Rapid crack propagation in loosely fitted PE liner pipe

Laboratory scale tests have been used to assess whether a loosely fitted PE liner within a rigid host pipe could, at any realistic working pressure, fail by rapid crack propagation (RCP). The standard 'S4' test method for RCP was modified, the usual cage of containment rings being replaced by a rigid, closed sleeve maintaining a predefined radial clearance from the unpressurised pipe. Pipe specimens of 125 mm diameter with wall thicknesses of 11.4 and 7.1 mm, made from a PE80 polyethylene in which RCP is normally possible at 0 degrees C, were tested with three different clearances as well as with the usual S4 cage. For pipe having an unpressurised clearance down to 2% or so of the diameter, the RCP critical pressure was increased by similar to 50% for both thicknesses; for smaller clearances, by progressively more. These results reinforce suspicions that pipe installation conditions may affect full scale RCP resistance.