GB2221749A - Equipment for sealing a metallic member - Google Patents

Abstract

An explosive charge suitable for completely or partially constricting a metallic tubular member 1 contains an inner polygonal box 2 and an outer cylindrical casing 3. Explosive 4 is placed between the box and the casing and buffer material 5 may be placed inside the inner box. The charge may be used to seal a subsea pipeline in an emergency or to partially constrict the legs of an offshore platform prior to dismantling and removal. <IMAGE>

Description

EQUIPMENT FOR SEALING A METALLIC MEMBER This invention relates to equipment suitable for sealing a metallic tubular member by deformation.

In recent years many oil and gas fields have been discovered and exploited offshore. The crude oil and gas are generally given preliminary treatment on offshore platforms which may be freestanding or floating, and then transported to onshore facilities for further treatment by subsea pipelines which may be several hundred kilometres long.

In order to control the flow of fluid, valves must be inserted in these pipelines. Furthermore, in order to isolate sections of the pipelines, should leaks or other damage occur, further safety valves are required. This is particularly the case with high pressure gas lines which are typically of the order of 12 inches (approximately 30 cm) ID and 5/8 inch (approximately 26 mm) wall thickness. Increasingly stringent safety legislations require the provision of more and more isolation valves, particularly close to the platforms.

This gives rise to further problems. The integrity of an unbroken pipeline is generally good, but suffers to some extent when breaks are made for the insertion of valves. Because valves require maintenance and replacement they must be removable and this generally means that they are connected to the pipelines by flanged connections which introduce points of weakness. Furthermore, maintenance and replacement means that the pipelines must be shut down completely at periodic intervals with loss of production. The greatest concentration of such valves occurs in the vicinity of the platforms where the water is deepest.

The problems of inaccessibility caused by depth of water are even greater in more recent and proposed developments for exploiting reserves in offshore locations where the water is too deep for surface platforms and production facilities are located subsea on templates on the sea bed.

Explosive cutters using narrow circular shaped charges are known for cutting pipelines. They cut without substantially deforming the line and thus leave it open.

Simple circumferential constriction gives rise to uncontrolled folding which can leave holes along the axis of closure Our copending UK application No. 8805449 relates to a method for sealing a metallic tubular member by detonating an explosive charge or charges on the exterior of the member in such a manner that the pipeline collapses inwardly along three or more folds and the folds compact on impact to seal the pipeline.

The charge is in the form of a box of polygonal cross-section with a cylindrical aperture for fitting around the pipeline.

We have now found that the effectiveness of the explosive charge is enhanced by placing the polygonal box around a suitable metallic member inside an outer cylindrical casing.

Thus according to the present invention there is provided an explosive charge suitable for use in completely or partially constricting a metallic tubular member which comprises an inner box of polygonal cross-section adapted to surround the member, and an outer cylindrical casing, the space between the box and casing being filled with explosive.

The present invention is particularly suitable for sealing submarine pipelines. Other suitable metallic members include risers and similar flowlines employed in the vicinity of offshore platforms.

The charges of the present invention may also be suitable for the constriction of tubular legs, caissons or cross-members of offshore platforms prior to their dismantle and removal.

In this aspect of the invention the charges may be used to alter the integrity of the member by partial constriction leading to the formation of hinge points. The strength of such members lies in their tubular form and the creation of hinge points leads to points of weakness facilitating dismantle.

The preferred charge has a box of hexagonal cross-section.

The inner box may be packed with a buffer material which surrounds the member to allow for irregularities in the member surface and to help maintain the surfaces watertight.

Suitable buffer materials include plastic, rubber or preferably closed cell foam.

The buffer material also enhances the effect of the explosive shock and helps to ensure the shock waves induce the correct number of folds.

The optimum number of folds depends on the diameter of the member as well as mathematical and practical considerations. The relationship is not linear, but in general, the greater the diameter of the member the greater the number of folds required. For practical reasons the preferred number of folds is either six or eight.

The cylindrical outer casing reduces the risks of pressure distortion possible with angled casings particularly in deep water environments.

Preferably, the explosive is chosen to ensure the occurrence of explosive crimping as the folds come together at or near the centre line of the member.

Suitable explosives include Trimonite and Amatol.

Conventional safe detonator systems may be employed.

The detonator(s) are preferably positioned at one end of the charge.

If desired, booster charges may be applied in a known manner.

According to another aspect of the invention there is provided a method for completely or partially constricting a metallic tubular member which method comprises detonating an explosive charge or charges as hereinbefore described on the exterior of the member in such a manner that the member collapses inwardly along three or more folds and the folds compact on impact to constrict the member.

The invention is particularly useful in the context of safety valves which may never be used but which must remain operative over a period of many years. Conventional isolation valves require frequent maintenance but explosive constrictors serving the same function do not. It is fortuitous that the temperature of the water at the sea bed is in the optimum temperature range for storing explosives.

If, however, for any reason, the charge or its detonator is to be removed or replaced, it is non-invasive and this operation can be carried out without necessarily shutting down the pipeline, unlike conventional valve replacement.

The invention is illustrated with reference to the accompanying drawing which is a cross-section of a member with the explosive charge in position.

The member 1 is surrounded by an inner casing 2, consisting of a box of hexagonal structure, and an outer cylindrical casing 3.

The explosive 4 is packed in the space between the inner and outer casings. Suitable buffer material 5 is placed inside the box surrounding the member.

The invention is further illustrated with reference to the following Examples.

ExamPle 1 An API 5L x 52 pipe of approximately 3 metres in length and 30 cm diameter with a wall thickness of approximately 1.4 cm was sealed at both ends under 500 psi N2 internal pressure and submerged in water at a depth of approximately 4 metres.

The explosive charge, comprising an inner hexagonal box of length 250 mm and side 195 mm containing closed cell foam and an outer cylindrical casing of diameter 410 mm containing 9 kg of Amatol explosive, was placed around the pipeline.

The charge was initiated using a ring of Superflex detonated by Cordtex taken above the surface of the water and fired with a military standard service detonator.

The resultant explosion caused a six lobe crimp with over 95Z closure in the pipe with slight splitting.

Example 2 The procedure for Example 1 was repeated using a reduced amount of explosive (6.4 kg) and a smaller sized explosive former. 95Z closure was achieved with three/four lobes but with no splitting.

Example 3 The procedure for Example 1 was again repeated using a larger pipe of approximately 40 cm diameter and 1.1 cm wall thickness. In this example 7.7 kgm Amatol was used with an octagonal shaped explosive former. The eight sided former successfully produced an eight lobe crimp again with almost total closure together with localised splitting due to the relatively thin wall of the pipeline.

Full details of the examples are given in the table.

EXPLOSIVE EXPLOSIVE FORMER Example Size of Pipe RESULTS (approximately) TYPE wt kg CYLINDRICAL POLYGON APERTURE SIZE diameter 30 cm DIAMETER HEXAGONAL SIX LOBE CRIMP 1 wall thickness AMATOL 90 410 mm LENGTE 250 mm > 95% CLOSURE 1.4 cm SIDE 195 mm SLIGHT SPLITTING diameter 30 cm DIAMETER HEXAGONAL THREE/FOUR LOBE CRIMP 2 wall thickness AMATOL 6.4 404 mm LENGTH 200 mm 95% CLOSURE 1.4 cm SIDE 195 mm NO SPLITTING diameter 40 cm DIAMETER OCTAGONAL EIGHT LOBE CRIMP 3 wall thickness AMATOL 7.7 480 mm LENGTH 250 mm > 95% CLOSURE 1.1 cm SIDE 178 mm LOCALISED SPLITTING

Claims (9)

Claims

1. An explosive charge suitable for use in completely or partially constricting a metallic tubular member comprising an inner box of polygonal cross-section adapted to surround the member, and an outer cylindrical casing, the space between the box and the casing being filled with explosive.

2. An explosive charge according to claim 1 wherein the polygon is a hexagon.

3. An explosive charge according to any of the preceding claims wherein a buffer material is present in the space between the inner box and the tubular member.

4. An explosive charge according to claim 3 wherein the buffer material is closed cell foam.

5. A method for completely or partially constricting a metallic tubular member which method comprises detonating an explosive charge or charges according to any of the preceding claims on the exterior of the member in such a way that the member collapses inwardly along three or more folds and the folds compact on impact to constrict the member.

6. A method for completely or partially constricting a metallic tubular member according to claim 5 wherein the member is a pipeline.

7. A method for completely or partially constricting a metallic tubular member according to claim 5 wherein the member is a leg of an offshore platform.

8. An explosive charge suitable for use in completely or partially constricting a metallic tubular member as hereinbefore described with reference to the accompanying drawings.

9. A method for completely or partially constricting a metallic tubular member as hereinbefore described with reference to Examples 1-3.