Effects of turbulent flow on the corrosion kinetics of X52 pipeline steel in aqueous solutions containing H2S

This work presents the electrochemical results obtained during the study of the corrosion of X52 pipeline steel sample, immersed in brines containing H₂S, under turbulent flow conditions. Linear polarisation resistance (LPR), electrochemical impedance spectroscopy (EIS), Electrochemical Noise (EN) and polarisation curves were used in order to determine the effect of turbulent flow upon the corrosion kinetics of the steel. It was found that flow has a considerable influence upon the electrochemical process occurring on the surface of the steel and the corrosion rate is increased.     

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.     

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.     

Fluoride induced corrosion of steel rebars in contact with alkaline solutions, cement slurry and concrete mortars

Corrosion behaviour of mild steel rebars has been studied in contact with 0.01 N NaOH, saturated lime water, cement slurry and embedded mortars having different concentrations of fluoride ions. Weight-loss, electrochemical DC cyclic polarisation and polarisation resistance, surface topographic and X-ray diffraction (XRD) techniques have been used to investigate the effects of fluoride ion on the corrosion behaviour of the material. Under all the conditions of the exposure it is observed that a low content of fluoride (?25 ppm) in the corrodent has deleterious action on the performance of the steel, where as at its higher content (?100 ppm) the ion has rather an inhibiting effect on corrosion rate. XRD studies of the corrosion product accumulated on the steel surface in the presence of fluoride ion indicate the predominance of magnetite oxide phase. Accelerating effect of the ion is observed to be due to depolarisation of cathodic reaction of the corrosion process. Observations show that in accelerating range of fluoride (?25 ppm) it has almost double corrosive effect than noted for equal concentration of chloride ion.     

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.     

Microstructure and corrosion behaviour of plain carbon steel–B4C composite produced by GTAW method in 3·5 wt-%NaCl solution

In this work, the corrosion behaviour of metal matrix composite plain carbon steel–B₄C was studied in 3·5 wt-%NaCl solution. The composite was locally produced as weld band on plain carbon steel by means of gas tungsten arc welding process and using nickel as wetting agent. Samples from weld band, heat affected zone and base regions were extracted precisely, and electrochemical techniques including open circuit potential, linear polarisation resistance, electrochemical impedance spectroscopy, potentiodynamic polarisation in combination with SEM-EDX surface analysis and microhardness were used for characterisation. The results showed that hardness value of made composite increased significantly to 642 HV10. However, the corrosion resistance of composite region during 7 days (168 h) of exposure to 3·5 wt-%NaCl solution was slightly reduced. This was attributed to the fact that B₄C particles play as cathode site for oxygen reduction; therefore, they increase the corrosion rate slightly.     

Influence of chromium additions on corrosion resistance of Co75·5Si13·5B9 Nb3Cu1 metallic glass in marine environment

Abstract

This study addressed the influence of Cr concentration on the corrosion resistance of Co_73·5Si_{13 ·5}B₉Nb₃Cu₁ metallic glass in simulated marine atmospheres with 1000 ppm of chlorides. Anodic and cyclic polarisation measurements were carried out to study the susceptibility to passivation and localised corrosion. The corrosion kinetics were analysed using dc electrochemical techniques. Every test was conducted using the same material in different states: amorphous, nanocrystalline and crystalline. The study also focused on changes in the magnetic properties of the material as a result of Cr addition and exposure to an aggressive medium. These properties depend mainly on the Cr concentration and the material state (amorphous, crystalline or nanocrystalline).     

Evaluation of a biocide effect upon microbiologically influenced corrosion of mild steel

The microbiologically influenced corrosion (MIC) is a very dangerous process, which affects the oil industry. The activity and microorganisms' growth at the pipelines steel cause surface modifications, which can induce a more complex corrosion process. The biocide evaluation for the MIC decrease has been normally based upon microbiological tests, and just a few references mention alternating methods which can be used as criteria for their evaluation. In this work, a commercial biocide was tested, using different electrochemical laboratory techniques, to determine its effect upon a biofilm generating bacteria consortium. Using microbiological techniques, the biocide lethal concentration was determined, and a concentration of 200 ppm was used to kill completely the consortium population in both, plancktonic and sessile parts. The electrochemical techniques: Polarisation Resistance (PR) and Electrochemical Impedance Spectroscopy (EIS), allowed describing the corrosion process associated to the microbial consortium and the biocide effect upon it.     

Aqueous corrosion behaviour of TiC-304L stainless steel cermets in a 3.5 wt% NaCl solution

High-density titanium carbide (TiC) based cermets were prepared using 10 to 30 vol% 304L grade stainless steel binder. A range of electrochemical techniques was applied to study the corrosion response in an aqueous solution (with 3.5 wt% NaCl), including potentiodynamic, cyclic and potentiostatic polarisation. Corroded samples were characterized using SEM and associated EDS, while the post-corrosion aqueous solutions were analysed by ICP-OES, to determine the dissolved solute ions and the composition of any particulate material released during corrosion. It is shown that by increasing the steel binder content the corrosion resistance of the cermets decreases slightly, which appears to be related to the preferential dissolution of the steel binder at higher rate when lower metallic content is selected. A general corrosion mechanism is seen, whereby the composites exhibit similar electrochemical characteristics. Single-phase analysis has confirmed that the 304L steel and TiC exhibit broadly similar oxidation properties, which eliminates the formation of galvanic couple at a controlled ratio between the metallic and ceramic phases.     

Corrosion behaviour of Terfenol-D

The corrosion behaviour of pseudo-binary compound Tb_0.3Dy_0.7Fe_1.92 (Terfenol-D) was studied in 3.5% NaCl and 0.01 N Na₂SO₄ solutions using Tafel polarisation, linear polarisation, electrochemical impedance spectroscopy and weight loss techniques. Electrochemical testing revealed the adverse effect of chloride ions, as corrosion rates were higher in 3.5% NaCl solutions than in 0.01 N Na₂SO₄ solutions. The effect of aeration was studied by conducting experiments in freely-aerated, deaerated and fully-aerated conditions. Absence of oxygen accelerated corrosion in chloride environment, due to increased hydrogen interaction in presence of destabilised surface films. The improved corrosion resistance in chloride-free environment was correlated with morphological features of the corroded surfaces. Micro-compositional analysis of the corrosion products revealed that the corrosion products were primarily rich in rare earth elements. A comparison of all experimental techniques showed that Tafel extrapolation and EIS techniques provided reliable estimates of corrosion rate.     

Influence of inclusion and grain boundary on corrosion behaviour of low alloy steel in cargo oil tank bottom plate environment

Corrosion behaviours of low alloy steels with various alloying element contents were studied in simulated corrosion environment (pH?=?0·85, 10% NaCl solution) of cargo oil tank (COT) bottom plate corrosion environment. Corrosion rate was measured, and the surface morphology of test steels was characterised using scanning electron microscope (SEM). The electrochemical results were investigated using polarisation curves and electrochemical impedance spectroscopy (EIS). The corrosion behaviour of inclusion was investigated using in situ SEM images and energy disperse spectroscopy (EDS) analysis. The effect of misorientation distribution on corrosion resistance of steel was evaluated using electron backscattered diffraction microscopy. The results showed that MnS dissolved into the simulated COT corrosion solution before steel matrix, whereas TiO₂ would not be dissolved. A 10–20 μm area was formed as a circular cathode around inclusion centre. The corrosion was inclined to occur in the place where curvature radius of inclusion is small. An increase in the proportion of low energy grain boundaries was conducive to the improvement of corrosion resistance especially in the early stages of corrosion.     

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.     

Substituted uracils as corrosion inhibitors for copper in 3% NaCl solution

Substituted uracils were tested as corrosion inhibitors of copper in 3% NaCl medium using electrochemical polarisation, impedance measurements and non-electrochemical techniques (weight loss, IR and UV-visible). This study permitted to follow the evolution of the inhibitory effect of the uracil derivatives, according to their substituents, on copper in 3% NaCl medium. Comparison of results showed that dithiouracil (DTUr) was the best inhibitor. The maximum inhibition efficiency reached 98% at 10⁻³ M. DTUr adsorbs on the copper surface according to the Frumkin isotherm model.     

Citric acid as natural corrosion inhibitor for aluminium protection

Abstract

The inhibition effect of citric acid on the corrosion behaviour of aluminium in 2M NaCl solution (pH 2) was studied with the help of potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and linear polarisation resistance (LPR) techniques. The experimental results showed that citric acid inhibits the corrosion of aluminium in NaCl solution and the inhibition efficiency depends on its concentration. The protection efficiency increases with citric acid concentration up to a critical value of 1·0 × 10^?5M. At higher concentrations, the inhibition efficiency reduced again with increasing concentration. The mechanism of inhibition was attributed to the adsorption of citric acid onto the metal surface.     

Effects of electrolyte thickness,chloride ion concentration,and an external direct current electric field on corrosion behaviour of silver under a thin electrolyte layer

ABSTRACT

Effects of electrolyte thickness, chloride ion concentration, and an external direct current electric field (DCEF) on the corrosion behaviour of silver under a thin electrolyte layer (TEL) were investigated using electrochemical and surface techniques. The results indicate the corrosion rate of silver increases with the decrease of TEL thickness and the increase of chloride ion concentration. Moreover, an interesting conclusion was drawn that the corrosion rate of silver near the positive plate of DCEF first increases and then decreases with the increase of electric field intensity. In a DCEF, different polarisation behaviours of silver at different positions were attributed to the differences of the local corrosion environment.     

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.     

Effect of heat treatment on corrosion behaviour of deposited Fe–40Al intermetallics

Abstract

A study using electrochemical techniques of the susceptibility to corrosion in 0·1M NaCl solution (pH 3) of atomised and deposited Fe–40Al (at.-%) intermetallic material at room temperature is reported. Specimens were heat treated at temperatures of 600 and 900°C for 24 and 72 h. Potentiodynamic polarisation, linear polarisation resistance, potential–time, and electrochemical current noise data were collected. The untreated material displayed higher corrosion resistance than the heat treated material. In the treated material, the corrosion resistance increased with both the time and temperature of heat treatment. Also, untreated material was more susceptible to pitting corrosion than heat treated material. As the temperature or the time of heat treatment was increased, the material became more resistant to pitting. This improvement in resistance to pitting was related to a decrease in surface defects, such as pores and cracks, and an increase in grain size. Thus, heat treatment lowered the number of active sites and helped the material to establish a more protective film.     

Sodium gluconate as corrosion and scale inhibitor of ordinary steel in simulated cooling water

The effect of sodium gluconate anion (SG) on the corrosion and scale inhibition of ordinary steel in simulated cooling water has been studied using weight loss, polarisation curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques. SG was studied in concentration from 10⁻⁴ M to 10⁻¹ M. Results obtained reveal that SG perform excellently as corrosion and scaling inhibitor for ordinary steel in simulated cooling water. An increase of SG concentration leads to the increase of the corrosion potential towards the positive direction. The inhibition efficiency was a low temperature dependence. The inhibitor mechanism was treated as an adsorption process according to Langmuir adsorption isotherm. The SEM/EDAX data show that was a corrosion and scale inhibitor.     

Screening of new corrosion inhibitors via electrochemical noise analysis

The inhibition efficiency of a series of organic compounds against corrosion of magnesium alloy AZ91 in a 50 wt.‐% aqueous solutions of ethylene glycol has been studied using polarisation curves and electrochemical noise (ECN) measurements. The comparative analysis of the results obtained has demonstrated unambiguously that the method of ECN is an effective tool for screening of new corrosion inhibitors which offers some advantages comparing to the common electrochemical techniques. The very fast measuring rate enables to instantaneously register and monitor the rate of the corrosion process and changes in its mechanism in presence of the organic additives. The measurements are performed at freely corroding “identical” electrodes without perturbation from the external signals, which could lead (as in the polarisation measurements), to changes in the surface structure, the adsorption of the inhibitor etc. The statistical analysis of the noise data (in terms of standard deviations) in the time domain shows that the noise intensity of the system correlates well with the intensity of the corrosion process. The total amount of the charges exchanged during the tests is a quantitative measure for the inhibiting effect of the substances under study, while the spectral analysis of the noise in the frequency domain can be used to characterise the type of the corrosion attack.     

Influence of sulphide ions on corrosion resistance of special austenitic stainless steels in phosphoric acid

Abstract

The influence of sulphide ions on the corrosion resistance of some special stainless steels in 40 wt-% H₃PO₄ with 330 ppm SO^2?₄ and 1000 ppm Cl^? at 80°C has been investigated using electrochemical (polarisation curves) and spectroscopic (infrared, SIMS) techniques. The behaviour of ZI NCDU 25–20 and ZI CNDU 25–25 commonly used in the phosphoric acid industry is compared with that of ZI CN 25–20 to estimate the role of the alloying elements. The corrosive effect of sulphide ions is confirmed: they shift the corrosion potential to more negative values and increase the anodic current in the active and passive states. In order of increasing corrosion rate the three steels are ranked as follows: ZI CNDU 25–25, ZI NCDU 25–20, ZI CN 25–20. The corrosion products consist largely of magnetite in a more or less oxidised state with chromium and nickel substituted for iron. The film formed on the ZI CNDU 25–25 alloy is more protective because of the high chromium content of the mixed oxide and the effect of molybdenum. The film retards the diffusion of corrosive ions through to the metal andfacilitates the development of passivity. However, the presence of a sufficiently high concentration of sulphides in solution prevents the establishment of passivity.