How to Calculate HDPE Butt Fusion Pressure and Time
In HDPE butt fusion welding, the required pressure and welding time depend on the pipe size, wall thickness, SDR, machine configuration, and the welding standard being used.
Different standards may specify different pressure and time parameters, even for the same pipe and the same butt fusion machine.
This article uses ISO 21307:2017 and DVS 2207-1 as examples to explain the basic pressure stages and calculation method used in butt fusion jointing.
1. Understanding the Butt Fusion Pressure Cycle
A typical butt fusion cycle includes three main pressure levels:
P1 —— Bead-up Pressure
P2 —— Heat Soak Pressure
P3 —— Fusion Jointing Pressure
t1 —— Bead-up Time
t2 —— Heat Soak Time
t3 —— Heater Removal Time
t4 —— Pressure Build-up Time
t5 —— Cooling Time
The overall process can be understood simply as:
Bead-up → Heat Soak → Heater Removal → Fusion → Cooling
During each stage, the pressure and time are controlled according to the welding procedure being followed.
2. How Are P1 and P3 Calculated?
The bead-up pressure P1 and fusion jointing pressure P3 can be calculated using the following formula:
The parameters in the formula are:
IP —— Interfacial Pressure, MPa
dn—— Nominal Pipe Outside Diameter, mm
en —— Nominal Pipe Wall Thickness, mm
S —— Total Piston Area of the Machine, mm²
P2 —— Drag / Soak Pressure Used in the Calculation, bar
In simple terms, the formula uses the pipe dimensions, welding standard, machine piston area and actual drag pressure to determine the required hydraulic gauge pressure.
3. What Is Total Piston Area?
Total piston area is a fixed parameter of the butt fusion machine.
It is determined by the hydraulic cylinder design and is already defined during machine production.
The operator normally does not need to calculate it manually.
In the pressure formula, the piston area is used to convert the required fusion force into the hydraulic pressure that needs to be applied by the machine.
This is also why two butt fusion machines welding the same pipe may require different gauge pressure values if their piston areas are different.
4. ISO 21307:2017 Calculation Example
Let us take the following pipe as an example:
OD 315 mm / SDR 11 HDPE Pipe
The welding procedure also specifies other parameters such as bead size, heat soak time, heater removal time, pressure build-up time and cooling time.
· Bead size: 3.4 mm
· Heat soak time t2: 344–430 s
· Heater removal time t3: max. 16 s
· Pressure build-up time t4: max. 12 s
· Cooling time t5: min. 19 min
5. DVS 2207-1 Calculation Example
Using the same:
OD 315 mm / SDR 11 pipe
with the same machine parameters:
Total piston area: 2002 mm²
Drag pressure: 10 bar
Pipe outside diameter: 315 mm
Wall thickness: 28.64 mm
6. Why Do ISO and DVS Give Different Pressure Values?
In the examples above, everything remains the same:
OD 315 mm, SDR 11, the same machine, the same piston area and the same drag pressure.
But the calculated pressure is different:
ISO example: approximately 32 bar
DVS example: approximately 29 bar
The reason is simple:
The welding standards use different process parameters.
For this reason, welding pressure and time values should always follow the procedure required by the project, local specification, pipe manufacturer or applicable welding standard.
Parameters from different welding procedures should not be mixed.
7. Pressure Is Only Part of the Butt Fusion Procedure
A complete butt fusion procedure includes more than just P1, P2 and P3.
Other important parameters include:
· Bead size
· Heat soak time
· Heater removal time
· Pressure build-up time
· Cooling time
The required pressure is mainly related to the pipe dimensions, welding standard, machine piston area and drag pressure.
Time-related parameters are normally determined according to the applicable welding procedure and pipe dimensions.
8. Use Our Online Butt Fusion Pressure Calculator
Manual calculation is useful for understanding how butt fusion pressure is determined.
But in day-to-day work, you may need to calculate pressure for different:
machine models, pipe sizes, SDRs, welding standards and drag pressures.
Repeating the calculation manually takes time and can easily lead to input errors.
To make this easier, we developed an online Butt Fusion Jointing Pressure Calculator.
Simply select or enter the welding standard, machine model, pipe size, SDR and actual drag pressure, and the calculator will automatically determine the required P1 / P3 gauge pressure.
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Conclusion
Butt fusion pressure calculation does not need to be complicated.
Once the welding standard is confirmed, the required pressure can be calculated from:
Pipe diameter + wall thickness + interfacial pressure + machine piston area + drag pressure
The complete welding procedure should then be followed for bead-up, heat soak, heater removal, fusion and cooling.
For frequent calculations involving different machines and pipe sizes, an online calculator can make the process faster and reduce calculation errors.
