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.     

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.     

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．...     

Corrosion of stainless steel 316L in simulated formation water environment with CO2–H2S–Cl

A synergistic effect of high concentration of chloride and H₂S on oxide formation and metal dissolution has been studied on 316L stainless steel by electrochemical measurements, inductive coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS). Chloride concentration had a significant effect on semiconductor properties of the oxide film, while the gases had little effect. A relatively high concentration of sulphur was found inside the oxide formed in a high chloride concentration electrolyte with high H₂S compared to the oxide formed in low concentrations, which indicates that sulphur entered the oxide film through local weakening of the oxide by the chloride.     

Corrosion behaviour of X52 pipeline steel in high H2S concentration solutions at temperatures ranging from 25°C to 140°C

Abstract

High temperature and high pressure immersion tests in an autoclave were employed to study the corrosion behaviour of X52 pipeline steel in aqueous solutions containing high concentrations of H₂S. The corrosion products generated were characterised using scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It was seen that at a constant H₂S concentration of 22 g/l, the corrosion rate increased with increasing temperature up to 90°C, thereafter decreased at 120°C and slightly increased again at 140°C while the corrosion rate increased with H₂S concentration at a temperature of 90°C. When the temperature and H₂S concentration increased, the corrosion product converted from iron rich to sulphur rich products in the following sequence: mackinawite→troilite→pyrrhotite, where the microstructure and stability of the corrosion products had an important effect on the corrosion rate. The corrosion film was formed through the combination of the outward diffusion of Fe²⁺ ions and the inward diffusion of H₂S and HS^? species.     

Corrosion of Three Commercial Steels Under ZnCl2 –KCl Deposits in a Reducing Atmosphere Containing HCl and H2S at 400–500°C

The corrosion of three commercial steels in a reducing atmosphere containing HCl plus H₂S in the presence of ZnCl₂–KCl deposits has been investigated at 400–500°C and compared with the corrosion of the same materials in a similar gas mixture free from H₂S. The presence of H₂S in the gas accelerated the corrosion of the three commercial steels beneath ZnCl₂–KCl deposits. All materials suffered from severe corrosion with partial detachment and spalling of the external scales. Degradation of the steels resulted from the penetration of chlorine-containing species through the scale formed initially down to the metal matrix, because chorine-rich species were detected close to the alloy/scale interface. Although the corrosion resistance generally increased with increasing Cr content, even the high-Cr stainless steel SS304 is still unable to provide good corrosion resistance against the ZnCl₂–KCl deposits in the presence of H₂S due to the bad adherence of the scales to the alloy. The mechanisms of attack are discussed on the basis of thermodynamic considerations and of the active-oxidation model.     

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.     

Fe3C influence on the corrosion rate of mild steel in aqueous CO2 systems under turbulent flow conditions

The corrosion and corrosion inhibition of mild steel in CO₂ saturated solutions were studied under turbulent flow conditions at different pH. Electrochemical measurements using a.c. and d.c. techniques in uninhibited solutions of pH 3.8 indicated the formation of protective surface films (FeCO₃) in short immersion times. However, as the exposure time was increased the corrosion rate always increased, an effect attributed to the increased surface area of Fe₃C residue from corrosion of the steel. At pH 5.5, the corrosion rate always increased with time, behaviour also associated with the presence of Fe₃C surface film. The huge cathodic area of Fe₃C seems to have a more important impact on the electrochemical behaviour than the poorly formed FeCO₃ products. The effect of Fe₃C on inhibition by a quaternary amine inhibitor at pH 3.8 is to increase the corrosion rate as the pre-corrosion time is increased. The Fe₃C causes either (a) a cathodic area increase reflected in the corrosion rate increase with time or (b) a potential gradient in the pores of the Fe₃C layer that prevents positively charge amine ions from reaching all anodic sites.     

TiO2纳米阵列超疏水膜的制备及耐腐蚀性能

采用阳极氧化法在纯钛表面制备TiO2纳米管阵列,使用六甲基二硅胺烷对TiO2纳米管阵列进行低表面能处理,得到超疏水表面．用接触角测量仪测定表面疏水性,采用SEM、EDS技术研究改性前后试样表面的形貌和元素组成,并利用极化曲线和电化学阻抗谱法研究了超疏水膜的耐腐蚀性能．结果表明,TiO2纳米管阵列经改性后超疏水效果明显,...     

Influence of cold gas spray parameters on the corrosion resistance of Al-Al2O3 coatings sprayed on carbon steel

ABSTRACT

This work describes the influence of standoff distance (SoD), and gas temperature on the morphology and corrosion resistance of Al-10%Al₂O₃ coatings deposited by cold gas spray (CGS) on carbon steel. The results showed that the standoff distance had little effect on the thickness and microstructure of the coating. However, a 100 °C decrease of the spraying temperature reduced the coating thickness by 300?µm. The use of electrochemical analyses and SEM images showed that all the coatings studied were able to protect the substrate during at least 1300?h of immersion, due to the dense microstructure obtained by CGS.     

Effect of temperature and fluid velocity on corrosion mechanism of low carbon steel in presence of 2-hydrazino-4,7-dimethylbenzothiazole in industrial water medium

The corrosion inhibition of 2-hydrazino-4,7-dimethylbenzothiazole on low carbon steel in industrial water has been investigated at different temperatures and fluid velocities at different concentrations of the inhibitor using mass loss, potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The results showed that corrosion resistance increased by increasing the inhibitor concentration. Optimization of the three variables has been made and correlating the results obtained using Box–Wilson statistical method. The adsorption process on low carbon steel surface obeys Flory–Huggins isotherm. The values of ΔG_ads obtained suggest that, the adsorption process of 2-HMBT on low carbon steel is chemisorption. The activation energy increased with increasing the concentration of inhibitors leading to decrease of the pre-exponential factor, and the entropy of activation increased negatively in the presence of inhibitor. SEM was used to identify the film formed on the metal surface.     

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.     

Hot corrosion behaviour of plasma sprayed YSZ/Al2O3 dispersed NiCrAlY coatings on Inconel-718 superalloy

Oxide dispersed NiCrAlY bond coatings have been developed for enhancing thermal life cycles of thermal barrier coatings (TBCs). However, the role of dispersed oxides on high temperature corrosion, in particular hot corrosion, has not been sufficiently studied. Therefore, the present study aims to improve the understanding of the effect of YSZ dispersion on the hot corrosion behaviour of NiCrAlY bond coat. For this, NiCrAlY, NiCrAlY + 25 wt.% YSZ, NiCrAlY + 50 wt.% YSZ and NiCrAlY + 75 wt.% YSZ were deposited onto Inconel-718 using the air plasma spraying (APS) process. Hot corrosion studies were conducted at 800 °C on these coatings after covering them with a 1:1 weight ratio of Na₂SO₄ and V₂O₅ salt film. Hot corrosion kinetics were determined by measuring the weight gain of the specimens at regular intervals for a duration of 51 h. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy techniques were used to determine the nature of phases formed, examine the surface attack and to carry out microanalysis of the hot corroded coatings respectively. The results show that YSZ dispersion causes enhanced hot corrosion of the NiCrAlY coating. Leaching of yttria leads not only to the formation of the YVO₄ phase but also the destabilization of the YSZ by hot corrosion. For the sake of comparison, the hot corrosion behaviour of a NiCrAlY + 25 wt.% Al₂O₃ coating was also examined. The study shows that the alumina dispersed NiCrAlY bond coat offers better hot corrosion resistance than the YSZ dispersed NiCrAlY bond coat, although it is also inferior compared to the plain NiCrAlY bond coat.     

Structure, morphology and chemical composition of sputter deposited nanostructured Cr-WS2 solid lubricant coatings

WS₂ and Cr-WS₂ nanocomposite coatings were deposited at different Cr contents (approximately 15-50 at.%) on silicon and mild steel substrates using an unbalanced magnetron sputtering system. X-ray diffraction (XRD) was used to study the structure of Cr-WS₂ coatings and the bonding structure of the coatings was studied using X-ray photoelectron spectroscopy (XPS). The characterization of different phases present in Cr-WS₂ coatings was carried out using micro-Raman spectroscopy. The XPS and Raman data indicated the formation of a thin layer of WO₃ on the surface of Cr-WS₂ coatings and the intensity of the oxide phase decreased with an increase in the Cr content, which was also confirmed using energy-dispersive X-ray analysis results. The surface morphologies of WS₂ and Cr-WS₂ coatings were examined using field emission scanning electron microscopy (FESEM) and atomic force microscopy. It has been demonstrated that incorporation of Cr in WS₂ strongly influences the structure and morphology of Cr-WS₂ coatings. The XRD and FESEM results suggested that increase in the Cr content of Cr-WS₂ coatings resulted in a structural transition from a mixture of nanocrystalline and amorphous phases to a complete amorphous phase. The cross-sectional FESEM data of WS₂ coating showed a porous and columnar microstructure. For the Cr-WS₂ coatings, a mixture of columnar and featureless microstructure was observed at low Cr contents (≤ 23 at.%), whereas, a dense and featureless microstructure was observed at high Cr contents. Detailed cross-sectional transmission electron microscopy (TEM) studies of Cr-WS₂ coatings prepared at Cr content ≤ 23 at.% indicated the presence of both nanocrystalline (near the interface) and amorphous phases (near the surface). Furthermore, high-resolution TEM data obtained from the nanocrystalline region showed inclusion of traces of amorphous phase in the nanocrystalline WS₂ phase. Potentiodynamic polarization measurements indicated that the corrosion resistance of Cr-WS₂ coatings was superior to that of the uncoated mild steel substrate and the corrosion rate decreased with an increase in the Cr content.     

An efficient protection of stainless steel against corrosion: Combination of a conversion layer and titanium dioxide deposit

In the present work, a novel process has been developed to improve the corrosion properties of ferritic stainless steels. Titanium oxide coatings have been deposited onto stainless steel by sol-gel process after a pre-functionalization of the substrate in a conversion bath. Gel titania was prepared by hydrolysis of a titanium butoxide through a sol-gel process. Duplex systems “conversion layer/uniform TiO₂ coating” have been prepared on stainless steels using a dipping technique and thermal post-treatments at 450 °C. The preparation of sol-gel coatings with specific chemical functions offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The morphology and structure of the coatings were analysed using scanning electron microscopy with field effect gun (SEM-FEG), Mass spectroscopy of secondary ions (SIMS) and X-ray diffraction (XRD). The anticorrosion performances and the ageing effects of the coatings have been evaluated in neutral and aggressive media by using several normalized tests.The results show that the conversion layer was not sufficient to protect steel but sol-gel TiO₂ coatings, anchored on the metal substrate via the conversion layer, show good adhesion with the substrate and act as a very efficient protective barrier against corrosion. So, duplex layers with TiO₂ nanoparticle coatings on steels exhibit an excellent corrosion resistance due to a ceramic protective barrier on metal surface. Analysis of the data indicates that the films act as geometric blocking layers against exposure to the corrosive media and increase drastically the lifetime of the substrate.     

Co2 corrosion inhibition of X-120 pipeline steel by a modified imidazoline under flow conditions

A study of the effect of flow conditions on the performance of a carboxyethyl-imidazoline as CO₂-corrosion inhibitor for API X-120 pipeline steel has been evaluated. Testing techniques include polarization curves, linear polarization resistance, electrochemical impedance spectroscopy and electrochemical noise measurements under stirred conditions (0, 250, 500, 1000 and 2500 rpm). All these techniques show that for the uninhibited solution, corrosion rate increases with an increase in the rotation speed, but for the inhibited solution, the lowest corrosion rate is obtained at 500 rpm, and it increases at lower or higher rotation speeds.     

Characterisation of CO2 corrosion scale in simulated solution with Cl– ion under turbulent flow conditions

Abstract

In the present work, characterisations such as surface morphology, cross-section image and composition of corrosion scale formed on the P110 steel under turbulent flow conditions with various Cl^– concentrations have been studied by means of scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The corrosion medium was the simulated solution of one oil/gas field, saturated with CO₂ at 100°C and 4 MPa. The tests were conducted corresponding to various Cl^– concentrations and varied flow velocities. It is concluded that Cl^– concentration and flow velocity have an important effect on the corrosion scales formed on the samples. In addition, the protective properties and adherence of the corrosion scales were characterised by the analysis of the scale formation and influence mechanisms associated with Cl^– concentration and flow velocity. Moreover, a lattice model is created to interpret and illuminate the corrosion process.     

The role of acid anion on the inhibition of the acidic corrosion of steel by lupine extract

The inhibitive effect of lupine (Lupinous albus L.) extract on the corrosion of steel in aqueous solution of 1 M sulphuric and 2 M hydrochloric acids was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization curves indicated that the lupine extract acts as a mixed-type inhibitor. EIS measurements showed that the dissolution process is under activation control. The inhibition efficiency of the extract obtained from impedance and polarization measurements was in a good agreement and was found to increase with increasing concentration of the extract. The obtained results showed that, the lupine extract could serve as an effective inhibitor for the corrosion of steel in acid media and the extract was more effective in case of hydrochloric acid. Theoretical fitting of the corrosion data to the kinetic-thermodynamic model was tested to show the nature of adsorption.     

H2S溶液中316L不锈钢TIG焊接头的腐蚀性能

文中通过极化曲线、交流阻抗、Mott-Schottky曲线、浸泡腐蚀试验等方法对316L奥氏体不锈钢TIG焊接头各区域在不同浓度H₂S溶液中的耐蚀性能进行了研究.极化曲线及交流阻抗结果表明,随着溶液中H₂S浓度的升高,焊接接头各区域的耐蚀性明显降低.另一方面对于相同浓度的H₂S溶液,316L基体的耐蚀性最好,其次是热影响区,焊缝区的耐蚀性最差.Mott-Schottky曲线结果表明,焊接接头在H₂S溶液中的表面钝化膜形成p-n结结构,掺杂浓度高达1022 cm-3,且掺杂浓度随H₂S浓度升高而增大,致使钝化膜防护性能降低.     

Enhanced corrosion resistance of porous NiTi with plasma sprayed alumina coating

In this study, corrosion behaviour of porous NiTi modified by plasma sprayed alumina coating has been investigated. Scanning electron microscopy and X-ray diffraction techniques were applied for the morphology and microstructure characterisation, while linear sweep voltammetry and electrochemical impedance spectroscopy were used for investigation of corrosion behaviour of coated and uncoated NiTi specimens. Induced couple plasma was conducted to measure ion release of the specimens in simulated body fluid at 37°C. The plasma sprayed Al₂O₃ coating on the porous NiTi improved the surface characteristics for biomedical applications. The alumina coating significantly hampered Ni ion release from the surface. In spite of slight decrease in corrosion resistance of the coated specimens, the corrosion mechanism changed from pitting to general corrosion. The breakdown phenomenon was not detected in the coated specimens, as well. Overall, it can be concluded the longevity of the coated specimen in the simulated biological system was enhanced, comparing to bare NiTi specimens.