GB2033995A

GB2033995A - Explosively De-coating Pipes

Info

Publication number: GB2033995A
Application number: GB7838806A
Authority: GB
Original assignee: Vickers Ltd
Current assignee: Vickers Ltd
Priority date: 1978-09-29
Filing date: 1978-09-29
Publication date: 1980-05-29

Abstract

A concrete coating 14 on an underwater pipe 13 is removed by detonating a relatively more powerful chase 6 in a longitudinally extending slot 15 in the coating 14 and relatively less powerful charges 7, 8 located adjacent the coating. The charges may be secured to a frame 1, 2, 3, 4, 5 to form an explosive device for fitting onto the pipe. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Underwater Operations This invention relates to underwater operations and is concerned with removing coatings of concrete or the like from underwater pipes.

It is conventional to apply a coating of, for example, concrete to pipes which are intended to be located underwater for, for example, extracting oil from the seabed. The concrete coating serves to ensure the negative buoyancy of the pipe and also to protect the pipe against mechanical damage. The presence of this coating can, however, be deleterious in certain circumstances.

For example it is sometimes necessary to effect repairs to underwater pipes by the use of fusion welding, explosive welding, or mechanical connectors. In order to achieve a repair in this way, it is generally necessary to remove the coating from the outer surface of the pipe.

According to one aspect of the present invention, there is provided a method of removing, from an underwater pipe, a surface coating of concrete or the like which method comprises (a) locating an explosive charge in a longitudinally extending slot provided in the pipe coating and placing further explosive charges adjacent to the coating at locations angularly displaced with respect to the location of the firstmentioned explosive charge; the explosive power of each of said further explosive charges being less than that of the first-mentioned charge, and (b) detonating the charges so as to sever the bond between the coating and the pipe and remove the coating.

According to a further aspect of the present invention, there is provided an explosive device for use in the above-defined method, which device comprises (a) a frame for fitting on to the coated pipe, (b) a first explosive charge secured to the frame for insertion into a longitudinally extending slot provided in the coating when the frame is in position on the pipe, and (c) further explosive charges secured to the frame for location adjacent to the surface of the coating when the frame is in position on the pipe, each of said further explosive charges being of lesser explosive power than said first-mentioned explosive charge.

In accordance with a particularly preferred embodiment, the frame is generally partcylindrical in configuration and includes at least one arcuate rib carrying cross-members and having free ends which are spaced apart by a distance less than the maximum diameter of the concrete coated pipe. The or each rib is resilient so that when the frame is urged laterally against the coated pipe the free ends of the rib(s) may be displaced apart so as to pass around opposite sides of the coated pipe and clip the frame on to the pipe. Advantageously the cross members extend normally to the plane of the rib(s) and preferably the explosive charges are mounted on the frame in the vicinity of the cross members. In a particularly preferred embodiment, the frame includes three cross-members and carries three explosive charges angularly displaced from one another by about 1200.

Advantageously the explosive power of the charge to be located in the slot is some 50% greater than the explosive power of the or each other explosive charge.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an end view of an explosive device in accordance with the present invention and Figure 2 is a section along the line Il-Il of Figure 1.

Referring to the drawings, there is shown an explosive device comprising a frame including a pair of C-shaped resilient ribs 1 and 2. The ribs 1 and 2 are secured together in spaced relationship by side cross members 3 and 4 and by an upper cross member 5. The side cross members 3 and 4 are secured to the ribs 1 and 2 at a position adjacent to the free ends of the ribs. The upper cross member 5 is secured to the ribs 1 and 2 at the centres of the ribs. Thus, the frame constituted by the ribs and cross-members has the configuration of a partial cylinder.

Mounted on the upper cross-member 5 is a linear explosive charge 6. The configuration of the charge is such that it extends inwardly towards the centre of the partial cylinder defined by the frame, A pair of additional linear explosive charges 7 and 8 is also included in the device.

One of these charges 7 is affixed to the frame in the vicinity of the side cross member 3 and the other charge 8 is affixed to the frame in the vicinity of the side cross member 4. The charges 6, 7 and 8 are all arranged so as to extend in the direction of the longitudinal axis of the cylinder defined by the frame. Each explosive charge comprises a copper tube containing an explosive composition. The explosive tubes contain similar compositions but in different amounts. The amount of explosive composition in the tube of charge 6 is about 50% greater than the amount present in the tube of charge 7 or 8. Thus the explosive power of charge 6 is greater than that of charge 7 or 8. A detonating device 9 is mounted on the frame and this is linked to the charges 6, 7 and 8 by suitable detonating cord 16 6 and by manifolds 17.Located on each rib 1 and 2 at a position between the free end of the rib and the explosive charge is a tubular guard member 10.

A coupling member 11 is secured to the upper cross m-ember 5 for engagement with the torpedo claw 12 of a submersible or the like.

In use of the device, its coupling member 11 is engaged in the torpedo claw 12 of the submersible and the submersible then descends to the pipe 1 3 to be worked upon. The pipe 13 is formed of steel and carries a concrete coating 14 which is to be removed by the device. A bituminous corrosion coating is present between the pipe 13 and the coating 14. Conventionally the pipe will generally have circumferential slots (not shown) in its concrete coating 14 in order to prevent spalling of the concrete when it passes over the laybarge stinger during the laying operation of the pipe. In the event that the coating does not include such circumferential slots, then such would need to be provided.

By suitably manoeuvring the submersible, the frame is presented laterally to the pipe and sprung over the pipe, the flexible nature of the ribs 1 and 2 allowing the free ends of the ribs to be displaced apart to a spacing which will allow the pipe to pass between the free ends of the ribs which then clip onto the pipe as a result of their natural tendency to revert to their non-deformed position. The guards 10 on the ribs shield the explosive charges 7 and 8 from contact with the pipe coating whilst this is being effected and thus prevent the charges 7 and 8 being damaged.

Once the frame has been clipped onto the coated pipe in this way, the coupling member 11 is released from the claw 12 of the submersible.

Then, the frame can be manoeuvred by the submersible manipulator so that it is located between a pair of adjacent circumferential slots and the explosive charge 6 enters a longitudinally extending slot 1 5 which has been previously provided in the coating 14. In this final position of the frame, the charge 6 is located in the slot 1 5 and the charges 7 and 8 are located on the surface of the coating 14, the three charges 6, 7 and 8 having included angles of about 1200 with respect to each other. Once this position has been achieved, the submersible returns to the surface and the explosive charges are detonated via the detonating device 9. The explosive charge 6 breaks the bond between the coating 14 and the surface of the pipe 13.The surface charges 7 and 8 crack the concrete coating 14 iocally and these cracked areas effectively serve as hinges to allow the concrete coating 14 to come clear of the pipe.

The explosive device thus effectively removes all of the concrete located between a pair of adjacent circumferential slots.

The amount of explosive used to remove the concrete coating in any given case should be the minimum required in order to avoid damage to the pipe itself. It has been found that the explosive can be used most efficiently if a more powerful charge is detonated in a longitudinally extending slot in the coating and less powerful charges are detonated at positions angularly displaced therefrom on the surface of the coating in accordance with the present invention.

Although the explosive device as above described is primarily intended for deployment by means of a submersible or the like, it will be appreciated that, circumstances permitting, it may be deployed by means of a diver.

Claims

1. A method of removing, from an underwater pipe, a surface coating of concrete or the like which method comprises (a) locating an explosive charge in a longitudinally extending slot provided in the pipe coating and placing further explosive charges adjacent to the coating at locations angularly displaced with respect to the location of the firstmentioned explosive charge, the explosive power of each of said further explosive charges being less than that of the first-mentioned charge, and (b) detonating the charges so as to sever the bond between the coating and the pipe and remove the coating.

2. A method in accordance with Claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

3. An explosive device for use in the method of Claim 1 which device comprises (a) a frame for fitting on to the coated pipe, (b) a first explosive charge secured to the frame for insertion into a longitudinally extending slot provided in the coating when the frame is in position on the pipe, and (c) further explosive charges secured to the frame for location adjacent to the surface of the coating when the frame is in position on the pipe, each of said further explosive charges being of lesser explosive power than said first-mentioned explosive charge.

4. An explosive device as claimed in Claim 3 wherein the frame is generally part-cylindrical in configuration and includes at least one arcuate rib carrying cross-members.

5. An explosive device as claimed in Claim 4 wherein the or each rib is resilient.

6. An explosive device as claimed in Claim 3, 4 or 5 wherein the cross members extend normally to the plane of the rib(s).

7. An explosive device as claimed in any one of Claims 3 to 6 wherein the explosive charges are mounted on the frame in the vicinity of the cross members.

8. An explosive device as claimed in any one of Claims 3 to 7 wherein the frame includes three cross-members and carries three explosive charges angularly displaced from one another by about 1200.

9. An explosive device as claimed in any one of Claims 3 to 8 wherein the explosive power of said first explosive charge is some 50% greater than the explosive power of the or each further explosive charge.

10. An explosive device as claimed in any one of Claims 3 to 9 wherein each explosive charge comprises a copper tube containing an explosive composition.

11. An explosive device as claimed in Claim 3 substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.