A sealing and isolating construction method for a coal gas pipeline under pressure

Abstract

This invention discloses a sealing and isolation construction method for gas pipelines under pressurized conditions, comprising the following steps: A connector with a valve is fixedly installed on the pipeline upstream of the section to be repaired, forming a controllable external passage; the valve is opened, and a process hole is drilled in the pipeline through the external passage, after which the valve is closed to isolate the medium; a sealing device is connected to the outside of the valve, the sealing device including a radially deformable sealing actuator; the valve is opened, and the sealing actuator in a contracted state is inserted into the pipeline, driving the sealing actuator to expand radially, so that the sealing surface fits tightly against the inner wall of the pipeline to form an annular sealing band; the sealing performance of the isolation barrier is verified, and if qualified, the downstream section to be repaired is treated and repaired; the sealing actuator is radially contracted and retracted, the valve is closed, and the connector is permanently sealed. This invention eliminates the risk of large-scale gas leakage during construction and, combined with necessary replacement and testing procedures, ensures the safety of personnel and the environment.

Description

Technical Field

[0001] This invention relates to the field of converter gas pipeline maintenance technology, and in particular to a sealing and isolation construction method for gas pipelines under pressurized conditions. Background Technology

[0002] Converter gas is an important byproduct of metallurgical production processes, and its pipeline system is responsible for the continuous transportation of this gas. The gas medium is characterized by high pressure, flammability, explosiveness, and the presence of toxic components such as carbon monoxide. Leaks can easily lead to poisoning, fires, or explosions, posing extremely high safety risks. In continuous steel production, gas pipelines need to operate for extended periods, making it difficult to shut down production for maintenance or modifications. Therefore, live tapping and sealing technology has become a crucial means of achieving pipeline maintenance without interrupting production.

[0003] Currently, the commonly used live sealing methods in the industry mainly rely on installing clamp valves and perforated junction boxes on pipelines, and then inserting a plug into the pipeline to achieve a mechanical seal. During construction, if the plug does not fit tightly against the inner wall of the pipeline, or if the pressure resistance of the sealing element is insufficient, gas leakage is very likely to occur. Leakage not only causes toxic and harmful gases to escape and accumulate in closed or semi-closed spaces, but may also form an explosive gas mixture, posing a serious threat to workers and surrounding facilities. Traditional plugs have a relatively simple structure, and under the continuous impact of high-pressure media in the pipeline, they are prone to displacement, vibration, or wear of the sealing surface, leading to seal failure. Especially for old pipelines with ellipticity or local deformation, traditional plugs cannot adapt to the shape of the pipe wall, often resulting in incomplete sealing and failing to guarantee reliable long-term isolation during maintenance. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a sealing and isolation construction method for gas pipelines under pressure that is safer, more reliable and tighter, more efficient and causes less damage to the pipeline, so as to solve the problems mentioned in the background art.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for sealing and isolating gas pipelines under pressure, comprising the following steps:

[0006] S1. Install a connector with a valve on the pipeline upstream of the section to be repaired to form a controllable external passage.

[0007] S2. Open the valve, and after opening a process hole in the pipeline through an external passage, close the valve to isolate the medium;

[0008] S3. Connect a sealing device to the outside of the valve. The sealing device includes a sealing actuator that can deform radially. Open the valve and send the sealing actuator, which is in a contracted state, into the pipeline. Drive the sealing actuator to expand radially so that the sealing surface fits tightly against the inner wall of the pipeline to form an annular sealing band, thereby establishing an internal isolation barrier.

[0009] S4. Verify the sealing performance of the isolation barrier. If it passes the test, process and repair the downstream pipe section to be repaired.

[0010] S5. Retract the sealing actuator radially and close the valve to permanently seal the connection.

[0011] As a further improvement of the present invention: step S1 includes:

[0012] At a predetermined location upstream of the section of pipe to be repaired, a short section with an opening made of the same material as the main pipe is welded, and the welded joint of the short section with the opening is subjected to non-destructive testing to ensure that its strength is not lower than that of the base material of the section of pipe to be repaired.

[0013] As a further improvement of the present invention: step S2 includes:

[0014] Install a clamp valve on the perforated short section and perform a sealing pressure test on the clamp valve. After the pressure test is qualified, connect the perforation box and the perforation machine to the clamp valve.

[0015] After the air in the opening box is replaced with nitrogen until the oxygen content is below the safety threshold, the opening machine is started to perform progressive cutting to open a process hole in the pipeline. After the opening is completed, the opening tool is retracted into the opening box and the clamp valve is closed.

[0016] As a further improvement of the present invention: step S3 includes:

[0017] A sealing box and a hydraulic sealing cylinder are installed on the clamp valve, and a folding sealing head is connected to the actuator of the hydraulic sealing cylinder. The folding sealing head includes at least a sealing head seat, an unfoldable or foldable pressure plate assembly, a transmission mechanism for driving the pressure plate assembly, and a sealing cup installed on the pressure plate assembly.

[0018] After filling the sealing box with nitrogen to verify the seal, start the hydraulic sealing cylinder and send the folded sealing head, which is in a folded state, through the clamp valve and process hole into the pipeline.

[0019] The transmission mechanism drives the pressure plate assembly to unfold, causing the sealing cup to expand radially and fit tightly against the inner wall of the pipe, thereby forming a seal against the pipe medium.

[0020] As a further improvement of the present invention: In step S5, after the maintenance work is completed, the driving pressure plate assembly is folded, the folded sealing head is retracted into the sealing box, the clamp valve is closed and the sealing actuator is removed, and finally the opening short section is permanently sealed.

[0021] As a further improvement of the present invention: the folding pressure plate assembly of the folding sealing head includes a symmetrically arranged front folding pressure plate group and a rear folding pressure plate group, and the transmission mechanism includes a diagonal tie rod;

[0022] One end of the diagonal tie rod is hinged to the actuator end of the hydraulic sealing cylinder, and the other end of the diagonal tie rod is hinged to the front folding pressure plate group and the rear folding pressure plate group respectively. When the hydraulic sealing cylinder drives the diagonal tie rod to move linearly, it drives the front folding pressure plate group and the rear folding pressure plate group to rotate relative to the sealing head seat body, so as to realize the unfolding or folding action.

[0023] As a further improvement of the present invention: the folding plug head further includes a guide wheel component, which is disposed at the front end and / or rear end of the plug head body, and is used to contact the inner wall of the pipe when the folding plug head travels in the pipe, so as to perform radial positioning and guidance;

[0024] The folding plug head also includes a horizontal adjustment block, which is located at the connection between the plug head seat and the hydraulic plugging cylinder actuator. The horizontal adjustment block is used to fine-tune the horizontal position of the folding plug head in the pipeline to compensate for the installation deviation of the pipeline centerline or the ellipticity of the pipeline.

[0025] As a further improvement of the present invention: the progressive cutting specifically refers to:

[0026] The drilling machine is controlled to cut in an intermittent feeding manner. After feeding a set distance, it pauses for a period of time to allow the heat in the cutting area to dissipate before continuing to feed until it completely penetrates the pipe wall thickness.

[0027] As a further improvement of the present invention: the length of the perforated short section is designed to be 1 / 3 to 1 / 2 of the pipe diameter, and the two ends of the perforated short section are machined with bevels for welding.

[0028] As a further improvement of the present invention: in step S4, when depressurizing the downstream pipe section to be repaired, the depressurization rate is controlled to not exceed 0.05 MPa / min, and the pipe section to be repaired is replaced with inert gas before the maintenance operation.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] This invention forms a hard isolation interface with flammable and explosive media through connectors and valves, and utilizes nitrogen replacement and multiple sealing verifications to eliminate the risks of leakage, poisoning, and explosion at the source. The radially deformable sealing actuator can actively expand and adapt to the inner wall of the pipeline to form an interference fit annular sealing band. Its sealing pressure is stable and controllable, effectively resisting media pressure fluctuations and ensuring absolute tightness of long-term sealing. The construction process achieves close connection of procedures, especially the rapid insertion and deployment of the sealing device, which greatly shortens the critical path operation time and reduces interference with the production process. The use of pressurized tapping technology and non-destructive connection method reduces damage to the pipeline structure strength and ensures the long-term service safety of the pipeline. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the method flow structure of the present invention.

[0032] Figure 2 This is a perspective view of the folding sealing head structure of the present invention. Detailed Implementation

[0033] In order to clearly and completely understand the technical solution, the present invention will be further described in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0035] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0036] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0037] An embodiment of the present invention provides a sealing and isolation construction method for a gas pipeline under pressurized conditions, comprising the following steps:

[0038] S1. Install a connector with a valve on the pipeline upstream of the section to be repaired to form a controllable external passage.

[0039] S2. Open the valve, and after opening a process hole in the pipeline through an external passage, close the valve to isolate the medium;

[0040] S3. Connect a sealing device to the outside of the valve. The sealing device includes a sealing actuator that can deform radially. Open the valve and send the sealing actuator, which is in a contracted state, into the pipeline. Drive the sealing actuator to expand radially so that the sealing surface fits tightly against the inner wall of the pipeline to form an annular sealing band, thereby establishing an internal isolation barrier.

[0041] S4. Verify the sealing performance of the isolation barrier. If it passes the test, process and repair the downstream pipe section to be repaired.

[0042] S5. Retract the sealing actuator radially and close the valve to permanently seal the connection.

[0043] In one embodiment of the present invention, step S1 includes:

[0044] At a predetermined location upstream of the section of pipe to be repaired, a short section with an opening made of the same material as the main pipe is welded, and the welded joint of the short section with the opening is subjected to non-destructive testing to ensure that its strength is not lower than that of the base material of the section of pipe to be repaired.

[0045] A short section of the same material is welded onto the pipe, and a protruding interface for installing valves is connected to the rigid outer wall of the pipe. The weld is then subjected to non-destructive testing to ensure strength, providing a stable operating platform.

[0046] In one embodiment of the present invention, step S2 includes:

[0047] Install a clamp valve on the perforated short section and perform a sealing pressure test on the clamp valve. After the pressure test is qualified, connect the perforation box and the perforation machine to the clamp valve.

[0048] After the air in the opening box is replaced with nitrogen until the oxygen content is below the safety threshold, the opening machine is started to perform progressive cutting to open a process hole in the pipeline. After the opening is completed, the opening tool is retracted into the opening box and the clamp valve is closed.

[0049] By installing and pressure testing a qualified clamp valve, a seal that can be cut off at any time is established between the pipeline medium and the external environment. The hole-opening equipment (hole opener) is not directly installed on the pipeline, but is installed in the hole-opening box above the valve, so that the entire hole-opening operation is confined to a closed cavity. Nitrogen is used to replace the air in the hole-opening box, reducing the oxygen content in the box to a safe threshold. At the moment when the hole-opening tool cuts the pipeline metal and the gas first enters the box after hole opening, the environment inside the box cannot support combustion or explosion due to lack of oxygen.

[0050] The progressive cutting specifically refers to:

[0051] The drilling machine is controlled to cut in an intermittent feeding manner. After feeding a set distance, it pauses for a period of time to allow the heat in the cutting area to dissipate before continuing to feed until it completely penetrates the pipe wall thickness.

[0052] Intermittent feed facilitates heat dissipation during cutting, preventing excessive thermal stress or deformation caused by localized overheating of the pipe wall, and protecting the structural strength of the pipe body. Cutting within a sealed junction box effectively collects the chips, preventing splashing. The cutting process is smooth and controllable, reducing vibration and impact. After the hole is opened, the tool can be safely retracted into the junction box before the valve is closed, with no media leakage throughout the entire process.

[0053] In one embodiment of the present invention, step S3 includes:

[0054] A sealing box and a hydraulic sealing cylinder are installed on the clamp valve, and a folding sealing head is connected to the actuator of the hydraulic sealing cylinder. The folding sealing head includes at least a sealing head seat, an unfoldable or foldable pressure plate assembly, a transmission mechanism for driving the pressure plate assembly, and a sealing cup installed on the pressure plate assembly.

[0055] After filling the sealing box with nitrogen to verify the seal, start the hydraulic sealing cylinder and send the folded sealing head, which is in a folded state, through the clamp valve and process hole into the pipeline.

[0056] The transmission mechanism drives the pressure plate assembly to unfold, causing the sealing cup to expand radially and fit tightly against the inner wall of the pipe, thereby forming a seal against the pipe medium.

[0057] The operation is carried out above the clamp valve and inside the nitrogen-filled and verified plugging box, ensuring that the working environment itself is closed and inert before the plugging head is inserted. Through the hydraulically driven transmission mechanism, the pressure plate assembly is forced to mechanically unfold, pushing the plugging cup to produce radial interference expansion, forming a large-area annular tight fit with the inner wall of the pipe, avoiding the risk of slow leakage or damage that may exist with the inflatable sealing bladder.

[0058] In one embodiment of the present invention, in step S5, after the maintenance work is completed, the pressure plate assembly is driven to fold, the folded sealing head is retracted into the sealing box, the clamp valve is closed and the sealing actuator is removed, and finally the opening short section is permanently sealed.

[0059] In one embodiment of the present invention, the folding pressure plate assembly of the folding sealing head includes a front folding pressure plate group and a rear folding pressure plate group arranged symmetrically, and the transmission mechanism includes a diagonal tie rod;

[0060] One end of the diagonal tie rod is hinged to the actuator end of the hydraulic sealing cylinder, and the other end of the diagonal tie rod is hinged to the front folding pressure plate group and the rear folding pressure plate group respectively. When the hydraulic sealing cylinder drives the diagonal tie rod to move linearly, it drives the front folding pressure plate group and the rear folding pressure plate group to rotate relative to the sealing head seat body, so as to realize the unfolding or folding action.

[0061] Furthermore, the folding plug head also includes a guide wheel component, which is disposed at the front end and / or rear end of the plug head body, and is used to contact the inner wall of the pipe when the folding plug head travels in the pipe, so as to perform radial positioning and guidance;

[0062] The folding plug head also includes a horizontal adjustment block, which is located at the connection between the plug head seat and the hydraulic plugging cylinder actuator. The horizontal adjustment block is used to fine-tune the horizontal position of the folding plug head in the pipeline to compensate for the installation deviation of the pipeline centerline or the ellipticity of the pipeline.

[0063] The sealing pressure test of the clamp valve in step S2 and the sealing verification by filling the sealing box with nitrogen in step S3 are both carried out using inert gas. The test or verification pressure is not less than 1.2 times the operating pressure of the pipeline medium, and the pressure is maintained for a predetermined time to check whether the pressure drop meets the preset qualified standard.

[0064] The step of replacing the air inside the perforated connecting box with nitrogen in step S2 continues until the oxygen content volume concentration inside the perforated connecting box is confirmed by a detection instrument to be reduced to below 1%.

[0065] The sealing verification of the isolation section formed by the blockage in step S4 includes pressure monitoring and / or foam leak detection. The pressure monitoring method involves installing a pressure gauge downstream of the isolation section to monitor whether the pressure drop exceeds the allowable range within a set time. The foam leak detection method involves applying leak detection fluid to the outer wall of the pipe or the connecting flange around the folded plug head and observing whether bubbles are generated.

[0066] In one embodiment of the present invention, the length of the perforated short section is designed to be 1 / 3 to 1 / 2 of the pipe diameter, and the two ends of the perforated short section are machined with bevels for welding.

[0067] In one embodiment of the present invention, in step S4, when depressurizing the downstream pipe section to be repaired, the depressurization rate is controlled to not exceed 0.05 MPa / min, and the pipe section to be repaired is replaced with inert gas before the maintenance operation.

[0068] This invention provides a sealing and isolation construction method for gas pipelines under pressurized conditions. Through modular process design and sealing structure coordination, it achieves efficient and safe sealing. The specific steps are as follows:

[0069] Phase 1: Construction Preparation 1. Safety Protection: Establish a 20m x 10m enclosed work area, equipped with gas detectors, explosion-proof tools, fire extinguishers, and emergency oxygen supply equipment. Workers must wear anti-static clothing and respirators and undergo pre-job safety training. For example, equip the area with 4 portable gas detectors (detection range 0-1000ppm) and 2 sets of positive pressure breathing apparatus; 4 workers, all holding special operation certificates. 2. Parameter Confirmation: Detect the operating pressure (controlled at 0.1-0.3MPa), medium temperature (≤80℃), and pipe diameter (applicable range DN300-DN1200) of the pipeline to be constructed. Record the pipe material (e.g., Q235B) and wall thickness (≥6mm). For example, record a pipe pressure of 0.2MPa and a temperature of 50℃, confirming no significant pipe deformation. 3. Equipment Inspection: Verify the operating status of equipment such as the hole punching machine, hydraulic sealing cylinder, and clamp valve, ensuring stable hydraulic system pressure (working pressure 15-20MPa) and no aging or damage to seals.

[0070] Phase Two: Prefabrication and Welding 1. Prefabrication of the Opening Short Section: Custom-made opening short sections (material consistent with the main pipe) are produced according to the pipe diameter. The short section length is 1 / 3 to 1 / 2 of the pipe diameter, with bevels at both ends (angle 30°±5°). For example, a custom DN600 short section (200mm length) with a 30° bevel angle and Q235B material. 2. Welding Operation: The opening short section is welded to the pre-set position upstream of the section to be sealed using a combination of argon arc welding for the root pass and manual arc welding for the cap pass. After welding, 100% non-destructive testing (ultrasonic testing + magnetic particle testing) is performed to ensure the absence of defects such as porosity and cracks, and that the weld strength is not lower than that of the base material. For example, argon arc welding for the root pass (current 120A, voltage 20V), and manual arc welding for the cap pass (current 180A, voltage 25V). Post-weld ultrasonic testing shows no defects, and magnetic particle testing shows no cracks.

[0071] Phase 3: Opening Operation 1. Valve Installation and Pressure Testing: Install a dedicated clamp valve (pressure rating ≥ 0.6 MPa) on the opening section. Verify the valve's sealing performance by performing a nitrogen pressure test (pressure 1.5 times the pipeline operating pressure, hold pressure for 30 minutes without leakage). For example, if installing a DN600 clamp valve (pressure rating 0.6 MPa), perform a nitrogen pressure test at 0.3 MPa (1.5 × 0.2 MPa), hold pressure for 30 minutes without pressure drop. 2. Opening Connector and Equipment Assembly: Install the opening connector on the clamp valve and connect the opening machine (spindle speed 5-10 r / min), ensuring the coaxiality error between the connector and the pipeline axis is ≤ 2 mm; after assembly, purge the air inside the chamber with nitrogen (oxygen content ≤ 1%). 3. Performing the drilling: Start the drilling machine and use progressive cutting (pause for 30 seconds every 10mm of feed to avoid overheating) until the drilling cutter completely penetrates the pipe; after drilling, retract the drilling cutter into the connecting box, close the clamping valve, release the residual pressure in the connecting box (down to 0MPa), and dismantle the drilling machine. For example, if the drilling machine spindle speed is 8r / min, the feed rate is 10mm / 30s, and the total drilling time is 40min; after drilling, retract the cutter, close the clamping valve, and release the pressure to 0MPa.

[0072] Phase 4: Sealing Operation 1. Sealing Equipment Installation: Hoist the sealing junction box and hydraulic sealing cylinder onto the clamp valve (hoisting error ≤ 5mm), and install the folding sealing head; the sealing head and sealing cylinder are connected by a pivot pin, ensuring the rocker arm rotates flexibly (maximum rotation angle 60°). For example, hoist the sealing junction box (error 3mm), and install the folding sealing head (10mm thick cup). 2. Nitrogen Pressure Pressurization and Sealing: Fill the sealing junction box with nitrogen (pressure 0.2MPa) to verify the sealing performance between the sealing junction box and the clamp valve (pressure drop ≤ 0.01MPa after 15 minutes of pressure holding). 3. Implementation of Sealing: Activate the hydraulic sealing cylinder to insert the folded sealing head into the pipeline; after positioning by the guide wheel component, control the diagonal tie rod component to drive the front / rear side folding plates to unfold (expansion angle 90°), so that the sealing cup (made of oil-resistant nitrile rubber, 10mm thick) tightly fits against the inner wall of the pipeline; after sealing, close the hydraulic lock of the sealing cylinder and maintain the sealing pressure (0.3-0.5MPa). For example, if the hydraulic cylinder pressure is 0.4MPa, after the sealing head unfolds, the cup fits against the inner wall of the pipeline; maintain nitrogen pressure at 0.2MPa, and the pressure drop after 15 minutes is 0.005MPa, which meets the requirements. Fifth Stage: Verification and Subsequent Operations 1. Sealing Effect Detection: Monitor the pressure change through the downstream pressure gauge of the sealing section (pressure drop ≤0.02MPa within 30 minutes), and use soapy water to check for bubbles around the sealing head to confirm that the sealing is qualified. For example, if the downstream pressure gauge shows a pressure drop of 0.01MPa after 30 minutes, and no bubbles are detected by soapy water, the sealing is qualified. 2. Pipeline Section Isolation and Modification: Vent the medium in the pipeline section to be repaired (slowly depressurize through the vent valve, depressurization rate ≤0.05MPa / min), and perform modification work such as pipe disconnection and valve replacement. For example, slowly depressurize to 0MPa, cut the valve section to be replaced (500mm in length), replace with a new valve, and then weld it back in place. 3. Unsealing and Finishing: After the modification is completed, retract the sealing head into the connecting box, close the clamp valve; remove the sealing equipment, install the plug (weld to the opening short section for sealing), and install a blind flange; finally, clean up the construction site and collect tools and waste. Key Component Description (Folding Sealing Head): The folding sealing head consists of the rear left / right folding pressure plate, diagonal tie rod component, guide wheel component, rear middle fixed pressure plate, sealing head seat, horizontal adjustment block, rocker arm, front middle fixed pressure plate, front left / right folding pressure plate, pin shaft, sealing cup, etc. The components include: guide wheel assembly: ensures accurate positioning of the plug head inside the pipeline (deviation ≤3mm); plug cup: achieves sealing through radial pressure after the pressure plate is unfolded (contact pressure ≥0.4MPa); horizontal adjustment block: allows for fine adjustment of the horizontal position of the plug head (adjustment range ±5mm) to accommodate pipeline ellipticity errors.

[0073] In summary, after reading this invention document, those skilled in the art can make various other corresponding modifications to the technical solutions and concepts based on this invention without creative mental effort, and all of these modifications fall within the scope of protection of this invention.

Claims

1. A method for sealing and isolating a gas pipeline under pressurized conditions, characterized in that, Includes the following steps: S1. Install a connector with a valve on the pipeline upstream of the section to be repaired to form a controllable external passage. S2. Open the valve, and after opening a process hole in the pipeline through an external passage, close the valve to isolate the medium; S3. Connect a sealing device to the outside of the valve. The sealing device includes a sealing actuator that can deform radially. Open the valve and send the sealing actuator, which is in a contracted state, into the pipeline. Drive the sealing actuator to expand radially so that the sealing surface fits tightly against the inner wall of the pipeline to form an annular sealing band, thereby establishing an internal isolation barrier. S4. Verify the sealing performance of the isolation barrier. If it passes the test, process and repair the downstream pipe section to be repaired. S5. Retract the sealing actuator radially and close the valve to permanently seal the connection.

2. The sealing and isolation construction method for a gas pipeline under pressurized conditions according to claim 1, characterized in that, Step S1 includes: At a predetermined location upstream of the section of pipe to be repaired, a short section with an opening made of the same material as the main pipe is welded, and the welded joint of the short section with the opening is subjected to non-destructive testing to ensure that its strength is not lower than that of the base material of the section of pipe to be repaired.

3. The sealing and isolation construction method for a gas pipeline under pressurized conditions according to claim 2, characterized in that, Step S2 includes: Install a clamp valve on the perforated short section and perform a sealing pressure test on the clamp valve. After the pressure test is qualified, connect the perforation box and the perforation machine to the clamp valve. After the air in the opening box is replaced with nitrogen until the oxygen content is below the safety threshold, the opening machine is started to perform progressive cutting to open a process hole in the pipeline. After the opening is completed, the opening tool is retracted into the opening box and the clamp valve is closed.

4. The sealing and isolation construction method for a gas pipeline under pressurized conditions according to claim 3, characterized in that, Step S3 includes: A sealing box and a hydraulic sealing cylinder are installed on the clamp valve, and a folding sealing head is connected to the actuator of the hydraulic sealing cylinder. The folding sealing head includes at least a sealing head seat, an unfoldable or foldable pressure plate assembly, a transmission mechanism for driving the pressure plate assembly, and a sealing cup installed on the pressure plate assembly. After filling the sealing box with nitrogen to verify the seal, start the hydraulic sealing cylinder and send the folded sealing head, which is in a folded state, through the clamp valve and process hole into the pipeline. The transmission mechanism drives the pressure plate assembly to unfold, causing the sealing cup to expand radially and fit tightly against the inner wall of the pipe, thereby forming a seal against the pipe medium.

5. The sealing and isolation construction method for a gas pipeline under pressurized conditions according to claim 4, characterized in that, In step S5, after the maintenance work is completed, the driving pressure plate assembly is folded, the folded sealing head is retracted into the sealing box, the clamp valve is closed and the sealing actuator is removed, and finally the opening short section is permanently sealed.

6. The sealing and isolation construction method for a gas pipeline under pressurized conditions according to claim 4, characterized in that, The folding pressure plate assembly of the folding sealing head includes a symmetrically arranged front folding pressure plate group and a rear folding pressure plate group, and the transmission mechanism includes a diagonal tie rod; One end of the diagonal tie rod is hinged to the actuator end of the hydraulic sealing cylinder, and the other end of the diagonal tie rod is hinged to the front folding pressure plate group and the rear folding pressure plate group respectively. When the hydraulic sealing cylinder drives the diagonal tie rod to move linearly, it drives the front folding pressure plate group and the rear folding pressure plate group to rotate relative to the sealing head seat body, so as to realize the unfolding or folding action.

7. A sealing and isolation construction method for a gas pipeline under pressurized conditions according to claim 6, characterized in that, The folding plug head also includes a guide wheel component, which is disposed at the front end and / or rear end of the plug head body, and is used to contact the inner wall of the pipe when the folding plug head travels in the pipe, so as to perform radial positioning and guidance; The folding plug head also includes a horizontal adjustment block, which is located at the connection between the plug head seat and the hydraulic plugging cylinder actuator. The horizontal adjustment block is used to fine-tune the horizontal position of the folding plug head in the pipeline to compensate for the installation deviation of the pipeline centerline or the ellipticity of the pipeline.

8. A method for sealing and isolating a gas pipeline under pressure as described in claim 3, characterized in that, The progressive cutting specifically refers to: The drilling machine is controlled to cut in an intermittent feeding manner. After each set distance of feeding, it pauses for a period of time to allow the heat in the cutting area to dissipate before continuing to feed until the pipe wall is completely penetrated.

9. A method for sealing and isolating a gas pipeline under pressure as described in claim 1, characterized in that, The length of the perforated short section is designed to be 1 / 3 to 1 / 2 of the pipe diameter, and both ends of the perforated short section are machined with bevels for welding.

10. A method for sealing and isolating a gas pipeline under pressure as described in claim 1, characterized in that, In step S4, when depressurizing the downstream pipe section to be repaired, the depressurization rate is controlled to not exceed 0.05 MPa / min, and the pipe section to be repaired is replaced with inert gas before the maintenance work.

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