Tests for holding time before unloading of oil tanker

To eliminate static risks during unloading of oil tanker, a holding time of 15 min before unloading is specified in relevant national standards. Simulation test is performed for static safety under currently available conditions to determine the holding time required before unloading of oil tanker. Before departuring from tankfarm, a float for measuring of surface potential in the oil tank of the truck is installed. The oil surface potential measurement device is deployed in the driver's cabin. During normal travelling and upon parking in filling stations, the oil surface potential within the tank is measured in real time. Furthermore, conductivity of oil, ground resistance of the tanker and other parameters are measured. Relevant results show that oil in the tanker may not produce high surface potentials during travelling or during holding time in the filling station. The highest potential measured in such circumstances is 260 V, and ground resistances of the tanker are all below 10⁶ Ω. Field tests were conducted in several cities in northern China during the representative autumns or winters. With consideration to relevant test results and specific features of tankers, it is determined that the holding time before unloading of oil tanker in the filling station can be reduced to 5 min when the ground resistance of the tanker is lower than 10⁶ Ω and the tanker is configured with metallic clapboards with the volume of each individual chamber lower than 18 925 L.