Extrusion & Post
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Cyclic pressure fatigue failure of general-purpose polyethylene PPR pipes
Fenómeno do problema
PPR/PP-R pipes suffer fatigue failure in the cyclic pressure test, and cracks initiate on the inner wall and expand outward.
Fatigue failure is the main mode of pipe failure in actual use.
Análise das causas
（1）The inner wall of the pipe has tiny defects that cause stress concentration
（2）The inner wall at the welding joint is not smooth, causing stress concentration
（3）The toughness of the pipe material is insufficient, and the fatigue crack expands 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
Solução
（1）Ensure that the inner wall of the pipe is smooth and free of defects, inner wall Ra≤3.2μm
（2）Improve the welding quality and avoid weld beads on the inner wall of the joint
（3）Select materials with good toughness to ensure elongation at break >500%
（4）Optimize the extrusion process and control the inner wall quality
（5）Ensure that the pipe wall thickness reaches the SDR design value, and select a higher SDR value if 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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