Types Of Corrosion Research Articles

Systematic quantitative investigation of the unscrewing process with regard to breakaway torque

Threaded connections make up the majority of separable connections used today. Their disassembly behaviour strongly depends on the conditions during the life-phase. With the trend towards circular economy, disassembly particularly for remanufacturing requires automation. For production systems this mandates a certain capability of adaptation towards different product conditions. In the regarded case of dismantling threaded connections, this is the automatic selection of appropriate robot tools. One important criterion for the tool-selection is the breakaway torque, which strongly depends on friction parameters within the threads and the head surface. Those are influenced by e.g. corrosion and head type. In this contribution, the results of a systematic experimental investigation of the breakaway torque of threaded connections is presented. The aim of the contribution is to determine the influence on the breakaway torque of typical factors appearing in automated disassembly systems. Therefore, a total of 90 experiments are conducted which include five factors: Nominal diameter; Screw head type; Corrosion; Plate material; Applied torque during assembly.

Improving the Corrosion Resistance of TNTZ in Hanks’ Solution after Thermomechanical Treatment

Ti-29Nb-13Ta-4.6Zr (TNTZ) is a new titanium alloy potentially to be used as bone implant material because of its advantages in terms of strength, ductility, non-toxicity, corrosion resistance, and biocompatibility. Its mechanical properties are suitable for bone applications; however, there are still problems related to its corrosion behavior when used for a long time. Therefore, this research aims to determine the corrosion rate and types, and provide corrosion prevention by applying the thermomechanical treatment on TNTZ in Hanks’ solution. The limitation of this research was in not conducting the TNTZ biocompatibility tests. This research was conducted using the potentiodynamic polarization method in Hanks’ solution as the corrosive medium at a temperature of 37°C and a pH of 6.8. Before corrosion testing, a TNTZ sample was treated with thermomechanical treatment combined with solution treatment at a temperature of 850°C and a holding time of 45 minutes, followed by rapid cooling (water quenching), and plastic deformation with deformation variations of 10%, 15%, and 20%, and it was ended with aging heat treatment at a temperature of 300°C and holding time for 1 hour. The novelties of this research are the valid data of corrosion rate and type of TNTZ, which were unavailable before, and corrosion prevention through thermomechanical treatment of TNTZ in Hanks’ solution. The thermomechanical treatment is proved to reduce the pitting corrosion in TNTZ. The results show that thermomechanical treatment and increased plastic deformation can reduce the value of the corrosion rate, as evidenced by the pre-thermomechanical and thermomechanical TNTZ corrosion rates with deformation variations of 10%, 15%, and 20%, respectively, which were 5.522 x 10-4 mmpy; 2.754 x 10-4 mmpy; 2.290 x 10-4 mmpy; and 2.064 x 10-4 mmpy, respectively. TNTZ, after thermomechanical treatment, had the lowest corrosion rate, i.e., 2.064 x 10-4 mmpy, while Ti-6Al-7Nb had the highest one, i.e., 3.05 x10-2 mmpy. The type of TNTZ corrosion is pitting corrosion, as shown by the loss of zirconium that reduced the volume, causing pits to occur. Meanwhile, after thermomechanical treatment, pitting corrosion happened on TNTZ because of the loss or release of zirconium. This research shows that after thermomechanical treatment, TNTZ is the best material compared to other materials for biomedical applications based on corrosion resistance.

An Experimental Evaluation of The Three Types of Corrosion, Passivation, Pitting, and Uniform Corrosion, by Electrodeposited Chromium-Nano Diamond Composite Coating on Porous Materials

Incorporation of nano scale particles in coatings of metals are known as nano composite coatings are a new form of materials with enhanced hardness, wear, and corrosion resistances. In this study, pre-alloy metal powder metallurgy specimens were subjected to electrolytic coating of pure chromium and Cr-ND (Chromium-nano diamond). The influences of the co-deposited ND particles on passivation, pitting and uniform corrosion behavior of the chromium coatings were experimentally inspected and compared with pure chromium coating and non-coated specimens. The corrosion behaviors of the samples were analyzed by Polarization Resistance, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy measurement methods under 3.5 %wt. NaCl solution. Furthermore, characterization tests were carried out using an optical microscope, SEM (Scanning Electron Microscope), EDS (Energy Dispersive X-Ray Spectroscopy), XRD (X-Ray Diffraction) and AFM (Atomic Force Microscope). According to the obtained results, it was observed that as compared to pure chromium coatings and non-coated specimens, a convincing improvement in the corrosion behavior of the Cr-ND coatings was obtained because of the incorporation of the ND particles in the chromium matrix.

Microscopic influence mechanisms of polysaccharide on the adsorption and corrosion inhibition performance of imidazoline on metal surface

Microbiologically influenced corrosion caused by biofilm adhesion is the most complex type of corrosion in the oil–gas pipeline. However, the mechanism of biofilm extracellular polymeric substances’ main components that influence the performance of corrosion inhibitors remains unclear. Therefore, molecular dynamics simulations were performed to gain insights into the aggregation and adsorption of alginate and imidazoline, representative compounds of extracellular polysaccharide and corrosion inhibitor, respectively, on iron surface. Results demonstrated that the corrosion inhibition of imidazoline was mainly due to the formation of a regular bilayer structure at high concentration that provided mass transport barrier and effectively expelled the corrosive Cl- and water from metal surface. However, this capability disappeared when high concentration alginates pre-adsorbed on the metal surface. It was mainly attributed to the fact that the alginates significantly decreased the imidazoline coverage on metal surface (up to 84%), wherein the majority of imidazoline molecules suspended in the bulk water. Moreover, high concentration alginate could form porous network structure with permeable channels, which allowed Cl- and water to pass through and approach the metal surface.

Reliability assessment of parallel wire suspender components considering interlayer corrosion variance

The suspenders bear the repeated stress caused by various cyclic actions during the bridge operation while the stress amplitude under dynamic load is smaller than under dead load. The steel wire degradation process is a typical corrosion fatigue degradation, in which the initial defects caused by surface corrosion are the main source of fatigue cracks and the crack development under operating load leads to the failure of the steel wire. The steel wires of the suspender are considered as a co-deformed parallel structural system. The corrosion process of steel wires in different layers are different for the diffusion paths of corrosion medium, which makes the bearing capacity of steel wires differs from each other. The suspender strength depends on the wire of lowest strength due to the Daniels effect, interlayer corrosion variance should be considered in the evaluation of suspender reliability. This paper investigates the interlayer corrosion variance of parallel steel wire suspenders on the basis of neutral salt spray test. It proposes a corrosion variance coefficient, and considers the stochastic degradation process of suspender. Combined with the daily traffic model, it establishes a sophisticated reliability evaluation method of suspender. The results are shown: The steel wires in each layer of test specimens are all severely corroded when the corrosion time reaches a certain degree. For the specimens with different damage types, the overall corrosion condition of the annular damaged specimen is the most severe; whereas that of the vertical damaged specimen is the least. Under experimental environment, the corrosion variance coefficients of sheath damaged specimens follow normal distribution. In the application of suspender evaluation, the service lifespan of wires varies obviously with the corrosion variance coefficient. The distribution of steel wire lifespan under different corrosion variance coefficients also follows normal distribution. The service lifespan of outer layer wires is longer than inner layer wires, and the overall reliability lies between the reliability of outer and inner layers.

Molecular Dynamics Model to Explore the Initial Stages of Anion Exchange involving Layered Double Hydroxide Particles.

A classical molecular dynamics (MD) model of fully unconstrained layered double hydroxide (LDH) particles in aqueous NaCl solution was developed to explore the initial stages of the anion exchange process, a key feature of LDHs for their application in different fields. In particular, this study focuses on the active corrosion protection mechanism, where LDHs are able to entrap aggressive species from the solution while releasing fewer corrosive species or even corrosion inhibitors. With this purpose in mind, it was explored the release kinetics of the delivery of nitrate and 2-mercaptobenzothiazole (MBT, a typical corrosion inhibitor) from layered double hydroxide particles triggered by the presence of aggressive chloride anions in solution. It was shown that the delamination of the cationic layers occurs during the anion exchange process, which is especially evident in the case of MBT-.

Nickel removal from wastewater using electrocoagulation process with zinc electrodes under various operating conditions: performance investigation, mechanism exploration, and cost analysis

Economically feasible approaches are needed for wastewater treatment. Electrocoagulation (EC) is an electrochemical treatment method that removes various pollutants from wastewater. It has grown in popularity over conventional treatment methods, especially in industrial wastewater, due to its high performance and the ability to remove toxic compounds. However, it is crucial to reduce the costs associated with EC for widespread implementation. It is also important to decrease nickel (Ni) concentrations in wastewater to prevent potential health and environmental problems. Therefore, this study investigates Ni removal from synthetic and real wastewater using electrocoagulation. Zinc, as a novel electrode, was used as the sacrificial anode. Several operating conditions were assessed, including current density, initial pH, electrolysis time, and spacing between electrodes. The maximum Ni removal efficiency, after 90 min, reached 99.9% at a current density of 10 mA/cm2 when the pH was 9.2 and the gap distance was 4 cm. The Ni removal rate reached 94.4% and 94.9% at a 2- and 6-cm spacing, respectively, after 90 min. Anode morphology, kinetic modeling, electrical energy consumption, and cost analysis were also investigated. The type of corrosion was uniform, which is easily predicted compared to pitting corrosion. The comparison between chemical coagulation and electrocoagulation was also reported. Experimental results indicated that the maximum Ni removal rates reached 99.89% after 90 min. The optimum spacing between electrodes was 4 cm, and the optimum current density was 10 mA/cm2. Additionally, the kinetic data were best represented through the second-order Lagergren model. The results demonstrated that the electrocoagulation performance was better than that of chemical coagulation for Ni removal. The maximum electrical energy consumption was 23.79 KWh/m3 for Ni removal.

Cathodic Corrosion Inhibition of Steel by Musa Paradisiaca Leave Extract

It is reported here that the phytochemicals present on the surface of the Musa paradisiaca (MPL) prevent water and other corroding agents from having direct access to the surface of mild steel. These phytochemicals were extracted from the MPL using 70% Ethanol solution and Weight Loss experiment was carried out with variation of temperature, time and concentration HCl and that of the MPL extract in % v/v. The inhibition eFFect of M. paradisiaca leaves of mild steel in aqueous solutions of Hydrochloric acid were investigated at 25, 35, 45 and 60 oC being immersed simultaneously and independently in the acid medium over a period of 12, 24, 48, and 72 hours. A protecting film appeared on the metal surface by the MPL extract via electron donation, hence, acting as the cathode. The temperature and immersion time were inversely proportional to inhibition effciency while concentration of MPL is directly proportional. FT-IR of the extract showed oxygen and nitrogen containing functional groups which are the general characteristics of a typical corrosion inhibitor, while the Gas Chromatography–Mass Spectrometry (GC–MS) investigation revealed different biomolecules thus suggesting that the plant extract consists of different molecules.

Design and performance evaluation of electromechanical impedance instrumented quantitative corrosion measuring probe based on conical rods

Previous study has proved that using electromechanical impedance instrumented bar-type corrosion measuring probe can realize the quantitative assessment of the corrosion amount. To gain more insights into the working mechanism and design better probes, this work examined a new type of corrosion measuring probe based on the conical rod, and evaluated their performance. Theoretical model of this type of new probes was established based on one dimensional piezo-elasticity theory, and the electrical impedance was derived to obtain first resonant and anti-resonant frequencies in longitudinal vibration mode. Two experiments were performed to validate the feasibility of the probe for corrosion measurement, including the artificial uniform corrosion experiment and the accelerated corrosion test. Comparisons between the theoretical predictions and the experimental results from the artificial uniform corrosion experiment were made, and good agreement was found. Effects of piezoelectric patch thickness and cone angle on first resonant and anti-resonant frequencies were also analyzed. In addition, a wireless impedance measurement system was preliminarily realized, which is very promising in developing the low cost and high accuracy online real-time monitoring technology for the pipeline corrosion monitoring.

Application of GIS technique in suitability assessment of groundwater in the Assin North and South municipalities, Ghana

The application of the GIS technique in the groundwater quality assessment of the Assin North and South Municipalities has been carried out to assess its suitability for drinking, domestic and irrigational uses. Data for this study was taken from the Community Water and Sanitation Agency office in Cape Coast. The World Health Organization (WHO) guidelines were used for the assessment of groundwater quality. The assessment of the irrigational water quality was based on Sodium Percentage, Sodium Adsorption Ratio, Residual Sodium Carbonate, permeability index, Magnesium hazard and Kelly index. The types of groundwater in the area include CaMgHCO3, mixed groundwater, NaCl, and CaMgSO4 based on the Piper diagram. The major factors controlling groundwater chemistry include rock weathering, ion exchange, and impacts of human activities. The groundwater is generally suitable for drinking and domestic purposes. However, some of the samples showed high concentrations of certain parameters including turbidity, NO3−, Mn, PO4, Fe, F−, EC, Cl−, and colour which make them unsafe for drinking without prior treatment in selected communities. The water quality index tool revealed that 29% of the groundwater samples are of excellent quality, 54% are of good quality, 10% are of poor quality, 2% are of very poor quality and 5% are unsuitable for drinking. It was observed that the communities within the middle zone of the study area have groundwater of poor quality compared to that of the extreme ends. The poor groundwater quality may be attributed to the impacts of anthropogenic activities including, galamsey, lack of hygienic conditions around boreholes, the use of pit latrine, and application of agrochemicals. Considering the irrigational use, the groundwater is generally suitable. However, about 20% show unsuitable quality based on magnesium hazard (MH), 5% show unsuitable quality based on Na%, 20% show suitable quality based on Kelly Index (KI) and 34% show corrosive groundwater type. Application of the Wilcox and the USSL classifications of irrigation water revealed that the groundwater is suitable for irrigational use. The study has revealed the effectiveness of integrating the GIS technique and hydrochemistry in the assessment of groundwater quality, spatial variation of the groundwater quality and processes affecting the groundwater chemistry and overall quality.

Use of orange peel extract as an inhibitor of stainless steel corrosion during acid washing in a multistage flash desalination plant

Environmentally friendly and cost-effective inhibitors based on orange peel extract (OPE) have been developed for potential applications in ejector tubes of a multistage desalination plant during the acid cleaning process. After conducting tests under both static and hydrodynamic circumstances, it was determined that the inhibitor formulation was effective against corrosion of stainless steel (SS) in 1 M HCl solution at 30 °C under the conditions tested. Electrochemical methods were used along with electron microscopy to collect information on the corrosion inhibition efficiency of the extract. Experiments were conducted for 1, 2, 3, 4, 6, 12, and 24 h, and the performance of OPE was compared to that of a commercial acid corrosion inhibitor to determine which performed better. The results revealed that OPE demonstrated outstanding corrosion inhibition performance compared to the commercial acid corrosion inhibitor. With remarkable inhibition efficacy for up to 24 h under both static and dynamic settings, 0.4% of OPE displayed typical mixed-type corrosion inhibitor behavior in the tested environment. All of the procedures that were used produced results that were in good agreement. Due to the synergistic action between the two compounds, the corrosion inhibition of OPE on SS was improved in 1 M HCl in the presence of iodide ions. In the absence of KI, OPE was found to inhibit SS corrosion at a concentration-dependent rate, with the concentration of OPE being the most significant factor. A study of the adsorption of OPE onto a SS surface revealed that the Langmuir adsorption isotherm controls the process. Based on the quantity of free energy of adsorption observed, it was determined that there is physical contact between the OPE and the surface of SS in this experiment. It was possible to identify the most effective phytochemicals for corrosion inhibition based on the findings of quantum chemical calculations, which were subsequently evaluated in the laboratory.Graphical abstract

Residual ultimate strength of large opening box girder with pitting corrosion damage under torsion and bending loads

ABSTRACT In this paper, the residual ultimate strength of large opening box girder with pitting corrosion under combined loads is investigated by ABAQUS software. A primary investigation was first conducted to compare the influences of corrosion types. Afterwards, effects of some studied parameters including the depth, density, volume, and location of the pit, which may affect the ultimate strength, were analyzed based on a series of FE results. It was concluded that the relative corroded volume loss has a non-negligible effect on the residual ultimate strength. For torsion and sagging cases, the side plates' pits significantly reduce the ultimate strength. For the hogging case, the effect of bottom plate pitting on the ultimate strength should be paid attention to. The interaction relationship between torsion and bending moment was analyzed. An interaction equation is proposed for evaluating the ultimate strength of large opening box girders with pitting damage under combined loads.

Corrosion inhibitory potential of selected flavonoid derivatives: Electrochemical, molecular⋅⋅⋅Zn surface interactions and quantum chemical approaches

Zinc metal corrosion inhibitor potential of some flavonoid derivatives, namely, naringenin (NRNG), morin hydrate (MNHD), and 6-hydroxyflavone (6-HFN), was investigated by measuring their inhibitory activities, determining their thermodynamic and kinetic adsorption mechanistic properties as well as comparing their molecular⋅⋅⋅Zn metal surface interaction strengths. The inhibition efficiencies were evaluated in 1.5 M hydrochloric acid (HCl) environment and different concentrations of the inhibitors (from 2.0 × 10−4 – 1.8 × 10−3 M) using gravimetric and various electrochemical methods at 30–60 °C. The molecular···metal surface interactions were determined using the density functional theory method by using the GGA/RPBE/DNP approach. Electrochemical studies show that 6-HFN and NRNG are the most and least effective corrosion inhibitors, with 77.54 and 70.46 maximum percentage inhibition efficiency, respectively. Atomic Absorption Spectroscopy technique was used to compare the concentration of the zinc ions that remained in the solution after gravimetric analysis in the absence and presence of the inhibitors at 30 °C; it was found that the inhibited solution contained less concentrations of zinc ions as compared to the uninhibited solution. Surface morphology techniques (e.g., 3D microscope) suggest that a localised type of corrosion took place on the metals, and the corrosion damage was minimal in the presence of the inhibitors. FT-IR showed a strong adsorption of the functional groups found in the inhibitor compounds, with CC functional group being strongly retained by all three inhibitors. The flavonoid inhibitor compounds were found to absorb chemically at low temperatures and physically at high temperatures. Langmuir adsorption isotherm was obeyed. The trend for molecular···metal surface interaction strengths follows the trend obtained from experimental findings on inhibition efficiency. Overall, the results suggest that all the molecules investigated are good corrosion inhibitors with a preference for those compounds in which there exists extended electron delocalization through the aromatic rings and in which there are minimal electron-withdrawing groups on the aromatic rings.

ANALISA KOROSI PADA TANGKI REAKTOR TRIGA 2000 MENGGUNAKAN METODE INSPEKSI ULTRASONIK DAN INSPEKSI VISUAL (UNDERWATER CAMERA)

A reactor is a process device where a reaction takes place, be it a chemical or nuclear reaction and not physically. Nuclear reactors are used for various purposes, namely to create, regulate, and maintain a nuclear chain reaction at a constant rate. One method of monitoring corrosion is using an ultrasonic device to measure the thickness of the tank wall and an underwater camera tool to visually see the damage that has occurred and will provide a quantitative estimate of the corrosion rate that occurs in the system by comparing the initial weight and weight after a certain time. The corrosion rate value on the TRIGA 2000 reactor wall is obtained through the weight reduction method, and has an average corrosion value of 0.10 mmpy, while the type of corrosion that occurs on the TRIGA 2000 reactor wall is the type of intergranular corrosion. protective coating by coating organic compounds (lubricant) and controlling humidity and temperature.

Scientific and practical bases for establishing and introducing integrated geological monitoring in Kupol Mine

The location of the Kupol gold–silver deposit governs complexity of its geological features within the Okhotsk–Chukotka Volcanic Belt in the zone of high tectonic activity. The present zones with different thermodynamic conditions in permafrost 250–300 m thick at the mining depth greater than 500 m, the cryopags in frozen rocks and in mineralized pressure water below the permafrost sole, the excessive tectonic stresses in thawed rocks, the aggressive physicochemical, chemical and biochemical conditions of the underground hydrosphere dictate the need to develop and introduce the integrated geological monitoring. The monitoring concept and contents are formulated based on the representation of the underground space (US) of a mine as a multicomponent system: fractured rock mass–underground water–microorganisms of underground water–gases of various genesis–load-bearing structures (supports). For each of the components, the necessity and directions of monitoring and observations are determined in the structure of the integrated monitoring system. The interrelation of all US components is shown, and special attention is paid to the operability and long-term stability of rock bolting systems as the main supporting structures that determine mine operation safety. It is emphasized that the mine support systems experience the multifactorial influence of four components: rocks, groundwater, microorganisms and gases. All types of corrosion of mine support systems, including biocorrosion, are identified and systematized, their nature is disclosed and the methodological aspects of recommended control and observations in the specific monitoring system are formulated, which ensures improvement of mining safety and elimination of emergencies through undertaking preventive measures.

Reliability evaluation of corroded pipeline under combined loadings based on back propagation neural network method

Corrosion is a common type of defect that causes failure of oil and gas pipelines. Pipelines often bear the combined loadings of axial compression force, bending moment and internal pressure in operation; therefore, it is of great significance to study the reliability of pipeline under different combined loadings. First, this work established a nonlinear finite element model of corroded pipeline for the typical internal corrosion defects of groove shape, and the reliability of the model and the accuracy of the finite element analysis method are verified. Then the burst pressure of pipeline under combined loadings is investigated. Second, this work established the BP network analysis and prediction model. The results of numerical simulation are used as samples to train the neural network. The prediction limit function value is output through the forward simulation function, which is compared with the objective function to judge whether the pipeline is reliable. Finally, back propagation neural network model calculated the reliability of pipeline under different working conditions combined with Monte Carlo method. The effects of load, corrosion depth, axial corrosion length, circumferential corrosion width and variation coefficient of parameters on pipeline reliability are analyzed. It is found that axial force and bending moment affect the reliability of corroded pipeline. Generally, the higher the combined loadings are, the lower the reliability is, but this law will be different due to the influence of corrosion parameters. In addition, the corrosion depth has the greatest influence on the reliability of corroded pipeline, followed by the corrosion width and the corrosion length. The coefficient of variation of corrosion depth has a great influence on the reliability of pipeline with high depth corrosion defect. These conclusions can provide references for the reliability evaluation of pipelines.

Corrosion inhibition of deposit-covered X80 pipeline steel in seawater containing Pseudomonas stutzeri

Under-deposit corrosion, a typical corrosion type, is a major threat to the safe running of pipeline steel in marine environment. Under-deposit corrosion behaviour and mechanism still require further investigation, especially when there is participation of microorganisms. In this work, the inhibition of corrosion of deposit-covered X80 pipeline steel due to the presence of Pseudomonas stutzeri in seawater containing CO2 was investigated using weight loss, electrochemical measurements, a wire beam electrode and surface analysis. The results show that steel corrosion rates decline rapidly due to the covered deposit in the presence or absence P. stutzeri, but corrosion rates were slower in the presence of P. stutzeri. The highest corrosion rates were (0.365 ± 0.021) mm/y and (0.230 ± 0.001) mm/y in abiotic and biotic conditions, respectively. The corrosion inhibition efficiency of P. stutzeri was reduced in the presence of deposits, because the deposits led to a lowered biological activity. The galvanic current density between deposit-covered and bare specimens in seawater was weakened by P. stutzeri, leading to diminshed corrosion, especially pitting corrosion.

Stress corrosion behavior of 2195-T8 Al-Li alloy with an artificial pit exposed to a 30vol% HNO3 solution

This paper experimentally studied the stress corrosion behavior of 2195-T8 Al-Li alloys with prefabricated pits in 30vol% HNO3. The microstructure was observed and determined by the scanning electron microscopy and the transmission electron microscopy. The typical corrosion features, i.e., regular or irregular corrosion pits and sub/intergranular corrosion, were investigated, and the role of stress were analyzed. The statistical results of the number and area of corrosion pits in various sizes were studied using an improved image processing method. Experimental results demonstrate that stress affects the intergranular corrosion or sub-intergranular corrosion of the alloy most, and promotes them to evolve into cracks under stress corrosion. Stress also plays a role in accelerating corrosion severity of certain corrosion feature. The number of corrosion pits with an area of 0–50 μm2 can be seen as an index to reflect the degree of corrosion. Besides, a corrosion phenomenon, i.e., the pit bottom in the site with the maximum stress locally suffering from no severe corrosion, was observed and discussed.

Study of carbon dioxide corrosion products by the X-ray diffraction method

The internal carbon dioxide corrosion is one of the most common types of corrosion in the gas fields development. The results of studying the composition of carbon dioxide corrosion products by X-ray diffraction method are presented. FeCO3 is the main product resulting from dissolution of steel upon carbon dioxide corrosion. Siderite is characterized by the phenomenon of isomorphism in the crystal structure (a change in the chemical composition of the phase at the same crystal structure). In this case, some of the iron ions in FeCO3 can be replaced by manganese, calcium, and magnesium ions. It is shown that phases of the precipitates of non-stoichiometric composition (CaxMgyMnzFe)CO3 thus formed are poorly crystallized which is attributed to the presence of defects in the crystal structure. They will exhibit inferior protective properties compared to stoichiometric FeCO3. The film of FeCO3 is packed, uniformly distributed and tightly adhering to the steel surface. An analysis of the diffraction patterns revealed a good crystallization of FeCO3. The shape of FeCO3 particles tends to a regular hexagonal habitus. The results obtained can be used in studying the resistance of corrosion products formed on the internal surfaces of gas production equipment under aggressive conditions in the presence of CO2 in produced and transported hydrocarbons.

Non-uniform corrosion influences on mechanical performances of stainless-clad bimetallic steel bars

As a type of corrosion-resistant reinforcement, the stainless-clad bimetallic steel bar (SCBSB) has the advantages of low price and good mechanical properties, which causes them to be widely used in engineering structures. In the actual service process of the structure, the steel bar always corrodes first on the side close to the concrete cover. This type of non-uniform corrosion characteristic may lead to the mechanical properties of steel bars being very different from those with ideal uniform corrosion. Therefore, studying the degradation law of the mechanical properties of SCBSBs with non-uniform corrosion has important engineering value and research significance. In this study, the non-uniform corrosion mechanism was described, and non-uniformly corroded SCBSB specimens at different corrosion degrees were obtained by the electrochemical accelerated corrosion method. Through tests and analyses, the mechanical properties and toughness degradation laws of the SCBSB with non-uniform corrosion were obtained. Models were proposed to predict the mechanical properties and toughness of SCBSBs with non-uniform corrosion at any corrosion degree. In addition, through a finite element analysis, the mechanical property degradation laws of SCBSBs with three corrosion forms were analyzed. According to the experimental results, it was suggested that the corrosion degree of SCBSBs should be controlled within 14.39% to meet engineering requirements. The resistances of reinforced concrete beam with different corroded degrees SCBSBs were discussed to clarify the effect of corrosion type on durability of reinforced concrete members.