Extrusion & Post
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Cyclic pressure fatigue failure of linear low-density polyethylene PPR pipes
Fenómeno del problema
PPR/PP-R pipes suffer fatigue failure in cyclic pressure tests, with cracks initiating on 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 exist on the pipe inner wall, causing stress concentration
(2) The inner wall at the welding joint is not smooth, causing stress concentration
(3) Pipe material toughness is insufficient, and fatigue cracks propagate quickly
(4) Improper extrusion process parameters cause processing defects on the pipe inner wall
(5) Pipe wall thickness design safety factor is on the low side
Solución
(1) Ensure the pipe inner wall is smooth and defect-free, with inner wall Ra≤3.2μm
(2) Improve welding quality to avoid weld beads on the joint inner wall
(3) Select materials with good toughness, ensuring elongation at break >500%
(4) Optimize the extrusion process and control inner wall quality
(5) Ensure pipe wall thickness reaches the SDR design value, and select a higher SDR value if necessary
Conclusión clave
Fatigue failure is caused by internal defects and stress concentration and needs to be improved from three aspects: pipe inner wall quality, welding quality and material toughness.
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