The effect of H_2S on the corrosion behavior of 316 L stainless steel was investigated using electrochemical methods by changing the gas condition from CO_2 to H_2S and then back to CO_2. The presence of H_2S showed a...The effect of H_2S on the corrosion behavior of 316 L stainless steel was investigated using electrochemical methods by changing the gas condition from CO_2 to H_2S and then back to CO_2. The presence of H_2S showed an acceleration effect on the corrosion of 316 L stainless steel in comparison with CO_2. The acceleration effect remained even after the complete removal of H_2S by CO_2, indicating that the passive film was irreversibly damaged. X-ray photoelectron spectroscopy(XPS) analysis indicated that the passive film was composed of Cr_2O_3, Fe_2O_3, and FeS_2 after being immersed in H_2S-containing solutions. The semiconducting property of the passive film was then investigated by using the Mott–Schottky approach. The presence of sulfides resulted in higher acceptor and donor densities and thus was responsible for the deterioration of passive films.展开更多
Herein, the effect of high chloride ion(Cl^-) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO_2 environment was demonstrated. The Cl^- concentration was ...Herein, the effect of high chloride ion(Cl^-) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO_2 environment was demonstrated. The Cl^- concentration was varied from 30 to 150 g/L and cyclic potentiodynamic polarization was conducted to investigate the influence of the Cl^- concentration on the corrosion potential(E_(corr)), passive breakdown potential(E_(pit)), and repassivation potential(E_(rep)). The results of the polarization curves revealed that 13Cr stainless steel is susceptible to pitting under high Cl^- concentration. The passive breakdown potential and repassivation potential decreased with the increase of Cl-concentration. The semiconducting behavior of the passive film was investigated by Mott-Schottky analysis and the point defect model(PDM). It was observed that the iron cation vacancies and oxygen vacancies were continuously generated by autocatalytic reactions and the higher Cl^- concentration resulted in higher vacancies in the passive film. Once the excess vacancies condensed at the metal/film interface, the passive film became locally detached from the metal, which led to the breakdown of the passive film.展开更多
When DC ground electrode of a high-voltage direct current(HVDC)transmission system is in the stage of early operation or in the case of failures and maintenance,an instantaneous large current will be generated and bri...When DC ground electrode of a high-voltage direct current(HVDC)transmission system is in the stage of early operation or in the case of failures and maintenance,an instantaneous large current will be generated and bring great potential safety hazards to the nearby buried oil/gas pipelines and facilities and operators.In order to ensure the safety of persons near the buried pipelines,we investigated the current interference of the HVDC ground electrode to buried pipelines and its personal safety distance(hereinafter referred to as a safety distance).Firstly,the model simulating the electromagnetic interference to buried pipelines was established by means of the numerical simulation technology.Then,the model was used to calculate the safety distance corresponding to eddy current interference of HVDC ground electrode to buried pipelines under different soil resistivities,pipeline lengths,pipeline anti-corrosion insulations,earth currents of ground electrode and pipeline sizes.Finally,the influence laws of above-mentioned factors on the interference degree of HVDC ground electrode were analyzed.And the following research results were obtained.First,the influence of pipeline length on the interference degree of interference of the HVDC ground electrode is great.The longer the pipeline,the greater the safety distance.When the pipeline is equal to or longer than 600 km,however,the safety distance is basically the same.Second,the effect of pipeline coating on the interference degree of HVDC ground electrode is great.As the coating surface resistivity increases,the safety distance increases gradually.Third,for multi-layer soil structures,the maximum single-layer resistivity can be taken as the overall resistivity.And correspondingly,the calculated safety distance obtained is the longest,and the evaluation result is more conservative.In conclusion,the safety distance diagrams of the pipelines with 4 lengths which are obtained based on the calculation results can be used as reference in the design of HVDC ground electrodes and pipelines,as well as the basis for selecting the safety distance of HVDC ground electrode or buried pipeline to be constructed.展开更多
基金financially supported by the National Natural Science Foundation of China (No.51271025)the Beijing Higher Education Young Elite Teacher Project
文摘The effect of H_2S on the corrosion behavior of 316 L stainless steel was investigated using electrochemical methods by changing the gas condition from CO_2 to H_2S and then back to CO_2. The presence of H_2S showed an acceleration effect on the corrosion of 316 L stainless steel in comparison with CO_2. The acceleration effect remained even after the complete removal of H_2S by CO_2, indicating that the passive film was irreversibly damaged. X-ray photoelectron spectroscopy(XPS) analysis indicated that the passive film was composed of Cr_2O_3, Fe_2O_3, and FeS_2 after being immersed in H_2S-containing solutions. The semiconducting property of the passive film was then investigated by using the Mott–Schottky approach. The presence of sulfides resulted in higher acceptor and donor densities and thus was responsible for the deterioration of passive films.
基金financially supported by the National Science and Technology Major Project of China (No. 2016ZX05028-004)
文摘Herein, the effect of high chloride ion(Cl^-) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO_2 environment was demonstrated. The Cl^- concentration was varied from 30 to 150 g/L and cyclic potentiodynamic polarization was conducted to investigate the influence of the Cl^- concentration on the corrosion potential(E_(corr)), passive breakdown potential(E_(pit)), and repassivation potential(E_(rep)). The results of the polarization curves revealed that 13Cr stainless steel is susceptible to pitting under high Cl^- concentration. The passive breakdown potential and repassivation potential decreased with the increase of Cl-concentration. The semiconducting behavior of the passive film was investigated by Mott-Schottky analysis and the point defect model(PDM). It was observed that the iron cation vacancies and oxygen vacancies were continuously generated by autocatalytic reactions and the higher Cl^- concentration resulted in higher vacancies in the passive film. Once the excess vacancies condensed at the metal/film interface, the passive film became locally detached from the metal, which led to the breakdown of the passive film.
基金Project supported by the Research and Technology Development Project of PetroChina Company Limited"Research and Development of Key Tech-nologies for Safety and Environmental Protection e Research and Application of Risk Prevention and Control Technology for High-Voltage Direct Current Regional Pipelines"(No.:2016D-4602).
文摘When DC ground electrode of a high-voltage direct current(HVDC)transmission system is in the stage of early operation or in the case of failures and maintenance,an instantaneous large current will be generated and bring great potential safety hazards to the nearby buried oil/gas pipelines and facilities and operators.In order to ensure the safety of persons near the buried pipelines,we investigated the current interference of the HVDC ground electrode to buried pipelines and its personal safety distance(hereinafter referred to as a safety distance).Firstly,the model simulating the electromagnetic interference to buried pipelines was established by means of the numerical simulation technology.Then,the model was used to calculate the safety distance corresponding to eddy current interference of HVDC ground electrode to buried pipelines under different soil resistivities,pipeline lengths,pipeline anti-corrosion insulations,earth currents of ground electrode and pipeline sizes.Finally,the influence laws of above-mentioned factors on the interference degree of HVDC ground electrode were analyzed.And the following research results were obtained.First,the influence of pipeline length on the interference degree of interference of the HVDC ground electrode is great.The longer the pipeline,the greater the safety distance.When the pipeline is equal to or longer than 600 km,however,the safety distance is basically the same.Second,the effect of pipeline coating on the interference degree of HVDC ground electrode is great.As the coating surface resistivity increases,the safety distance increases gradually.Third,for multi-layer soil structures,the maximum single-layer resistivity can be taken as the overall resistivity.And correspondingly,the calculated safety distance obtained is the longest,and the evaluation result is more conservative.In conclusion,the safety distance diagrams of the pipelines with 4 lengths which are obtained based on the calculation results can be used as reference in the design of HVDC ground electrodes and pipelines,as well as the basis for selecting the safety distance of HVDC ground electrode or buried pipeline to be constructed.
