GB2394694A

GB2394694A - Submarine saw

Info

Publication number: GB2394694A
Application number: GB0225318A
Authority: GB
Inventors: Ronald Wraith
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-10-31
Filing date: 2002-10-31
Publication date: 2004-05-05
Anticipated expiration: 2022-10-31
Also published as: GB2394694B; GB0225318D0

Abstract

A submarine saw 10, for cutting a pipe (Fig 2,11), having a band saw blade 12 is disclosed. The saw also has guide means 14, 16 and 18 and a drive means which cause the blade 12 to move along a continuous path. The path includes a linear first portion A through which band saw blade 12 passes in direction B, and a second linear portion C through which blade 12 travels in direction D. Sections A and C are parallel to each other and separated by a distance E which is less than the diameter of the smallest circle partially defined by the tightest bend of said path. A blade tension adjuster 24 causes guide means 14 to move relative to drive means 20 and thereby adjust the tension in blade 12. Drive means 20 is driven by hydraulic motor (Fig 2,32) via gearings (Fig 2,34) and drive shaft (Fig 2,36).

Description

-1 SUBMARINE SAW

The present invention relates to a saw and particularly, but not exclusively, to power saws for use under water.

During the installation and maintenance of sub-sea pipe work, for example as used by the gas and oil industries, it is often necessary to cut such pipes where they are located on the sea bed. In particular it may be necessary to cut a section of pipe from an extremely long pipe which forms part of a network of pipes. Typically the saw presently used to cut such a pipe would be a diamond coated wire band saw. This type of saw has a continuous loop of diamond coated wire which is driven around a path by one or more drive wheels and one or more free spinning guide wheels.

A portion of the path is exposed and the wire rotating through the path a high speed is brought into contact with the pipe being cut. This form of saw suffers from the disadvantage that, when in contact with the pipe, the wire blade applies a torque to the pipe attempting to rotate the pipe around its axis. This in fact manifests itself in the saw attempting to rotate around the pipe and requires that the saw be firmly fixed and stabilized relative to the pipe. However, this torque also increases the likelihood of the wire blade becoming jammed in the cut and when this happens the torque attempting to rotate the saw around the pipe is significantly increased and can result in the saw moving relative to the pipe and therefore requiring realigning with the pipe in order that a clean cut is completed. In extreme examples the saw and pipe may even become separated during the cutting process. Furthermore, this jamming may result in damage to the drive wheels and/or the power source driving this wheel.

Alternatively it will require that the power source is protected by a complex protection system.

Japanese patent publication No JP 08-090336 also describes a cutting device. This device utilises a band saw to cut parts of

-2 a nuclear reactor, including pipes, into smaller more manageable pieces for disposal. The device described therein is not suitable for cutting sections from long lengths of pipe and is specifically designed for cutting pipe into chunks for disposal.

Although not typically used for submarine cutting of the type described, above a device which may be used for cutting smaller pipes is a single blade reciprocating saw. Such a saw suffers from the disadvantage that as the motion of the saw slows and changes direction the blade and in turn the cutting device powering the movement of the blade are inclined to jump. This results in a less even cut and in particular the jumping of the blade increases the likelihood of its jamming which may result in damage to the blade. The uneven movement of the blade, jamming and jumping, applies additional strain and indeed may damage the drive means of the blade.

Preferred embodiments of the present invention seek to overcome the above described disadvantages of the prior art.

According to the present invention there is described a saw comprising: cutting means in the form of a continuous flexible blade; guide means for causing said cutting means to move along a continuous path; and drive means for driving said cutting means around said path; wherein said path includes first and second substantially linear portions arranged substantially parallel to each other and separated by a distance less than the diameter of a smallest circle partially defined by the tightest bend of said path.

By using a continuous flexible band cutting means, such as a band saw, the advantage is provided that the saw blade is less likely

to jam and/or jump than the blade of a reciprocating saw, thereby reducing the likely damage to both the saw and the drive means and providing a better cut. By using the guide means to reduce the distance between the two parallel portions of the path of the blade the advantage is provided that the section cut from the pipe can be reduced to a minimum. For example, a saw of the type described in JP 08-090336, having a band saw passing around one drive wheel and one free spinning wheel, the size of the section cut from the pipe will be the diameter of these wheels. For the purposes to which the device of JP 08-090336 is intended this is sufficient since the device is required to cut pipes into chunks.

However, this is not the case for the present invention where a narrow cut is preferable. It would in theory be possible to reduce the diameter of the drive and free spinning wheels to reduce the width of the cut. However, such a reduction is limited by the band saw blade which requires a certain rigidity in order to cut and as a result the flexibility of the blade is therefore limited. Thus the smallest wheel around which the blade can form a tight bend (turning through approximately 180 ) will typically have a diameter of 300 mm. If the blade is forced to bend around a tighter wheel than this, damage is likely to occur to the blade. For example the blade will not return to a linear form after passing round such a wheel. Furthermore, the drive wheel will not grip the blade efficiently and the blade is likely to become detached from the drive and free spinning wheels. Thus, the larger the wheel of the drive means the better the grip between the drive means and the band saw blade. If the band saw blade is less likely to slip it is more likely to provide an even cut. Therefore by pinching the blade close together, causing the first and second substantially linear portions to be separated by a distance smaller than the diameter of the tightest bend, the advantage is provided that a small width cut can be provided from a large diameter driving means, thus not losing drive efficiency or making the blade likely to slip and jump.

-4- In a preferred embodiment said cutting means travels through said first portion of said path in a first direction and said cutting means travels through said second portion of said path in a second direction opposite to said first direction.

By arranging that the cutting means travels through the first and second portions of the path in opposite directions the advantage is provided that the turning moment around the axis of the pipe being cut produced by the cutting means travelling in the first direction is cancelled by the moment caused by the cutting means travelling in the second direction. As a result, if the blade were to jam whilst cutting the pipe the device is not caused to rotate around the axis of the pipe, reducing the need for stabilising the device relative to the pipe.

Furthermore, because the blade is travelling through the first and second portions in opposite directions and these portions are located close to one another, as defined above, the advantage is provided that the torque produced by the blade on the pipe is reduced the closer the first and second portions of the path are to each other. This torque is that experienced in the vicinity of the cut and results in an attempt to cause the pipe/saw to rotate around an axis parallel to the axis of the drive means.

Because this torque is reduced this has the advantage that the likelihood of the blades becoming jammed is reduced since the saw is less inclined to attempt to rotate itself around the above described axis. Furthermore, in the event that the blade does become jammed this reduced torque reduces the likelihood of damage to the blade and reduces the requirement for stabilization of the device relative to the pipe.

In a preferred embodiment at least one edge of said cutting means is serrated.

In a preferred embodiment said guide means comprises a plurality of nondriven wheels.

In a further preferred embodiment said drive means comprises at least one driven wheel.

In a preferred embodiment at least one said driven wheel is adjustable in distance relative to at least one other wheel, so as to adjust the tension in said cutting means.

In a preferred embodiment said distance between said first and second portions is less than 20 mm and preferably between 5 mm and 15 mm.

The saw may further comprise a U-shaped frame wherein at least one nondriven wheel and at least one driven wheel are mounted adjacent distal ends of said frame.

Alternatively the saw may further comprise a U-shaped frame wherein at least one first driven wheel and at least one second driven wheel are mounted adjacent distal ends of said frame.

In a preferred embodiment said guide means causes the distance between said first and second portions of said path to be less that a diameter of said first or second driven wheels.

In a preferred embodiment said saw is adapted to cut pipes.

In another preferred embodiment a body of said saw, adapted to move relative to said cutting means, is fixed in use to said pipe by straps.

In a preferred embodiment the saw is adapted to work under water.

A preferred embodiment of the present invention will now be described, by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which: Figure 1 is a side view of a saw of the present invention;

Figure 2 is an end view of the saw of Figure 1; and Figure 3 is a sectional plan view along the line III-III.

Referring to Figures 1, 2 and 3, a submarine saw 10, for cutting a pipe 11, has a cutting means 12, in the form of a continuous flexible band, hereinafter referred to as a band saw blade 12, and guide means 14, 16 and 18 which cause the cutting means 12 to move along a continuous path. The saw also has drive means 20 which drives said cutting means around the path. The path includes a substantially linear first portion A through which band saw blade 12 passes in direction B. and a second substantially linear portion C through which blade 12 travels in direction D. Sections A and C are substantially parallel to each other and separated by a distance E which is less than the diameter of the smallest circle partially defined by the tightest bend of said path. In this instance the tightest bend is defined either around guide means 14 or drive means 20 and therefore distance E is less than diameter F of guide means 14.

Further guide means, in the form of horizontal rollers 22 assist in preventing the blade 12 from becoming detached from the drive means 20 and guide means 14, 16 and 18. A blade tension adjuster 24 causes guide means 14 to move relative to drive means 20 and thereby adjust the tension in blade 12. Guide means 14, 16 and 18 and drive means 20 are contained within housings 26.

Housings 26 are attached to U-shaped frame 28 by hinges 30.

Drive means 20 is driven by hydraulic motor 32 via gearings 34 and drive shaft 36. The saw also has a body 38 which consists of a vertical portion 40 and a horizontal pipe engaging portion 42. In use horizontal pipe engaging portion 42 is attached to pipe 11 by straps 44. Frame 28 is attached to vertical portion 40 of body 38 by carriage 46, which allows frame 28 to move up and down relative to vertical portion 40 of body 38. Carriage 46 and frame 28 are moved relative to vertical portion 40 of body 38 by hydraulic piston 48 which is fixed relative to carriage 46.

Ram 50 of hydraulic piston 48 is fixed relative to body 38 by connecting portion 52.

In use saw 10 is introduced to pipe 11 by placing pipe engaging portion 42 on pipe 11. Straps 44 are used to fix saw 10 to pipe 11. Since pipes of this type often become partially buried in the sea bed it is necessary to dig under the pipe 11 in order that the straps 44 can be attached. This method of fixing the saw 10 relative to pipe 11 is particularly convenient since the location of straps 44 along pipe engaging portion 42 is not critical. Once the saw 10 is correctly located, hydraulic motor 32 causes drive means 20 to rotate. This in turn causes blade 12 to follow the path around drive means 20 and guide means 14, 16 and 18.

Frame 28 is then lowered, by hydraulic ram 48, towards pipe 11 and blade 12 then starts to cut into pipe 11. Hydraulic ram 50 continues to push frame 28 which in turn causes blade 12 to cut through pipe 11. Hydraulic piston 48 and ram 50 are controlled by a pressure release valve which prevents excessive pressure being applied between blade 12 and pipe 11.

Once the cut is complete the frame 28 is withdrawn by a ram 50 and saw 10 detached from pipe 11 by removal of straps 44.

It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example hydraulic piston 48 and ram 50 may be removed and the frame 28 moved relative to pipe 11 by an operator. Furthermore, the saw 10 may be attached and actuated from a ROV (Remotely Operated Vehicle). Alternatively, for small or lightweight pipes a handheld device not requiring body 40 or carriage 46 may be used.

Claims

-8 Claims

1. A saw comprising: cutting means in the form of a continuous flexible blade; guide means for causing said cutting means to move along a continuous path; and drive means for driving said cutting means around said path; wherein said path includes first and second substantially linear portions arranged substantially parallel to each other and separated by a distance less than the diameter of a smallest circle partially defined by the tightest bend of said path.

2. A saw according to claim 1, wherein said cutting means travels through said first portion of said path in a first direction and said cutting means travels through said second portion of said path in a second direction opposite to said first direction.

3. A saw according to either claim 1 or 2, wherein at least one edge of said cutting means is serrated.

4. A saw according to any one of the preceding claims, wherein said guide means comprises a plurality of non-driven wheels.

5. A saw according to any one of the preceding claims, wherein said drive means comprises at least one driven wheel.

6. A saw according to claim 5, wherein at least one said driven wheel is adjustable in distance relative to at least one other wheel, so as to adjust the tension in said cutting means.

- 9 -

7. A saw according to any one of the preceding claims, wherein said distance between said first and second portions is less than 20 mm

8. A saw according to claim 7, wherein said distance between said first and second portions is between 5 mm and 15 mm.

9. A saw according to any one of claims 5 to 8, further comprising a Ushaped frame wherein at least one non-driven wheel and at least one driven wheel are mounted adjacent distal ends of said frame.

10. A saw according to any one of claims 5 to 8, further comprising a Ushaped frame wherein at least one first driven wheel and at least one second driven wheel are mounted adjacent distal ends of said frame.

11. A saw according to claim 10, wherein said guide means causes the distance between said first and second portions of said path to be less that a diameter of said first or second driven wheels.

12. A saw according to any one of the preceding claims, wherein said saw is adapted to cut pipes.

13. A saw according to any one of the preceding claims, wherein a body of said saw, adapted to move relative to said cutting means, is fixed in use to said pipe by straps.

14. A saw according to any one of the preceding claims, wherein said saw is adapted to work under water.

15. A saw substantially as hereinbefore described with reference to the accompanying drawings.