Electrofusion Welding Technology and Process
Electrofusion welding, a crucial connection technology in polyethylene piping systems, is widely used in various fields. Its working principle primarily relies on a heating wire pre-placed within the electrofusion fitting. By applying electricity, the inner surface of the fitting and the outer surface of the pipe are melted. After a certain cooling time, the welding is achieved.
In the electrofusion welding process, well-designed electrofusion fittings are particularly critical. Their basic working principle utilizes the Joule effect; through the heating of a resistance coil, the material on the inner surface of the fitting melts, thereby achieving the fusion of the pipe and fitting.
Electrofusion fittings, such as sleeves, equal diameter tees, reducing tees, and elbows, are indispensable components in polyethylene piping systems. They can connect main and branch pipes or spigot fittings made of different types of polyethylene materials and materials with different melt flow rates. Currently, most electrofusion fittings are equipped with digital identification systems, where welding parameters and other important information are stored in the form of codes on data carriers such as barcodes or magnetic cards. The welding controller can automatically read these parameters and precisely control the welding process.
Next, we will explore the unique features of electrofusion welding.
Electrofusion welding not only requires a specialized electrofusion welding machine but also has wide applicability, capable of connecting pipes of various sizes and specifications, and suitable for pipes and fittings of different grades and materials. Its welding process is less affected by environmental and human factors, has a fast construction speed, and low equipment investment and maintenance costs. Furthermore, electrofusion welding is simple and easy to operate, produces reliable weld quality, has a smooth inner wall, and does not affect flow rate.
After understanding the characteristics of electrofusion welding, we will further discuss its operation process.
First, before welding, it is necessary to ensure that the power supply voltage is stable and meets the requirements, and clean the power output connector to ensure good conductivity. Next, prepare the necessary tools and materials, including a fully automatic electrofusion welding machine, electrofusion fittings, a cutter, a screwdriver, a marker, and a measuring tape. Cut the pipe to the required length, ensuring the end face is perpendicular to the axis, and controlling the end cutting error within 5mm. Next, measure the length of the electrofusion fitting and mark the corresponding position on the pipe end. Then, scrape the welding surface to remove oxide layers, oil, dirt, and other impurities. Finally, clean the pipe surface with anhydrous alcohol or methyl ethyl ketone (MEK) and make the final markings. After these preparations are completed, the electrofusion welding can begin.
Pipe and Fitting Insertion Redraw the lines on the pipe, determining the position to be half the length of the electrofusion fitting from the end face. Then, insert the cleaned electrofusion fitting into the pipe to be welded, ensuring the outer edge of the fitting is flush with the previously marked line. Next, tighten the locking screws on the fitting using a screwdriver to prevent the pipe from being accidentally pulled out during welding. Finally, install the electrofusion clamp to secure the assembly to be welded (see Figure 5-6 for the correct electrofusion welding clamp installation method), ensuring the fitting and pipe are completely coaxial, with misalignment controlled within 2%, while avoiding applying any external force to the electrofusion fitting.
Note: Before starting welding, ensure the fittings have been removed from their packaging and are clean and dry.
Output Connector Connection: Securely connect the welding machine output to the fitting terminals, ensuring a smooth connection. If the power source is far from the welding machine, a low-voltage alarm may occur. In this case, consider replacing the cable with a thicker one or using a generator.
Welding Operation: Strictly follow the welding machine operating procedures and avoid interference from surrounding magnetic fields. During welding, the welding machine should be set to "Automatic" mode, and welding data should be input using a scanner (pen), or parameters can be manually entered in "Manual" mode. After parameter input, turn on the welding switch to start the timer. If manual mode is selected, welding parameters should be determined according to the fitting's product manual.
It is recommended to use automatic mode for parameter scanning, as the welding machine will automatically perform time correction compensation. If manual mode is used, manual adjustments and compensation can be made according to the fitting information card.
Natural Cooling: After the welding timer ends, the electrofusion welding machine will enter a cooling state. During the cooling process, ensure natural cooling and do not apply any external force to the welded parts. After cooling, disassemble the fixture.
Post-Welding Inspection
After welding, check whether the material inside the hole is pushed up and whether any material is squeezed out at the weld. A qualified weld should not produce smoke, fire, or premature shutdown during the electrofusion process, and material should be ejected from the inspection hole of the electrofused component.
Next, we will introduce the operation process of electrofusion saddle welding.
Follow the product instructions for precise hole drilling.
Key Parameters of Electrofusion Welding
The core parameters of electrofusion socket welding and electrofusion saddle welding include voltage, heating time, cooling time, and resistance value. These key parameters are usually provided by the pipe component manufacturer.
Electrofusion Welding Construction Points and Precautions
Basic Requirements
Before welding, ensure that the surface to be welded is free of contamination or oxidation. If such conditions exist, appropriate surface treatment is required. The welding area must also be kept dry. Furthermore, attention must be paid to the fit clearance, out-of-roundness, insertion depth, and axial alignment and positioning between the pipe and fitting to ensure that the assembly is welded without axial pressure.
Using professional alignment fixtures can effectively reduce alignment errors and relative movement during the welding process. When the pipe is inserted into the fitting and kept coaxial, good and uniform contact can be achieved between the outer surface of the pipe and the inner surface of the fitting. If an angle is found between the pipe axis and the fitting axis during insertion, this will increase friction, affecting the contact quality between the outer surface of the pipe and the inner surface of the fitting, and ultimately potentially adversely affecting the weld quality. Furthermore, this angle may also cause significant stress at the weld site after welding.
Welding Equipment and Power Requirements:
Electrofusion welding equipment must comply with relevant national specifications and standards and require regular routine maintenance. According to CJJ63-2018 "Technical Standard for Polyethylene Gas Pipeline Engineering," electrofusion butt connection equipment should be calibrated and verified regularly, with a cycle not exceeding one year. If a generator is used as the power source, its power output and operating characteristics must be considered to ensure it can power an inductive load.
Energy Input Method Selection:
The energy input methods for welding machines can be divided into three categories: current control, voltage control, and energy control. Because most heating elements exhibit a positive temperature coefficient of resistance, the input energy gradually decreases with increasing temperature when using constant voltage welding. This helps prevent carbonization and overheating, and ensures the stability of the control process. Therefore, this input method is widely used.
Welding Voltage Control
In electrofusion welding, controlling the welding voltage is crucial. Both excessively high and low voltages can adversely affect weld quality. Therefore, the voltage setting must be carefully checked and confirmed to be within the appropriate range before welding. Simultaneously, voltage changes must be closely monitored during welding to ensure smooth welding and high-quality completion.
Welding Time
With the heating wire resistance and welding machine voltage kept constant, welding time becomes a key factor affecting heating power. Excessive welding time can lead to overheating and carbonization, while also softening and deforming the inner wall of the pipe, especially in saddle-shaped pipe fittings. Insufficient welding time may result in insufficient penetration or overheating of the heating wire accessories due to excessive welding power requirements.
Cooling Time
The cooling process aims to ensure the joint reaches sufficient strength. If the cooling time is too short, the weld joint may be subject to external disturbance due to incomplete cooling, thus reducing weld strength. During the cooling process, the welded components should be kept clamped to prevent external interference from affecting weld strength. Furthermore, forced cooling measures should not be taken during the cooling stage.
Pipe and Fitting Stiffness Electrofusion welding recommends using SDR11 or thicker polyethylene pipe. Although some manufacturers offer electrofusion fittings suitable for SDR33, for saddle-shaped fitting welding, it is generally limited to SDR11 or thicker polyethylene pipe. These limitations should be clearly indicated on the fitting packaging. Higher stiffness of the pipe and fittings helps to quickly build up melt pressure, thereby shortening welding time or increasing weld strength.
Material Weldability Electrofusion welding has broad compatibility and can join pipes of different SDRs and grades. However, to ensure weld quality, the two materials at the weld interface should have similar weldability.
Ambient Temperature Ambient temperature also has a certain impact on electrofusion welding. When welding in low-temperature environments, preheating may be necessary to improve weld quality. Conversely, high-temperature environments can also adversely affect the welding process and results, thus requiring careful precautions.
Impact of Ambient Temperature:
Electrofusion welding generally requires no special precautions when ambient temperature variations are within a certain range. However, in extreme environments, adjustments to the energy output to the pipe fittings may be necessary, such as by changing the input voltage or adjusting the welding time, to ensure weld quality. Simultaneously, direct sunlight should be avoided to prevent uneven temperature distribution in the pipes (fittings). Appropriate protective measures should be taken in windy, dusty, rainy, or snowy weather conditions to prevent contamination. Especially when welding large-diameter pipes, the distal end of the pipe should be capped to prevent drafts.
Safety and Standards:
Welding operators must possess the appropriate qualifications and wear gloves, goggles, and other protective equipment during operation to ensure safety. In addition, the welding equipment for polyethylene (PE) pipes should comply with the GB/T2062-2020 standard, while the production, design, construction acceptance and operation should follow the CJJ63-2018 industry standard and the TSGD2002-2006 technical rules.
