Pressure-sealing device for gas pipelines: The "non-stop surgery tool" for the city's energy arteries In the complex underground pipeline system of the city, the safe operation of gas pipelines is crucial for the cooking fires of thousands of households and the pulse of industrial production. However, as the service life of the pipelines increases, problems such as corrosion and aging, as well as third-party damage, are inevitable. How can maintenance and renovation operations be completed while ensuring continuous gas supply to users? The pressure-sealing device for gas pipelines has emerged, becoming a "special equipment" to ensure the unobstructed flow of the city's energy arteries. This article will systematically analyze the core essence of this key technology from dimensions such as technical principles, device classification, equipment composition, and operation procedures. I. Technical Challenges and Solutions for Gas Pipeline Sealing Pressure-sealing of gas pipelines refers to a special technical process carried out on pipelines while they are in normal operation and the medium is continuously flowing. It involves using specialized equipment to perform operations such as making holes, sealing, and replacing pipes. Compared with traditional shutdown and venting operations, the core value of this technology lies in "no shutdown" - it not only does not affect the normal gas usage of downstream users but also can safely and efficiently complete the maintenance tasks. However, the particularity of gas pipelines poses severe challenges to the sealing operation. In urban gas pipelines, spiral weld steel pipes are widely used. These pipes have poor ellipticity and inner wall smoothness, and there is a raised spiral weld on the inner wall. The accumulated iron filings, impurities, and pressure fluctuations of the transported medium in the pipeline may all affect the tightness of the sealing. Moreover, as the operating pressure of the pipeline changes from low pressure to medium pressure (up to 1.2 MPa or more), higher requirements are imposed on the sealing performance of the sealing device. It is precisely because of these challenges that the pressure-sealing device for gas pipelines has undergone decades of technological iterations, evolving into various forms suitable for different working conditions, thus forming a complete equipment system. II. Main Types of Sealing Devices and Their Technical Principles According to the sealing principle and the different applicable working conditions, the pressure-sealing devices for gas pipelines can be mainly classified into the following categories: Porous cup-type sealing device The cup-type sealing technology is widely adopted in Western developed countries. Its principle is to use a cutting machine to make a saddle-shaped hole on the pipeline, then use a sealing device to push the rubber cup-shaped sealing ring into the pipe through hydraulic transmission, moving it in the opposite direction of gas supply to achieve the purpose of sealing the gas source. The advantages of this device are that the opening time is short, the pushing force on the rubber cup when it moves in the pipeline is large, the sealing effect is good, and the applicable pressure range is wide. However, the traditional rubber cup type sealing device has two major problems: Firstly, the sealing surface is a sloping plane. After entering the pipeline, it is affected by the ellipticity of the pipeline and experiences uneven force, which is prone to cause wrinkles and gas leakage; Secondly, the iron filings generated after the pipeline is opened cannot be carried away by the airflow and accumulate at the opening, affecting the sealing effect. In response to these issues, the R&D team made improvements to the rubber cup structure: they adopted a multi-seam sealing design, which solved the problem of difficult sealing under both high and low pressure conditions; they also developed a debris removal device to push the iron filings away from the sealing area. 2. Expansion barrel-type sealing device The expansion barrel type sealing device is mainly designed for more severe pipeline conditions and is widely used in high and medium pressure urban gas pipelines in China. Its principle is as follows: first, under pressure conditions, a cutting machine with holes is used to completely cut the pipe section that needs to be renovated or repaired. Then, the sealing barrel (with a high-pressure-resistant rubber sheet attached to its outer surface) is sent into the center of the pipeline along the cut hole using the sealing device. Through the transmission device of the sealing device, the barrel is expanded to seal the gas source. Since the sealing hole covers the entire pipe diameter, it will not be affected by the presence of impurities or deformation in the pipe. However, this method requires the complete cutting of the pipe, which is time-consuming, costly, and may also have an impact on traffic. 3. Plunger-type valve changer For the replacement of pressure regulating equipment such as release valves and pressure regulating boxes in urban gas valve wells, the R&D team has developed a special piston-type valve replacement device with separable sealing heads and bottom plugs. This device meets the requirements for efficient pressure-bearing valve replacement operations and ensures uninterrupted gas supply to households, significantly reducing labor intensity and construction costs. 4. Foldable sealing device The folding type plug-in is a relatively new technology. It involves inserting a folded plug-in head through a non-uniform diameter hole into the pipeline. Once in place, it unfolds to achieve the sealing effect. This device combines the advantages of a small opening size and high sealing reliability, and is suitable for operations in space-constrained environments. 5. Small and lightweight sealing equipment For the working conditions in the narrow spaces of urban gas pipelines, the industry has developed a series of small and lightweight pressure-bearing opening and sealing devices, opening machines, and pipe fittings as supporting equipment. These devices enable mechanized operations, reduce the pollution of natural gas venting to the environment, and improve the safety, efficiency and quality of on-site sealing operations. To meet the pressure maintenance needs of the introduction pipes in front of buildings and indoor pipelines, specialized supporting equipment has also been developed, enhancing the safety and convenience of construction. III. Composition of the core system of the sealing device A complete pressure-sealing device for gas pipelines consists of a complex equipment system composed of multiple subsystems. Drilling machine system The hole-making machine is the core equipment for performing pressure-bearing pipe hole drilling. Its working principle is to drill the required-sized holes on the pipe wall while the pipe is in operation. This is achieved through a special sealing structure and cutting tools. During the hole-making process, the center drill first penetrates the pipe wall for positioning, followed by the ring cutter for circular cutting. The saddle-shaped plates cut off must be completely removed to prevent them from falling into the pipe and causing an accident. Modern hole-making machines have precise feed control and reliable sealing performance. Before performing the hole-making operation, it is necessary to check whether the center drill and the cylinder cutter are installed perpendicularly to the centerline of the pipeline; during the hole-making process, the rotational speed and feed rate are judged through the equipment operation procedures and the cutting sound to ensure the quality of the hole-making. 2. Occluder System