1, PE pipe with pressure hole and plugging
With the extensive application of PE pipe in urban gas pipe network, the repair and repair of PE gas pipe has become an important work in the daily operation and management of gas transmission and distribution companies. There are three general cases:
(1) for small holes and cracks in local pipelines, electric fusion saddle pipe fitting can be used to block the damaged part and fuse the saddle pipe fitting with the pipe wall through electric fusion welding machine, so as to repair the pipeline.
(2) when the pipeline below D200 is damaged, the softness of the pipeline can be used to crush the pipeline at both ends of the damaged place with a special gas pipe press (for the pipeline from D63 to D200, the gas source cannot be completely cut off with the compressor), then cut off the gas source, and then repair the damaged place.
(3) for large diameter pipe damage, drill holes at both ends of the damage (special PE pipe drilling tools), and then plug the isolation ball plug (cup or capsule type) into the hole to seal the pipe. Finally, the damaged part in the middle is cut and replaced. For the emergency repair that does not allow gas stopping, two more holes can be drilled on the outside of the isolation ball (leather bowl) and connected to the bypass pipe for temporary air supply.
1.1 with pressure hole opening and plugging equipment
The principle of PE pipe with pressure opening and sealing is the same as that of metal pipe opening and sealing. The equipment includes a pressure opening machine, a frame and a lower plugging device, which is suitable for pipe diameter D160 ~ D300mm, temperature -10 ~ +40℃ and medium pressure ≤ 0.4mpa.
1.2 weld connection between saddle pipe fitting and pipe to be opened
One of the key problems in PE pipe with pressure opening and sealing is: how to ensure the welding quality between the saddle pipe fitting and the pipe to be opened. Construction units in PE gas pipeline maintenance, often encounter the pipeline to be opened and pipe fitting is not matched. Because the welding parameters (such as voltage and heating time) of the electromelt connection machine or the electromelt pipe fittings produced by different manufacturers may be different, therefore, when the electromelt connection, the voltage and heating time of the electrified heating shall be carried out according to the parameters provided by the manufacturer of the electromelt connection machine or the electromelt pipe fittings. Before welding, the construction unit should evaluate the welding process of the pipe (piece) to determine whether it can be welded. In fact, in view of the PE with pressure hole sealing this kind of "special" construction, the construction unit of different manufacturers of PE pipe, pipe welding process evaluation is unrealistic. To sum up, the existence of the above problems hinders the popularization and application of the sealing technology of PE pipe with pressure opening.
2. Electric fusion connection of PE pipes and pipe fittings
2.1 special circumstances requiring electrofusion connection
"Regulations of technology of PE gas pipeline engineering" (CJJ63-2008) regulation, different levels and quality of melt flow rate (MFR) difference (190 ℃, 5 kg) condition is not less than 0.5 g/min raw materials of polyethylene pipes, pipe fittings and pipe accessories, and welding end standard size ratio (SDR) of polyethylene gas pipe connection, the fused connection must be used. PE pipes with nominal diameter less than 90mm should be connected by electric welding (because the pipe with a smaller diameter has a smaller welding section size when hot fusion butt welding is used, and the welding strength cannot be guaranteed, so only electric welding socket welding can be used).
2.2 factors affecting the quality of electrofusion connection
Gas fused the PE pipe fittings fused connected to the air tightness resistance study of injection PE100 fused fittings for the welding test, come to a conclusion: the longer duration of electricity, gas PE fused fitting air tightness resistance rising, when pass gas fused pipe fittings, PE pipe tightness after reaching the highest resistance of fused connections, as the current time continue to extend, gas fused pipe fittings, PE pipe fused connection instead of air tightness resistance began to reduce. This is mainly because: when the electrification time is too short, the pipe, pipe fitting is not fully fused, there are gaps between the pipe, pipe fitting; If the electrification time is too long, the melting between pipe and pipe fittings is too much, and the cavity is generated after cooling. Only when the electrification time is moderate, there will be no gaps and holes between pipes and pipe fittings, and the air tightness of PE gas pipe fittings and pipe electrofusion connection reaches the highest. With the increase of the resistance of copper resistance wire, the air tightness of PE gas pipe fittings keeps increasing. When the resistance of copper resistance wire increases to the maximum value, the air tightness of PE gas pipe fittings and pipe electrofusion connection tends to be stable. This is mainly because: when the copper resistance wire resistance is too low, the resistance wire heat is not enough, the pipe, pipe plastic resin can not fully melt, so that there are gaps between the pipe, pipe. The closer the MFR of pipe and pipe fitting is, the better its compatibility is, and the better the air tightness after the pipe fitting is connected by electrofusion. The size of the fit between pipes and fittings increases, and the air tightness decreases after the electrofusion connection. Only when the fit size of pipes and fittings is between 0.05 and 0.20mm, the gap and hole will not appear after the electrofusion, and the air tightness is good after the electrofusion connection.
2.3 quality inspection of electrofused saddle type connection
For the hot melt joint, it is mainly to check the symmetry and alignment of the joint flanging, and to carry out the flanging cutting test. Generally, material problems such as mismatched melt mass flow rate and dampness, and operational problems such as improper setting of pressure, temperature and time parameters can be found. For the fusion joint, the fusion condition of the joint is covered in the fused pipe fitting. In the case that the molten material does not overflow in large quantities, the quality inspection can only be judged from the observation hole on the fused pipe fitting, and the quality problem caused by the inconsistency of the material itself and the axis is often not found.
PE duct tape pressure tapping and plugging technology has certain actual application value and development prospects, with the percentage of PE pipe in city gas pipeline network increasing, PE material quality criteria, and further improve and implement the engineering construction standard, PE material market, further standardize the technology bring with metal pipeline pressure opening sealing technology widespread application, play its role in the gas pipe network maintenance repair.