Novel approach to PE pipe insertion using four-lobe vacuum collapse

Abstract

The authors have researched, and partially developed, a novel concept for temporarily reducing the external diameter of a polyethylene (PE) pipe and then allowing recovery to full diameter as a close fit within a host main. The novelty lies in the four-lobed collapsed pipe geometry, which provides an efficient reduction of overall outside diameter without excessive strain and in the achievement and maintenance of this collapsed shape by vacuum. The further attraction of this approach is that controlled release of the vacuum provides a substantial primary recovery of the original pipe size and shape. The inventive discovery that makes possible the control of the four-lobe collapse state involves strict and progressive control of the collapse process, which can, in principle, be conducted downstream of the extrusion process, making continuous manufacturing, and indeed, coiling, feasible. Alternatively the collapse process could be made an on site operation immediately before insertion. The present work was largely conducted using a highly elastic grade of PE (Dow-DuPont ‘engage' polymer) that maximised the high shape recovery potential of the process. Using this tough, rubbery form of PE pipe it was demonstrated that almost full pipe geometry could be recovered after release of vacuum. The technique is also applicable to conventional pipe grade PE materials, but with their stiffer viscoelastic properties recovery would require some internal pressure and perhaps elevated temperature for full recovery of circularity. The ‘engage' PE polymers were found to be potentially useful materials for pipe lining since they are intrinsically tough and appear to be entirely weld compatible with conventional PE pipes. Engage liners could be electrofused to PE pipe. Iron pipe lined with a pressurised engage pipe was artificially fractured and subjected to severe angular offset without damage to the lining.