PE pipe material is a polyolefin polymer compound, its molecules are composed of carbon and hydrogen elements, no harmful elements, health and reliability. In the process of processing, use and disposal, it will not adversely affect the human body and the environment, and it is a green building material. PE pipe not only has good toughness and flexibility, but also has excellent welding performance. The welding effect in the pipeline connection process is reliable and the cost is low; at the same time, it has good air tightness, corrosion resistance and good resistance to rapid crack transmission, so it is widely used in Municipal, petroleum, chemical, gas and other construction fields. The application of PE pipe is the promotion project of scientific and technological achievements of the Ministry of Construction in 2004. In recent years, the company has carried out research on PE pipe hot melt welding technology, and the research results have been successfully used in gas projects in the Pearl River Delta region, and achieved good economic and social benefits.

1. welding preparation. The preparation for hot melt welding construction is as follows:

① Install the slips consistent with the pipe specifications into the rack;

② Prepare enough supports to ensure that the pipe to be welded can be at the same height as the center line of the frame and can be easily moved;

③ Set the temperature of the heating plate to 200~230 ℃ (this data is based on Hangzhou Huanzhong welding machine as a reference, and the specific temperature is subject to the data provided by the manufacturer);

④ Turn on the power of the welding machine, turn on the heating plate, milling cutter and oil pump switch and test run.

2. welding. The welding process flow is as follows: check the pipe and clean the pipe end → fasten the pipe → mill the pipe end with a milling cutter → check the misalignment and gap of the pipe end → heat the pipe and observe the small hemming height → weld the pipe and cool it to the specified time → take out the pipe. In the welding process, the operator should refer to the parameters of the welding process card for operation, and if necessary, should be adjusted according to the weather, ambient temperature and other changes:

① Check whether the specification and pressure grade of the pipe to be welded are correct, and check whether there are bumps, bumps and scratches on the surface. If the depth of the scar exceeds 10% of the pipe wall thickness, it should be partially removed before use;

② Use soft paper or cloth dipped in alcohol to remove oil or foreign matter at the two pipe ends;

③ Place the pipe to be welded in the rack slip, so that the length of the two ends is equivalent (as short as possible without affecting milling and heating, it should be kept 20~30mm), and the part outside the pipe rack is supported by support, so that the pipe axis is at the same height as the center line of the rack, and then fasten it with the slip;

4 into the milling cutter, first turn on the power switch of the milling cutter, and then close the two ends of the pipe, and appropriate pressure, until the two ends have a continuous chip (chip thickness is 0.5~10mm, by adjusting the height of the milling blade can adjust the chip thickness), remove the pressure, wait a moment, and then back off the movable frame, turn off the milling cutter power;

⑤ Take out the milling cutter, close the two pipe ends, and check the alignment of the two ends (the misalignment of the two ends of the pipe shall not exceed 10% of the wall thickness, which shall be improved by adjusting the straightness and elastic slips of the pipe; The gap between the two ends of the pipe cannot exceed 0.3mm (below de225mm mm), 0.5mm(de225mm mm ~ 400mm) and 1mm (above de400mm mm). If the requirements are not met, milling shall be performed here until the requirements.

⑥ After the temperature of the heating plate reaches the set value, put it into the rack and apply the specified pressure until the smaller curls on both sides reach the specified height, and the pressure decreases to the specified value (the two sides of the pipe end just keep in contact with the heating plate to absorb heat). After the time is reached, loosen the movable rack, quickly take out the heating plate, and then close the two pipe ends. The switching time is shortened as much as possible, take out the connected pipe.

3. welding parameters and welding parameters directly related to: temperature, time, pressure. The welding process graph is shown as a graph of pressure versus time during the welding process.

Welding process curve

Pa1 heating pressure pa2 endothermic pressure pf1 welding pressure pf2 cooling pressure ta1 heating time Tu switching time (including heating plate withdrawal time) tf1 pressurization time tf2 cooling time

4. welding inspection practice has proved that polyethylene gas pipeline is easy to damage and leak parts, is the pipe interface. The key to the success and failure of the project is the quality of the pipeline connection. Therefore, strict interface quality acceptance is very important for underground gas pipeline engineering. Polyethylene pipe joints need to do destructive testing to check the internal quality.

(1) After the polyethylene pipeline is connected, the construction self-inspection and third-party acceptance should be strengthened, and a certain proportion of the interface should be appropriately extracted for internal inspection.

(2) Check the welding data records of all welding joints

(3) The appearance quality inspection shall be conducted at 100%. Supervision and other acceptance units shall select a certain proportion of welded joints for appearance inspection according to the construction quality, and the number shall not be less than 10% of the number of welded joints, and the number of welded joints for each welder shall not be less than 5.

(4) Each project shall be subjected to interface destructive test. For the interface of hot-melt connection, 3% of welding joints shall be extracted, and no less than 1 is recommended. Destructive test can cut the weld into 4 pieces to check the internal fusion. Incomplete fusion is regarded as unqualified, and tensile test can also be done to see if the tensile strength meets the design and specification requirements. For unqualified interfaces, double sampling inspection shall be carried out for the welder's interfaces. If unqualified interfaces are found again, all interfaces constructed by the welder shall be reworked.