Study On The Movement Of Residual Water In The Products Oil Pipeline

The corrosion product blocked the filter of valves and pumps, and caused emergencyshutdown of product-oil pipeline for many times in China, which is caused by that pipelinewas not cleaned and dried after pressure test by using water. As the density of water is largerthan that of oil and stable water–oil emulsion cannot be formed, the residual water is trappedat some place in the upward pipeline under the effect of gravity. The movement anddistribution of the residual water is studied and the reasons why the residual water cannot beremoved are analyzed.The goniometer and tensionometer are used to study the wettability of solid surface andthe effects of pre-wetting, pipeline material and icon concentration on the wettability areanalyzed. As icon concentration has little impact on the interfacial tension, contact angle canbe used to evaluate the wettability of the surface instead of surface absorption energy. Theresults show that carbon steel is hydrophilic and acrylic is hydrophobic. The effects ofpipeline material on the wettability are not only on the final contact angle, but also on thewetting process: the contact angle becomes stable after a long period of time in steel surface,but almost immediately in acrylic surface.Two loops of different diameter are used to study the movement and distribution of theresidual water. In horizontal pipeline, the flow patterns mostly are stratified flow. Because ofgravity, the residual water shows completely different behavior in the upward pipeline. Whilethe superficial velocity of oil is low, most water is trapped at the lower section of the pipelinewith a flow pattern of inhomogeneous dispersed flow with back flow at the bottom wall, onlysome water droplets could keep entrained in the oil and been pushed away. While the oilsuperficial velocity increases, most residual water could be drained off. There are still somedroplets circulating at the bottom of the pipeline, because of dropping and coalescing unlessthe superficial velocity of oil could reach the critical velocity. There is little difference withthe inclination increasing (from5°to30°). Although no water disappears through the video,water could also be detected by using conductivity pins because of hydrophilic of the steelwall and high surface absorption energy.Small perturbation is introduced at the inlet of the pipeline to simulate the instability ofthe interface by using commercial software Fluent. In the horizontal pipeline, the small perturbation cannot grow larger to cause the instability of the interface, the flow pattern keepsstratified until all the water is drained off. In the upward pipeline, the interface becomesunstable under the effects of gravity. The residual water will reach a dynamic balance andcannot be drained off at low oil superficial velocity. The simulation results agree well withexperimental results, which indicate that it is reliable to study the interface instability byintroducing small perturbation at inlet.The unique Doughnut Cell and conductivity pin were used to study the effects of watercut and superficial velocity on the wetting condition of wall. At the same time, the effects ofoil physical properties, such as density and viscosity on the stability of water droplet werealso studied. According to the corrosion rate, three different kinds of wetting condition weredefined: water wetting, intermittent wetting and oil wetting. The oil of high density and highviscosity could promote oil wetting and keep the wall from corrosion.