Corrosion Potential Distribution Research Articles

Comparative validation of corrosion simulation accuracy in patch-repaired reinforced concrete structures

ABSTRACT The evaluation of patch-repaired concrete’s performance, along with the development of a practical design guideline, necessitates considering multiple factors such as the quality of the existing concrete and the types of repair concrete used. The numerical model presented herein offers insights into the distribution of corrosion potential and corrosion rate in reinforcing steel, thereby assisting in monitoring the performance of the patch-repaired system. This model is constructed based on an analysis of the polarization behavior of steel across different concrete mixtures, with its validity confirmed through comparison with empirical results. Particularly, the model accounts for imperfect bonding between the patch and the substrate, a critical factor in repair effectiveness. The numerical outputs demonstrate consistent potential profiles, with minimal differences observed between empirical and simulated results. The incorporation of additional layers at the interface can significantly impact potential measurements, highlighting the discontinuity between the patch and substrate. Visual inspections further validate the numerical predictions by evidencing the corrosion rate distribution on steel surfaces under various patch repair scenarios.

Numerical simulation of electrochemical mechanism of steel rebar corrosion in concrete under natural climate with time-varying temperature and humidity

In order to analyze and predict the corrosion ratio and rust layer distribution of steel rebar embedded in reinforced concrete under time-varying climatic conditions, a self-balancing steel corrosion model was established by connecting the environmental temperature, humidity, external chloride ions and oxygen concentration to the potential distribution and current density of the steel using finite element method. The model covered the whole corrosion process of steel rebar in concrete under natural climate, including the steel rebar depassivation, steel corrosion propagation and the rust layer expansion on the surface of steel rebar. In the proposed model, the microcell and macrocell corrosion were coupled by electrochemical polarization, and the cathode-to-anode area ratio was determined by the time-varying chloride distribution at the rebar surface. Taking the diffusion of chloride ions and oxygen in concrete into account, the distribution of corrosion potential of reinforcement, the change of corrosion current density of reinforcement, and the distribution of rust layer on the surface of reinforcement can be obtained based on the variation of natural temperature and humidity. The proposed model was validated utilizing the experimental data from the literatures. On this basis, a discussion about the influence of long-term climatic environments on the corrosion kinetics were conducted. The results suggest that environmental temperature and relative humidity affect the steel corrosion process mainly by affactting the chloride and oxygen diffusion coefficients, concrete resistivity, and concentration of dissolved oxygen in concrete pore solution. The corrosion current density of steel in concrete is sensitively influenced by the environmental temperature more than relative humidity. Although the initial exposure time has a significant impact on the accumulation process of chloride on steel surface within one climatic cycle, it has little influence on the final chloride distribution at the end of the period. However, the initial exposure time remarkably influences the evolution profile of rust layer thickness during the climatic cycle. The steel rebar initially exposed to a higher temperature suffers from more severe corrosion than that initially exposed to a lower temperature.

Study on mechanism of differential concentration corrosion

The pipeline easily gets corroded in a seawater environment. The oxygen in the seawater is one of major parameters causing the corrosion. In practice, the corrosion due to the oxygen concentration difference, i.e. differential concentration corrosion (DCC), cannot be avoided. However, a one-dimensional DCC model cannot satisfactorily predict the corrosion because the oxygen distribution near the pipe wall is two-dimensional. In this regard, a two-dimensional DCC model was proposed in this study to numerically investigate the distribution of corrosion potential and current in the ionic conductive layer near the pipe wall as well as the overall corrosion current. The results show that DCC plays a significant role in determining the corrosion potential and current. Without considering DCC, a large corrosion potential and current exist at the location with high oxygen concentration near the pipe wall, whereas the occurrence of the low corrosion potential and current corresponds to the location with low oxygen concentration. However, as DCC is considered, at the location with high corrosion potential, cathodic polarization was produced and the corrosion rate decreases; at the location with low corrosion potential, anodic polarization was produced and the corrosion rate increases. In general, the corrosion potential can be homogenized in terms of DCC.

A comparison study on the natural and half-soaking galvanic accelerated corrosion of reinforced concrete based on an improved electrochemical model

In order to investigate the half-soaking galvanic accelerated corrosion and natural corrosion comparatively, an improved electrochemical model was established. Taking the diffusion of ions, potential distribution and polarization into consideration, the difference between two corrosion methods were essentially revealed. By changing the boundary conditions of the model, Finite Element Method (FEM) was applied to simulate corrosion potential distribution, ions concentration and current density both on the steel–concrete interface and within concrete. In natural corrosion, macrocell corrosion was coupled with microcell corrosion, and the anodic and cathodic current densities were self-balanced. To model the real corrosion under natural environment, the cathodic to anodic area ratio (Ac/Aa) of macrocell was assumed to be changing with the development of corrosion. In galvanic accelerated corrosion, the influence of external ions concentration on current density was considered, which eventually affected the distribution of rust layer of steel rebar. The simulation results agree well with the test data collected from literatures. A further discussion indicates that impressed current density significantly affects the time ratio of natural corrosion to galvanic accelerated corrosion, while the NaCl solution concentration shows no clear influence on time ratio. The bearing capacities of the corroded steel rebar under half-soaking method (HSM) and natural corrosion will show no clear difference, but the HSM method is not very appropriate for studying the corrosion cracking process of reinforced concrete.

Two-dimensional numerical analysis of differential concentration corrosion in seawater pipeline

PurposeThe purpose of this paper is to develop a new two-dimensional differential concentration corrosion mathematical model based on the knowledge that oxygen distribution on the surface of the seawater pipe is two-dimensional.Design/methodology/approachThe ionic conductive layer element near the pipeline wall is regarded as the research object, and the finite element method is adopted to obtain the oxygen distribution in the layers and the natural corrosion potential and natural corrosion current of each element. Then, these element sets are regarded as a whole circuit and each element as a node on the circuit; the equation is satisfied by the corrosion potential after polarization is derived for each element according to Kirchhoff’s second law.FindingsMatlab is used to solve the equation sets, and the overall corrosion current is calculated. The results are quite different from those considered without the differential concentration corrosion. If the differential concentration corrosion is not considered, the location with high oxygen concentration on the pipeline wall has a large corrosion potential and current. If corrosion is considered, the potential will cause polarization and the positions with original higher corrosion potential will produce anodic polarization. Meanwhile, the speed of corrosion also decreases. At the same time, the position with original lower corrosion potential will produce cathodic polarization, and the corrosion current is also increased, namely, the corrosion current and the potential will be homogenized.Originality/valueA two-dimensional model for the study of concentration corrosion is proposed creatively. Based on the knowledge of electricity, a discrete equation of corrosion potential after polarization is derived. The distribution of corrosion potential and corrosion current is obtained by solving the equation, and the mechanism of concentration corrosion is analyzed. The law of concentration polarization corrosion is also obtained.

A self-balanced electrochemical model for corrosion of reinforcing steel bar in considering the micro-environments in concrete

Based on the electrochemical mechanism of steel corrosion, an improved electrochemical model was established to numerically simulate the corrosion of reinforcement in concrete under marine environment. The corrosion potential distribution and current density of corroded reinforcement were deduced from the corresponding micro-environments on the surface of steel bar, including oxygen, chloride ions, temperature and relative humidity. The equilibrium of gaseous oxygen and dissolved oxygen in pore solution was considered in the model. And the diffusion of invasion mediums in cement matrix and interfacial transition zone (ITZ) were also taken into account. The anode and cathode areas on the surface of steel bar was determined by the time-varying distribution of chloride ions rather than a fixed ratio to achieve the self-balance between macrocell and microcell corrosion. The simulation results agree well with the experimental data. The numerical analysis indicates that the growth of environmental chloride ions concentration will enhance the non-uniformity of chloride ions distribution, but does not contribute much to the increase of maximum rust layer thickness on steel surface. In the propagation stage of corrosion, oxygen concentration is a key factor in controlling corrosion reactions compared to chloride ions. Moreover, environment temperature has a positive effect on both the range of active areas on surface of steel rebar and rust layer thickness.

Data mining to effect of key alloying elements on corrosion resistance of low alloy steels in Sanya seawater environmentAlloying Elements

In this paper, the relationship model between seawater environment, chemical composition and corrosion potential of low alloy steel is established and the distribution of corrosion potential of low alloy steel with changes in key alloying elements is excavated. The research was carried out with the following steps: Firstly, the relationship model between corrosion potential of low alloy steel and its influencing factors was established by data dimension reduction and artificial neural network (ANN). Secondly, key alloying elements of experimental steels were selected out by Pearson correlation analysis, then the corrosion resistance element model was visualized to show the effect of key alloying elements on corrosion potential of low alloy steel. Finally, corrosion potential of low alloy steel with the change of key alloying elements was classified and visualized by classification method. The mining results can reflect the validity of the proposed mining methods to a certain extent and provide an intuitive data basis for the development of high-quality and low-cost low alloy steels.

Research into the corrosion behavior of carbon steel in simulated reverse osmosis product water and seawater using a wire beam electrode

Purpose– The purpose of this study was to explore the differences in the corrosion behavior of carbon steel in simulated reverse osmosis (RO) product water, and in seawater.Design/methodology/approach– The wire beam electrodes (WBE) and coupons made from Type Q235 carbon steel and were immersed in simulated reverse osmosis product water, and in seawater, for fifteen days. The corrosion potential distribution on the WBE at different times was measured. The corrosion rates of the carbon steel in different solutions were obtained using weight loss determinations. The different corrosion behavior of carbon steel in the two kinds of solution was analyzed.Findings– The results showed that the average corrosion potential, micro-cathode potential and micro-anode potential of the WBE decreased with time in simulated RO product water. During this period, the maximum potential difference between micro-cathodes and micro-anodes on the WBE surface also decreased with time. The potential difference was more than 260mV at the beginning of the test and was still greater than 110mV after fifteen days of immersion. The positions of cathodes and anodes remained basically unchanged and corrosion took place on the localized anode during the experiments. The average corrosion potential, micro-cathode potential and micro-anode potential on the WBE surface also decreased with time in the simulated seawater. However, the maximum potential difference between micro-cathode and micro-anode on the WBE surface in the simulated seawater was much smaller than was the case in simulated RO product water. It was 37.8 mV at the beginning of the test and was no more than 12mV after two days immersion. The positions of cathode region and anode kept changing, leading to overall uniform corrosion. The actual corrosion rate on the corroded anode region in simulated RO product water was greater than was the case in simulated seawater.Originality/value– The corrosion behavior differences of carbon steel between in RO product water and in seawater were revealed by using wire beam electrodes (WBE). From the micro point of view, it explained the reason why the actual corrosion rate of carbon steel in RO product water was greater than that in sea water. The results can be helpful to explore future corrosion control methods for carbon steel in RO product water.

Cover Picture: Materials and Corrosion. 11/2014

Cover:The left image shows the corrosion potential distribution in volts on the cross‐sectional surface of a friction stir spot weld (FSSW) made in AZ31B magnesium alloy, obtained through the scanning reference technique (SRET). The color gradient represents the relative corrosion potential of the local area to the corrosion potential of the base metal. The weld nugget is observed to be noble to the host material, resulting in the formation of a macrogalvanic cell and subsequent accelerated corrosion in the boundary between the weld nugget and the base metal. An optimized microcapillary polarization methodology was utilized to analyze the corrosion rates of individual microstructural zones. The pictures on the right show the capillary used for local polarization experiments, and the corroded spot on the sample that was produced as a result of testing.Microcapillary polarization confirmed the noble behaviour of the stir zone, and demonstrated lower corrosion rates of this microstructural zone in 0.1 M NaClO4 as compared with the rest of the weld. Contrary to the SRET results, microcapillary polarization investigation revealed that there is no potential gradient between the thermo‐mechanically affected zone and the base metal.More detailed information can be found in: Y. Savguira, T. H. North, S. J. Thorpe, Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy, Materials and Corrosion 2014, 65, 1055.

Localized Corrosion Behaviour in Dissimilar Friction Stir Welds Made in AZ31B/AZ80 Magnesium Alloys

IntroductionMagnesium alloys can be successfully joined by friction stir welding (FSW) to achieve high mechanical integrity of the weld. Previous work done on the corrosion performance of friction stir spot welds (FSSW) in AZ31B has shown that the local corrosion behaviour of the weld can be studied successfully by scanning reference electrode technique (SRET) and by microcapillary polarization (MCP)1,2. Both techniques identified that the weld region in AZ31B joints was more cathodic than the bulk material, resulting in the accelerated corrosion of the region adjacent to the weld. To date the majority of available literature examining the localized corrosion behaviour of FSW joints focused on similar metal welds.The present work investigates the localized corrosion behaviour of a dissimilar metal FSW weld made between AZ31 and AZ80 magnesium alloys. The paper presents the corrosion potential distribution on the cross-sectional surface of the weld along with corrosion rates estimated by mass loss testing.Experimental MethodsAll samples were butt welded using a flat shoulder tool from 5 mm thick AZ31B and AZ80 sheets.SRET experimental procedures are described elsewhere1. The reference electrode chosen for this investigation was a 10 µm diameter platinum wire encapsulated in a glass tube. The measurements were performed in 0.086 M NaCl electrolyte solution with a scanning speed of 2 µm/sec. Lines scans were performed every 250 µm.Mass loss testing was conducted by submerging samples in 0.086M NaCl solution for a duration of 120 hours. The samples were imaged and analyzed to produce a corrosion rate.Results and DiscussionsMicrostructural examination of the cross section of a stir zone in a dissimilar weld in figure 1a shows a distinct separation between the AZ31 and the AZ80 magnesium sheets. This was further confirmed by electron dispersive x-ray (EDX) mapping shown in figure 1b. The intensity of the blue color represents the concentration of aluminum in the alloy. As expected AZ80 that is composed of 8 wt. % Al as compared with 3 wt. % Al present in AZ31, shows an intense blue color on the EDX map. A well-defined boundary is observed at the interface between the two sheets. It is suggested that minimal intermixing and aluminum diffusion is occurring during the welding process. As a result the stir zone is composed of two distinct zones made from the parent metal.Mass loss testing has shown that the weldment corroded approximately 2.5 times faster than the parent AZ31B base metal and approximately 12 times faster than the parent AZ80 alloy. The above occurs due to a galvanic couple formed between the relatively noble AZ80 and the active AZ31. Figure 1 c and d shows a representative specimen of a sample post mass loss testing. It is interesting to note that the corrosion on the bottom surface (figure 1d) occurred on the AZ31 side, a result that is expected if in fact the formed galvanic cell dominates the corrosion behaviour of the weld. The corrosion on the top surface (figure 1c) occurred on the AZ80 side, suggesting the displacement and the subsequent formation of a thin layer of AZ31 the entire stir zone on the top surface.Conclusions and Future WorkSuccessful butt welding of AZ31/AZ80 has shown a sharp gradient in aluminum concentration across the stir zone. Minimal mixing and diffusion of aluminum is observed at the interface between the two metal sheets. Further work examines the corrosion performance of these welds through corrosion potential mapping using SRET.ReferencesA. James, T. H. North, S. J. Thorpe, ECS Trans. 41(25) 193 (2012)Y. Savguira, T. H. North, S. J. Thorpe, Mater. Corros. (2013) DOI:10.1002/maco.201307410

Microcapillary Polarization of Friction Stir Welds Made in AZ31B Magnesium Alloy

IntroductionMagnesium alloys can be successfully joined by friction stir welding (FSW) to achieve high mechanical integrity of the weld. Preliminary work done on the corrosion performance of friction stir spot welds (FSSW) in AZ31B by James et al. 1 identified that the weld region was more cathodic than the bulk material, resulting in the accelerated corrosion of the region adjacent to the weld. Most of the research on the corrosion of FSW joints focuses on spot welds; little information is available on the corrosion behaviour of FSW seam welds.The present work investigates the individual corrosion potential/current of various weld zones in FSW, and compares it to information obtained from FSSW.Experimental MethodsAll samples were welded using a flat shoulder tool with thread matching that of a standard M4 metric thread. The welds were made in two 1.6 mm AZ31B overlapping sheets.FSSW samples were produced using a tool rotational speed of 3000 rpm and 4 seconds dwell time. To produce the FSW samples, a tool rotational speed of 1400 rpm and transverse speed of 180 mm/min were used.Microcapillary polarization was performed by methods modified from literature2. A microcapillary with an inner diameter of 40 μm was filled with the 0.1M NaClO4 electrolyte, and both the platinum mesh electrode along with the 3M KCl Ag/AgCl reference electrode were placed inside the capillary cell. The sample was polarized from a potential that is rounded to the nearest 50 mV below the recorded open cell potential to a potential that is 100 mV nobler than Ecorr. The corroded area was examined after the experiment through SEM imaging and Image J software.Results and DiscussionsThree distinct microstructural regions of the weld were analyzed in this investigation: stir zone (SZ), thermo-mechanically affected zone (TMAZ), and base metal (BM). The average microcapillary polarization results are summarized in figure 1. Each zone was tested at least three times, and the corrosion potential and current were found through Tafel extrapolation of individual graphs, the results are given in figure 1b. Measurements from bulk polarization of AZ31B in 0.1M NaClO4 are also included. The results obtained from bulk and microcapillary polarizations of the BM are statistically the same. The results show a potential gradient between the noble SZ and the active BM, confirming previous findings by James et al. 1 who examined the corrosion potential distribution on the cross sectional surface of a FSSW joint using the scanning reference electrode technique (SRET).Additionally, the reported SRET results showed that the TMAZ was noble to the BM, but failed to explain why a noble region (TMAZ) corroded faster than the adjacent active region (BM).In this investigation, little difference in the corrosion potential (ECorr) and current (ICorr) is observed between the TMAZ and the BM regions. The results suggest the formation of the macrogalvanic cell between the noble SZ and the active TMAZ is the primary cause in the accelerated corrosion attack at the interface between the two regions, hence explaining optical observations of localized pitting in the TMAZ region.Conclusions and Future WorkThis work investigated the corrosion potential and current of individual microstructural regions of a FSSW joint. The accelerated corrosion attack of the TMAZ was explained by the formation of a macrogalvanic cell between the active TMAZ and the noble SZ. Further work examines the corrosion performance of the same microstructural regions on a FSW joint, and compares it to the information obtained in this investigation. ReferencesA. James, T. H. North, S. J. Thorpe, ECS Trans. 41(25) 193 (2012)T. Suter, H. Bohni, Electrochim. Acta, 47, 191 (2001)

Chromate Inhibition of Filiform Corrosion on Organic Coated AA2024-T3 Studied Using the Scanning Kelvin Probe

The influence of in-coating strontium chromate pigment dispersions on the kinetics and mechanism of HCl-induced filiform corrosion (FFC) affecting polyvinyl butyral coated AA2024 T3 aluminum alloy is studied using a scanning Kelvin probe. FFC initiation and propagation are detected by imaging time-dependent changes in local free corrosion potential distribution patterns. Area rates of coating delamination fall from to zero as the volume fraction is increased from zero to 0.06. Increasing over the same range produces minimal change in filament-head values but depresses filament tail and intact coating values by up to 0.3 V. It is proposed that filament tail depression results from increased polarization of cathodic reduction reactions at sites of high pH, where insoluble is the predominant reduction product. It is further proposed that intact coating depression results from reversible, nonfaradaic adsorption of at the oxide-covered aluminum surface. Both effects are implicated in FFC inhibition, as is pH buffering by which acts in conjunction with adsorption to forestall anodic attack at the coating-substrate interface. © 2004 The Electrochemical Society. All rights reserved.

薄い水膜下における鋼の腐食電位分布

薄い水膜下における鋼の腐食電位分布

Potential variation of a temporarily protective oil coating before its degradation

A wire-beam electrode using mild steel wires was developed and used to study the potential variation of temporarily preventive oil coating before its degradation. It was found that the distribution of corrosion potential on the surface of oil-coated wire-beam electrode was heterogeneous before the degradation of temporarily protective oil coating. At the early stage of immersion, the distribution of corrosion potential gradually shifted to a higher potential range with increasing of immersion time. When the distribution of corrosion potential reached to a highest potential range, it began to shift negatively to a lower potential range. It is suggested that this situation may be due to metal corrosion taking place at the metal/coating interface. The distribution of corrosion potential on oil-painted wire-beam electrode followed a normal probability distribution before the degradation of oil coating. With increasing of immersion time, the distribution of corrosion potential on oil-painted wire-beam electrode may change from normal probability distribution before the degradation of oil coating to discontinuous binomial distribution after the degradation of oil coating.

Electrochemical technique for investigating temporarily protective oil coatings

A wire-beam electrode using mild steel wires has been developed and used to study temporarily preventive oil coatings in terms of the heterogeneous electrochemical states after immersion in a salt solution. It has been found that the electrochemical states on the surface of the wire-beam electrode are homogeneous compared with an oil-painted electrode. The distribution of corrosion potential on oil-painted wire-beam electrodes is heterogeneous and follows a discontinuous binomial probability distribution. Polarization resistance of each oil-coated wire sensor is randomly distributed over a given range of resistance and follows a log-normal probability distribution. The distribution of corrosion potential over a high potential range can be increased, distribution of polarization resistance over a low resistance range can be decreased and eliminated by adding oil-soluble inhibitor. With increasing concentration of oil-soluble inhibitor, the distribution of anodic polarization resistance of oil coatings may change from discontinuous binomial distribution to exponential distribution and to log-normal probability distribution, the distribution of cathodic polarization resistance of oil coatings will transform from discontinuous binomial distribution to log-normal probability distribution.

The electrochemical mechanism in the erosion-corrosion damage of carbon steel by gas-liquid two-phase flow.

The erosion-corrosion characteristics of a carbon steel commonly used as a piping material subjected to an impinging gas-liquid two-phase jet were investigated. The localized damage was observed, and the range of the erosion rate under the experimental conditions was beteen 45 mm/year and 87 mm/year. It became clear that the principal mechanism of this damage was the occurrence of pitting corrosion caused by the corrosion potential distribution on a specimen and the rapid growth of pits. The significance of flow-induced potential distribution on a specimen was demonstrated by use of an array of test pieces insulated electrically from each other. This potential distribution induced by the flow distribution on a specimen also gave crucial effects on the location where the erosion-corosion damage occurred. Namely, erosion-corrosion damage took place locally, just at the part of the specimen where the corrosion potential was shifted to more nobler than the pitting potential of the condition of interest. This corrosion potential distribution was caused by the distribution of the oxygen supply rate and deposition and/or removal of oxydizer corrosion product (γ-FeOOH). These were originally caused by the flow distribution. This erosion-corrosion damage was completely inhibited by keeping the pitting potential nobler than the corrosion potential ; for example, by the addition of NaNO2 to the system.