Like all polyethylene pipes, PE-RT II is a high-density HDPE non-polar material, and there are currently no very effective NDT techniques and methods. The quality of electrofusion fittings joints is mainly guaranteed by process control.
Process control should start with people, machines, materials, methods and rings.
1) Personnel
Welding workers must be trained and qualified and managed effectively.
2) Welder
Electrofusion welding equipment shall conform to GB/T 20674.2-2006 [Polyethylene System Welding Equipment for Plastic Pipes and Fittings Part 2:
Electrofusion connection] (ISO 12176-2), routine maintenance should be carried out regularly.
Winter construction, must be able to identify the ambient temperature and temperature compensation of electric welding machine. The welding voltage must be stable at 39.5V ± 0.5V.
Before welding, it is necessary to determine the matching between the power of the welding equipment and the welding energy required by the electrofusion pipe fittings to avoid "small horse-drawn cart" and the formation of false welding/virtual welding. Especially for large-diameter electrofusion fittings (e. g.> dn200), it is necessary to use high-power electrofusion welding machines, whereas for small-diameter fittings
Electrofusion pipe fittings can only be used with low-power electrofusion welding machines, otherwise it will be "big horse-drawn trolley", resulting in overheated shotcrete of electrofusion pipe fittings, welding "risk" and even danger. Especially on the construction site, there are often different specifications of electrofusion pipe fittings. When welding different specifications of pipe fittings, we must pay attention to the power of the electrofusion welding machine. We must not be lazy, one welding machine cannot hit the world, and we cannot weld to the end with the same parameters.
3) Material: Before welding, check the pipes and fittings, which should be produced from the same material, and check whether the specifications, dimensions and assembly gaps meet the requirements. Pipes and fittings with obvious defects or excessive scratches shall be marked and shall not be used.
4) Method: The welding method should be strictly in accordance with the construction specifications and process parameters.
5) Environment: including the construction site infrastructure and natural environment. The infrastructure should be able to provide stable power supply for welding machine operation. If the power supply wiring exceeds 50m, the cross-sectional area of the conductor must be checked to meet the requirements. When it exceeds 100m, use the generator as much as possible. If a generator is used as a power source, the power size and operating characteristics should be considered. The natural environmental factors mainly consider the weather temperature and trench working surface conditions. Check the bottom of the trench before placing the pipe in the trench and during backfilling to ensure that the pipe is not damaged by sharp objects such as stones or metal sheets. In extreme weather conditions such as strong winds and low temperatures, appropriate measures should be taken. See "Winter Construction Tips". With the process control of electrofusion welding, there is also a simple method to check the quality of the joint on site.
Field Operation of 2. Electrofusion Joint Quality Check
The operation of electrofusion joint quality inspection on site is mainly visual inspection.
1) Check the surface treatment of the welding part, there should be obvious and sufficient (full circle) scraping marks.
2) Check that the molten material during welding should not flow out of the pipe, or within the acceptable range, a small amount of melt slightly and evenly overflows).
3) Check that the overflow along the circumferential direction of the pipe should be uniform. If the top surface of the pipe is less and the bottom surface is more, it means that the pipe assembly is not aligned, or the pipe fittings are not supported during welding.
4) Check that the resistance wire of the electrofusion pipe fitting does not overflow with the spilled material during welding.
5) Check the change of the observation hole. Generally speaking, after the welding is completed, the observation hole will protrude to indicate the completion of the welding process, so check the view.
The position of the observation hole changes. If the observation hole does not appear, it means that there is no welding or false welding, such as welding large-size electrofusion pipe fittings with a low-power welding machine, and the power is not enough. If only a small amount of observation holes come out, it means that the gap between pipe fittings is too large, the melting area does not form enough molten pool and melting pressure, and the welding strength may not meet the requirements.
If the observation hole spits slurry, the molten area is overheated. There are many reasons for the observation hole to emit slurry. It is necessary to check whether the welding temperature is correct. If the temperature is too high during welding, slurry will emit. It should be checked whether the wrong welding bar code has been scanned, such as small-size electrofusion welding, but it has been swept into large-size welding.
The pipe fitting bar code; Should check whether the welding voltage is stable; Check whether there is a short circuit caused by dislocation of resistance wire during welding. If the pipe and pipe fittings are assembled brutally, the pipe is smashed in with a hammer, which may also cause the resistance wire to be smashed and displaced, resulting in parallel short circuit. The power of the welding machine should also be checked, instead of "big horse-drawn trolley", welding small-diameter fused pipe fittings with high-sized welding machine, etc.
6) Check the inner wall of the pipe at the welding position, and there shall be no collapse or wrinkle of the inner wall.
Note: The welding process shall be strictly followed during construction. Otherwise, the relevant welding voltage, welding time and other processes are not suitable,
Causing weld failure, endangering the safety of the pipeline system.