Extrusion & Post
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Cyclic pressure fatigue failure of low density polyethylene PPR pipes
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.
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
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
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.
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