Experimental Corrosion Rates Research Articles

Development of experimental error-Driven model for prediction of corrosion rates of amines based on their chemical structures

This work investigated the relationships between amine corrosion rates and their chemical structural properties for application in the development of a Gaussian Process Regression (GPR) model for chemical structure-based prediction of corrosion rate of any amine. The GPR model accounted for experimental errors, which widened its scope to accurately predict the true corrosion rates, being restricted only to error associated with the trained model. The Average Absolute Deviation (AAD) between experimental corrosion rates and model predicted rates was 4.26 % for the test data, and 5.32 % for two test data unknown to the model. This showed that the model is generalizable and its predictions are accurate. This work also developed a user-friendly Graphical-User Interface, which allows a user to define any amine's structure to provide needed information to calculate its surface tension and steric effects for use as input variables to the model in predicting the corrosion rate of the amine.

Modelling of corrosion rate in the drinking water distribution network using Design Expert 13 software.

This study is focused on the modelling of the composite effect of corrosion factors using Design Expert 13 software on the corrosion rate in the water distribution network of Patna (Bihar), India. A total of nine variables, including pH, temperature, total dissolved solid (TDS), alkalinity, calcium hardness, chloride, sulphate, dissolved oxygen (DO) and time, were considered for modelling. The physicochemical parameters were determined through regular monitoring of water samples. The corrosion rate was determined by the direct monitoring of water distribution pipes using adjustments of seven GI coupons for 45, 90, 135, 180, 225, 270 and 315days. Modelling was performed for various corrosion factors using the low-level and high-level experimental ranges. Nine of the corrosion factors, i.e. pH, temperature, TDS, alkalinity, calcium hardness, chloride, sulphate, DO and time, were considered in this study. The data used for low-level and high-level range were 7.28, 23, 430, 115, 24, 18, 10.94, 3.5 and 0 and 7.86, 28, 704, 284, 180, 98, 38.7, 6.8 and 315, respectively. Using the Box-Behnken design (BBD), 160 runs were conducted, including ten replicates at the central point of each block. The results of ANOVA indicate that the values of R2, adjusted R2 and predicted R2 are 0.9714, 0.9507 and 0.8941, respectively. The value of R2 (0.9714) was close to 1, which indicates a good fit. The adequate precision was found to be 30.8442, indicating a good signal. The coefficient of variance discusses reproducibility, and in this case, it was 9.90%. On the basis of the ANOVA result, the quadratic model is well-fitted and can be accepted as a suitable model. A total of seven parameters, such as chloride, sulphate, hardness, alkalinity, pH, calcium and hardness, were used for the design of the experimental corrosion rate (CR). Corrosion rate as observed by direct monitoring of the water distribution system was 1.37, 3.08, 1.90, 1.38, 1.09, 2.05 and 1.45 MPY for 45, 90, 135, 180, 225, 270 and 315days, respectively. These individual CR versus synthetic aqueous solutions were used to validate the interaction of the response surface. It was observed that the trend of individual corrosion rates in synthetic aqueous solutions and the interaction of composite variables with corrosion rates in a quadratic model of response surfaces were clearly correlated.

Modeliranje inhibitornog ponašanja ekstrakta lista papaje na koroziju mekog čelika u 1,5 m HCL

This current study employed the predictive models driven by the artificial neural network (ANN) and multiple regression (MR) to forecast the corrosion inhibition of mild steel in 1.5 M HCl by the leaves of the Carica papaya plant. Corrosion studies were carried out using the weight loss method at room temperature. The corrosion rate of the mild steel coupon, obtained from the study environment was predicted taking into cognizance the influence of the independent variables viz: the time of exposure, the concentration of HCl (1.5 M), and the concentration of the papaya leaf juice. The fresh papaya leaves were obtained within the surrounding of the Federal University of Technology, Owerri, Imo State, Nigeria. A grinding machine powered by an internal combustion engine was used for grinding the fresh leaves, and a white cloth was utilized to squeeze out the juice. Filtration of the produced juice was done twice with a clean white cloth. Different bowls containing mild steel coupons (5.0 x 5.0 x 0.1 cm) and HCl (1.5 M) solutions were treated with Carica papaya leaf extracts at concentrations of 5 ml, 10 ml, 15 ml, and 20 ml. Results indicated that the highest inhibition efficiency of 95.91% was observed after 120 hours when 20 ml of papaya leaf extract was added. Conversely, the highest corrosion rate of 114.19 mpy was recorded after 24 hours of exposure to HCl (1.5 M) with 5 ml of papaya leaf extract. Generally, the addition of papaya leaf extract in different concentrations added to 1.5 M HCl resulted in a decrease in the rate of mild steel corrosion over time. It was noted that the prediction of the experimental corrosion rate by the artificial neural network offered a lesser error in comparison with that obtained by multiple regression according to the error margin obtained after the prediction of the experimental corrosion rate.

Assessment of Corrosion Potential Based on Water Quality Index in the Distribution Network of Urban Patna, Bihar, India

Corrosion in the distribution network pipe can lead to pipe failure and water quality problems. This study assesses the corrosion or scaling potential based on the Water Quality Index (WQI) of drinking water in the distribution networks of Patna, Bihar, India. The water samples were collected from 18 points of the distribution network. In situ parameters like temperature, pH, electrical conductivity, and TDS were measured. Other parameters such as Alkalinity, Total hardness, Calcium, Magnesium, Chloride, Residual chlorine, Sulfate, Nitrate, and Dissolved oxygen were examined in the laboratory. Corrosiveness indicators, such as the Langelier saturation index (LSI), Ryznar stability index (RSI), Puckorius scaling index (PSI), Larson-Skold index (Ls), and Aggressive index (AI) are being used for water sample corrosion prediction. Experimental Corrosion rate (CR) is analyzed to show the actual prediction of corrosion. WQI was calculated to observe the effect of water quality on Corrosiveness indices and CR. A general conclusion was reached that LSI concludes 66.67% corrosive, 22.22% scaling, and 11.11% neutral, RSI concludes 88.88% corrosive, 5.56% scaling, and 5.56% neutral, PSI indicates 38.88% corrosive, 5.56% scaling, and 55.56% neutral, Ls indicates 94.44% scaling, and 5.56% corrosive, AI indicates 77.78% corrosive, and only 22.22% scaling. The average Experimental Corrosion rate is found at 1.91 mils per year. In this study, a weak correlation (r = 0.35) between Corrosion rate and WQI has been observed. A weak correlation is also observed between corrosion rate and corrosiveness indices (r < 0.5). It is concluded that the Corrosiveness Indices fail to represent the actual behavior of water.

Inhibitive performance of 4-Methoxyphenethylamine on low-carbon steel in 1 M hydrochloric acid: Kinetics, theoretical, and mathematical views

The current study looked at the inhibition performance of 4-Methoxyphenethylamine (MPTA) in 1 M HCl. Besides the experimental investigation, a theoretical and mathematical attempt to correlate some chemical characteristics and inhibitor efficacy was also made. The inhibiting effect was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss techniques. Corrosion rate was evaluated as function of time, MPTA concentration, and temperature. The results show that MPTA suppressed both cathodic and anodic processes of low-carbon steel corrosion in acidic solutionby adsorption on the surface, which followed a Langmuir adsorption isotherm. Maximum corrosion inhibition efficiency was 91% at 30 °C and 200 ppm. Kinetics studies revealed that the corrosion reaction was behaved according to the first order mechanism. Mathematical studies showed a high correlation coefficient was obtained between predicated and experimental corrosion rate. The 6-311G (d, p) base set and Density Functional Theory (DFT) were employed. MPTA's inhibitory capabilities were discovered to be connected to the charge on the nitrogen atom as well as the total of the net charges of the six atoms in the cyclic ring. MPTA was studied in a three states, ground state (1), oxygen protonated state (2), nitrogen protonated state (3). Physical characteristics such as dipole moment, hardness, ionization energy, and softness of MPTA and its protonated states were computed. Theoretical order of inhibitor efficiency was 2 > 3 > 1. It is concerned with an experimental, theoretical, and mathematical explanations between electronic and structural characteristics of MPTA and its inhibitor efficiency.

Empirical models of corrosion rate prediction of steel in reinforced concrete structures

Corrosion rate is one of the most important input parameters in corrosion-induced damage prediction models as well as in calculation of service-life for reinforced concrete structures. In most cases, instantaneous measurements or constant corrosion rate values used in damage prediction models is irrelevant. The new factors appearing such as corrosion-induced cover cracking, concrete quality to change the corrosion rate should be taken into consideration. This study shows several empirical models to predict the corrosion rate and their limits of application. The predicted values of steel corrosion rate using four empirical models are compared with the measured values of a series of 55 experimental samples collected from the literature. The results show that the empirical models overestimated the experimental corrosion rate. Using model proposed by Liu and Weyers provided the best agreement with the experimental data.
 Keywords:
 corrosion rate; prediction model; reinforced concrete; chloride ions; reinforcement corrosion.

The Influence of Test-Panel Orientation and Exposure Angle on the Corrosion Rate of Carbon Steel. Mathematical Modelling

The effects of both test-panel orientation and exposure angle on the atmospheric corrosion rates of carbon steel probes exposed to a marine atmosphere were investigated. Test samples were exposed in a tree-shape metallic frame with either three exposure angles of 30°, 45° and 60° and orientation north-northeast (N-NE), or eight different orientation angles around a circumference. It was found that the experimental corrosion rates of carbon steel decreased for the specimens exposed with greater exposure angles, whereas the highest corrosion rates were found for those oriented to N-NE due to the influence of the prevailing winds. The obtained data obtained were fitted using the bi-logarithmic law and its variations as to take in account the amounts of pollutants and the time of wetness (TOW) for each particular case with somewhat good agreement, although these models failed when all the effects were considered simultaneously. In this work, we propose a new mathematical model including qualitative variables to account for the effects of both exposure and orientation angles while producing the highest quality fits. The goodness of the fit was used to determine the performance of the mathematical models.

Synergistic Effect of O2 and H2S on the Corrosion Behavior of N80 Steel in a Simulated High-Pressure Flue Gas Injection System

The aim of this work was to understand the synergistic effect of O2 and H2S on the corrosion behavior of N80 steel in a simulated high-pressure flue gas injection system. Weight loss measurements show that the presence of O2 and an increase in temperature significantly accelerated the general corrosion rate of the N80 steel. We calculated a gray relational grade between different impact factors and the general corrosion rate from the results of an orthogonal experimental corrosion rate. The grade ranking of impact factors was: O2 concentration (0.817) > temperature (0.706) > total pressure (0.689) > H2S concentration (0.665) > CO2 concentration (0.517). Surface characterization of corrosion scales was done using scanning electron microscopy, energy-dispersive spectroscopy, x-ray powder diffraction, and 3D optical microscope analysis. The results show that in the O2-H2S-CO2-H2O coexistence system the products were composed mainly of FeCO3, FeS, Fe2O3, Fe3O4, and elemental sulfur. The results of the corrosion rate test and the characterization show that the presence of O2 greatly accelerated the corrosion process and changed the corrosion mechanism. Elemental sulfur, which was generated by the reaction between the H2S and the O2, participated in the corrosion process of the N80 steel. It could be considered that the synergistic effect of O2 and H2S accelerated the corrosion of the N80 steel. In addition, the porous structures of the corrosion scales and the severe local pits show that the high content of O2 inhibited the formation of FeCO3 and aggravated the corrosion of N80 steel.

Water flow velocity and oxide film formation effect on copper pipe corrosion

An overall mathematical model for copper pipe corrosion in flowing water was derived based on mass transfer fundamentals where we introduced the effects of boundary layer velocity, bulk flow velocity and the surface oxide protective film on the corrosion rate. A set of experiments were conducted in a straight 10mm diameter copper pipe, flow of water include six velocities of maximum value 7.33m/sec at 200C and 350C. The good agreement between the calculated and experimental corrosion rate values were achieved , the agreement reached 92% .

Water flow velocity and oxide film formation effect on copper pipe corrosion

An overall mathematical model for copper pipe corrosion in flowing water was derived based on mass transfer fundamentals where we introduced the effects of boundary layer velocity, bulk flow velocity and the surface oxide protective film on the corrosion rate. A set of experiments were conducted in a straight 10mm diameter copper pipe, flow of water include six velocities of maximum value 7.33m/sec at 200C and 350C. The good agreement between the calculated and experimental corrosion rate values were achieved , the agreement reached 92% .

Black powder formation by dewing and hygroscopic corrosion processes

The presence of black powder in natural gas pipelines can lead to equipment erosion, valve failure, instrumentation malfunction, and increased pressure drop. However, despite its impact on downstream and midstream operations, black powder production is poorly understood. In the present work, black powder formation as a result of corrosion was investigated by simulating sales gas conditions in a glass cell. Steel specimens were systematically exposed to a range of CO2, H2S, and O2 partial pressures at differing water condensation rates. The potential for hygroscopic material assisting black powder formation was also investigated. Friable corrosion products found in dewing conditions consisted of siderite (FeCO3), mackinawite (FeS), and hematite (Fe2O3). The expected mass of corrosion products, as determined from experimental corrosion rates, are in line with the high levels of black powder that can be experienced. The presence of hygroscopic NaCl crystals facilitated corrosion at relative humidities as low as 33%.

Acetic Acid Corrosion of Mild Steel: Mechanism and Prediction

The effect of acetic acid on the internal corrosion of pipeline steel have been studied by numerous researchers1. It is commonly believed that acetic acid is an additional corrosive species which is directly reduced at the metal surface, hence, provides the electron sink required for iron dissolution reaction to progress faster. This idea is stemming from an analogy to CO2 corrosion where carbonic acid, the hydrated form of CO2, has been conventionally considered to be electrochemically active. However, depending on the environmental conditions, inconsistent trends for the effect of acetic acid on observed corrosion rates were reported1. The vast majority of the previous studies investigate the effect of acetic acid together with CO2 corrosion. However, the complexity of the water chemistry associated with CO2 corrosion and the additional twist by introducing acetic acid makes any mechanistic discussions difficult in such systems. The present study is a systematic investigation of acetic acid effect on aqueous corrosion of mild steel. The polarization behavior of acidic solutions at various acetic acid concentrations were used to discuss the underlying mechanism of the corrosion process. It was hypothesized that if acetic acid is not an electroactive species, the purely charge transfer controlled cathodic currents should not increase by increasing acetic acid concentrations2. The experimental steady state voltammograms obtained on an API-X65 mild steel rotating disk electrode at pH range from 3 to 5 and acetic acid concentrations up to 1000 ppm verified the aforementioned hypothesis. No significant increase of charge transfer cathodic currents were observed by increasing acetic acid concentration while the limiting currents followed a linear correlation with its concentration. Additionally, a significant inhibitive effect was observed on both cathodic and anodic currents in the presence of acetic acid. The polarization behavior of the system was further quantified by a comprehensive mathematical model3. The model was developed by solving the Nernst-Plank equation through the diffusion layer using newsman’s “BAND” algorithm, which accounts for molecular diffusion, electro-migration, convective flow, homogeneous reactions as well as the two electrochemical reaction, iron dissolution and hydrogen ion reduction at the metal surface. The inhibitive effect of acetic acid was shown to correlate with a Temkin type adsorption isotherm for acetic acid, with a good approximation. A reasonable agreement with the experimental voltammograms were obtained, confirming that acetic acid is not a significant electro-active species in the conditions considered in the present study. The experimental corrosion rates obtained using linear polarization resistance measurements at temperatures from 30 to 50 oC, rotation rates from 125 to 2000 rpm, pH from 3 to 5 and acetic acid concentrations from 0 to 1000 ppm were compared with the values predicted by the model as shown in Figure below, where a reasonable agreement were found. The inconsistent reports of the effect of acetic acid on the observed corrosion rates may therefore be explained by considering these two opposing effects: - Acetic acid increases the limiting current by buffering the surface concentration of hydrogen ions, therefore increasing its concentration would increase the corrosion current linearly, if it is under mass transfer control. - Acetic acid inhibits the charge transfer rates of both cathodic and anodic reactions, therefore increasing its concentration would decrease the corrosion current, if it is under charge transfer control.

Measurable and Influential Parameters That Influence Corrosion Performance Differences between Multiwall Carbon Nanotube Coating Material Combinations and Model Parent Material Combinations Derived from Epoxy-Amine Matrix Materials.

Protective coatings are often erroneously thought of as perfect environmental barriers for metal substrates; however, a host of corrosion inducing environmental contaminants permeate through defect-free coatings. Carbon nanotubes are high aspect ratio nanofillers with unique mechanical, electrical, and polymer interaction properties with well-established yet, for practical reasons, often unrealized potential. The research objective was to quantify and understand the influential effects and relationships between low concentration levels of multiwall carbon nanotubes (MWCNT) dispersed into epoxy-amine matrix materials and the different water hydrogen bonding interactions on corrosion rates of steel substrates. We hypothesize that when water directly hydrogen bonds with polymer, substrate and/or MWCNTS, the localized water's capacity to transfer environmental contaminants through the coating, i.e., to and from the substrate, diminishes due to a reduced potential to contribute to the formation of water hydration shells and therefore aid in diminishing the corrosion rate. We measured the absolute pre-exposure water content, and monitored to delineate between the ratio and shifting ratio of in situ free versus bound water hydrogen bonding interactions at the coating/air interface using ATR-FTIR spectroscopy in a 5% NaCl fog environment in an attempt to correlate these differences with experimental corrosion rates. Free water content was reduced from ∼20% to <1% of the total water concentration when 1.0 wt % MWCNTs was dispersed into the parent polymer network. Concurrently, the bound water content was measured to shift from ∼2% to >80% with the same MWCNT concentration. The MWCNT bound water resulted in 25% less corrosion for the same steel substrates albeit the measured water vapor diffusivity was the same for each material combination evaluated. Interestingly, the measured pre-exposure bound water content was predictive of which material would corrode slowest and fastest, i.e., the ratio of starting water states seems to be mechanistically related to the corrosion process and the values have potential to predict corrosion rates for a variety of samples evaluated.

Inhibition Performance and Adsorptive Behavior of Three Amino Acids on Cold-Rolled Steel in 1.0 M HCl—Chemical, Electrochemical, and Morphological Studies

Three selected amino acids, namely, serine (Ser), threonine (Thr), and glutamine (Glu), were tested as corrosion inhibitors for cold-rolled steel (CRS) in 1.0 M hydrochloric acid (HCl) solutions at different temperatures (283 K to 333 K). Chemical (weight loss) and electrochemical (Tafel polarization) methods were used in this study. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, was also used. Experimental corrosion rates determined by the Tafel extrapolation method were compared with those obtained using the EFM technique and the weight-loss method. Morphologies of the corroded and the inhibited surfaces were studied by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Tafel plots showed that the three tested amino acids act as mixed-type inhibitors. The three tested amino acids appeared to function through adsorption following the Temkin adsorption isotherm model. Glu was found to inhibit corrosion of steel more effectively than Ser and Thr.

Modeling steel corrosion under supercritical CO2 conditions

AbstractCorrosion in the presence of CO2 was studied under supercritical conditions (high pressure and moderate temperature) using different carbon steels and various corrosion resistant alloys (CRA's). An objective of this work was, among others, to put the results in perspective relative to various CO2 corrosion models that have been developed and published over the years. In particular, the NORSOK, FREECORP, and OLI models were used for comparison, while others were discussed as well. The systems investigated were (a) supercritical CO2 (SC CO2) saturated with water (no separate water phase), (b) a water mist phase in equilibrium with SC CO2, (c) a water/brine phase in equilibrium with SC CO2. It was found that the OLI model best simulates the experimental corrosion rates observed in system (c) where coupons were corroded in the aqueous phase at high velocities in the rotating cage. The varying susceptibility of different carbon steels to corrosion under these conditions is highlighted. CRA steels are comparatively more resistant.

Empirical equation of CO2 corrosion with presence of low concentrations of acetic acid under turbulent flow conditions

The presence of organic acid species in formation water of oil and gas reservoirs has long been suspected to contribute to the corrosivity of CO2 corrosion. The effect had been regarded as secondary until new findings in the 1980s and 1990s revealed the increase in corrosion rate in CO2 environment with the presence of acetic acid species. This is potentially detrimental as most of the predictive models used in corrosivity assessment of the field do not incorporate considerations of the effects of acetic acid species. This paper presents experimental corrosion rates of carbon steel in CO2 environments with the presence of low concentrations of acetic acid species under the turbulent flow conditions, based on linear polarisation resistance analysis. The experimental corrosion rates are compared with the corrosion rates predicted by industrial predictive models such as Norsok and Cassandra. Based on the findings, the authors can conclude that acetic acid species increase the corrosion rate of carbon steel in CO2 corrosion and standard predictive models do not capture this effect. An empirical equation is proposed to cater for the presence of low concentrations of acetic acid in CO2 corrosion under turbulent conditions.

Monitoring corrosion and corrosion control of iron in HCl by non-ionic surfactants of the TRITON-X series – Part II. Temperature effect, activation energies and thermodynamics of adsorption

The inhibition characteristics of non-ionic surfactants of the TRITON-X series, namely TRITON-X-100 (TX-100), TRITON-X-165 (TX-165) and TRITON-X-305 (TX-305), on the corrosion of iron was studied in 1.0 M HCl solutions as a function of inhibitor concentration (0.005–0.075 g L −1) and solution temperature (278–338 K). Measurements were conducted based on Tafel extrapolation method. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, is also presented. Experimental corrosion rates determined by the Tafel extrapolation method were compared with corrosion rates obtained by the EFM technique and an independent method of chemical analysis. The chemical method of confirmation of the corrosion rates involved determination of the dissolved cation, using ICP-AES (inductively coupled plasma atomic emission spectrometry). The aim was to confirm validation of corrosion rates measured by the Tafel extrapolation method. Results obtained showed that, in all cases, the inhibition efficiency increased with increase in temperature, suggesting that chemical adsorption occurs. The adsorptive behaviour of the three surfactants followed Temkin-type isotherm. The standard free energies of adsorption decreased with temperature, reflecting better inhibition performance. These findings confirm chemisorption of the tested inhibitors. Thermodynamic activation functions of the dissolution process were also calculated as a function of each inhibitor concentration. All the results obtained from the methods employed are in reasonable agreement.

Electrochemical frequency modulation and inductively coupled plasma atomic emission spectroscopy methods for monitoring corrosion rates and inhibition of low alloy steel corrosion in HCl solutions and a test for validity of the Tafel extrapolation method

The inhibition effect of glycine (Gly) towards the corrosion of low alloy steel ASTM A213 grade T22 boiler steel was studied in aerated stagnant 0.50 M HCl solutions in the temperature range 20–60 °C using potentiodynamic polarization (Tafel polarization and linear polarization) and impedance techniques, complemented with scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, is also presented here. Experimental corrosion rates determined by the Tafel extrapolation method are compared with corrosion rates obtained by electrochemical, namely EFM technique, and chemical (i.e., non-electrochemical) method for steel in HCl. The chemical method of confirmation of the corrosion rates involved determination of the dissolved cation, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of analysis. Corrosion rates (in mm y −1) obtained from the electrochemical (Tafel extrapolation and EFM) and the chemical method, ICP, are in a good agreement. Polarization studies have shown that Gly is a good “green”, mixed-type inhibitor with cathodic predominance. The inhibition process was attributed to the formation of an adsorbed film on the metal surface that protects the metal against corrosive agents. Scanning electron microscopy (SEM) and energy dispersion X-ray (EDX) examinations of the electrode surface confirmed the existence of such an adsorbed film. The inhibition efficiency increases with increase in Gly concentration, while it decreases with solution temperature. Temkin isotherm is successfully applied to describe the adsorption process. Thermodynamic functions for the adsorption process were determined.

Corrosion Behavior of Tin-Plated Carbon Steel and Aluminum in NaCl Solutions Using Electrochemical Impedance Spectroscopy

The corrosion behavior of both tin-plated carbon steel and aluminum (Al 1100) in NaCl solutions were studied using electrochemical impedance spectroscopy (EIS). The study objectives were to compare their corrosion behavior in concentrated brine solution, establish the equivalent electrical circuit diagrams of their corrosion phenomena, and consequently develop steady-state corrosion models for estimating the corrosion rates in the given solution. The steady-state corrosion rates for the tin-plated carbon steel increased significantly when the concentration of NaCl was increased from 1.0M to 1.5M. The increase in corrosion rate of the tin-plated steel is attributed to reduced charge transfer resistance due to the breakdown of the surface tin plating at high chloride concentrations. In contrast, there was little incremental change in the corrosion rates of aluminum when the NaCl concentration was increased from 1.0M to 1.5M. This is attributed to the known formation of a stable, passivating surface oxide film on aluminum which inhibits corrosion. The surface passivating film did not show any significant evidence of degradation with increase in chloride concentration. Using MATHLAB and the experimental corrosion rate data, a mathematical corrosion model was derived for the two samples to describe their steady-state corrosion in NaCl electrolyte solutions.

Validation of corrosion rates measured by the Tafel extrapolation method

This paper discusses the validity and limitations of the Tafel extrapolation method for the determination of corrosion rates for activation-controlled corrosion processes. Experimental corrosion rates determined by the Tafel method are compared with corrosion rates obtained by an independent chemical (i.e., non-electrochemical) method for iron in hydrochloric acid, iron in 3.5% NaCl, and for titanium in boiling 1 M sulfuric acid. The methods of confirmation of the corrosion rates involved colorimetric analysis of the dissolved cation or the use of an ion-implanted inert Xe marker. Additional examples taken from the literature involving other metals and other methods of validation are also discussed.