Screening And Study On Corrosion Inhibition Mechanism Of New Corrosion Inhibitor For Natural Gas Pipeline Steel In HCL Pickling Medium

For natural gas gathering and transportation pipelines,Ca CO₃ composition accounts for the majority of scale formation,which seriously affects the safe and efficient operation of the natural gas gathering and transportation system.In practical situations,HCl and H₂SO₄ acid pickling are usually used for descaling treatment.In the process of descaling,the pickling solution also has obvious corrosion effect on the pipeline,and the service time of the pipeline will be shortened.At present,there is a high cost-effective way of reducing its corrosion to add a certain buffer to the descaling solution.Because the reaction principle between low Cr steel and inhibiter is very complex,if the application is not reasonable,the generation of micro galvanic cells will accelerate the corrosion,resulting in very serious safety and economic problems.At present study of low Cr pipeline steel especially for 3Cr and 5Cr steel acidification corrosion inhibitor and acidification technology is relatively less,the corrosion inhibition behavior of HOAT on the surface of X60 pipeline steel was first studied,then the possible adsorption centers of straight organic small molecules containing S and O on the surface of 3Cr steel were analyzed and discussed,and finally the corrosion inhibition performance and adsorption mechanism of two drugs for treating various diseases as environmentally friendly corrosion inhibitors for 5Cr pipeline steel were developed and studied.1)1-hydroxy-7-azabenzotriazole derivatives were screened and studied by experimental methods.The corrosion inhibition performance of HOAT for X60 Pipeline Steel in 1 M HCl solution was studied.The inhibition behavior of HOAT on the surface of X60 steel was studied by potentiodynamic polarization curve,impedance spectroscopy,weight loss method and morphology observation.It was confirmed by weight loss method that the inhibition effect of HOAT on X60 steel surface was enhanced with the increase of HOAT content.However,it is inversely proportional to the temperature factor,that is,the corrosion inhibition effect decreases with the increase of temperature.In addition,HOAT is also a kind of inhibitor.The adsorption mechanism of HOAT on the outer layer of X60 steel also belongs to the category of chemisorption and satisfies the Langmuir model.Finally,the adsorption mechanism of HOAT on the surface of X60 pipeline steel is discussed by Quantum Chemistry Method.2)DBP of 3,3'-dihydroxylinolenic acid was screened.The corrosion inhibition performance of 3,3'-dihydroxylinolenic acid for 3Cr steel in a certain solution environment and its inherent principle are studied by experiment and theoretical calculation.Combined with the experimental polarization curve,it can be observed that the corrosion inhibition efficiency of 3,3'-dihydroxylinic acid for 3Cr steel in hydrochloric acid solution can reach 85%at 298 K with 5 m M concentration.In addition,with the increase of temperature,the corrosion inhibition ability of 3,3'-dihydroxylinolenic acid for 3cr steel in acidic environment decreased to a certain extent.When the ambient temperature was raised to 318 K,the corrosion inhibition efficiency of 3,3'-dihydroxylinic acid was 71.6%.Therefore,it can be concluded that increasing temperature is not conducive to the formation of a stable protective film on the surface of 3Cr steel.Scanning electron microscopy(SEM)and atomic force microscopy(AFM)tests show that 3,3'-dihydroxylinolenic acid can effectively slow down the corrosion of3cr steel in hydrochloric acid solution.Combined with the corresponding isothermal model,it can be realized that the adsorption mechanism of this component in the outer layer of 3cr steel satisfies Langmuir process,and the value of Gibbs free energy of adsorption is-29.9 k J/mol,which indicates that the adsorption change of this component in the outer layer of 3Cr steel can be promoted spontaneously,and the reaction changes of physical and chemical aspects are confirmed.In addition,molecular dynamics simulation shows that 3,3'-dihydroxylinolenic acid has good corrosion inhibition performance for 3Cr steel.3)The corrosion inhibition effect of CLP as an environmentally friendlyinhibition on 5Cr steel surface in 1 M hydrochloric acid solution was investigated by means of electrochemical test,immersion experiment,scanning electron microscope observation and theoretical calculation.The electrochemical results showed that there is a down-regulation corrosion effect for 5Cr steel with CLP in hydrochloric acid environment.The electrochemical results show that CLP can delay the corrosion process of 5Cr steel in solution environment to a great extent.At this time,the retarding effect is proportional to the content of CLP.According to the experimental study,the most ideal inhibitor efficiency can be achieved 92.4%.In addition,SEM results further support the conclusion of electrochemical test.According to quantum chemical calculation and molecular dynamics simulation,CLP molecules,CLP molecules under solvation conditions,CLPH⁺and CLPH⁺molecules under solvation conditions have lower energy gap values and higher dipole moment values,and can be adsorbed almost flatly on the surface of 5Cr steel.This means that CLP molecules can provide efficient protection for 5Cr steel under different conditions.In addition,the protonated clozapine molecule and the solvated clozapine molecule have better theoretical parameter values,which indicates that they can provide more efficient protection for the corrosion inhibition of 5Cr steel.4)The corrosion inhibition ability of metodazole for 5Cr steel in hydrochloric acid is confirmed by means of ectrochemical test,immersion test,observation tests by canning electron microscope and theoretical calculation,and the possible inhibition mechanism was also revealed.According to the electrochemical impedance test,the maximum corrosion inhibition efficiency can reach 94.4%.The results of immersion experiment are highly consistent with the results of SEM and electrochemical test.From the theoretical calculation results,it can be found that neutral conditions and protonated metodazole molecules have higher energy gap and lower dipole moment in solvated and unsolvated environments,and both can be adsorbed on the metal surface in parallel,which is also corresponding to its efficient corrosion inhibition performance.In addition,by comparison it is found that under the solvation condition,the protonated metodazole molecule has the highest binding energy,which is the easiest to react with 5Cr steel and presents the optimal inhibition performance.The molecular of metodazole in the state has more excellent theoretical parameter,which indicates that it can provide more efficient protection for the inhibition of corrosion of 5Cr steel.