Resistance of polyethylene water pipeline systems to surge pressure

The guidelines given in BS CP 312 : Part 2 :1973 are recommended to the UK water industry for the design of polyethylene pipeline systems to take into account the effect of transient (surge) pressure fluctuations with respect to fatigue. These guidelines were based on earlier experience with unplasticised poly(vinyl chloride) sewer rising mains and are generally considered too conservative for more flexible polyethylene systems. A group representing the UK water industry including a material supplier, product manufacturers, and water companies was formed in 1991 to discuss and investigate this apparent anomaly. By measuring a number of in service installations known to experience surge pressures, a maximum rate of change of pressure realistically possible during a surge event was established. This rate of pressure change was used in high amplitude cyclic pressure tests carried out in the laboratory on notched pipe and fitting assemblies. No failures or discernible deterioration occurred in any of the products subjected to this repeated cyclic testing, designed to simulate the number of worst case events feasible in the projected lifetime. It was concluded that the current guidelines are very conservative and alternative recommendations are proposed applicable to polyethylene pipe systems up to at least 180 mm diameter. PRCPA/1232