Extrusion & Post
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Insufficient long-term hydrostatic strength of general-purpose polyethylene PPR pipes
Problem Phenomenon
PPR/PP-R pipes break in long-term hydrostatic tests (1000h, 8760h) and cannot meet the ISO 15874 requirements.
Insufficient long-term strength affects the service life and design safety factor of the pipes.
Cause Analysis
（1）The molecular weight of the raw material is low or the molecular weight distribution is unreasonable
（2）The extrusion temperature is improper, and the material is partially degraded
（3）The pipe wall thickness is insufficient or uneven
（4）The cooling rate is improper, and the crystallinity is inappropriate
（5）The welding joint is a weak point with insufficient strength
Solution
（1）Select special grades that meet the PPR pipe standard (MFR 0.2-0.5g/10min)
（2）Strictly control the extrusion temperature at 200-220°C to avoid material degradation
（3）Ensure that the pipe wall thickness meets the SDR value requirements and is uniform
（4）Optimize the cooling conditions to ensure a reasonable crystallinity (50-60%)
（5）Strengthen the quality control and inspection of welding joints
Key Takeaway
Insufficient long-term hydrostatic strength is caused by material selection and processing quality, and needs to be comprehensively controlled from raw materials, processes, and welding.
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