Piperoll level 603/18/2023 The squeezing effect of the rollers compresses the polyethylene polymer chains – partly non elastically – in a predominantly circumferential direction.Īs this chain compression is a mainly non-elastic process, the liner pipe will not revert on its own when it emerges from the rollers, and whilst there will be some degree of natural reversion, particularly if the process is carried out in hot weather, the application of internal hydraulic pressure is necessary to reverse this chain compression so as to achieve a close fit of the liner within the host pipe. The close-fit of the liner inside the host pipe additionally enhances the buckling collapse resistance of the liner pipe under surge vacuum conditions or external hydraulic pressure due to ground water when empty. This ensures The maximum possible flow capacity is achieved following lining. ![]() After insertion, the liner pipe ends are closed with suitable fittings, the liner pipe is filled with water and pressurised hydraulically in a series of carefully controlled steps until a close fit with the host pipe is achieved. Consequently the process of liner pipe insertion into the host pipe can be carried out as for a conventional PE pipe sliplining operation. The key feature of the process is that, apart from some limited initial die swell as the product pipe emerges from the processing equipment, the applied diameter reduction remains stable without a requirement to maintain the PE liner pipe in tension. The roller reduction process also results in a slight elongation of the PE liner pipe, typically by approx. The reduced diameter liner pipe is then inserted into the host main and reverted, normally by hydraulic pressurisation, although natural reversion of the liner may give a sufficient close fit, depending on the particular process and project parameters. In these processes, the reduced diameter is maintained without the application of axial tension to the liner pipe. ![]() Diameter reductions of between 10% and 20% are typically quoted, depending on the process used. The basic principle is that a PE100 liner pipe is pushed through a set of rollers which squeezes the pipe and reduces its diameter. This is a concentric reduction/expansion process. ![]() In practice, there are limits to the amount of diameter reduction that can be applied in concentric reduction processes (this and die drawing), whilst to achieve a close fit throughout a host pipe of varying diameter there are limits to the amount of diameter variation that can be accommodated, and both of these limitations need to be understood and taken into account when choosing the liner diameter and the roller dimensions for the particular application. Once the PE100 liner pipe is in the required position it is reverted to a close fit with the host main by the application of internal pressure, thus reversing the deformation process. For all close-fit PE lining methods, during the reduction process the outside diameter of the PE100 pipe is reduced to less than the minimum bore diameter of the host pipe.
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