Study On Corrosion Behavior Of HP13Cr Stainless Steel Under Synergistic Action Of Diamond-Like-Carbon Film And Corrosion Inhibitor

HP13Cr stainless steel has high hardness,high wear resistance and excellent resistance to deformation.It is one of the most commonly used materials in the field of oil production and pipeline transportation in the oil and gas field industry.However,in the harsh environment of oil and gas fields,high concentrations of Cl^-will increase the local corrosion sensitivity of stainless steel,thereby reducing the service life of pipeline steel,and ultimately leading to serious economic losses and safety accidents.Therefore,how to improve the service life of stainless steel in the harsh environment of oil and gas is one of the problems to be solved,which is the key to realizing the economy and reliability of the oil and gas industry.In this thesis,Nitrogen-doped diamond-like carbon（N-DLC）films were doped on the surface of HP13Cr stainless steel by plasma-enhanced chemical vapor deposition.The effects of different nitrogen-doped amounts on the composition,structure and corrosion behavior of the films were studied.In addition,tea polyphenols were extracted from tea as corrosion inhibitors,and the effect of tea extract addition on the corrosion inhibition efficiency of HP13Cr stainless steel was investigated.The effects of DLC films and corrosion inhibitors on the corrosion behavior of HP13Cr stainless steel were investigated by Atomic force microscopy,Infrared spectroscopy,Raman spectroscopy,X-ray photoelectron spectroscopy,potentiodynamic polarization curves,electrochemical impedance spectroscopy,electrochemical noise,corrosion thermodynamics calculation,Frumkin isothermal adsorption calculation,Hurst index calculation and other techniques,and the related mechanism was discussed.The main results are as follows:The addition of nitrogen can significantly reduce the size and number of defects in DLC films,thereby improving the corrosion resistance of HP13Cr stainless steel.The corrosion current density of DLC film doped with 5sccm（Standard-state Cubic Centimeters per Minute）nitrogen in 3.5 wt.%Na Cl solution is 6.46×10^-9A/cm²,which is one order of magnitude lower than that of DLC film without nitrogen doping.However,the incorporation of excessive nitrogen will increase the number of C-N sp²bonding in the film,so the corrosion rate is significantly accelerated.After long-term exposure to Na Cl solution,the dissolution of hydrogen and nitrogen ions in the N-DLC film will lead to the change of the micro-area water chemical environment in the pores of the film,which will change the structure and composition of the film.The durability of N-DLC film with a nitrogen content of 10 sccm is the highest.Tea extract has an obvious corrosion inhibition effect on the corrosion process of HP13Cr stainless steel in the Na Cl solution.As the concentration of tea extract increased from 0.1 g/L to 0.3 g/L,the molecules of corrosion inhibitors were the mutual attraction,the coverage of corrosion inhibitors increased,and the corrosion inhibition efficiency increased from 17.24%to 62.07%.When the concentration of tea extracts increased to 0.4 g/L and 0.5 g/L,the corrosion inhibitor molecules mainly showed mutual exclusion,resulting in the desorption of the covered corrosion inhibitor molecules on the metal surface,the coverage of the corrosion inhibitor decreased significantly,and the corrosion inhibition efficiency decreased.When the concentration was 0.5 g/L,the corrosion inhibition efficiency decreased to 10.35%.The model established based on this study can effectively clarify the relationship between the healing time of scratched DLC film and the incubation period of localized corrosion.Under the action of corrosion inhibitor,the scratched DLC film on the surface of HP13Cr stainless steel can be healed in 3.5 wt.%Na Cl solution for about 10 h.The incubation period before pitting corrosion of DLC film scratch is about 40 h,and the self-healing time of DLC film is less than that of local corrosion.The corrosion inhibitor can repair the scratched area of DLC film before pitting occurs,avoid the occurrence of severe local corrosion at the scratched area,and improve the service life of HP13Cr stainless steel.