RU2155262C2 - Device for cutting by blasting - Google Patents

Abstract

FIELD: oil-and-gas producing industry; applicable in cutting by blasting of members of structures of offshore oil and gas production platforms during their dismantling. SUBSTANCE: device has cylindrical body whose cavity accommodates explosive charge and means of initiation, and plugs are installed on both sides of explosive charge in immediate contact with it. Plugs are distinguished by the fact that they are made of successively arranged along body axis three parts whose extreme ones are made of ductile metal, and middle one, of plastic material with acoustic stiffness which is lower than that of material of plug extreme parts. Total height of a plug equals or exceeds 0.9 of explosive charge diameter. Acoustic stiffness of ductal metal of plug extreme parts shall amount to R≥30•10⁶kg•s^-1•m^-2, and acoustic stiffness of material of plug middle part equals (4-10) 10⁶kg•s^-1•m^-2 and its weight does not exceed 10% of plug total weight. Weight of plug part adjacent to explosive charge equals not more than 10-20% of plug total weight. EFFECT: increased efficiency in cutting of thick-walled solid steel pipes and breakage of multiple conductors whose interpipe space filled with cement mortar or some other filling material of low stiffness. 4 cl, 1 dwg

Description

 The invention relates to the oil and gas industry and can be used for cutting explosion of structural elements of offshore oil and gas platforms during their dismantling.

 For cutting cylindrical pipes from the inside, a cumulative pipe cutter is widely used [1]. This device is selected as an analog. It consists of an annular cumulative charge lined with copper, a housing and an initiation system. The pipe is cut using a flat annular cumulative jet. However, the capabilities of this device for cutting thick-walled pipes are limited. Firstly, the length of the jet pipe cutter and, therefore, the depth of cut, cannot exceed half the inner diameter of the pipe. In addition, the efficiency of the internal pipe cutter is reduced due to the fact that during the formation of the jet it experiences a tensile strain in the region, which leads to crushing of the jet into separate sectors.

 The closest technical solution to the claimed is a pipe cutter [2], consisting of an explosive charge, an initiation system and two metal plugs. This device is selected as a prototype. The principle of its operation is based on the explosive property of explosives. Upon initiation of a charge in the center and after reflection of the detonation wave (DW) front from metal plugs, an increase in the intensity of shock waves (SW) occurs in the wall of the cut pipe. When they repeatedly collide in the pipe wall, a further increase in pressure is observed, which, when the tensile strength of the pipe material is exceeded, leads to its destruction in the plane of symmetry of the explosive charge. The prototype contains several disadvantages.

 The main disadvantage of the pipe cutter [2] is that it has application restrictions with the blasting mechanism of operation. The pipe cutter is not capable of destroying monolithic steel pipes with a large wall thickness, and is also not suitable for cutting large-sized multi-pipe conductors, the annular space of which is filled with cement mortar or other non-rigid aggregate (water, air).

In the prototype, the material of the metal plug is not defined in any way, in particular, its acoustic rigidity is not indicated, but it is argued that when the front of the DW is reflected from the plug, the pressure of the explosion products (PV) increases. It is known that with a normal incidence of the DW front on an obstacle, two types of flow are possible. When the acoustic stiffness of the obstruction ρc _o , where ρ is the density of the obstruction, c ₀ is the speed of sound in it, is greater than ρ _VV D _VV , where ρ _{VV is the} density of the VV, D _BB is the detonation velocity of the VV, then in this case the air pressure relative to the pressure at the front, the DW actually increases, which is assumed in [2]. The described case ρc _o > ρ _VV D _VV is satisfied for most metals. If we keep in mind that for high-explosive explosives, the parameter ρ _BB D _BB ~ 14 conventional units (ρ _BB ~ 8 km / s, D _BB ~ 1.7 g / cm ³ ), then this group includes metals starting from aluminum ( ρ = 2.73 g / cm ³ , c _o = 5.25 km / s) and heavier metals.

However, there is a considerable group of metals located in density lower than aluminum for which ρc _o <ρ _BB D _BB . In this case, there is a weakening of the PV pressure, and not amplification. Thus, a contradiction is found between the proposed principle of operation of the pipe cutter [2] and the impossibility of its implementation with a certain material of a metal plug.

 The technical problem to be solved is to increase the efficiency of the device when cutting thick-walled monolithic steel pipes, as well as during the destruction of multi-pipe conductors, the annular space of which is filled with cement mortar. The fundamental basis for solving the problem is to replace the blasting mechanism of the device with a blasting high-explosive one with the decisive role of the latter. In this case, the destruction of the pipe wall will be due to its circumferential deformation, which, when the limit value is exceeded, leads to the appearance of an annular crack. The deformation of the pipe is a consequence of the selection of explosive energy in the radial direction. Increasing the efficiency of the device is achieved by increasing the coefficient of energy extraction in the radial direction, for which the pipe cavity in the axial direction must be reliably closed. Structurally, this problem is solved using a combined stub.

The inventive device explosive cutting (UVR) is shown in the drawing. A water-blasting device containing a cylindrical body, in the cavity of which an explosive charge and initiating means are placed, plugs are installed on both sides of the charge in direct contact with them, plugs are made of three parts adjacent to each other along the axis of the shell, the last of which are made of ductile metal, and the average - from plastic with an acoustic stiffness lower acoustic impedance material covers edge portions, wherein the total height h ₂ of the charge plug and the diameter d ₃ satisfies yayut h ₂ ≥ 0,9d ₃ condition. The value of the acoustic stiffness of the metal of the extreme parts of the stub should be R ≥ 30-10 ⁶ kg • s ^-1 • m ^-2 , and the acoustic stiffness of the material of the middle part of the stub is (4-10) • 10 ⁶ kg • s ^-1 • m ^-2 and its mass does not exceed 10% of the total mass of the stub. The part of the plug adjacent to the explosive charge has a mass of not more than 10-20% of the total mass of the plug.

The high-explosive action of the explosive charge in the radial direction will be more effective, the smaller the PV cavity in the axial direction will increase. At the beginning, the plug “holds” the axial cavity expansion due to acoustic rigidity. And here, in the case of steel, as well as other heavy metals, when R ≥ 30 • 10 ⁶ kg • s ^-1 • m ^-2 , the plug performs this function most effectively. However, the duration of this phase with a reasonable length of the plug (i.e., its mass) can be no more than several tens of microseconds and is determined by the double sound travel time along the length of the plug, while the duration of the entire process of pipe destruction can be measured in milliseconds. It is clear that an additional mechanism should be present here, contributing to an increase in the high explosive impact in the radial direction. In the proposed device, it is associated with the use of the combined design of the plug and is caused by the blasting effect of explosion products on it.

After exposure to PV, a two-dimensional flow of its material occurs in the plug. The stub displacement rate in the axial (longitudinal) direction and, accordingly, the PV cavity growth are inversely proportional to R. This is a negative factor, but due to the use of material with R ≥ 30 • 10 ⁶ kg • s ^-1 • m ^-2 as a stub, it can be reduced to to a minimum. The transverse (radial) flow of the plug material occurs when the shock-compressed plug is unloaded into the pipe wall. Due to it, an increase in the diameter of the plug and clogging of the cavity occurs. Its growth in the axial direction becomes impossible and PV having a pressure exceeding the yield strength of the material of the pipe wall must expand in the radial direction, which ultimately leads to the destruction of the pipe. Thus, under the blasting effect of the PV, a plastic plug forms from the plug in the axial direction and the high-explosive effect of the device in the radial direction increases.

The effectiveness of locking the plug cavity of the pipe is determined by the ratio of the transverse velocity u ₁ to longitudinal u ₀ . It is necessary that this UVR parameter be maximum. In this case, the leakage of PV energy in the axial direction will be the minimum possible. For steel, this parameter is η = u ₁ / u _o ~ 0.7 (u _o ~ 0.85 km / s, u ₁ ~ 0.6 km / s for the case when TG5 / 5 is taken as an explosive, and the wall pipe mainly represents cement mortar). If the plug is made of fluoroplastic F-4, R ≅ 8 • 10 ⁶ kg • s ^-1 • m ^-2 , then in this case u ₁ increases to 1.5 km / s, however, the longitudinal speed increases even more noticeably, u ₀ = 2.5 km / s. It increases in comparison with steel three times and the parameter η for fluoroplastic decreases to 0.6. Those. replacing steel with fluoroplastic degrades the properties of water-blasting. However, it is possible to create an IWR with a combined plug shown in the drawing. For such a plug, the longitudinal velocity will be, like steel, u _o ~ 0.85 km / s, since the bulk of the plug consists of steel, and the transverse one will be determined by fluoroplastic, u ₁ = 1.5 km / s. Then η = u ₁ / u _o = 1.8. And the set technical task will be solved.

Structurally, the combined UVR plug consists of three parts: part a, c are made of material with R ≥ 30 • 10 ⁶ kg • s ^-1 • m ^-2 (steel, copper), part b is made of material whose acoustic rigidity R = (4-10) • 10 ⁶ kg • s ^-1 • m ^-2 (PMMA, fluoroplast, caprolon, etc.). The mass of part b shall not exceed 10% of the mass of the plug. In this case, the longitudinal size of the stub increases insignificantly, and the average density of the stub is close to the density of the “hard” material. At the same time, this is enough to reliably and quickly block the inner section of the pipe. Part b is located after the steel disk a. The height of this disk h ₁ should be such that the mass of the disk a is 10-20% of the total mass of the stub. The purpose of this part is reduced to uniform compression of part b and the absence of its crushing under the action of PV. Since the parts a and the plug also experience a transverse flow and must form a plastic shutter, its material must be plastic. Consequently, strong alloy steels in the manufacture of the plug must prefer steel grade St. 3.

The selection of the mass of the UVR plug is made on the condition that it should exceed the mass of the cut pipe in the radial direction. This limitation follows from the initial conditions of operation of the water supply system. After blasting, the air pressure acts uniformly in all directions, radial and axial, and reports the speed in accordance with their mass. In the radial direction, the mass is determined by the wall thickness (D-d ₃ ), the density of its material ρ ₆ , in the axial ρ ₂ • h ₂ • d ₃ . Then, taking into account the cylindrical geometry, we write the condition for choosing the mass or size h ₂ plugs:
ρ ₆ • (D ² -d $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ) ≤ 4ρ ₂ • h ₂ • d ₃ , (1)
where ρ ₂ is the density of the stub. In the future, the plug after wedging practically stops in the inner pipe.

где D - скорость детонации ВВ, μ - отношение массы ВВ к массе трубы. Подставляя в (2) D = 8000 м/с, v = 400 м/c, а также с учетом того, что μ << 1, получим
μ ≥ 0,02 (3)
При расчете μ необходимо учесть следующее. ВВ сообщает импульс во всех направлениях равномерно: в радиальном импульс передается стенке трубы, в осевом импульс воспринимают заглушки. В соответствии с принятыми условиями масса каждой заглушки равна массе в радиальном направлении (см. (1)). Тем самым мы считаем, что начальная скорость каждой заглушки также будет составлять v = 400 м/с. Тогда с учетом указанных замечаний параметр μ через геометрию УВР, приведенную на фиг. 1, определится как

где где ρ₃ плотность ВВ.Condition (1) is not enough to determine the parameters of the water management system. It is necessary to calculate the explosive charge mass sufficient to cut the pipe, depending on its parameters. It was experimentally determined that if a radial velocity of more than 400 m / s is given to the pipe wall using an explosive, then this energy is sufficient to achieve deformation of the steel pipe exceeding the limit (50-60%). After that, its destruction will occur with the formation of through annular cracks. Radial velocity can be estimated using the Garni formula:

where D is the explosive detonation velocity, μ is the ratio of the explosive mass to the mass of the pipe. Substituting in (2) D = 8000 m / s, v = 400 m / s, and also taking into account the fact that μ << 1, we obtain
μ ≥ 0.02 (3)
In calculating μ, the following must be taken into account. The explosive gives a pulse in all directions evenly: in a radial pulse it is transmitted to the pipe wall, and plugs perceive in the axial pulse. In accordance with the accepted conditions, the mass of each plug is equal to the mass in the radial direction (see (1)). Thus, we believe that the initial velocity of each stub will also be v = 400 m / s. Then, taking these remarks into account, the parameter μ through the water-velocity geometry shown in FIG. 1, defined as

where where ρ _{3 is the} density of explosives.

Excluding from (1) and (4) the parameter ρ ₆ • (D ² -d $\genfrac{}{}{0ex}{}{\text{2}}{\text{3}}$ ) characterizing the properties of the pipe being cut, and assuming that the density of the explosive is ρ ₃ ~ 1.8 g / cm ³ , and the density of the plug is taken to be equal to the density of steel, ρ ₂ ~ 7.8 g / cm ³ , we obtain a relationship between the height of the plug and the diameter of the charge ₃ :
h ² ≥ 0.9 • d ₃ (5)
which is crucial in the claims. With the specified parameters of the water management system (d ₃ , h ₂ ), the dimensions of the pipe being destroyed are calculated according to (1) or (4). Thus, equations (1) - (5) completely determine the parameters of a high-explosive blasting water blast and an object that the air-blast can cut.

 The drawing shows the claimed UVR. In case 7, the explosive charge 1 is located, in direct contact with it are two composite plugs 2. To activate the device, one of the plugs has an initiation system 3 consisting of an electric detonator (ED) and a detonating cord (LH). cut conductor, consisting of outer 4 and inner 5 pipes, the annular space of the conductor is filled with cement mortar 6.

 After applying an electrical impulse to the ED circuit, the explosive charge of explosive 1 is blown up by means of a high-voltage explosive. During the interaction of the explosive with composite plug 2, a plastic plug forms from it. The increase in the dimensions of the cavity in the axial direction stops, almost all of the PV energy is used for radial deformation of the pipe wall. When its circumferential deformation exceeds the limiting value (50-60%), an annular through crack is formed and the conductor is completely divided into two parts.

For a specific design, the water-cooling device had an aluminum case with a wall thickness of 2 mm and an outer diameter of 146 mm, explosive charge diameter d ₃ = 141 mm, charge length h ₃ = 600 mm, charge density ρ ₃ ~ 1.8 g / cm ³ . The composite plug had a total height of h ₂ = 140 mm, with a steel part having a height of 20 mm and a caprolon disk of 6–25 mm. The rest of the plug was made of steel Art. 3. On one of the plugs was a socket with a D-22 type ED. From the ED to the explosive charge, the initiating pulse was transmitted using a detonating cord with a diameter of 8 mm. The UVR was installed in a conductor with an inner diameter of 148 mm and an outer diameter of 720 mm. The annulus was filled with cement mortar.

Sources of information
1. Shooting and explosive equipment. Handbook Ed. L.Ya. Friedlander. 2nd edition, revised and supplemented. M., Nedra, 1990.

 2. Chernyshev V.K., Zharinov E.I., Buzin V.N., Kudelkin I.D., Zimakov S.D. , Ionov A.I., Bidlo N.P. Pipe cutter. Patent 2093660. BI, 1997, N 23.

Claims (4)

1. An explosive cutting device containing a cylindrical body, in the cavity of which an explosive charge and its initiation system are placed, plugs are installed on both sides of the charge in direct contact with it, characterized in that the plugs are made of sequentially placed along the axis of the body adjacent to each other a friend of three parts, the extreme of which are made of ductile metal, and the middle one is made of plastic with acoustic stiffness, less acoustic stiffness of the end parts of the plug, while the overall height and ₂ h and the diameter d stub charge ₃ satisfy the condition h ₂ d ₃ ≥ 0.9. 2. The explosive cutting device according to claim 1, characterized in that the acoustic rigidity of the metal of the extreme parts of the plug is not less than 30 • 10 ⁶ kg • s ^-1 • m ^-2 . 3. The explosive cutting device according to claim 1, characterized in that the acoustic rigidity of the material of the middle part of the plug is (4 - 10) • 10 ⁶ kg • s ^-1 • m ^-2 , and its mass does not exceed 10% of the total mass of the plug.  4. An explosive cutting device according to claim 1, characterized in that the part of the plug adjacent to the explosive charge has a mass of not more than (10 - 20)% of the total mass of the plug.