Extrusion & Post
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Cyclic pressure fatigue failure of linear low density polyethylene PPR pipes (Variant: strengthened measures)
Fenómeno del problema
PPR/PP-R pipes fail by fatigue in cyclic pressure tests, with cracks initiating at the inner wall and propagating outward.
Fatigue failure is the main failure mode of pipes in actual use.
In particular, additional attention is needed on the original basis; this problem is more prominent and requires key attention.
Análisis de la causa
(1) Micro defects on the pipe inner wall cause stress concentration
(2) Unsmooth inner wall at welding joints produces stress concentration
(3) Insufficient pipe material toughness, fast fatigue crack propagation
(4) Improper extrusion process parameters cause processing defects on the pipe inner wall
(5) Low design safety factor of pipe wall thickness
(6) On the original basis, additional attention is needed as process parameter fluctuations or equipment status changes have aggravated this problem
Solución
(1) Ensure pipe inner wall is smooth and defect-free, inner wall Ra≤3.2μm
(2) Improve welding quality, avoid weld beads on joint inner walls
(3) Select materials with good toughness, ensure elongation at break >500%
(4) Optimize the extrusion process, control inner wall quality
(5) Ensure pipe wall thickness reaches the SDR design value; select a higher SDR value when necessary
(6) And strengthen process monitoring; on the original basis, additional attention is needed, with special attention to parameter stability
Conclusión clave
Fatigue failure is caused by internal defects and stress concentration; it needs to be improved from three aspects: pipe inner wall quality, welding quality, and material toughness.
Targeted preventive measures need to be taken in different production scenarios.
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