| 摘要 |
The present invention provides a multi-layered corrugated cylindrical tubular structure formed from a strip (10) of material having one edge reduced in diameter by a step portion (16) and reduced in length by corrugations (18). The strip may be formed on a forming arrangement comprising confronting corrugating rollers (74, 76) having regions formed with corrugating undulations of differing height and an un-corrugated portion.
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