Study Of Corrosion On X80 Steel Under Gas-liquid Two-phase Flow

In the process of natural gas gathering,pipelines often face local corrosion failure risks by erosion of corrosive gas and water two-phase flow.This paper is mainly focused on X80 steel and revolves around carbon dioxide gas and water two-phase flow.The corrosion condition of local area in the horizontal pipe was studied and the corrosion mechanism was analyzed to provide guidance for further corrosion research work and protection in the gathering pipelines.During the research process,a set of device that was able to conduct a series of experiments under gas-liquid two-phase flow in the atmosphere of carbon dioxide was designed and constructed.And the liquid film was in a state of dynamic balance.Conductance probe was used to measure the thickness of liquid film and the wave evolution was simulated by FLUENT.On the basis of above study,wire beam electrode(WBE)was used to get the corrosion information and FEI Nova Nano-SEM 450 was used to get the microstructure on the surface of the electrodes.This paper studied the influence of liquid film and gas velocity on corrosion in the pipes under different liquid holdups.Furthermore,the corrosion information at two different angles circumferentially along the cross-section of the horizontal pipe was measured after rotating the pipe(15°&30°).According to the results,mass transfer happens not only on the gas-liquid interface but also occurs when the wave crest of liquid phase is cut into the gas core.The liquid film is in a state of flow and wave motion coupled with the erosion caused by a higher gas velocity.All of these have influence on the mass transfer and internal corrosion process.Specifically:(1)In the horizontal pipe,the liquid film thickness gets thinner with the increase of gas velocity.The film thickness in the semi-circle pipe is obviously thinner than that in the circle pipe.Also,the liquid film distribution is approximately in a crescent shape,tending to the double-circle model.(2)Migration of the anode region also exhibits certain regularity under certain range of the liquid film thickness.Main anode areas tend to generate where the liquid film is the thinnest.(3)Corrosion circumferentially along the pipe at different angles is not the same,which is mainly related to the difference of liquid film distribution.Attention should be paid on local corrosion of the side wall when there are liquid accumulations.(4)In the experimental pipes,the corrosive gases are more likely to diffuse in the region where the liquid film is thinner.The distribution properties of the liquid film also play an important role in the corrosion process of the liquid/solid interface.(5)In the flow state,thickness of liquid film and gas speed is influenced by each other.There exists a critical liquid thickness range(0.5mm~5mm).When the film thickness is thinner than 0.5mm or higher than 5mm,uniform corrosion will happen.