Assessing the ability of interactive pipe liners to withstand host-pipe failure

Abstract

This paper presents an investigation into the behaviour of a number of pipe liner materials, with the specific aim of determining their ability to remain intact during failure of the cast iron host main. Three different liner systems have been evaluated along with an unlined control. One of the liners (epoxy resin lining) is a non-structural technique, whereas the other two (Subcoil and a new development) are semi-structural (or interactive) liners. Metallographic analysis and tensile tests were carried out on small samples cut from the cast iron host pipe in order to characterise the basic properties of the cast iron. Metallography revealed a microstructure typical of a grey cast iron, consisting of acicular graphite flakes with some rosettes; etching with 2% Nital acid etch revealed the presence of pearlite. Tensile tests on small samples cut from the pipes indicated significant non-linearity in the stress-strain response. Lined cast iron pipes were tested to failure in four-point bending. A circumferential notch was machined into the wall of some of the pipes, in order to simulate the reduction in host-pipe strength due to corrosion. In addition some tests were carried out under applied internal water pressure, to determine if this had any effect on liner behaviour. Both interactive liners survived host-pipe failure, whilst, as expected, the non-structural liner did not. A simple method was developed which enabled the bending moment curvature relationship in a bend test to be modelled from tensile data; this model gave satisfactory agreement with the experimental data.