Long term corrosion of X70 steel and iron in humid supercritical CO2 with SO2 and O2 impurities

Abstract

The corrosion of X70 steel and iron in supercritical CO₂/SO₂/O₂/H₂O environment were investigated after a 454 h exposure. Optical microscopy was applied to observe the morphology of etch pits and synthesise the three-dimensional morphology. X-ray diffraction and X-ray photoelectron spectroscopy were employed to detect the composition of product scales. Experimental results verified that the localised corrosion occurred on the X70 steel sample under corrosion product deposits. Ferrous sulphate, sulphur and iron sulphide were detected as the corrosion products.     

Updated CO2/H2S internal corrosion model of natural gas pipelines based on flow field calculations

The ‘A line’ of the Sichuan Natural Gas East Transportation in China was used as the subject of the study, and an existing CO₂/H₂S corrosion model was utilised to predict the uniform corrosion rate. Then, the flow parameters were simulated by computational fluid dynamics based on turbulence theory, and the influence on the corrosion rate of the pipeline was analysed in a detail to more accurately describe the corrosion problems of natural gas pipelines that contain CO₂/H₂S. After that, an updated CO₂/H₂S corrosion model under the influence of flow filed was proposed by modifying the existing CO₂/H₂S corrosion model. The actual condition was calculated by the updated CO₂/H₂S corrosion model. Results show that flow parameters, namely, velocity, turbulent kinetic energy and phase distribution, affect pipeline corrosion. The flow parameters did not change significantly at the small scale changes in the pipeline (5 and 15°) of a broad and smooth flow channel of the large diameter gas transport pipeline. The shape of corrosion often appears in the form of an elliptical sheet. The corrosion location and the corrosion rate calculated by the updated model are consistent with the wall thickness detection data in the site conditions, which verified that the updated CO₂/H₂S corrosion model is valid. The updated CO₂/H₂S corrosion model influenced by the flow field can predict the corrosion distribution and the corrosion rate of the three-dimensional key positions in natural gas pipelines.     

High-temperature corrosion of Cr2O3-forming alloys in CO-CO2-N2 atmospheres

The corrosion of Fe–28Cr, Ni–28Cr, Co–28Cr, and pure chromium in a number of gas atmospheres made up of CO–CO₂(–N₂) was studied at 900°C. In addition, chromium was reacted with H₂–H₂O–N₂, and Fe–28Cr was reacted with pure oxygen at 1 atm. Exposure of pure chromium to H₂–H₂O–N₂ produced a single-phase of Cr₂O₃. In a CO–CO₂ mixture, a sublayer consisting of Cr₂O₃ and Cr₇C₃ was formed underneath an external Cr₂O₃ layer. Adding nitrogen to the CO–CO₂ mixture resulted in the formation of an additional single-phase layer of Cr₂N next to the metal substrate. Oxidizing the binary alloys in CO–CO₂–N₂ resulted in a single Cr₂O₃ scale on Fe–28Cr and Ni–28Cr, while oxide precipitation occurred below the outer-oxide scale on Co–28Cr, which is ascribed to the slow alloy interdiffusion and possibily high oxygen solubility of Co–Cr alloys. Oxide growth followed the parabolic law, and the rate constant was virtually independent of oxygen partial pressure for Fe–28Cr, but varied between the different materials, decreasing in the order chromium >Fe–28Cr>Ni(Co)–28Cr. The formation of an inner corrosion zone on chromium caused a reduction in external-oxide growth rate. Permeation of carbon and nitrogen through Cr₂O₃ is thought to be due to molecular diffusion, and it is concluded that the nature of the atmosphere affects the permeability of the oxide.     

P110钢在CO2／H2S环境中的适用性研究

采用高温高压实验设备辅以失重法,研究了CO2／H2S腐蚀环境中P110钢的腐蚀性能,用SEM、EDS和XRD等分析了腐蚀产物．分别用电化学充氢及NACE TM0177A法对P110钢进行耐氢损伤试验．结果表明,虽然P110钢在试验环境中的均匀腐蚀速率很小,未发生点蚀,但随着充氢量的增加,强度、伸长率及断面收缩率均降低．...     

Comparison of corrosion scales formed on KO8OSS and N8O steels in CO2/H2S environment

Abstract

Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied to analyse the microstructure and composition of the corrosion scale formed on KO80SS and N80 tubes with carbon dioxide (CO₂) and hydrogen sulphide (SO₂). The corrosion scales of both KO80SS and N80 tubes were of the double layer structure, and not only uniform corrosion but also localised corrosion was observed. The crystal of the surface layer is laminar. The main phase in the outer layer is calcium carbonate (CaCO₃), and the inner scale consisted of iron carbonate (FeCO₃) for KO80SS steel and FeS_0·9 with a little amount of FeCO₃ for N80 steel respectively. Additionally, the electrochemical techniques were used to investigate the characteristics of the corrosion scales. The results indicated that the polarisation resistance R_p of KO80SS steel film was nobler than that of N80 steel film. Finally, the corrosion current I_corr of KO80SS steels was lower than that of N80 steels. Corrosion scale of KO80SS tube steels is more protective to the matrix than that of N80 tube steels.     

Effect of Al and Ce oxide layers electrodeposited on OC4004 stainless steel on its corrosion characteristics in acid media

The changes in the corrosion characteristics of stainless steel OC4004 in 0.1 M HNO₃ after electrodeposition of thin Al and Ce oxide films on it has been investigated. The Ce₂O₃–CeO₂ layers have been found to possess a pronounced stabilizing effect on the steel passive state and on its corrosion resistance, respectively, whereas the Al₂O₃ layers do not improve considerably the corrosion behaviour of the SS/Al₂O₃ system. A twice-lower corrosion current was observed with a ternary SS/Al₂O₃/Ce₂O₃–CeO₂ system in the passive region, while the zones of potentials, where the steel is in a stable passive state, are not changed. The obtained results permit the assumption that the cerium oxides layer acts as an effective cathode playing a determining role with respect to the improvement of the corrosion behavior of the steel. It has been concluded that when the SS/Al₂O₃/Ce₂O₃–CeO₂ system is used in media containing nitric acid, the corrosion will proceed at potentials where the passive state of steel would not be disturbed.     

Electrochemical study of corrosion behaviour of carbon steel A106 and stainless steel 304 in aqueous monoethanolamine

Abstract

Corrosion behaviour of carbon steel A106 and stainless steel 304 (SS304) in aqueous monoethanolamine was studied by performing electrochemical polarisation experiments. Potentiodynamic curves were studied and compared under conditions with different temperatures, carbon loading and O₂ percentage in purging gases. It was found that corrosion of A106 and SS304 was promoted under conditions with higher temperature. While the presence of O₂ speeds the corrosion of A106, it has a negligible impact on SS304 at 80°C and lowers the corrosion rate at 40°C. Corrosion rates and other important parameters were calculated based on the electrochemical curves for A106. Sample surfaces after tests were examined by scanning electron microscopy and energy dispersive spectroscopy. Mechanisms involved in iron dissolution and passivation from oxide films were discussed.     

Corrosion and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in a CO2-Containing Solution

The electrochemical corrosion and stress corrosion cracking (SCC) behaviors of X70 pipeline steel in CO₂-containing solution were studied by electrochemical measurements, slow strain rate tensile tests, and surface characterization. The results found that the electrochemical corrosion of X70 steel in aerated, alkaline solution is an activation-controlled process, and a stable passivity cannot develop on steel. Corrosion rate of the steel increases with the CO₂ partial pressure. The enhanced anodic dissolution due to the additional cathodic reaction in the presence of CO₂, rather than the film-formation reaction, dominates the corrosion process. The mass-transfer step through FeCO₃ deposit is the rate-controlling step in corrosion of the steel. The susceptibility of steel to SCC and the fracture brittleness increase with the CO₂ partial pressure. The enhanced fracture brittleness is attributed to the evolution and penetration of hydrogen atoms into the steel, contributing to crack propagation. The formed deposit layer is not effective in reducing hydrogen permeation due to the loose, porous structure.     

Corrosion of magnesium in humid air

The influence of ambient concentrations of carbon dioxide on the atmospheric corrosion of magnesium has been studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), revealing the development and growth of corrosion products. The surfaces investigated by AFM were prepared by ultramicrotomy, using a diamond knife, to generate a smooth finish without using water or lubricant. Sputter-deposited Mg films were also studied with mechanically polished samples used to monitor the overall corrosion process. The exposures were performed at 22.0 °C in a synthetic environment with precise control of relative humidity (95%) and CO₂ (0 or 350 ppm). Corrosion is localized in the absence of CO₂ and is related to noble inclusions in the metal matrix. After corrosion product removal, relatively deep pits are evident. In contrast, pitting is inhibited in the presence of CO₂ with relatively uniform corrosion product development; further, the noble inclusions have no effect on the distribution of corrosion. The inhibitive effect of CO₂ is also observed in the long-term exposures, showing that CO₂ reduces the average corrosion rate. Mechanisms are introduced to explain the effects of CO₂ and the roles of the noble inclusions on the corrosion behaviour.     

Protective effect in sulfuric acid media of alumina and ceria oxide layers electrodeposited on stainless steel

The influence of thin layers of Al₂O₃ and Ce₂O₃-CeO₂, electrodeposited on stainless steel OC4004, on the corrosion behaviour of the systems Al₂O₃/SS, Ce₂O₃-CeO₂/SS and Al₂O₃-Ce₂O₃-CeO₂/SS has been studied in sulfuric acid medium. A pronounced stabilizing effect on the passive state of steel and enhancement of its corrosion resistance has been established both for the samples as deposited and for the thermally treated Ce₂O₃-CeO₂/SS systems. In comparison to them the layers of Al₂O₃ have a substantial impact on the corrosion resistance of the Al₂O₃/SS system only in the cases when the system is not subjected to thermal treatment. The consecutive deposition of Al₂O₃ and Ce₂O₃-CeO₂ films on SS gives as a result an outstanding corrosion-protective effect, whereupon the corrosion potential of the system Al₂O₃/Ce₂O₃-CeO₂/SS is shifted in positive direction with ∼ 0.3 V for the samples as deposited and with ∼ 1 V—for the thermally treated samples. The so established favourable effect has been explained by the increased concentration of chromium oxides in the surface passive film, caused by the presence of cerium oxides, as well as by their action as cathode, effective with respect to the reduction corrosion reaction, shifting strongly the potential (at which this reaction is occurring) in positive direction.     

Microstructure and corrosion behaviour of Al2O3–13 wt-% TiO2 laser alloyed magnesium alloys

Nanostructured Al₂O₃–13?wt-% TiO₂ was prepared on AZ91D magnesium alloy surface by laser surface alloying to improve its corrosion resistance. The microstructure of the laser surface alloyed specimens before and after corrosion tests was characterised by scanning electron microscope and optical microscope (OM). The phase and element composition were investigated by X-ray diffractometer and energy-dispersive spectrometry. An electrochemical workstation was used to evaluate the corrosion behaviour of the specimens. Results showed that the laser surface alloyed layer was primarily composed of Mg and Mg₁₇Al₁₂. Al₂O₃ and TiO₂ existed in the form of agglomerated particles. The corrosion resistance was improved after laser surface alloying.     

In situ observation of CO2 corrosion under high pressure

Direct observation of corrosion phenomena under special environments is still a challenge. Here, we reported on an in situ method for CO₂ corrosion imaging under high pressure. The simultaneously recording of the surface morphology changes and Fe ions release can clearly reveal the detailed process of CO₂ corrosion from active dissolution to film deposition and pitting attack. It indicated that the cooperative initiation of corrosion pits was triggered by local environmental variations relating to an initial active dissolution of the steel surface. The result also suggested that stereomicroscope be a suitable method for directly observing corrosion phenomena in high pressure conditions.     

3 Cr 钢和碳钢在含 CO2环境中的腐蚀速率对比

模拟长庆苏里格油田的液体环境,并通入CO2,采用腐蚀失重法,对比研究了普通3Cr钢和碳钢在高温高压和常温常压两种条件下的腐蚀行为。结果表明:该模拟腐蚀环境中,3Cr钢和碳钢在常温常压条件下的腐蚀速率分别为0.118 mm/a及0.408 mm/a,碳钢的腐蚀速率是3Cr钢的3倍多;当温度和压力提高后,3Cr钢的腐蚀速率为1.59 mm/a,与碳钢的1.54 mm/a相当。     

Development of high performance gas carburising furnace

Abstract

We developed a high performance gas carburising furnace (N-BBH) to overcome the inherent disadvantages of gas carburising furnaces. More than 90% reduction in CO₂ emission was achieved using a small amount of carrier gas in the air tight heating chamber and by precise control of the atmosphere during carburising. No conditioning time was required because the air does not enter either the heating chamber or the pre-chamber when opening the furnace. Carburising speed was higher than that of low pressure carburising because of a high carbon transfer coefficient (β) and high carbon potential (CP). Decreasing the oxidation components, such as CO₂, O₂ and H₂O, and using nitrogen gas or atmospheric gas with high CP, reduced intergranular oxidation 50% or more compared with conventional gas carburising.     

Corrosion investigation of J55 steel under simulated enhanced oil recovery conditions using CO2 flooding

The present work investigated corrosion behaviour of J55 tubing steels and solution equilibrium chemistry of the produced water under simulated CO₂ flooding environments at various temperatures. The corrosion rates were calculated by weight loss method carried out with or without one kind of imidazoline based inhibitor in autoclave. Surface morphologies of corrosion product films formed on samples were analysed using scanning electron microscopy (SEM). Meanwhile, the concentrations of main solution species in experimental produced water were tested. The solution equilibrium chemistry of dissolved CO₂ in the produced water was also calculated and analysed. The results indicated that corrosion rate of J55 significantly increased when temperature exceeded 55°C and greatly decreased with the effect of inhibitor especially when the imidazoline based inhibitor exceeds 150 ppm, σ Fe concentration increased with the increase in temperature, especially when temperature exceeded 44°C. The H₂CO₃ concentration declines by about 3 orders of magnitude compared to CO₂(aq) concentration and the yielded HCO₃^? concentration is about 0·2–0·35 times of the H₂CO₃ concentration.     

Effect of Al2O3 reinforcement and precipitates on corrosion behaviour of 2618 and 6061 aluminium MMCs

ABSTRACT

The corrosion resistance features of two different Metal Matrix Composites based on 6061 and 2618 aluminium alloys reinforced by 20% Al₂O₃ particles by stir casting process, were studied in 3.5% NaCl and compared. The composites and their respective base alloys were characterised in terms of microstructure by optical and scanning electron microscopy and in terms of corrosion resistance by polarisation curves and electrochemical impedance. Results show how the presence of Al₂O₃ has different effects depending on matrix composition. In 6061 MMC, Al₂O₃ promotes the formation of Mg₂Si which has a cathodic behaviour altering the pitting susceptibility of the composite. In 2618 MMC, the high content of Cu induces a strong uniform attack. The subsequent increase in the Open Circuit Potential caused a pitting attack.     

Improving the Na2SO4-induced corrosion resistance of Ti3AlC2 by pre-oxidation in air

Ti₃AlC₂ suffers severe Na₂SO₄-induced corrosion attacks at temperatures higher than 800 °C in air. A convenient and efficient pre-oxidation method is proposed to enhance the corrosion resistance of Ti₃AlC₂. The corrosion weight-changes of the pre-oxidized samples were decreased by about four orders of magnitude compared with those of the untreated specimens. The mechanism on improvement of corrosion resistance was investigated by means of thermogravimetric analysis, X-ray diffraction and scanning electron microscopy/energy-dispersive spectroscopy. A continuous and adherent α-Al₂O₃ scale was prepared by high-temperature pre-oxidation treatment in air. The preformed dense Al₂O₃ scale has good compatibility with the Ti₃AlC₂ substrate, and consequently, can act as an efficient barrier against corrosion. Long-time corrosion tests demonstrate that the Al₂O₃ scale conserves after corrosion attack and is capable of long-term stability.     

基于磁过滤技术的热障涂层表面Al2O3 覆盖层抗CMAS腐蚀性能

为了提高热障涂层（TBC）的抗沉积物（主要成分为CaO、MgO、Al₂O₃和SiO₂,简称CMAS）腐蚀性能,采用磁过滤阴极真空电弧（FCVA）技术在TBC表面上制备了致密的Al₂O₃覆盖层,比较和分析了Al₂O₃改性TBC和沉积态TBC的润湿行为和抗CMAS腐蚀性能。结果表明：使用FCVA技术制备Al₂O₃覆盖层的过程对7%（质量分数）氧化钇稳定的氧化锆（7YSZ）相的结构无明显影响,且经Al₂O₃改性的TBC综合性能均优于沉积态TBC。在1250 ℃、CMAS腐蚀条件下,Al₂O₃覆盖层有效地限制了熔融CMAS在TBC表面上的扩散行为。同时,Al₂O₃填充了7YSZ柱状晶之间的间隔并且阻碍了熔融CMAS的渗透,证明了FCVA可作为一种制备Al₂O₃涂层的新方法以提高TBC的抗CMAS腐蚀性能,且Al₂O₃涂层及其制备过程对TBC的热震性能均无消极影响。     

Abrasion resistances of CO2 corrosion scales formed at different temperatures and their relationship to corrosion behaviour

The abrasion resistances of CO₂ corrosion scales formed on API P110 grade carbon steel at different temperatures and CO₂ corrosion behaviour of P110 carbon steel have been investigated utilising weight loss method, scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that as the film forming temperature increased, the abrasion rate of CO₂ corrosion scales increased firstly and then decreased, the variation trend was similar to that of the corrosion rate, and the maximal abrasion rate was present at 70°C rather than 100°C, at which the maximal corrosion rate was obtained and CO₂ corrosion scales were loose and porous and were composed of FeCO₃, Fe₃C and CaCO₃. The abrasion resistances of CO₂ corrosion scales formed at 100°C was reinforced by the sand particles embedded easily in the loose and porous layer, together with a very hard residual skeleton, Fe₃C. In addition, CaCO₃ was worn out easily and substituted by SiO₂ during abrasive wear.     

天然气管线钢CO2腐蚀研究进展

天然气管线面临日益严重的CO₂腐蚀问题。针对管线内特定的腐蚀环境,总结了当前CO₂腐蚀在反应机理、影响因素以及腐蚀控制方面的研究进展,最后展望CO₂腐蚀研究今后的发展方向。