Hot melt welding process of the hottest PE pipe

PE pipe hot melt welding process

with the start of national west to East Gas Transmission and other key projects, polyethylene PE (polyethylene) pipeline is increasingly widely used. At present, this product has been widely used in gas, natural gas, water supply and other fields

pe pipeline has the characteristics of easy construction, fast speed, corrosion resistance, no pollution, long service life, etc. There are two main methods for PE pipe connection: hot melt connection and electrofusion connection. At present, the main pipeline is mainly connected by hot melt. The principle of hot melt connection is to stick the mating surface of two PE pipes close to the heating tool and heat its flat end face until it melts. After removing the heating tool, close the two molten end faces together and keep them under pressure until the joint cools down to make it a whole

I. welding preparation. The preparations for hot melt welding construction are as follows:

① install the slip consistent with the pipe specification into the rack

② prepare enough supports to ensure that the pipes to be welded can be at the same height as the center line of the rack and can be moved easily

③ set the heating plate temperature 200 ~ 230 ℃ (this data is based on the welding machine supplied by Hangzhou Donglei machinery factory, and the specific temperature is subject to the data provided by the manufacturer) carbon: carbon black, graphite, carbon hollow ball, carbon fiber

④ turn on the power supply of the welding machine, turn on the switches of the heating plate, milling cutter and oil pump and test run

II. Welding. The welding process flow is as follows: check the pipe and clean the pipe end → tighten the pipe → mill the pipe end with a milling cutter → check the dislocation and gap of the pipe end → heat the pipe and observe the minimum crimping height → weld and cool the pipe to the specified time → take out the pipe. During the welding process, the operator should operate with reference to the parameters of the welding process card, and if necessary, it should be properly adjusted according to the changes of weather, ambient temperature and so on:

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

② use soft paper or cloth dipped in alcohol to remove oil or foreign matters at the ends of the two tubes

③ place the pipe to be welded. 4. Install it electrically in the frame slip, so that the protruding length of both ends is equal (as short as possible without affecting milling and heating, preferably 20~30mm). The part outside the pipe frame is supported by a support, so that the pipe axis is at the same height as the center line of the frame, and then fasten it with the slip

④ insert the milling cutter, first turn on the power switch of the milling cutter, then close both ends of the pipe, and apply appropriate pressure until there are continuous chips at both ends (the chip thickness is 0.5 ~ 10mm, and the chip thickness can be adjusted by adjusting the height of the milling insert), remove the pressure, wait a moment, and then withdraw the movable frame and turn off the power supply of the milling cutter

⑤ take out the milling cutter, close the two pipe ends, and check the alignment of the two ends (the dislocation of the two ends of the pipe can not exceed 10% of the wall thickness, which can be improved by adjusting the straightness of the pipe and the elastic slip; the gap between the two ends of the pipe can not exceed 0.3mm (below de225mm), 0.5mm (de225mm~400mm), 1mm (above de400mm). If it does not meet the requirements, it should be milled here until it meets 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 minimum crimping on both sides reaches 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 for heat absorption). After the time is reached, loosen the movable frame, take out the heating plate quickly, and then close the two pipe ends. The switching time is as short as possible. After cooling to the specified time, relieve the pressure and loosen the slip, Take out the connected pipe

III. welding process parameters are directly related to welding: temperature, time and pressure. The welding process curve is expressed as the relationship between pressure and time in 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

IV. welding inspection practice has proved that the most easily damaged and leaking part of polyethylene gas pipeline is the pipeline interface. The key to the success or failure of the project is the quality of pipeline connection. Therefore, strict interface quality acceptance is very important for underground gas pipeline engineering. The polyethylene pipe interface needs to be equipped with a damage test fixture: 3T rotating wedge tensile test can be used to check the internal quality

(1) after the connection of polyethylene pipes, the construction self inspection and third-party acceptance should be strengthened, and a certain proportion of interfaces should be selected for internal inspection

(2) check the welding data records of all welding interfaces

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

(4) interface destructive test shall be carried out for each project. For the interface of hot-melt connection, 3% welded junctions shall be selected, and it is recommended that not less than 1. Destructive test can cut the welded junction into 4 strips and check the internal fusion. Incomplete fusion is regarded as unqualified, and tensile test can also be done to see whether 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. (end)