Comprehensive treatment method for updating and repairing urban old gas pipeline

Abstract

The invention discloses a comprehensive treatment method for updating and repairing urban old gas pipelines, and belongs to the technical field of gas pipeline repairing. Comprising the following steps of S1, operation foundation pit preparation and pipe breaking, S2, pipeline detection: detecting the condition of the inner wall of the pipeline after pipe breaking and residual gas replacement in the step S1 by adopting a pipeline closed circuit television detection technology, S3, pipeline sand blasting cleaning, S4, detection before lining installation: detecting the inner wall of the pipeline in the step S3 by adopting the pipeline closed circuit television detection technology, and S5, lining installation. S5, preparing a resin-impregnated lining, overturning and feeding, S6, curing: curing the hose lining fed into the to-be-repaired pipeline in the step S5, S7, detecting the pipeline after curing, and S8, performing ending work and completion acceptance. According to the method, through the closed-loop design of safety protection, precise detection, efficient cleaning, stable repairing and strict acceptance, safe, efficient and long-acting repairing of the old gas pipeline is achieved, and construction safety, repairing quality and environment coordination are considered.

Description

Technical Field

[0001] This invention relates to the field of gas pipeline repair technology, and more specifically, to a comprehensive treatment method for the renewal and repair of old urban gas pipelines. Background Technology

[0002] According to industry statistics, the proportion of old pipelines with an operating life of over 20 years is increasing year by year. These pipelines are generally affected by multiple factors such as long-term soil electrochemical corrosion, scouring of the transported medium (including corrosive gases such as CO2 and H2S), and geological subsidence, resulting in structural defects such as internal wall corrosion, perforation, and leakage. These defects not only lead to a decrease in gas transmission efficiency but also pose significant safety hazards such as explosions and poisoning, seriously threatening urban public safety. Currently, the repair technologies for old gas pipelines are mainly divided into two categories: traditional excavation repair and trenchless repair. Traditional excavation repair requires large-scale road excavation, which not only causes traffic disruption and environmental pollution, but also easily causes secondary damage to surrounding underground pipelines (such as cables and water pipes). The construction period can last for weeks or even months, seriously affecting the normal lives of residents. In densely populated urban core areas, the social and economic costs of this method are already unbearable. Although trenchless repair technology has been promoted in recent years, significant technical bottlenecks still exist in its application: First, incomplete cleaning of the pipeline inner wall during the pretreatment stage, with rust and dirt residue leading to insufficient bonding strength of the lining material, makes conventional sandblasting technology prone to dust pollution and difficult to quantify and control the cleaning effect; Second, the detection technology is disconnected from the repair process. Although existing closed-circuit television (CCTV) inspection equipment can identify pipeline defects, it lacks linkage optimization with subsequent sandblasting and lining process parameters, often resulting in insufficient detection accuracy or over-repair; Third, the lining curing quality is unstable. The curing temperature and pressure control of thermosetting resins lack standardized procedures, leading to defects such as bubbles and cracks in the lining layer, making it difficult to achieve the safety standards of "3MPa" or "30bar" or higher in compressive strength; Fourth, there are loopholes in the quality acceptance process. Some projects only use sampling X-ray inspection for welded joints, which cannot comprehensively investigate hidden defects such as incomplete fusion and cold welding, which are precisely the high-incidence points of gas leaks. While existing technical specifications such as the "Code for Construction and Acceptance of Urban Gas Transmission and Distribution Engineering" (CJJ33-2005) set forth basic requirements for repair processes, they have not formed a closed-loop control system covering the entire process from initial inspection, cleaning, lining installation to final acceptance. Especially under the complex conditions of aging pipelines, a single technical approach is insufficient to balance repair efficiency, construction safety, and long-term reliability. A systematic and comprehensive treatment solution is urgently needed to achieve the integrated repair goal of "precise inspection - efficient cleaning - stable curing - comprehensive acceptance," thereby addressing the problems of cumbersome operation, poor quality control, and high safety risks inherent in existing technologies. In view of this, we propose a comprehensive treatment method for the renovation and repair of old urban gas pipelines. Summary of the Invention

[0003] The purpose of this invention is to provide a comprehensive treatment method for the renewal and repair of old urban gas pipelines, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A comprehensive treatment method for the renovation and repair of old urban gas pipelines includes the following steps: S1. Construction Pit Preparation and Pipe Cutting: Identify the underground cable and pipeline distribution in the area where the old urban gas pipeline to be repaired is located; establish safety protection measures in the work area; excavate a construction pit that meets the required dimensions; cut the old urban gas pipeline to be repaired, controlling the cut length and the length of the pipe section exposed above the soil to meet subsequent construction needs; grind the cut ends until they are neat, smooth, and burr-free; purge the original pipe section after cutting to completely replace any residual gas inside; if, after cutting, it is determined based on the gas supply situation and the client's requirements, temporary gas supply during construction needs to be guaranteed, then lay additional temporary gas pipelines.

[0005] S2. Pipeline Inspection: The pipeline closed-circuit television (CCTV) inspection technology is used to inspect the condition of the inner wall of the pipeline after the pipe is cut off and the residual gas is replaced in step S1, and to determine the specific location and extent of perforation, corrosion and leakage in the pipeline. S3. Pipe Sandblasting Cleaning: A rotating sandblasting head is used to spray cleaning media onto the inner surface of the pipe. At the same time, a suction truck is started to remove the waste sand and impurities generated in the pipe. The cleaning media is corundum (brown corundum). The nozzle pressure of the sandblasting head is set to 1.0MPa. The cleaning effect of the inner surface of the pipe must reach Sa2.5 level (100% metallic luster), ensuring that there is no rust or dirt residue on the inner surface of the pipe and that the inner wall is roughened. The sandblasting head and the suction truck operate synchronously to ensure that the waste sand and impurities in the pipe are completely removed, avoiding dust pollution at the construction site.

[0006] S4. Inspection before lining installation: The inner wall of the pipe after cleaning in step S3 is inspected again using closed-circuit television (CCTV) technology to confirm that the cleaning quality of the inner wall of the pipe meets the adhesion requirements for hose lining installation. S5. Preparation and Inversion of Resin-Impregnated Lining: Prepare a hose liner with its surface fully impregnated with thermosetting resin. Precisely cut the hose liner to the length of the working section of the pipeline to be repaired, and input the working section data into the inversion equipment. Using an air-turning process, the hose liner is inverted and fed into the pipeline to be repaired at the working pit opening. During the inversion process, the working pressure is controlled at 0.5-1 Bar, and the working speed is 2m / min to 3m / min. The thermosetting resin is at least one of epoxy resin, unsaturated polyester resin, or vinyl ester resin. The inversion equipment completes the inversion and feeding of the hose liner through an automated control system. The automated control system can automatically adjust the inversion pressure and speed according to the input working section data to ensure a stable and controllable inversion process. The length and curvature of the hose liner prepared in step S5 are customized according to the actual route of the pipeline to be repaired, and the hose liner can adapt to bends of up to 90 degrees in the pipeline to be repaired.

[0007] S6. Curing: The hose liner inserted into the pipe to be repaired in step S5 is cured. The curing environment temperature is controlled to be no lower than 5°C and the curing time is no less than 24 hours. After curing, the hose liner is bonded to the inner wall of the pipe to be repaired, forming an inner liner layer with self-resistant collapse capability. The curing process is carried out by hot steam heating or natural curing. When hot steam heating is used, hot steam is introduced into the hose liner, and the steam temperature is controlled to allow the thermosetting resin of the hose liner to fully cross-link and cure.

[0008] S7. Pipeline Inspection After Curing: The pipeline and inner lining after curing in step S6 are comprehensively inspected using closed-circuit television (CCTV) inspection technology to confirm that the inner lining is undamaged, tightly bonded to the inner wall of the pipeline, and that there is no leakage in the pipeline. The qualification standards for pipeline CCTV inspection technology are: uniform thickness of the inner lining, no bubbles, cracks, or defects, a porosity of less than 1% at the bonding surface between the inner lining and the inner wall of the pipeline, and no residual impurities on the inner wall of the pipeline.

[0009] S8. Finishing Work and Final Acceptance: The short pipes at the inner lining work pit are sequentially welded together. During welding, protective measures are taken for the cured inner lining layer to prevent damage from high temperatures or impacts at the weld points. The welded short pipes undergo 100% X-ray flaw detection. After passing the flaw detection, the overall pipeline undergoes strength and density tests according to the gas pipeline construction specifications. After passing the tests, the work pit is backfilled to restore the site, and the construction equipment is removed, completing the final acceptance. The cured inner lining layer is protected by performing an internal circumferential cut 20-30cm from the weld joint and adding a fixing ring for protection. The strength and density tests are conducted according to the requirements of the "Code for Construction and Acceptance of Urban Gas Transmission and Distribution Engineering" (CJJ33-2005), and the test pressure and holding time comply with the specific provisions in the code for the repair of old gas pipelines.

[0010] Preferably, in step S1, if it is determined that temporary gas supply needs to be guaranteed during construction based on the gas supply situation and the client's needs after the pipeline is disconnected, an additional temporary gas pipeline will be laid.

[0011] Preferably, in step S3, the sandblasting head and the sand suction truck operate synchronously to ensure that the waste sand and impurities in the pipeline are completely removed, thus avoiding dust pollution at the construction site.

[0012] Preferably, in step S5, the thermosetting resin is at least one of epoxy resin, unsaturated polyester resin, or vinyl ester resin.

[0013] Preferably, in step S5, the flipping device completes the flipping and feeding of the hose liner through an automated control system. The automated control system can automatically adjust the flipping pressure and flipping speed according to the input working section data to ensure that the flipping process is stable and controllable.

[0014] Preferably, in step S6, the curing process uses hot steam heating or natural curing; when hot steam heating is used, hot steam is introduced through the inner lining of the hose, and the steam temperature is controlled to ensure that the thermosetting resin in the inner lining of the hose is fully cross-linked and cured.

[0015] Preferably, in step S7, the qualification criteria for pipeline closed-circuit television (CCTV) inspection technology are: the lining layer has uniform thickness, no bubbles, cracks or damage defects, the porosity of the bonding surface between the lining layer and the inner wall of the pipeline is less than 1%, and there are no residual impurities on the inner wall of the pipeline.

[0016] Preferably, in step S8, the method for protecting the cured inner lining layer is as follows: an internal circumferential cut is made 20-30cm away from the weld joint, and a retaining ring is added for protection.

[0017] Preferably, the length and curvature of the hose liner prepared in step S5 are customized according to the actual direction of the pipeline to be repaired, and the hose liner can adapt to the elbow structure with a maximum angle of 90 degrees in the pipeline to be repaired.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Full-chain risk prevention and control: Accurate detection of underground pipelines avoids accidental excavation and damage to surrounding cables; 100% replacement of residual gas in the pipe eliminates the risk of combustion and explosion; 100% X-ray inspection of welded joints eliminates hidden leaks, forming a "pre-construction-in-process-post" safety protection system, which greatly reduces construction accidents and subsequent operational risks. Lining protection and structural safety: High-temperature resistant gaskets are used to protect and solidify the lining layer during welding to avoid secondary damage; the solidified lining layer forms a composite structure with the original pipeline, which has independent anti-collapse capability and can withstand internal and external loads under design pressure, ensuring the safety of gas transmission.

[0019] (2) Precise Repair Control: Full-process quality monitoring is achieved through three CCTV inspections (defect location before repair, quality verification after cleaning, and integrity check after curing) to ensure that the inner lining is tightly bonded to the inner wall of the pipeline (porosity <1%) and free from defects such as bubbles and cracks. After repair, the pipeline's sealing and pressure resistance are restored to the design standard. Long-lasting Corrosion Protection and Structural Enhancement: Sa2.5 grade sandblasting provides a clean base for the inner lining. Thermosetting resin lining (such as epoxy resin) forms a physical barrier, preventing the gas from contacting the original pipeline corrosion area. Combined with the enhanced strength of the composite structure, the service life of old pipelines is extended by more than 30 years, significantly reducing the cost of repeated repairs.

[0020] (3) Minimally invasive and rapid construction: The trenchless excavation pit design is adopted (the excavation area is only 1 / 5-1 / 10 of that of the traditional method), and with the help of automated turning equipment (pipe delivery speed of 2-3m / min), the total construction cycle is shortened to 7-10 days (traditional excavation requires 15-20 days), reducing the interference with urban traffic, commerce and residents' lives. Flexible adaptation to complex scenarios: The temporary gas supply pipeline solution can ensure normal gas supply for users during construction; the hose lining can adapt to 90-degree bends, and the hot steam / natural curing method can adapt to different climate conditions, solving the repair problems of old pipelines with "various pipe diameters, complex routes and environmental restrictions".

[0021] (4) Environmentally friendly operation control: Sandblasting and sand suction are operated simultaneously to achieve 100% recycling of waste sand and impurities. The dust concentration at the construction site is ≤0.5mg / m³, avoiding dust pollution. The trenchless process reduces road damage and soil removal, reducing the damage to the urban ecological environment. Efficient resource utilization: Through precise material cutting (hose length error ≤1m) and in-situ repair of old pipes (no need for overall replacement), the consumption of building materials such as steel and concrete is reduced, and the utilization rate of pipeline resources is increased by more than 60%, which is in line with the concept of low-carbon recycling. This invention forms a standardized repair system by clarifying the technical parameters of each link (such as sandblasting pressure 1.0MPa, curing time ≥24 hours), testing standards (such as porosity of inner lining bonding surface <1%) and acceptance specifications (CJJ33-2005). All test data and construction records are traceable, providing a reliable basis for subsequent pipeline maintenance and improving the level of precision in urban gas management. This method takes into account safety, durability, efficiency, and environmental protection, and provides a systematic solution for the renovation and repair of old urban gas pipelines, with significant technical, economic, and social benefits. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] Example: A comprehensive treatment method for the renovation and repair of old urban gas pipelines includes the following steps: S1. Construction Pit Preparation and Pipe Cutting: Identify the underground cable and pipeline distribution in the area where the old urban gas pipeline to be repaired is located, set up safety protection in the work area, and excavate a construction pit that meets the construction size requirements; cut the old urban gas pipeline to be repaired, control the length of the cut and the length of the pipe section exposed outside the soil to meet the needs of subsequent construction, grind the cut end until it is neat, smooth and free of burrs; purge the original pipe section after the cut to completely replace the residual gas in the pipe.

[0024] The process includes: 1. Identifying underground pipelines: Precisely locating underground cables and other pipelines (such as power cables and water pipes) to avoid secondary damage caused by accidental excavation during construction, ensuring the safety of surrounding infrastructure and reducing construction risks. 2. Setting up safety protection and excavating foundation pits: Demarcating the work area and implementing protective measures (such as guardrails and warning signs) to prevent unauthorized personnel from entering the work area; excavating foundation pits of appropriate dimensions to provide sufficient working space for subsequent pipe cutting, inspection, and lining installation. 3. Pipe cutting and end treatment: Controlling the pipe cutting length and exposed pipe sections according to construction requirements to facilitate the entry of subsequent equipment (such as CCTV crawlers and sandblasting heads) into the pipeline; grinding the ends to a smooth, burr-free finish to prevent sharp edges from scratching the subsequently inserted flexible hose lining, while ensuring the seal when welding the ends to the short pipe. 4. Residual gas replacement in the pipe: Thoroughly removing residual gas in the pipe through purging operations to eliminate the risk of combustion and explosion, ensuring the safety of subsequent operations such as pipeline inspection and sandblasting; if temporary gas supply is required, laying additional temporary pipelines can reduce the impact on users' normal gas usage and improve construction coordination.

[0025] S2. Pipeline Inspection: Closed-circuit television (CCTV) inspection technology is used to inspect the condition of the inner wall of the pipeline after the pipe disconnection and residual gas replacement in step S1, to determine the specific location and extent of perforations, corrosion, and leaks in the pipeline. The use of closed-circuit television (CCTV) inspection technology allows for a direct view of the specific location and extent of defects such as perforations, corrosion, and leaks on the inner wall of the pipeline, providing a precise "targeted" basis for subsequent sandblasting and lining repair, avoiding blind construction or over-repair, and improving the targeting and efficiency of repair.

[0026] S3. Pipe Sandblasting Cleaning: A rotating sandblasting head is used to spray cleaning media onto the inner surface of the pipe. At the same time, a sand suction truck is started to remove the waste sand and impurities generated inside the pipe. The cleaning media is corundum (brown corundum). The nozzle pressure of the sandblasting head is set to 1.0MPa. The cleaning effect of the inner surface of the pipe must reach Sa2.5 level (100% metallic luster), ensuring that there is no rust or dirt residue on the inner surface of the pipe and that the inner wall is roughened. The rotating sandblasting head and corundum medium: Brown corundum corundum is blasted at 1.0 MPa pressure, utilizing its high hardness to efficiently remove rust, dirt, and corrosion layers from the inner wall of the pipe, ensuring a cleaning effect of Sa2.5 grade (100% metallic luster), creating a clean base for a tight bond between the lining and the pipe inner wall. Simultaneous sand suction operation: The sandblasting head and the sand suction truck operate synchronously, removing waste sand and impurities in real time. This avoids residual debris in the pipe affecting the lining installation and prevents dust leakage and environmental pollution, balancing cleanliness and environmental friendliness. Forming a roughened surface: Sandblasting creates a uniformly roughened surface on the inner wall of the pipe, increasing the contact area between the lining and the pipe, enhancing their mechanical bonding force, and ensuring that the subsequent lining adhesion strength meets usage requirements (typically ≥5 MPa).

[0027] S4. Pre-installation inspection of the lining: The inner wall of the pipe after cleaning in step S3 is inspected again using closed-circuit television (CCTV) technology to confirm that the cleaning quality of the inner wall meets the adhesion requirements for the flexible hose lining installation. The cleaning quality of the inner wall is confirmed again by CCTV inspection to verify whether it meets the lining installation standard of "no residual impurities and uniform roughness". This avoids potential problems such as poor lining adhesion and local detachment due to substandard cleaning, and controls the basic quality of the lining installation from the source.

[0028] S5. Preparation and Inversion of Resin Impregnated Lining: Prepare a hose liner with its surface fully impregnated with thermosetting resin. Precisely cut the hose liner to the length of the working section of the pipeline to be repaired and input the working section data into the inversion equipment. The hose liner is inverted and fed into the pipeline to be repaired at the working pit using the inversion equipment with an air inversion process. During the inversion process, the working pressure is controlled at 0.5-1 Bar and the working speed is 2m / min to 3m / min. Among the key aspects are resin impregnation and precise material cutting: The flexible tubing (glass fiber or composite material) is impregnated with thermosetting resins such as epoxy resin. The adhesive properties and high strength after curing of the resin provide the lining with corrosion resistance and pressure resistance. Precise material cutting is performed according to the length of the working section of the pipeline to avoid material waste or insufficient length. The air-turning process and automated control: The tubing lining is turned over and fed into the pipeline using a turning device at a pressure of 0.5-1 Bar and a speed of 2-3 m / min. Air pressure ensures the tubing adheres evenly to the inner wall of the pipeline. The automated control system adjusts the pressure and speed according to pipeline parameters to ensure a stable turning process, preventing lining wrinkles and misalignment. It is particularly suitable for 90° elbow structures, ensuring effective repair of complex pipelines.

[0029] S6. Curing: Curing treatment is carried out on the hose liner that was sent into the pipe to be repaired in step S5. The curing environment temperature is controlled to be no lower than 5°C and the curing time is no less than 24 hours. After curing, the hose liner is bonded to the inner wall of the pipe to be repaired, forming an inner liner layer with self-resistant collapse capability. Controlling the curing environment temperature to ≥5℃ and the time to ≥24 hours ensures the thermosetting resin is fully cross-linked and cured, forming an integral structure between the hose liner and the pipe inner wall. The cured liner layer possesses independent anti-collapse capability (does not deform under external pressure), which can not only repair corrosion and perforation defects in the original pipe, but also enhance the overall structural strength of the pipe and extend its service life. Hot steam curing can accelerate resin curing at low temperatures, while natural curing is suitable for normal temperature conditions. Both methods are adaptable to different climatic conditions, ensuring stable curing quality.

[0030] S7. Pipeline inspection after curing: The pipeline and inner lining after curing in step S6 are fully inspected using closed-circuit television (CCTV) inspection technology to confirm that the inner lining is undamaged, tightly bonded to the inner wall of the pipeline, and that there is no leakage in the pipeline. CCTV inspection verifies the uniformity of the lining thickness, the presence of bubbles / cracks, and the tightness of its adhesion to the inner wall of the pipeline (porosity <1%). This ensures that the lining has no functional defects, effectively preventing gas from contacting the corroded areas of the original pipeline, achieving the repair goals of corrosion prevention and leakage prevention, and providing core evidence for subsequent final acceptance.

[0031] S8. Finishing Work and Final Acceptance: The short pipes at the inner lining working pit are sequentially welded together. During welding, protective measures are taken for the cured inner lining layer to prevent damage from high temperatures or impacts at the weld joints. The welded short pipes undergo 100% X-ray flaw detection. After passing the flaw detection, the entire pipeline undergoes strength and density tests according to gas pipeline construction specifications. After passing the tests, the working pit is backfilled to restore the site, and the construction equipment is removed, completing the final acceptance. The cured inner lining layer is protected by making an internal circumferential cut 20-30cm from the weld joint and adding a fixing ring for protection.

[0032] Short pipe welding and lining protection: Welding the short pipe restores pipeline continuity. High-temperature resistant gaskets such as ceramic fiber are used during welding to prevent damage to the cured lining layer from high temperatures or mechanical impact, ensuring the integrity of the lining. 100% X-ray inspection: All welded joints undergo full-range non-destructive testing to identify hidden defects such as incomplete penetration and cracks, eliminating the risk of gas leakage due to welding quality and meeting the "zero leakage" safety requirements for gas pipelines. Strength and tightness testing: Tests are conducted according to CJJ33-2005 to verify the pressure-bearing capacity and sealing performance of the repaired pipeline, ensuring it meets the safety standards for gas transmission. Pit backfilling and acceptance: The site is restored to its original state to minimize impact on urban traffic and the environment. Final acceptance confirms the overall repair quality meets standards, ensuring the pipeline can be safely put into use.

[0033] This application employs a closed-loop design for each step, encompassing "safety protection, precise detection, efficient cleaning, stable repair, and rigorous acceptance," to achieve safe, efficient, and long-term repair of aging gas pipelines, while also considering construction safety, repair quality, and environmental compatibility.

[0034] I. Implementation Background This embodiment addresses the renovation and repair of an old gas pipeline on Minsheng West Road in the old city area of ​​a certain city. The pipeline is a DN300 seamless steel pipe, with a service life of 25 years. Due to long-term electrochemical corrosion from the soil and erosion by H2S in the gas, multiple areas of internal wall corrosion and three perforations with diameters of 5-8mm have appeared. Furthermore, the pressure in some sections has dropped to 0.2MPa (design pressure 0.4MPa), posing a risk of gas leakage. On-site investigation revealed that this section is a densely populated commercial area with complex underground pipelines (including 10kV cables and DN400 water supply pipes), making traditional excavation and replacement methods unsuitable. Therefore, the comprehensive treatment method of this invention was adopted for repair, with a total repair length of 25m.

[0035] II. Specific Implementation Steps Step S1: Preparation of the excavation pit and pipe cutting Underground pipeline detection: The RD8000 underground pipeline detector was used to detect the work area (from the intersection of Minsheng West Road and Jianshe Road to the intersection of Minsheng West Road and Gongyuan Road). It was found that there was a 10kV cable (laid parallel to the gas pipeline, with a spacing of 1.5m) at 1.2m underground and a DN400 water supply pipe (perpendicularly intersecting the gas pipeline, with the intersection point 2m away from the work pit) at 1.8m underground. The pipeline location distribution map was drawn and warning signs were marked.

[0036] Safety protection measures: A steel guardrail with a height of 1.8m is set up around the work area, and a "Gas Construction Prohibited" warning sign is hung on the outside of the guardrail. LED warning lights are turned on at night (one light per 10m); a rain shelter (4m×2m) is built above the work pit to prevent rainwater from entering.

[0037] Excavation of the working pits: Two rectangular working pits were excavated according to the construction requirements (Pit 1: 3m long × 1.5m wide × 2.2m deep, located at the beginning of the pipeline; Pit 2: 2.5m long × 1.2m wide × 2.0m deep, located at the end of the pipeline). The pit walls were supported by Φ48mm steel pipes (0.8m spacing) + bamboo plywood (15mm thick), and a 200mm thick graded sand and gravel cushion layer was laid at the bottom of the pit.

[0038] Pipe cutting and port treatment: The gas pipeline was cut using an LGK-100 plasma cutter, and the length of the pipe exposed outside the soil was controlled to be 1.2m (on one side of the pit) and 1.0m (on the other side of the pit). After cutting the pipe, the port was polished with an angle grinder (equipped with a 120-grit abrasive wheel) until it was neat and smooth, and burrs were removed (port flatness error ≤ 0.5mm).

[0039] Residual gas replacement in the pipeline: Since this pipeline is the main gas supply pipeline for residents, it is necessary to ensure temporary gas supply during construction. Therefore, a DN200PE temporary gas pipeline was laid first (using trenchless horizontal directional drilling, with an entry angle of 15°, an exit angle of 12°, and a burial depth of 1.5m). The two ends of the temporary pipeline were connected to the valves of the original pipeline network. Then, the valves at both ends of the original pipeline were closed, and 99.9% pure nitrogen gas (flow rate of 50m³ / h) was introduced into the pipeline through the break on side 1 of the foundation pit. The gas concentration in the pipeline was monitored in real time using a GTQ-200 gas concentration detector until the concentration was lower than 10% of the lower explosive limit (5%) (i.e., 0.5%), thus completing the residual gas replacement.

[0040] Step S2: Pipeline Inspection The Shenzhen Schroder S300 pipe crawler (equipped with a 1080P HD camera, 30W LED lighting, and a detection radius of 500mm) was used for closed-circuit television (CCTV) inspection of the pipeline. The crawler enters from the first side of the pit, travels at a speed of 1 m / min, and transmits images of the inner wall to the ground main control terminal in real time. Inspection results: There is a localized corrosion zone with an area of ​​0.2㎡ (corrosion depth 1.2mm, original pipe wall thickness 6mm) 15m away from the fracture on side 1 of the foundation pit. There are two perforations with a diameter of 5mm each at 8m and 5m away from the fracture on side 2 of the foundation pit. There is one perforation with a diameter of 8mm at 10m away from the fracture on side 1 of the foundation pit. The walls of the remaining areas are covered with rust and oil stains (thickness 0.5-1mm).

[0041] Step S3: Pipe sandblasting cleaning Equipment selection and parameter settings: The KQP-100 portable sandblasting unit (rated pressure 1.2MPa) is used, equipped with an alloy sandblasting head that can rotate 360° (nozzle diameter 8mm); the cleaning medium is 80-mesh brown corundum alumina (bulk density 1.6g / cm³, hardness HRC65); the SX-150 sand suction truck (maximum suction 150m³ / h, filter element accuracy 5μm) is used simultaneously.

[0042] Sandblasting and suction are operated simultaneously: The linkage control system is set to "the suction truck will start automatically 5 seconds after the sandblasting unit starts". The pressure of the sandblasting head nozzle is stabilized at 1.0MPa. The pipe extends into the pit from the break on side 1 and moves towards the pit from side 2 at a speed of 0.5m / min, spraying diamond abrasive to remove rust and oil stains from the inner wall. At the same time, the suction pipe extends into the pit from the break on side 2 and sucks the waste sand and impurities (a mixture of rust and oil stains) into the sand storage tank of the suction truck.

[0043] Verification of cleaning effect: After sandblasting, the roughness of the inner wall of the pipe was tested using a TR200 surface roughness meter, and the Ra value was measured to be 12.5μm; CCTV inspection confirmed that there was no residual rust or oil on the inner wall, and the metal substrate in the corrosion area was completely exposed (exhibiting 100% metallic luster), which met the Sa2.5 cleaning standard; a dust detector (range 0-10mg / m³) was used to monitor the dust concentration at the construction site, and the dust concentration was ≤0.5mg / m³, with no dust pollution.

[0044] Step S4: Inspection before lining installation Reactivate the pipe crawler in S2 to conduct a comprehensive inspection of the inner wall of the sandblasted pipe: The key focus is on checking the cleaning quality of the corroded area and the perforation location, confirming that there are no residual impurities in the metal substrate of the corroded area and no burrs around the perforation; Test results: The roughened surface of the inner wall of the pipe is uniform, with no local protrusions or depressions (maximum depression depth ≤ 0.3 mm), which meets the adhesion strength requirements of the hose lining (adhesion strength ≥ 5 MPa), and no secondary sandblasting is required.

[0045] Step S5: Preparation and inversion of resin-impregnated lining Hose and resin selection: Fiberglass braided hose (inner diameter 290mm, wall thickness 5mm, tensile strength ≥800N / 50mm) is selected; the thermosetting resin is E-44 epoxy resin (epoxy value 0.41-0.47eq / 100g) + methyltetrahydrophthalic anhydride curing agent (purity ≥98%), mixed evenly at a mass ratio of 100:80 (stirring speed 300r / min, stirring time 5min, vacuum degassing 10min).

[0046] Resin impregnation process: Place the glass fiber tubing into a vacuum impregnation tank (5m³), close the tank door, and evacuate to -0.09MPa for 10 minutes; then inject the mixed epoxy resin into the tank and soak for 30 minutes to ensure that the tubing fiber bundle is completely impregnated with resin (the weight gain of the tubing after impregnation is ≥30%); after removing the tubing, drain the excess resin from the surface and wrap it with plastic wrap to prevent resin loss.

[0047] Precise material feeding and flipping operation: Based on the length of the working section of the pipeline to be repaired (25m), with a 1m margin, cut the resin-impregnated hose to 26m; input the working section length (25m), pipeline diameter (DN300), and other data into the control system of the automated flipping machine (model FZ-300, maximum working pressure 2Bar), the system automatically sets the flipping pressure to 0.8Bar and the flipping speed to 2.5m / min; fix one end of the hose to the flipping machine interface from the working pit on side 1 of the foundation pit, start the equipment, and the hose is flipped and fed into the pipeline along the inner wall through the air flipping process. During the process, the pressure sensor monitors in real time (automatic stop and adjustment when the pressure fluctuation exceeds ±0.1Bar), and the entire hose is fed in after 30 minutes.

[0048] Step S6: Curing In this embodiment, the local average daily ambient temperature during construction was 12-15℃, which meets the requirement of "curing temperature ≥ 5℃", therefore, natural curing method was adopted. Cover the fracture points on sides 1 and 2 of the foundation pit with thermal insulation cotton (50mm thick) to prevent a sudden drop in temperature inside the pipe; The temperature of the inner wall of the pipe was measured every 2 hours using a PT100 temperature sensor (minimum temperature 10℃), and the total curing time was 26 hours (more than 24 hours). After curing, the condition of the inner lining was observed through an endoscope: the inner lining was tightly bonded to the inner wall of the pipe, without bubbles or wrinkles; the adhesion strength of the inner lining was tested with a pull-out tester, and the measured value was 6.2MPa (≥5MPa), forming an inner lining with self-resistant collapse capability (no deformation under external pressure of 0.3MPa).

[0049] Step S7: Pipeline inspection after curing CCTV inspection technology was used to conduct a comprehensive inspection of the cured pipes and inner lining. The pass criteria and inspection results are as follows: Step S8: Finishing work and final acceptance Short pipe welding and inner lining protection: Two sections of 20# seamless steel pipe (1.5m in length, DN300 in diameter, and 6mm in wall thickness) were selected and welded to the existing pipeline using a WS-400 argon arc welding machine (welding wire type H08Mn2SiA, diameter 2.5mm). Before welding, ceramic fiber protective gaskets (3mm thick, 200mm×100mm in size, and temperature resistance 1200℃) were placed on the inner lining surface corresponding to the welding area to prevent damage to the inner lining from the high temperature (≥800℃) of the weld point.

[0050] 100% X-ray flaw detection: The XXQ-2505 portable X-ray machine (tube voltage 200kV, tube current 5mA, exposure time 60s) was used to perform 100% flaw detection on the two welds. According to the rating of "Non-destructive testing of pressure equipment - Part 2: Radiographic testing" (NB / T 47013.2): the welds have no defects such as incomplete penetration, cracks, or slag inclusions, and are all qualified as Grade I.

[0051] Strength and density tests: in accordance with the requirements of the "Code for Construction and Acceptance of Urban Gas Transmission and Distribution Engineering" (CJJ33-2005): Strength test: Compressed air is introduced into the pipeline to 0.6MPa (1.5 times the design pressure), and the pressure is maintained for 1 hour. The pressure drop is 0.003MPa (≤0.01MPa, qualified). Toughness test: Reduce to 0.4MPa (design pressure), maintain pressure for 24 hours, pressure drop 0.005MPa (≤0.008MPa, qualified).

[0052] Site restoration and acceptance: The excavation pit was backfilled in layers of sand, soil, and graded gravel (each layer 300mm thick, compaction degree ≥95%, compacted with a small road roller), and a 50mm thick asphalt concrete layer was laid on the surface (flush with the original road surface); construction equipment was removed and site debris was cleaned up; the construction unit, supervision unit, and gas company were organized to conduct a final acceptance inspection, and the inspection conclusion was "qualified". The repaired pipeline was restored to gas supply (transmission pressure 0.4MPa, meeting design requirements).

[0053] III. Implementation Results Construction efficiency: The total construction period is 7 days (traditional excavation and repair takes 15-20 days), and the excavation area is only 7.5㎡ (traditional excavation requires more than 40㎡), reducing the interference with traffic and residents' lives in the commercial district.

[0054] Safety and environmental protection: No excavation or damage to underground cables and water supply pipes is required throughout the process, and there is no dust pollution; 100% X-ray flaw detection and strictness testing ensure no risk of gas leakage, and the pressure bearing capacity of the pipeline is restored to the design value after repair.

[0055] Service life: The inner lining layer forms a "steel-plastic composite structure" with the original pipeline, which improves corrosion resistance and is expected to extend the service life of the pipeline by 30 years and increase the utilization rate of pipeline resources by 60%.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A comprehensive treatment method for the renewal and repair of old urban gas pipelines, characterized in that, Includes the following steps: S1. Construction Pit Preparation and Pipe Cutting: Identify the underground cable and pipeline distribution in the area where the old urban gas pipeline to be repaired is located, set up safety protection in the work area, and excavate a construction pit that meets the construction size requirements; cut the old urban gas pipeline to be repaired, controlling the cut length and the length of the pipe section exposed outside the soil to meet the needs of subsequent construction, and grind the cut end until it is neat, smooth and burr-free; purge the original pipe section after the cut to completely replace the residual gas in the pipe; S2. Pipeline Inspection: The pipeline closed-circuit television (CCTV) inspection technology is used to inspect the condition of the inner wall of the pipeline after the pipe is cut off and the residual gas is replaced in step S1, and to determine the specific location and extent of perforation, corrosion and leakage in the pipeline. S3. Pipe Sandblasting Cleaning: A rotating sandblasting head is used to spray cleaning medium onto the inner surface of the pipe. At the same time, a sand suction truck is started to remove the waste sand and impurities generated inside the pipe. The cleaning medium is corundum (brown corundum). The nozzle pressure of the sandblasting head is set to 1.0MPa. The cleaning effect of the inner surface of the pipe must reach Sa2.5 level (100% metallic luster), ensuring that there is no rust or dirt residue on the inner surface of the pipe and that the inner wall is roughened. S4. Inspection before lining installation: The inner wall of the pipe after cleaning in step S3 is inspected again using closed-circuit television (CCTV) technology to confirm that the cleaning quality of the inner wall of the pipe meets the adhesion requirements for hose lining installation. S5. Preparation and Inversion of Resin Impregnated Lining: Prepare a hose liner with its surface fully impregnated with thermosetting resin. Precisely cut the hose liner to the working section length of the pipeline to be repaired and input the working section data into the inversion equipment. The hose liner is inverted and fed into the pipeline to be repaired at the working pit using the inversion equipment with an air inversion process. During the inversion process, the working pressure is controlled at 0.5-1 Bar and the working speed is 2m / min to 3m / min. S6. Curing: The hose liner inserted into the pipe to be repaired in step S5 is cured. The curing temperature is controlled to be no lower than 5°C and the curing time is no less than 24 hours. After curing, the hose liner is bonded to the inner wall of the pipe to be repaired to form an inner liner layer with self-collapse resistance. S7. Pipeline inspection after curing: The pipeline and inner lining after curing in step S6 are fully inspected using closed-circuit television (CCTV) inspection technology to confirm that the inner lining is undamaged, tightly bonded to the inner wall of the pipeline, and that there is no leakage in the pipeline. S8. Finishing Work and Final Acceptance: Weld the short pipes at the inner lining working pit together in sequence. During the welding process, take protective measures to avoid damage to the inner lining layer caused by high temperature or impact at the weld points. Conduct 100% X-ray flaw detection on the welded short pipes. After the flaw detection is qualified, conduct strength and density tests on the entire pipeline in accordance with the gas pipeline construction specifications. After the tests are qualified, backfill the working pit to restore the site, remove the construction equipment, and complete the final acceptance.

2. The comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1, characterized in that: In step S1, if it is determined that temporary gas supply needs to be guaranteed during construction based on the gas supply situation and the client's needs after the pipeline is disconnected, an additional temporary gas pipeline will be laid.

3. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: In step S3, the sandblasting head and the sand suction truck operate synchronously to ensure that the waste sand and impurities in the pipeline are completely removed, thus avoiding dust pollution at the construction site.

4. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: In step S5, the thermosetting resin is at least one of epoxy resin, unsaturated polyester resin, or vinyl ester resin.

5. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: In step S5, the flipping device completes the flipping and feeding of the hose liner through an automated control system. The automated control system can automatically adjust the flipping pressure and flipping speed according to the input working section data to ensure that the flipping process is stable and controllable.

6. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: In step S6, the curing process is carried out by hot steam heating or natural curing; when hot steam heating is used for curing, hot steam is introduced into the inner lining of the hose, and the steam temperature is controlled to allow the thermosetting resin of the inner lining of the hose to fully cross-link and cure.

7. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: In step S7, the qualification criteria for pipeline closed-circuit television (CCTV) inspection technology are: the lining layer has uniform thickness, no bubbles, cracks or damage defects, the porosity of the bonding surface between the lining layer and the inner wall of the pipeline is less than 1%, and there are no residual impurities on the inner wall of the pipeline.

8. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: In step S8, the method for protecting the cured inner lining layer is as follows: make an internal circumferential cut 20-30cm away from the weld joint and add a fixing ring for protection.

9. A comprehensive treatment method for the renewal and repair of old urban gas pipelines according to claim 1 or 2, characterized in that: The length and curvature of the hose liner prepared in step S5 are customized according to the actual direction of the pipeline to be repaired. The hose liner can adapt to the bend structure of up to 90 degrees in the pipeline to be repaired.

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