CO2-containing Environment Research Articles

Flow-accelerated corrosion behavior of 13Cr stainless steel in a wet gas environment containing CO2

This work investigated the flow-accelerated corrosion (FAC) behavior of 13Cr in a wet CO2-containing environment at different flowing gas velocities and impinging angles, with the natural-gas pipeline environment simulated by a self-assembled impingement jet system. Surface morphology determination, electrochemical measurements, and hydromechanics numerical analysis were carried out to study the FAC behavior. The results demonstrate that pitting corrosion was the primary mode of corrosion in 13Cr stainless steel. High-flow-rate gas destroyed the passive film and decreased the pitting potential, resulting in more serious corrosion. The corrosion degree with various impact angles showed the following order: 90° > 60° > 45°. The shear force and the electrolyte from the flowing gas were concluded to be the determinant factors of FAC, whereas the shear force was the main factor responsible for destroying the passive film.

Corrosion Behavior of 3% Cr Casing Steel in CO2-Containing Environment: A Case Study

Introduction:The production casing of 3% Cr steel has encountered severe internal corrosion in Huizhou Oilfield. To disclose corrosion behavior of inner casing, a series of corrosion exposure tests were systematically conducted on 3% Cr coupons in terms of in-field conditions.Material and Methods:Influence of exposure time, temperature, and water-cut on the CO2corrosion of 3% Cr steel was investigated, and analyses on weight loss, composition and morphology of corrosion product, and Tafel polarization curves were further carried out.Result:The results showed that the corrosion rate of 3% Cr steel increased with increasing temperature, but such trend descended when the temperature exceeded 65°C due to formation of an compact and adherent corrosion product film on the surface of 3% Cr coupons. While varying exposure time from 7 days to 14 days, the corrosion rate decreased, and the Cr and O enrichment was determined in the corrosion products. The corrosion rate of 3% Cr steel increased with a continuous increment of water-cuts, especially when the water-cut was larger than 40%.Conclusion:The localized corrosion can happen at the lower water-cut due to the presence of amorphous films. The main corrosion products were FeCO3, Cr5O12, Fe2O3, and Fe-Cr. Entry of CO2to the simulated formation water caused an increase in the anodic Tafel slope, and accelerated dissolution of 3% Cr steel.

Study on the corrosion behaviours of API X65 steel in wet gas environment containing CO2

ABSTRACTAn impingement jet system was used to study the corrosion of API X65 steel in a wet CO2-containing environment via electrochemical tests, surface analysis technique and computational fluid dynamics simulation. The corrosion rate decreased in the wet environment compared to that in the bulk solution. When under flow condition, corrosion rate increased with the flowing velocity, especially when above the critical flowing velocity. Continuous electrolyte film was formed and electrochemical reaction started to occur in about 70% RH, and the critical RH appeared at 70–80%, above which pit size and amount remarkably increased with flow velocity.

Galvanic corrosion of a welded joint in 3Cr low alloy pipeline steel

The corrosion behavior of a semi-automatic gas tungsten arc welded joint in 3Cr steel was investigated in a CO2-containing environment. Assessment of the galvanic corrosion interactions of the different regions in the joint was carried out through microelectrochemical measurements and immersion tests. The weld zone (WZ) was determined to be the most cathodic region while the base metal (BM) was the most anodic region. The heat affected zone (HAZ) underwent little galvanic interaction, as its free potential was close to the coupled potential. The galvanic coupling effects theoretically derived from the corrosion current densities before and after coupling were in good agreement with the results of the immersion tests.

Effect of Cr content on the corrosion performance of low-Cr alloy steel in a CO2 environment

Low-Cr alloy steel demonstrates lower corrosion rate than does C steel in a high-temperature and high-pressure CO2-containing environment. This study aimed to clarify the role of the Cr content in mitigating corrosion and reports the performance of 1%Cr, 2%Cr, 3%Cr, 4%Cr, 5%Cr, and 6.5%Cr steels. The results show that low-Cr alloy steel in CO2 at 80°C and 0.8MPa possesses spontaneous prepassivation characteristics when the Cr content is 3% or higher. Furthermore, the formation and peel-off of a prepassivation film on 3%Cr–6.5%Cr steels surfaces during polarization demonstrate that adequate amount of Cr in the steel substrate can cause protective layer. The main component of prepassivation film on 3%Cr steel is Cr(OH)3. Thus, the role of Cr is revealed. An adequate amount of Cr in the steel substrate causes the formation of protective Cr(OH)3 layer, which helps low-Cr steel to possess prepassivation characteristics. Prepassivation is the reason why low-Cr steel has a lower corrosion rate than C steel.

Comparative Study of BaY0.1Ce0.9O3-δ Membrane with BaY0.1Zr0.9O3-δ Protective Layers Synthesized with Spray Pyrolysis and Magnetron Sputtering Methods

Acceptor-doped perovskite-type oxides including BaY0.1Ce0.9O3- d (BYCO) are known for excellent proton conductivity under fuel cell operating conditions and applicable in electrolysers, reactors and sensors. However, chemical stability of this oxide is relatively poor. Originating from oxide’s high basicity BaCeO3 reacts easily with H2O and CO2, forming BaCO3, CeO2 and Ba(OH)2. At the same time zirconia based electrolyte, typically with high grain boundary resistance for protons, exhibit good chemical stability and seems to be attractive as chemical barrier layer for ceria based proton conductor. In this study, BaY0.1Zr0.9O3- d (BYZO) protective layers were synthesized onto BaY0.1Ce0.9O3- d substrate using spray pyrolysis and magnetron sputtering methods, and characterized using electrochemical and microstructural analysis methods. Stability tests at carbon CO2containing environment were conducted. Powder for BYCO substrate was prepared by ultrasonic spray pyrolysis method. Substrates were sintered at 1500 °C in powder bed and afterward polished to obtain flat surfaces, which were coated with BYZO protective layers. Dual layer electrolytes obtained were sintered at 1350 °C between BYCO pellets, then characterized with scanning electron microscopy, x-ray diffraction and FIB-TOF-SIMS methods. Electrochemical characterization was carried out at temperature range from 550 to 800 °C. Arrhenius plots with good linearity for four different systems (uncoated polished BYCO, uncoated unpolished BYCO, magnetron sputtered BYZO at BYCO and spray pyrolyzed BZYO at BCYO) were constructed and activation energies Ea were calculated. Lowest activation energy has been found for the polished uncoated substrate (0,35 eV). For the magnetron sputtered and spray pyrolyzed layers Ea values were 0,37 eV and 0,38 eV, respectively. Highest activation energy was observed for unpolished substrate (0,39 eV), suggesting barium ion deficit in the near-surface layer, which can be removed by polishing. Thus, BYZO films deposited increase slightly the activation energy values compared with non-coated membranes. As expected, total ionic conductivity differs greatly from polished to unpolished and from coated to non-coated membrane. Lowest conductivity was characteristic for uncoated polished membranes with the smallest surface area (also the smallest length of three phase boundary between electrolyte, platinum and gas phase) and highest conductivity was characteristic for uncoated unpolished membrane with the highest surface area. BYZO layer synthesized using spray pyrolysis gave worse conductivity compared with BYZO layer synthesized using magnetron sputtering. This is very likely caused by lower homogeneity and higher grain boundary resistance of the layer prepared using spray pyrolysis. In this study it has been demonstrated, that electrical conductivity depends on the microstructure of studied layers as well as on the interfacial structure of solid-gas-Pt boundary of the membrane. Protective BYZO layers significantly affected the time stability of the BYCO membrane in the CO2 containing environment.

Characterization of the Corrosion Layer on Pipeline Steel in Sweet Environment

CO2 corrosion, or ‘sweet corrosion,’ is the most prevalent form of attack encountered in oil and gas pipelines. Corrosion of carbon steel in CO2-containing environment is very complex and requires extensive attention. Various mechanisms have been proposed to explain the phenomenon. However, these mechanisms either apply to very specific conditions or have not received widespread recognition or acceptance. To establish a fundamental understanding of CO2 attacks on steel, it is essential to conduct further studies to investigate the formation, composition, microstructure, and characteristics of the surface film induced by carbon dioxide corrosion. In this study, corrosion behavior of API pipeline steel has been assessed in 2 g/l NaCl solution purged with CO2 as the corrosive media. Specimens were immersed in the corrosive solution (open system) for 15, 45, 100, and 185 h. In this study, scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were employed systematically to characterize the composition, microstructure, and formation of the surface film on API X42 steel.

Fabrication of Ni-BaZr0.8Y0.2O3-δ Composite Membrane for Hydrogen Separation

Hydrogen is an important raw material for production of ammonia, methanol, liquid hydrocarbons, etc. The application of membrane technology is expected to considerably reduce the capital and energy cost in hydrogen production. Composite membranes consisting of BaCeO3-based proton conductor and electronic conductor (e.g. nickel) have been developed for this application. However, these membranes (e.g. Ni–BaZr0.8–xCexY0.2O3–δ (Ni-BZCY), 0.4 ≤ x ≤ 0.8) suffered serious performance loss in CO2-containing environment at 900 oC due to the reaction between BaCeO3 and CO2.[ 1 , 2 ] In order to avoid the chemical stability issue of BaCeO3, CO2-tolerant hydrogen membranes have been developed, e.g., RE6WO12-δ (RE: rare earth metal), Ca-doped LaNbO4, Ce0.8Sm0.2O2-δ, and Ni-La0.4875Ca0.0125Ce0.5O2-δ. However, the permeation fluxes of those membranes are significantly lower than that of Ni-BZCY membranes due to their low proton conductivity and/or electronic conductivity. Among the proton conductors that are tolerant to CO2, BaZr0.8Y0.2O3–δ (BZY) possesses the highest bulk proton conductivity.[ 3 ]However, single phase BZY membrane shows very low hydrogen flux due to the relatively poor electronic conductivity. The low flux may be resolved in a similar way to Ni-BZCY membranes: combining BZY with highly electronic-conducting Ni to form Ni-BZY composite membrane. Ni-BZY membrane is expected to possess both high hydrogen permeation flux and chemical stability, which are the key factors for successful adoption of Ni-BZY hydrogen permeation membrane for practical applications. However, there has been no report on Ni-BZY composite membrane for hydrogen permeation study, probably due to the difficulty in obtaining dense membrane with large BZY grains. The sintering of Ni-BZY membrane needs to be performed below the melting point of Ni (~1453 oC). Unfortunately, due to the highly refractory nature, BZY samples prepared through the traditional solid state reaction method needs to be sintered at extremely high temperatures (1700-2100 oC) for a long time (24 h) to reach relatively high density. At a sintering temperature of 1400 oC, conventional solid state reaction method can only produce BZY with low relative density and small grain size. Moreover, BZY has a low grain boundary proton conductivity due to the blocking effect of space charge layer.[ 4 ]Small grain size and large number of grain boundaries will greatly limit the total proton conductivity of BZY.In this work, the sintering behavior, microstructure, and phase composition of the Ni-BZY from different methods were investigated. Dense Ni-BZY membranes with large BZY grains were successfully achieved through a two-step solid state reaction method.Fig. 1 shows the surface and cross-section SEM images of sintered Ni-BZY membrane. The membrane is very dense. The size of BZY grains is about 1 μm. The size of Ni particles is rather large, ~ 5-10 μm. The membrane is conductive at room temperature, suggesting a connective network of Ni is formed. The flux of a 0.40-mm-thick Ni-BZY membrane at 900 oC in wet 20 and 40% H2 are 3.4 and 4.3*10-8 mol/cm2s, respectively. These values are highest among all non-BaCeO3-based hydrogen membranes, suggesting the Ni-BZY is very promising in the application for hydrogen separation. Acknowledgements We gratefully acknowledge the financial support from the HeteroFoaM Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DESC0001061, and the DOE Office of Nuclear Energy’s Nuclear Energy University Programs.

Empirical Prediction of Carbon-Steel Degradation Rates on an Offshore Oil and Gas Facility: Predicting CO2 Erosion-Corrosion Pipeline Failures Before They Occur

Summary Various sections of carbon-steel pipework removed from an offshore facility were found to have experienced severe degradation, partly attributed to an insufficient inhibitor dose rate, as discussed in a previous case study (Hu et al. 2011b). An investigation was conducted to compare the predictive capability of an empirical model generated with data from a submerged-impinging-jet laboratory apparatus. The model was assessed in its ability to determine the rate of thickness loss for carbon-steel pipework subjected to a CO2-containing erosion-corrosion environment, reviewing to what extent the prediction agrees with inspection data. The investigation considers whether the developed tool could have predicted pipework failures on the facility, comparing it with the degradation rate calculated from a leak that occurred within the past 2 years. The program of experiments set out to create a means of prediction with the material-loss data from submerged-impinging-jet tests over a range of conditions replicating those within the line. Information pertaining to the temperature, production rate, and sand loading was collated for the offshore facility. These data were used along with mass-loss results to predict the degradation rate on the asset as a function of time over a 5-year period. This in turn was used to predict the total thickness loss of the pipework wall as a function of time. Consideration was also given to the current use of inhibition (10 ppm Inhibitor A) as well as the predicted thickness losses as a function of time had a candidate inhibitor been used instead (50 ppm Inhibitor B). Limitations of the model are presented, along with suggestions for ways to develop the model further.

Electrochemical Behavior of Tubular Steel Corrosion in Brine Containing High Contents of H<sub>2</sub>S and CO<sub>2</sub>

There were little works about electrochemical corrosion behaviors that appeared in high H2S and CO2 containing environment. In this work, the electrochemical behaviors of tubular steel API-P110 in buffered acidic NaCl solutions saturated with high H2S and CO2 containing gases, were investigated by potentiodynamic sweep technique. Analysis of the results shows corrosion density declines with increasing CO2 content in H2S/CO2. The corrosion potential of steel moves towards more negatively with the increase of CO2 content in H2S/CO2. In pH 2.9 solution, Passivity appears in high H2S and CO2, but no passivity shows in due to decreasing in high H2S. In pH 5.3 solution, cathodic liming density comes out and increases with the increasing CO2 content in H2S/CO2, however, no cathodic liming density comes out in H2S.

Thermal stability of Ba(Zr0.8−xCexY0.2)O2.9 ceramics in carbon dioxide

In situ x-ray diffraction spectra (25–1000 °C) have been measured as a function of temperature for proton-conducting Ba(Zr0.8−xCexY0.2)O2.9 (x=0.0–0.4) ceramics in CO2 atmosphere. Atomic vibrations before and after exposure to CO2 were obtained by using the micro-Raman scattering (150–1600 cm−1). Ba(Zr0.8Y0.2)O2.9 and Ba(Zr0.6Ce0.2Y0.2)O2.9 reveal a promising thermal stability in CO2 without apparent decomposition up to 1000 °C. However, Ba(Zr0.5Ce0.3Y0.2)O2.9 and Ba(Zr0.4Ce0.4Y0.2)O2.9 exhibit thermally stable below 550 °C and then proceed an obvious chemical decomposition of BaCO3 and Zr0.8−xCexY0.2O2 above 550 °C, which were clearly evidenced by the Raman vibrations of 1057 and 466 cm−1, respectively. A first-order orthorhombic-hexagonal structure transition was confirmed in BaCO3 in the region of 810–850 °C upon heating. This study suggests that the Ba(Zr0.8−xCexY0.2)O2.9 ceramics with x≤0.2 are promising candidates for proton-conducting applications in CO2-containing environment.

Inhibitor performance under liquid droplet impingement conditions in CO 2-containing environment

Oil and gas production and transport facilities are often constructed from relatively cheap carbon steel and, usually, inhibitors are then applied to mitigate corrosion, CO 2 being a particular threat. A proper inhibitor formulation should reduce the corrosion rate by a factor of at least 10, under actual operating conditions. Severe corrosion may occur when film forming inhibitors are removed from the steel by high liquid shear forces. In gas production, impingement of liquid drolets carried in wet, CO 2-containing gas may cause such erosion-corrosion. Current knowledge about the mechanism of flow induced removal of such protective inhibitors films is limited. The performances of commercial inhibitors under impact conditions are generally unknown and appropriate test methods for establishing critical conditions are lacking. The API RP-14E formula is often used for estimating critical erosion-corrosion velocities in uninhibited corrosive systems, but this formula is not applicable to inhibited systems. This paper focuses at correlating droplet impact velocity with performances of inhibitor films. Impact is simulated by collision of rotating steel coupons, mounted on a disc, against a liquid jet. To avoid drying of the samples between two collisions, the samples are also continuously wetted during rotation. A marked difference in performance between two commercial inhibitors was found. One inhibitor gave protection outside, but severe corrosion within the impact zone. The other inhibitor gave exactly the opposite behaviour. The equipment was shown to be capable of demonstrating differences in inhibitor performance as function of type and concentration. Critical impact velocities have been obtained for different inhibitors. The performance of the inhibitors tested were shown to be temperature and concentration dependent. The potential of an inhibitor to regain its protective properties, after failure above a critical velocity, could also be studied. This appeared to be a function of temperature for the two inhibitors tested. In principal, the equipment may be used for establishing critical velocities for the onset of erosion-corrosion under liquid droplet impact conditions for corrosion product films.