Extrusion & Post
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Cyclic pressure fatigue failure of heat-resistant polyethylene PPR pipes
Problem Phenomenon
PPR/PP-R pipes suffer fatigue failure in cyclic pressure tests, with cracks initiating from the inner wall and expanding outward.
Fatigue failure is the main failure mode of pipes in actual use.
Cause Analysis
(1) Micro defects on pipe inner wall cause stress concentration
(2) Unsmooth inner wall at welded joint causes stress concentration
(3) Pipe material toughness insufficient, fatigue cracks propagate fast
(4) Improper extrusion process parameters cause processing defects on pipe inner wall
(5) Pipe wall thickness design safety factor low
Solution
(1) Ensure the pipe inner wall is smooth and defect-free, inner wall Ra≤3.2μm
(2) Improve welding quality, avoid weld beads on the inner wall of joints
(3) Select materials with good toughness, ensure elongation at break >500%
(4) Optimize extrusion process, control inner wall quality
(5) Ensure pipe wall thickness reaches the SDR design value, select a higher SDR value if necessary
Key Takeaway
Fatigue failure is caused by internal defects and stress concentration, and needs to be improved from the three aspects of pipe inner wall quality, welding quality and material toughness.
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