Pre-welding precautions
Pre-treatment and clamping:
The pipe end face is cut flat to remove oxide layer and impurities;
After clamping, the misalignment is less than 10% of the wall thickness, and the coaxiality deviation is less than 0.5% of the pipe diameter.
Flanging Preheating:
Apply flanging pressure to form a uniform initial flanging, ensuring full contact between the heated surfaces
Heat Absorption Stage:
After the heating plate temperature stabilizes, reduce the pressure and maintain the set heat absorption time to allow the contact surfaces to fully melt.
Switching Stage:
Quickly remove the heating plate (strictly control the switching time) to avoid oxidation or cooling of the molten surface.
Pressure Increase and Welding:
Rapidly apply welding pressure; the pressure increase time must match the wall thickness to ensure fusion of the molten interface.
Pressure Holding and Cooling:
Maintain the welding pressure until cooling is complete to prevent stress cracking of the joint. Do not move the workpiece during cooling.
The centering gap before pipe welding is shown in the table below
| Pipe outer diameter (mm) | Centering Gap(mm) |
|
≤355 |
0.5 |
|
400~630(excluding) |
1.0 |
|
630~800(excluding) |
1.3 |
|
800~1000(inclusive) |
1.5 |
|
＞1000 |
2.0 |
Heating Plate Temperature : 210±10℃
Welding Process Diagram
Wall Thicknes(mm) |
Interface Pressure Coefficient(calculated at 0.10 N/mm² ± 0.01)(mm) |
Heat Absorption Time
|
Switching Time(S) |
Pressure Increase Time(S) |
Cooling Time(Min) |
|
＜4.5 |
0.5 |
135 |
5 |
6 |
6 |
|
4.5~7 |
0.5 |
135~175 |
5~6 |
6~7 |
6~12 |
|
7~12 |
1.0 |
175~245 |
6~7 |
7~11 |
12~20 |
|
12~19 |
1.0 |
245~330 |
7~9 |
11~17 |
20~30 |
|
19~26 |
1.5 |
330~400 |
9~11 |
17~22 |
30~40 |
|
26~37 |
2.0 |
400~485 |
11~14 |
22~32 |
40~55 |
|
37~50 |
2.5 |
485~560 |
14~17 |
32~43 |
55~70 |
Note
Flanging pressure, butt joint pressure, and cooling pressure are all calculated at 0.10 N/mm² ± 0.01.
Heat absorption pressure is calculated at less than 0.01 N/mm² but not equal to 0.
All pressure values should include drag pressure.
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Conclusion
The official German standard for hot-melt welding of PP pipes is DVS 2207-11, which specifically regulates the welding (butt/socket) process of heating elements for polypropylene (PP-H/PP-B/PP-R/PP-RCT), suitable for applications such as water supply, chemical processing, and industrial fluid transportation. The above outlines the complete process, core parameters, key operating points, and inspection specifications. |