Extrusion & Post
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Cyclic Pressure Fatigue Failure of High-Density Polyethylene PPR Pipes
Fenómeno do problema
PPR/PP-R pipes suffer fatigue failure in the cyclic pressure test, with cracks initiating on the inner wall and propagating outward.
Fatigue failure is the main failure mode of pipes in actual use.
Análise das causas
（1）Minor defects on the inner wall of the pipe cause stress concentration
（2）The inner wall at the welded joint is not smooth, producing stress concentration
（3）The toughness of the pipe material is insufficient, and the fatigue crack propagates fast
（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
Solução
（1）Ensure the inner wall of the pipe is smooth and defect-free, 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 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
Conclusão principal
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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