Study On The Effect Of Nitrogen And Phosphorus In Water Inorganic Salt On The Corrosion Of Carbon Steel X70

At present,one of the prime reasons of eutrophication of water in our country is the excessive of nitrogen and phosphorus.At the same time the oil and gas storage and transportation will often be used in the eutrophic water environment.This paper analyzed the effects of eutrophication on pipeline steel from the angle of the corrosion and chose phosphorus salts of typical and X70 steel commonly used steel as the research subject.By using electrochemical impedance spectroscopy,polarization curve,loss-weight method,corrosion morphology observation and product analysis this paper studied the effect of inorganic nitrogen and phosphorus salt the corrosion of X70 carbon steel from different aspects.The results are as following:?1?The results of the weight loss method show that the corrosion inhibition of X70 steel is more obvious with the increase of nitrogen and phosphorus concentration;?2?It was found that the corrosion degree of carbon steel in nitrogen and phosphorus inorganic salt solution was significantly different from the increase of solution concentration and forming the corrosion layer with different morphologies;?3?The AC impedance spectrum and polarization curve test showed that the inhibition effect of nitrogen and phosphorus in water environment of inorganic salts on carbon steel have different degrees of inhibition,size: nitrogen: NaNO₂ > NaNO₃ >?NH₄?₂SO₄,phosphorus: Na₂HPO₄ > NaH₂PO₄ > Na₃PO₄;?4?The analysis showed that the product?NH₄?₂SO₄ could make the corrosion product more compact by promoting Si and Ca oxides forming;NaNO₂ and NaNO₃ not only can promote Si and Ca oxide formation,but also can accelerate the formation of dense iron oxide product film on the surface of carbon steel,but the NaNO₂ stronger;phosphate salt by corresponding crystallization on the carbon steel surface adsorbed on the surface of carbon steel,corrosion inhibition,and meantime NaH₂PO₄ can promote Ca oxide formation to increase the surface of carbon steel corrosion film thickness of corrosion inhibition.The results of this paper can not only provide a reference for the safety of oil and gas storage and transportation equipment,but also provide a theoretical basis for anti-corrosion of carbon steel.