GB2216624A - Method for sealing a metallic tubular member - Google Patents

Abstract

A metallic tubular member is sealed by exploding a charge on the exterior circumference of the member in such manner of the member collapses inwardly along three or more folds and the folds compact on impact to seal the member. The charge may surround the member in a hexagonal lock, a saddle lock, a triangular lock or in a three/four symmetrically spaced longitudinals strips. The method is particularly suitable for sealing a subsea pipeline in an emergency. <IMAGE>

Description

SEALING A METALLIC TUBULAR MEMBER This invention relates to a method for sealing a ztistallic tubular member, for example a pipeline, by deforming it and to equipment for Carrying out tTh task.

In reoent years many oil and gas fields have keen 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 nay 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 ID and 5/8 inch wall thickness. Increasingly stringent safety legislations require the provision of more and more isolation valves, partictilarly 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 commected 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 evea greater in more recent and proposed developments for exploiting reseves in offshore locations where the water is too deep for surface platforms and production faci2ties are located subsea on templates an 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 uncontroflel folds which can leave boles along the asLs of closure.

We have now discovered that an explosive charge nay be used to seal a metallic tubular member by exploding a charge on the exterior circumference of the member with such force that the wail of the member collapses inwardly and forms a solid compacted mass which, in the case of a pipeline, in effect acts as an emergency isolation valve.

Thus, according to the present invention there is provided a method for sealing a metallic tubular member which method comprises detonating an explosive charge or charges on the exterior of the in such manner that the member collapses inwardly along three or more folds and the folds compact on impact to seal the member.

The optimum number of folds depends on both the diameter and wail thickness of the member. The relationship is not linear, bit in general, the greater the diameter of the member, the greater the number of folds required.

The charge preferably surrounds the member in a bex of polygonal croscs-sections suitably hexagonal.

Other bit less preferred configurations include a saddle box, i.e. a box resting on the upper half of the member, a triangular bag, ani four or three symmetrically spaced longitudinal strips.

Preferably, the explosive is chosen to ensure the occurrence of explosive welding as the folds impinge on one another at or near the centre line of the member. Suitable explosives include Trimonite and Amatol.

Conventional detonators nay be employed.

When the preferred configuration of a multi-faceted box with polygonal cross-section is employed a detonator is preferably positioned at one and.

If desired, booster charges may also be applied in Imawn manner.

According to another aspect of the invention there is provided an explosive constrictor for a metallic tubular member comprising an explosive charge or charges shaped to surround or rest on the meber in such manner that when detonation occurs the member collapses inwardly along three or more folds and the folds compact on impact to seal the The chaise is preferably in the form of a box of polygonal cross-section, suitably hexagonal, with a cylixxfrical aperture for fitting around the member.

The explosive is placed around and in intimate contact with the member and is enclosed by the polygonal box which forms a collar around the member.

The invention will be described with reference to a pipeline bit it is to be understood that it is suitable for closing any metallic tubular member.

The invention is particularly useful in the context of safety valves which nay never be used bit 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 replaéd, 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 but not limited with reference to the following Examples and Figures 1 to 4 of the accompanying drawings.

Figures 1 and 3 are views of pipelines after detonation of the charge, Figure 2 is a section on the constricted area, and Figure 4 is a section above a constricted area.

Example 1 The steel pipe used in small scale tests bad the following description: API-STD-5LX Grade 2, 60.3mm o.d., 3.9mm w.t. Seamless.

Although at first sight a simple box surrounding the pipe might appear to be a uniform constriction type charge, this is not the case since there will be more explosive over the pipe at the box corners than at the box faces. This configuration gives folding along four major lines.

The trial used an empty pipe in air employing a 72 x 72 x 160mm box. The pipe was centred in the box with the detonator parallel to the longitudinal axis of the pipe in the centre of a corner area at the end of the box.

The explosive was Trimonite and the detonator was 8 Star.

Figure 1 clearly shows the effect of the charge in cosstricting the pipe (1) by deforming it along four folds (2).

As can be seen from Figure 2, the pipe is essentially closed and there are no through wall breaks. The only cracks (3) in the section are Joining the lines as the four lobes (2) closed. There is also noticeable thickening of the pipe wail as it was deformed in the folding process. The section clearly shows the four lobe structure formed by the box charge and the equality of the lobes.

Example 2 A similar pipe but of larger dimensions was taken: 32cm o.d., 1.4cm w.t.

In this case the explosive charge was packed around the pipe in a hexagonal box each side of which was 21.6an long. the length of the box was 20am.

Figure 3 shows the effect of the charge in constricting the pipe (4) by deforming it along six folds (5).

Figure 4 clearly shows the closure of the pipe (4) by the impacting of the six lobes (5).

Examples 3 - 4 An API 5L x 52 pipe of approximately 3 metres in length, 32 cms diameter and a wall thickness of approximately 1.4 cms was used.

The tests were carried out in air with the pipe ends open using Trimonite or Amatol explosive and an electrical detonation system.

The explosive was packed around the pipe in a hexagonal box. The results obtained from using different quantities of explosive are given in the accompanying Table.

Examples 5 - 7 These were performed using a similar pipe submerged in 4 m of water and under an internal pressure of 500 psi N2. The explosive used was Amatol and again both the quantity of explosive used and the size of the box were varied. The results are also given in the Axle.

The examples clearly show that the effective sealing of a pipeline can be achieved both in and out of water by using the method of the present invention.

EXAMPLE POSITION PIPE INTERNAL EXPLOSIVE EXPLOSIVE DETONATION RESULT OF PIPE ENDS PRESSURE FORMER SYSTEM TYPE Wt. Kgm. 3 In Air Open Ambient Trimonite 8.7 HEXAGON ELECTRICAL 99% Length 200mm symmetrical Side 216mm closure 4 " Amatol 7.4 HEXAGON 99% Length 200mm symmetrical Side 216mm " closure 5 IN WATER HEXAGON Electrical using 100% closure depth 4m. CLOSED 500 psi 7.8 Length 250mm Cordtex and 6 lobes Nitrogen Side 216mm tetryl boosters severe splitting 6 " " " 5.4 HEXAGON 98% closure Length 250mm 5 lobes Side 205mm " slight splitting 7 5.6 HEXAGON Electrical using > 95% closure Length 250mm Cordtex and 6 lobes Side 205mm Superflex ring slight splitting train

Claims (10)

Claims:

1 A method for sealing a metallio tubular member which method coopriees detonating an explosive charge or charges on the exterior of the member in such manner that the member collapses inwardly along three or more folds And the folds compact on impact to seal the er.

2 A method according to claim 1 wherein the charge surrounds the member in a box of polygonal cross-section.

3 A method according to claim 2 wherein the polygon is a hexagon.

4 A method according to any of the preceding claims wherein the member is a pipeline.

5 An explosive constrictor for a metallic tubular member which member comprises an explosive charge or charges shaped. to surround or rest on the member in such er that when detonation occurs the member collapses inwardly along three or more folds and the folds compact on impact to seal the

6 An explosive constrictor according to claim 5 wherein the charge is in the form of a box of polygonal eross-seotion. with a cylindrical aperture for fitting around the member.

7 A method according to claim 6 wherein the polygonal cross-section is a hexagonal cross-section.

8 An explosive constrictor according to claim 5 therein the explosive is placed around and in intimate contact with the member and is enclosed by the polygonal box which forms a collar around the member.

9 A method for sealiRg a metallic tubular member as hereinbefore described with reference to Examples 1 - 7.

10 An explosive constrictor for a metallic tubular member as hereinbefore described with reference to Examples 1 - 7.