Examining the Behaviour of an Interactive Pipe Liner Under Conditions that May Occur

The water industry has used renovation techniques to extend the life of its assets for a number of years, beginning with sliplining in the 1970s. These techniques have evolved with time and the use of an interactive liner, where the liner withstands only some of the service loads, with the remainder borne by the host main, is now an established concept. Previous work by the authors has shown that along with the accepted gap-spanning and holebridging criteria, interactive liners are also capable of surviving a circumferential (or ring) failure event, as may be experienced by distribution mains under flexural loading. This paper describes work in which a lined host main, in an as- failed condition is subjected to deflections representative of those which may be seen in service following circumferential fracture. The results of a scoping study suggested that fracture surfaces may experience both longitudinal and transverse displacements post- fracture, leading to tensile and shear displacements of the liner in the vicinity of the host main fracture. A series of experiments were carried out on cast iron host pipes that had been lined with a medium density polyethylene thin- walled liner. These lined pipes contained a simulated transverse fracture. The fracture plane was subjected to varying degrees of shear displacement (up to ~50 mm) and longitudinal separation (up to ~20 mm). The tests were carried out for host/pipe liner systems with a variety of longitudinal gaps. The pipes were held at a pressure of 10 bar for a period of approximately 12 days (˜1,000,000 seconds) to allow creep deformation to take place. The ability of the liner to withstand such deflections over a period of time was hence determined. The aim of the work was to show to what extent displacements such as those discussed above affect the behaviour of a liner under service conditions. The implications of the results of this work on the current design guidelines need further consideration. However, if the outcomes are favourable, and a whole life costing approach shows the merits of such techniques, this could lead to an increased use of interactive liners, with many potential benefits to both the water industry and the customer. Keywords : Interactive Liner, Shear Testing, Mechanical Testing, Host Pipe Fracture.