Effect of electrification in ball valves on ignition risk in liquid pipeline systems

Abstract

Quantitative analysis of the electrostatic hazard in a liquid flow system requires a knowledge of the electrification at constrictions in pipelines to assess the possibility of incendive discharge from the plant and the liquid. Data on the electrostatic charge generated during the flow of toluene and toluene plus water through a ball valve are reported. Immiscible water concentrations greater than 0.1–0.2% (v/v) in toluene are found to markedly increase electrification and it is considered that the flow of the liquid through the valve, and not pipeline flow, is the major source of the high levels of electrostatic charge generated during the processing of two-phase systems. The conditions required for an incendive spark from an insulated component in the valve are described, and it is shown that these can be satisfied during the flow of toluene and toluene plus water. Only in exceptional plant situations could the presence of a valve increase the possibility of discharges from the liquid surface in a single phase system; however, the presence of free water produces charge densities on the liquid at which discharges from its surface may be possible.