The spread behaviors of the underwater oil droplet on smooth brass substrate were studied using high⁃speed microscopic imaging technology. Chemical and physical modifications were made on the surface of the brass sheet to change its surface properties, and the controllable regulation of superoleophilic–superoleophobic wettability gradient of the surface was achieved successfully. The spreading length and contact angle of the oil droplet rising to different modified surfaces were tested. Different from that in air condition, influence of water surrounding the oil droplet must be considered, which is complicated in water. In this work, on the basis of the energy conservation mechanism, quantitative relationship among the eigenvalues for the spreading behaviors of the oil droplet rising to the surfaces, such as droplet dimensionless spreading length, the droplet impact velocity, droplet size, droplet properties, viscosity of the water and surface wettability, were obtained. An optimized spreading dynamic model was constructed to describe the spreading behaviors of underwater oil droplets on surfaces with different wetting properties, to give support for the design of new oil⁃water separation equipment.

Non⁃metallic pipeline has become the new direction of oil and gas pipeline technology because of its excellent performance. However, the electrostatic problem during the oil transportation process threatens the safe operation of pipeline. Based on diffuse double layer theory, the electrostatic electrification mechanism of metal and nonmetallic pipes is analyzed and compared. The effects of flow regime, pipe properties and oil properties on the oil flow electrification are systematically elucidated. The main forms and hazards of electrostatic discharge of oil pipeline are analyzed in detail. Moreover, a series of electrostatic control and hazard protection measures are put forward from the perspectives of avoiding electrostatic generation and neutralizing static electricity.