Introduction to the high-pressure pipeline sealing technology: Conducting precise "minimally invasive surgery" on the energy arteriesIn the operation and maintenance of long-distance oil and gas pipelines and urban high-pressure gas distribution networks, how to safely replace damaged sections of pipelines or old valves without stopping the medium flow or reducing the system pressure has always been a core technical challenge faced by the industry. The high-pressure pipeline sealing technology is the "golden key" to solving this problem. This technology, known as a "minimally invasive surgery" for pipelines, can precisely isolate the area to be worked on while keeping the pipeline in normal operation.cI. Definition and Technical Principles of High-Pressure Pipeline Sealing Technology High-pressure pipeline sealing refers to a special construction technique where, while the pipeline is maintaining a pressure level (typically above 2.5 MPa to 10 MPa), a dedicated mechanical device is used to completely isolate and block the section of the pipeline that needs renovation or maintenance from the operating pipeline. This allows for operations such as replacement, maintenance, or adding branch lines. This technology falls under the category of special-level hot work operations and is highly hazardous. Therefore, throughout the process, the construction risks must be strictly controlled to ensure safety. The core working principle can be summarized as "bypass diversion and local blocking": First, special blocking three-way valves are welded on the operating pipeline. Using a pressure-bearing opening equipment, precise holes are drilled on the pipeline; then, the specially made blocking heads are sent into the pipeline, unfolded at the predetermined position and closely adhering to the pipe wall to achieve complete blockage of the medium; if it is necessary to replace the pipeline section, a temporary bypass pipeline needs to be set up to allow the medium to bypass the operation area and continue to be transported downstream; after the operation is completed, the blocking heads are retrieved, and the opening is permanently closed through the plug-in blocking process to restore the original state of the pipeline. II. Main Types of High-Pressure Sealing Equipment According to the structural form and working principle of the sealing head, the high-pressure pipeline sealing equipment can be mainly divided into the following types: Self-sealing occluder This is the most common type of equipment used in the sealing of high-pressure pipelines. The sealing head of this device adopts a multi-layer line-sealed cup structure. Through axial compression, the cup expands radially and forms a tight fit with the inner wall of the pipeline. Compared with the traditional lip-edge sealing method, the multi-layer line-sealing can simultaneously adapt to high and low pressure conditions, solving the problem of leakage that a single sealing structure is prone to under pressure fluctuations. The plug-type sealing device is usually equipped with a debris sweeping device, which can push the iron filings generated by the opening hole away from the sealing surface, avoiding scratching the cup. 2. Disc-type plugger The disc-type plugter adopts a disc-shaped sealing structure. It uses hydraulic drive to make the sealing disc tightly adhere to the pipe wall. This sealing method is suitable for large-diameter and high-pressure pipelines. It is reliable in sealing, but the equipment has a large volume and requires certain operating space. The pipelines under the jurisdiction of Sinopec Pipeline Storage and Transportation Company mainly adopt the high-pressure disc-type plugging construction technology. 3. Capsule-type occluder The capsule-type plug is sealed by the inflated capsule. The working pressure is generally no more than 0.5 MPa and it belongs to a low-pressure sealing device. Its advantages are good flexibility and strong adaptability to pipeline deformation. It is often used as an auxiliary sealing device or for low-pressure pipeline operations. In the combined high-low pressure sealing process, the capsule-type plug is commonly used for sealing the crude oil in the reserved pipeline segment. III. Core Process Flow of High-Pressure Pipeline Sealing A complete operation for sealing a high-pressure pipeline usually involves the following key procedures: Step 1: Preparations and pipe fitting welding First, a welding process guideline is compiled based on the pipe material and pressure parameters, and a welding process assessment is conducted. The excavation of the operation pit must ensure sufficient operation space and a safe slope to prevent landslides. Subsequently, the sealing three-way joints and balance short sections are welded at the predetermined positions. Before welding, the ellipticity (not exceeding 1%) and wall thickness of the pipeline must be measured, and areas with deformation and severe corrosion should be avoided as much as possible. After welding, weld pass inspection must be carried out, and only when it is qualified can the next process be entered. Step 2: Installation of the clamp valve and hole drilling operation Install the clamp valve onto the sealing three-way, assemble and debug the hole-making machine. Before making the holes, it is necessary to conduct an overall tightness pressure test on the hole-making machine and the valve, with the test pressure being equal to the operating pressure of the pipeline. The high-pressure hole-making machine is equipped with two sets of high-pressure balancing devices. Even if one set fails, it can be promptly switched to ensure the high reliability of the hole-making process. The cutting tool is crucial. For high-strength pipeline steels such as X80, high-strength hard alloy materials are used. The tool angle is specially designed, and a toothed structure is adopted to ensure the smoothness of the hole opening. The toothed parts are welded using the welding process used in military armored infantry combat vehicles, which can ensure that there will be no tooth loss problems due to welding quality. After the hole opening is completed, the hole opening tool is recovered, the valve is closed, the medium inside the hole opening machine is discharged through the vent valve, and then the hole opening machine is dismantled. Step 3: Sealing operation Assemble and debug the plug device, calculate the plug size, install the plug device onto the plug clamp valve. For high-pressure plugging, connect a balance pipe to balance the pressure, check for no leakage at all connection points, and then lower the plug head. After the plug is in place, empty the medium in the pipe section to be worked on through the vent line, and perform nitrogen replacement. During plugging, follow the principle of "first high pressure then low pressure, first inner side then outer side". Step 4: Bypass diversion (if continuous operation is required) If it is necessary to replace the pipe section, a bypass line needs to be connected to the blocked three-way valve to conduct the transported medium, enabling the main line bypass line to transport the medium simultaneously. In this way, the medium in the modified pipe section stops flowing, and all the medium goes through the bypass line, ensuring that the downstream users are not affected. Step 5: Cut the pipe, replace it and align the joints After the blocking is completed, the pipe is cut using mechanical methods to avoid the safety risks brought by flame cutting. Before cutting the pipe, the wheel spacing of the cutting machine needs to be checked to ensure that the chain is in a straight line and tightly bound, to prevent shaking during movement.