Key points for installation and maintenance of PE pipe gas transportation

I. Installation Key Points

Pipe and Fitting Selection: You must use gas-specific PE pipe that complies with "Buried Polyethylene (PE) Piping Systems for Gas, Part 1: Pipes" (GB 15558.1-2015). Substituting ordinary PE water pipe is strictly prohibited. Gas-specific pipe is specially optimized for resistance to methane permeation and corrosion from sulfides in the gas. Ordinary water pipe cannot meet safety requirements. Fittings must match the specifications and material of the pipe. For example, electric fusion fittings and hot-melt butt fittings must be marked "For Gas Use." The grade of the fittings must be no lower than that of the pipe (e.g., SDR11 pipe corresponds to SDR11 fittings). This prevents joint failure due to incompatible fittings.

Pre-construction preparations: Before construction, pipes and fittings must be visually inspected for scratches (deepness exceeding 10% of the pipe wall thickness requires rejection), dents, bubbles, and other defects. Product certificates and factory inspection reports must be verified, and the production date confirmed. (PE pipes stored for more than one year require retesting for physical properties.) Furthermore, a site survey must be conducted based on the design drawings to identify the location of existing underground pipelines (such as water pipes and cables), and avoidance routes must be marked to avoid damage to other infrastructure during construction. Appropriate construction equipment must also be prepared. For example, hot-melt butt welders and electric fusion welders must be calibrated in advance for temperature (typically 190 ± 10°C) and pressure to ensure they are in proper working order.

Pipeline Laying Specifications: For underground installation, trenches must be excavated according to design requirements. The trench bottom must be leveled. If the soil contains gravel or hard objects, a 10-15cm thick layer of fine sand or soil must be laid to prevent damage to the pipes from sharp objects. The trench depth must meet specifications and should be no less than 0.8m below roadways, no less than 0.6m below sidewalks, and no less than 0.7m when crossing farmland to prevent deformation from ground loads. During installation, the pipe bending radius must meet requirements (for cold bending, the bending radius for pipes with a nominal diameter of dn ≤ 50mm must be no less than 5 pipe diameters, and for pipes with a nominal diameter of dn > 50mm, no less than 10 pipe diameters). Forced bending or pulling of the pipe is strictly prohibited to prevent cracks in the pipe wall.

Interface Connection Operation: The interface connection is the core of the installation process, and the method should be selected based on the pipe diameter. Hot-melt butt welding is preferred for nominal diameters dn ≥ 90mm. First, clean the pipe ends of the pipes of any oil or impurities. Heat the ends with a hot-melt welder until they are molten (heating time depends on the pipe diameter; for example, for a dn 110mm pipe, the heating time is approximately 20 seconds). Then, quickly butt the pipes together and apply the specified pressure (calculated based on the pipe specifications, typically 0.1-0.3MPa). Cool the pipes to room temperature while maintaining pressure to ensure a tight fusion and strength no less than that of the pipe itself. For nominal diameters dn < 90mm, an electric-melt socket connection is used. Insert the pipe into the electric-melt fitting to the marked position, ensuring the correct insertion depth. Then, connect the electric-melt welder and weld according to the parameters (voltage and time) marked on the fitting. After welding, allow the pipes to cool to room temperature before moving them to prevent loosening. After connection, the joints must be visually inspected. Butt-fusion joints should have no visible gaps and uniform flanges. Electric-fusion joints should have no excessive material overflow or incomplete fusion. A pressure test should be performed if necessary (the test pressure should be 1.5 times the working pressure, and a 1-hour pressure hold with no pressure drop is acceptable).

Backfill and Marking: After the pipeline is laid and the joints have cooled, backfill must be carried out promptly. The backfill must be compacted layer by layer. The first layer (the layer directly in contact with the pipe) should be fine sand or plain soil, with a thickness of at least 10 cm. The use of hard objects such as stones and bricks is strictly prohibited to prevent damage to the pipe under pressure. The compaction level of each layer must meet the required standards: at least 85% for the 0.5 m above the pipe top and at least 90% for the 0.5 m above. In addition, gas warning tape should be installed above the pipe trench (10-30cm from the top of the pipe). The tape should be printed with the words "Gas Pipeline Excavation Prohibited." Ground markers should be placed at key locations, such as pipe bends, tees, and valves, indicating the pipeline's direction, buried depth, and affiliated unit to facilitate identification during future maintenance.

II. Maintenance Key Points

Daily Inspection and Monitoring: Establish a regular inspection system. Municipal pipe networks should be inspected at least weekly, and residential courtyard pipes should be inspected at least once every two weeks. Focus on checking the integrity of ground markers and any third-party construction (such as road excavation or landscaping). If any construction is detected, immediate on-site monitoring should be conducted, and the construction party should be informed of the location of the underground gas pipeline to prevent excavation damage. Furthermore, a gas leak detector should be used to test for leaks at pipe joints, valves, and pressure regulating boxes. This is especially important after rain or in cold weather, as soil settlement may loosen joints, necessitating more frequent inspections. For buried pipelines, pressure monitoring can be used to regularly record pipeline pressure changes. Any abnormal pressure drop should be promptly identified as a leak.

Pipeline Corrosion and Aging Prevention: Although PE pipes are highly resistant to soil corrosion, long-term exposure to sunlight (such as for outdoor exposed pipes) can accelerate aging. Sun protection measures should be implemented for exposed PE pipes, such as wrapping them with sun-proof sleeves or applying sun-proof paint, to prevent UV exposure from embrittlement. Furthermore, regular inspections of the surrounding environment are necessary. If the pipelines are located near chemical plants, sewage wells, or other locations where corrosive media may be generated, soil corrosivity should be monitored. If the soil is highly corrosive, anti-corrosion measures (such as applying anti-corrosion film around the pipe trench) should be implemented to prevent corrosion from affecting the pipe's service life.

Joint and Valve Maintenance: Regularly inspect joint seals. For exposed joints (such as those inside the surge tank), clean any impurities around them quarterly and observe for signs of gas leaks (such as an odor or a leak detector alarm). For buried joints, any abnormalities such as bubbles or withered weeds in the ground should be promptly excavated and inspected to prevent leaks from causing safety incidents that could be caused by untreated leaks. Meanwhile, pipeline valves require regular maintenance. Open and close valves monthly to prevent the valve core from sticking. Operate slowly during opening and closing to avoid sudden pressure surges and drops that could damage the pipeline. Check the valve stuffing boxes every six months. If leaks are detected, replace the packing to ensure proper sealing.

Emergency Measures: Develop a gas leak emergency plan. Once a leak is detected, immediately activate the emergency plan. First, close the valves upstream and downstream of the leak to cut off the gas source. Establish a warning area, prohibiting unauthorized personnel from entering and prohibiting open flames (e.g., smoking and mobile phone use) to prevent explosions. Next, use a leak detector to locate the leak. If the leak is at a joint, reweld or replace the pipe fittings. If the pipe is damaged, cut the damaged section, replace it with a new pipe, and reconnect. After repairs, perform a pressure test. Gas supply can only be restored if it passes the test.

Long-term performance evaluation: PE pipe gas transmission systems are typically designed for a 50-year service life. Regular long-term performance evaluations are required. Pipe samples should be taken every 10 years to test indicators such as tensile strength, elongation at break, and impact resistance. If significant performance degradation is observed (e.g., a decrease in tensile strength exceeding 20%), a replacement plan should be promptly developed to avoid safety hazards caused by pipe aging. Furthermore, a pipeline archive should be established, documenting information such as pipe installation time, location, specifications, and maintenance records to provide data support for long-term maintenance.