GB2023777A - Detonating device - Google Patents

Abstract

A detonating device comprises a detonator (22) and an explosive composition (27) physically separated by a member (3). The member is displaceable between a first position in which a first portion of the member (3) lies between the detonator (22) and the composition (27) and forms a barrier to ignition propagation from the detonator (22) to the composition (27) and a second position in which a second portion of the member (3) lies between the detonator (22) and the composition (27) and allows ignition propagation from the detonator (22) to the composition (27). The member (3) may be of metal with the second portion in the form of a bore (13) containing an ignitable material (15). A compression spring (11) may bias the member (3) to its first position, and compressed gas may be admitted via conduit (8) to move the member to the second position. <IMAGE>

Description

SPECIFICATION Improvements in or relating to detonating devices This invention relates to detonating devices and more particularly, but not exclusively, is concerned with detonating devices suitable for initiating explosions during, for example, explosive welding operations carried out under water.

According to the present invention, there is provided a detonating device comprising: (i) A detonator, (ii) an explosive composition spaced from the detonator, and (iii) a member including first and second portions and being displaceable between first and second positions so that either the first portion or the second portion, respectively, is interposed between the detonator and said composition, said first portion being such that it constitutes a barrier between the detonator and the explosive composition when said member is in the first position so that firing of the detonator does not cause ignition Of said composition and said second portion being such that it constitutes an ignition path from the detonator to the composition when said member is in said second position so that the firing of the detonator causes ignition of said composition.

In a particularly preferred embodiment fluid pressure is used to displace the member from its first to its second position.

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 a vertical section through a detonating device in accordance with the present invention and suitable for initiating the necessary explosion when explosively welding an underwater pipe to a surrounding annular flange, Figure 2 is a horizontal section through the device of Fig. 1 along line ll-ll, and Figure 3 shows schematically the detonating device of Figs. 1 and 2 and its associated electrical circuitry.

Referring to the Figs. and particularly Figs.

1 an 2, the device comprises a body 1 formed of a synthetic plastics material, such as a linear polyamide (e.g. Nylatron) and including a bore 2. A longitudinally extending member 3 of rectangular cross-section is mounted for displacement along the bore 2. The member 3 includes a piston 4 at one end and a hub 5 at the other. The piston 4 carries a sealing ring 6 so as to produce a pressure tight seal between the piston 4 and the bore 2. That end of the bore 2 nearest the piston 4 is closed by an end cap 7 which includes a conduit 8. One end of the conduit 8 communicates with the bore 2 and the other end terminates in a socket 9 adapted to receive a gas line (not shown). A sealing ring 7a is provided between the end of the body 1 and the end cap 7.That end of the bore 2 nearest the hub 5 is closed by an end cap 1 0. A compression spring 11 is carried on the hub 5, one end of the spring being received by, and abutting against the end of, a recess in end cap 10 and the other end of the spring abutting against a collar 1 2 carried by the member 3. The member 3 is generally formed of brass but includes a portion in the form of a transverse bore 13, in which is located a material 1 5 capable of igniting when the detonator of the device is fired. The material may be, for example, a pellet of pentaerylthritol tetra nitrate (PETN).

The body 1 includes a further bore 1 6 at right angles to, and intersecting, bore 2.

Mounted in this bore 1 6 is a brass sleeve 1 7 containing a brass detonator housing 18. The upper part of the housing 1 8 includes a bore 1 9 and the lower part of the housing 1 8 includes a bore 20 coaxial with bore 1 9. A detonator cap 21 formed of a synthetic plastics material (e.g. Nylatron) and carrying an electrical detonator 22 is located within the bore 1 9 and is retained therein by a spring 23 and a cap 24 which is formed of a synthetic plastics material (e.g. Nylatron) and is screwed into the end of the detonator housing 1 8. Detonator cables 25 for carrying electrical current to the detonator 22 pass through a bore 26 in the end cap 24 and a bore in detonator cap 21.

Provided in bore 20 of the detonator housing 1 8 is a booster charge in the form of a copper tube 27 containing an explosive composition (e.g. PETN).

The member 3 including piston 4, hub 5 and collar 1 2 is axially displaceable in the body 1 and is normally held in a first position (as shown in Figs. 1 and 2) by the spring 11.

In this first position it is a brass portion of the member 3 which is interposed between the detonator 22 and the booster charge. If the detonator 22 is fired with the member in this first position, the brass portion of the member 3 interposed between the detonator 22 and the booster charge acts as a barrier and prevents ignition of the composition in the tube 27. By introducing compressed gas into the bore 2 of body 1 via the conduit 8, the member 3 can be axially displaced along the bore 2 in the body against the action of the spring 11 so that it occupies a second position in which said portion of the member 3 comprising the ignitable material 1 5 is interposed between the detonator 22 and the booster charge.When the detonator 22 is fired with the member 3 in this second position, the ignitable material 1 5 forms an ignition path between the detonator 22 and the explosive composition in tube 27; thus the detonator 22 ignites the material 1 5 and this in turn ignites the explosive composition of the booster charge.

Referring now particularly to Figs. 2 and 3, a single pole microswitch 30 is mounted on the body 1 in a position such that it is actuated by the collar 1 2 when the member 3 is in its first position. Three similar single pole microswitches 31, 32 and 33 are mounted on the end cap 10 in positions such that they are actuated by the collar 1 2 when the member 3 is in its second position. Microswitch 30 is linked to a surface console (not shown) by a screened electrical umbilical in a manner such that when the member 3 is in its first position the indication UNARMED is given on the console. The microswitch 31 is linked to the surface console such that when the member 3 is in its second position the indication ARMED is given on the console.Microswitches 32 and 33 complete the electrical circuit between the firing cables 34 and the detonator cables 25. The arrangement also includes a solenoidoperated valve 36 in a gas line 37 which valve enables gas to be conveyed from the line to the socket 9 and thence into the bore 2 of the body 1. When the solenoid is deactivated, gas is allowed to vent out of the body 1 so that the member 3 returns to its first position under the influence of the spring 11.

In use, in carrying out the explosive welding of an underwater pipe to a flange surrounding the pipe, an inflatable main explosive charge is placed against the interior of the pipe where the weld is to be formed and the detonating device is positioned so as to enable it to detonate the main charge when fired. Conventionally, the main charge is inflated using nitrogen gas and gas from this source may be used to displace the member from its first to its second position. In this case, the valve 36 is incorporated in the gas line from the source to the main explosive charge and a branch pipe 38 is fitted downstream of the valve to link the line with the socket 9 in body 1.After completing the various operations of sealing the gap between the outer surface of the pipe and the inner surface of the flange in the location where the weld is to be formed and removing water from this gap, the solenoid of valve 36 is electrically operated from the console so as to allow gas to enter the body via the conduit 8 (and to inflate the main explosive charge). The introduction of gas into the tubular body causes the member to move to its second position and thus the UNARMED indication of the console is extinguished and replaced by the ARMED indication as the member reaches its second position. When the member is in its second position, the explosive chain between the detonator 22 and the booster charge is completed and the detonator 22 is operably connected to the firing cables 34 via the detonator cables 25.Then the detonator 22 can be fired when desired from the console via the firing cables. Firing of the detonator 22 causes ignition of the explosive composition in the tube 27 (via the ignitable material 1 5 in bore 13) and this in turn detonates the main explosive charge to effect the welding of the pipe to the flange.

It will be apparent that in the event that there is a failure in the gas supply or an electrical failure in the solenoid, prior to arming, the member 3 will remain in its first position wherein that portion of the member 3 which is interposed between the detonator 22 and booster charge constitutes a solid interface and prevents the explosive composition in the tube 27 being ignited on firing of the detonator 22. Even if there should be a failure of the solenoid of of the gas supply after arming, the member will automatically return to its first position and render the device UNARMED under the influence of the spring 11.

Claims (8)

1. A detonating device comprising: (i) a detonator, (ii) an explosive composition spaced from the detonator, and (iii) a member including first and second portions and being displaceable between first and second positions so that either the first portion or the second portion, respectively, is inerposed between the detonator and said.

composition, said first portion being such that it constitutes a barrier between the detonator and the explosive composition when said member is in the first position so that firing of the detonator does not cause ignition of said composition and said second portion being such that it constitutes an ignition path from the detonator to the composition when said member is in said second position so that the firing of the detonator causes ignition of said composition.

2. A device as claimed in Claim 1 and including a means biasing the member towards its first position.

3. A device as claimed in Claim 1 or 2 wherein said member includes a piston displaceable along a first bore in a body portion and a means is provided to introduce fluid into the bore to displace the member along the bore from the first to the second position.

4. A device as claimed in claim 3 wherein said second portion of said member is in the form of a bore in said member, which bore is located transversely with respect to said first bore and contains an ignitable material.

5. A device as claimed in Claim 4 wherein said ignitable material is pentaerythritol tetranitrate.

6. A device as claimed in Claim 4 or 5 wherein said body portion includes another bore which intersects said first bore and is in alignment with the bore of said member when said member is in said second position, said detonator and said explosive composition being located within said another bore on opposite sides of said first bore.

7. A device as claimed in any one of the preceding claims wherein said explosive composition is pentaerythritol tetranitrate.

8. A detonating device as claimed in Claim 1 substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 3 of the accompanying drawings.