HDPE pipe is a high-density polyethylene pipe. Due to its excellent corrosion resistance, wear resistance, insulation, and portability, it is widely used in various pipeline projects.
HDPE pipe electrofusion welding is one of the commonly used connection methods in HDPE pipeline systems. It is to put the HDPE Electrofusion Fittings with pre-buried resistance wire on the pipe or pipeline components, and then pass the current. The resistance wire heats up to melt the connection parts on the pipe and the pipe fittings. Under the action of the resin expansion pressure, the resin molecules on both sides of the connection interface are re-entangled, and the connection purpose is achieved after cooling.
Electrofusion connection is a process in which electrofusion pipe fittings connect pipes with the support of electrofusion welding machines.
HDPE pipe electrofusion welding procedure
1. Cut the pipe and mark the depth of the pipe insertion into the fitting;
2. Scrape the pipe end;
The scraper should be used to remove the old layer on the surface of the pipe end (the scraping thickness is generally 0.2mm), and the scraped surface should not be contaminated again.
3. Wipe the pipe fitting
The welding area of the pipe fitting should be wiped with clean cotton fabric or special wipe paper.
4. Clamp the pipe fitting
Special clamps should be used to fix the components to be connected as much as possible. The out-of-roundness of the pipe should not exceed 1.5% of the outer diameter of the pipe, otherwise it should be corrected on the corresponding clamp.
There should be a suitable gap between the pipe and the fitting. It is generally appropriate to insert it with a slight force (large-diameter pipe fittings need to be knocked in with a wooden hammer). Too large or too small a gap will affect the quality of the interface.
5. Welding
Connect the wires according to the operating requirements of the electric fusion welder, and input the necessary parameters to the welder. Start the welder, and the welding will be completed automatically.
6. Cooling
The welding machine plug can be removed and the clamp can be disassembled only after the welding area has reached the cooling time.
Factors affecting the quality of electric fusion connection
1. The influence of power supply fluctuation on interface quality
For a given electric fusion pipe fitting, the resistance value of the embedded resistance wire inside is certain. At this time, the power consumed by the resistance heating is only related to the voltage (current) provided by the welding machine.
The voltage (current) value provided by the welding machine must have an upper limit. Beyond this upper limit, the excessive heat load on the surface of the heating wire will cause the resin around it to overheat and decompose. Of course, the voltage value must also have a lower limit. Below this lower limit, the heating wire will not be able to generate enough heat, and the resin at the welding interface will not be able to be fully entangled.
In this sense, an electric fusion welding machine is equivalent to a voltage (current) source. It must be able to keep the voltage (current) provided to the electric fusion pipe fitting within the allowable fluctuation range when the power supply voltage fluctuates greatly. This indicator is one of the most important indicators of the welding machine. Because the voltage fluctuation of the power supply is often large at the actual construction site. Of course, there will be some differences in the resistance value of the internal heating wire between the same pipe fittings. Even if the power supply voltage (current) is the same, it will cause a certain power fluctuation.
2. The influence of welding time on interface quality
When the heat transfer conditions are the same, the energy consumed by each specification of pipe fittings during welding should be the same. If the heating energy is constant, the amount of energy consumed is only related to time. Practice shows that the welding time must be controlled within a reasonable range.
When the heating time is less than the shortest welding time, that is, the energy consumed is at a lower limit, the molecules at the interface cannot be fully entangled, and the mechanical strength and air tightness cannot achieve the purpose of reliable connection.
When the heating time exceeds the maximum time, that is: too much energy is consumed, which may cause a large amount of molten resin to overflow the observation hole, and too much heat accumulation will also cause the resin to decompose and produce smoke. Make the interface quality deteriorate.
3. Effect of ambient temperature on welding quality
If the ambient temperature of the welding process is different, it means that the heat conduction conditions of the pipe fittings during the welding heating process have changed, which will cause the change of the total energy required for welding, which is also reflected in the change of welding time. The actual test shows that when the ambient temperature changes in the range of -5 to +40℃, the correction value of the welding time is about 0.5 to 1%℃ (the welding time parameters given by the electric fusion pipe fittings are generally given at an ambient temperature of 20℃).
4. The influence of poor operation on welding quality
The so-called poor operation generally refers to two aspects. One is that the clamping and positioning of pipes and pipe fittings during welding and the scraping and wiping of pipe fittings do not meet the specification requirements;
The other is that errors occurred when the welding parameters were input to the welding machine, which will have an adverse effect on the interface quality or cause welding failure.
It is particularly important to point out that scraping the pipe port is very important and necessary. Especially for pipes with a long storage period, scraping is more important, otherwise it will greatly increase the rate of bad interfaces and even cause 100% welding failure.
