The operation skills and techniques for pressure sealing: Dual guarantees of technology and safety In the field of pipeline operation and maintenance, pressure-sealing is a crucial technology. When there is a leakage in an in-service pipeline that requires emergency repair, or when pipeline renovation or branch connection needs to be carried out without stopping the transportation, pressure-sealing technology provides a safe and reliable solution. This technology, without interrupting the medium transportation or discharging the internal medium of the pipeline, uses specialized equipment and processes to isolate and seal specific parts of the pipeline, creating safe conditions for subsequent maintenance and renovation operations. Pressure-sealing operations involve high-risk factors such as high pressure and flammable/explosive media, and have extremely high requirements for the skill level and process mastery of the operators. This article will start from the technical principle of pressure-sealing, systematically elaborate on its core operational skills, main process methods, operation process control, and quality and safety guarantee measures, providing a comprehensive technical reference for technicians engaged in pipeline emergency repair and maintenance. I. Overview and Basic Principles of Pressure-Resistant Sealing Technology Pressure-sealing refers to the technology of forming temporary or permanent sealing isolation inside or outside a pipeline through mechanical or chemical methods when the pipeline is operating normally and filled with pressurized media. This technology blocks the flow of the medium and creates safe working conditions for subsequent maintenance, renovation, or connection of branch lines. Compared with the traditional method of shutting down the pipeline for purging, pressure-sealing avoids production interruptions, medium losses, energy waste, and the time and economic costs associated with restarting, especially in fields with high requirements for continuous operation such as petrochemicals, urban gas, heating and water supply. The basic principle of pressure sealing can be summarized as "external isolation and internal blocking" or "double sealing and double insurance". Depending on the location of the sealing, it can be divided into two major categories: external sealing and internal sealing. External sealing involves applying pressure to the outer wall of the pipeline and using mechanical clamps or composite materials to seal the leakage point; internal sealing, on the other hand, forms a sealing surface inside the pipeline using a dedicated sealing head or sealing airbag to block the flow of the medium. In practical engineering, the more commonly used method is to use the pressure opening technology to create an operation hole on the pipeline, and then insert the sealing head from the opening to enter the pipeline interior, achieving pipe section isolation. The core of the pressure-sealing technology lies in "dynamic sealing" - establishing a reliable sealing system under the conditions of medium flow and pressure. This requires extremely high standards for the structural design of the sealing equipment, the performance of the sealing materials, and the skill level of the operators. A successful pressure-sealing operation needs precise coordination in multiple aspects such as pressure balance, sealing surface treatment, and mechanical operation. II. Core operational skills for pressure sealing operations Pressure-sealing operations are a highly technical task that requires operators to possess a wide range of professional skills. The following will be elaborated from several core aspects. Force balance and judgment skills are the fundamental skills for pressure-sealing operations. Operators need to accurately determine the internal pressure of the pipeline, the characteristics of the medium, and the patterns of pressure changes during the sealing operation. During the process of inserting the sealing head into the pipeline, a pressure difference will be formed between the front and back of the sealing head. Operators need to achieve pressure balance through the bypass pipeline or pressure balance holes; otherwise, the sealing head may fail to reach the correct position or be pushed out by the medium due to excessive pressure difference. Mastering the timing of pressure balance operation and judging whether pressure balance has been completed requires rich experience and precise perception. Operators must be able to proficiently use monitoring equipment such as pressure gauges and pressure transmitters to accurately read and understand pressure data. The operation skills for blocking equipment cover the correct use of various specialized equipment. The main equipment involved in pressure-sealing operations include: pressure-opening machines, blocking devices, clamp valves, hydraulic pump stations, blocking heads, bypass pipelines, etc. Operators need to be familiar with the structural principles, performance parameters, operation procedures, and common fault handling methods of each type of equipment. Taking the blocking device as an example, operators need to master the selection and installation of the blocking head, the connection between the blocking device and the clamp valve, the feed speed and depth control of the blocking rod, and other key operations. The operation of the hydraulic pump station requires mastering skills such as pressure regulation, flow control, and oil circuit switching to ensure that the blocking head is smoothly and accurately delivered to the predetermined position. Pipe welding and opening skills are the key technologies in the pressure-sealing operation of metal pipelines. Pressure-opening operations require the welding of transition short sections and clamp valves on the pipeline, which imposes extremely high requirements on the welding quality - the weld seam not only needs to withstand the internal pressure of the pipeline, but also the additional loads generated during the opening and sealing operations. Operators need to master the special techniques of pressure welding, including the selection of welding parameters, interlayer temperature control, and welding deformation control. For the opening operation, precise control of the feed speed and cutting parameters of the opening tool is required to ensure the opening quality and avoid damaging the opposite side wall of the pipeline or generating burrs that affect the sealing effect. The treatment of the sealing surfaces and the sealing techniques directly affect the success or failure of the sealing operation. The sealing surfaces between the sealing head and the inner wall of the pipeline need to form a reliable seal, which requires the selection of the correct sealing head, a clean sealing surface without debris, and a good contact between the sealing head and the pipe wall. For different types of pipes (such as steel pipes, cast iron pipes, PE pipes) and different medium conditions, the sealing methods and sealing materials are all different. Operators need to master the characteristics and application scope of various sealing materials (such as rubber sealing rings, expanded graphite, polytetrafluoroethylene, etc.), be able to select the appropriate sealing scheme according to the on-site conditions, and proficiently complete the cleaning of the sealing surface, the installation and compression operation of the sealing parts. Emergency response skills are the safety guarantee for personnel performing pressure sealing operations in emergency situations. Although the pressure sealing operation has well-established technical plans and safety measures, the on-site conditions are complex and changeable, and unexpected situations such as stuck sealing heads, failure of seals, and hydraulic system malfunctions may occur. Operators need to remain calm, quickly determine the cause of the failure, and take correct emergency response measures, such as emergency pressure relief, rapid removal of the sealing head, and activation of bypass protection. Regular emergency drills are an effective way to cultivate this skill. III. Main Process Methods of Pressure-Resistant Sealing Pressure sealing techniques vary depending on the type of pipeline, operating conditions, and operational requirements. There are several widely used techniques. The following describes several of the most commonly employed methods. The disc-type plugging process is the most mature pressure-bearing plugging method and is applicable to steel pipelines. The process is as follows: First, two transitional short sections are welded at the predetermined plugging position of the pipeline, and clamping valves and hole-opening machines are installed respectively. Two holes are opened on the pipeline - one for installing the plugging head and the other for installing the bypass connector; through the bypass pipeline, the medium before and after the plugging section is connected to ensure continuous material supply to the downstream during the plugging operation; then, the disc-type plugging head is sent into the pipeline through the plugging hole, and the plugging head expands inside the pipeline, relying on the contact between the sealing disc and the pipe wall to form a seal and block the flow of the medium. After the plugging is completed, the isolation section can be repaired or renovated. After the operation is completed, the plugging head is removed, the plug is installed to close the hole, the clamping valve and the transitional short section are removed, and the pipeline is restored to its original state. The disc-type plugging process is applicable to various pressure levels and pipe diameters, the plugging is reliable, and it is the mainstream process for pressure-bearing plugging. The sleeve-type sealing technology is similar to the disc-type sealing technology, but its sealing head adopts a cylindrical structure, and the sealing surface is the annular gap between the outer wall of the cylinder and the inner wall of the pipeline. The sleeve-type sealing is suitable for smaller-diameter pipelines. Its sealing head is compact in structure and easy to operate.