Extrusion & Post
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Insufficient Long-Term Hydrostatic Strength of High-Density Polyethylene PPR Pipes
Problem Phenomenon
PPR/PP-R pipes rupture 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 unsuitable
（5）The welded joint, as a weak point, has insufficient strength
Solution
（1）Select a special grade that meets 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 the pipe wall thickness meets the SDR value requirement and is uniform
（4）Optimize the cooling conditions to ensure a reasonable crystallinity (50-60%)
（5）Strengthen the quality control and inspection of welded joints
Key Takeaway
Insufficient long-term hydrostatic strength is caused by material selection and processing quality, and needs comprehensive control from raw materials, processes, and welding.
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