Location Prediction Method Of Internal Corrosion In Water-containing Crude Oil Pipeline Based On Water Wetting

Internal corrosion of pipeline in petroleum industry is highly risky and the induced pipeline cracking may give rise to potential injury to personnel and environmental issues.The oil-water two phase flow and oil-gas-water three phase flow is often observed in gathering and transportation pipeline.Because the produced crude oil contains all kinds of corrosion species of which the corrosion mechanisms are different with water as the reaction medium.The coupling effects of multiple corrosion species can lead to a series of more complex physicochemical reactions.What's more,the corrosion species in different crude oil pipelines all around the world differs,and current studies on corrosion mechanisms of certain corrosion species are not universally applicable.It is generally accepted that water phase that wets the steel surface determines the initiation of corrosion.The thesis aims at proposing a universally applicable location prediction method of internal corrosion in water-containing crude oil pipeline based on water wetting mechanism.So that we can effectively predict the corrosion location before safety hazards and economic losses,which are caused by pipeline leakage resulting from corrosion,happen and provide a reliable basis for pipeline integrity management.This work has important guiding significance and reference value for the design,maintenance and safety evaluation of water-containing crude oil pipelines.Effects of various factors on the process of how water phase wets the inner wall of the pipeline are studied,such as fluid flow rate,pipe inclination,phase inversion phenomenon,movement of dispersed phase droplets,and the wettability of the pipe wall to reveal the influence of hydrodynamic characteristics of oil-water two-phase flow on corrosion location.The work in this paper is concluded as follows:(1)The oil-water two-phase flow tests under different pipeline operation conditions were done.The phase wetting state and water layer thickness of different pipe walls,such as carbon steel surface prewetted by water(hydrophilic surface),carbon steel surface prewetted by crude oil(unstable hodropobic surface)and PVC surface(stable hydropobic surface),were measured by the electrode sensor to obtain a series of phase wetting map and water layer thickness map.The influence of the wettability of internal pipe wall on the water wetting behavior was also studied.(2)Since the droplet size distribution of the dispersed phase is an important part of the water wetting model in the paper,the droplet size of the dispersed phase in the pipeline under different flow conditions is measured,and the droplet size distribution function is fitted to accurately calculate the the dispersed phase droplet size distribution under different flow conditions.(3)Multiple groups of contact angle experiments on surfaces with different wettabilities were done by controlling variables to study the influences of facors(such as temperature,crude oil types,sample surface roughness and so on).Experiment results were analyzed in details.(4)Combined with the experiment results The simulation in this work was done by Eulerian-Eulerian method to study key parameters(such as water cut,mixture velocity,oil viscosity and various inclination angles of pipes)that dominated oil-water distribution and water wetting behavior in the pipe.Water accumulation and flow behavior in the pipe were studied,especially at the pipe elbow.(5)The calculation equation of the maximum droplet size of dispersed phase in Brauner water wetting model was improved based on experiment data.The water concentration at the pipe bottom can be calculated by the water wetting model based on the Karabelas model and the equation of dispersed phase droplet size distribution.The value of water concentration was compared with phase inversion point of the same oil-water system to obtain the critical condition when droplets of dispersed phase started to accumulate at pipe bottom.A method for discriminating the formation of continuous water layer at the pipe bottom was established,and a method for predicting the corrosion location in the pipeline was proposed with the consideration of the continuous water layer formation mechanism on surfaces with different wettabilities and the combination of calculation method of water droplets being entrained and re-entrained.