GB2203989A - Method & device for effecting rotary action under water - Google Patents

Abstract

Concrete weight coating 20 on a subsea pipeline (18, Fig 1) is cut by a rotary saw blade 32 driven by a hydraulic motor 36. Air is supplied into a shroud 38 through linings 54, 56 from a compressor (70, Fig. 1). At least some water is replaced by air adjacent the blade. This reduces the power required and allows the blade to be used for longer periods before cracks develop from the bases of gullets at the blade edge. The reason for cracking is not fully understood, but tests show that the provision of air at least partly counteracts whatever effect the water has in promoting cracking. A modified shroud contains solidified foam-material (94, Fig. 4) which conforms closely to the blade, and the air supply may optionally be dispensed with. In the illustrated embodiment, the saw blade rotational axis is movable relative to the shroud 38 towards coating 20 from position 40 to position 42. In an alternative embodiment, the shroud (110, Fig. 5),moves with the saw blade towards the coating (20). A tool other than a saw blade may be used, such as a rotary grinder, buffer, wire wheel brush, or abrasive disc. The tools may be used for removing marine growth or corrosion from offshore structures. <IMAGE>

Description

METHOD & DEVICE FOR EFFECTING ROTARY ACTION UNDER WATER The invention relates to methods and devices by which- an operation under water can be effected using a rotary member e.g. cutting, particularly, though not exclusively, cutting the concrete weight coating of a pipeline to enable removal of the coating preparatory to repair of the pipeline.

Our co-pending-United Kingdom patent application No. 8628386 describes how concrete weight coating is cut and removed and that description is an example of effecting rotary action under water to which the present invention can be applied.

A method of effecting rotary action under water, according to the invention, comprises using a rotating member and providing air or solid material or both in place of at least some water adjacent the rotating member.

For example, the rotating member may be partly within a shroud into which air is introduced.

For example, the solid material may be a solidified foam or some other material which conforms closely to the rotating member.

For example, the foam may be introduced into a shroud and allowed to solidify around the rotatory member.

For example, air may be introduced into the interface between the solid material e.g. foam and the rotatory member.

A device, according to the invention, for effecting rotary action comprises a rotatory member such as a cutter for example, means for driving the rotatory member, and means by which air or solid material or both are or may be provided in place of at least some water adjacent the rotatory member.

For example, the last mentioned means is a shroud with an inlet through which air can be introduced.

Alternatively, the shroud conforms closely to the rotatory member and is present adjacent the rotatory member in place of water, in use.

For example, the shroud an outer wall containing solidified foam conforming closely to the rotatory member.

It is optional whether air is introduced into such a closely-conforming shroud. If air is to be introduced, the shroud has an air inlet which communicates for example with the space between the foam and the mouth of the shroud or with the interface between the solid material of the shroud e.g. foam and the rotatory member.

Performance of the method and embodiments of apparatus for performing the method will now be described with reference to the accompanying drawings, in which: Figure 1 shows apparatus for cutting the concrete weight coating of a pipe under water; Figure 2 is an elevation part section of a rotary cutter device forming part of the apparatus shown in Figure 1; Figure 3 is an elevation of a shroud forming part of the device shown in Figure 2; Figures 4 and 5 are elevations similar to Figure 2 showing, respectively, second and third embodiments of rotary cutter device.

Figure 1 shows apparatus as arranged for trial use in a dock comprising a dock-side 10, dock wall 12 and dock-bottom 14. The dock contains water to a level 16. A length of steel pipe 18 representing, for example, an offshore oil or gas pipeline is supported by means not shown on-the docktbottom 14. The pipe 18 has a concrete weight coating 20. A concrete cutting machine 22 is mounted on the pipe 18 and, for example, is as described in UK Patent Application No. 8628386. The machine 22 comprises a frame 24 held on the pipe 18 by endless roller chains 26.

The frame 24 has rollers 28 engaging the coating 20 and can be orbited around the pipe 18 by -manual rotation of a handle (not shown) driving sprockets engaging the chains 26. The frame 24 carries a rotatory cutte device 30 which can be turned on its mounting so as to be direcLed or circumferential or longitudinal cutting Of the coating n the dt.

of the former, the frame 24 orbits around the pipe ] ; in the course o the latter, the cutter device is moved with its mounting alongnthe frame 24 by manual operation of a handle driving a pinion engaging a rack running along the frame 24. The rack and pinion are not shown. The cutter device 30 can be moved on its mounting towards and away from the concrete coating 20, as explained below.

The cutter device 30 (Figures 2 & 3) comprises a rotatory member in the form of a diamond-tipped rotary saw blade 32 held in an arbor 34 mounted on the output shaft of a hydraulic in motor 36. The blade 32 is partly within a shroud in the form of a fixed guard 38 which is supported independently of the motor 36 on the motor mounting assembly. The axis of rotation of the motor 36, when the cutter device 30 is moved fully away from the concrete coating 20 is at 40, and when it is moved fully towards the concrete coating 20 is at 42. Such adjustment of the cutter device 30 is effected by a handwheel (not shown) driving a screw working through a nut on the mounting of the device.

The guard 38 comprises two walls 48, 50 one at either side of the blade 32. Each wall has a slot 52, 53, respectively. The wall 48 carries fittings 54, 56 secured by locknuts 58 and interconnected by tubing 60 of synthetic plastics material (e.g. 10 mm outside diameter). The tubing 60 connects the fittings, 54, 56 to a T-connector 62 which is, in turn, connected to-a hose-connector assembly 64.

As examples of components suitable for use in the cutter device 30 may be quoted the following: the motor 36; type F-11-28 available from the Volvo company; and the blade 32; a 400 millimetres diameter size, with a 25 mm (1 inch) central hole, of the kind available from the Norton Construction company or from the Defiant Diamond Tools company.

Figure 1 shows an air compressor 70 (typically of the kind available from the Hydrovane company delivering 4000 cubic litres of air per minute (140 cubic feet per minute) at a pressure of 7 x 105Pa (7 bars).

The compressor 70 delivers air via some 25 metres of air hose 72 (e.g.

18 mm inside diameter) to the interior of the guard 38, the hose 72 being connected to the connector assembly 64. The hose length is chosen to suit the site. The air passes from the connector assembly via the tubing 60 to the fittings 56, 54 and thence through the wall 48. The air leaves the fittings via ports such as the-port 74 (Figure 2) opening within the guard 38.

Figure l shows a typical test set-up in a dock containing water some 9 metres deep. For offshore work in actual practice, the sea depth would be some 10 to 38 metres, the pipe-and concrete coating being the same as shown i.e. typically for example, steel pipe having an outside diameter of 914 mm and a wall thickness of 15.88 mum. The concrete weight coating is nominally 118 mm thick, for example. The hose 72 is tied to the hydraulic lines (not shown) extending between power-pack on the dock side and the hydraulic motor 36.

Typically, the power-pack supplies a constant flow of oil of 60 litres per minute with the power-pack pressure relief valve set at a maximum ptessureaf 245 bar.

With the blade 32 fully withdrawn into the guard 38 and not cutting the pressures of the oil delivered by the power-pack were as shown below, depending on whether the guard was at the 12 o'clock position on the pipe (guard 38 upright) or at the 6 o'clock position (guard inverted), and on whether the air was flowing: GUARD UPRIGHT GUARD INVERTED AIR OFF 245 BAR 245 BAR AIR ON 119 BAR 238 BAR Clearly, the air which is provided in place of at least some water adjacent the blade 32 reduces the resistance presented to the rotation of the blade by the water.

The effect of air flow to the guard is shown below during cutting of the concrete:- AVERAGE TIME AVERAGE TIME LONGITUDINAL CUT CIRCUMFERENTIAL CUT MINUTES MINUTES AIR OFF 11 34 AIR ON 6 26 In the case of the circumferential cut, the average is the average of the times of several circumferential cuts, in each of which the guard moves from an upright (12 o'clock) position to inverted (6 o'clock) position and back to the upright position. In the case of the longitudinal cut, the average is the average time of several longitudinal cuts at 12 o'clock and-of half that number at 6 o'clock.

It was found that, without the air supply, the blade 32 developed many radial cracks from the bases of the gullets at the blade edge after some 6 metres cutting.

Once such cracks developed, the blade had to be discarded, but with the air supply cutting could continue for some 14 metres before cracks were detected.

Figure 4 shows a second embodiment of rotary cutter device. The shroud 90 in this case comprises outer walls 92 containing solidified foam material e.g. polyurethane foam 94 of closed cell structure. The foam 94 extends downwardly at 96 within the walls 92 at each side of the slots 52, 53 in the walls 92. The foam 94 has a slot 98 corresponding to the slots 52, 53.

Air under pressure can be introduced into the shroud at an air inlet 100, which at its inner end communicates with the interface 102 between the foam 94 and a side face of the cutter blade 32. If desired, a second inlet (not shown) can be provided communicating with the interface at the opposite side of the blade 32. Alternatively (or in addition) to the inlet 100 or inlets corresponding thereto, an air inlet P03 can be provided communicating with the slot 98.

The blade 32 is movable in relation to the shroud 90 as described with reference to Figure 3.

Figure 5 shows a third embodiment of rotary cutter device, which is similar to that shown in Figure 4 but in which the blade 32 is not movable (except for rotation) in relation to the shroud 110. Instead, the shroud 110 moves with the blade 32 as it approaches or recedes from the work, e.g. the concrete 20. The shroud 110 includes walls 112.

In Figures 4 and 5, the rate of air supplied can be less than the rate in the case of Figures 2 and 3 and may be very small. As an alternative the supply of air may be dispensed with altogether.

In Figures 4 and 5 the polyurethane foam 94 conforms very closely to the blade 32 and to the arbor 34. In a preferred example of making the shroud 90 or 110, the foam 94 is injected into the shroud in the presence of the blade 32 and allowed to solidify. The foam is injected as a two-component mixture and is of the kind used for insulation. It is an expanding type of foam and solidifies to give a closed cell structure, which is preferred though it is not essential. The foam is a consumable and is replaced periodically. The blade 32 is then rotated so that it cuts itself free and runs within the foam which conforms closely to it.

The slot 98 is formed in Figure 4 as a subsequent operation. The slot 98 is preferably wide enough to accommodate the arbor 34 with clearance at diametrally opposite edges of the arbor.

In a further modification (not shown), the shroud contains seals which engage opposite sides of the blade 32 so as to prevent or reduce the ingress of water into the shroud.

The invention includes a method and device in which air is not supplied to the shroud, but in which air is trapped in the shroud by its shape, or its conformity to the blade or other rotatory member or by seal means arranged between the shroud and the rotatory member, for example, so that the air replaces at least some water which otherwise would be present adjacent the rotatory member.

The invention is of particuar utility in relation to a rotatory cutter device, such as a device having a saw blade. However, the invention is applicable to other rotatory devices, whether they effect a cutting action or not, such as a rotatory grinder; buffer; wire wheel brush; or abrasive disc or wheel device for cleaning or cutting for example. Such devices are applicable underwater for example in procedures for removing marine growth or corrosion layers from offshore pipelines or structures, bridges, piers or ships' hulls or for cutting, cleaning or grinding the same in the course of repair or maintenance.

It is anticipated that the invention will enable improvements in power consumption to be achieved with very many rotatable underwater tools. In the case of a cutter blade, the invention can enable the blade's peripheral speed to be maintained in the region of 40 to 45 metres/second using for example an 83 litres/minute hydraulic motor to drive the blade, the motor being supplied with hydraulic fluid at 21 mega-Pascals (3000 pounds-force-per square inch) or less. This enables the motor to be energised using relatively simple hydraulic lines compared with those which would be necessary if higher hydraulic pressures were used.

Claims (15)

1. A method of effecting rotary action under water comprising using a rotating member and providing air or solid material or both in place of at least some water adjacent the rotating member.

2. A method according to claim 1, the rotating member being partly within a shroud, the air being provided by supplying air into the shroud under pressure.

3. A method according to claim 1, the rotating member being partly within a shroud, the air being provided as air retained in the shroud by the shape of the shroud, or by its conformity to the rotating member or by seal means between the shroud and the member.

4. A method according to claim 1, the solid material being part of a shroud in which the rotating member is received.

5. A method according to claim 4 the shroud conforming closely to the rotating member.

6. A device for effecting rotary action under water comprising a rotatory member such as a cutter for example, means for driving the member, and means by which air or solid material or both are or may be provided in place of at least some water adjacent the rotatory member.

7. A device according to claim 6 comprising a shroud in which the rotatory member is partly received, and means connected to the shroud for supplying air under pressure into the shroud.

8. A device according to claim 6 comprising a shroud in which the rotatory member is partly received and which conforms closely to the rotatory member.

9. A device according to claim 8 the shroud comprising air inlet means communicating with an interface between the shroud and the rotatory member.

10. A device according to claim 8 or claim 9 the shroud comprising foam which after placement around the rotatory member has been allowed to solidify in close conformity therewith.

11. A method according to claim 1 substantially as herein described with reference to Figures 1 to 3; or Figures 1 and 4; or Figures 1 and 5.

12. A device according to claim 6 substantially as herein described with reference to Figures 2 and 3.

13. A device according to claim 6 substantially as herein described with reference to Figure 4.

14. A device according to claim 6 substantially as herein described with reference to Figure 5.

15. Apparatus substantially as herein described with reference to Figures 1 to 3; or with reference to Figures 1 and 4; or with reference to Figures 1 and 5.