Study On The Optimization Of Moisture Gathering Pipeline Pigging Period

For the moisture gathering pipelines using corrosion inhibitor pre-coat to control internal corrosion, pigging must be carried out before periodic coating, so the determination of pigging period depends on failure rate of pipe inwall’s corrosion inhibitor film. In this paper, the instruments such as homemade thickness measuring device for corrosion inhibitor film and electrochemical workstation are used to study on the failure rule of corrosion inhibitor and optimization of the corrosion inhibitor coating period, in order to provide theoretical guidance on the choice of the pigging period for the field.Using the thickness measuring device for oil-soluble corrosion inhibitor pre-coat film to study on the changing rule of pre-coat film thickness with blowing time, the results show that the thickness of corrosion inhibitor film decreases dramatically at the beginning of blowing, then there is a little change in the remaining time. A mathematical model of flowing failure of oil-soluble corrosion inhibitor film suffering from the shear is established by theoretical analysis, the structure of corrosion inhibitor film can be divided into two layers, the upper layer is liquid membrane, failing rapidly under the shearing action of blowing medium, while the lower is the adsorption layer with flowing less easily, losing efficacy mainly through diffusion function. Using the Fluent numerical simulation, experimental pipeline device and electrochemical workstation to study the effect of pipeline flowing characteristics to the corrosion inhibitor failure, and the results of numerical simulation and experiments show that liquid holdup and velocity of gas ph ase are the main influence factors. The influence of added concentration of water-soluble corrosion inhibitor to corrosion effect is studied by 2273 electrochemical workstation, and the results show that the corrosion effect is best when the concentration is 200ppm; meanwhile the synergy effect of water-soluble corrosion inhibitor and oil-soluble corrosion inhibitor is best when the concentration of water-soluble corrosion inhibitor comes to this value, then the corrosion effect decreases along with increase of the concentration. The blender and electrochemical workstation are used to study the relationship between the metal electrode corrosion current density and the shear time, under the synergy of oil soluble pre-coat film and water-soluble corrosion inhibitor, the results show that there is a approximate linear correlation between current density and shear time, and the analysis shows that corrosion current density is proportional to corrosion rate, then obtaining relational expression of pigging period and corrosion rate on the basis of that consequence, then optimize the pigging period in view of the actual situation, and the pigging period can be extended from 30 days to 45 days.