Stress corrosion cracking of A588 steel weldments in flue gas related environments

This study investigated stress corrosion cracking (SCC) of A588 steel welds as determined by U-bend immersion tests and slow strain rate tensile (SSRT) tests to evaluate the steel’s cracking susceptibility in various regions of the weldments. The immersion test results indicated that the fusion zone (FZ) had better corrosion resistance than the other regions in the weld. It was also demonstrated that the columnar grain boundaries exhibited a higher resistance to corrosion than the grain interior of the FZ. However, the coarse elongated ferrite in the FZ is susceptible to hydrogen embrittlement (HE), which results in the formation of microcracks. As a result, a severe degradation of the weld’s tensile properties in the saturated H₂S solution was observed. Scanning electron microscope (SEM) fractographs of tensile specimens reveal a cleavage fracture in the coarse-grained heat-affected zone (CGHAZ) and featherlike rupture in the FZ, both indicating a high sensitivity to HE.     

三种压力管道金属材料的流动加速腐蚀性能研究

建立一套温度、压力、流速可控的流动加速腐蚀试验装置, 模拟某蒸汽冷凝水管线工况, 对20钢、Q345R钢、304不锈钢三种材料进行了流动加速腐蚀试验, 采用电化学测量方法得到三种钢的Tafel曲线. 应用扫描电镜(SEM)和能谱仪(EDS)对腐蚀产物膜的厚度、形貌与组分进行了分析. 结果表明, 相同工况条件下, 腐蚀速度从大到小依次为20钢、Q345R钢、304不锈钢; 20钢的腐蚀产物膜结构为球状; Q345R钢存在两种腐蚀产物膜结构, 即网状结构和片状结构; 304不锈钢腐蚀产物膜的结构为片状, 有效的保护了基体材料.     

Corrosion behavior of Zr−Nb alloys in 360°C water and 500°C supercritical water

The corrosion behavior of Zr−0.4 wt.%Nb and Zr−1.5 wt.%Nb alloys was investigated in 360°C water and 500°C supercritical water. The two Zr−Nb alloys showed a similar corrosion rate in both corrosion conditions. However, in the 500°C supercritical water, the corrosion rate was increased by 23 times when compared to that of the 360°C water based on the weight gain at 240 days. In terms of the relationship between the corrosion and the precipitate characteristic, the β−Nb precipitates in the Zr−Nb alloys were considered to play an important role in the excellent corrosion resistance in the 360°C water, but its beneficial effect was not maintained in the 500°C supercritical water. The oxide characterization revealed that the tetragonal phase stability was more easily decreased from the interface to the surface in the oxide formed in the 500°C supercritical water.     

Pressurized water reactor fuel crud and corrosion modeling

Pressurized water reactors circulate high-temperature water that slowly corrodes Inconel and stainless steel system surfaces, and the nickel/iron based corrosion products deposit in regions of the fuel where sub-cooled nucleate boiling occurs. The deposited corrosion products, called ‘crud’, can have an adverse impact on fuel performance. Boron can concentrate within the crud in the boiling regions of the fuel leading to a phenomenon known as axial offset anomaly (AOA). In rare cases, fuel clad integrity can be compromised because of crud-induced localized corrosion (CILC) of the zirconium-based alloy. Westinghouse and the Electric Power Research Institute have committed to understanding the crud transport process and develop a risk assessment software tool called boron-induced offset anomaly (BOA) to avoid AOA and CILC. This paper reviews the history of the BOA model development and new efforts to develop a micro-scale model called MAMBA for use in the Consortium for Advanced Light Water Reactor Simulation (CASL) program.     

Investigation of the local response of the steel–concrete interface for corrosion measurement

An equivalent circuit representation for the steel–concrete interface is determined from direct potential measurements at the steel surface. The local response of steel–concrete interface to a given polarization applied at the concrete surface is investigated using an Ag/AgCl embedded reference electrode and a test system which allows simultaneous measurements at the steel–concrete interface and on the concrete surface. It is shown that the impedance spectrum on Nyquist plot for the steel–concrete interface comprises of a single arc. The equivalent circuit representation of the steel–concrete interface comprising of a parallel combination of a constant phase element (CPE) and a resistance was found to be suitable for representing the observed frequency response above 10 mHz. The parameters for the equivalent circuit obtained from the frequency-domain impedance measurements are shown to provide close prediction of the transient time-domain response from a linear polarization resistance measurement. The equivalent circuit was found to be suitable for interpreting the transient response of the steel–concrete interface during the linear polarization measurements. Available results indicate that while the response of steel undergoing active corrosion exhibits a distinctive CPE behavior, the passive steel approaches a pure capacitor. The value of resistance when the measured current increases linearly with time during a linear polarization measurement from the concrete surface provide acceptable measurements of the charge transfer resistance, and the Ohmic resistance of the concrete.     

Corrosion wear behavior of Al-bronzes in 3.5% NaCl solution

The corrosion wear behaviors of two aluminum bronzes, Cu-14Al-X and QAl9-4, in 3.5% NaCl solution were investigated on a pin-on-block reciprocating tester. It was found that the wear loss of the bronzes in 3.5% NaCl solution was lower than that in water and in air, i.e., it exhibited “negative” synergy between corrosion and wear. To understand the corrosion wear mechanism of the bronzes, the corrosion rate and polarization curves of Cu-14Al-X and QAl9-4 in 3.5% NaCl solution were determined. The worn surfaces of the specimens were examined, and the wear tracks were measured using scanning electron microscopy. The corrosion patinas formed on the specimen surfaces were studied with x-ray photoelectron spectroscopy and electron probe microanalysis. The corrosive solution was shown to play an important role in cooling of the specimen surfaces during the wear, thus preventing the specimen’s surface hardness from being reducing, induced by frictional heat during the sliding wear. On the other hand, the bronzes suffered from dealloying corrosion; a noble copper subsurface and patina formed on the specimen surface in the corrosive solution, which had a passive function for further corrosion. The noble copper subsurface experienced strain hardening during the corrosion wear, resulting in an increase of the surface hardness and thus an increase in wear resistance.     

The inhibition effect of two commercial compounds on interface steel/natural softened water

The protection against the corrosion of the carbon steel in aqueous environment by commercial inhibitors, based of nitrite and alkanolamine, has been studied by electrochemical impedance spectroscopy (EIS) and several analytic methods. An inhibitor’s efficiency has been determined with the two compounds on polished surface in presence of softened water. The results show that the two inhibitors act by the formation of protective layer on interface steel/electrolyte but the efficiency is more important in the case of the nitrite compound thanks to the formation of film with thickness estimated by Atomic force microscopy (AFM) at 0.8 μm after 102 days of immersion. In the case of the nitrites, the inhibitor film is a porous layer, weak conductor and presents a considerable increase of the charge transfer resistance with time. This is a result of an interest protection of the surface against corrosion. The low frequencies limit (L _LF) reaches about 150 kOhm cm² after 59 days of immersion. In the case of the alkanolamine, XPS (X-Rray Spectroscopy) show that the film formed is richer of Fe ions but is offered a considerable protection of the interface, its thickness is about 0.26 μm and L _LF reaches about 35.5 kOhm cm² after 61 days of immersion. The influence of surface state is discussed in this paper, in fact on raw surface steel, no inhibitor efficiency is observed. A few protections are given with a crude surface in contact with water softened in presence of the nitrite compound.     

Effect of Iron-Aluminide Coating on the Fracture Mechanism of Ferritic–Martensitic Steel in Coal-Fired Boilers Environment

Oxidation of Metals - Due to the coal combustion that generates halides, steel components can confront hot corrosion during applications at high temperature. The hot-dipping...     

Influence of chromizing treatment on the corrosion behavior of AISI 316 stainless steel in supercritical water oxidation

SCWO, sometimes referred to as hydrothermal waste processing, uses the solvating traits of water in its supercritical condition to effectively destroy liquid organic wastes. One major problem in the supercritical water oxidation process is corrosion, because all metallic tubes in the process are exposed to high temperature and high pressure as well as severe corrosive species such as Cl⁻, F⁻, S²⁻, and O²⁻. The presence of Cl⁻ when the pH of a solution is very low and the solution has excess oxygen causes active corrosion and metal loss by metal-chloride and/or oxychloride formation. This study performed a chromizing treatment on 316 stainless steel and immersion tests in supercritical water. Weight change of chromized steels and untreated steels was measured, and the chemical state and composition of oxide films on 316 stainless steel were investigated. On the basis of SCWO tests using distilled water, the oxide layer was found to be very thin and homogeneous and weight gain was observed regardless of testing temperature, while the chromizing treatment slightly reduced weight gain. In the case of SCWO tests using salt water, weight loss was observed regardless of testing temperature and its corrosion mode was pitting by chloride ion, while chromizing treatment greatly decreased the corrosion rate.     

The Effect of Coating Thickness on Corrosion Resistance of Hydroxyapatite Coated Ti6Al4V and 316L SS Implants

Hydroxyapatite (HAP) has been coated onto Ti6Al4V and 316L SS substrates by sol-gel method. The coating thicknesses for the analysis were about 40 and 72 μm. Adhesion and corrosion tests have been conducted on uncoated and HAP-coated substrates. The coatings were characterized by XRD, SEM, and adhesion analysis. The corrosion resistance was examined in vitro by potentiodynamic polarization technique in Ringer’s solution at room temperature. Electrochemical analysis indicated that the highest corrosion susceptibility was found on 72-μm-coated 316L SS, and the 40-μm HAP-coated Ti6Al4V showed the highest corrosion resistance. It was observed that the coating thickness was an effective parameter on both adhesion and corrosion resistance. It was shown that adhesion and corrosion resistance decreased with increasing coating thickness on both substrates.     

Influence of ammonia on the corrosion behavior of Ti−Al−Zr alloy in 360°C water

The influence of ammonia on the corrosion behavior of Ti−Al−Zr alloy was evaluated in pressurized water at 360°C for 600 days. The results of the corrosion test indicated that the addition of ammonia accelerated the corrosion and hydrogen pickup rates. The oxide scales were composed of a double layer structure, and an inner layer was covered by an outer layer of oxide grains. The XRD studies on the oxide scales showed that the anatase-TiO₂ was continuously transformed into rutile-TiO₂ as the corrosion proceeded. When the same weight gain was considered, the oxide layer grown in water appeared to have a much higher rutile weight fraction than that grown in the ammonia aqueous solution. The deterioration of the corrosion behavior by the ammonia could be mainly attributed to the retardation in the transformation of the oxide structure from a metastable anatase phase to a stable rutile one.     

Corrosion Protection of Light Alloys Using Low Pressure Cold Spray

Corrosion attack of aluminum- and magnesium-based alloys is a major issue worldwide. This study provides a report on the electrochemical behavior of several types of protective metal coatings obtained by low pressure cold spray (LPCS) and describes the performance of the latter’s corrosion resistance properties. In this manner several metal feedstock compositions were cold sprayed on AA2024-T3 Alclad substrate. Electrochemical methods, such as open circuit potential and potentiodynamic polarization, were used in combination with materials characterization techniques to assess the performance of LPCS protective coating layers. All sprayed samples were tested in the accelerated corrosion salt spray chamber for a time period of up to 500 h to obtain corrosion kinetics data, and with specific attention being focused on the characterization of the coating’s microstructural and mechanical properties. The overall conclusion of this study is that the LPCS process could be utilized to deposit corrosion protection coatings of light alloys as well as to repair aluminum and aluminum cladding structures during overhaul maintenance schedule in industry.     

Selection of corrosion inhibitors for the protection of oil production equipment

The corrosion behavior of steel in a hydrogen-sulfide medium is studied in model solutions simulating stratal water in some oil fields located in Perm’ oblast. A comparative analysis of the corrosion inhibitors used in the oil fields is presented. Some inhibitors are found to have a significant residual effect. Original Russian Text ? R.K. Vagapov, V.S. Bizyaeva, V.I. Kichigin, 2007, published in Korroziya: Materialy, Zashchita, 2006, No. 4, pp. 24–28.     

Corrosion and Erosion-Corrosion Processes of Metal-Matrix Composites in Slurry Conditions

The corrosion and erosion-corrosion (EC) processes of four metal-matrix composites (MMCs) in a simulated cooling water environment have been assessed in this article. The MMCs consisted of two Ni-base and two Fe-base matrices alloyed with different concentrations of chromium, molybdenum, boron, silicon, and carbon; the matrices were reinforced with tungsten carbide (WC) particles. The corrosion behavior has been investigated using a combination of potentiostatic polarization and post-tests surface analysis. The EC processes were studied by in situ electrochemical techniques measuring the current density and corrosion potential response at different slurry temperatures and sand content. At static conditions it was found that as the temperature increased, there was a transition from a homogeneous corrosion of the matrix to an interfacial corrosion mechanism. The Ni-base MMCs showed a better corrosion resistance and interestingly a highly alloyed matrix did not significantly improved MMC’s corrosion resistance. In the in situ EC tests, the Fe-base MMCs showed a constant increase in the current density at all sand contents. Whereas, significant changes were not observed in the Ni-base MMCs below 0.5 g/L. Although sand content had an effect on the monitored current density (the current increased as the sand content increased) this effect was less pronounced above 3 g/L.     

Electrochemical and XPS studies of AISI 316L stainless steel after electropolishing in a magnetic field

The thermodynamic stability and corrosion resistance of surface oxide layer are the most important features of stainless steels. Electrochemical polishing (EP) is the most extensively used surface technology for austenitic stainless steels. We have modified this surface technology by introducing a magnetic field to the system. With this new process called the magnetoelectropolishing (MEP) we can improve metal surface properties by making the stainless steel more resistant to halides encountered in a variety of environments.In this paper, the corrosion research results are presented on the behaviour of the most commonly used material - medical grade AISI 316L stainless steel. The corrosion investigations have been concerned on the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and polarisation curves studies in the Ringer’s body fluid under room temperature (25 °C). The X-ray photoelectron spectroscopy (XPS) was performed on 316L samples after three treatments: MP - abrasive polishing (800 grit size), EP - conventional electrolytic polishing, and MEP - magnetoelectropolishing. The comparison of the corrosion behaviour of the stainless steel’s surface after these processes was also carried out. The purpose of XPS studies was to reveal the surface film composition and the reason of this modified corrosion behaviour. It has been found that the proposed MEP process modifies considerably the composition of the surface film and improves the corrosion resistance of the same 316L SS studied.     

Atmospheric corrosion of metals in regions of cold and extremely cold climate (a review)

The results of atmospheric corrosion tests on a series of metals and alloys in marine and industrial atmospheres of the Earth’s regions with cold and very cold climate (Antarctic, sub-Arctic, Russian Far East) are considered. The class of most dangerous corrosive damage includes special types such as pitting, exfoliation corrosion, crevice corrosion and corrosion-induced cracking. Long-term prognosis is made concerning the influence of global warming on the atmospheric corrosion in cold climate regions. Original Russian Text ? A.A. Mikhailov, P.V. Strekalov, Yu.M. Panchenko, 2008, published in Korroziya: Materialy, Zashchita, 2007, No. 7, pp. 1–16.     

Mathematical modeling on the corrosion of unprotected structure due to stray current resulting from cathodic protection system

Mathematical modeling on the corrosion of unprotected structures due to a stray current resulting from a nearby cathodic protection system was carried out using the boundary element method. The model consists Laplace’s equation with non-linear boundary conditions (Tafel equations) and the iterative technique to determine the mixed potential of the unprotected structure. The model is applied to an unprotected bare structure as well as a coated structure with several defects. The amount and the location of corrosion along the unprotected structure correlate strongly with experimental results within the experimental conditions studied.     

Quantitative characterisation of steel/cement paste interface microstructure and corrosion phenomena in mortars suffering from chloride attack

Chloride ions constitute one of the deleterious agents that may cause or promote corrosion of steel reinforcement in concrete. The influence of chloride ingress on mortar microstructure (including microstructural alterations of hydration products and of pore structure) has been studied by the authors on the basis of cross-section image analysis of reinforced mortar specimens [D.A. Koleva, J. Hu, A.L.A. Fraaij, N. Boshkov, Influences of chloride ions on plain and reinforced mortars, investigated by combined microstructure and electrochemical approaches, Paper 315, Eurocorr 2005, September 4–8 ’05, Lisbon, Portugal]. This paper specifically pursues exploring the morphological aspects and chemical compositions of the corrosion products deposited on steel surface. For this purpose, scanning electron images (SEM) were taken on the cylindrical surface of steel reinforcement and also on the corresponding positions on cement paste surface for visualisation and microstructural investigations of corrosion products. In addition, energy dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) are employed for quantitative characterisation of the corrosion products at the steel–paste interface. Electrochemical impedance spectroscopy (EIS) is used to estimate the corrosion current and corrosion rate for the reinforced mortars. The EIS measurements are in good agreement with the microstructural observations and quantitative analysis of various corrosion products. The combination of electrochemical measurements with quantitative microstructure analysis of the steel–paste interface constitutes a reliable and useful tool for quantitative characterisation of the interface microstructure and thereby provides better insight into the electrochemical processes during corrosion of the steel reinforcement in concrete.     

Synergistic inhibition between Schiff’s bases and sulfate ion on corrosion of aluminium in sulfuric acid

The effect of Schiff’s bases alone and Schiff’s bases with additive Na₂SO₄ on the corrosion of aluminium in H₂SO₄ have been investigated by using weight loss method. The present study revealed that aluminium in H₂SO₄ has been more efficiently inhibited by Schiff’s bases in the presence of additive Na₂SO₄ than Schiff’s bases alone due to the synergistic effect between Schiff’s bases and Na₂SO₄. Inhibition efficiency was found maximum upto 95.02% for aluminium in H₂SO₄ by Schiff’s bases in presence of additive NaNa₂SO₄. The adsorption of inhibitor accords with the Langmuir adsorption isotherm. Results obtained in both the cases indicate the dependence of inhibition efficiencies on the concentration of Schiff’s bases, additive Na₂SO₄ and also on the concentration of H₂SO₄ solution. The results show the increasing trends of inhibition efficiency with the concentration. The article is published in the original.     

Corrosion inhibition of aluminum 6063 using some pharmaceutical compounds

The corrosion inhibition characteristics of some pharmaceutical compounds on aluminium 6063 in 0.5 mol l⁻¹ H₃PO₄ has been studied using weight loss and galvanostatic polarization techniques. Results showed that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface. The inhibition efficiency increased with increasing inhibitor concentration, but decreased with increasing temperature. The adsorption of first group pharmaceutical compounds on the metal surface is found to obey Frumkin’s adsorption isotherm, but the adsorption of second group pharmaceutical compounds is found to obey Temkin’s adsorption isotherm. Thermodynamic parameters for adsorption process were determined. Galvanostatic polarization studies showed that first and second groups’ pharmaceutical compounds are mixed-type inhibitors and the results obtained from the two techniques are in good agreement.