Quality Control of Hot Melt Butt Joint of 1. PE-RT II Pipeline
Like all polyethylene pipes, PE-RT Type II is a non-polar high-density polyethylene (HDPE) material and is currently available.
There are no effective NDT techniques and methods. The quality of hot melt butt joints is mainly guaranteed by process control, which should be
From the man, machine, material, law, ring all aspects.
People: welding workers must be trained and qualified, and subject to effective management.
Machine: welding equipment should meet the requirements of the relevant standards and often maintain in good working condition.
Materials: Before welding, pipes and fittings should be inspected to ensure the diameter, standard dimension ratio (SDR) and wall thickness and tolerance of their production.
and so on are in accordance with the provisions. Pipes and fittings with obvious defects or excessive scratches shall be marked and shall not be used. at the beginning of laying
Before and during the laying process, attention should be paid to check whether the pipe has serious surface defects; if the surface defect depth exceeds the nominal
For 10% of the wall thickness, the defective pipe shall be cut off or repaired according to relevant procedures.
Method: welding method should be strictly in accordance with the relevant construction specifications and process parameters.
Environmental factors mainly consider the weather and trench operation surface conditions. Inspection before placing the pipe in the trench and during backfilling
At the bottom of the trench, ensure that the pipe is not damaged by sharp objects such as stones or metal sheets.
In conjunction with process control, there is also a simple method to initially check the quality of the joints on site.
Field operation 2. quality inspection of PE-RT type II hot-melt butt joints
On-site operation of quality inspection of joints, including visual inspection, flanging size inspection, visual inspection after crimping and bending
Inspection.
(1) Field visual inspection standard for welded joints
Geometric shapes. The flanging should be smooth and symmetrical along the entire outer circumference, with uniform, full and round dimensions. The flanging should not have a cut or
For notch-like defects, the weld height shall not be lower than the pipe surface (A in Figure 1). The misalignment of welded parts shall not exceed the wall thickness of the pipe.
10% (V in Figure 2).

1) Different process conditions will also cause different flanging shapes. Its width B is affected by material type, production process (extrusion or injection molding), type of heating plate used, temperature and welding cycle. Therefore, it is difficult to determine a set of flanging width values. However,
Practice has proved that controlling the size of the flanging according to the following geometric dimensions can generally ensure the quality of the weld:
The flanging width B = 0.35~0.45e,e is the pipe wall thickness;
flanging height H = 0.2~0.25e;
Height from middle seam of flanging to outer wall of pipe (circumferential seam height) h = 0.1 ~ 0.2e
The selection of the above coefficients should follow the principle of "small pipe diameter, choose a larger value; large pipe diameter, choose a smaller value. such as dn90
For pipes, the width of flanging (welding ring) can be selected as 0.45e, while for dn250 pipes, the width of flanging can be selected as 0.35e. in the same
The welding flanging obtained under the conditions shall be basically the same, and shall not exceed ± 20% of the average value. You can use the width ruler to check

2) When welding pipes and fittings, since the pipes are extruded and the fittings are injection molded, the width of the flanging will be different.
3) If the tips of the flanging rolls on both sides are not in contact with the pipe wall, the flanging height is too low, usually due to insufficient welding pressure or
The heating temperature is too low.
4) If the flanging height is too large, it is generally caused by excessive butt pressure (the melting finger of the material is too high). Molten parts are formed
After flanging, the remaining semi-molten parts stick together. This kind of weld has great potential harm.
5) If the two curling axes are different, it is mainly caused by poor positioning of the clamping or deviation of the outer diameter of the pipe. Should be as far as possible to ensure that the pipe clamping pipe
The deviation of the outer diameter of the material shall not exceed 5% of the wall thickness.
6) The uneven flanging on the same side is usually due to uneven milling or excessive axial clearance of the butt clamp.
7) Use a suitable tool to cut off the flanging for inspection. The flanging should be solid and smooth with a wide root (see Figure 4). root is relatively

The narrow and curled hollow cuffing may be caused by excessive pressure or no heat absorption. There shall be no dirt on the bottom surface of the bead.
The joint shall be rejected if impurities, holes, offsets or damage are found.
8) Reverse bending test for flanging. The flanging shall be subjected to reverse bending test every few centimeters to check whether there is any crack defect. If crack is found
seam, indicating that there are fine dust impurities at the sintering interface. This may be due to contact with a dirty heating plate (see Figure 8).
Note: the construction process should be strictly in accordance with the welding process, otherwise, the relevant welding temperature, welding pressure, welding time and other work
The process is not suitable, resulting in weld failure, endangering the safety of the pipeline system.