Research On The Protection Of Corrosion Inhibitor For J55 Oil Pipeline Steel Corrosion Against Crevice Corrosion

Multi-phase flow involving oil with high content of S2-,Cl-,water and sand can cause corrosion to oil pipes,storage containers and separation equipments easily.Moreover,crevice corrosion of connection devices,scouring abrasion of equipments by sands which can deposit to form scale leading to pipe plugging are often encountered in flow lines of oil exploitation.To address the above severe problem,both water-solubility and oil-solubility inhibitors imidazoline salt(MQ)and quinoline salt(QA)were screened out.The inhibition efficiency(IE)was studied by weight loss method,electrochemical method,crevice simulation and scratching method.The inhibition effect and mechanism of the inhibitors against crevice corrosion in experimental solution were investigated by crevice simulation.The kinetic equation for film growth of inhibitor was derived from current-time curve through scratching method.The equivalent circuit of inhibitor film which clarifies the reason that the inhibition efficiency cannot realize 100%was modeled through electrochemical impedance spectroscopy(EIS).Based on the features such as anodic polarization and fast absorption for inhibitor,itsfunction of dispersing solid particles was investigated.Additionally,a formulation of complex inhibitor possessing functions of preventing oil pipeline from corrosion and scale formation was screened out by orthogonal experimental method.The results show that:(1)For severe corrosion,crevice corrosion and sediment in oil exploration because of high content of S2-,Cl-,H+.The good corrosion of inhibition imidazoline quaternary ammonium salt corrosion inhibitors(MQ)and quinoline quaternary ammonium salt corrosion inhibitors(QA)was synthesized,and its structure was characterized by FT-IR.(2)The corrosion inhibition efficiency was studied in the simulated corrosion medium(5wt%NaCl+0.5wt%CH3COOH saturated H2S solution).At 30?,imidazoline inhibitor MQ when adding 0.4wt%J55 oil pipe steel corrosion rate is 0.0324mm.a-1.At 90?,adding 0.5wt%corrosion inhibitor,corrosion rate of J55 steel oil pipe 0.0635mm.a-1.At 30? when quinoline quaternary ammonium salt corrosion inhibitor(QA)concentration of 0.7wt%,the corrosion rate of J55 steel decreased from 2.2530mm.a-1 to 0.0586 mm.a-1,the inhibition rate was 98.4%;At 90?,adding 0.7wt%quinoline quaternary ammonium salt corrosion inhibitor(QA)can decrease the corrosion rate of J55 oil pipe dropped from original 3.2568mm.a-1 to 0.0625 mm.a-1,the inhibition rate was 98.08%.The corrosion rate was less than 0.076mm.a-1 for the industry standard requirements of the petroleum industry,belongs to the scope of corrosion resistance.The MQ is an anodic-type inhibitor while the QA is a mixed-type inhibitor,and their inhibition mechanism for J55 steel can be fitted by Langmuir isotherm equation.The activation energyvalues of corrosion reaction for the both inhibitors to J55 steel are positive,which means that the apparent absorption of the inhibitors corresponds to an exothermic process,so the higher the temperature,the smaller the absorption capacity and the lower efficiency of corrosion.(3)The crevice corrosion protective performance and its mechanism were studied in 0.5 wt%NaCl+0.5wt%CH3COOH solution saturated by H2S using by aperture inner corrosion evaluation device.The results show that with MQ or QA inhibitor addition in the experimental solution,the inhibitor can diffuse into simulated crevice andis contained into the crevice,thus the pH value of the crevice increases andCl-/S2-concentration decrease.The higherthe concentration of MQ or QA inhibitor in the experimental solution,the larger the pH value and the lower the Cl-/S2-concentration in the crevice.With 0.5wt%MQ or 0.7wt%QA addition,the pH value and Cl-/S2-concentration of the crevice become the same as that of the solution outside crevice after 72 hours,as a result,the problem of occluded cell accelerating corrosion caused by crevice is reasonably solved.The MQ or QA inhibitor diffusing into the crevice forms passive film on the surface of material inside the crevice by physical absorption,so that the corrosion current remains unchanged over time to make a small electrochemical noise.The passive film possesses higher surface resistance and lower capacitance than bare metal,and the higher surface resistance effectively prevents the corrosion of metal inside the crevice,however,the lower capacitance restricts theIE to realize 100%.Both MQ and QA have incredibly fast absorption rate,and the higher inhibitor concentration,the faster formation rate of the passive film through absorption.With 0.1 wt%MQ addition,it takes 41s to form absorption passive film,and with continuous increase of MQ to 0.2wt%,merely 20s is needed.As for QA,it has a relatively faster absorption rate so that less than 10s is spent.(4)The scratch method as the research techniques,through electrochemical measurements,the growth speed of membrane was studied,and the protective mechanism of corrosion inhibitor and corrosion inhibitor film dynamics process was illuminated.The kinetic equation for film growth of MQ and QA inhibitor are described as follows:r=2.05×10-4exp(13.452×103/RT)and r=1.47×10-2 exp(8.674×103/RT)respectively.The film-formation frequency factor of QA inhibitor is 1.47×10-2s and that of MQ inhibitor drops two orders of magnitude,which makes a faster film-formation rate for the QA inhibitor.The activation energy for film-formation of MQ inhibitor is-13.452kJ that is lower than-8.647kJ of QA inhibitor,implying that MQ inhibitor can produce a more compact passive film.(5)The prevention and control of particle reunionabout imidazoline corrosion inhibitor(MQ)was studied by the means of gravity sedimentation,it can provide the basis in order to prevent the pipelineabout small and medium-sized sand deposit together 0.5 g of CaCO3 and SiO2 was added into the 1L waterof Jingbian Oil Production Plant(CaCO3:SiO2 mass ratio of 1:2,median particle size of 4?m).The experimental results show that MQ(0.2wt%?0.4wt%)inhibitor is capable of dispersing small particles into the experimental solution well and pceventing aggregation.The orthogonal experiment results showed that 0.2wt%cniathylenetriaminepentaacetic acid(DTPA),0.3wt%imidazoline and the stirring time were 10min,which could make the corrosion inhibitor have good dispersing performance.Experiments were carried out on 100%(100 wt%imidazoline).The experimental results show that 0.2 wt%DTPA and 0.3wt%MQ can play a good anti-corrosion scale effect by the simulated rest device.