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