Experimental Study On Erosion-Corrosion Behavior Of Pipeline Steel By Cl^-/HCO₃^- In Liquid-Solid Two-Phase Flow

In recent years,the total mileage of long-distance pipelines in my country has continuously broken new highs.X80 steel has the advantages of high strength,high toughness and high resistance to stress corrosion cracking,and is widely used in pipeline construction.At present,the exploration and development of oilfields is mainly based on water injection.The composition of the reinjection water is relatively complex.The medium contains not only sand,but also many salts,such as chloride and bicarbonate.Under such conditions,it is easy to induce erosion and corrosion damage of pipeline materials,resulting in failure of equipment and pipelines.In this paper,X80 steel is selected as the research object,and the erosion corrosion mechanism of X80 steel under dual ion environment is studied by observing surface morphology,measuring weight loss,electrochemical impedance spectroscopy and polarization curve.Firstly,the corrosion performance of X80 steel in different concentrations of sodium chloride and sodium bicarbonate mixed solution under static conditions was studied experimentally.The results show that in a single chloride ion environment,with the increase of chloride ion concentration,the thickness of the oxide layer generated on the surface of X80 steel gradually becomes thinner,and its corrosion resistance is weakened.In the dual-ion solution containing chloride ions and bicarbonate ions,the thickness of the oxide layer of X80 steel increases,and the corrosion resistance increases,indicating that the addition of bicarbonate ions has a certain protective effect on the material.Then,the effects of single chloride ion and bicarbonate ion on the scour corrosion performance of X80 steel were investigated.It is found that in the bicarbonate ion environment,the bicarbonate concentration has no significant effect on the erosion corrosion performance of X80 steel,while in the chloride ion environment,with the increase of the chloride ion concentration,the erosion corrosion mass loss increases significantly.Finally,the scour corrosion mechanism of X80 steel was studied in a dual-ion environment with different concentrations of chloride ions and bicarbonate ions.The results show that after adding different concentrations of bicarbonate to the chloride ion solution,the mass loss of X80 steel by scour corrosion is decreased.The mass loss of chloride ion mixed solution erosion corrosion decreased by 70%.In the analysis of synergistic effect,it was found that in the mixed solution of 0.75wt% bicarbonate and 1wt% chloride ion,the proportion of synergy was reduced to 2%.When there are both bicarbonate ions and chloride ions in the solution,the bicarbonate ions will be adsorbed to the surface of the material faster to form ferrous carbonate precipitation.The concentration is reduced,thereby slowing the erosion and corrosion damage of X80 steel by chloride ions.