Self-holding type seabed hydraulic clamp and control method

Abstract

The self-holding type seabed hydraulic clamp comprises a mounting support, clamping calipers are arranged in the mounting support in the horizontal direction, the two ends of the clamping calipers are connected with clamping hydraulic cylinders, the clamping hydraulic cylinders are connected with self-locking hydraulic cylinders, and rear end covers are arranged at the rear ends of the self-locking hydraulic cylinders. The invention further discloses a control method of the self-holding type seabed hydraulic tongs. The problem that the reliability is low when pressure maintaining clamping is achieved through an energy accumulator in an existing seabed hydraulic clamp is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of offshore drilling equipment, and particularly relates to a self-holding subsea hydraulic tong, and also relates to a control method for the self-holding subsea hydraulic tong. Background Art

[0002] For offshore geological exploration and scientific research operations, subsea coring is an important means to directly obtain the formation state. Through a 5.5-inch or 7.5-inch drill pipe string connected from the water surface to the bottom of the well, a coring tool is sent into the drill pipe, and a coring operation can be completed by taking the core and fishing it out. During the coring process, due to the combined action of ocean currents, surges, and ship heave, the drill pipe string will be in irregular motion. For the bottom of the well, the movement of the drill pipe will cause irregular up and down "cavitation" of the drill bit and the coring tool. If the movement of the drill pipe is not controlled, coring faults and wellbore collapses may occur during coring, ultimately resulting in the inability to carry out the coring task.

[0003] The prior art usually uses a subsea baseplate to assist in the coring operation. The subsea baseplate consists of a baseplate body and a subsea hydraulic tong. The drill pipe is drilled into the formation after being guided by the upper and lower bell mouths of the baseplate. The baseplate itself has a large underwater weight. After being placed on the seabed mud line, it can effectively reduce the bending degree of the drill pipe after it enters the formation. The subsea hydraulic tong is installed between the upper and lower bell mouths. During coring, the hydraulic tong clamps the drill pipe. Due to the self-weight of the subsea baseplate, the drill bit at the bottom of the well will be in a static state. At this time, when the coring tool is lowered, the quality of coring will be greatly improved. The subsea hydraulic tong is an important component of the subsea baseplate. During drilling, the subsea hydraulic tong opens to facilitate the lowering of the drill string. During coring, the subsea tong closes to clamp and stabilize the drill pipe, improving the coring success rate. The subsea baseplate is usually lowered and recovered using a wire rope. In case of an emergency, when the wire rope breaks or the winch for retracting and releasing fails, the drill pipe clamping function of the subsea hydraulic tong can be used to recover the subsea baseplate by recovering the drill pipe. Therefore, the reliability of the subsea hydraulic tong clamping is the key to recovering the subsea baseplate using the drill pipe. Existing subsea hydraulic tongs usually use a hydraulic method to drive the hydraulic cylinder to push the subsea tong to clamp and release. For the continuous clamping function of the subsea hydraulic tong, the pressure maintaining ability of the accumulator is often used to keep the pressure in the clamping hydraulic cylinder constant, thereby achieving a stable clamping force application. In addition, the accumulator can also ensure to a certain extent that the clamping force is not affected when the hydraulic power source fails.

[0004] During the process of retrieving the subsea baseplate with the drill pipe, the retrieval duration is long, and the ship is constantly in motion during the retrieval process. Coupled with the vibration generated by the elasticity of the drill pipe in water, extremely high requirements are imposed on the clamping stability of the subsea clamp. Once the clamping force of the subsea clamp becomes smaller, the vibration during the retrieval process will cause the subsea clamp to continuously loosen, and ultimately may lead to an accident where the subsea baseplate falls to the seabed. For the subsea hydraulic clamp that uses an accumulator for pressure-holding clamping, if the power source fails, the accumulator will be the only power source to maintain the clamping force. However, in the actual use process, since the sealing elements such as the hydraulic cylinder, pipe joints, and valve parts cannot achieve zero leakage, during the pressure-holding clamping process of the accumulator, the clamping force will gradually decrease as the oil leaks. At the same time, as a device that uses compressed air for pressure-holding, the accumulator is in direct contact with the ambient seawater, and a sudden decrease in seawater temperature during the lifting process will also cause the clamping force to decrease. Therefore, during the process of lifting the subsea baseplate with the drill pipe, due to concerns about clamping reliability, the operator needs to constantly pay attention to the internal pressure of the subsea hydraulic clamp to prevent accidents caused by a decrease in the clamping force of the subsea hydraulic clamp. This inevitably requires adding underwater sensors and also considering the problem of signal transmission to the water surface. The investment in the underwater clamping force monitoring system will significantly increase the installation cost of the subsea baseplate. Therefore, using the accumulator to maintain pressure to achieve the clamping of the subsea hydraulic clamp and continuously monitor the clamping force data has problems of low reliability and excessively high installation costs. With the increasing intensity of China's marine exploration and scientific research operations year by year, the current method of using a subsea hydraulic clamp to clamp the drill pipe to retrieve the subsea baseplate can no longer meet the increasingly stringent safety and cost reduction requirements. It is particularly urgent to propose a new type of safer and lower-cost subsea hydraulic clamp. Summary of the Invention

[0005] One object of the present invention is to provide a self-holding subsea hydraulic clamp to solve the problem of low reliability of the existing subsea hydraulic clamp using an accumulator to achieve pressure-holding clamping.

[0006] Another object of the present invention is to provide a control method for the above self-holding subsea hydraulic clamp.

[0007] The technical solution adopted by the present invention is that the self-holding subsea hydraulic clamp includes an installation bracket. Inside the installation bracket, a clamping caliper is arranged horizontally. Both ends of the clamping caliper are connected to a clamping hydraulic cylinder, the clamping hydraulic cylinder is connected to a self-locking hydraulic cylinder, and a rear end cover is arranged at the rear end of the self-locking hydraulic cylinder.

[0008] The characteristics of the present invention also lie in that

[0009] The installation bracket includes a cylinder. A through hole is radially opened in the middle of the cylinder along the extending direction. A subsea clamp installation flange is sleeved in the through hole. The subsea clamp installation flange is arranged horizontally. A baseplate connection flange is arranged at the top of the cylinder, and a guide cylinder installation flange is arranged at the bottom of the cylinder.

[0010] The clamping caliper includes a caliper body. One end of the caliper body is connected to the piston rod of the clamping cylinder through a thread. A chuck body fixing groove is formed at the other end of the caliper body. Two sets of chucks are arranged in a conical shape in the chuck body fixing groove. The contact surface between the chucks and the caliper body is fastened by chuck bolts. The chucks are in direct contact with the surface of the drill pipe. Multiple rows of chuck teeth are designed on the chucks. Pressure blocks are respectively arranged at the upper and lower ends of the chucks, and the pressure blocks are fitted with the upper and lower surfaces of the caliper body.

[0011] The clamping cylinder includes a clamping cylinder barrel. A clamping piston is arranged at one end inside the clamping cylinder barrel. A front end cover of the clamping cylinder is arranged at the front section of the clamping piston. The clamping piston is connected to a clamping piston rod. The clamping piston rod penetrates through the front end cover of the clamping cylinder, and the end of the clamping piston rod is connected to the caliper body.

[0012] At the other end inside the clamping cylinder barrel, a spring, a self-locking piston, and a front end cover of the self-locking cylinder are arranged in sequence. One end of the spring contacts the clamping piston, and the other end of the spring is provided with the self-locking piston. Limit blocks are arranged on both the clamping piston and the self-locking piston on the side close to the spring.

[0013] The self-locking piston is connected to a self-locking piston rod. The self-locking piston rod is connected to the self-locking piston through a thread, and the self-locking piston rod penetrates through the front end cover of the self-locking cylinder. The self-locking cylinder includes a self-locking cylinder barrel. The self-locking cylinder barrel communicates with the clamping cylinder barrel. A front end cover of the self-locking cylinder is arranged on the side of the self-locking cylinder barrel close to the clamping cylinder barrel. A rear end cover of the self-locking cylinder is arranged on the side of the self-locking cylinder barrel far from the front end cover of the self-locking cylinder. A rear end cover is arranged behind the rear end cover of the self-locking cylinder, and a locking thrust piston is arranged behind the front end cover of the self-locking cylinder.

[0014] The thrust piston is connected to a locking push rod. The locking push rod is connected to a locking push rod fixing disk. A number of engaging teeth are evenly arranged circumferentially on the locking push rod fixing disk. A retaining ring is clamped on the outer periphery of the number of engaging teeth. The retaining ring is a conical ring. The retaining ring is connected to an unlocking push rod. The unlocking push rod is connected to an unlocking push rod fixing disk. The unlocking push rod fixing disk is connected to an unlocking thrust piston. The self-locking piston rod penetrates through the thrust piston, the locking push rod fixing disk, the retaining ring, the unlocking push rod fixing disk, and the unlocking thrust piston in sequence.

[0015] Both ends of the self-locking piston rod are smooth sealing surfaces, and the middle part where it engages with the engaging teeth is a rough surface. A through hole is axially opened in the self-locking piston rod, and the through hole introduces gas into the rear end cover. The engaging teeth include an engaging tooth body, and the engaging tooth body is in the shape of a 1 / 6 hollow frustum. The outer peripheral dimensions of the engaging tooth body match the conical ring of the retaining ring. The contact surface between the engaging tooth body and the retaining ring is designed to be conical and the cone angles are kept consistent. Grooves are opened on the inner wall of the engaging tooth body, and engaging tooth surfaces are arranged in the grooves. The engaging tooth surfaces are arc-shaped plates with multiple rows of teeth. The engaging tooth surfaces are fixedly embedded in the grooves of the engaging tooth body by using engaging tooth fixing bolts. The installation planes of the engaging tooth body and the engaging tooth surfaces are also designed to be conical. After the engaging tooth surfaces are installed, they form a certain angle with the central axis of the self-locking piston rod; The locking push rod includes a locking push rod body. Two spherical grooves are opened at the end of the locking push rod body, and thrust steel balls are installed in the spherical grooves. A locking push rod gland is arranged at the end of the locking push rod body, and the locking push rod gland is fastened by a push rod fastening bolt; The unlocking push rod includes an unlocking push rod body. One spherical groove is opened at the end of the unlocking push rod body, and a thrust steel ball is installed in the spherical groove. An unlocking push rod gland is arranged at the end of the unlocking push rod body, and the unlocking push rod gland is fastened by a push rod fastening bolt.

[0016] Another technical solution adopted by the present invention is

[0017] A control method for a self-holding subsea hydraulic tong, which realizes the free switching of the self-holding subsea hydraulic tong under 5 working modes by using the cooperation of the self-holding subsea hydraulic tong with an external hydraulic source and hydraulic valve components, and is specifically implemented according to the following steps:

[0018] S1. Initial mode of the subsea hydraulic tong, specifically:

[0019] The initial mode of the subsea hydraulic tong is the state when the subsea hydraulic tong is not working. At this time, all the electromagnets in the three-position four-way directional control valves coded as SV1 and SV2 are powered off, and the X1 and X2 ports of the self-locking hydraulic cylinder are connected to the oil tank and are in an unoperated state;

[0020] The A and B ports of the clamping hydraulic cylinder are connected to the oil tank, the spring is in a free release state, and the oil volume in the clamping hydraulic cavity and the self-locking hydraulic cavity in the clamping hydraulic cylinder determines the position of the clamping piston rod;

[0021] S2. Loosening mode of the subsea hydraulic tong, specifically:

[0022] After the subsea chassis is lowered to the seabed, in order to facilitate the lowering of the sampling tool, all the subsea hydraulic tongs are opened. At this time, the b-position electromagnet of SV1 is powered on, the a-position electromagnet is powered off, all the electromagnets of SV2 are powered off, and the self-locking hydraulic cylinder is in an unoperated state;

[0023] The hydraulic source supplies oil to the pressure port P. After being shunted by the shunt and manifold valve DV1 through SV1, it enters the port A of the two clamping hydraulic cylinders. The clamping piston chamber is filled with oil, and the clamping piston rod is pushed to retract. At the same time, the elastic force of the spring will cause the hydraulic oil in the self-locking piston chamber to be squeezed out, and after merging at DV2 at port B, it flows back to the fuel tank through SV1. The two shunt and manifold valves play a role in keeping the retracting speed of the clamping piston rods consistent.

[0024] S3. Subsea hydraulic tong clamping mode, specifically:

[0025] During subsea coring operations, the subsea hydraulic tongs need to clamp the drill pipe. At this time, the a-position electromagnet of SV1 is de-energized, the b-position electromagnet of SV1 is de-energized, all the electromagnets of SV2 are de-energized, and the self-locking hydraulic cylinder is in an unoperated state. The hydraulic source supplies oil to the pressure port P. After being shunted by the shunt and manifold valve DV2 through SV1, it enters the port B of the two clamping hydraulic cylinders. The self-locking piston chamber is filled with oil, and the self-locking piston rod is pushed to extend.

[0026] At the same time, the elastic force of the spring will cause the hydraulic oil in the clamping piston chamber to be squeezed out, and after merging at DV1 at port A, it flows back to the fuel tank through SV1, and the clamping piston rod is pushed to extend. The two shunt and manifold valves play a role in keeping the extending speeds of the clamping piston rod and the self-locking piston rod consistent. As the pressure in the self-locking piston chamber increases, the spring is gradually compressed, and the clamping force applied by the clamping piston rod on the drill pipe through the clamping tongs also increases. The check valve CV1 installed at the inlet of SV1 plays a role in maintaining the clamping force to a certain extent when the pressure at port P drops.

[0027] S4. Subsea hydraulic tong locking mode, specifically:

[0028] When the subsea template needs to use the drill pipe for emergency recovery, this mode is enabled. First, the subsea hydraulic tongs should be in the state of clamping the drill pipe according to the method described in S3, so that the pressure at port P reaches the maximum, and the clamping force of the subsea hydraulic tongs on the drill pipe also reaches the maximum. At this time, keep the a-position electromagnet of SV1 energized and the b-position electromagnet de-energized, and at the same time, keep the b-position electromagnet of SV2 energized and the a-position electromagnet de-energized. The pressure oil at port P enters the control oil port X1 of the two self-locking hydraulic cylinders through SV2, and the pressure at port P drops. Due to the function of CV1, the thrust of the clamping hydraulic cylinder does not change, and the corresponding clamping force of the subsea hydraulic tongs does not change either.

[0029] The locking thrust piston chamber of the self-locking hydraulic cylinder starts to be filled with oil, and the locking thrust piston is pushed to squeeze the engaging teeth to move. The engaging teeth bite the self-locking piston rod under the restriction of the retaining ring. At the same time, the engaging teeth push the unlocking thrust piston to drain the hydraulic oil in the chamber back to the fuel tank. As the pressure at port P reaches the maximum again, the engaging teeth move to the limit position, and the biting force on the self-locking piston rod also reaches the maximum.

[0030] Power off all the electromagnets of SV1 and SV2, and reduce the pressure in all hydraulic chambers of the clamping cylinder and the self-locking cylinder to the minimum. Due to the action of the spring, it will continuously provide a thrust force equal in magnitude and opposite in direction to the drill pipe clamping force for the self-locking piston rod. Thanks to the conical mating surface between the engaging teeth and the retaining ring and the design of the inclined engaging surface between the engaging teeth and the self-locking piston rod, the elastic force of the spring will cause the engaging teeth to lock with the self-locking piston rod. Since the position of the self-locking piston rod is locked, the subsea hydraulic tongs continuously clamp the drill pipe through the spring, achieving mechanical self-locking without relying on hydraulic power.

[0031] S5. Unlock the subsea hydraulic tongs, specifically:

[0032] When the subsea hydraulic tongs in the locked state need to be unlocked, ensure that the hydraulic source supplies oil to the pressure port P, make the a-position electromagnet of SV1 energized and the b-position electromagnet de-energized. The hydraulic oil enters the B port of the two clamping cylinders through SV1, and the pressure in the self-locking piston chamber increases. When the pressure at the P port reaches the maximum, the elastic force of the spring acting on the self-locking piston rod and the hydraulic thrust provided by the self-locking piston chamber cancel each other out, and the unlocking operation is ready.

[0033] At this time, make the a-position electromagnet of SV2 energized and the b-position electromagnet de-energized. The hydraulic oil enters the control oil port X2 of the two self-locking cylinders through SV2, and the unlocking thrust piston chamber starts to be filled with oil, pushing the unlocking thrust piston to move the engaging teeth in the direction away from the retaining ring. The radial force exerted by the retaining ring on the engaging teeth disappears, and the clamping force of the engaging teeth on the self-locking piston rod is lost, and the position lock of the self-locking piston rod is released. After the lock is released, de-energize the two electromagnets of SV2, and the clamping and loosening of the subsea hydraulic tongs can be achieved by controlling SV1.

[0034] The beneficial effects of the present invention are as follows: The present invention meets the working condition of using the drill pipe for recovery in case of emergency for the subsea template. The subsea hydraulic tongs have a self-holding function, can achieve stable clamping of the drill pipe without an external hydraulic source and accumulator, and at the same time do not require an additional underwater clamping monitoring system, having certain advantages in terms of reliability and cost compared with the existing subsea hydraulic tongs, specifically including the following aspects:

[0035] (1) Reliable self-holding function. The engaging teeth are used to bite and lock the piston rod. Under the action of the spring, the clamping cylinder pushes the clamping tong body to continuously clamp the drill pipe. At the same time, due to the elastic force of the spring, the biting force between the piston rod and the engaging teeth does not change, and the piston rod realizes mechanical self-locking.

[0036] (2) Lower installation cost. Since there is no need for the pressure maintaining of an underwater accumulator and the self-holding function of the subsea hydraulic tongs is reliable enough, during the process of recovering the subsea template using the drill pipe, there is no need to detect the clamping force, saving the installation cost of the underwater data acquisition, transmission, and surface data display units, and significantly reducing the cost of the entire subsea template.

[0037] (3) High integration and good maintainability. The installation bracket of the subsea clamp, the clamping hydraulic cylinder, the clamping pliers body, the self-holding hydraulic cylinder, etc. are all integrally designed and assembled along the clamping direction, and each component can be disassembled and installed separately, which is convenient for use and maintenance. Description of the Drawings

[0038] Figure 1 is a perspective view of the self-holding subsea hydraulic clamp of the present invention;

[0039] Figure 2 is a side view of the self-holding subsea hydraulic clamp of the present invention;

[0040] Figure 3 is a top view of the self-holding subsea hydraulic clamp of the present invention;

[0041] Figure 4 is a schematic structural diagram of the installation bracket of the self-holding subsea hydraulic clamp of the present invention;

[0042] Figure 5 is a schematic structural diagram of the caliper body of the self-holding subsea hydraulic clamp of the present invention;

[0043] Figure 6 is a sectional view of the self-holding subsea hydraulic clamp of the present invention;

[0044] Figure 7 is a schematic structural diagram of the self-locking hydraulic cylinder of the self-holding subsea hydraulic clamp of the present invention;

[0045] Figure 8 is a schematic structural diagram of the engaging teeth of the self-holding subsea hydraulic clamp of the present invention;

[0046] Figure 9 is a structural diagram of the locking push rod in the self-holding subsea hydraulic clamp of the present invention;

[0047] Figure 10 is a structural diagram of the unlocking push rod in the self-holding subsea hydraulic clamp of the present invention;

[0048] Figure 11 is a structural diagram of the unlocking push rod in the self-holding subsea hydraulic clamp of the present invention;

[0049] Figure 12 is a schematic control diagram of the self-holding subsea hydraulic clamp of the present invention.

[0050] In the figure, 1. mounting bracket, 1-1. mounting bracket body, 1-2. base plate connecting flange, 1-3. subsea clamp mounting flange, 1-4. guide cylinder mounting flange; 2. clamping caliper, 2-1. slip, 2-2. caliper body, 2-3. pressing block, 2-4. slip bolt; 3. clamping cylinder, 3-1. clamping piston rod, 3-2. front end cover of clamping cylinder, 3-3. clamping piston, 3-4. spring, 3-5. clamping cylinder barrel, 3-6. self-locking piston; 4. self-locking cylinder, 4-1. self-locking piston rod, 4-2. front end cover of self-locking cylinder, 4-3. locking thrust piston, 4-4. self-locking cylinder barrel, 4-5. locking push rod, 4-51. locking push rod body, 4-52. locking push rod gland, 4-53. thrust steel ball, 4-54. push rod fastening bolt, 4-6. locking push rod fixing plate, 4-61. push rod fixing plate body, 4-62. push rod fixing bolt, 4-7. engaging teeth, 4-71. engaging teeth body, 4-72. engaging teeth surface, 4-73. engaging teeth fixing bolt, 4-8. retaining ring, 4-9. unlocking push rod, 4-91. unlocking push rod body, 4-92. unlocking push rod gland, 4-10. unlocking push rod fixing plate, 4-11. unlocking thrust piston, 4-12. rear end cover of self-locking cylinder, 5. rear end cover, 6. flow dividing and collecting valve, 7. three-position four-way directional control valve, 8. check valve. Detailed implementation mode

[0051] The present invention will be described in detail below in conjunction with the accompanying drawings and the specific implementation mode.

[0052] Embodiment 1

[0053] The self-holding subsea hydraulic clamp of the present invention, as Figure 1 , Figure 2 , Figure 3 shown, includes a mounting bracket 1. A clamping caliper 2 is arranged horizontally inside the mounting bracket 1. Both ends of the clamping caliper 2 are connected to a clamping cylinder 3. The clamping cylinder 3 is connected to a self-locking cylinder 4. A rear end cover 5 is arranged at the rear end of the self-locking cylinder 4. The clamping caliper 2 moves inside the mounting bracket 1 under the push of the clamping cylinder 3. The clamping caliper 2 applies two clamping forces with the same magnitude and opposite directions in the radial direction of the drill pipe, and can clamp and release the drill pipe at any position of the drill pipe. The clamping cylinder 3, the self-locking cylinder 4 and the rear end cover 5 are connected by bolts to form a driving mechanism, and the clamping caliper 2 as an executing mechanism is connected by threads to form a clamping clamp. The clamping caliper 2, the clamping cylinder 3 and the self-locking cylinder 4 are integrated on the same axis, and the clamping clamp is installed on the mounting bracket 1 through a flange to form a self-holding subsea hydraulic clamp.

[0054] Embodiment 2

[0055] As Figure 4As shown in the figure, the mounting bracket 1 includes a cylinder. A through hole is radially opened in the middle of the cylinder along the extending direction. A subsea clamp mounting flange 1-3 is sleeved in the through hole. The subsea clamp mounting flange 1-3 is horizontally arranged. Square holes are opened around the subsea clamp mounting flange 1-3 to facilitate observing the position of the clamping caliper 2 from the outside. A base plate connecting flange 1-2 is arranged at the top of the cylinder, and a guide cylinder mounting flange 1-4 is arranged at the bottom of the cylinder. The base plate connecting flange 1-2 is responsible for bolt connection with the subsea base plate body, and the guide cylinder mounting flange 1-4 is responsible for bolt connection with the drill pipe guide cylinder.

[0056] As Figure 5 shown in the figure, the clamping caliper 2 includes a caliper body 2-2. One end of the caliper body 2-2 is connected to the piston rod of the clamping hydraulic cylinder 3 by thread. A chuck body fixing groove is opened at the other end of the caliper body 2-2. Two sets of chucks 2-1 are arranged in a conical shape in the chuck body fixing groove. The contact surface between the chuck 2-1 and the caliper body 2-2 is fastened by chuck bolts 2-4. The chuck 2-1 directly contacts the surface of the drill pipe. Multiple rows of chuck teeth are designed on the chuck 2-1 to increase the clamping contact area with the drill pipe, and the bearing capacity of the clamped drill pipe is guaranteed. Pressure blocks 2-3 are respectively arranged at the upper and lower ends of the chuck 2-1. The pressure blocks 2-3 are fitted with the upper and lower surfaces of the caliper body 2-2. The chuck bolts 2-4 and the pressure blocks 2-3 facilitate the replacement of the chuck 2-1 when it is damaged.

[0057] As Figure 6 shown in the figure, the clamping hydraulic cylinder 3 includes a clamping hydraulic cylinder barrel 3-5. A clamping piston 3-3 is arranged at one end inside the clamping hydraulic cylinder barrel 3-5. A clamping hydraulic cylinder front cover 3-2 is arranged in front of the clamping piston 3-3. The clamping piston 3-3 is connected to a clamping piston rod 3-1. The clamping piston rod 3-1 passes through the clamping hydraulic cylinder front cover 3-2, and the end of the clamping piston rod 3-1 is connected to the caliper body 2-2. Both ends of the clamping piston rod 3-1 are connected to the clamping piston 3-3 and the caliper body 2-2 by thread respectively to transmit the clamping force. The clamping hydraulic cylinder barrel 3-5, the clamping piston 3-3, the clamping piston rod 3-1 and the clamping hydraulic cylinder front cover 3-2 form the clamping hydraulic cavity of the clamping hydraulic cylinder 3 to drive the movement of the clamping piston rod 3-1 to drive the caliper body 2-2.

[0058] At the other end inside the clamping hydraulic cylinder barrel 3-5, a spring 3-4, a self-locking piston 3-6, and a front end cover 4-2 of the self-locking hydraulic cylinder are sequentially arranged. One end of the spring 3-4 contacts the clamping piston 3-3, and the other end of the spring 3-4 is provided with the self-locking piston 3-6. The clamping hydraulic cylinder barrel 3-5, the clamping piston 3-3, the self-locking piston 3-6, and the spring 3-4 form a spring chamber. The spring 3-4 expands and contracts in the spring chamber to form an elastic force on the clamping piston 3-3 and the self-locking piston 3-6. Limit blocks are arranged on one side of the clamping piston 3-3 and the self-locking piston 3-6 close to the spring 3-4 to prevent damage caused by excessive compression of the spring 3-4. The spring chamber is a closed chamber. When the relative positions of the two pistons change, the spring 3-4 expands and contracts, and the gas inside the spring chamber also expands or contracts. To prevent the internal air pressure in the closed chamber from being too high and affecting the operation of the subsea tong.

[0059] The self-locking piston 3-6 is connected to the self-locking piston rod 4-1. The self-locking piston rod 4-1 is threadedly connected to the self-locking piston 3-6. The self-locking piston rod 4-1 penetrates through the front end cover 4-2 of the self-locking hydraulic cylinder. The clamping hydraulic cylinder barrel 3-5, the self-locking piston 3-6, the front end cover 4-2 of the self-locking hydraulic cylinder, and the self-locking piston rod 4- form a hydraulic chamber of the self-locking piston chamber of the clamping hydraulic cylinder 3 for driving the movement of the self-locking piston rod 4-1. The clamping hydraulic cylinder 3 and the self-locking hydraulic cylinder 4 share the same self-locking piston rod 4-1 and the front end cover 4-2 of the self-locking hydraulic cylinder.

[0060] The self-locking hydraulic cylinder 4 includes a self-locking hydraulic cylinder barrel 4-4. The self-locking hydraulic cylinder barrel 4-4 communicates with the clamping hydraulic cylinder barrel 3-5. A front end cover 4-2 of the self-locking hydraulic cylinder is arranged on one side of the self-locking hydraulic cylinder barrel 4-4 close to the clamping hydraulic cylinder barrel 3-5. A rear end cover 4-12 of the self-locking hydraulic cylinder is arranged on the side of the self-locking hydraulic cylinder barrel 4-4 away from the front end cover 4-2 of the self-locking hydraulic cylinder. A rear end cover 5 is arranged behind the rear end cover 4-12 of the self-locking hydraulic cylinder. A locking thrust piston 4-3 is arranged behind the front end cover 4-2 of the self-locking hydraulic cylinder. The self-locking piston rod 4-1, the front end cover 4-2 of the self-locking hydraulic cylinder, the locking thrust piston 4-3, and the self-locking hydraulic cylinder barrel 4-4 form a locking hydraulic chamber. By external pressurization, the locking thrust piston 4-3 is pushed to move to the right.

[0061] As Figure 7As shown, the thrust piston 4-3 is connected to the locking push rod 4-5. The locking push rod 4-5 is connected to the locking push rod fixing plate 4-6. A number of engaging teeth 4-7 are evenly arranged circumferentially on the locking push rod fixing plate 4-6. The locking push rod 4-5 and the locking thrust piston 4-3 are mechanically connected and move in the same direction, thereby pushing the engaging teeth 4-7 to move to the right. A retaining ring 4-8 is clamped on the outer circumference of a number of engaging teeth 4-7. The retaining ring 4-8 is a conical ring. The retaining ring 4-8 is installed in the self-locking cylinder barrel 4-4 by means of threads. While the engaging teeth 4-7 move to the right, the engaging teeth 4-7 will perform a radial movement along the conical surface of the retaining ring 4-8. The engaging teeth 4-7 gradually come into contact with the self-locking piston rod 4-1. As the pressure in the locking hydraulic chamber increases, the radial thrust exerted by the retaining ring 4-8 on the engaging teeth 4-7 gradually increases, and the biting force of the engaging teeth 4-7 on the self-locking piston rod 4-1 also gradually increases. The self-locking piston rod 4-1 is locked by the engaging teeth 4-7 and cannot move.

[0062] The retaining ring 4-8 is connected to the unlocking push rod 4-9. The unlocking push rod 4-9 is connected to the unlocking push rod fixing plate 4-10. The unlocking push rod fixing plate 4-10 is connected to the unlocking thrust piston 4-11. The self-locking piston rod 4-1 sequentially passes through the thrust piston 4-3, the locking push rod fixing plate 4-6, the retaining ring 4-8, the unlocking push rod fixing plate 4-10, and the unlocking thrust piston 4-11. The self-locking piston rod 4-1 moves within the self-locking cylinder 4. Corresponding sealing elements and guide rings are provided at the relative movement positions of the front end cover 4-2 of the self-locking cylinder, the locking thrust piston 4-3, the unlocking thrust piston 4-11, and the rear end cover 4-12 of the self-locking cylinder with respect to the self-locking piston rod 4-1, which play the roles of sealing the chamber pressure and guiding. The self-locking piston rod 4-1, the unlocking thrust piston 4-11, the rear end cover 4-12 of the self-locking cylinder, and the self-locking cylinder barrel 4-4 form an unlocking hydraulic chamber. By external pressurization, the unlocking thrust piston 4-11 is pushed to move to the left. The unlocking push rod 4-9 and the unlocking thrust piston 4-11 are mechanically connected and move in the same direction, thereby pushing the engaging teeth 4-7 to move to the left and gradually disengaging from the retaining ring 4-8. When moving a certain distance, the retaining ring 4-8 no longer exerts a radial force on the engaging teeth 4-7, and the biting force of the engaging teeth 4-7 on the self-locking piston rod 4-1 drops to 0. The locking of the engaging teeth 4-7 on the self-locking piston rod 4-1 is released, and the self-locking piston rod 4-1 can move freely within the self-locking cylinder barrel 4-4.

[0063] Considering the seals between the self-locking piston rod 4-1 and the front end cover 4-2 of the self-locking hydraulic cylinder, the locking thrust piston 4-3, the unlocking thrust piston 4-11, and the rear end cover 4-12 of the self-locking hydraulic cylinder, during the entire relative movement stroke of the self-locking piston rod 4-1 with these components, the surface of the self-locking piston rod 4-1 should be a smooth sealing surface to facilitate better fitting of the seal to the piston rod and ensure the sealing effect. At the same time, since the engaging teeth 4-7 need to mechanically engage the self-locking piston rod 4-1, during the entire relative movement stroke of the self-locking piston rod 4-1 with the engaging teeth 4-7, the surface of the self-locking piston rod 4-1 should be a rough surface to prevent the engaging teeth 4-7 from scratching the sealing surface. Therefore, both ends of the entire self-locking piston rod 4-1 are smooth sealing surfaces, and the engaging part in the middle is a rough surface.

[0064] A through hole is axially provided in the self-locking piston rod 4-1, and the through hole introduces gas into the rear end cover 5. The rear end cover 5 and the self-locking hydraulic cylinder 4 form an end cover closed cavity through a seal. The closed cavity of the rear end cover 5 further increases the volume of the spring cavity, so that the pressure in the cavity will not rise too high when the spring is compressed. During normal operation, low-pressure nitrogen is introduced through the gas filling hole on the rear end cover 5, which can improve the service life of the spring 3-4 to a certain extent.

[0065] Embodiment 3

[0066] There are 3 sets of locking push rods 4-5 and unlocking push rods 4-9 in the self-locking hydraulic cylinder 4, which are arranged opposite to each other at an angle of 120° on the locking thrust piston 4-3 and the unlocking thrust piston 4-11. The locking push rod fixing plate 4-6 and the unlocking push rod fixing plate 4-0 are responsible for radially fixing the corresponding push rods to prevent the push rods from shifting and skewing during the application of thrust. The number of engaging teeth 4-7 is also 3 sets, and they are arranged at an angle of 120° around the self-locking piston rod 4-1 during installation to ensure that the acting directions of the forces of the locking push rod 4-5, the unlocking push rod 4-9, and the engaging teeth 4-7 are in the same plane. At the same time, there is no mechanical connection between the engaging teeth 4-7 and each push rod, and they can achieve free contact and disengagement. During operation, the engaging teeth 4-7 are pushed to move by the contact and extrusion of the push rod on the end face, thereby realizing the locking and unlocking functions of the self-locking piston rod 4-1.

[0067] As Figure 8As shown in the figure, the engaging teeth 4-7 include an engaging tooth body 4-71. The engaging tooth body 4-71 is in the shape of a 1 / 6 hollow frustum. The outer peripheral dimension of the engaging tooth body 4-71 matches the conical ring of the retaining ring 4-8. The contact surface between the engaging tooth body 4-71 and the retaining ring 4-8 is designed to be conical and the cone angles are kept consistent. A groove is formed on the inner wall of the engaging tooth body 4-71, and an engaging tooth surface 4-72 is arranged in the groove. The engaging tooth surface 4-72 is an arc-shaped plate with multiple rows of teeth. The engaging tooth surface 4-72 is fixedly inlaid in the groove of the engaging tooth body 4-71 by using an engaging tooth fixing bolt 4-73. The installation plane of the engaging tooth body 4-71 and the engaging tooth surface 4-72 is also designed to be conical. After installation, the engaging tooth surface 4-72 forms a certain angle with the central axis of the self-locking piston rod 4-1, and this angle is usually controlled within 2 to 5° to facilitate the realization of the self-locking function of the engaging teeth 4-7.

[0068] As Figure 9 shown in the figure, the locking push rod 4-5 includes a locking push rod body 4-51. Two spherical grooves are formed at the end of the locking push rod body 4-51, and a thrust steel ball 4-53 is installed in the spherical grooves. A locking push rod gland 4-52 is arranged at the end of the locking push rod body 4-51, and the locking push rod gland 4-52 is fastened by a push rod fastening bolt 4-54. As Figure 10 shown in the figure, the unlocking push rod 4-9 includes an unlocking push rod body 4-91. One spherical groove is formed at the end of the unlocking push rod body 4-91, and a thrust steel ball 4-53 is installed in the spherical groove. An unlocking push rod gland 4-92 is arranged at the end of the unlocking push rod body 4-91, and the unlocking push rod gland 4-92 is fastened by a push rod fastening bolt 4-54.

[0069] There are differences in the dimensions and types of the locking push rod 4-5 and the unlocking push rod 4-9, mainly due to the different contact areas of the conical surfaces of the engaging teeth 4-7 at the large and small end faces. The locking push rod 4-5 contacts the large end face of the engaging teeth 4-7, and the unlocking push rod 4-9 contacts the small end face of the engaging teeth 4-7. Threads are formed at the ends of the locking push rod 4-5 and the unlocking push rod 4-9, and they are screwed into the corresponding threaded holes of the locking thrust piston 4-3 and the unlocking thrust piston 4-11 for fastening. The thrust steel ball 4-53 is used as the contact element between the push rod and the engaging teeth 4-7. During the locking and unlocking processes of the engaging teeth 4-7, there are movements in two directions along the axial and radial directions of the self-locking piston rod 4-1. The thrust steel ball 4-53 slides on the engaging tooth body 4-71 and transmits the axial thrust. Due to the rolling of the thrust steel ball 4-53, the lateral force generated by the radial movement of the engaging teeth 4-7 on the push rod is offset, and the stability and service life of the push rod during the locking and unlocking processes are improved. As Figure 11As shown in the figure, the locking push rod fixing disc 4-6 includes a push rod fixing disc body 4-61. The push rod fixing disc body 4-61 is a hollow disc, and a number of push rod mounting holes are evenly opened inside the circumference of the disc. After the push rod passes through the push rod mounting holes, it is fastened by two push rod fixing bolts 4-62 on the inner and outer rings. The locking push rod fixing disc 4-6 and the unlocking push rod fixing disc 4-10 have the same type but different dimensions, and are respectively installed at the ends of the locking push rod 4-5 and the unlocking push rod 4-9.

[0070] Embodiment 4

[0071] The control method of the self-holding subsea hydraulic tong of the present invention realizes the free switching of the self-holding subsea hydraulic tong under 5 working modes by the cooperation of an external hydraulic source and hydraulic valve components, such as Figure 12 As shown in the figure, the specific implementation steps are as follows:

[0072] S1. Initial mode of the subsea hydraulic tong, specifically:

[0073] The initial mode of the subsea hydraulic tong is the state when the subsea hydraulic tong is not working. At this time, all the electromagnets in the three-position four-way directional control valves 7 coded as SV1 and SV2 are in the power-off state, and the X1 and X2 ports of the self-locking hydraulic cylinder 4 are connected to the oil tank and are in the non-working state.

[0074] The A and B ports of the clamping hydraulic cylinder 3 are connected to the oil tank, the spring 3-4 is in the free release state, and the oil volume in the clamping hydraulic cavity and the self-locking hydraulic cavity in the clamping hydraulic cylinder 3 determines the position of the clamping piston rod 3-1. In this mode, only the frictional resistance of the piston rod needs to be overcome externally to adjust the position of the clamping caliper 2.

[0075] In case of emergency, without external hydraulic power, the subsea hydraulic tong is opened by the lifting force of the drill pipe so that the drill pipe can be smoothly taken out from the subsea base plate.

[0076] S2. Loosening mode of the subsea hydraulic tong, specifically:

[0077] After the subsea base plate is lowered to the seabed, to facilitate the lowering of the sampling tool, the subsea hydraulic tong is fully opened. At this time, the b-position electromagnet of SV1 is powered on, the a-position electromagnet is powered off, and all the electromagnets of SV2 are powered off, and the self-locking hydraulic cylinder 4 is in the non-working state.

[0078] The hydraulic source supplies oil to the pressure port P. After being shunted by the shunt manifold valve 6 coded as DV1 through SV1, it enters the A ports of the two clamping hydraulic cylinders 3, and the clamping piston cavity is filled with oil, pushing the clamping piston rod 3-1 to retract; at the same time, the elastic force of the spring 3-4 will cause the hydraulic oil in the self-locking piston cavity to be squeezed out, and after merging at DV2 at the B port, it flows back to the oil tank through SV1;

[0079] Two flow dividing and collecting valves 6 here play a role in keeping the retracting speed of the clamping piston rod 3-1 consistent.

[0080] S3. Subsea hydraulic tong clamping mode, specifically:

[0081] During subsea coring operation, it is necessary for the subsea hydraulic tong to clamp the drill pipe. At this time, the a-position electromagnet of SV1 is de-energized, the b-position electromagnet of SV1 is de-energized, all electromagnets of SV2 are de-energized, and the self-locking cylinder 4 is in an unoperated state. The hydraulic source supplies oil to the pressure port P. After being divided by the flow dividing and collecting valve 6 coded as DV2 through SV1, it enters the B ports of the two clamping cylinders 3, and the self-locking piston cavity is filled with oil, pushing the self-locking piston rod 4.1 to extend;

[0082] At the same time, the elastic force of the spring 3.4 will cause the hydraulic oil in the clamping piston cavity to be squeezed out, flow back to the oil tank through SV1 after confluence at DV1 of the A port, and push the clamping piston rod 4-1 to extend;

[0083] Two flow dividing and collecting valves 6 here play a role in keeping the extending speeds of the clamping piston rod 3-1 and the self-locking piston rod 4-1 consistent; as the pressure in the self-locking piston cavity increases, the spring 3-4 is gradually compressed, and the clamping force applied by the clamping piston rod 3-1 on the drill pipe through the clamping caliper 2 also increases accordingly. The check valve 8 installed at the inlet CV1 of SV1 plays a role in maintaining the clamping force to a certain extent when the pressure at the P port drops.

[0084] S4. Subsea hydraulic tong locking mode, specifically:

[0085] When the subsea base needs to use the drill pipe for emergency recovery, this mode is enabled. First, the subsea hydraulic tong should be in the state of clamping the drill pipe according to the method described in S3, so that the pressure at the P port reaches the maximum, and the clamping force of the subsea hydraulic tong on the drill pipe also reaches the maximum;

[0086] At this time, keep the a-position electromagnet of SV1 energized and the b-position electromagnet de-energized, and at the same time, keep the b-position electromagnet of SV2 energized and the a-position electromagnet de-energized;

[0087] The pressure oil at the P port enters the control oil ports X1 of the two self-locking cylinders 4 through SV2, and the pressure at the P port drops. Due to the action of CV1, the thrust of the clamping cylinder 3 does not change, and the corresponding clamping force of the subsea hydraulic tong does not change either;

[0088] The locking thrust piston cavity of the self-locking cylinder 4 starts to be filled with oil, pushing the locking thrust piston 4-3 to squeeze and move the engaging teeth 4-7. The engaging teeth 4-7 bite the self-locking piston rod 4-1 under the restriction of the retaining ring 4-8. At the same time, the engaging teeth 4-7 push the unlocking thrust piston 4-11 to drain the hydraulic oil in the cavity back to the oil tank. As the pressure at the P port reaches the maximum again, the engaging teeth 4-7 move to the limit position, and the biting force on the self-locking piston rod 4-1 also reaches the maximum;

[0089] Power off all the electromagnets of SV1 and SV2, and reduce the pressure in all hydraulic chambers of the clamping cylinder 3 and the self-locking cylinder 4 to the minimum. Due to the action of the spring 3-4, it will continuously provide a thrust force equal in magnitude and opposite in direction to the drill pipe clamping force for the self-locking piston rod 4-1. Thanks to the conical mating surface between the engaging teeth 4-7 and the retaining ring 4-8 and the design of the inclined engaging surface between the engaging teeth 4-7 and the self-locking piston rod 4-1, the elastic force of the spring 3-4 will cause the engaging teeth 4-7 to lock with the self-locking piston rod 4-1. Since the position of the self-locking piston rod 4-1 is locked, the subsea hydraulic tongs continuously clamp the drill pipe through the spring 3-4, achieving mechanical self-locking without relying on hydraulic power.

[0090] S5. Unlock the subsea hydraulic tongs, specifically:

[0091] When the subsea hydraulic tongs in the locked state need to be unlocked, ensure that the hydraulic source supplies oil to the pressure port P, make the a-position electromagnet of SV1 energized and the b-position electromagnet de-energized. The hydraulic oil enters the B port of the two clamping cylinders 3 through SV1, and the pressure in the self-locking piston chamber increases. When the pressure at the P port reaches the maximum, the elastic force of the spring 3-4 acting on the self-locking piston rod 4-1 and the hydraulic thrust provided by the self-locking piston chamber cancel each other out, and the unlocking operation is ready.

[0092] At this time, make the a-position electromagnet of SV2 energized and the b-position electromagnet de-energized. The hydraulic oil enters the control oil port X2 of the two self-locking cylinders 4 through SV2, and the unlocking thrust piston chamber starts to fill with oil, pushing the unlocking thrust piston 4-11 to move the engaging teeth 4-7 in the direction away from the retaining ring 4-8. The radial force exerted by the retaining ring 4-8 on the engaging teeth 4-7 disappears, and the clamping force of the engaging teeth 4-7 on the self-locking piston rod is lost, and the position lock of the self-locking piston rod 4-1 is released. After the lock is released, de-energize the two electromagnets of SV2, and the clamping and loosening of the subsea hydraulic tongs can be achieved by controlling SV1.

[0093] The self-holding subsea hydraulic tong of the present invention has a compact structure and a reasonable layout, and includes a self-holding subsea hydraulic tong body composed of a subsea tong mounting bracket, a clamping cylinder, a clamping caliper, and a self-locking cylinder. The clamping cylinder is composed of a self-locking piston, a self-locking piston rod, a clamping piston, a clamping piston rod, a spring, etc. The spring is installed between the two pistons. After the hydraulic cylinder drives to clamp the drill pipe, the self-locking piston rod is fixed, and the clamping piston rod maintains a constant clamping force on the drill pipe under the action of the spring force. The self-locking cylinder is composed of a locking thrust piston, an unlocking thrust piston, engaging teeth, a retaining ring, a push rod and other mechanisms. The self-locking cylinder and the clamping cylinder are integrally installed and share a self-locking piston rod. Through the combined action of the locking thrust piston and the push rod, the engaging teeth are driven to move axially. Due to the limitation of the retaining ring, the engaging teeth move radially to realize the engaging and locking of the clamping piston rod. When unlocking, the unlocking thrust piston is used to push the engaging teeth to move in the reverse direction to realize unlocking, and thus the functions of locking and unlocking the clamping piston rod at any position are realized.

[0094] The control method of the self-holding subsea hydraulic tong of the present invention can realize the continuous and stable clamping force of the drill pipe by relying on the spring force under the premise of no external hydraulic power through the oil supply control of different oil ports of the subsea hydraulic tong. The control method of the self-holding subsea hydraulic tong of the present invention has high reliability, does not require additional electrical systems, improves the operation smoothness, can greatly reduce the installation cost of the equipment, and is easy for daily maintenance and replacement.

Claims

1. Self-holding subsea hydraulic tongs, Characterized in that, it includes a mounting bracket (1), a clamping caliper (2) is arranged horizontally inside the mounting bracket (1), both ends of the clamping caliper (2) are connected to a clamping hydraulic cylinder (3), the clamping hydraulic cylinder (3) is connected to a self-locking hydraulic cylinder (4), and a rear end cover (5) is arranged at the rear end of the self-locking hydraulic cylinder (4).

2. The self-holding subsea hydraulic tongs according to claim 1, Characterized in that, the mounting bracket (1) includes a cylinder, a through hole is radially opened in the middle of the cylinder along the extending direction, a subsea tong mounting flange (1-3) is sleeved in the through hole, the subsea tong mounting flange (1-3) is horizontally arranged, a base plate connecting flange (1-2) is arranged at the top of the cylinder, and a guide cylinder mounting flange (1-4) is arranged at the bottom of the cylinder.

3. The self-holding subsea hydraulic tongs according to claim 1, Characterized in that, the clamping caliper (2) includes a caliper body (2-2), one end of the caliper body (2-2) is connected to the piston rod of the clamping hydraulic cylinder (3) by thread, a chuck body fixing groove is opened at the other end of the caliper body (2-2), two sets of chucks (2-1) are arranged in a conical shape in the chuck body fixing groove, the contact surface between the chuck (2-1) and the caliper body (2-2) is fastened by a chuck bolt (2-4), the chuck (2-1) directly contacts the surface of the drill pipe, multiple rows of chuck teeth are designed on the chuck (2-1), pressing blocks (2-3) are respectively arranged at the upper and lower ends of the chuck (2-1), and the pressing blocks (2-3) are fitted with the upper and lower surfaces of the caliper body (2-2).

4. The self-holding subsea hydraulic tongs according to claim 3, Characterized in that, the clamping hydraulic cylinder (3) includes a clamping hydraulic cylinder barrel (3-5), a clamping piston (3-3) is arranged at one end inside the clamping hydraulic cylinder barrel (3-5), a clamping hydraulic cylinder front end cover (3-2) is arranged in front of the clamping piston (3-3), the clamping piston (3-3) is connected to a clamping piston rod (3-1), the clamping piston rod (3-1) penetrates through the clamping hydraulic cylinder front end cover (3-2), and the end of the clamping piston rod (3-1) is connected to the caliper body (2-2).

5. The self-holding subsea hydraulic tongs according to claim 4, Characterized in that, a spring (3-4), a self-locking piston (3-6), and a self-locking hydraulic cylinder front end cover (4-2) are sequentially arranged at the other end inside the clamping hydraulic cylinder barrel (3-5), one end of the spring (3-4) contacts the clamping piston (3-3), the other end of the spring (3-4) is provided with the self-locking piston (3-6), and limiting blocks are arranged on both sides of the clamping piston (3-3) and the self-locking piston (3-6) close to the spring (3-4).

6. The self-holding subsea hydraulic tongs according to claim 5, Characterized in that, The self-locking piston (3-6) is connected to the self-locking piston rod (4-1). The self-locking piston rod (4-1) is threadedly connected to the self-locking piston (3-6), and the self-locking piston rod (4-1) penetrates through the front end cover (4-2) of the self-locking hydraulic cylinder. The self-locking hydraulic cylinder (4) includes a self-locking hydraulic cylinder barrel (4-4). The self-locking hydraulic cylinder barrel (4-4) is communicated with the clamping hydraulic cylinder barrel (3-5). A front end cover (4-2) of the self-locking hydraulic cylinder is arranged on one side of the self-locking hydraulic cylinder barrel (4-4) close to the clamping hydraulic cylinder barrel (3-5). A rear end cover (4-12) of the self-locking hydraulic cylinder is arranged on one side of the self-locking hydraulic cylinder barrel (4-4) away from the front end cover (4-2) of the self-locking hydraulic cylinder. A rear end cover (5) is arranged behind the rear end cover (4-12) of the self-locking hydraulic cylinder, and a locking thrust piston (4-3) is arranged behind the front end cover (4-2) of the self-locking hydraulic cylinder.

7. The self-holding type subsea hydraulic tong according to claim 6, characterized in that, the thrust piston (4-3) is connected to the locking push rod (4-5). The locking push rod (4-5) is connected to the locking push rod fixing disc (4-6). A plurality of engaging teeth (4-7) are circumferentially and uniformly arranged on the locking push rod fixing disc (4-6). A retaining ring (4-8) is clamped on the outer periphery of the plurality of engaging teeth (4-7). The retaining ring (4-8) is a conical ring. The retaining ring (4-8) is connected to the unlocking push rod (4-9). The unlocking push rod (4-9) is connected to the unlocking push rod fixing disc (4-10). The unlocking push rod fixing disc (4-10) is connected to the unlocking thrust piston (4-11). The self-locking piston rod (4-1) sequentially penetrates through the thrust piston (4-3), the locking push rod fixing disc (4-6), the retaining ring (4-8), the unlocking push rod fixing disc (4-10), and the unlocking thrust piston (4-11).

8. The self-holding type subsea hydraulic tong according to claim 7, characterized in that, both ends of the self-locking piston rod (4-1) are smooth sealing surfaces, and the middle part where it engages with the engaging teeth (4-7) is a rough surface. A through hole is axially formed in the self-locking piston rod (4-1), and the through hole introduces gas into the rear end cover (5). The engaging teeth (4-7) include an engaging tooth body (4-71). The engaging tooth body (4-71) is in the shape of a 1 / 6 hollow frustum. The outer peripheral dimension of the engaging tooth body (4-71) matches the conical ring of the retaining ring (4-8). The contact surface between the engaging tooth body (4-71) and the retaining ring (4-8) is designed to be conical and the cone angles are kept consistent. A groove is formed in the inner wall of the engaging tooth body (4-71), and an engaging tooth surface (4-72) is arranged in the groove. The engaging tooth surface (4-72) is a circular arc plate with multiple rows of teeth. The engaging tooth surface (4-72) is fixedly inlaid in the groove of the engaging tooth body (4-71) by using an engaging tooth fixing bolt (4-73). The installation plane of the engaging tooth body (4-71) and the engaging tooth surface (4-72) is also designed to be conical. After installation, the engaging tooth surface (4-72) forms a certain angle with the central axis of the self-locking piston rod (4-1).

9. The self-holding type subsea hydraulic tong according to claim 8, characterized in that, The locking push rod (4-5) includes a locking push rod body (4-51). Two spherical grooves are formed at the end of the locking push rod body (4-51). Thrust steel balls (4-53) are installed in the spherical grooves. A locking push rod gland (4-52) is arranged at the end of the locking push rod body (4-51). The locking push rod gland (4-52) is fastened by a push rod fastening bolt (4-54). The unlocking push rod (4-9) includes an unlocking push rod body (4-91). One spherical groove is formed at the end of the unlocking push rod body (4-91). Thrust steel balls (4-53) are installed in the spherical groove. An unlocking push rod gland (4-92) is arranged at the end of the unlocking push rod body (4-91). The unlocking push rod gland (4-92) is fastened by a push rod fastening bolt (4-54).

10. A control method for a self-holding subsea hydraulic tong, which realizes the free switching of the self-holding subsea hydraulic tong under 5 working modes by using the cooperation of the self-holding subsea hydraulic tong described in the above-mentioned claim 9 with an external hydraulic source and hydraulic valve components. It is characterized in that The implementation is specifically carried out according to the following steps: S1. The initial mode of the subsea hydraulic tong, specifically: The initial mode of the subsea hydraulic tong is the state when the subsea hydraulic tong is not working. At this time, all the electromagnets in the three-position four-way directional control valves (7) coded as SV1 and SV2 are in the power-off state. The X1 and X2 ports of the self-locking hydraulic cylinder (4) are connected to the oil tank and are in the non-working state; The A and B ports of the clamping hydraulic cylinder (3) are connected to the oil tank. The spring (3-4) is in the free release state. The oil volume in the clamping hydraulic cavity and the self-locking hydraulic cavity in the clamping hydraulic cylinder (3) determines the position of the clamping piston rod (3-1); S2. The loosening mode of the subsea hydraulic tong, specifically: After the subsea baseplate is lowered to the seabed, to facilitate the lowering of the sampling tool, all the subsea hydraulic tongs are opened. At this time, the b-position electromagnet of SV1 is powered on and the a-position electromagnet is powered off. All the electromagnets of SV2 are powered off. The self-locking hydraulic cylinder (4) is in the non-working state; The hydraulic source supplies oil to the pressure port P. After being shunted by the shunt and manifold valve (6) coded as DV1 through SV1, it enters the A ports of the two clamping hydraulic cylinders (3). The clamping piston cavity is filled with oil, and the clamping piston rod (3-1) is pushed to retract; at the same time, the elastic force of the spring (3-4) will cause the hydraulic oil in the self-locking piston cavity to be squeezed out, and after merging at DV2 at the B port, it flows back to the oil tank through SV1; the two shunt and manifold valves (6) play a role in keeping the retraction speed of the clamping piston rod (3-1) consistent; S3. The clamping mode of the subsea hydraulic tong, specifically: During the subsea coring operation, the subsea hydraulic tong is required to clamp the drill pipe. At this time, the a-position electromagnet of SV1 is powered off and the b-position electromagnet is powered off. All the electromagnets of SV2 are powered off. The self-locking hydraulic cylinder (4) is in the non-working state; the hydraulic source supplies oil to the pressure port P. After being shunted by the shunt and manifold valve (6) coded as DV2 through SV1, it enters the B ports of the two clamping hydraulic cylinders (3). The self-locking piston cavity is filled with oil, and the self-locking piston rod (4-1) is pushed to extend; Meanwhile, the elastic force of the spring (3-4) will squeeze out the hydraulic oil in the clamping piston chamber. After confluence at port A DV1, it will flow back to the oil tank through SV1, and push out the clamping piston rod (4-1); the two flow dividing and collecting valves (6) play a role in keeping the extending speeds of the clamping piston rod (3-1) and the self-locking piston rod (4-1) consistent; as the pressure in the self-locking piston chamber increases, the spring (3-4) is gradually compressed, and the clamping force applied by the clamping piston rod (3-1) on the drill pipe through the clamping caliper (2) also increases. The check valve (8) installed at the inlet CV1 of SV1 plays a role in maintaining the clamping force to a certain extent when the pressure at port P drops. S4. Subsea hydraulic tong locking mode, specifically: When the subsea template needs to use the drill pipe for emergency recovery, this mode is enabled. First, the subsea hydraulic tong should be in the state of clamping the drill pipe according to the method described in S3, so that the pressure at port P reaches the maximum, and the clamping force of the subsea hydraulic tong on the drill pipe also reaches the maximum; at this time, keep the a-position electromagnet of SV1 energized and the b-position electromagnet de-energized, and at the same time, keep the b-position electromagnet of SV2 energized and the a-position electromagnet de-energized; the pressure oil at port P enters the control oil port X1 of the two self-locking hydraulic cylinders (4) through SV2, and the pressure at port P drops. Due to the action of CV1, the thrust of the clamping hydraulic cylinder (3) does not change, and the corresponding clamping force of the subsea hydraulic tong also does not change. The locking thrust piston chamber of the self-locking hydraulic cylinder (4) starts to be filled with oil, pushing the locking thrust piston (4-3) to squeeze and move the engaging teeth (4-7). The engaging teeth (4-7) engage the self-locking piston rod (4-1) under the restriction of the retaining ring (4-8). At the same time, the engaging teeth (4-7) push the unlocking thrust piston (4-11) to drain the hydraulic oil in the chamber back to the oil tank. As the pressure at port P reaches the maximum again, the engaging teeth (4-7) move to the extreme position, and the biting force on the self-locking piston rod (4-1) also reaches the maximum. Power off all the electromagnets of SV1 and SV2, and the pressure in all the hydraulic chambers of the clamping hydraulic cylinder (3) and the self-locking hydraulic cylinder (4) drops to the minimum. Due to the action of the spring (3-4), it will continuously provide a thrust for the self-locking piston rod (4-1) that is equal in magnitude and opposite in direction to the drill pipe clamping force. Thanks to the conical mating surface between the engaging teeth (4-7) and the retaining ring (4-8) and the design of the inclined engaging surface between the engaging teeth (4-7) and the self-locking piston rod (4-1), the elastic force of the spring (3-4) will lock the engaging teeth (4-7) and the self-locking piston rod (4-1). Since the position of the self-locking piston rod (4-1) is locked, the subsea hydraulic tong continuously clamps the drill pipe through the spring (3-4) to achieve mechanical self-locking without relying on hydraulic power. S5. Subsea hydraulic tong unlocking, specifically: When the subsea hydraulic tongs in the locked state need to be unlocked, ensure that the hydraulic source supplies oil to the pressure port P, so that the a-position electromagnet of SV1 is energized and the b-position electromagnet is de-energized. The hydraulic oil enters the B ports of the two clamping cylinders (3) through SV1, and the pressure in the self-locking piston chamber increases. When the pressure at the P port reaches the maximum, the elastic force of the spring (3-4) acting on the self-locking piston rod (4-1) and the hydraulic thrust provided by the self-locking piston chamber cancel each other out, and the unlocking operation is ready; At this time, make the a-position electromagnet of SV2 energized and the b-position electromagnet de-energized. The hydraulic oil enters the control oil port X2 of the two self-locking cylinders (4) through SV2, and the unlocking thrust piston chamber starts to be filled with oil, pushing the unlocking thrust piston (4-11) to make the engaging teeth (4-7) move in the direction away from the retaining ring (4-8). The radial force exerted by the retaining ring (4-8) on the engaging teeth (4-7) disappears, and the clamping force of the engaging teeth (4-7) on the self-locking piston rod is lost, and the position lock of the self-locking piston rod (4-1) is released; after the lock is released, make the two electromagnets of SV2 de-energized, and the clamping and loosening of the subsea hydraulic tongs can be realized by controlling SV1.

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