Evolution of dissolution process at the interface of carbon steel corroding in a CO2 environment studied by EIS,”

a b s t r a c t The evolution of interfacial phenomena during CO 2 corrosion of C1018 carbon steel was characterized by EIS (Electrochemical Spectroscopy Impedance) and LPR (Linear Polarization Resistance). Turbulent conditions were simulated by a channel flow cell with deoxygenated 3 wt.% NaCl solution at 80°C and pH 6 during 158 h. EIS helped in the characterization of the dynamic mechanism during the formation of the unprotective porous Fe 3 C layer, and subsequent precipitation of the protective FeCO 3 layer inside the cementite. The experimental response of the active states at the interface was characterized by electrical passive elements with constant phase parameter analogs showing good agreement with the experimental results

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Licenciatura en Educació

The Influence of pH on localized corrosion behavior of X65 Carbon Steel in CO2-Saturated Brines

Pitting and localized corrosion of carbon steel is considered to be a complex process influenced by a wide range of parameters such as temperature, bulk solution pH and chloride ion concentration. Solution pH is known to influence corrosion product characteristics and morphology in CO2 and H2S-containing corrosion systems. However, from the perspective of pitting corrosion in CO2-saturated environments, the extent to which bulk pH of solutions and the presence of corrosion products influence localized attack is still not clearly understood. This paper presents an investigation into the role of pH on the characteristics of corrosion product and pitting corrosion behavior of X65 carbon steel in CO2-saturated brine. Pitting corrosion studies were conducted over 168 hours at 50°C in 3.5 wt.% NaCl solutions at different bulk pH (buffered to pH values of 6.6 and 7.5 in some cases) in order to understand and correlate the role of pH on corrosion product morphology, chemistry, initiation and propagation of pits within each distinct environment. Corrosion product composition and morphology are identified through a combination of electrochemical and surface analysis techniques, which include Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The extent of corrosion damage of the carbon steel is evaluated through the implementation of surface interferometry to study discrete pit geometry; namely, the size, depth and aspect ratio. Results indicate that the process of pit initiation and propagation of carbon steel in CO2 corrosion environment is different depending upon bulk solution pH. At low pH (pH values starting at 3.8), pitting initiates faster and propagates steadily along with significant uniform corrosion due to the formation of ‘amorphous’ form of FeCO3. At higher pH, uniform corrosion is significant, while pitting initiates with increasing protection from crystalline FeCO3. At a pH value of 7.5, pitting corrosion initiation occurs after and/or during pseudo-passivation is achieved due to the formation of a ‘protective and pseudo-passivating’ FeCO3 film

Corrosion inhibition of carbon steel in chloride solutions by some amino acids

The corrosion inhibition of carbon steel was investigated in stagnant naturally aerated chloride solutions using amino acids as environmentally safe corrosion inhibitors. The corrosion rate was calculated in the absence and presence of the corrosion inhibitor using the polarization technique and electrochemical impedance spectroscopy. The experimental impedance data were fitted to theoretical data according to a proposed electronic circuit model to explain the behavior of the alloy/electrolyte interface under different conditions. The corrosion inhibition process was found to depend on the adsorption of the amino acid molecules on the metal surface. Cysteine, histidine, phenylalanine and arginine have shown remarkably high corrosion inhibition efficiency. The corrosion inhibition efficiency was found to depend on the structure of the amino acids. The mechanism of the corrosion inhibition process is based on the adsorption of the amino acid molecules on the active sites of the metal surface. Results obtained from potentiodynamic polarization indicated that the inhibitors are mixed-type inhibitor

A FORMAÇÃO DA CAMADA PROTETORA DE FeCO3 E O CONTROLE DA CORROSÃO POR CO2 EM CONDIÇOES DE FLUXO TURBULENTO

The formation of a protective layer of iron carbonate (FeCO3) can reduce the rates of corrosion and prolong the useful life of carbon steel. However, turbulent flow conditions in this layer can easily be damaged and thus compromise the protection of the steel. In this work, will be presented a methodology based on the chemical aspects of the mechanism of formation of iron carbonate layer in a Thin Channel Flow Cell (TCFC). Electrochemical techniques were used to measure the corrosion rate and corrosion potential on the surface of steel API X65 exposed to aqueous solution of 1 wt.% NaCl purged with CO2 at 2 atm, pH 6.6 and 80°C in turbulent flow conditions. The surfaces and cross sections of the samples were characterized by means of Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDS) analysis. The results confirm the nucleation and growth of iron carbonate layer: the extension of supersaturation of the solution and the corrosion rate have decreased, and the corrosion potential has increased. The surface analysis showed dense and uniform FeCO3 layer with c.a. 20 µm thick after 120 hours in turbulent flow conditions

The influence of SO₂ on the tolerable water content to avoid pipeline corrosion during the transportation of supercritical CO₂

A systematic study is undertaken to establish the influence of sulphur dioxide (SO2) concentration on the critical water content required to avoid substantial levels of internal corrosion during the transport of supercritical CO2 for carbon capture and storage (CCS) applications. Corrosion experiments were performed on X65 carbon steel in autoclaves containing supercritical CO2 at 80 bar and 35°C in the presence of 0, 50 and 100 ppm (mole) SO2. General and localised corrosion rates were determined over a period of 48 hours through the implementation of gravimetric analysis and surface profilometry, respectively. Analysis of corrosions products formed on the steel surface was performed using x-ray diffraction, Raman spectroscopy and scanning electron microscopy. The results indicate that the presence of SO2 reduces the critical water content required to maintain a general corrosion rate below 0.1 mm/year. Furthermore, the water content required to avoid excessive localised corrosion is far less than that to prevent significant general corrosion. Localised corrosion rates close to 1 mm/year were observed in the absence of SO2 when the CO2 system was water-saturated, but below water contents of ~1800 ppm (mole) and ~500 ppm, general and localised corrosion rates (respectfully) were found to be below 0.1 mm/year even in the presence of 100 ppm SO2. The research presented highlights that reducing water content is a more favourable option compared to reducing SO2 content to minimise internal pipeline corrosion during transportation. Consideration is also afforded to the consumption of impurities in the closed system experiments