Patent Application
20050040071
The invention relates to the transporting of textile sheathed detonating cord and more particularly to methods used in the packaging of textile detonating cord to achieve a shipping classification allowing shipment of the detonating cord by commercial aircraft. Also the invention relates to the design of an explosive diode to restrict detonation transfer to one direction only.
Detonating cords typically contain a secondary high explosive core encased in an outer textile sheath and plastic jacket. Typical explosive materials used are PETN, RDX, HMX, HNS, and PYX. These textile wrapped detonating cords are used extensively in the petroleum exploration and production industry to initiate other explosive components used in various downhole tools. The textile wrapping provides a highly flexible structure that can be easily threaded through perforating guns. Some examples of components that textile detonating cords are used with are perforating shaped charges, setting tools, and similar items. The well locations where these components are used are widely scattered around the world sometimes in very remote locations. It is highly desirable to be able to ship detonating cord by air from a central store location to the remote field location needing the material. However the regulations governing the shipment of explosives by air are quite stringent.
Basically the regulations require that detonating cord explosive materials be packaged in such a manner that an ignition or detonation in one container shall be confined to that container and will not propagate to another container. In practical terms, this means that the maximum amount of detonating cord allowed to detonate in a package is twelve inches to thirty-six inches.
The prior art has several examples of packaging methods that have been used to meet the air shipping regulations for explosive materials. U.S. Pat. No. 4,586,602 discloses a detonating cord transport system where the detonating cord is wound on a plurality of separator support members that provide crossover locations at frequent intervals. At these crossover points, a severing means is wrapped around the cord so that the detonation of one cord portion will sever the continuing cord length at the crossover point without initiating the cord. The maximum length of cord that can detonate without encountering a crossover point is approximately one foot. Packaging of detonating cord using this method is quite laborious and involves inserting severing means around the cord and cable ties to anchor the cord in position.
U.S. Pat. No. 4,817,787 discloses a different packaging method where a mounting board of insulating material, such as expanded polystyrene, is used to hold the cord. Walled paths are molded into the mounting board through which the cord can be threaded. The cord path has a series of loop regions and adjoining parallel regions through which the parallel cord is separated by the wall. The purpose of the wall is to provide a safety distance where the detonation of a length of cord will cause the adjacent parallel length of cord to be severed without initiation. The minimum wall thickness required for the expanded polystyrene is about 0.205″ minimum.
U.S. Pat. No. 4,895,249 discusses a packaging method that is claimed to be an improvement over the detonating cord transport system disclosed in the '602 patent. This patent discloses a method that increases the labor efficiency of packaging detonating cord and efficiencies in the quantity of detonating cord per package. In this patent, the detonating cord is also wound on a plurality of separator support members. The cord is wound in loops that cross over itself at frequent locations. At the crossover points a severing means is inserted which serves as a means of stopping the detonation at the crossover point. A preferred example of a severing means is a nylon-reinforced rubber hose that is slit and placed around one cord section at the crossover point. Each separator support layer can accommodate about 25 feet of detonating cord. Twenty stacked layers will therefore allow a total of 500 feet of detonating cord to be shipped in one package.
The prior art disclosed in both the '602 patent and the '787 patent rely on a separate severing means to actually cut the detonating cord. For this system to work, the detonating cord must follow a path very close to the adjacent strand being actually severed. The detonation of the cord will accelerate the independent severing means at high velocity. The material being accelerated actually causes the severing of the detonating cord. Fog the '249 patent, the severing means is a metal foil sleeve placed over the detonating cord at an actual crossover point.
Both of these packaging methods require that the detonating cord be bent back to either cross over itself or pass close by in a parallel orientation to insure severing of the detonating cord. Placing severe bends in the detonating cord remains in this packaging orientation for an extended period of time.
In the preferred embodiment of this invention, the detonating cord can be space apart at a greater distance that allows the radius of the loop to be increased to avoid damaging the detonating cord. Also the cord sections pass each other at the severing location in an arcuate configuration that avoids any sharp bends in the detonating cord. This packaging method allows the detonating cord to be stored in this configuration for an extended length of time. Also since no separate severing means is required, there will be a resultant material and labor costs.
It is the objective of the present invention to provide an improved method for packaging detonating cord that will meet the requirements for shipment by commercial air carriers in the United States and internationally. It is another objective of the present invention to obviate the need for a severing means and instead rely on the detonation properties of the cord to sever itself. It is another object of the present invention to provide an explosive diode whereby the propagation of detonation is restricted to one direction only.
A diode cutoff block is shown in
The block can be made out of a variety of materials such as metal, wood, or plastic. From a cost and weight standpoint, the preferred material is usually plastic. The dimensions of the block are determined by the quantity of explosive loading in the detonating cord. Typically textile detonating cords have an explosive loading ranging from 4 grains per foot to 400 grains per foot. A typical textile detonating cord for the oil well servicing industry has a coreload of about 80 grains per foot. With a higher coreload detonating cord, the distance between the thru holes must be increased slightly and the block made thicker. The actual dimensions are determined by evaluating the severing capabilities of various samples of detonating cord in different block dimensions. ‘For an 80 gr/ft detonating cord, the distance between thru holes ranges from 0.250″ to about 1.250″. The loop needs to have a minimum detonating cord length of about 6 inches to allow adequate severing of the detonating cord.
The diode cutoff block illustrated in
When the hinged block is closed, an air blast channel 26 is formed similar to that in the one-piece block. The functioning of the block 20 is identical to the cutoff block 10 described earlier. When a length of detonating cord detonates, the air blast from the cord will sever the adjacent length prior to the detonation front passing around the loop and back through the block.
It is also possible to use a diode block as a directional cutoff device.
The diode cutoff direction is illustrated by the arrow (56). If the main detonating cord lead 40 is initiated at the top of the figure, the detonation wave will progress towards the bottom of the figure. The main detonating cord will initiate the jumper detonating cord at the hog ring connection (44). The jumper detonating cord is much shorter than the main detonating cord lead that has a series of loops 40a, 40b, 40c in it. Thus the detonation front from the jumper cord 44 will arrive at the diode block 10 and sever the main detonating cord lead at 50/52 before the detonation front from the main lead 40 arrives at the block. Thus the block 10 will function as an explosive diode, permitting the detonation front to pass through the block only in the direction opposite that of the cutoff direction 56.
The length of each loop is about twelve inches. In this design the maximum length of detonating cord that may be detonated is about eighteen inches before the detonating cord will be severed in a diode cutoff block. Each detonating cord transport section holds about eighteen feet of detonating cord. By stacking multiple transport sections, larger quantities of detonating cord can be packaged. For example, stacking twenty-eight transport sections will allow packaging 500 feet of detonating cord in an outer 4G fiberboard box.
Thus, block 20 in
The term “block” is intended to mean a three-dimensional elongated object with one or more flat faces, and otherwise of any convenient shape for defining the longitudinal blast passageway(s) and lateral channel(s) called for in the appended claims.
The foregoing disclosure and the embodiments shown in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.
