Electrostatic ignition hazards arising from fuel flow in plastic pipelines

The use of electrically insulating synthetic materials, such as plastics, for fuel pipelines and other fuel handling components is now becoming widespread. In the case of buried or underground pipelines in filling station forecourts the use of these materials offers superior corrosion resistance and increased longevity. This in turn reduces the risk of pollution due to fuel leakage. It is well reported that the flow of fuel under certain conditions in metal pipes can produce significant levels of electrostatic charge on the fuel. Little work, however, has been undertaken on plastic pipe where charge can accumulate at the fuel/pipe wall interface.This paper reports on tests performed on a full-scale, high-density, polyethylene pipework system. During the tests, an iso-octane/toluene fuel mix of controlled and known electrical conductivity was transferred through the system at varying flow rates. Both buried and free-standing pipeline configurations were simulated. A number of test runs were performed yielding considerable data relating to the resultant electrostatic activity including electrostatic potential, the nature and location of electrostatic discharges and the discharge energy. The influence of components such as in-line valves and couplings, which have a metallic component, are also evaluated. The extensive data resulting from this study are presented graphically. The paper concludes with an analytical section and draws important conclusions with regard to the parameters influencing the degree of ignition hazard present.