Determination of biocorrosion of low alloy steel by sulfate‐reducing Desulfotomaculum sp. isolated from crude oil field

In this study corrosion behavior of low alloy steel, in the presence of anaerobic sulfate‐reducing Desulfotomaculum sp. which was isolated from an oil production well, was investigated. In order to determine corrosion rates and mechanisms, mass loss measurements and electrochemical polarization studies were performed without and with bacteria in the culture medium. Scanning electron microscopic observations and energy dispersive X‐ray spectra (EDS) analysis were made on steel coupons. The effect of iron concentration on corrosion behavior was determined by Tafel extrapolation method. In a sterile culture medium, as the FeSO₄ · 7H₂O concentration increased, corrosion potential (E_cor) values shifted towards more anodic potentials and corrosion current density (I_cor) values increased considerably. After inoculation of sulfate‐reducing bacteria (SRB), E_cor shifted towards cathodic values. I_cor values increased with increasing incubation time for 10 and 100 mg/L concentrations of FeSO₄ · 7H₂O. Results have shown that the corrosion activity changed due to several factors such as bacterial metabolites, ferrous sulfide, hydrogen sulfide, iron phosphide, and cathodic depolarization effect.     

1‐Methyl‐3‐pyridine‐2‐yl‐thiourea as inhibitor for acid corrosion of stainless steel

The inhibiting effect of 1‐methyl‐3‐pyridine‐2‐yl‐thiourea (MPT) on the corrosion of stainless steel in 0.5 M H₂SO₄ solution was investigated using weight loss and potentiostatic polarization techniques. The percentage inhibition efficiencies and surface coverage degrees increased with increasing additive concentration. Potentiostatic polarization studies revealed that MPT is of the mixed‐type inhibitor in 0.5 M H₂SO₄ solution. The adsorption of this inhibitor is also found to obey the Langmuir adsorption isotherm. From the adsorption isotherm, value of the ΔG_ads for the adsorption process was calculated. From the corrosion rate obtained at 25–55 °C E_a, ΔH_a and possible mechanism have been proposed. Scanning electron microscopy (SEM) was done from the surface of the exposed sample indicating uniform film on the surface.     

Corrosion resistance of the anti‐sulfide steel in the CO2/H2S containing solutions

The present work primarily investigates the corrosion characterization of the common P110 steel and the anti‐sulfide P110SS steel in CO₂‐containing solution with or without hydrosulfuric acid (H₂S) at 70 °C. The electrochemical techniques such as potentiodynamic polarization sweep and electrochemical impedance spectroscopy (EIS) were used to disclose the differences of the corrosion mechanisms between both P110 and P110SS steels in CO₂‐containing solution with various additions of H₂S. The EIS data fitted by ZsimpWin software were analyzed and discussed. The experimental results indicated that H₂S could accelerate and also inhibit the corrosion attack according to the changes of corrosive environments.     

Corrosion characteristics of boronized AISI 8620 steel in oil field water containing H<Subscript>2</Subscript>S

The corrosion behaviours of non-boronized and boronized AISI 8620 steels in both oil field water and H₂S-saturated oil field water have been investigated by means of immersion test, electrochemical method, X-ray diffraction and scanning electron microscopy. The experimental results show that boronized steel has better corrosion resistance to as-received oil field water and H₂S-saturated oil field water than the non-boronized steel. Both non-boronized and boronized steels have reacted with H₂S and form corrosion film of FeS, which could not retard the corrosion process due to pores and cracks in the FeS film, and large scale of pitting corrosion is found on non-boronized AISI 8620 steel surface. The immersion corrosion of non-boronized AISI8620 in both corrosion solutions can be divided into two stages: the rapid corrosion stage with high slope and the gradual corrosion stage with low slope, corresponding to uniform corrosion and corrosive product scaling off the surface, respectively. The better corrosion resistance shown by boronized AISI 8620 steel is ascribed to lower corrosion current as compared with the non-boronized AISI8620 steel.     

Adsorption effect of 1‐((2‐hydroxynaphtalen‐1‐yl) (phenyl)methyl)urea on the carbon steel corrosion in hydrochloric acid media

The adsorption effect of 1‐((2‐hydroxynaphtalen‐1‐yl)(phenyl)methyl)urea (HNPU) on corrosion behavior of carbon steel in 1 M hydrochloric acid solution was investigated using weight loss, potentiostatic polarization, and infrared spectroscopy methods. Surface morphology was studied by scanning electron microscopy (SEM). The experimental results, suggest that HNPU inhibited the corrosion of carbon steel in acid solution and the inhibition efficiencies increased as the concentration of the compound in the solution was increased. The calculated inhibition efficiencies from the two investigated methods were in good agreement. Potentiostatic polarization measurements indicate that HNPU acts as a mixed‐type inhibitor. The adsorption of the inhibitor on the carbon steel surface obeys Langmuir adsorption isotherm. The values of activation energy and the thermodynamic parameters, such as adsorption equilibrium constant (K_ads), adsorption free energy (ΔG_ads), adsorption heat (ΔH_ads), and adsorption entropy (ΔS_ads) values were calculated and discussed. The results obtained from infrared spectra, confirmed the adsorption of inhibitor on the alloy surface after immersion in acidic solution containing HNPU. The SEM analysis indicated that there are more lightly corroded and oxidative steel surface for the specimens after immersion in acidic solution containing HNPU than that in blank.     

The Influence of the Desulfovibrio desulfuricans 14 ATCC 27774 on the corrosion of mild steel

The involvement of sulphate‐reducing bacteria (SRB) in microbially influenced corrosion (MIC) of steel and the serious implications associated with their presence in industrial environments have long been known and extensively described. Desulfovibrio desulfuricans ATCC 27774 is an interesting metabolic case of SRB, as it can use both sulphate and nitrate as respiratory substrates during lactate oxidation. This strain has been extensively studied from both a biochemical and structural point of view but, so far, restricted information is available concerning its role in MIC. This work describes a comparative study of the corrosive aggressivity of ATCC 27774 strain towards mild steel when grown either in lactate/sulphate or lactate/nitrate media. The carbon source and electron acceptor's consumption rates were analysed and the metabolic features were correlated with weight loss measurements and SEM observations.     

Corrosion behaviour of oil well casing steel in H2S saturated NACE solution

Abstract

The corrosion behaviour of oil well casing steel in H₂S saturated NACE solution (5 wt-%NaCl+0·5 wt-%CH₃COOH) was investigated by means of electrochemical methods, X-ray photoelectron spectroscopy and scanning electron microscopy. It was found that the investigated oil well casing steel can react with hydrogen sulphide in the H₂S saturated NACE solution at 25°C. During the reaction, corrosion films of mackinawite (FeS) form on the steel surface and the hydrogen atoms diffuse into steel matrix. The further corrosion of iron with H₂S can be retarded, and hydrogen permeation flux decreased, by the presence of the mackinawite film, which acts as a protective barrier provided it remains intact.     

Long-term corrosion behaviour of carbon steel and stainless steel in Opalinus clay: influence of stepwise temperature increase

ABSTRACT

Carbon steel (C-steel; E24 and S235 grades) and stainless steel (316L) electrodes were corroded in situ in Opalinus clay under anoxic conditions in a vertical descending borehole. The electrodes were exposed at ambient temperature for two years, and then at 85°C for five years. In situ electrochemical impedance spectroscopy showed that the instantaneous corrosion rate of C-steel decreased over time down to 1?µm?year^?1, followed by steady state. Microbial and chemical investigations showed that sulphate and thiosulphate reducing prokaryotes were present in the porewater and at the metal surface. Post mortem characterisation revealed contrasting corrosion aspects. The E24 corrosion interface was thick and contained magnetite, mackinawite, hydroxychloride and siderite, together with more oxidised species (goethite, greigite, elemental sulphur). The S235 corrosion interface was thinner and contained siderite and mackinawite. Corrosion damage of the 316L electrode was negligible, and the surface was covered by a thin fringe of pyrite.     

Surface analytical studies of metal dusting of iron in CH4‐H2‐H2S mixtures

The metastable iron carbide, cementite (Fe₃C), occurs as an intermediate phase during the high temperature corrosion process called “metal dusting”. The kinetics and thermodynamics of metal dusting of iron have been studied by Grabke et al. [1–5] using CO‐H₂‐H₂O and CH₄‐H₂ gas mixtures. H₂S additions to carburising atmospheres impede the carbon transfer and retard the onset of metal dusting [6–14], thus allowing to study the early stages of the process. In this work the metal dusting process was studied in CH₄‐H₂‐H₂S atmospheres at 700 °C. Segregation experiments and surface analyses showed that S segregates on iron surfaces as well as on cementite surfaces. By means of Auger electron spectroscopy (AES), scanning Auger electron microscopy (SAM) and energy dispersive X‐ray analysis (EDX) it was shown that coke contains graphite, cementite and iron particles with adsorbed sulphur.     

Laboratory‐simulated fuel‐ash corrosion of superheater tubes in coal‐fired ultra‐supercritical‐boilers

The corrosion behaviour of a number of Ni‐base alloys of different composition together with a highly‐alloyed austenitic stainless steel has been investigated with and without coating of the samples with alkali‐containing synthetic coal ash. The effects of various parameters have been studied, namely the Cr content (from 20 to 28 mass % Cr), the test temperature (700 and 775°C), the SO₂ content in the gas (1 vol% and 0.25 vol % SO₂) and the alkali sulphate content of the ash (10 and 30 mass%). The results can be explained on the basis of the differences in corrosion mechanisms resulting primarily from the composition of the alloys tested.     

Untersuchungen über den Einfluß von Schwefelwasserstoff und Schwefeldioxyd auf die Korrosion chemisch beständiger Chrom-Nickel-Stähle in schwefelsaurer Natriumsulfatlösung

Investigations into the influence of hydrogen sulphur dioxide on the corrosion of chemically resistant chrome nickel steels in a sulphuric acid chrome nickel steels in a sulphuric acid solution of sodium sulphate By measuring the current/potential curves and determining the weight losses, the influence of H₂S and SO₂ on the corrosion of an 18/8 Cr? NI steel and of an 18/8 Cr? Ni stell with 2pCMo and 2.8pC Cu in sodium sulphate solution has been investigated. H₂S and SO₂ have the effect of shifting the rest potential towards the electronegative side, compared with a solution flushed with nitrogen, enlarging the potential range of active dissolution, and greatly increasing the dissolution, and greatly increasing the corrosion rate in the active zone. From the results of the measurements, it may be concluded that the metal dissolution is catalyzed by hydrogen sulphide ions and probably by reduction products of the sulphur dioxide. This catalyzing effect is not confined to the zone of activation overpotential but also occurs in the zone of the active plateau, the shape of which is largely determined by the migration phenomena. SO₂also has the effect of increasing the dissolution rate in the passive condition.     

The effect of H2S concentration on the corrosion behavior of carbon steel at 90 °C

The electrochemical behavior of SAE-1020 carbon steel in 0.25 M Na₂SO₄ solution containing different concentrations of H₂S at 90 °C was investigated using the methods of weight loss, electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the corrosion rate of carbon steel increased significantly with the increase of H₂S concentration. H₂S accelerated the corrosion rate of SAE-1020 carbon steel by a promoted hydrogen evolution reaction. Severe corrosion cavities were observed on the carbon steel surface in the solutions containing H₂S due to cementites stripped off from the grain boundary. The loose corrosion products formed on the steel surfaces were composed of mackinawite.     

Corrosion behavior of twinning‐induced plasticity (TWIP) steel

In this study, the corrosion behavior of twinning‐induced plasticity (TWIP) steel i.e. Fe‐Mn‐Al‐Si steel subjected to cold‐working (0, 20, and 35%), was examined in acidic (0.1 M H₂SO₄), alkaline (0.1 M NaOH) and chloride‐containing (3.5% NaCl) environments, using potentiodynamic polarization experiments. Interestingly, cold‐working did not show any significant change in the corrosion susceptibility of TWIP steel in all the three environments. However, TWIP steel showed the highest corrosion susceptibility in acidic environment and the lowest in alkaline environment. Scanning electron microscope analysis of the corroded TWIP steel samples revealed high‐localized attack in acidic environment and some pitting corrosion in chloride‐containing solution.     

Korrosionsreaktiorren von elementarem Schwefel mit unlegiertem Stahl in wäßrigen Medien

Corrosion reactions between elemental sulphur and plain carbon steel in aqueous media Plain carbon steels are rather severely attacked by elemental sulphur at room temperature in the presence of aqueous media. The corrosion occurs preferentially at the places where the two solid substances iron and sulphur are in contact with each other and results in shallow pit formation. At the same time the pH is also decreased slightly and small amounts of H₂S and sulphate ions are formed. Neutral salts stimulate the corrosion process whereas phosphates inhibit it and the alkaline media such as Na₂CO₃ and ethylamine with pH > 12 prevent it completely. The latter can be made use of for corrosion protection. At high salt concentrations (c > 1 mol/l) the corrosion rate, however, decreases with increasing salt concentration. The corrosion rate may increase with increasing flow velocity of the medium, but the corrosion takes place uniformly. The results of electrochemical investigations show that the reduction of sulphur occurs at the corrosion product FeS and is the rate controlling step. No sulphur reduction is observed on platinum electrodes when no FeS is present. It is assumed that the starting reaction to initiate corrosion in the system Fe/S/H₂O is a slight disproportionation of S to H₂SO₄ resulting in the formation of FeS.     

Corrosion behaviour of carbon steel coated with Zr‐based metallic glass

Zr₅₅Cu₃₀Al₁₀Ni₅ glassy alloy samples were prepared by the single roller melt spinning technique in an argon atmosphere. Amorphous ribbons were coated on carbon steel by the electron beam technique. Subsequently, the coated region was remelted to study its effect on the corrosion performance. The microstructure of the ribbons and of coated steel samples was characterized by X‐ray diffraction (XRD) and optical microscopy (OM). Potentiodynamic polarization studies were carried out in 0.1 M Na₂SO₄ electrolytes at pH = 8 and pH = 2. The coated samples showed a significant increase in corrosion resistance compared to the base carbon steel in both sulphate electrolytes. The pitting corrosion behaviour of the coated samples has been examined in 0.01 M NaCl electrolyte and was found to be poor. Furthermore, the galvanic and crevice corrosion behaviour of these alloys has been evaluated in the chloride electrolyte.     

A new steel with good low‐temperature sulfuric acid dew point corrosion resistance

In this work, new steels (1#, 2#, and 3#) were developed for low‐temperature sulfuric acid dew point corrosion. The mass loss rate, macro‐ and micro‐morphologies and compositions of corrosion products of new steels in 10, 30, and 50% H₂SO₄ solutions at its corresponding dew points were investigated by immersion test, scanning electron microscopy (SEM) and energy‐dispersive spectrometry (EDS). The results indicated that mass loss rate of all the tested steels first strongly increased and then decreased as H₂SO₄ concentration increased, which reached maximum at 30%. Corrosion resistance of 2# steel is the best among all specimens due to its fine and homogeneous morphologies of corrosion products. The electrochemical corrosion properties of new steels in 10 and 30% H₂SO₄ solutions at its corresponding dew points were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results demonstrated that corrosion resistance of 2# steel is the best among all the experimental samples due to its lowest corrosion current density and highest charge transfer resistance, which is consistent with the results obtained from immersion tests.     

Corrosion Behavior of Low-Alloy Pipeline Steel Exposed to H<Subscript>2</Subscript>S/CO<Subscript>2</Subscript>-Saturated Saline Solution

Immersion experiments were carried out to study H₂S/CO₂ corrosion behavior of low-alloy pipeline steel in terms of microstructure, corrosion kinetics, corrosion phases, microscopic surface morphology, cross-sectional morphology and elemental distribution. The experimental results indicated that the microstructure of designed steel was tempered martensite. The corrosion rate followed exponential behavior. H₂S corrosion dominated the corrosion process, and the corrosion products were mackinawite, greigite and troilite. The corrosion products changed from mackinawite/greigite to mackinawite/troilite, and mackinawite dominated the corrosion phases. The corrosion products became more compact with immersion time, which led to decrease in corrosion rate. The chromium and molybdenum content in the corrosion product was higher than that in the steel substrate.     

Corrosion behaviour of carbon steel in different concentrations of HCl solutions containing H2S at 90 °C

The corrosion behavior of SAE-1020 carbon steel in H₂S-containing solutions with different concentration of HCl at 90 °C was investigated by weight loss, electrochemical measurements, SEM and XRD analysis. The results showed that the corrosion rate of carbon steel increased with increasing HCl concentration. Uniform corrosion was found on the carbon steel surface in H₂S + HCl solutions, while corrosion cavities were observed in the solution only containing H₂S. The ratio of Faradaic process of total corrosion process increased with the increase of HCl concentration. The corrosion products were solely composed of mackinawite in the H₂S-containing solutions with or without HCl.     

Influence of tensile stress on corrosion behaviour of high‐strength galvanized steel bridge wires in simulated acid rain

Corrosion behaviour of the high‐strength galvanized steel wires under tensile stress was researched by electrochemical polarization and salt spray test (SST) using simulated acid rain as electrolyte. Electrochemical polarization and SST results showed corrosion rate rose significantly with increasing tensile stress; white grains were observed by SEM after polarization, while cellular and dendritic crystals appeared on the rust layer after SST. XRD and TG‐DTA results revealed (Zn(OH)₂)₃ · ZnSO₄ · 5H₂O was the main corrosion product, and traces of Fe₂(SO₄)₂O · 7H₂O, Fe₂(SO₄)₃, Fe₂O₃ · H₂O were also detected. A three‐stage corrosion process for the galvanized steel wires during SST was proposed.     

H2S and O2 influence on the corrosion of carbon steel immersed in a solution containing 3 M diethanolamine

Aqueous solutions with 3 mol L⁻¹ (M) diethanolamine (DEA) concentration are extensively used in the gas processing industry to remove acid gases. However, the degradation of the DEA and the formation of heat-stable salts (HSS) lead to severe corrosion problems. Even worse, equipment corrosion can be magnified by the unavoidable presence of sulphide acid and dissolved oxygen as a result of hydrocarbon (natural gases and crude oil) processing. The aim of this work is to study the combined corrosion effects of DEA, sulphide acid and oxygen on carbon steel. Electrochemical methods revealed that in the 3 M DEA medium without oxygen, corrosion processes are modulated by adsorbed DEA film formation. Furthermore, it was shown that the addition of oxygen and 15 × 10⁻³ mol L⁻¹ (15 mM) H₂S produced the formation of an adherent film on the carbon steel surface. Chemical analyses by EDAX revealed a homogeneous film of corrosion products composed of iron oxide and sulphide formed in DEA solution containing O₂ and H₂S, respectively. Equivalent circuits were used to estimate the parameters associated with ion diffusion through the formed corrosion films. The results showed that the presence of H₂S induced the formation of thin iron sulphide films that provide protective properties to the metal. It is concluded that the presence of oxygen in a sweetening plant should be avoided as DEA degradation can be produced with the subsequent decrease in chelating process efficiency and the increase in corrosion problems.