Influence of the sulphate reducing bacteria on API‐X70 steel corrosion

The corrosion behaviour of API X70 immersed in a specific medium with a strain of thermophilic sulphate reducing bacteria (SRB) was analysed. Anaerobic corrosion test was carry out for 32 days at 50 °C. During the exposure time, pH, sulphate (SO) and hydrogen sulphide (H₂S) concentration were measured. Corrosion potential, linear polarization resistance and potentiodynamic polarization curve were used in order to get the influence of the SRB in the corrosion phenomenon. Scanning electron microscopy was used to determine corrosion morphology. Results show that the SRB activity influenced the overall corrosion process. The anodic branches in the polarization curves show a passivity feature, whereas, the cathodic branches were not affected. A localized corrosion attack was found.     

Investigations on the effect of chloride on the general corrosion behavior of low‐alloy steels in oxygenated high‐temperature water

This project focused on investigations on the effect of chloride contaminations on the general corrosion and crack initiation behavior of low‐alloy steel (German reactor pressure vessel steel 22NiMoCr3 7) in oxygenated high‐temperature water (HTW). Therefore, tests were performed in oxygenated HTW without chloride and at different chloride contamination levels up to 50 ppb. Chloride was added either permanently or temporarily to simulate a chloride transient during plant operation. During these tests, electrochemical noise (EN) and electrochemical impedance spectroscopy (EIS) measurements were performed to monitor the electrochemical behavior depending on the adjusted environment conditions, especially the effect of chloride on the degradation of low‐alloy steel. After the tests, the specimens were examined macroscopically and microscopically. In addition, the oxide layer thickness was determined using the focused ion beam (FIB) technique and different surface analysis techniques as, e.g., TOF‐SIMS were performed to analyze the composition of the oxide layer. A change of the corrosion behavior of the tested specimens was revealed by the applied electrochemical methods EN and EIS during high‐temperature testing. In addition, the applied post‐test investigations showed a decrease in the oxide layer thickness due to permanently increased chloride concentrations in the HTW. Temporary transients, however, did not cause a long‐term memory effect as shown by both, the electrochemical and the metallographic post‐test investigations.     

Understanding the effect of surfactant aggregation on corrosion inhibition of mild steel in acidic medium

Corrosion inhibition by surfactant molecules is related to the surfactant's ability to aggregate at interfaces and in solution. Understanding the factors that affect aggregation as well as the state of aggregation of surfactant molecules on metal surfaces is, therefore, an important prerequisite to understanding corrosion inhibition by surfactant molecules. This article investigates the relationship between surfactant aggregation and mild steel corrosion inhibition in acidic medium using cetyl pyridinium chloride and cety trimethyl ammonium bromide.     

Electrochemical studies on the effect of pyrazolo‐containing compounds on the corrosion of carbon steel in 1 M sulphuric acid

The effect of some synthesized pyrazolo containing compounds on the corrosion of carbon steel in 1 M H₂SO₄ was investigated. The investigation involved electrochemical polarization methods (potentiodynamic, Tafel extrapolation and the determination of the polarization resistance). A significant decrease in the corrosion rate of carbon steel was observed in the presence of the investigated compounds. The results show that these compounds act as mixed type inhibitors, but the cathode is more preferentially polarized. The relative inhibition efficiency of these compounds depends on both the nature and concentrations of the investigated compounds. Compounds are found to adsorb on the carbon steel surface according to the Langmuir adsorption isotherm.     

Electrochemical and theoretical investigation on the corrosion inhibition of mild steel by thiosalicylaldehyde derivatives in hydrochloric acid solution

Inhibitory effect of three Schiff bases 2-{[(2-sulfanylphenyl)imino]methyl}]phenol (A), 2-{[(2)-1-(4-methylphenyl)methylidene]amino}-1-benznethiol (B), and 2-[(2-sulfanylphen-yl)ethanimidoyl)]phenol (C) on corrosion of mild steel in 15% HCl solution has been studied using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. The results of the investigation show that the compounds A and B with mean efficiency of 99% at 200 mg/L additive concentration have fairly good inhibiting properties for mild steel corrosion in hydrochloric acid, and they are as mixed inhibitor. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on mild steel surface. Adsorption of these inhibitors follows the Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K_ads, ΔG_ads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, E_a, activation enthalpies, ΔH^∗, and activation entropies, ΔS^∗, were calculated by the obtained corrosion currents at different temperatures. Obvious correlation was found between the corrosion inhibition efficiency and the calculated parameters. The obtained theoretical results have been adapted with the experimental data.     

Influence of chloride and moisture content on steel rebar corrosion in concrete

Reinforced mortar samples were exposed in humidity chambers with different relative humidity or exposed in cyclic moisture conditions. The rebars were in an “as received” condition meaning that the preexisting oxide scale were intact. The lowest chloride concentration that initiated corrosion was 1% Cl^? by mass of cement, corrosion was then observed for samples exposed at 97% relative humidity. It is suggested that the corrosion rate decreases when samples are exposed to a relative humidity lower than 97%. The results indicate that threshold levels should be evaluated at rather humid conditions (97%) despite the fact that the maximum corrosion rate at higher chloride levels is observed in the interval 91–94%. For samples exposed to cyclic moisture conditions, a lower chloride concentration was needed to initiate corrosion compared to samples exposed in static moisture conditions.     

Electrochemical corrosion behaviour of a Ti‐IF steel and a SAE 1020 steel in a 0.5 M NaCl solution

Investigations concerning the electrochemical corrosion behaviour of low carbon (LC) and ultra‐low carbon (ULC) steels are relatively scarce and limited. The present study aims to compare electrochemical impedance parameters and potentiodynamic polarization curves of an LC steel and an ULC Ti‐interstitial free (IF) steel evidencing the effects of carbon content and pearlite fraction on the electrochemical corrosion behaviour. Corrosion tests were carried out in a 0.5 M NaCl solution at 25 °C with a pH range between 6.5 and 6.8. It was found that the IF steel sample presents an electrochemical corrosion resistance, which is slightly higher than that of the LC steel sample.     

Initiation of chloride‐induced corrosion of steel in concrete: role of the interfacial zone

This paper provides a brief review of research aimed at characterising the steel–concrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH ～12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride‐induced corrosion because it counters the generation of ‘anodic acidity’ that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full‐scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non‐traditional cements.     

Electrochemical corrosion behavior of X80 pipeline steel in a near‐neutral pH solution

In this work, the electrochemical corrosion behavior of X80 pipeline steel was investigated in a near‐neutral pH solution using electrochemical impedance spectroscopy (EIC) and photo‐electrochemical (PEC) measurements as well as X‐ray photo‐electron spectroscopy (XPS) technique. The effects of hydrogen‐charging and stress were considered. The results show that the steel is in an active dissolution state, and a layer of corrosion product is formed and deposited on the electrode surface, which is subjected to further oxidation to form ferric oxide and hydroxide. Photo‐illumination enhances anodic dissolution of the steel when it is under anodic polarization due to destroying of the corrosion product film. When the steel is under cathodic polarization, the cathodic current density decreases upon laser illumination due to the photo‐oxidation of hydrogen atoms generated during cathodic reactions, which behaves as an anodic reaction to offset the cathodic current density. Hydrogen‐charging and stress decrease the corrosion resistance of the steel and enhance the dissolution rate of the steel.     

Influence of chromizing treatment on the corrosion behavior of AISI 316 stainless steel in supercritical water oxidation

SCWO, sometimes referred to as hydrothermal waste processing, uses the solvating traits of water in its supercritical condition to effectively destroy liquid organic wastes. One major problem in the supercritical water oxidation process is corrosion, because all metallic tubes in the process are exposed to high temperature and high pressure as well as severe corrosive species such as Cl⁻, F⁻, S²⁻, and O²⁻. The presence of Cl⁻ when the pH of a solution is very low and the solution has excess oxygen causes active corrosion and metal loss by metal-chloride and/or oxychloride formation. This study performed a chromizing treatment on 316 stainless steel and immersion tests in supercritical water. Weight change of chromized steels and untreated steels was measured, and the chemical state and composition of oxide films on 316 stainless steel were investigated. On the basis of SCWO tests using distilled water, the oxide layer was found to be very thin and homogeneous and weight gain was observed regardless of testing temperature, while the chromizing treatment slightly reduced weight gain. In the case of SCWO tests using salt water, weight loss was observed regardless of testing temperature and its corrosion mode was pitting by chloride ion, while chromizing treatment greatly decreased the corrosion rate.     

The effect of molybdate concentration and hydrodynamic effect on mild steel corrosion inhibition in simulated cooling water

The effects of two important factors namely concentration and hydrodynamics on the inhibition efficiency of molybdate were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy tests. Results showed that molybdate was capable of inhibiting the corrosion of mild steel in simulated cooling water. The inhibition efficiency of molybdate was increased with increasing both its concentration and water circulation velocity. These two factors seem to promote the adsorption of molybdate and oxygen ions on the metal surface, leading to the formation of a protective layer with a greater charge transfer resistance and lower permeability. A model is also proposed which facilitates the probable mechanism of inhibition.     

Inhibition effect of 2-amino-4-methylpyridine on mild steel corrosion: Experimental and theoretical investigation

The effect of 2-amino-4-methylpyridine (AMP) on the corrosion behavior of mild steel (MS) in 0.5 M HCl is investigated with electrochemical methods and theoretical calculations. The electrochemical tests show that the polarization resistance of MS increasing the presence of AMP in acid solution. Adsorption of AMP on MS surface is a physical and obeys the Langmuir isotherm. The quantum parameters signaled adsorption occurs on amine and methyl substituents of AMP. The inhibition efficiency is related to frontier orbital’s energy band gap of AMP, which are 5.357 and 6.490 eV for neutral and protonated molecules in aqueous solution, respectively.     

The co‐operative effect of chloride ions and some natural extracts in retarding corrosion of steel in neutral media

Effect of lupine and damsissa extracts on the corrosion of steel in 0.5 M Na₂SO₄ solution free from and containing 0.01 or 0.1 M NaCl were examined by potentiodynamic and electrochemical impedance spectroscopy techniques. Potentiodynamic polarization curves measurements indicated that damsissa and lupine extracts behave as anodic type inhibitors. Nyquist impedance plots showed type of distorted semicircle whose size increases with increasing concentrations of lupine or damsissa extract. Increasing chloride ion concentration in the solution led to increase of the inhibition efficiency of the extract and this behaviour was explained on the basis of co‐operative mechanism of adsorption. Kinetic–thermodynamic model was used to clarify the nature of adsorption and showed good fit to the experimental data. The results indicated that lupine extract is more effective as corrosion inhibitor for steel in neutral media containing chloride ions than damsissa extract.     

Experimental and theoretical studies for mild steel corrosion inhibition in 1 M HCl by two new benzothiazine derivatives

The inhibition effect of new heterocyclic compounds, namely 2-aryl-benzothiazin-3-one (P1) and 3-aryl-benzothiazin-2-one (P2) on mild steel corrosion in 1 M HCl was investigated using electrochemical measurements. The results indicated that the inhibition efficiency depends on concentration and molecular structure of the investigated compounds. It is also found that the inhibition of P1 is greater than P2. The molecular structure effect on the corrosion inhibition efficiency was investigated using DFT calculations. The structural and electronic parameters were calculated and discussed. The obtained results show that the experimental and theoretical studies agree well and confirm that P1 is the better inhibitor.     

Influence of N,N′‐dimethylaminoethanol as an inhibitor on the chloride threshold level for corrosion of steel reinforcement

The aim of this study is to examine the influence of N,N′‐dimethylaminoethanol (DMEA) as an inhibitor on the chloride threshold level for corrosion of steel in a concrete contaminated by chlorides. The experiment has been carried out in a saturated Ca(OH)₂ solution and chloride contaminated concrete containing different chloride and DMEA level. The critical point of corrosion onset is concluded by combining the open‐circuit potential (E_corr) with corrosion current (I_corr), which is decided by electrochemical impedance spectra (EIS) in the solution. Besides, the EIS has also been applied to determinate the chloride threshold level in the chloride contaminated concrete. It has been found that the presence of DMEA represented as an amino‐alcohol inhibitor, exerts little influence on the chloride threshold level for corrosion of steel in the solution. Similarly, the effect of the DMEA on the chloride threshold level in the chloride contaminated concrete, is also negligible.