Chloride-containing Media Research Articles

Neural network analysis of safe life of the oil and gas industrial structures

Purpose is to study safe life of industrial (metal) structures under long-time operation in the corrosive-active media of oil and gas wells with the help of neural network analysis. Methods. The MATLAB system (MATrix LABoratory) was selected as the tool environment for interface modelling; the system is developed by Math Works Inc. and is a high-level programming language for technical computations. Of the three existing learning paradigms, we used the “with teacher” learning process, as we believed that a neural network had correct answers (network outputs) for each input example. The coefficients were adjusted so that the network gave answers being as close as possible to the known correct answers. Findings. An artificial neural network has helped obtain a generalized diagram of the expected areas of high viscoplastic characteristics of carbon steels used to manufacture metal structures in the oil and gas industry. While applying the trained neural networks, generalized dependences of the corrosion rates of structural steels on the parameters of media with different concentrations of chlorine ions, sulphate ions, hydrogen sulphide, carbon dioxide, carbon dioxide, and oxygen ions were obtained; they were the basis to predict corrosion behaviour of steels. Originality. For the first time, the possibility of applying neural network modelling to predict local corrosion damage of structural pipe steels has been shown in terms of the “steel 20 – oxygen and chloride-containing medium” system. For the first time, the technological possibility has been demonstrated to use neural network analysis for engineering predictive assessment of corrosion activity of binary systems of simulated solutions, which are most often found under industrial conditions of the oil and gas sector of the economy. Practical implications. The proposed technology of using the neural network analysis will make it possible to expand a range of predicted values beyond experimental data, i.e. to predict the value of Vcor in very dilute or concentrated salt solutions within the acidified and neutral pH ranges. It should be noted that the error of the prediction results shown by the neural network will increase along with distancing from the scope of experimental data.

Probabilistic approach to calculation of durability of reinforced concrete pile exposed to chlorides

In this paper, a deformation model of a reinforced pile subjected to load and chloride-containing medium is applied to predict the behavior of the pile. The model takes into account the probabilistic nature of corrosion processes, the variation of geometric and strength characteristics of the pile, as well as the probabilistic nature of the load. A methodology for calculating the stress-strain state and durability of the pile, taking into account all stages of the process of its interaction with chloride-containing medium, has been developed and the design analysis has been carried out.

Corrosion behavior of austenitic steels in chloride-containing media during the operation of plate-like heat exchangers

Corrosion behavior of austenitic steels in chloride-containing media during the operation of plate-like heat exchangers

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Corrosion inhibition of aluminium alloy in NaCl solution by glycerol from biodiesel production

It was evaluated the potential of using crude glycerol, a by-product of biodiesel production from vegetable oil, as a «green» corrosion inhibitor for aluminum alloys in the neutral chloride-containing medium. It was found that it has inhibitory properties and efficiently protects aluminum alloys from corrosion in 0.1% NaCl solution; the degree of protection was up to 79%. The protective action of crude glycerol increases with increasing its concentration to 2.5 g/l. Impedance modulus of aluminum alloy increases in inhibited corrosion solution. The mechanism of corrosion inhibition is the physical and partially chemical adsorption of molecules of crude glycerol components, and probably the formation of copper-glycerol complexes on the metal surface. The adsorption of the studied inhibitor is described by the Frumkin isotherm. Energy dispersive x-ray analysis confirmed the formation of an organic protective layer on the metal surface.

Investigation of the Effect of Volumetric Hydrophobization on the Kinetics of Mass Transfer Processes Occurring in Cement Concretes during Corrosion.

The entry of aggressive substances into the pore structure of concrete causes the development of corrosion processes and leads to the destruction of the cement stone structure. Hydrophobic additives provide high density and low permeability and are an effective barrier to the penetration of aggressive substances into the structure of cement stone. To assess the contribution of hydrophobization to the durability of the structure, it is necessary to know how much the processes of corrosive mass transfer slow down. To study the properties, structure and composition of the materials studied in the work (solid and liquid phases) before and after exposure to liquid-aggressive media, experimental studies were carried out using chemical and physicochemical analysis methods: determination of density, water absorption, porosity, water absorption and strength of cement stone; differential thermal analysis; quantitative analysis of calcium cations in liquid medium by complexometric titration. The article presents the results of studies of the effect on the operational characteristics of the introduction of a hydrophobic additive of calcium stearate into the cement mixture at the stage of concrete production. The effectiveness of volumetric hydrophobization was evaluated to prevent the penetration of an aggressive chloride-containing medium into the pore structure of concrete destruction and the leaching of calcium-containing components of cement stone. It was found that the introduction of calcium stearate in an amount of 0.8-1.3% by weight of cement increases the service life of a concrete product during corrosion in liquid chloride-containing media with a high degree of aggressiveness by four times.

A comparison of the inhibitory activity of 3-alkyland 3-hydroxyalkyl-5-amino-1H-1,2,4-triazoles against copper corrosion in chloride-containing environments

Copper is widely used as a material for technical solutions in microelectronics, as well as for the manufacture of various heat exchange equipment used in aggressive environments. Corrosion inhibitors are used for the reduction of the corrosive activity of the environment. This article presents the results of a study of the anticorrosion activity of a number of derivatives of the class 3-alkyl- and 3-hydroxyalkyl-5-amino-1H-1,2,4-triazole with respect to copper corrosion in chloride-containing environment. Over the course of the study, 3-alkyl- and 3-hydroxyalkyl-5-amino-1H-1,2,4-triazoles with different lengths of the alkyl substituent were synthesized. The structure of these compounds was confirmed using NMR spectroscopy and HPLC/MS analysis. Based on the results of electrochemical and direct corrosion tests, regularities were established for the inhibitory activity of the obtained compounds in acidic (1% HCl solution) and neutral (borate buffer solution, pH = 7.4) chloride-containing media. In in a neutral media, the greatest protective effect was obtained for 3-propyl-5-amino-1H-1,2,4-triazole I, which has the shortest alkyl radical without modification by an OH group. As the concentration increased in the range from 0.01 to 10.0 mmol/L, the inhibitory activity increased. With an increase in the length of the alkyl radical and/or the introduction of an OH group, a decrease or absence of a protective effect was observed. At the same time, in an acidic medium, the introduction of a hydroxyl group into the alkyl substituent of 5-amino-1H-1,2,4-triazole increased anti-corrosion efficiency only with sufficient length of the carbon chain. The highest protection degree was obtained for 17-(5-amino-1H-1,2,4-triazol-3-yl)heptadecan-7-ol IV at a concentration of 10.0 mmol/l and it reached a value of 97%.

Corrosion inhibition of magnesium alloy AZ31 in chloride-containing solutions by aqueous permanganate

In this work, corrosion of the AZ31 magnesium alloy was examined in 0.05 M NaCl solutions containing 0.01–0.150 mol/dm3 of potassium permanganate as a corrosion inhibitor. A set of electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen evolution measurements revealed high inhibitor effectiveness at relatively high (0.150 mol/dm3) KMnO4 concentrations. Based on data of energy-dispersive X-ray analysis, scanning electron microscopy, and Raman spectroscopy, a mechanism of the corrosion inhibition of AZ31 alloy by potassium permanganate in chloride-containing media was proposed.

Intensity of Mass Transfer Processes in Concrete with Inhibitors in Chloride Corrosion

The article presents the results of a study of the effect of alkaline and alkaline-earth metal nitrates added to concrete cement stone on the intensity of mass transfer processes occurring during corrosion in a highly aggressive liquid chloride-containing medium. The studies were carried out on samples of cement stone from Portland cement of the CEM I 42.5 N brand with W/C = 0.3 in a 2 % MgCl2 solution. As inhibitory additives, KNO3 NaNO3, Ca(NO3)2, Zn(NO3)2, Mg(NO3)2 were introduced into the cement mixture in an amount of 0.5 % by weight of cement. When additives of nitrates of alkaline or alkaline-earth metals are introduced into the cement mixture at the stage of concrete production, the rate of mass transfer corrosion processes decreases by 1.5 times. It was found that inhibitors do not have a significant effect on the change in the strength of concrete cement stone during chloride corrosion. The mass transfer indicators (coefficients of mass conductivity and mass transfer, the density of the flow of the transferred components) were determined, according to which the periods of reaching the limiting concentration of chloride ions at the surface of steel reinforcement in concrete during corrosion in 2 % MgCl2 solution were calculated. To achieve such concentration of chloride ions at the surface of steel reinforcement in concrete without an inhibitory additive, it will take 174 days, in concrete with 0.5 % KNO3 additive – 260 days.

Mathematical Modeling of the Corrosion Behavior of Austenitic Steels in Chloride-Containing Media During the Operation of Plate-Like Heat Exchangers

Mathematical models that describe the dependences of the critical temperatures of pitting formation of AISI 304, 08Kh18N10, AISI 321, 12Kh18N10T steels in model circulating waters with pH 4…8 and chloride concentrations from 350 to 600 mg/l on their chemical composition and structure have been developed. They are based on linear squares regressions and a feed-forward neural network for reduced feature numbers. Using the developed mathematical models, it was found that the critical pitting temperatures of these steels increase with an increase in the pH of the circulating water, the number of oxides up to 3.95 μm in size, the average distance between titanium nitrides, the Cr content and a decrease in the concentration of chlorides in the circulating waters, the average distance between oxides and average austenite grain diameter. At the same time, it was found that the geometric dimensions of the steel structure most intensively affect their pitting resistance in circulating waters, and the effect of their chemical composition is minimal and is determined by the amount of Cr, which contributes to an increase in the pitting resistance of steels, probably increasing the solubility of nitrogen in the austenite solid solution. It is proposed to use the developed mathematical models to select the optimal heats of these steels for the production of heat exchangers and predict their pitting resistance during their operation in circulating waters.

Electron beam surface remelting enhanced corrosion resistance of additively manufactured Ti-6Al-4V as a potential in-situ re-finishing technique

This study explores the effect of surface re-finishing on the corrosion behavior of electron beam manufactured (EBM) Ti-G5 (Ti-6Al-4V), including the novel application of an electron beam surface remelting (EBSR) technique. Specifically, the relationship between material surface roughness and corrosion resistance was examined. Surface roughness was tested in the as-printed (AP), mechanically polished (MP), and EBSR states and compared to wrought (WR) counterparts. Electrochemical measurements were performed in chloride-containing media. It was observed that surface roughness, rather than differences in the underlying microstructure, played a more significant role in the general corrosion resistance in the environment explored here. While both MP and EBSR methods reduced surface roughness and enhanced corrosion resistance, mechanical polishing has many known limitations. The EBSR process explored herein demonstrated positive preliminary results. The surface roughness (Ra) of the EBM-AP material was considerably reduced by 82%. Additionally, the measured corrosion current density in 0.6 M NaCl for the EBSR sample is 0.05 µA cm−2, five times less than the value obtained for the EBM-AP specimen (0.26 µA cm−2).

Breaking OER and CER scaling relations via strain and its relaxation in RuO2 (101)

Green hydrogen production from abundant water sources is an important component of renewable energy storage. Water oxidation catalysts are typically considered bound by adsorbate scaling relations, limiting their activity for the oxygen evolution reaction (OER) as well as selectivity between OER and the chlorine evolution reaction (CER) that compete in saline water streams. RuO2 is highly active for both reactions, and recent measurements have shown that the OER activity is greater on undercoordinated, high index facets compared to the lowest energy (110) facet often studied. The growth of such orientations as epitaxial films, however, can result in appreciable strain and potential surface faceting via its relaxation. We find the activity and selectivity toward OER and CER vary with thickness in epitaxial (101) RuO2 thin films: OER activity decreases four times as film thickness increases from 8 nm to 48 nm, while CER activity is comparable. Thus, strain and its relaxation can be used to break scaling relationships between OER and CER, highlighting the important role that defects play in selective oxidation processes on RuO2 in chloride-containing media.

Determining the role of individual and combined chemical elements in the pitting corrosion process of austenitic Fe-Cr-Ni steels

This paper reports a study into the role of individual (S, P, N, C, Si, Mn, Ni, Cr) and combined (Q1=S, Q2=S+P, Q3=S+P+N, Q4=S+P+N+C, Q5=S+P+N+C+Si, Q6=S+P+N+C+Si+Mn, Q7=S+P+N+C+Si+Mn+Ni, Q8=Q=S+P+N+C+Si+ Mn+Ni+Cr) elements in five steel AISI 304 smelting cycles. The correlation between the rate of corrosion K in chloride-containing media and the specific magnetic susceptibility c0 of austenite (matrix), the low content Рdof d-ferrite, and the percentage of elements has been established. Taking into consideration the order of arrangement and influence of other present components, a set of the different-shaped graphic models of K dependences on c0, Рd, and percentage of elements was found. However, the sum of the eight calculated individual and combined elements (Q8) of the models coincides with the sum of the same elements (Q=Q8) of steel smelting samples that were subjected to experimental measurements of c0 and Рd. The curves of the reported models were compared with experimental dependences of K on c0, Рd. The positive and negative role of individual and combined elements in the process of pitting resistance of steel smelting cycles has been identified. Given this, it is assumed that the effect exerted on K by individual and combined elements in the intervals before and after their critical content may be ambiguous. Hence, one value K can correspond to several values of the contents of elements, c0, Рd. A proof of that is the coincidence between the calculated models K of corrosion on the same total content of Q8 for steel samples determined experimentally. The positive (negative) and ambiguous role of elements in the process of corrosion and the possibility of predicting corrosion tolerance of austenitic steels are assumed. The experimental dependence K on c0 and Рd has been established; the greater c0 and Рd, the lower the corrosion rate K. The studied steels contained d-ferrite in the low limits of 0.01...0.1 %.

The Study of Metal Corrosion Resistance near Weld Joints When Erecting Building and Structures Composed of Precast Structures

Corrosion processes of the most common steel grades in various environments are the subject of numerous studies. At the same time, the corrosion of welded joints hidden in concrete thickness has not yet been studied. The authors set themselves the task of investigating this process. For this purpose, the corrosion resistance of several metals (grade St.3, U7 and their weld joints) was studied in standard test solutions, simulating a concrete pore liquid, containing sodium carbonates and hydrocarbonates, and sodium chlorides. Data on comparative corrosion resistance in saline media for specified materials were obtained. It was shown that the corrosion rate depends on the ease of CO2 ingress into the solution, and, to a lesser degree, on the metal microstructure. The surface character of the metal samples and the composition of corrosion products were investigated by scanning electron microscopy and an X-ray diffraction analysis. Chemical forms of surface compounds were determined. For the first time, it is clearly shown that the electrode coating flowing during welding does not always protect the weld from corrosion, as was previously believed. The corrosion rate, in this case, is just the same as at the surface of the metal plate of a similar composition. In the conclusion of this work, it is emphasized that in the case of alkaline and chloride-containing media, the protective coating falling from the electrode to the weld does not protect it sufficiently from corrosion.

The use of the short-lived radioisotope <sup>188</sup>Re in the analytical practice of rhenium determination

The possibility of using the short-lived radioisotope 188Re (16.9 h) in the radioactive-tracer technique for estimation of the losses occurred during sample preparation and for analysis of the solutions with a low rhenium content is shown. The radioisotope was obtained in an 188Re generator, which is a glass column filled with aluminum oxide with a pre-adsorbed parent isotope 188W (69.4 days) that forms 188Re during β-decay. The latter in the form of a perrhenate ion was selectively washed into an aqueous solution, which was used to obtain a labeled solution. The values of rhenium losses and their distribution over the stages of sample preparation of carbon-containing raw materials (e.g., high-viscosity oil) including sintering, leaching, filtration and evaporation are estimated. It is shown that the greatest amount of rhenium is lost at the stage of sintering. However, the use of MgO + KMnO4 mixture minimize the losses occurred at this stage and, hence, the total losses of rhenium. A rapid procedure of rhenium determination using the method of radiometric correction with substoichiometric separation is described. The method is based on the quantitative extraction of a stable complex of tetraphenylphosphonium cation (TPhPh) with the perrhenate ion by dichloroethane. The extraction constant of (C6H5)4PReO4 complex is (3.03 ± 0.75) × 106. The extraction of the perrhenate ion not complexing with TPhPh does not exceed 1 – 2 %. The developed method provides rhenium determination in the sample at a level of 1 – 100 μg. A 10-fold excess of Zn2+ and Ni2+ present in a chloride-containing medium affects the determination of rhenium. The anions , , and have the most pronounced interfering effect whereas , , and Cl– do not interfere with the determination.

Ofloxacin degradation in chloride-containing medium by photo-assisted sonoelectrochemical process using a mixed metal oxide anode

A photo-assisted sonoelectrochemical (UV/US/EC) hybrid process using a mixed metal oxide (MMO) (e.g., Ti/Ru0.3Ti0.7O2) electrode was evaluated with the aim of investigating the degradation and mineralization of ofloxacin (OFL) in a chloride-containing medium. Under optimized condition (30 mA/cm2, 0.05 mol/L NaCl, 10 mL/min, and natural pH), the OFL concentration decayed to 0 in 5 min and, after only 60 min of treatment, ~60% TOC was removed. The comparison of different combinations of UV, US, and EC techniques showed that the UV/US/EC and UV/EC techniques were the most advantageous, due to the production of highly reactive radicals through photolysis of electrochemically generated active chlorine species. A significant reduction in OFL was only achieved in the presence of NaCl, compared to Na2SO4 as supporting electrolyte, demonstrating that DSA® electrodes have high electrocatalytic activity for chlorine evolution. Under real conditions, the percentage of OFL removal from the river water sample was 97% after 10 min of treatment. Phytotoxicity tests indicated that it is possible to reduce the toxicity of the solution using NaCl as supporting electrolyte. In addition, a mineralization pathway for OFL was proposed for the process in question.

Laves phase precipitation and sigma phase transformation in a duplex stainless steel microalloyed with niobium.

Duplex stainless steels are used to replace austenitic steels in industrial applications, especially in the chemical industry where corrosion resistance in chloride-containing media is an important requirement. According to literature, niobium has a great influence on the transformation of the phases of these steels (ferrite, austenite and sigma). Given the interest in evaluating this property in terms of wear resistance and corrosion of the material, the aim of this study was to evaluate the effect of niobium on the formation in austenitic-ferritic stainless steel SEW 410 Nr 1.4517 after heat treatment at 850ºC for 15, 30 and 60 minutes. The niobium contents studied were 0.2; 0.5 and 1.5 wt%. Measurements of microhardness, electrochemical tests in saline solution containing 3.5% sodium chloride and wear resistance were carried out. The results show that an increase in niobium content and sigma phase leads to an increase in hardness and wear resistance, associated with a decrease in corrosion potential. Therefore, the use of niobium in austeno-ferritic stainless steel is recommended when wear resistance is an important factor to be considered.

Mathematical modeling of selective dissolution of AISI 304 steel in circulating chloride-containing waters during operation of heat exchangers

Purpose. Investigation of the effect of chloride-containing medium, chemical composition and structural heterogeneity of AiSi304 steel on selective dissolution of metals ΔCr, ΔNi and ΔFe from stable pits.
 Research methods. X-ray structural analysis, optical microscopy, energy dispersive microanalysis, analysis of the developed linear regression mathematical models of the second order for corrosion losses of metals from pits.
 Results. Based on the analysis of the developed linear regression mathematical models of the second order for corrosion losses of metals from pits, it was found that ΔFe from pits on the surface of AISI 304 steel in model circulating water with pH = 4...8 and chloride concentration of 300 and 600 mg / l decrease with an increase in it. the amount of oxides (1.98...3.95 microns), the average diameter of the austenite grain and increase when the average distance between the oxides and the volume of b- ferite in steel increases. It is proved that ΔNi from pits decreases with an increase in the amount of oxides in steel (1.98...3.95 μm), the volume of b- ferite and a decrease in the average diameter of austenite grain.
 It was determined that ΔCr of steel from pits mainly depends on the concentration of chlorides in the model circulating water, the amount of oxides (1.98 ... 3.95 μm), the average diameter of the austetin grain and the volume of b-ferite. It is hypothesized that this is due to the intensity of adsorption of chlorine ions on imperfections in the structure of AISI304 steel near these oxides at the intersection with the grain boundaries of austenite, where pits nucleate and grow.
 Scientific novelty. It was established for the first time that the coefficient of selective dissolution of Cr from pits on the surface of AISI 304 (ZCr ) steel in the circulating waters of the river decreases with an increase in the volume of b-ferite in the steel, the average diameter of austenite grain and a decrease in the amount of oxides. This can facilitate the transition of metastable pits to stable ones. Moreover, this process is autocatalytic; therefore, it does not depend on the parameters of the model circulating water.
 Statement of tasks. Based on the established features of selective dissolution of ΔCr, ΔNi and ΔFe from pits on the surface of AISI304 steel, to study the effect of its plastic defermation on pitting resistance in chloride-containing model circulating waters.
 Practical value. The developed mathematical models are used to assess the pitting resistance of AISI304 steel in model circulating waters, depending on its parameters and the environment where heat exchangers made of this steel operate.

A Combined Experimental and Computational Approach to Study Crevice Corrosion of Stainless Steels

In the present work, a dual experimental and computational technique is used to study crevice corrosion of ferritic stainless steels in chloride-containing media. A specifically designed three-electrode set-up is developed to monitor current and potential during the incubation, initiation and propagation stages. At the same time, a 3D finite element model is implemented to examine the galvanic coupling prevailing in the experimental set-up and to provide a mechanistic interpretation of the obtained results. The asymptotic current and potential measured at the end of the experiments are thought to be more realistic indicators of crevice corrosion kinetics than the commonly used depassivation pH. The technique also allows highlighting several physicochemical effects including chloride concentration, pH, temperature as well as the effect of surface pretreatment. Finally, an in-depth examination of the simulated current and potential distributions inside the crevice reveals that any extension of the propagation outside the confined geometry will report the ohmic drop out of the crevice, which radically impacts the initiation and propagation modes.

Protective Efficiency of ZrO2/Chitosan “Sandwich” Coatings on Galvanized Low-Carbon Steel

Enhanced corrosion efficiency of low-carbon steel was achieved by newly developed hybrid multilayers, composed of low-carbon steel coated with an electrodeposited zinc sublayer (1 µm), a chitosan (CS) middle layer and ZrO2 coating by the sol–gel method (top-layer). The middle chitosan layer was obtained by dipping galvanized steel substrate in 3% tartatic acid water solution of medium molecular-weight chitosan, composed of β-(1–4)-linked D-glucosamine and N-acetyl-D-glucosamine with a deacetylation degree of about 75–85% (CS). The substrates were dipped into CS solution and withdrawn at a rate of 30 mm/min. One part of the samples with the CS layer was dried at room temperature for 2 weeks, and another part at 100 °C for 1 h, respectively. After CS deposition treatment, the substrates were dipped into an isopropanol sol of zirconium butoxide with small quantity of polyethylene glycol (PEG400). The dipping-drying cycles of the ZrO2 coatings were repeated three times. After the third cycle, the final structures were treated at 180 °C. The samples were denoted as T25, which consists of the CS middle layer, and dried at RT and T100 with the CS middle layer treated at 100 °C, respectively. The samples were characterized by means of differential thermal analysis (DTA-TG), XRD analyses, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Hydrophobicity properties were evaluated by measuring the contact angle with a ramé-hart automated goniometer. Two electrochemical tests—potentiodynamic polarization technique (PD) and electrochemical impedance spectroscopy (EIS)—have been used to determine the corrosion resistance and protective ability of the coatings in a 5% NaCl solution. The results obtained by both methods revealed that the applied “sandwich” multilayer systems demonstrate sacrificial character and will hopefully protect the steel substrate in corrosion medium containing chloride ions as corrosion activators. The newly obtained hybrid multilayer coating systems have dense structure and a hydrophobic nature. They demonstrated positive effects on the corrosion behavior at conditions of external polarization independent of their various characteristics: morphology, grain sizes, surface roughness and contact angle. They extend the service life of galvanized steel in a chloride-containing corrosion medium due to their amorphous structure, hydrophobic surface and the combination of the positive features of both the chitosan middle layer and the zirconia top layer.