Research Of Naphthenic Acid Corrosion On Different Structure Elbow By Numerical Simulation Method

With the increasing amount of high-acid crude oil, naphthenic acid corrosion problems in oil processing and transport equipment are growing. The leakage accident caused by refining high-acid crude oil occurs frequently, serious threat the safety production. It is difficult to accurately predict the corrosion area because of multitudinous of influence factors and complex corrosion mechanism. Based on the simulation result of the flow field in eccentric reducing elbow in an enterprise crude oil distillation unit, and combined with the naphthenic acid corrosion factors and the thickness of the pipe, identify the factors of corrosion rate increase under certain conditions and these factors were used to predict the naphthenic acid corrosion area in this thesis. Finally, a naphthenic acid flow-induced corrosion mathematics model was established combined with the naphthenic acid corrosion mechanism and was used to calculate the corrosion rate of the eccentric reducing elbow.The distribution of the flow velocity, wall shear stress, turbulence kinetic energy and other hydrodynamic parameters in eccentric reducing elbow was identified and their influence to the corrosion was analyzed in this thesis. The eccentric reducing elbow corrosion simulation result was analyzed by contrasting with the pipe wall thickness, and ultimately identify the wall shear stress is the most influential hydrodynamic parameters of the naphthenic acid corrosion, the flow-induced naphthenic acid corrosion area can be predicted by using wall shear stress.The flow field in ordinary elbow, eccentric reducing elbow, concentric reducing elbow were simulated in this thesis. The simulation result shows that in ordinary elbow, the elevated levels of wall shear stress were found along the elbow intrados. In eccentric reducing elbow, the elevated levels of wall shear stress were found along the both sides of the elbow, and wall shear stress along the elbow intrados is proportional to the length of straight pipe, wall shear stress along the both sides of elbow is inverse proportion to the length of straight pipe. When the eccentric reducing elbow straight pipe length is 200mm, wall shear stress variation as follows:reducer diameter ratio is between 1?1.7, wall shear stress along the elbow intrados is inverse proportion to the reducer diameter ratio. Reducer diameter ratio higher than 1.7, wall shear stress along elbow intrados keep stable. Wall shear stress along both sides of the elbow is inverse proportion to the reducer diameter ratio. Wall shear stress along both sides of elbow keep stable when the reducer diameter ratio between 1?1.7.When the reducer diameter ratio higher than 1.7, wall shear stress along both sides of elbow is proportional to the reducer diameter ratio. When the reducer diameter ratio is lower, the maximum wall shear stress in concentric reducing elbow occurs along the elbow intrados and the section near 45°,135° of the outlet straight pipe. When the reducer diameter ratio is higher, the maximum wall shear stress in concentric reducing elbow occurs along the upper half of the straight pipe after the reducer and the extrados of the outlet regions.Finally, naphthenic acid flow-induce corrosion model was established combined with the fluid flow, mass transfer and chemical reaction three different physical-chemical process in this thesis. A prediction was made for the eccentric reducing elbow corrosion rate by using this model and to verify the practicable of the model.