Horizontal pipe opening: A core technology that has been underestimated In pipeline maintenance, repair and renovation projects, horizontal hole drilling is a seemingly routine but highly technical operation. Unlike vertical hole drilling, when the angle between the hole axis and the horizontal plane is less than 30°, the construction difficulty increases exponentially. The influence of gravity on the main shaft, the control of cutting accuracy, and the guarantee of sealing reliability - each aspect is testing the engineering technology and equipment level. This article will systematically analyze the technical connotation of pipeline horizontal hole drilling from four dimensions: technical principles, operation procedures, application scenarios, and innovative breakthroughs. 1. Technical Challenges of Horizontal Hole Drilling: Why Can't We Simply "Drill a Hole"? Horizontal pipe opening refers to the operation of mechanically cutting an opening on the horizontal or nearly horizontal pipe section while the pipeline is in operation. Compared with conventional vertical opening, horizontal opening faces three major technical challenges. The control of gravitational influence is the primary challenge. In a horizontal state, the main shaft of the hole-making machine experiences deflection due to its own weight, resulting in uneven force distribution for the center drill and the tube cutter during the cutting process. Without taking technical measures, the consequences could range from slight deviation of the hole-making position to complete blockage of the tool or tearing of the pipe wall. Taking the replacement project of a pressure guiding pipe for the second West-to-East Gas Transmission Line as an example, the operation site is located at Valve Room 3 in Horgos, Xinjiang, with the pipeline design pressure reaching 12 MPa and the operating pressure being 7.2 MPa. During the hole-making and sealing process, the technicians must take special measures to reduce the gravitational influence on the main shaft in the horizontal state to ensure the accuracy of hole-making and the tightness of sealing. The difficulty in chip removal during cutting cannot be ignored either. When making horizontal holes, the chips cannot be naturally discharged like they do in vertical hole drilling. The iron chips accumulate in the cutting area, which not only affects the cutting quality but also may cause the tool to overheat or get stuck. This problem is particularly prominent for small-diameter pipes - when the four-way valves are placed horizontally, if the cavity cannot accommodate too many iron chips, it will cause the sealing block at the bottom to tilt during the sealing process, affecting the sealing effect and even potentially damaging the machine. The complexity of sealing and testing further raises the technical threshold. Horizontal openings require the installation of a closed cavity composed of three-way valves, valves, and opening connectors on the pipe wall, followed by a tightness pressure test. The air or water inside the cavity must be completely expelled; otherwise, safety accidents may occur during the opening process. In underwater horizontal opening operations, to ensure that all the water inside the cavity is completely expelled, the nitrogen pressure needs to be 0.2 MPa to 0.3 MPa higher than the water pressure at the operation point, and the stabilization time should be no less than 1 hour to verify the sealing performance of all connection parts. II. Standard Operating Procedure for Horizontal Hole Drilling: Ten Steps from Preparation to Completion Horizontal pipe opening is a systematic project, and its operation process involves multiple key steps, each of which requires precise control. Selection and Preparation of Homework Points The drilling operation points should be selected on the straight pipe section, and efforts should be made to avoid pipeline welds. The center drill must never fall on the weld. When measuring the wall thickness of the pipeline, efforts should be made to avoid severely corroded areas. After determining the drilling points, the anti-corrosion layer needs to be cleaned. If necessary, the welds at the cutting part of the drilling tool should be appropriately ground. For buried pipelines, manual excavation of operation pits is required to protect the underground ancillary facilities of the valve room. 2. Pipe joint welding and inspection Welding and sealing the three-way fittings and the balance short sections are the key preparations before opening the holes. Before welding, it is necessary to measure that the ellipticity of the pipeline at the sealing point does not exceed 1%. The wall thickness of the pipeline should be measured to avoid deformed and severely corroded areas. After welding, non-destructive testing of the weld seams must be conducted. Only when it is qualified can the next process be carried out. 3. Equipment Installation and Tightness Test Install the clamp valve onto the sealing tee, and the ball valve onto the balance short section. Assemble and debug the hole-making machine, calculate the hole-making size, and install it onto the valve. Conduct a comprehensive tightness pressure test on the hole-making machine and the valve, with the test pressure not lower than the operating pressure of the pipeline. In the underwater operation scenario, the equipment needs to be lifted and installed underwater as a whole, assisted by divers, and the cavity needs to be drained and pressure verified. 4. Hole-making operations and process monitoring Start the hydraulic station and related equipment, and control the hole-making machine through the control system. Lower the lower cylinder cutter until the distance between the center drill tip and the top of the pipe is approximately 25.4 mm (1 inch). Start the hole-making process and monitor the pressure during the drilling in real time. The drilling speed should not be too fast. Confirm that the center drill has penetrated the pipe wall, then continue to extend the shaft until the tip of the cylinder cutter is about 25.4 mm away from the pipe wall. Perform the cutting and hole-making operation. The hole-making operation takes a long time, and it needs to be confirmed by professionals whether the hole is completely opened. 5. Equipment Disassembly and Subsequent Processes After the hole is drilled, the hole drilling tool is retrieved, the valve is closed, and the natural gas in the hole drilling machine is discharged through the vent valve on the hole joining device. Then, the hole drilling machine is removed. Subsequent procedures such as plugging, pipe replacement, and inserting the plug handle need to be carried out until all the operations are completed. III. Technical Subdivisions and Application Scenarios of Horizontal Hole Opening The horizontal opening technology is not a single mode; instead, it has developed multiple technical branches based on different working conditions. High-pressure level sealing and opening of the hole In high-pressure scenarios such as the main gas pipeline, the horizontal openings need to withstand a pipe internal pressure of over 10 MPa. In the replacement project of the pressure guiding pipe for the West-to-East Gas Transmission Line II, the designed pressure at the opening operation point reached 12 MPa, while the operating pressure was 7.2 MPa.