Characterisation of calcareous deposits on freely corroding low carbon steel in artificial sea water

Abstract

Calcareous deposits were formed on steel under cathodic protection conditions in artificial sea water at various potentials from ?0·900 to ?1·400 V(SCE). The deposition calcareous layers were characterised by electrochemical impedance spectroscopies, scanning electron microscopy observations and X-ray diffraction analyses. At 20°C, the deposits were composed of calcite CaCO₃ when formed at various potentials in solution 1, of brucite Mg(OH)₂ and aragonite CaCO₃ when formed at potentials from ?0·900 to ?1·200 V(SCE) and only of brucite when formed at potentials E??1·300 V(SCE) in solution 2. Magnesium seems to influence the corrosion behaviour of freely corroding steel by causing calcium carbonate to precipitate as aragonite. Aragonite is more effective in covering the surface than calcite and is therefore more functional in preventing oxygen from reaching the steel surface, thereby lowering the corrosion rate.     

The atmospheric corrosion kinetics of low carbon steel in a tropical marine environment

The atmospheric corrosion kinetics of low carbon steel exposed for up to 36 months in marine and industrial sites was studied by weight loss measurements. The results show that the mechanism and kinetics of the atmospheric corrosion process presents transition behaviour in marine environments with high chloride ion content and high relative humidity, whereas no transition appears in industrial environment. The average corrosion velocity in marine site reaches a maximum during the period of transition and then fluctuates in a certain range; however, the instantaneous corrosion velocity follows different exponential functions before and after the period of transition.     

Atmospheric corrosion of carbon steel in Colombia

The corrosion behaviour of carbon steel at six test sites in Colombia and its relationship with exposure time and environmental characteristics of each site were investigated. The corrosion products were characterized by XRD, SEM and EDS. It was found that in Barranquilla, the most aggressive site, corrosion depends mainly on chlorides. Furthermore, in the more aggressive environments there was a greater tendency to formation of protective corrosion products. Lepidocrocite and goethite were found as major constituents of rust. A structure not reported in the literature was found, corresponding to strings of several hundred micrometers long and consisting of lepidocrocite plates.     

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.     

The impact of additional nitrates in mild steel corrosion in a seawater/sediment system

This paper investigates the impact of additional nitrate sources on mild steel coupon corrosion in a seawater/sediment system. The results show that addition of 5 mM of nitrate sources significantly increased the weight loss of coupons after 20 weeks. SEM results indicate increase in microbial populations and corrosive products in the non-autoclaved and the nitrate-treated environments. EDX analyses revealed an increase in contents of carbon, calcium, magnesium, phosphorus and sodium with the exception of iron with an increase in incubation time.     

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.     

Inhibitory action of aqueous coffee ground extracts on the corrosion of carbon steel in HCl solution

The effects of aqueous extracts of spent coffee grounds on the corrosion of carbon steel in a 1 mol L⁻¹ HCl were examined. Two methods of extraction were studied: decoction and infusion. The inhibition efficiency of C-steel in 1 mol L⁻¹ HCl increased as the extract concentration and temperature increased. The coffee extracts acted as a mixed-type inhibitor with predominant cathodic effectiveness. In this study, the adsorption process of components of spent coffee grounds extracts obeyed the Langmuir adsorption isotherm. The chlorogenic acids isolated do not seem to explain the corrosion inhibition observed during the use of the coffee extracts.     

Corrosion of vertical mild steel strips in seawater

This paper describes the corrosion loss profiles of 1 m long vertical steel strips attached to a raft and exposed for 1 year in calm natural seawater on the Australian eastern seaboard. The upper parts of the strips were exposed to the atmosphere and the lower parts immersed to depths varying from 0.3 to 0.9 m. It was found that, irrespective of the precise ratio of atmospheric/immersion exposure, corrosion in the splash zone was much higher than that at the waterline and in the atmosphere. There was also significant corrosion in the immersion zone, immediately below the waterline, consistent with classical observations. Above the water line there was only moderate variability in corrosion between the strips but there was much greater variability in corrosion loss for the parts of the strips fully immersed. Mass loss observations are compared with observations of the corrosion and pitting patterns observed in the various zones. Potential reasons for these observations are considered. The observations have implications for explaining aspects of accelerated low water corrosion (ALWC).     

Effect of cations on corrosion of zinc and carbon steel covered with chloride deposits under atmospheric conditions

The effect of sodium, calcium, and magnesium chlorides deposited on zinc and carbon steel surfaces was studied under atmospheric conditions. The cations strongly affected the corrosion rate of zinc, whereas they had a significantly lower impact on the corrosion of carbon steel. The corrosivity of cations of chloride salts for zinc increased in order of Mg²⁺ < Ca²⁺ < Na⁺. The higher corrosion resistance of zinc treated with calcium and magnesium chlorides was connected to prevention of formation of hydrozincite during zinc exposure in wet air. It was observed that zinc weight loss and the carbonate to simonkolleite ratio in corrosion products were correlating. The principal protective effect of bivalent cations can be seen in the decrease of pH of the surface electrolyte, which was caused by hydrolysis of such cations and subsequent formation of simonkolleite that blocked the cathodic sites.     

Corrosion inhibition of carbon steel in hydrochloric acid solution by fruit peel aqueous extracts

The inhibitive action of the aqueous extracts of fruit peels against corrosion of carbon steel in a 1 M HCl solution was investigated using electrochemical impedance spectroscopy, potentiodynamic polarization curves, weight loss measurements and surface analysis. We analyzed aqueous extracts of mango, orange, passion fruit and cashew peels in different concentrations and found that the extracts act as good corrosion inhibitors for the tested system. The inhibition efficiency increases with increasing extract concentration and decreases with temperature. The adsorption of components of the fruit peel extracts on the surface of the carbon steel follows the Langmuir adsorption isotherm.     

Erosion–corrosion of carbon steel in simulated tailing slurries

This paper investigates the synergism of mechanical and electrochemical factors in erosion–corrosion. The fact that active corrosion in the tailing slurry donates a small portion of total material loss indicates that the synergism results mainly from corrosion-enhanced erosion. As theoretically predicted, the erosion rates in corroding slurry under same hydrodynamic condition is a linear function of logarithmic corrosion rate, suggesting that the corrosion-induced surface plasticity is the dominate mechanism of corrosion-enhanced erosion. The reduced resistance to plastic deformation in surface layer while exposed to corroding media is demonstrated by the in situ micro-hardness measurements. The erosion-enhanced corrosion in flowing slurry of steel is a result of dynamic plastic deformation caused by erodent impingement.     

Electrochemical effect of cationic gemini surfactant and halide salts on corrosion inhibition of low carbon steel in acid medium

In this paper, the corrosion inhibition of cationic gemini surfactant, in the absence and presence of halide salts (NaCl, NaBr and NaI) on steel in HCl was investigated at 20 ± 1 °C. The effects of pH, immersion time and salt concentration on the corrosion inhibition of steel were studied using weight loss, open circuit potential and electrochemical impedance spectroscopy. Inhibition efficiency increases by increasing surfactant concentration. Synergistic effect between surfactant and salts was studied. The inhibition efficiency increases by increasing salt concentration. This composite inhibitor containing gemini surfactant and halide was efficient and low-cost for steel corrosion inhibition in HCl.     

Pitting corrosion in low carbon steel influenced by remanent magnetization

A new type of experiment is performed using a closed magnetic circuit configuration in order to study the influence of the magnetic field on pitting corrosion in low carbon pipeline steel. The statistical assessment of the pitting corrosion data shows that the magnetic field in the material under test reduces the extreme pit depths and also the average depth of the pit population. It is proposed that reduction in pit depth under the influence of remanent magnetization can be explained based on the behavior of the paramagnetic corrosion products under the influence of the magnetic field gradient produced inside pits.     

Corrosion behavior of each phase in low carbon microalloyed ferrite–bainite dual-phase steel: Experiments and modeling

In situ observation of the initial corrosion behavior of a low carbon microalloyed ferrite–bainite dual-phase steel showed that the corrosion originated from the inside of ferrite and ferrite boundary. In addition, a model for describing the corrosion behavior of each phase in multiphase steel was established. Based on this model, a method to quantitatively assess the corrosion rate of each phase was presented by white light interference, and the relationship between the surface roughness and corrosion morphology was also established. Meanwhile, the galvanic corrosion at phase-scale and the influence of phase distribution on service safety of multiphase steel were discussed.     

Corrosion inhibition of carbon steel in tetra-n-butylammonium bromide aqueous solution by benzotriazole and Na3PO4

The corrosion inhibition behavior of benzotriazole, Na₃PO₄ and their mixture on carbon steel in 20 wt.% (0.628 mol l⁻¹) tetra-n-butylammonium bromide aerated aqueous solution was investigated by weight-loss test, potentiodynamic polarization measurement, electrochemical impedance spectroscopy and scanning electron microscope/energy dispersive X-ray techniques. The inhibition action of BTA or SP or inhibitors mixture on the corrosion of carbon steel is mainly due to the inhibition of anodic process of corrosion. The results revealed that inhibitors mixtures have shown synergistic effects at lower concentration of inhibitors. At 2 g l⁻¹ BTA and 2 g l⁻¹ SP showed optimum enhanced inhibition compared with their individual effects.     

Comparative studies on the corrosion properties of a Fe-Mn-Al-Si steel and an interstitial-free steel

Recent developments in a group of super ductile Fe-Mn-Al-Si steels with high-manganese content demands for more research in the corrosion behavior of such steels. The corrosion properties of the Fe-Mn-Al-Si steel was studied in acidic (0.1 M H₂SO₄), alkaline (0.1 M NaOH) and chloride-containing (3.5% NaCl) environments, using immersion and polarization experiments and compared with that of interstitial-free (IF) steel. In acidic solution, the Fe-Mn-Al-Si steel exhibited significantly lower corrosion resistance than that of IF steel. Though the Fe-Mn-Al-Si steel showed lower corrosion resistance as compared to IF steel in chloride solution, the difference was not as substantial as observed in acidic medium. However, in alkaline solution, the Fe-Mn-Al-Si steel showed no significant difference in the corrosion resistance in comparison with that of IF steel, and moreover exhibited substantially high corrosion resistance than in acidic and chloride solution. The post-corrosion characterization studies showed higher corrosion attack of the Fe-Mn-Al-Si steel exposed to acidic solution as compared to that in alkaline and chloride solutions, which is consistent with the corrosion measurement data.     

Inhibitory action of biodegradable modified vanillin on the corrosion of carbon steel in 1 M HCl

The effects of two biodegradable corrosion inhibitors derived from vanillin and aminophenol (Meta: VPAP and Para: VOAP) on the corrosion of carbon steel in 1 M HCl solution were examined. The efficiency of these inhibitors on carbon steel corrosion increased by increasing the concentration and decreased by increasing the temperature. The inhibitors adsorbed on carbon steel physically and obeyed the Langmuir isotherm. The potentiodynamic measurements showed mixed-type inhibitor. The geometry of the inhibitors showed that VPAP has slightly higher efficiency in corrosion inhibition than VOAP. The inhibitors showed good biodegradability in the environment within 28 days.     

The influence of zirconium additions on the corrosion of magnesium

Sixteen custom binary Mg–Zr alloys and four commercial Zr-containing Mg-alloys were used to investigate the role of Zr on the corrosion of Mg. Mg–Zr alloys were manufactured with a range of different Zr concentrations. It was observed that the Mg–Zr alloys with a smaller mean Zr particle size had more Zr dissolved in solid solution. Both the Zr in solid solution and in metallic particle form were observed to have a deleterious effect on the corrosion rate of Mg. However, this deleterious effect is less pronounced to effect in alloys with multiple alloying additions.     

The changing topography of corroding mild steel surfaces in seawater

The corrosion of mild steel exposed to marine immersion conditions typically is not uniform although it is often idealized as such. Anodic regions and micro-pits develop very quickly after first exposure and eventually there is the development of shallow broad pits. This transition of the surface topography and the processes involved are still not completely understood. The present paper presents a number of images typical of the sequential evolution of the surface topology of mild steel corroding in sub-tropical coastal seawater. The sequence consists of the development of anodic areas, development of small pits and shallow broad pits, the apparent coalescence of small pits into larger localized corrosion and eventually the appearance of stepped or benched, perhaps irregular-shaped broad or macro-pits. This sequence is typical of that which has been observed many times and this suggests it is reasonable to infer a generic sequence that describes the changing surface of corroding mild steel in seawater. It will assist in developing a better understanding of the evolution of corrosion processes for mild steel in seawater and assist in identifying the various controlling processes.     

A study on the initial corrosion behavior of carbon steel exposed to outdoor wet-dry cyclic condition

The initial corrosion behavior of carbon steel subjected to outdoor wet-dry cyclic exposure and exposure under natural environments have been investigated. The weight loss results indicate a transition from corrosion acceleration to deceleration during the early stage of corrosion of carbon steel under both conditions. The corrosion kinetics under both conditions follow empirical equation D = Atⁿ. Outdoor wet-dry cyclic exposure significantly promoted the initiation but the rate of corrosion was about three times as fast. The morphology of corrosion surfaces and cross-section of rust layer have been examined using SEM and the compositions have been analyzed using XRD and EPMA.