Corrosion study of the X52 steel immersed in seawater with a corrosion inhibitor using a rotating cylinder electrode

A corrosion study of API X52 steel was carried out in natural seawater with several concentrations of a corrosion inhibitor (10, 100 and 200 ppm) using a rotating cylinder electrode (RCE) to control the hydrodynamic conditions at environment temperature, atmospheric pressure and 24 h of the exposition time. The rotation speed used was 1000 rpm (turbulent flow). The electrochemical techniques used in the corrosion studies were: linear polarisation resistance (LPR), electrochemical impedance spectroscopy (EIS) and polarisation curves (PCs). The superficial analysis was made using a scanning electron microscope (SEM). The results show a good correlation between electrochemical techniques used. In addition, under turbulent flow, the test solution with 10 ppm had the smallest corrosion rate (CR). It is important to mention that the morphology of the corrosion in all experiments was localised corrosion.     

Measuring the corrosion rate of steel in concrete – effect of measurement technique,polarisation time and current

Both on‐site investigations and laboratory studies have shown that different corrosion rates are obtained when different commercially available corrosion rate instruments are used. The different electrochemical techniques and the measurement parameters used, i.e. polarisation current and time, are in some studies considered the main reasons for the variations. This paper presents an experimental study on the quantitative effect of polarisation time and current on the measured polarisation resistance – and thus the corrosion current density – of passively and actively corroding steel. Two electrochemical techniques often used in instruments for on‐site corrosion rate measurements are investigated. On passively corroding reinforcement the measured polarisation resistance was for both techniques found to be highly affected by the polarisation time and current and no plateaus at either short or long polarisation times, or low or high polarisation currents were identified. On actively corroding reinforcement a large effect of the polarisation time was also found, but only a minor effect of the polarisation current. The effect of the polarisation time was, however, practically independent of the corrosion rate for actively corroding steel. For both techniques guidelines for polarisation times and currents are given for (on‐site) non‐destructive corrosion rate measurements on reinforcement steel in concrete.     

Effect of turbulent flow on the anodic and cathodic kinetics of API X52 steel corrosion in H2S containing solutions. A rotating cylinder electrode study

This work presents the electrochemical kinetics results measured during the corrosion of API X52 pipeline steel immersed in aqueous environments, containing dissolved hydrogen sulfide (H₂S) under turbulent flow conditions. In order to control the turbulent flow conditions, a rotating cylinder electrode (RCE) was used. Five different rotation rates were studied: 0 (or static conditions), 1000, 3000, 5000 and 7000 rpm. It was found that the turbulent flow increases the corrosion rate and the corrosion mechanism for X52 steel exhibits a significant dependence on mass transfer on the cathodic kinetics.     

Corrosion behaviour of HVOF-sprayed Co–Cr–W–C coating in NaCl solution

Stellite 6 (Co–Cr–W–C) coating was deposited on carbon steel substrate by high-velocity oxyfuel spraying. The electrochemical corrosion behaviour of the coatings was investigated in 3.5% NaCl solutions at 25°C by means of polarisation studies and electrochemical impedance spectroscopy (EIS) measurements. The immersion time before corrosion tests was 0.5 and 24?h. The results showed that the corrosion rate of the coatings was lower than that of the steel substrate by one order of magnitude. An active–passive behaviour was observed during anodic polarisation of the coatings at both immersion times. The degree of substrate attack after polarisation tests of coated samples was not considerable. EIS measurement showed that two-time constants were observed in Nyquist plots of the coatings.     

Study of the pitting corrosion of superduplex stainless steel and X-65 carbon steel during erosion–corrosion by cyclic polarisation technique

Erosion-enhanced corrosion behaviour of X-65 carbon steel and UNS S32750 superduplex stainless steel was investigated by electrochemical cyclic polarisation. The tests were performed using a jet slurry device coupled with a potentio-galvanostat at various jet velocities of 4, 6.5 and 9?m?s^?1 and impingement angles of 30 and 90? in a 3.5?wt-% NaCl water containing 6?wt-% silica sand particles. The results showed that increasing the jet velocity and impingement angle increased the corrosion rate of both alloys. Negative hysteresis and greater E_rp than OCP were observed for superduplex stainless steel in all erosion–corrosion conditions that indicated the pitting resistance of the alloy. However, the low resistance of carbon steel against pitting during erosion–corrosion was demonstrated by positive hysteresis in the cyclic polarisation curves as well as SEM images of the eroded surfaces.     

Investigations on the re-passivation of carbon steel in chloride containing concrete in consequence of cathodic polarisation

Although the complex changes at the steel–concrete interface due to cathodic polarisation are widely acknowledged to have a beneficial influence concerning the cathodic protection (CP) of steel in concrete, some questions concerning the repassivation of carbon steel in consequence of cathodic polarisation are still not satisfactorily clarified. In the recent literature, some indications are presented that repassivation occurs after a certain time of polarisation. Therefore, the investigations discussed in this paper aim to clarify, to what extent the re-passivation of carbon steel due to cathodic polarisation occurs, and if the ennoblement of OCP is a sufficient indication for repassivation. In a first step, the corrosion state of five nominal equal test specimens was determined by electrochemical impedance spectroscopy (EIS). After determining the initial corrosion state by evaluating the charge transfer resistance and the polarisation resistance, respectively, the specimens were polarised cathodically. Impedance data were recorded before, during and after polarisation. The impedance data were evaluated by equivalent circuit fitting with special attention to charge transfer resistances and the impact of diffusion on the corrosion and polarisation behaviour. The results indicate that the reduction of oxides and oxygen diffusion during cathodic polarisation has strong impact on the systems behaviour and that repassivation effects occur after switching off the polarisation current and during depolarisation, respectively.     

Development and evaluation of miniature electrodes for electrochemical measurements in a CO2 top of line corrosion environment

ABSTRACT

Top of line corrosion (TLC) is a degradation mechanism which establishes itself in ‘wet gas’ pipelines under significant temperature difference between the internal fluid and the outer pipe wall. Laboratory evaluation of TLC is based predominantly on the mass loss method which is an averaging approach. Hence, a real-time and spatially resolved corrosion response would add an extra dimension in terms of corrosion measurement. This work presents a new apparatus to explore the ability of a miniature three-electrode cell to provide instantaneous corrosion measurements in a TLC scenario. The electrochemical system is integrated into a buoyancy-driven flow TLC setup and is used to monitor instantaneous corrosion rates for X65 carbon steel over 20h through a combination of linear polarisation resistance, electrochemical impedance spectroscopy and Tafel measurements. The electrochemical responses are compared with gravimetric results under identical conditions and generating repeatable, accurate and instantaneous data to provide more insight into TLC mechanism.     

基于电化学方法5Cr钢熔化焊接头CO2腐蚀行为

为了获得5Cr钢熔化焊焊接接头的动态腐蚀特性,采用基于电极电位的电化学方法进行5Cr钢焊接接头耐CO₂腐蚀行为的研究,建立了基于极化曲线下的腐蚀模型,研究了不同填充材料的焊接接头的耐腐蚀性. 研究发现,在温度为40 ℃,CO₂分压为10个大气压等加速腐蚀条件下,低铬焊丝的焊缝区域的自腐蚀电位最正,腐蚀速率最小,高铬焊丝的焊缝区域的自腐蚀电位较正,腐蚀速率较小,无铬焊丝的焊缝自腐蚀电位最负,腐蚀速率最大. 对比只反应腐蚀前后质量变化的失重法,电化学方法反映了腐蚀周期任一时刻的动态腐蚀速率,基于电化学腐蚀模型下的腐蚀速率与失重法测量结果相吻合. 验证了电化学腐蚀模型的正确性. 结果表明,低铬钢匹配适当的低铬焊丝可使得焊接接头具有较强的耐CO₂腐蚀性能.     

Nitrogen-based corrosion inhibitor film study using weight loss and electrochemical methods in static and turbulent conditions

There is an increasing demand from oil and gas industry to ensure the integrity of assets and the enviroment in the critical conditions found in presalt wells. This study evaluates new formulations of corrosion inhibitors with different types and alkoxylation degrees of nitrogen-based inhibitors to assess corrosion behavior of carbon steel (API X65). For these studies, corrosion rates were determined through measurements of weight loss and linear polarization resistance (LPR). In the case of electrochemical measurements, experiments were carried out in a laminar flow and in a turbulent flow regime. All data were collected in the presence of CO₂ and CO₂/H₂S mixtures. The results revealed that corrosion protection of carbon steel critically depends on the nitrogen-based inhibitor's alkoxylation type and degree as well as the condition to which they are exposed. It was possible to notice that an ethoxylated amine whose inhibition efficiency in the presence of CO₂ was about 10%, when exposed to H₂S environment at the same temperature showed an efficiency of 86%. It was also observed that the inhibitor with a higher ethoxylation degree presented better efficiencies than the one with a lower degree.     

Corrosion inhibition of 304 stainless steel by Paecilomyces variotii and Aspergillus niger in aqueous environment

The presence of microorganisms influences corrosion of metallic materials by either an accelerating or an inhibiting effect. While most studies have focused on corrosion influenced by bacteria, especially sulphate-reducing bacteria, fungus (or mould) is another form of microorganisms which can significantly affect corrosion processes. This study investigated the effects of two common fungi, Paecilomyces variotii and Aspergillus niger, on corrosion of 304 stainless steel immersed in aqueous environment for up to 28 days. Biofilm formation was observed by SEM. Instead of accelerating corrosion, electrochemical studies such as potentiodynamic polarisation and electrochemical impedance spectroscopy have shown inhibitive effects of these fungi to corrosion of 304 stainless steel.     

Morphology and composition of Zn–Ni alloy obtained from sulphate bath containing complexing agent

ABSTRACT

Zn–Ni alloys were electrodeposited on stainless steel from a sulphate bath in the presence of EDTA (ethylenediaminetetraacetic acid) as a complexing agent. The electrochemical behaviour of the bath was studied by cyclic voltammetry (CV), chronoamperometry (CA). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed a change in surface morphology; the phase structure corresponds to the face centre cubic (fcc) structure attributed to the γ phase (Ni₅Zn₂₁). The corrosion measurements of the obtained deposits with various EDTA concentrations were studied using potentiodynamic polarisation. Results showed that the deposit obtained in the presence of a low EDTA concentration (0.25?g?L^?1) exhibits better corrosion resistance.     

Role of thickness on electrochemical behaviour of Ni2Si coatings in NaCl solution

Abstract

Ni₂Si intermetallic coatings were deposited on a substrate of 420 stainless steel using a high velocity oxy-fuel (HVOF) process. The electrochemical corrosion behaviour of the coatings in 3.5% NaCl solution was investigated by means of Tafel polarisation tests and electrochemical impedance spectroscopy (EIS) measurements. Two coatings with different thicknesses, 55 and 115?μm, were investigated. The results showed that the corrosion rate of the thicker coating was lower than that of stainless steel by one order of magnitude. Local attack of the substrate was observed after the polarisation test of this coating, while the coating was still intact. The thinner coating and the stainless steel substrate showed similar corrosion rates. In this case, the substrate was severely attacked after the polarisation test. Two time constants were observed in the EIS spectra of both coatings which were related to charge transfer processes and pore resistance, respectively.     

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.     

The role of different surface damages in corrosion process in alkaline sour media

By applying different electrochemical methodologies to 1018 carbon steel/different electrolytic media interfaces, surfaces with generalised and blistered damages, commonly present in the oil refinery catalytic plants, were obtained. Afterwards, a freshly polished carbon steel surface as well as the damaged surfaces were characterised by electrochemical impedance spectroscopy and scanning electronic microscopy (SEM). The SEM results reveal that the damaged surfaces present films with different physical properties.In spite of the surface modification, the corrosion mechanism of these interfaces in a medium simulating catalytic plants condensates of the refineries in Mexico (0.1 M (NH₄)₂S, 0.4 mM NaCN (10 ppm CN⁻), pH=8.8) turned out to be the same. It was also found that the corrosion process presents the following steps: charge transfer resistance of steel oxidation in the metal/corrosion product film interface and the diffusion processes of Fe²⁺ and H^o ions through the corrosion product film. It was demonstrated that when there was no damage on the surface (freshly polished surface), a homogeneous film was formed instantaneously upon introducing carbon steel into the sour media. The corrosion process in this film occurs in three stages. On the surface with generalised corrosion the three stages are favoured, particularly that of atomic hydrogen process (inducing blistering). Meanwhile, the blistered surface presents a higher charge resistance of steel oxidation and the Fe²⁺ and atomic hydrogen diffusions through the corrosion products are slower than those presented on the other surface states.     

Effects of turbulent flow on the corrosion inhibition properties of 2‐mercaptobenzimidazole

The electrochemical techniques, that is, polarization resistance (R_p) and potentiodynamic polarization curves, were used in order to determine the effect of turbulent flow on the corrosion inhibiting effect of 2‐mercaptobenzimidazole (2‐MBI) on API 5L X52 grade steel samples immersed in a 3% NaCl aqueous solution saturated with CO₂ at 60 °C. Turbulent flow conditions were controlled using a rotating cylinder electrode (RCE). An inhibition efficiency of 98% was measured at a concentration of 10 ppm of 2‐MBI at a rotation rate of 5000 rpm. This efficiency value is similar to those efficiency values measured at 25 and 40 ppm 2‐MBI and at the same rotation rate. These observations suggest that as the turbulent flow conditions increase the corrosion inhibiting effect of 2‐MBI is enhanced. 2‐MBI follows a Langmuir adsorption isotherm. The calculated values of adsorption equilibrium constant (K_ads) and adsorption free energy ($\Delta G_{{\rm ads}}^{{\rm o}} $ ) suggest that the adsorption process taking place is chemical. The polarization curves indicate that the 2‐MBI does not modify the electrochemical mechanism of the anodic (Fe dissolution) and cathodic (hydrogen evolution) reactions. It is suggested that 2‐MBI decreases the rate at which these reactions occur, blocking the active sites on the steel surface.     

Microbiologically influenced corrosion of ferritic steel–zirconium-based metal waste form alloy under simulated geological repository environment

The present work focused on investigating the microbiologically influenced corrosion (MIC) susceptibility of ferritic steel–Zr-based metal waste form (MWF) alloy in simulated ground water media, cultured with a common biofilm former Bacillus sp. Total viable count studies showed a good bacterial attachment on the surface of MWF alloy. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) examination of the biofilm MWF surface revealed preferential adhesion of microbes on Fe–Zr-rich intermetallic phases. Anodic polarisation and electrochemical impedance spectroscopic (EIS) studies showed active corrosion potential (E_corr), higher passive current density (I_pass) and decreased polarisation resistance (R_p) values, confirming the corrosion susceptibility of MWF alloy under Bacillus sp. biofilm.     

Effect of methanol on the corrosion behaviour of Al-Cu Alloys in sulphuric acid

The effect of Cu additions (1, 3 and 5?at.-%) on the corrosion behaviour of Al in 0.5?M H₂SO_4?+?2?ppm hydrofluoric acid?+?methanol at 50°C, environment found in a direct methanol fuel cell, has been evaluated using electrochemical techniques. Electrochemical techniques included potentiodynamic polarisation curves, electrochemical impedance spectroscopy and electrochemical noise measurements measurements. Methanol concentrations included 1, 5, 10 and 20?M. Results have shown that corrosion resistance increases with increasing the methanol concentration. The addition of Cu to Al increases the corrosion rate of the former by the formation of micro galvanic cells, inducing localised typo of corrosion also.     

Corrosion of galvanised steel under an electrolytic drop

Described here for the first time is an investigation of the local corrosion behaviour of galvanized steel using an electrolytic droplet comprising chloride and sulphate ions. The maximal height of the electrolytic layer and the diameter varied between 500-1100 μm with a total diameter between 1.47-3.35 mm, respectively. These measurements were possible by using microelectrodes as reference and counter electrodes, which could be inserted into the electrolyte droplet thus forming an electrochemical microcell. Polarization curves as well as electrochemical impedance spectroscopy plots were recorded under the electrolyte droplet configuration allowing the determination of the polarisation resistance R_p and the proportionality constant k of the Stern and Geary equation. The influence of temperature, chloride concentration, pH and the thickness of the electrolytic layer on the corrosion rate of galvanised steel were studied.     

Corrosion of biomaterials: anodic treatment and evaluation of 316L stainless steel in simulated body fluid

The influence of electropolishing at different conditions on the electrochemical behaviour of 316L stainless steel (316L SS) in simulated body fluid (SBF) was investigated. Accordingly, 316L SS samples were electropolished in several electropolishing baths of H₃PO₄ and H₂SO₄ at 2–6 applied volts and 50–110°C for different time intervals. The corrosion behaviour then was studied by means of potentiodynamic polarisation technique and electrochemical impedance spectroscopy in SBF at 37°C. The surface morphology was also investigated by scanning electron microscopy. The results proved that the treated samples had better corrosion resistance than nonpolished one. The highest corrosion resistance was observed for the treated sample at 5?V and 90°C in 10:90 ratio of acidic electrolyte (H₃PO₄:H₂SO₄) for 15?min. Moreover, the corrosion resistances of anodically treated samples were found to be dependent greatly on applied volt, bath temperature, polishing time and phosphoric to sulphuric acids ratio.     

Effect of heat treatment on H2S corrosion of a micro-alloyed C–Mn steel

The H₂S corrosion resistance of a C–Mn pipeline steel with three different microstructures has been evaluated using electrochemical techniques with a 3% wt. NaCl solution at 50 °C. Microstructures included martensite, ferrite, and ferrite + bainite. Electrochemical techniques included potenthiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and electrochemical noise (EN) measurements. Most of the tests lasted 24 h. All techniques showed that the highest corrosion rate corresponded to the steel with a martensitic microstructure; up to one order of magnitude higher than the corrosion rate for steels with a ferritic + bainitiic microstructure, whereas the steel with the ferritic microstructure showed the lowest corrosion rate. EIS tests showed that the corrosion process was under charge transfer control, whereas EN results indicated that the three steels exhibited a clear tendency towards a localized type of corrosion. However, for longer immersion times, the steel with a martensitic microstructure tended to exhibit a mixture of uniform and localized attack. Results were discussed in terms of grain size, grain boundary energy, amount and distribution of particles found in each steel.