Electrochemical behaviour of Ni-base alloys exposed under oil/gas field environments

The electrochemical behaviour of Ni-base alloys (Inconel 625, Inconel 718, G3 and Incoloy 825) is carried out at 80 °C in CO₂/H₂S corrosion environments using cyclic potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. The passivity mechanisms are analysed and discussed. In addition, some significant characterisation parameters such as E_corr, I_pass, E_pit, E_pp, ΔE and I_pass in cyclic polarisation curves are analysed and compared to reveal the corrosion resistance of various Ni-base alloys. The equivalent circuit model and ZsimpWin software are utilised to discuss the Nyquist plots of various Ni-base alloys. The diffusion mechanism in EIS measurement is discussed. The result shows that the corrosion resistance of the Ni-base alloys to CO₂ corrosion or CO₂/H₂S corrosion follows the sequence: Inconel 625 > G3 > Inconel 718 > Incoloy 825. H₂S works as a cathodic depolariser with accelerating initiation of the corrosion process.     

Corrosion of N80 carbon steel in oil field formation water containing CO2 in the absence and presence of acetic acid

Corrosion behaviour of N80 carbon steel in formation water containing CO₂ was studied by polarization curve technique, electrochemical impedance spectroscopy, weight loss test, scanning electron microscope, and X-ray diffraction. Effects of temperature and acetic acid concentration on the corrosion behaviour of N80 carbon steel were discussed. The results showed that increasing temperature not only enhanced the dissolution of steel substrate, but also promoted the precipitation of FeCO₃, the addition of acetic acid enhanced localized corrosion attack on N80 carbon steel. FeCO₃ was the main corrosion product. And there was a transition region between CO₂ corrosion control and HAc corrosion control.     

Understanding corrosion via corrosion product characterization: I. Case study of the role of Mg alloying in Zn-Mg coating on steel

In the present work the corrosion inhibitive role of Mg in Zn-Mg coatings is considered for different stages of corrosion. Corrosion product characterization was carried out using XRD, IRRAS, MEB-FEG-EDS on technical Zn-Mg coatings after various exposure times in a standardized cyclic corrosion test. The results are compared with artificial corrosion products obtained by chemical and electrochemical synthesis. The importance of the ageing and the role of the atmospheric CO₂ on the nature and morphology of the corrosion products are discussed. The corrosion resistance of Zn-Mg alloy is correlated with the stabilization of simonkolleite against its transformation into smithsonite, hydrozincite, and zincite during ageing cycles in presence of CO₂. The stabilization appears to be due to the preferential formation of magnesium carbonates. Thermodynamic modeling and titrometric analysis demonstrate that Mg²⁺ enhances simonkolleite during dry-wet cycling by (1) removing carbonate from the environment and thereby limiting of the transformation of simonkolleite into zincite, smithsonite, and hydrozincite and by (2) buffering the pH of the electrolyte around 10.2 due to the precipitation of Mg(OH)₂ preventing the dissolution of zinc based corrosion products into soluble hydroxide complexes.     

Chemistry of corrosion products on Zn-Al-Mg alloy coated steel

Zn-Al-Mg alloy (ZM) coating provides a decisively enhanced corrosion resistance in a salt spray test according to DIN EN ISO 9227 (NSS) compared to conventional hot-dip galvanised zinc (Z) coating because of its ability to form a very stable, well adherent protecting layer of zinc aluminium carbonate hydroxide, Zn₆Al₂(CO₃)(OH)₁₆·4H₂O on the steel substrate. This protecting layer is the main reason for the enhanced corrosion resistance of the ZM coating. Surface corrosion products on ZM coated steel consist mainly of Zn₅(OH)₆(CO₃)₂, ZnCO₃ and Zn(OH)₂ with additions of Zn₅(OH)₈Cl₂ · H₂O and a carbonate-containing magnesium species.     

Corrosion characteristics of LiBH4 film exposed to a CO2/H2O/O2/N2 mixture

LiBH₄ films were prepared by pulsed laser deposition using a LiB target in a background pressure of hydrogen. The corrosion characteristics of LiBH₄ films were measured by exposing them to a gas mixture of CO₂/H₂O/O₂/N₂ at ambient temperature for 1–24 h. Scanning electron microscopy images show some cracks on the surface of corrosion films, which could act as easy paths for H₂O and CO₂ to further react with Li⁺ and B³⁺. The X-ray photoelectron spectroscopy results and theoretical analysis show that LiBH₄ tends to react with H₂O and CO₂ to form Li₂B₄O₇, Li₂CO₃ and LiOH during the corrosion process.     

Corrosion behaviour of AZ31B magnesium alloy in NaCl solutions saturated with CO2

Corrosion behaviour of AZ31B magnesium alloy in different concentrations of NaCl solution saturated with CO₂ was studied by electrochemical techniques, Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray. The corrosion rate increases with increasing NaCl concentration both in the presence and absence of CO₂. The corrosion rate in NaCl solution saturated with CO₂ is bigger than that in single NaCl solution. The inhibitive effect of CO₂ is also observed with immersion time increased in NaCl solution saturated with CO₂, showing that CO₂ reduces the average corrosion rate due to the formation of insoluble products.     

Steel corrosion behaviour in carbonated alkali-activated slag concrete

Steel bars embedded in an alkali-activated slag (AAS) concrete were exposed (after curing for 28 days) to an accelerated carbonation test (3% CO₂, 65% relative humidity (RH), and 25 °C temperature) and a laboratory environment (0.03% CO₂, 65% RH, and 25 °C). Ordinary Portland cement (OPC) was also tested for comparative purposes and exposed to identical experimental conditions. The corrosion behaviour of uncarbonated and carbonated AAS and OPC concretes was tested for different times, performing corrosion potential, linear polarization resistance, and electrochemical impedance spectroscopy measurements. Corrosion products were analysed using the Mössbauer technique. The main corrosion products found were magnetite (Fe₃O₄), wüstite (FeO), and goethite (α-FeOOH).     

Experimental studies on corrosion of cement in CO2 injection wells under supercritical conditions

The corrosion performance of cement exposed to supercritical CO₂ environments has been investigated under static and dynamic conditions by SEM, EDS, XRD and physical analysis. The dissimilarity of attack was compared in two exposure conditions i.e. gaseous CO₂ and liquid CO₂ by measuring compressive strength, permeability and penetration depth. The corrosion degree becomes more severe with increasing temperature and exposure time in both phase states of CO₂. Experimental results were comparable in magnitude of change to the field observations. The corrosion mechanism and kinetics have been discussed to evaluate corrosion behavior of the cement.     

Mechanical properties of CO2 corrosion product scales and their relationship to corrosion rates

In order to evaluate the protective ability of CO₂ corrosion scale to steel under flow conditions at various CO₂ partial pressures, the mechanical properties of the scale, i.e., Young′s modulus, fracture toughness, interfacial fracture toughness and adhesion strength between the scale and steel were determined by nano-indentation, Vickers’ indentation and tensile test. The influences of flow rate and CO₂ partial pressure on these mechanical properties as well as the correlations between the properties and corrosion rates were investigated. The interfacial fracture toughness between the scale and steel can evaluate the protective ability of the scale to steel effectively.     

Inert anode composed of Ni–Cr alloy substrate, intermediate oxide film and α-Al2O3/Au (Au–Pt, Au–Pd, Au–Rh) surface composite coating for aluminium electrolysis

An inert anode composed of alloy substrate, intermediate oxide film and surface composite coating for aluminium electrolysis has been fabricated. The intermediate oxide film (ZrO₂/Y₂O₃) provides good adhesion and mutual diffusion resistance between the substrate and the surface coating which consists of α-Al₂O₃ particles embedded in Au (Au–Pt, Au–Pd, Au–Rh) matrix. The results of electrolysis test revealed that aluminium with high purity (>99.999%) can be produced. It is demonstrated that the inert anode exhibits superior erosion and corrosion resistance during aluminium electrolysis, especially in low-temperature (800 °C) electrolytes.     

Material characterization and corrosion performance of nickel electroplated in supercritical CO2 fluid

The surface roughness, microhardness, crystal structure and corrosion performance of nickels electroplated at atmospheric pressure and in supercritical CO₂ fluid, respectively, are compared. The experimental results showed that nickel electroplated in the latter case exhibited a lower surface roughness and a higher hardness. In HCl solution, the nickel deposited in supercritical CO₂ fluid had a lower anodic current density and a higher polarization resistance. The advantage of emulsified supercritical CO₂ fluid for electroplating was demonstrated.     

CHARACTERISTICS AND FORMATION MECHANISM OF CORROSION SCALES ON LOW--CHROMIUM X65 STEELS IN CO2 ENVIRONMENT

利用高温高压CO₂腐蚀模拟实验以及ESEM, EDS, XPS和SEM等分析技术, 研究了4种不同含Cr量的X65管线钢的腐蚀速率、腐蚀形态和腐蚀产物膜结构特征. 结果表明: 含Cr量高的钢平均腐蚀速率小, 无Cr和含1\%Cr的钢的腐蚀形态为局部腐蚀, 含3%和5%Cr的钢的腐蚀形态为全面腐蚀. 在高温高压CO₂腐蚀环境中, 含Cr钢的腐蚀产物膜为FeCO₃和Cr(OH)₃竞争沉积形成的多层结构, 其中1Cr-X65和3Cr-X65的腐蚀膜具有3层结构, 5Cr-X65的腐蚀膜是双层结构. Cr在腐蚀产物膜层中出现局部富集, 远高于基体中的Cr含量. 高含Cr量使腐蚀产物膜中的Cr(OH)₃含量高, 并提高了腐蚀膜的保护性能, 从而引起腐蚀形态发生转变, 腐蚀速率降低. FeCO₃和Cr(OH)₃共沉积层膜对低铬钢的抗CO₂腐蚀性能具有关键的影响.     

The behaviour of praseodymium 4-hydroxycinnamate as an inhibitor for carbon dioxide corrosion and oxygen corrosion of steel in NaCl solutions

Praseodymium 4-hydroxycinnamate (Pr(4OHCin)₃) was investigated as a novel corrosion inhibitor for steel in NaCl solutions, and found to be effective at inhibiting corrosion in both CO₂-containing and naturally-aerated systems. Surface analysis results suggest that the corrosion inhibition ability of Pr(4OHCin)₃ in the naturally-aerated corrosion system could be attributed to the formation of a continuous protective film. For the CO₂-containing system, the corrosion inhibition efficiency of Pr(4OHCin)₃ was predominantly because of formation of protective inhibiting deposits at the active electrochemical corrosion sites, in addition to a thinner surface film deposit.     

A study of 4-carboxyphenylboronic acid as a corrosion inhibitor for steel in carbon dioxide containing environments

4-Carboxyphenylboronic acid (CPBA) has been found to be an efficient carbon dioxide (CO₂) corrosion inhibitor for steel in aqueous media. The results indicate that the addition of CPBA to CO₂ containing sodium chloride solutions at a low concentration is able to retard corrosion anodic reactions, reduce corrosion current densities, increase charge transfer and total resistances, resulting in more uniform and smoother steel surfaces. These effects are attributed to the formation of a barrier layer on steel surface, which provides metal surface protection. The inhibitor was also found to mitigate corrosion by promoting random distribution of minor anodes.     

The inhibition of CO2 corrosion of N80 mild steel in single liquid phase and liquid/particle two-phase flow by aminoethyl imidazoline derivatives

The inhibitory behaviour of 2-undecyl-1-aminoethyl imidazoline (AEI-11) and 2-undecyl-1-aminoethyl-1-hydroxyethyl quaternary imidazoline (AQI-11) on CO₂ corrosion of N80 mild steel in single liquid phase and liquid/particle two-phase flow was investigated using weight loss, linear polarization, potentiodynamic polarization, EIS methods and SEM observations. The two compounds inhibited the CO₂ corrosion of N80 steel and the extent of inhibition was dependent on the flow conditions and particulate content. In both phases, AQI-11 exhibited better inhibition ability than AEI-11 due to the polycentric adsorption sites on its structure. Theoretical calculation on the inhibition abilities of the compounds and their modes of adsorption are reported.     

Corrosion of Ti3AlC2 at 800–1100 °C in Ar–0.2% SO2 gas atmosphere

Ti₃AlC₂ was corroded between 800 and 1100 °C in an Ar–0.2% SO₂ gas atmosphere according to the equation: Ti₃AlC₂ + O₂ → rutile-TiO₂ + α-Al₂O₃ + (CO or CO₂). The scales that formed on the Ti₃AlC₂ were thin and rich in α-Al₂O₃, whose growth rate was exceedingly slow. The TiO₂ was present either as the outermost surface scale or a mixture inside the α-Al₂O₃-rich scale. In the Ti₃AlC₂, the activity and diffusivity of Ti were low, whereas those of Al were high. This was the main reason for the superior corrosion resistance of Ti₃AlC₂ over TiAl.     

Corrosion behaviour of AIP NiCoCrAlYSiB coating in salt spray tests

NiCoCrAlYSiB coatings were deposited by arc ion plating (AIP) and annealed/pre-oxidised under various conditions. The corrosion behaviour of as-deposited and annealed/pre-oxidised coatings was studied by salt spray testing in a neutral mist of 5 wt% NaCl at 35 °C for 200 h. The results showed that the as-deposited NiCoCrAlYSiB coating behaved poorly while the annealed and pre-oxidised ones performed much better in salt spray tests. The dense microstructure in annealed coatings and formation of α-Al₂O₃ scales on the surface during pre-oxidation improved the corrosion resistance in salt spray test. The corrosion process was investigated from the aspects of corrosion products, and its electrochemical mechanism was proposed as well.     

Effect of carbon dioxide on the atmospheric corrosion of Zn–Mg–Al coated steel

The atmospheric corrosion of line hot dip ZnMgAl coating was investigated at low and ambient concentration of CO₂ as a function surface chloride concentration and temperature and compared to conventional hot dip galvanised (GI) and Galfan coatings. The corrosion of zinc coatings was enhanced in low CO₂ conditions and ZnMgAl material was more affected than GI, and in the range of the Galfan coating. An obvious pH effect was underlined in low CO₂ conditions. Layered double hydroxide (LDH) and simonkolleite were mainly formed on ZnMgAl coating in the absence of CO₂ while hydroxycarbonate and simonkolleite were dominating in ambient air.     

Corrosion product formation on Zn55Al coated steel upon exposure in a marine atmosphere

The formation of corrosion products on Zn55Al coated steel has been investigated upon field exposures in a marine environment. The corrosion products consisted mainly of zinc aluminium hydroxy carbonate, Zn_0.71Al_0.29(OH)₂(CO₃)_0.145·xH₂O, zinc chloro sulfate (NaZn₄(SO₄)Cl(OH)₆·6H₂O), zinc hydroxy chloride, Zn₅(OH)₈Cl₂·H₂O and zinc hydroxy carbonate, Zn₅(OH)₆(CO₃)₂ were the first three phases were formed initially while zinc hydroxy carbonate Zn₅(OH)₆(CO₃)₂ was formed after prolonged exposure in more corrosive conditions. The initial corrosion product formation was due to selective corrosion of the zinc rich interdendritic areas of the coating resulting in a mixture of zinc and zinc aluminium corrosion products.     

Role of alloyed copper on corrosion resistance of austenitic stainless steel in H2S–Cl− environment

Corrosion test, surface analysis and thermodynamic calculation were carried out in the H₂S–Cl⁻ environments to clarify the role of alloyed Cu on the corrosion resistance of austenitic alloys. The alloyed Cu improved pitting corrosion resistance in the H₂S–Cl⁻ environment. The surface film of Cu-containing alloy indicated double layer consists of copper sulfide and chromium oxide, and the copper sulfide was able to exist stably compared to iron sulfide and nickel sulfide. It is concluded that the copper sulfide would enhance the formation of chromium oxide film which improve the pitting corrosion resistance in the H₂S–Cl⁻ environment.