Extrusion & Post
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Cyclic Pressure Fatigue Failure of Polypropylene PPR Pipe
Fenómeno del problema
PPR/PP-R pipes undergo fatigue failure in the cyclic pressure test, and cracks initiate on the inner wall and expand outward.
Fatigue failure is the main failure mode of pipes in actual use.
Análisis de la causa
(1) There are tiny defects on the inner wall of the pipe, causing stress concentration
(2) The inner wall at the welding joint is not smooth, generating stress concentration
(3) The toughness of the pipe material is insufficient, and fatigue cracks expand quickly
(4) Improper extrusion process parameters cause processing defects on the inner wall of the pipe
(5) The design safety factor of the pipe wall thickness is low
Solución
(1) Ensure the inner wall of the pipe is smooth and free of defects, with inner wall Ra≤3.2μm
(2) Improve the welding quality to avoid weld beads on the inner wall of the joint
(3) Select materials with good toughness, ensuring an elongation at break >500%
(4) Optimize the extrusion process and control the inner wall quality
(5) Ensure the pipe wall thickness reaches the SDR design value, and select a higher SDR value when 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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