Accelerated Corrosion Environment Research Articles

Research on nonlinear corrosion law of epoxy coating on steel bridges based on image processing

This paper adopted the accelerated corrosion test method to study the corrosion law of epoxy coatings on steel bridges. An image processing algorithm based on MATLAB was used to perform grayscale conversion, normalized histogram drawing, and binary image processing on the surface morphology images of coated specimens. Four coated specimens were prepared and placed in the cyclic accelerated corrosion environment. The coated specimens were subjected to the accelerated corrosion test for 90 days, observed changes in coating thickness and corrosion area rate and analyzing the corrosion laws of epoxy coatings in different corrosion environments. Using image processing technology to process images of coating corrosion and analyze the corrosion mechanism of coatings. The research results indicate that the corrosion rate of epoxy coatings exhibits a non-linear corrosion law of slow corrosion in the early stage and accelerated corrosion in the middle and later stages. The corrosion rate of epoxy coatings in saltwater corrosive environments is faster than in freshwater corrosive environments. Based on the corrosion laws and mechanisms of coatings, a nonlinear corrosion function model for epoxy coatings on steel bridges under different accelerated corrosion environment was established, which has a high correlation with experimental data

Fatigue life prediction of stay cables under vehicle load considering corrosion variability

The combined effect of environmental corrosion and fatigue loads can accelerate the failure of stay cables. To ensure the safe operation of stay cables, this paper proposed a method for evaluating the fatigue life of stay cables, considering the variability of steel wire corrosion within the cable. Firstly, the relationship between the mean value and the standard deviation of uniform corrosion depth was established based on the experimental data of the corroded steel wires under the artificial accelerated corrosion environment. Then, the model of cable time-vary corrosion under the actual service environment was substituted, and the distributions of the weight loss rate of steel wires were obtained. Subsequently, a method for calculating the fatigue life of stay cables considering the corrosion variability of steel wires in the cable was proposed based on the parallel system theory and the Miner linear cumulative damage criterion. Finally, the North Channel Bridge (NCB) of Hangzhou Bay Bridge was used as an example, and the fatigue life distribution of stay cable under the combined action of corrosion and vehicle load was predicted. The results indicate that considering the corrosion variation of steel wires in the cable leads to a reduction in the fatigue life of stay cables, and neglecting this variability in fatigue life prediction methods is unsafe and non-conservative.

Applicability of AC impedance method for measuring time-variant corrosion rate to cracked and crack-repaired reinforced concrete

Several models of the time-variant corrosion rate (CR) have been proposed to predict the service life of reinforced concrete (RC) structures based on polarization resistance (PR) monitoring. However, few of them have verified the accuracy by comparing the estimated corrosion weight loss (CWL) obtained from the PR monitoring with the actual CWL. In addition, few studies have measured the time-variant CR on crack-repaired RC specimens, and the evaluation of repair efficacy is clearly an essential step in the maintenance of the structures. This study aims to clarify the applicability of the alternating current (AC) impedance method, one of the PR methods, to cracked and crack-repaired RC. The CRs in such RC in an accelerated corrosion environment were measured every one to three months over three years using the AC impedance method. To confirm accuracy, the corroded area and CWL of the steel bars were measured. The results clarify that the measurement area of the AC impedance method was almost equal to the corroded area, which indicates that the corrosion area should be calculated in addition to the CWL for accuracy verification. The results also show that the AC impedance method can be applied to cracked and crack-repaired RC for measuring time-variant CR. The CR increases rapidly after crack initiation but becomes constant with time, and early crack repair can delay corrosion progress in cracked RC to the same extent as in uncracked concrete.

TiCr transition layer promoting the growth of high-stability TiCrN coating for titanium bipolar plate

High chemical stability under the harsh acidic working condition of proton exchange membrane fuel cell (PEMFC) is of great importance for bipolar plates. In present study, a series of TiCr alloys from amorphous to nanocrystalline state are designed as transition layers to promote the growth of smooth and dense TiCrN surface layer as coating material for Ti bipolar plate. Under the accelerated corrosion environment of PEMFC (0.5 M H2SO4 + 2 ppm HF, 80 °C with air, 0.2 V vs. Hg/Hg2SO4), the double-layer TiCr/TiCrN coating exhibits excellent long-term stability. A low current density of 0.25 μA/cm2 and a small interfacial contact resistance (ICR) of 6.5 mΩ cm2 are observed after 100 h corrosion test for the double-layer TiCr/TiCrN, which are much lower than the values of 1.35 μA/cm2 and 13.5 mΩ cm2 for single-layer TiCrN after 70 h corrosion test. These results indicate the high potential of double-layer TiCr/TiCrN as the coating material for Ti bipolar plate.

Research on the Corrosion Behavior of Q235 Pipeline Steel in an Atmospheric Environment through Experiment.

Low-carbon steel pipelines are frequently used as transport pipelines for various media. As the pipeline transport industry continues to develop in extreme directions, such as high efficiency, long life, and large pipe diameters, the issue of pipeline reliability is becoming increasingly prominent. This study selected Q235 steel, a typical material for low-carbon steel pipelines, as the research object. In accordance with the pipeline service environment and the accelerated corrosion environment test spectrum, cyclic salt spray accelerated corrosion tests that simulated the effects of the marine atmosphere were designed and implemented. Corrosion properties, such as corrosion weight loss, morphology, and product composition of samples with different cycles, were characterized through appearance inspection, scanning electron microscopy analysis, and energy spectrum analysis. The corrosion behavior and mechanism of Q235 low-carbon steel in the enhanced corrosion environment were studied, and the corrosion weight loss kinetics of Q235 steel was verified to conform to the power function law. During the corrosion process, the passivation film on the surface of the low-carbon steel and the dense and stable α-FeOOH layer formed after the passivation film was peeled off played a role in corrosion resistance. The passivation effect, service life, and service limit of Q235 steel were studied and determined, and an evaluation model for quick evaluation of the corrosion life of Q235 low-carbon steel was established. This work provides technical support to improve the life and reliability of low-carbon steel pipelines. It also offers a theoretical basis for further research on the similitude and relevance of cyclic salt spray accelerated corrosion testing.

Mechanical degradation and corrosion characterization of riveted joints for CFRP/Al stacks in simulated marine environments

Mechanical performance and durability of CFRP/aluminum joints in accelerated corrosion environment have to be considered before designing composite-metallic hybrid structures. In this work, the corrosion behavior and mechanical properties of CFRP/aluminum stacks and riveted joints were evaluated by cyclic salt spray tests to simulate marine environments. The rivet head and aluminum substrate in coupled region experienced severe galvanic corrosion with heavy formation of corrosion products. CFRP laminate suffered substantial matrix swelling and even resin hydrolysis after continuously exposing to moisture environments. Joint strengths fluctuated very slightly while failure displacement gradually increased when interfacial corrosion between CFRP/Al stacks occurred. Corrosion products were identified by several characterization techniques with the corresponding corrosion mechanisms. In general, this work is expected to bring new knowledge to understand corrosion behavior and durability of rivet joints for the CFRP/Al stacks in accelerated corrosion environments and provide experimental results for benchmarking in particular designing CFRP-strengthened aluminum structures.

3D X-ray Micro-CT Analysis of Rebar Corrosion in Reinforced Concrete Subjected to a Chloride-Induced Environment.

The paper presents experimental investigations of the concrete covers’ protective ability to counteract rebar corrosion in reinforced concrete cubes. The concrete sample was subjected to a chloride-induced environment to get corroded and combined with an un-corroded sample. The chloride-accelerated technique can induce a high degree of corrosion within a controlled time. Moreover, detailed and thorough experimental measurements and analyses of reinforcement loss due to corrosion and its influence on concrete microstructure, were studied through 3D X-ray micro-computed tomography. The rebar outside the concrete was heavily corroded due to the chloride-accelerated test, whereas, only local surface corrosion products appeared inside the concrete. It turned out that the concrete cover showed protective ability to counteract the reinforcing-steel corrosion mechanism despite the accelerated corrosion environment. Moreover, the bond strength between the reinforcement rebar and concrete was not visibly affected since the failure force in the pull-out test and failure mechanisms, observed by 3D X-ray micro-CT, were similar for corroded and un-corroded samples. The failure occurred due to radial cracks with a maximum width equal to approximately 0.25 mm.

Multifaceted geopolymer coating: Material development, characterization and study of long term anti-corrosive properties

Abstract Geopolymers are traditionally used as construction and building material to partially replace Portland cement consumption. The versatile properties of geopolymer present it for use as a multifunctional material and geopolymer cementitious coating is an emerging part of it. In attempts to develop green and sustainable geopolymer coating material for advanced application, we studied geopolymeric coating of varying Na/Si ratio and alkaline molarities and their long term corrosion resistant properties on mild steel to protect it from surface corrosion. Chemical characterization was performed using combination of powerful characterization tools, more specifically mineralogical assessment by X-ray diffractometer, bonding arrangements by Fourier transform infrared spectroscopy and microstructural details by Field emission scanning electron microscopy techniques. Time of flight secondary ion mass spectroscopy was also used as novel characterization approach to envision the coating-substrate interface and for elemental mapping at the interface which delivered useful information about occurrence of strong covalent bonds between Si–O–Fe in the form of Fe2OSi+ mass fragment with m/z ratio 156. The material was further investigated in terms of adhesion strength and water/salt resistant, following accelerated salt fog test by ASTM codes. Geopolymer with varying Na/Si ratio and alkaline molarity exhibited change in XRD amorphicity and microstructure. Results also displayed that even at low Na/Si ratio geopolymeric coating performs high adhesion with iron with no considerable change in corrosion resistant properties. The maximum adhesion of developed material with mild steel was 14.68 M.Pa. after 28 day ambient curing which presented its functional suitability. Coating sustained point load upto 5 kgs and showed adequate water and salt resistance upto 3 months. In accelerated corrosion environment, optimized geopolymer coating displayed adequate corrosion resistance and displayed rust rating 9. Overall we obtained an optimized material which is well suited for coating of buried mild steel pipes to replace contemporary cement mortar coating in terms of properties, durability, cost effectiveness and environmental sustainability.

Low-cycle fatigue behavior and corrosion mechanism of pre-corroded 2A70-T6 aluminum alloy

PurposeIn summary, it can be found that the current research on the simulation of natural atmospheric dry–wet alternating accelerated corrosion mainly focused on the study of electrochemical corrosion process and the study of corrosion rate; the micro-pre-corrosion mechanism of materials in this environment, especially for materials. The specific effects of fatigue and fracture performance still lack detailed research. Accordingly, this study aims to more realistically simulate the effect of natural atmospheric corrosion environment on the corrosion resistance and fatigue performance of aircraft skin.Design/methodology/approachIn this study, the uniaxial strain control method was used to test the fatigue performance of pre-corrosion samples under simulated natural atmospheric corrosion using MTS809 tensile-torque composite fatigue machine. Scanning electron microscopy, X-ray energy spectrum analysis, atomic force microscopy and X-ray diffraction analysis were used. Fatigue fracture, corrosion morphology and corrosion products were analyzed.FindingsThe results show that the deep corrosion pit caused by pre-corrosion environment leads to multi-source initiation of crack; the fatigue life of pre-corroded sample decreases by about one-half, chloride ion invades the material and promotes intergranular corrosion; life prediction results show that the natural atmospheric corrosive environment mainly affects the plastic term in the Manson–Coffin formula resulting in a decrease in fatigue life.Originality/valueInnovative experimental schemes and materials are used and the test temperature and relative humidity are strictly controlled. The corrosion failure mechanism of 2A70-T6 aluminum alloy under alternating wet and dry accelerated corrosion environment and its influence on fatigue behavior were obtained.

The effect of three luminescent ionic liquids on corroded glass surfaces – A first step into stained-glass cleaning

Corrosion in medieval stained-glass represents a challenging issue in Conservation Science, being mainly composed by calcium salts. Model glass materials were produced and then subjected to an accelerated corrosion environment. Early stage glass corrosion layers observed were afterwards cleaned with luminescent ionic liquids (ILs). The effectiveness of the treatment was compared with Ethylenediaminetetraacetic acid solution and high levels of humidity, both of which have caused alterations on the glass surface. With the ILs, detectable morphological or chemical alterations were avoided and the gel-layer remains on the glass surface, indicating that these are a viable alternative to conventional cleaning methods.

Effect of thermal shock process in accelerated environment spectrum on the fatigue life of 7B04-T6 aluminum alloy

The effect of thermal shock, in an accelerated-corrosion environment spectrum, on the fatigue and corrosion behavior of 7B04-T6 aluminum alloy, was determined. The environment spectrum consists of two modules, namely: salt-spray corrosion and thermal shock. The effect of thermal shock on the mechanical properties was determined via tensile tests; SEM, DCS, and XRD were used to determine the effect of thermal shock on the corrosion products. In addition, the corrosion resistance of the products was ascertained through electrochemical testing. The results show that the mechanical properties and fatigue life of the aluminum alloy will decline with prolonged thermal shock time. The thermal shock process may result in denser surface corrosion products than those formed on the no thermal shock specimens, and transformation of some Al (OH)3 into AlOOH. AlOOH may have resulted in improved corrosion resistance and hence a lower decrease in the fatigue life after corrosion, compared with that of the no thermal shock specimen. Repeated corrosion/thermal shock may have delayed further decease in the fatigue life. Therefore, selection of an appropriate equivalent thermal shock temperature and time was essential for designing the environmental spectrum.

Durability of CFRP strengthened steel circular hollow section member exposed to sea water

This paper presents the results from a research program to investigate the durability of CFRP strengthened steel circular hollow section (CHS) members with and without embedded glass fibre reinforced polymer (GFRP) at ambient (24°C±4°C) and 50°C temperatures under accelerated corrosion environment. The beams were tested to failure under four-point bending. It was found that the accelerated corrosion adversely affected the durability of the strengthened beams at both temperatures and the embedded GFRP enhanced the durability. Durability design factor has also been recommended. The proposed theoretical approach predicts ultimate loads reasonably compared to experimental value of ultimate loads.

Numerical studies on CFRP strengthened steel circular members under marine environment

The durability of carbon fibre reinforced polymer (CFRP) strengthened steel circular hollow section (CHS) members has now become a real challenge to researchers. In addition, various parameters that may affect the durability of such members have not been revealed yet. This paper presents brief experimental results and the first finite element (FE) approach of CFRP strengthened steel CHS beams conditioned in simulated sea water, along with an accelerated corrosion environment at ambient (24 ± 4 °C) and 50 °C temperatures. The beams were loaded to failure under four-point bending. It was found that the strength and stiffness reduced significantly after conditioning in an accelerated corrosion environment. Numerical simulation was implemented using the ABAQUS static general approach. A cohesive element was utilised to model the interface element and an 8-node quadrilateral in-plane general-purpose continuum shell was used to model CFRP elements. A mixed mode cohesive law was deployed for all the three components of stresses in the proposed FE approach, which were one normal component and two shear components. The validity of the FE models was ascertained by comparing the ultimate load and load vs deflection response from experimental results. A range of parametric studies were conducted to investigate the effects of bond length, adhesive types, thickness and diameter of tubes. The results of parametric studies indicated that the adhesive with high tensile modulus performed better and durability design factors varied from section to section.

Modeling and identification of uniform corrosion damage on a thin plate using a Bayesian framework

Corrosion remains one of the primary mechanisms of structural degradation facing the civil and commercial infrastructure. In this study we consider the problem of estimating the degree of corrosion in a plate structure using only the structure׳s vibrational response to impact excitation. Specifically, a thin aluminum plate was twice placed in an accelerated corrosion environment resulting in varying levels of corrosion damage. At each damage level, the impulse response at three different locations was simultaneously measured with resistive strain gauges. From this data, a Ritz model with Timoshenko beam basis functions was used in a Bayesian framework to estimate the average plate thickness. The approach is first illustrated on a numerical model of the plate, and then applied to the experimental structural response. While the approach is able to accurately estimate the thickness of the “healthy” plate, the quality of the estimates degrades as the corrosion begins to alter the thickness in localized regions of the plate. This is reflected in the thickness estimates which show increasing variance with the degree of corrosion.

Impact of magnetization state on the corrosion of sintered Nd-Fe-B magnets for e-motor applications

We have created an accelerated corrosion environment for sintered Nd–Fe–B magnets in e-motor applications. E-motor working conditions are complex, and standard magnet corrosion tests only cover a small subset of possible parameters (e.g., samples are usually tested in the demagnetized state). In this work magnetized and demagnetized sintered Nd–Fe–B magnets were placed in gearbox oil, and exposed to temperature cycles (θmax = 130 °C) using an autoclave. Beforehand the magnets were pre-immersed in saturated water-based salt solution to account for water and de-icing salt that might interfuse gearbox oil over time. The corrosive behavior was studied for two commercial magnet grades, “high grade” (8.9 wt% dysprosium) and “low grade” (3.1 wt% dysprosium); and monitored by weight loss, structural analysis (scanning electron microscopy and energy dispersive X-ray) as well as magnetic characterization. The magnetized samples corroded significantly faster than their demagnetized counterparts. Strong differences in the corrosion rates of the “low grade” and “high grade” material are discussed. We concluded that the magnetization state is one key parameter that needs to be considered in corrosion tests for e-motor applications.

Corrosion of aluminium, stainless steels and AISI 680 nickel alloy in nitrogen‐based fuels

AbstractNitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface.

Electrochemical Charaterization of Steel Concrete under Multi-Factors Influence

The corrosion of steel concrete under the multi-factor of hygrothermal marine environment and flexural stress-salt spray accelerated corrosion environment was studied by potentodynamic polarization method and electrochemical impedance spectroscopy. Under the hygrothermal marine environment (Wan-ning), with the prolonging of period, passive film on the steel was depolarized, and when the period was two years, the steel started corrosion. The result show that flexural stress could accelerate chlorine ion permeation rate on the concrete, and make passive film depolarize more early. With the passive film’s depolarization, the interfacial reaction of steel/concrete develops from electrochemical activation to mass transport limitation, and the reaction resistance decrease.

Stress corrosion cracking for 316 stainless steel clips in a condensate stabilizer

In one of the gas processing facilities in Abu Dhabi, UAE; a case of 316L stainless steel material failure occurred in the fractionating column due to stress cracking corrosion twice in a cycle of less than 2 years. This paper studies the stress corrosion cracking behavior of the 316L stainless steel in an accelerated corrosion environment and compares it with a higher corrosion resistant nickel alloy (Inconel 625). The experimental work was designed according to ASTM G36 standard, the samples were immersed in a boiling magnesium chloride medium which provided the accelerated corrosion environment and the tested samples were shaped into U-bend specimens as they underwent both plastic and elastic stresses. The specimens were then tested to determine the time required for cracks to initiate. The results of the experimental work showed that the main mode of failure was stress corrosion cracking initiated by the proven presence of chlorides, hydrogen sulfide, and water at elevated temperatures. Inconel 625 samples placed in the controlled environment showed better corrosion resistance as it took them an average of 56 days to initiate cracks, whereas it took an average of 24 days to initiate cracks in the stainless steel 316L samples. The scanning electron microscopy (SEM) micrographs showed that the cracks in the stainless steel 316L samples were longer, wider, and deeper compared to the cracks of Inconel 625.

Reliability Assessment of Land Grid Array Sockets Subjected to Mixed Flowing Gas Environment

Land grid array (LGA) sockets are used as separable interconnects between printed circuit boards, and high I/O integrated circuit components. Because the socket contacts with the component and the circuit board on both sides, low and stable contact resistances among these interfaces are desirable for the reliable electrical connection of the LGA package. This paper compares the contact resistance degradation of two LGA socket designs, silver particles in an elastomer column, and silver-plated-nickel in an elastomer film, subjected to accelerated corrosion environment, or so-called mixed flowing gases (MFG). Increased contact resistance was observed in the sockets due to corrosion products over the contact surface after metal corrosion. Corrosion products were analysed using environmental scanning electron microscopy (E-SEM), energy dispersive spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). AgCl, Aga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, and Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> were identified after silver corrosion; NiCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , and MS were found after Ni corrosion. The nickel corrosion product bridged the adjacent contacts as whiskers with time. The lifetime can be estimated by an acceleration factor: two day MFG Battelle Class II exposure equals one year of field service. The shelf life of conductive elastomer LGA sockets is expected to be longer than five years.

The effect of relative humidity on the corrosion-resisting property of fluorocarbon coating

The effect of relative humidity on the corrosion-resisting property of fluorocarbon coating was investigated by water vapor transmission technique and electrochemical impedance spectroscopy technique. Measurements were carried out on samples, which were tested in an accelerated corrosion environment for the same time (300, 500, 800 and 1000 h). The experimental results were obtained as follows: (i) The water absorption, coating resistance and corrosion rate of metal under the coating changed with relative humidity and aging time, the results obtained by EIS are good consistent with those by water vapor transmission technique; (ii) when the subject investigated presented two time constant, the goodness of fit by EEC R(C(R(CR))) was inferior to that by EEC R(C(R(QR))), but the error of parameters acquired from the former was smaller, by which we could analyze the experiment result quantitatively. With the appearance of diffusion layer on the metal, the difference of metal capacitance was aggravated, the error of parameters acquired from EEC R(C(R(C(RW)))) was bigger than that from EEC R(C(R(Q(RW)))).