关键词: 石油, 多相流, 腐蚀, 电化学, 动力学模型

Abstract:

The stratified oil-water flow regime is always encountered in long-distance crude oil transmitting pipelines, and then the acid-containing water layer probably lead to the serious internal corrosion of the bottom of the pipe, which becomes a significant threat to the long-term safe running. The multiphase flow, mass transfer, chemical reaction and electrode kinetics pose a challenge to corrosion prediction. A novel flow-induced corrosion kinetics model was proposed on the basic theory of multiphase flow dynamics and corrosion kinetics. Firstly, a mass transfer model under the oil-water three-layer flows was established. Secondly, based on the mass-transfer calculation of the ions across the bulk solution and the corrosion film, a prediction method for the multiphase flow corrosion was established according to the current density equilibrium of the anodic and cathodic electrochemical reactions. The interrelationship between the corrosion process and the ion mass transfer, electrode reactions and the dynamic growth of the corrosion film was revealed. Furthermore, the effects of CO₂ partial pressure and temperature on the corrosion evolution were investigated. The results indicate that the CO₂ partial pressure and temperature could change the ion concentration by altering the moving direction of the equilibrium reactions. The diffusion coefficient was the intrinsic factor to determine the mass transfer process. Moreover, the corrosion evolution process was determined by two factors: the dynamic growth of corrosion film and the electrode reactions. The continuous growth of corrosion film could impede the mass transfer of the ions involved in the reactions, thereby hindering the corrosion process, while the increment of ion concentration and mass transfer could speed the electrode reactions and then promote the corrosion process.

Key words: petroleum, multiphase flow, corrosion, electrochemistry, kinetics model