Corrosion Zone Research Articles

A chemo-micromechanical damage model of concrete under sulfate attack

It is essential to explore the corrosion cracking of concrete under sulfate attack to predict the service performance and durability of concrete structures. The damage degree of concrete caused by sulfate attack is quantitatively investigated. Based on the damage mechanism of the local cracking stage, a chemo-micromechanical damage model of sulfate attack of concrete is established by elasto-damage mechanics. The progressive degradation behavior of concrete under sulfate attack is divided into three zones, including the chemical corrosion zone, the damaged concrete zone by expansive stress, and the intact concrete zone. The proposed chemo-micromechanical damage model can quantitatively determine the effects of chemical sulfate corrosion on mechanical properties of concrete. In addition, the present model considers the interaction among corrosion products, the damaged concrete, the intact concrete and uncorrupted hydration products. The comparison between the calculation results and the available experimental data shows that the proposed model is feasible for corrosion cracking analysis. Based on the proposed model, the influencing factors of concrete damage are discussed. With the increase of corrosion degree, the content of corrosion products, the expansion coefficient of corrosion products and the initial radius of corrosion products, the elastic moduli of concrete decrease after sulfate attack. When the tensile strength and rigidity of concrete matrix reduce, the effective elastic moduli of concrete after sulfate attack also deteriorate. The numerical results exhibit that the proposed chemo-micromechanical model is of notable significance to the application of the chemo-mechanical coupling problems of cementitious composite materials.

Influence of well watercut on pumping parameters

The article deals with the impact of well watercutting on the reliability of field pipelines and pumping parameters. As a result of the analysis of statistical data on the number of accidents over the last 9 years, it has been established that the main part of accidents is associated with high watercut oil. Besides, approaching the value of the volume fraction of water in the emulsion to a critical one can lead to a pressure drop beyond the standard values. The article deals with the impact of well watercut on the reliability of field pipelines and pumping parameters. As a result of the analysis of statistics on the number of accidents over the past 9 years, it has been established that the main share of accidents is associated with high watercut of well products. Its high content is the reason for intense corrosion and erosion wear of pipe material, which leads to formation of in-pipe corrosion zones and, as a result, pipeline leaks.

Reducing the Carbonation Zone and Steel Corrosion Zone Widths of Recycled Aggregate Concrete by Optimizing Its Mixing Process

AbstractThe optimization of mixing processes is an effective approach for strengthening the microstructure of the interfacial transition zone (ITZ) in recycled aggregate concrete (RAC). This study ...

Carbonation resistance study and inhomogeneity evolution of recycled aggregate concretes under loading effects

Carbonation-load coupling effects can aggravate the inhomogeneity of recycled aggregate concrete (RAC) which contains old attached mortar (OAM) and new added mortar (NAM). In this study, these mortars are first distinguished using an iron oxide. Afterwards, accelerated carbonation coupled with four-point bending effects are applied on the RAC samples, and the carbonation depths in compressive, load-free and tensile zones are compared. The loading rate equals to 40% RAC flexural strength. The microstructures of the mortars in different zones are then compared. Moreover, a computing method for the steel corrosion zone widths of the RACs is proposed after the figures determined using the OAMs and NAMs in different zones as samples are compared. The results show that the carbonation depths of RACs present a significant difference which is more remarkable compared with natural aggregate concrete. Besides, the load shows significant impacts on the mortar microstructure and steel corrosion zone width. Specifically, the effect of tensile stress on OAMs is more obvious than that on NAMs, but there is no such difference in compressive zone. Furthermore, using the OAMs in tensile zone as the samples concludes the highest steel corrosion zone width which is suggested to be used to evaluate the carbonation service life of RAC structures for avoiding the overestimation of structure safety.

Bending performance of connection-corroded welded hollow spherical joints

Indoor swimming pools are a typical aggressive environment in which long-span steel structures are prone to corrosion, especially in the connection position of joints. In order to evaluate the impact of the corrosion on the mechanical properties of joints, a corrosion test of Q235 steel in a swimming pool environment was carried out for 48 and 72 months respectively. The surface pitting distribution of the corrosion specimens was measured and statistically analyzed, and a probability distribution model of surface pit depth was established. Then, a finite element model of welded hollow spherical joint, which could simulate local corrosion and pit distribution, was established, and the parameter analysis of connection-corroded joints on bending performance was conducted. The results demonstrated that the hoop corrosion range and corrosion depth rate were the most sensitive parameters to the bending performance. Taking the number of hoop corrosion zones and corrosion depth rate as parameters, the bending bearing capacity degradation rates of connection-corroded joints based on a specific guarantee rate and different conditions were obtained. Finally, a convenient method for evaluating the joints' bending bearing capacity degradation rate was proposed, which could provide a reference for studying the mechanical properties of similar connection-corroded joints and evaluating the safety performance of grid structures.

Effect of non-uniform corrosion on the cracking propagation of the RC specimens

This paper investigates the influence of non-uniform corrosion of the mild steel reinforcement on the cracking propagation of the concrete cover. Partial surface of the reinforcement was coated by an epoxy resin in order to prevent the covered surface of the steel from corrosion. As a result, the reinforcement was corroded partially along the surface by an impressed current in this way. The corrosion propagation of the steel reinforcement and the corrosion-induced cracking process was investigated during different corrosion periods. The width and the cracking paths were observed carefully. The results showed that two cracking paths would happen to the concrete cover due to the non-uniform corrosion of the steel reinforcement, including the corrosion-induced crack along the radius direction of the concrete cover and two branches in the secant direction of the corrosion zone. The aggregate of the concrete could also influence the propagation of the cracking path significantly.

Stress-deformed state of the apparatus taking into account the influence of the location of mechanical damage in the zone of corrosive wear

Technological apparatuses of oil and gas refinery and petrochemical industries are the most responsible operational units, since they are used to carry out various technological processes in a continuous mode under the influence of high pressures, temperatures and aggressive working mediums. Due to the design features of the devices, corrosive wear can be both uniform and uneven, as well as concentrate in the areas most prone to corrosion damage. Various scenarios of corrosion damage and different zones of corrosion of constructional elements of the apparatus during operation can radically change the stress-deformed state, worsening the forecast and bringing the apparatus closer to the limiting state. Also, possible negative consequences on the device can be caused by mechanical damage - “risks” that are formed during mounting, repair or during transportation to the installation site. The mutual influence of the most unfavorable zones of corrosion damage to the apparatus and the presence of “marks” in these zones under the influence of operating loads can contribute to the development of the most negative variant of the development of an emergency situation. Currently, work on modeling the stress-deformed state of devices with different levels of accumulated damage, identifying the most loaded areas and the most unfavorable possible outcomes is relevant. This paper investigates the interconnection between the impact on the stress-deformed state of an apparatus with a “shirt” of operational loads, corrosion damage and the presence in this zone of a mechanical defect of the “risk” type with its various locations.

Modeling of the stressed-deformed state of the apparatus under pressure at corrosion

Vessels and apparatuses operating under pressure at hazardous production facilities are operated under conditions of many factors that limit the safe service life. These factors include elevated pressures and temperatures, damage during operation, exposure to both static and cyclic loads, etc. The most common and determining damage to metal equipment is corrosion wear. Corrosion wear negatively affects reliability during operation, gradually reducing the strength of the technical device by reducing wall thicknesses and thereby bringing the object closer to its ultimate state. As a rule, visual inspection and thickness measurements make it possible to identify corrosion zones, analyze these zones and give recommendations for further operation or replacement of defective areas. However, some designs of vessels and apparatuses do not give the opportunity to carry out work on the assessment of the corrosion state in full, and in this regard, there is a possibility that adverse sections will be skipped. Especially such problems arise when diagnosing devices with multiple workspaces. Currently, the work on modeling equipment of this type with the use of specialized software systems for assessing the stress-deformed state taking into account all the factors present and identifying the most unfavorable zones with maximum effective stresses is relevant. In this paper, we study the interconnection between the effect on the apparatus with a shirt of operating parameters when modeling various scenarios of corrosion wear.

Design of Concrete Building Structure in Marine Corrosion Zones

Zhao, H.R., 2020. Design of concrete building structure in marine corrosion zones. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 266–270. Coconut Creek (Florida), ISSN 0749-0208.Building structures in offshore areas are extremely susceptible to chloride ion erosion in seawater or marine atmospheric environment, causing problems such as corrosion and swelling of steel rebar, spalling of concrete protective layer, etc., reducing the service life of the structure, and increasing the maintenance and operating costs of the structure. This paper attempts to enhance the design concrete building structures in the marine corrosion zones from the two aspects of durability and service life. To this end, it summarizes the principles of chloride ion erosion of reinforced concrete structures in coastal areas based on existing research, and explores the destruction mechanism of reinforced concrete structures under the action of chloride ions and external loads. Finally, the new method suitable for durability design of reinforced concrete structures in marine corrosion zone was proposed. The study found that the chloride-induced corrosion to the structure in the marine environment can cause the corrosion of the steel bars and accelerate the corrosion rate; a time-varying reliability model of the reinforced concrete structure was proposed; the increase in the thickness of the steel protective layer in the concrete can effectively improve the durability and service life of the structure. The research findings provide a theoretical basis for the durability design of concrete structures in offshore environments or marine corrosion zones.

Experimental study on the corrosion behavior of X70 steel under asymmetric dynamic DC interference

AbstractThe corrosion behavior of X70 steel in simulated soil environment under asymmetric dynamic direct current (DC) interference was studied by immersion tests. The experimental results showed that the negatively asymmetric dynamic DC interference would induce localized corrosion. Under the same dynamic period of 160 ±80 s, when the negative half‐wave current density remained stable at −10 mA/cm2 and the positive half‐wave one decreased from 7 to 1 mA/cm2, the equivalent diameters of the localized corrosion zones became smaller and the steel samples demonstrated typical pitting corrosion morphologies. To further explore the effect of asymmetric dynamic DC interference on the localized corrosion behavior of carbon steel, a variety of experimental measurements were carried out including real‐time DC potential monitoring, in‐situ near‐surface pH measurements, cyclic voltammetry, and Mott–Schottky tests. It was found that the localized corrosion behavior was probably related to the breakdown of passive film formed on the metal surface exposed to negatively asymmetric DC current generated high pH conditions.

Development of Robotic Nondestructive Testing of Steel Corrosion of Prestressed Concrete Bridge Girders using Magnetic Flux Leakage System

This paper describes the development and validation of a new magnetic-based corrosion detection device integrated in a robotic system. The system nondestructively scans the length of AASHTO-type prestressed concrete I-girders of bridges. The system includes two primary subsystems: an independent magnetic flux leakage (MFL) system for nondestructive testing, and a robotic rover to transport the MFL system along the girder’s length with navigation around transverse diaphragms. The MFL unit inspects prestressing steel strands embedded in concrete and detects cross-section losses caused by corrosion. The MFL is designed with two permanent magnets to magnetize embedded strands and multiple Hall-effect sensors to detect normal and axial magnetic flux leakage. The system is evaluated by testing a laboratory mockup girder and further applied on a field girder. Resulting magnetic signals from both normal and axial Hall-effect sensors are recorded using a newly developed and integrated data acquisition system. Finite element simulations through multi-physics 3D transient analysis aided the development of the new MFL system components, including appropriate magnets strength and dimensions, as well as the verification of the developed system. The effects of lateral reinforcements on nearby section loss are obtained from tests and analyzed with numerical models. Results indicate that the system can successfully disclose magnetic leakage signals at the corrosion zone.

Elucidation of orientation relations between Fe-Cr alloys and corrosion products after high temperature SO2 corrosion

The early stages of corrosion of Fe-Cr-model alloys (2 and 9 % Cr) were investigated after exposure at 650 °C in 0.5 % SO2 containing gas by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The impact of the grain orientation of the base alloy on the orientation relations of the corrosion products is presented. After 2 min – 5 min exposure the formation of a multi-layered corrosion zone was discovered. A clear orientation relationship between ferrite and the (Fe,Cr)3O4 spinel could be demonstrated. The obtained results show the importance of the grain orientation on oxidation resistance.

Determination of the corrosion resistance of low alloyed steels by magnetic method

An innovative method of measuring and control of the steel corrosion rate by changing magnetic characteristics is developed. The impact of heat treatment on the corrosion rate of the samples of high-carbon steels (maximum corrosion loss is observed at a tempering temperature of 400°C) is attributed to the appearance of micro-galvanic pairs (MGP) between the phase components of the material. MGP undergo redistribution under heat treatment thus changing conditions of the galvanic current flow. The structural phase composition, in turn, determines the magnetic properties of steel and correlation between the magnetic properties and corrosiveness. The goal of the study is demonstration of the possibility and expediency of using the magnetic parameters of steel for determination of the steel corrosion rate. A close correlation dependence is observed between the coercive force and the electrochemical potential (relative to the silver chloride electrode) which are direct indicators of the corrosiveness. Case study of a pipeline made of 09G2S steel along which change in the coercive force attained 25% revealed rather high risk of developing micro-galvanic pairs. A rapid method of scanning magnetic parameters is proposed to detect potentially corrosive zones. A multi-parameter approach can be used to solve the problem of the ambiguity of the relationship between the corrosiveness and magnetic parameters. Harmonic decomposition of magnetic hysteresis loops of 45Kh steel samples is used to obtain a number of odd harmonics. Some of them weakly correlate with the corrosion loss, whereas complexes of several harmonics correlate to a greater extent. The results can be used in technical diagnostics and prediction of the corrosion activity of steel structures before their operation. The results can be used in technical diagnostics and forecasting of the corrosiveness of steel structures prior to their operation.

Study of corrosion behavior of Pb–Ag alloy electrodes in the zinc sulfuric acid solution by scanning reference electrode technique

The corrosion behavior of four commercial Pb–Ag alloys electrodes in the zinc sulfuric acid solution was investigated using scanning reference electrode technique (SRET). The results show that SRET is more sensitive for studying not only the uniform corrosion behavior of the Pb–Ag electrodes, but also the localize corrosion of the Pb–Ag electrodes. Under free corrosion conditions, lead corrosion (anodic) zone appeared on the edge of electrode while hydrogen evolution reaction (cathodic) zone appeared on the centre of the specimen. The absolute anodic potential and localize corrosion of the four electrodes decreased with the increase of immersion time. At the end of 10 h of free corrosion condition, the electrode Pb-0.69% Ag alloy displays the best corrosion resistance, followed by the electrodes Pb-0.62% Ag alloy, Pb-0.25% Ag-0.1% Ca alloy and Pb-0.56% Ag alloy. During polarization study and potential decay, the electrode Pb-0.69% Ag alloy had the lowest Quasi Electromotive Force (QEMF), followed by the electrodes Pb-0.62% Ag alloy, Pb-0.25% Ag-0.1% Ca alloy and Pb-0.56% Ag alloy, it means that the electrode Pb-0.69% Ag alloy had the highest corrosion resistance, followed by the electrodes Pb-0.62% Ag alloy, Pb-0.25% Ag-0.1% Ca alloy and Pb-0.56% Ag alloy in the zinc sulfuric acid solution. Also, linear polarization confirms the same trend as that of the SRET.

Investigations on the dynamic water-wetting process relating to the internal corrosion

ABSTRACT Numerical simulations were performed to investigate the wall water wetting process relating to the internal corrosion in an elbow system. In the simulations, the standard k-ε model and VOF method were used to reveal the water wetting mechanism. The water wetting time and frequency are proposed to characterize the internal corrosion. The results indicate that the wetting process is mainly controlled by the inner layer. For the case with a larger water fraction, the water tends to form a long-lasting low-frequency wetting process. However, for the case with a smaller water fraction, the water may be trapped into the oil phase and it appears as a discrete water wetting. At the elbow part, there is an increment of the wetting process when the angle is less than 30° and then it goes down. Combining the results of this study with the results of previous studies, the regions with a longer wetting time and a higher wetting frequency can be viewed as the high-risk corrosion zone.

Equivalent elastic modulus of reinforcement to consider bond-slip effects of coastal bridge piers with non-uniform corrosion

Coastal bridge piers in marine environments are vulnerable to non-uniform corrosion due to wetting-drying cycles and high chloride concentration of seawater. This paper presents a methodology to analyze the seismic performance of coastal bridges by modifying the elastic modulus of reinforcement, while considering the effects of bond-slip and non-uniform corrosion. Tensile stress-slip relationships of reinforcement with uniform and non-uniform corrosion are first derived. Then, a method to determine the equivalent elastic modulus of reinforcement with non-uniform corrosion is introduced. The proposed methodology is validated based on cyclic test results of bridge pier specimens under uniaxial and biaxial loading actions. Through further numerical simulation, the effects of mass loss ratio and corrosion zone height on seismic performance of coastal bridge piers are examined. Compared to the method of using an interface element, the proposed method of using equivalent elastic modulus of reinforcement is simpler for the numerical simulation of bond-slip for coastal bridge piers. Results showed that the steel-to-concrete interfacial bond behavior slightly influences the peak strength of coastal bridge piers. However, it can significantly reduce the energy dissipation capacity and residual displacement of structural components.

Protection of fuel filter with alkaline and acid zinc coatings

Galvanic coatings are applied so that the surface of the base material obtains appropriate properties, corrosion resistance, durability, aesthetic appearance, and long-term application in the appropriate industry. In this paper, the aim was to protect steel fuel filters with alkaline and acid zinc coatings of different thicknesses. The coating of zinc, which is applied from the alkaline electrolyte, provides good corrosion protection with excellent coating flexibility. The thickness of the coating by the X-ray fluorescence method was tested, followed by coating tests, corrosion resistance, and electrochemical tests. The results of adhesion showed a high quality coating, as no corrosion occurred during the test. The corrosion resistance tested by the salt chamber method speaks of the appearance of white and red corrosion. On alkaline electrolyte coatings, white corrosion occurred after 168 hours of exposure to the salt test, while on white zinc samples there was a white corrosion after 240 hours of exposure. Tafel polarization diagrams have been determined: corrosion potentials, current intensities, anode and cathode Tafel coefficients and calculated corrosion rates. The active and passive corrosion zone is determined by the cyclic voltammetry.

Investigation of Corrosion of 304 Stainless, Inconel 625, and Haynes 230 in a Chloride-Salt-Based Thermal Storage Medium

One of the critical challenges for latent heat thermal energy storage systems in concentrating solar power applications is corrosion of metallic alloys as containment and heat transfer fluid tube materials in corrosive salts at high temperatures. In this study, the effects of MgCl2 on the corrosion of stainless steel 304, Inconel 625, and Haynes 230 alloys were investigated through embedded metal samples in the graphite foam/MgCl2 storage medium. Four experimental testing modules were fabricated, and experimental tests were conducted under controlled environment by heating the testing modules to and keeping them at 750 °C for 100, 200, 500, and 1000 h. The estimated corrosion rates based on the weight losses for stainless steel 304, Inconel 625, and Haynes 230 were 94, 9, and 8 μm/year, respectively. The fitted equations for the loss of the thickness as functions of the exposure time show that the corrosion rates decrease with the exposure time. The results on the corrosion zones or depths and chromium segregation ranges of the experimental samples are also presented.

Research on Corrosion Resistance of Al2O3-MgAl2O4 Refractories and SiC-MgAl2O4 Refractories to Gasifier Slag

Spinel-containing refractory is a kind of potential chromium-free refractory for coal gasification because MgAl2O4 spinel has good slag resistance. Corundum-spinel refractories with w(Al2O3)=94%, w(MgO)=5% and SiC-spinel refractories with w(SiC)=64%, w (Al2O3)=5% were prepared. The crucible specimens were tested for slag corrosion with commercial gasifier slag at 1 500°C for 1 h in reducing atmosphere. XRD analysis were researched on the sidewall of the crucible after slag test. Microstructure and chemical composition of samples in slag corrosion zone were analyzed by SEM and EDS. The results show that the slag resistance of SiC-MgAl2O4 refractory was significantly better than Al2O3-MgAl2O4 refractory. The corundum particles were decomposed into fine particles by the slag, and the microstructure was destroyed. The oxidation of the surface of the silicon carbide particles formed a high-viscosity glass phase with the infiltrated slag, which was benefit to prevent the slag penetration into the interior. And a solid solution of (Mg, Fe)O·Al2O3 composite spinel was formed in matrix of the sample after slag penetration because MgAl2O4 absorbed FeO in the slag. It is speculated that the spinel solid solution repairs and strengthens the structure of the matrix, which improves the slag resistance.

Deterioration of mode II fracture toughness, compressive strength and elastic modulus of concrete under the environment of acid rain and cyclic wetting-drying

There are some concrete structures subjected to both impacts of acid rain and cyclic wetting-drying, such as the concrete bridge pier and dam in an acid rain zone, and therefore, it is of great significance to study the deterioration of concrete material parameters under such combining impacts. The parameters investigated in this paper mainly include the corrosion depth, mode II fracture toughness, compressive strength and elastic modulus. Additionally, the chemical composition and thermal stability of corroded products distributed in severe, mild and free corrosion zones were measured by using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). To study the pure mode II fracture toughness of deteriorated concrete, anti-symmetrical four-point bending (ASFPB) tests were conducted on the corroded concrete specimens. The test results indicate that the dissolving corrosion caused by H+ occurs in the corrosion zone of concrete, while the swelling corrosion caused by SO42- mainly occurs in the severe corrosion zone. The thermal stability of corroded products distributed in the severe, mild and free corrosion zone of concrete decreases gradually. The pure mode II fracture toughness of concrete almost decreases linearly with increasing the number of cyclic wetting-drying, and increase with increasing the pH value of simulated acid rain. Moreover, there is a good linear relationship between pure mode II fracture toughness and compressive strength of concrete under both impacts of simulated acid rain and cyclic wetting-drying. The elastic modulus of corrosion concrete decreases with the increase of wetting-drying cycles, and it decreases with decreasing the pH value of simulated acid rain solutions.