall and rotated about its own axis to cut through the pipe wall. The cutting head is then rotated and makes one revolution to cut right through the pipe wall to separate an upper pipe section from a lower pipe section. To keep the cut open as cutting proceeds, wedges 62 are fired into the cut around the pipe as the cutting head rotates and leaves an open cut behind it.

Description

Cutting Apparatus This invention relates to cutting apparatus and in

particular to apparatus for the cutting of pipes, where a pipe is to be divided into two pipe lengths One particular application is the cutting of underwater pipes or pipes when an offshore oil or gas rig or platform has to be decommissioned and removed from site.

Offshore structures will have production conductor pipes and, in many cases, platform legs extending from the structure above sea level, through the sea and into the sea bed where they are typically drilled or piled and cemented in place during installation. When the structure is to be removed, the pipes have to be cut at or below the sea bed (known as the mudline) to divide the pipe into a part which remains in the sea bed and a part which extends from the mudline to the structure and which can then be removed.

Many processes have been proposed to enable this cutting to take place For example, US Patent Specification 4,389,765 discloses a unit for cutting through piling sections, from inside the pile. Two cutting disks rotate around the axis of the pile to gradually cut through the pile wall.

According to the invention, there is provided a method of cutting a tubular wall using a cutting head which has a disc-like cutting blade wherein the blade is advanced in a generally radial direction into cutting contact with the wall, the blade is driven in rotation about its own axis to make a cut right through the wall, the cutting head is then rotated about the axis of the tubular wall to make a cut right through the wall in a single pass, and wedges are placed in the cut as the cutting progresses to keep the cut open as the blade moves around the circumference of the wall The cutting head is preferably located inside the tubular wall and cuts from inside to outside, but it is also possible for the cutting head to be located outside the tubular wall and to cut from outside to inside.

The cuthng blade will have a series of teeth around its circumference, and the teeth may be arranged with a first set of teeth having tips lying on a first pitch circle and a second set of teeth having tips lying on a second pitch circle smaller than the first pitch circle, with the second teeth interspersed between the first teeth, and the second teeth having a greater thickness (axial dimension) than the first teeth.

Arranging the blade teeth in this way allows the cutting to be done by the first teeth, with the second teeth following in the cut to remove swarf. Typically, the first teeth may have a thickness of 4 mm with the second teeth having a thickness of 6 mm.

The wedges can be placed into the cut, behind the blade, to keep the cut open and to prevent binding on the blade. The wedges can be fired or pushed into the cut so that they are held in place in the cut by friction and, as the cut progresses, by the weight of the pipe above the cut.

The invention also provides apparatus for cutting through a pipe wall to separate the pipe into two pipes, the apparatus comprising a body for insertion within the bore of the pipe to be cut, means for securing the body against the internal pipe wall, and a cutting head mounted on the body, wherein the cutting head comprises a disc-like blade, means for driving the blade in rotation about an axis generally parallel to the pipe axis, means for advancing the blade axis radially towards the pipe wall so that the blade Cuts right through the pipe wall, and means for driving the blade around the circumference of the pipe.

The cutting head preferably includes means for inserting wedges in the cut made by the blade, as the blade travels around the circumference of the pipe. The wedge inserting means may comprise a magazine which holds a number of wedges, a firing bay, means for advancing wedges into the firing bay, and a piston for firing wedges from the firing bay radially outwardly into the cut made by the blade.

The means for securing the body in the pipe wall comprises a set of radially movable jaws, retained on the body by leaf springs, and actuable to move outwardly into contact with the pipe wall by means of wedges arranged between the jaws and the body.

The blade is preferably mounted on a spindle, and the spindle is mounted in a spindle body, with a drive motor associated with the body, to drive the blade in rotation. The spindle body is mounted on a slideway and a second motor controls movement of the spindle body along the slideway, in a generally radial direction.

The second motor can drive the spindle body through a feed screw The slideway itself can be mounted on the cutting head base plate in different positions, in accordance with the diameter of the pipe to be cut, to give the necessary available stroke for the movement on the shdeway between a position where the blade is not in contact with the pipe wall, and a position where the blade has penetrated nght through the pipe wall.

The cutting head is driven in rotation as a unit, and the drive for the head may be located at the end of the body opposite to that where the cutting head itself is located.

The various motors and actuators within the apparatus will preferably be hydraulically operated, and there may be a single hydraulic feed to the body and manifolds within the body to direct hydraulic fluid pressure to different components of the apparatus.

According to a further aspect of the invention, there is provided a cutting blade for slitting a metal wall, the blade having a series of teeth around its circumference, the teeth being arranged with a first set of teeth having tips lying on a first pitch circle and a second set of teeth having tips lying on a second pitch circle smaller than the first pitch circle, with the second teeth interspersed between the first teeth, and the second teeth having a greater thickness (axial dimension) than the first teeth, Preferably first and second teeth alternate around the blade circumference, but it may be possible to have, for example, three first teeth followed by one second tooth followed by three first teeth and so on around the circumference, The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view showing pipe cutting apparatus according to the invention in place in a pipe to be cut; Figure 2 is a perspective view of a body of the apparatus of Figure 1; Figure 3 is an end view of the body of Figure 2, taken on the right hand end of the body; Figure 4 is an axial section on the lines A-A from Figure 3, Figure 5 is an elevation corresponding to the section of Figure 4; Figure 6 is a partial section taken on the lines B-B from Figure 3; Figure 7 is a perspective view of the cutting head; Figure 8 is a view of the cutting head of Figure 7 but taken from the opposite side of the mounting plate; Figure 9 is a view similar to Figure 8 but taken from a different angle, and with the wedge dispenser removed; Figure 10 is a view similar to Figure 9 but taken from a different angle; Figure 11 is a section through the blade advance slide guide; Figure 12 is a section through the wedge deployment device; and Figure 13 is a view of the wedge deployment device taken in the direction of the arrow X in Figure 12.

Figure 1 illustrates the primary application for which the present invention is intended. A pipe 10 is shown in section. This pipe is part of an offshore oil or gas production installation and the pipe 10 is embedded in the seabed 12.

When the structure is to be dismantled and removed from the seabed, it is necessary to cut the pipes 10 which are cemented into the seabed, so as to leave seabed free of obstructions. The pipe should be cut just below the mudline 14.

To cut the pipe, a body 16 is lowered down the pipe until it reaches the correct position adjacent the mudline, Expanding arms 18 then expand to lock the body 16 in position within the pipe, and a cutting head 20 is then activated to cut through the pipe wall, as indicated by dotted lines 22. Once the cut is completed, the upper half of the pipe can be lifted away from the seabed, leaving the seabed unobstructed.

The body 16 is lowered down the pipe on a supporting cable, with the necessary hydraulic supply line indicated schematically at 24.

Figures 2 to 6 show the body 16 in more detail. The body has bump strips 26 spaced evenly around the circumference, at a diameter slightly less than the diameter of the pipe in which the body will be deployed. Between the bump strips 26 there are radially extendable jaws 28 which can be driven radially outwards to secure the body in a pipe. The jaws are retained on sprung retention wires 30 extending between the bump strips 26, and the pipe has a central hollow cylinder 32.

At one end, the body has an end plate 34, and a drive off take 36 can be seen mounted eccentricafly on that end plate 34.

Figure 3 shows the jaws 28 in their non-extended position, and the retaining wires extending in a straight line between adjacent bump strips 26.

Figure 4 shows the jaws 28 in cross-section. Surrounding the inner cylinder 32, there are expanding rings 38, 40 The rings 38 are fixed, but the rings 40 can be advanced towards the fixed rings 38 to cause the jaws 28 to be forced outwards, as a result of the co-operation between the wedge surfaces of the jaws 28 and of the rings 38, 40. The sliding rings 40 are biased by hydraulic cylinders 42, and in Figure 4 two such cylinders are shown, one activating the left hand sliding rings 40 and the other activating the right hand sliding rings 40 The cutting head 20 shown in Figure 2 is mounted on a mounting plate 44 which is fixed to a drive tube 46 extending through the cylinder 32. At the right hand end (Figure 4) the drive tube has an annular gear 48 which engages with a pinion (not shown) driven by a hydraulic motor 50. The motor 50 thus rotates the cutting head on an axis of rotation coaxial with the body 16.

Figures 7 to 10 show the cutting head 20. It will be seen that the head has a mounting plate 51, with a cutting blade 52, and a wedge deployment device 54. It can be seen from this figure that the blade 52 is mounted on an axis 56, and this axis can slide in a radial direction on guide slides generally indicated at 58. When the cutting head is in operation, the blade 52 will be advanced radially outwards to allow the teeth of the blade to make contact with and cut right through the wall of the pipe 10.

The wedge deployment device has a magazine 60 storing about fifteen wedges 62. Details of the operation of the wedged deployment device will become apparent from the following discussion.

Figure 8 shows the cutting head 20 from the opposite side of the mounting plate 50. It will be seen here that two hydraulic motors are provided. The first motor 64 drives the blade 52 in rotation and the second motor 66 is responsible for advancing the blade axis 56 in a radial direction. A piston/cylinder unit 68 is operated to bring the next wedge from the magazine 60 into the firing position.

The motor 66 drives a feed screw 70 (Fig 9) which engages with a feed nut 72 to advance a carriage 74 which supports the motor 64 and the cuthng blade 52. This carriage can be seen particularly clearly in Figure 9. The advancing mechanism for the radial movement of the blade axis 56 also has a secondary adjustment with a fixed slide guide 80 and a movable slide 82 connected to the guide with a dovetail engagement. The relative radial positron of the guide 80 and the slide 82 will be set before the body is lowered into the pipe to be cut, in accordance with the pipe diameter and wall thickness, to ensure that the available stroke controlled by the motor 66 is sufficient to enable the blade to be advanced to cut right through the pipe wall.

The motor 66 drives the feed screw 70 through a transfer box 71.

Figures 12 and 13 show the wedge deployment mechanism which is also shown in Figures 7 and 8 and which locates on the mounting plate 51 where indicated at 84 in Figure 10. As will be seen from Figure 13, the wedge deployment mechanism is located partly above and partly below the mounting plate 50. Figure 13 shows one wedge 62 in position ready to be fired, and the wedge will be fired from this position by activation of a firing cylinder 86. Once that wedge has been fired, a further wedge will be advanced from the magazine 60 into the firing position, and this will be done by retracting the piston of a cylinder 68 which pivots a pivot arm 88 about a pivot axis 90 to raise the stack of wedges 62 so that the top one reaches the firing position where it is gripped by spring-loaded plungers (not shown). The cylinder 68 is then again operated to allow the rest of the wedges to be returned to the magazine 60 until it is their turn to be fired.

In use, once the body has been located in the appropriate place in the pipe, and locked in place using the jaws 28, the motor 66 will drive the feed screw 70 to advance the blade 52, which is being rotated by the motor 64, until the teeth of the blade make contact with the inner surface of the pipe. The teeth first have to cut sufficient material from the pipe wall to penetrate right through the pipe wall, and once full penetration has been achieved the cutting head 20 can start to rotate to cause the pipe wall to be cut all the way around.

To prevent the saw cut from closing up and jamming the blade 52, wedges 60 are fired into the cut at intervals, once the cut has been established by the blade. The wedges will then keep the cut open and therefore prevent the weight of the pipe binding on the saw blade.

It is also a feature of the apparatus described that the blade 52 has a unique configuration, with some of the teeth (the first teeth) being design ed make the cut into the metal pipe wall and others of the teeth (the second teeth) being designed to open up the cut and remove swarf as the cut proceeds. The second teeth are on a smaller pitch circle than the first teeth, so that they do not come into contact with the pipe wall until the first teeth have bitten into the wall a certain distance, but they are thicker, ie have a greater axial dimension, so that when they do enter the cut, they clean the cut out and remove swarf before the wedges are fired into the cut.

A blade of this type can be used in other applications, where a metal surface is to be cut or slit, especially underwater applications.

Claims

1. A method of cutting a tubular wall using a cutting head which has a disc-like cutting blade wherein the blade is advanced in a generally radial direction into cutting contact with the wall, the blade is driven in rotation about its own axis to make a cut right through the wall, the cutting head is then rotated about the axis of the tubular wall to make a cut right through the wall in a single pass, and wedges are placed in the cut as the cutting progresses to keep the cut open as the blade moves around the circumference of the wall.

2. A method as claimed in Claim 1, wherein the cutting head is located inside the tubular wall and cuts from inside to outside.

3. A method as claimed in Claim 1, wherein the cutting head is located outside the tubular wall and cuts from outside to inside.

4 A method as claimed in any preceding claim, wherein the cutting is carried out underwater.

5. A method as claimed in any preceding claim, for cutting a tubular wall of an underwater pipe of an offshore structure.

6. A method as claimed in any preceding claim, wherein the wedges are placed into the cut behind the blade, to keep the cut open and to prevent binding on the blade.

7. A method as claimed in any preceding claim, wherein the wedges are fired into the cut so that they are held in place in the cut by friction and, as the cut progresses, by the weight of the pipe above the cut.

8. Apparatus for cutting through a pipe wall to separate the pipe into two pipes, the apparatus comprising a body for insertion within the bore of the pipe to be cut, means for securing the body against the internal pipe wall, and a cutting head mounted on the body, wherein the cutting head comprises a disc-like blade, means for driving the blade in rotation about an axis generally parallel to the pipe axis, means for advancing the blade axis radially towards the pipe wall so that the blade cuts right through the pipe wall, and means for driving the blade around the circumference of the pipe.

9 Apparatus as claimed in Claim 8, wherein the cutting head includes means for inserting wedges in the cut made by the blade, as the blade travels around the circumference of the pipe.

10. Apparatus as claimed in Claim 9, wherein the wedge inserting means comprises a magazine for holding a number of wedges, a firing bay, means for advancing wedges into the firing bay, and a piston for firing wedges from the firing bay radially outwardly into a cut made by the blade.

11. Apparatus as claimed in any one of Claims 8 to 10, wherein the means for securing the body in the pipe wall comprises a set of radially movable jaws, retained on the body by leaf springs, and actuable to move outwardly into contact with the pipe wall by means of wedges arranged between the jaws and the body

12. Apparatus as claimed in any one of Claims 8 to 11, wherein the blade is mounted on a spindle, and the spindle is mounted in a spindle body, with a drive motor associated with the body, to drive the blade in rotation

13. Apparatus as claimed in Claim 12, wherein the spindle body is mounted on a slideway and a second motor controls movement of the spindle body along the slideway, in a generally radial direction

14. Apparatus as claimed in Claim 13, wherein the second motor drives the spindle body through a feed screw -11 -

15. Apparatus as claimed in Claim 13 or Claim 14, wherein the slideway itself can be mounted on the cutting head base plate in different positions, in accordance with the diameter of the pipe to be cut, to give the necessary available stroke for the movement on the slideway between a position where the blade is not in contact with the pipe wall, and a position where the blade has penetrated right through the pipe wall.

16. Apparatus as claimed in any one of Claims 8 to 15, wherein the cutting head is driven in rotation as a unit, and the drive for the head is located at the end of the body opposite to that where the cutting head itself is located.

17. Apparatus as claimed in any one of Claims 8 to 16, wherein the motors and actuators within the apparatus are hydraulically operated, and there is a single hydraulic feed to the body and manifolds within the body to direct hydraulic fluid pressure to different components of the apparatus.

18. Apparatus as claimed in any one of Claims 8 to 16, wherein the motors and actuators within the apparatus are electrically operated

19. A cutting blade for slitting a metal wall, the blade having a series of teeth around its circumference, the teeth being arranged with a first set of teeth having tips lying on a first pitch circle and a second set of teeth having tips lying on a second pitch circle smaller than the first pitch circle, with the second teeth interspersed between the first teeth, and the second teeth having a greater thickness (axial dimension) than the first teeth

20. A blade as claimed in Claim 19, wherein first and second teeth alternate around the blade circumference.

21 Apparatus for cutting through a pipe wall substantially as herein described with reference to the accompanying drawings.