Intergranular attack and intergranular stress corrosion cracking of Alloy 690 TT in high temperature lead‐containing caustic solution

Immersion tests were carried out in high temperature lead‐containing caustic solution in a static autoclave. The results showed samples with three surface statuses of Alloy 690 TT suffered from intergranular attack (IGA) after immersion in 10% sodium hydroxide (wt%) with 10 g/L of litharge at 330 °C for different times. With the increasing immersion time, IGA became more severe. Wire cutting samples had the most serious IGA, ground samples followed and electro‐polished samples had the slightest IGA. IGA had developed into IGSCC only in wire cutting samples due to the existence of residual stress. All the specimens at different immersion time tests lost weight. To the same cold‐work samples, with the increasing immersion time, the weight loss increased. No IGA was found in 10% sodium hydroxide solution at 330 °C after 720 h immersion. When adding 100 ppm litharge into 10% sodium hydroxide solution, slight IGA was produced. IGA became more serious and the weight loss of the specimens with three surface statuses increased with the increase of lead concentration. As the results of 1% sodium hydroxide solution containing 10 g/L litharge and 4% sodium hydroxide solution containing 10 g/L litharge at 330 °C for 720 h immersion tests, only slight IGA occurred and the weight of samples with three surface statuses increased. The pH value played an important role in lead‐induced corrosion in caustic solution.     

Inhibition von Niedertemperaturkreisläufen in Kraftwerken mit Lithiumhydroxid

Inhibition of low temperature circulating systems with lithium hydroxide in power stations Corrosion current density measurements of mild steel St 37 in deionized, air-saturated water between 20 and 60°C showed that addition of small quantities of lithium hydroxide (ca. 25 ppm) protects against corrosion attacks similar to pitting corrosion and is found adequate even up to 5 ppm chloride ion concentration. Constant strain rate tests of mild steel St 37 showed no indication of stress corrosion cracking (SCC) at 70°C, up to 500 ppm lithium hydroxide, and 100 ppm chloride ion concentration. Metallographic examination of specimens indicated intergranular stress cracking with cracks of 1–30 m?m depth in environments containing 2%, 4%, and saturated lithium hydroxide (with solid excess salt) at 70°C. Accumulation of lithium hydroxide should therefore be avoided. No SCC was observed in austenitic stainless steel X 5 CrNi 18 9 specimens in the above environments.     

Characterization of ASR damage in concrete using nonlinear impact resonance acoustic spectroscopy technique

This research reports on a successful application of the nonlinear impact resonance acoustic spectroscopy (NIRAS) technique for the characterization of progressive damage in standard concrete specimens. Damage in the specimens is introduced, following ASTM C 1293 testing procedures, through the deleterious alkali–silica reaction (ASR), which leads to the formation of a gel-like reaction product, microcracks, and interfacial debonding between cement and aggregate phases. The microcracks and debonded interfaces act to increase the nonlinearity of concrete. The response of the specimen to impact loading is analyzed to obtain a nonlinearity parameter, which is used as a measure of damage. Measurements are performed on concrete prisms undergoing the ASTM C 1293 expansion test; three aggregates with varying reactivity are examined. The results from the expansion test are compared with those from the NIRAS measurements. For potentially reactive aggregate, the NIRAS technique offers a more definitive assessment of the damage state of the specimen and can be used to distinguish marginally reactive aggregates. The NIRAS results not only demonstrate a clear distinction between nonreactive and reactive aggregates using the nonlinearity parameter, but also the capability to quantitatively track ASR-induced damage in concrete, potentially forming the foundation for field assessment and monitoring.     

Initiation of chloride‐induced corrosion of steel in concrete: role of the interfacial zone

This paper provides a brief review of research aimed at characterising the steel–concrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH ～12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride‐induced corrosion because it counters the generation of ‘anodic acidity’ that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full‐scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non‐traditional cements.     

Stress corrosion cracking behaviour of Al‐Li alloy 8090‐T8171 plate exposed to various synthetic environments

The stress corrosion cracking (SCC) behaviour of 8090‐T8171 plate material was investigated in short transverse direction performing constant load tests and constant extension rate tests under permanent immersion conditions. At an applied stress of 100 MPa, smooth round tensile specimens were exposed to synthetic environments containing chlorides and various nonhalide anions. Environment‐induced cracking was not observed in aqueous solutions of 0.6 M NaCl, LiCl, NH₄Cl, or MgCl₂. In 0.6 M NaCl solutions containing 0.06 M Na₂SO₄ or Na₃PO₄, the SCC behaviour of 8090‐T8171 plate was similar to that observed in pure 0.6 M NaCl solution. Sodium chloride solutions with additions of nitrate, hydrogen carbonate, or carbonate promoted stress corrosion cracking. Threshold stresses below 100 MPa were obtained from constant load tests using the latter environments. When sodium sulfite or sodium hydrogen phosphate was added, values being 100 MPa or slightly higher were determined. Lithium and ammonium present as cations in mixed salt electrolytes accelerated SCC failure. Lithium chloride solutions containing nitrate, hydrogen carbonate, carbonate, or sulfite were highly conducive to stress corrosion cracking. Very low SCC resistance was found for alloy 8090‐T8171 exposed to synthetic environments with additions of ammonium salts. Constant extension rate tests were carried out using notched tensile specimens. Displacement rates were in the range 2 × 10^?6 ? 2 × 10^?5 mms^?1. Aqueous 0.6 M NaCl solutions with additions of 0.06 M NH₄HCO₃, (NH₄)₂SO₄, or Li₂CO₃ promoted environment‐induced cracking with 8090‐T8171 plate, as indicated by severe degradation of notch strength. The constant extension rate testing technique did not indicate SCC susceptibility using sodium chloride solutions containing sodium sulfate or lithium sulfate. For specimens exposed to substitute ocean water a slight degradation of notch strength was found at the lowest displacement rate applied.     

Effects of asymmetrical rolling on through-thickness microstructure and texture of body-centered cubic (BCC) tantalum

In conventional symmetric rolling (SR), the microstructure and texture inhomogeneities along the thickness are intractable problems for body-centered-cubic (BCC) metals with high stacking fault energy. In this study, high-purity tantalum was selected as a representative case, and a new asymmetrical rolling (ASR) technique was developed to alleviate this inhomogeneity. Specimens were rolled to 80% thickness reduction using 90-degree cross SR and 90-degree cross ASR; two different rolling speed ratios, namely, 1.1 and 1.2, were adopted in ASR. The through-thickness texture and microstructure were characterized via X-ray diffraction and electron backscatter diffraction. Results showed that the ASR deformed specimens presented more homogeneous through-thickness microstructure and texture than SR-deformed specimens possibly due to the highly uniform accumulative shearing strain distribution introduced by ASR. Therefore, textural and microstructural uniformity increased with increasing rolling speed ratio in ASR.     

不同配合比混凝土的电化学除氯效果研究

    采用60V稳压电源、饱和氢氧化钙溶液、钛金属网阳极对圆柱体混凝土试件进行连续14天的电化学除氯实验,研究不同配合比混凝土试件的通电量、氯离子排出量和混凝土中残余氯离子含量.结果表明：相同电场作用条件下,水灰比越小,混凝土电化学除氯时通过的电量越少,除氯效果越差;掺入硅灰、矿渣使通过混凝土的电量值明显减少,电化学除氯效果变差;掺粉煤灰混凝土的电化学除氯效果接近甚至高于基准混凝土.因此,针对不同配合比混凝土应采用不同的电化学除氯电压和除氯时间才能达到理想除氯效果.     

Electrochemical Behavior of 316 L Stainless Steel in Alkaline Environments Containing Chloride Ion

This article intends to study corrosion of 316 L stainless steel alloy in simulated concrete environments. A composition of 0.1 M sodium hydroxide plus 0.1M potassium hydroxide with different pH (9, 11 and 13) and 0, 3 and 10 wt % sodium chloride concentration has been utilized for this manner. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to study electrochemical behavior. The results of potentiodynamic polarization indicate that the formed passive layer becomes more stable and its failure takes place later as increasing pH. Electrochemical impedance test also has confirmed the obtained results and also showed that the corrosion resistance of the sample assessed over dilution time. At a solution with high alkalinity (pH 13) results showed increase in total impedance after 24 h of dilution related to passive film stabilization which did not observed in samples with lower pH. In this work, electrochemical behavior of 316 L stainless steel in alkaline environments of simulated concrete is studied with chlorine ion addition and pH adjustment.     

Influence of a biopolymer admixture on corrosion behaviour of steel rebars in concrete

Among the multitude of concrete structure pathologies, corrosion of rebars is one of the most important problems of concrete durability. In the context of sustainable development, it appears of primary importance to develop new means to protect the rebars against corrosion. This study aims to develop a new eco‐friendly and corrosion‐inhibiting admixture based on EPS 180 exopolysaccharides, biopolymers used in coatings already studied for the corrosion inhibition on steel in seawater. C15 rebars embedded in CEMI and CEMV cement paste containing EPS 180 were immersed in natural seawater and their electrochemical behaviour was studied using open circuit potential measurements and electrochemical impedance spectroscopy. These tests highlight the decrease of the cathodic reaction kinetics due to the EPS 180 action at the rebars surface, and the absence of effect on the passive layer. Capillary imbibition tests carried out on cement paste and mortars showed that although limiting the imbibition kinetics for cement pastes, the EPS 180 did not influence the water imbibition of mortars. Tests comparing capillary imbibition of soaked cement pastes and mortars with EPS 180 solution and the same samples containing the EPS 180 admixture highlight that the corrosion inhibition induced by EPS 180 admixture is more due to the modification of the cement – rebars interface than to the clogging of the cement porous network.     

Investigations of an ethanolamine‐based corrosion inhibitor system for surface treatment of reinforced concrete

Laboratory investigations were performed to assess the efficacy of a proprietary ethanolamine‐based corrosion inhibitor system when applied to the surface of reinforced concrete specimens that were chloride‐contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately eighteen months thereafter. Gravimetric measurements of the quantities and distribution of corrosion on the steel were also made on completion of the exposure tests. Analysis of aqueous extracts from treated concrete revealed that the ethanolamine component of the inhibitor system penetrated to depths of more than 15 mm within the concrete. It was found that, for inhibitor‐treated specimens, there was some reduction in the corrosion rate of pre‐corroding steel at low cover depths in non‐carbonated concrete with modest levels of chloride contamination. At higher levels of chloride contamination and in carbonated specimens, however, the ethanolamine‐based inhibitor was apparently ineffective under the conditions investigated.     

Quantification of Tafel coefficients according to passive/active state of steel carbonation‐induced corrosion in concrete

Statistical quantification of Tafel coefficients is investigated in this study for isolated steel rebar embedded in concrete. The survey is supported by a wide experimental campaign carried out earlier to characterize the passive and active states of carbonation‐induced corrosion of steel. Electrochemical measurements (polarization resistance, corrosion potential, Tafel coefficients) and gravimetric estimations of iron loss were regularly conducted over 417 days on 108 concrete specimens. The statistical analysis reveals that the mean value of Tafel coefficients, both cathodic and anodic, is higher under active corrosion, which seems to contradict the general tendency found for chloride‐induced corrosion, while their coefficient of variation is smaller. The statistical inference was based on the first step of distributions fitting the experimental data and then on the second step of goodness‐of‐fit tests. The most suitable of the distributions proposed were the Burr, Rayleigh, and Gamma distributions. A similar analysis was made for the corrosion potential and polarization resistance. The findings of the study will be valuable for probabilistic approaches to corrosion where probabilistic distributions are required.     

Evaluation of the corrosion inhibition of salts of organic acids in alkaline solutions and chloride contaminated concrete

This paper summarizes the results of testing on salts of organic acids for evaluating their use as inhibitors of rebar corrosion in chloride‐contaminated concrete. Initially a screening based on electrochemical tests in alkalinized calcium hydroxide solutions was performed on a number of carboxylic acid salts with different number of carbon atoms in the chain and carboxylic groups, also covering substances with hydroxyl and amine group substituents. The screening was completed by testing on carbon steel rebars in concretes with chlorides and substances added at 1:1 molar ratio, focused on sodium lactate, sodium oxalate and sodium borate for comparison. The monitoring of free corrosion potential and linear polarization resistance of steel bars have confirmed significant inhibition only for lactate. Corrosion was only restricted to occluded zones where the access of substance was limited by disadvantageous geometry, producing shallow attacks. Results of further tests in saturated calcium hydroxide solution are reported in order to assess the inhibition ability of lactate as a function of its content, chloride content and pH.     

The use of pumice as a coating for the reinforcement of steel against corrosion and concrete abrasions

This study presents the results of corrosion resistance for pumice collected from pyroclastic exposure in the Van, Kayseri, Nevsehir and Osmaniye regions of Turkey. The corrosion resistance of reinforced steel (RS) and mass losses of concrete specimens were investigated. The specimens were exposed to 5 and 10% sodium sulphate solutions. Reinforced steel mass losses and compressive strengths of concrete were measured. Improvements of the compressive strength and corrosion resistance were observed for specimens with the increasing layers of coating. The corrosion rates of pumice coated specimens were lower than the control specimens. There was a close relationship between type of pumice coating and reinforcement corrosion. Corrosion ratio decreased with increasing amounts of reactive SiO₂. The alkalinity of the concrete, permeability of the concrete cover, the quality of the concrete and the corrosion environment were crucial factors in influencing the effectiveness of the concrete cover for corrosion protection of reinforced steel. All pumice concretes offered excellent resistance to corrosion, where Osmaniye pumice (OP) best increased corrosion resistance of reinforced steel.     

Electrochemical behaviour of the tin anode in alkaline-stannate plating baths

In order to determine the conditions for tin plating, the anodic oxidation and passivation of tin have been investigated in sodium stannate solution in the absence and in the presence of sodium hydroxide. Both galvano-static and potentiostatic techniques were used. It was found that the passivation of this electrode is a complex process consisting of several steps. The passivation time increases with increasing stannate concentration and with decreasing current density. Addition of sodium hydroxide to the bath increases the passivation time. At low current densities and high alkali concentrations, passivation does not occur and the anode remains active and dissolves continuously as stannite.X-ray diffraction and electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy) examination confirmed the existence of tin(II) and tin(IV) oxides and hydroxides in the passive films formed potentiostatically in sodium stannate solutions in the absence and in the presence of sodium hydroxide.     

Looking for a surface treatment to deposit a reactive element with potential industrial use in high temperature oxidation field

In order to introduce a so‐called reactive element simultaneously at all the surfaces of a NiCr (Ni‐20wt.%Cr‐1.5wt.%Si) metallic substrate alloy, an easy to apply surface treatment was used: an yttrium containing thin film (constituted of a hydrated yttrium hydroxide nitrate) was electrodeposited from a mixed water‐ethanol solution. After a thermal conversion treatment at 600 °C under argon, leading to an Y₂O₃ coating, specimens were submitted to high‐temperature oxidation testing, under artificial air at atmospheric pressure, in order to evaluate in these conditions the effect of the coatings on the behaviour of the studied alloy. Expected effects of the introduced reactive element (REE) were effectively shown: decrease of the coated sample weight gain, suppression of the formation of the base metal oxides and change of the oxide grains morphology.     

Embeddable reference electrodes for corrosion monitoring of reinforced concrete structures

Mixed‐metal oxide (MMO), graphite and laboratory‐made Ag/AgCl electrodes were electrochemically characterized to be used as reference electrodes embedded in concrete structures. Electrodes were studied in both, aqueous solutions of pH ranging from 7 to 13.5 and embedded into cement mortars; and the electrochemical studies were carried out in the absence and presence of chloride ions. Potential evolution, polarisation behaviour, galvanostatic pulse response and impedance characteristics of the electrodes were carried out in aqueous solutions. Besides, the electrochemical stability of the electrodes embedded in mortar was studied for an exposure period of two years. It was found that the MMO pseudo‐reference electrode is pH‐sensitive, the graphite pseudo‐reference electrode is oxygen sensitive and the Ag/AgCl pseudo‐reference electrode is chloride sensitive. Then, regarding the corrosion monitoring of steel rebars, care should be taken to avoid misleading interpretations of the corrosion potential measurements. However, any of them can be used to measure the corrosion rate of the rebars by means of traditional electrochemical techniques.     

Concrete cover cracking owing to reinforcement corrosion – theoretical considerations and practical experience

Reinforcement corrosion might lead to cracking and spalling of the concrete cover owing to the volume expansion associated with the deposition of some of the possible corrosion products. This is not only aesthetically unpleasing, it might also accelerate deterioration processes or become a safety issue for passing traffic. The present paper discusses first the mechanisms of carbonation‐ and chloride‐induced reinforcement corrosion and considers the chemistry of aqueous iron in order to identify the type of corrosion products as well as their location of formation. Furthermore, practical examples are summarised in order to compare the documented behaviour of a number of real structures with the theoretical considerations made. It is shown that for the case of purely chloride‐induced (pitting) corrosion, precipitation of corrosion products is strongly delayed or may even not occur. Implications are discussed with respect to time‐to‐corrosion prediction models and visual inspection of reinforced concrete structures. Both the theoretical considerations and the practical experience illustrate that relying on outwardly visible signs to detect internally on‐going corrosion must be done with caution if localised reinforcement corrosion cannot be excluded.     

Effects of nonhalide anions on the stress corrosion cracking behaviour of alloy 7475 in the tempers T651 and T7351

The stress corrosion cracking behaviour of 7475 plate material in the tempers T651 and T7351 was investigated performing constant load tests. Short transverse specimens were permanently immersed in aerated aqueous 0.6 M sodium chloride solutions with additions of 0.03 M sodium sulphate, 0.03 M sodium nitrate and 0.1 M sodium bicarbonate. Chloride solutions containing sulphate, nitrate or/and bicarbonate promoted environment‐induced cracking. A short transverse threshold stress below 50 MPa was found for 7475‐T651 plate material. Neutral 0.6 M NaCl solution was less conducive to stress corrosion cracking. Specimens of alloy 7475 in the overaged temper T7351 failed at applied stresses above 300 MPa. This failure resulted from overload fracture caused by a reduction of cross‐sectional area due to pitting corrosion, as confirmed by fractography showing severe pitting attack. Fractographic examinations of 7475‐T7351 specimens failed during immersion in chloride‐nitrate‐bicarbonate containing solutions with or without addition of sulphate after long exposure time periods revealed slight transgranular stress corrosion cracking, too. Pronounced transgranular environment‐induced cracking was observed on the fracture surfaces of specimens which were exposed to an aqueous solution containing chloride, sulphate, nitrate, and bicarbonate for 30 days at applied stress and were subsequently tensile tested in an inert environment.     

Stainless steel reinforcing bars – reason for their high pitting corrosion resistance

In harsh chloride bearing environments stainless steel reinforcing bars offer excellent corrosion resistance and very long service life for concrete structures, but the high costs limit a more widespread use. Manganese bearing nickel‐free stainless steels could be a cost‐effective alternative. Whereas the corrosion behavior of stainless steels in alkaline solutions, mortar and concrete is quite well established, only little information on the reasons for the high pitting resistance are available. This work reports the results of pitting potential measurements in solutions simulating alkaline and carbonated concrete on black steel, stainless steel DIN 1.4301, duplex steel DIN 1.4462, and nickel‐free stainless steel DIN 1.4456. Duplex and nickel‐free stainless steels are fully resistant even in 4 M NaCl solutions with pH 13 or higher, the lower grade DIN 1.4301 shows a wide scatter between fully resistant and pitting potentials as low as +0.2 V SCE. In carbonated solutions with pH 9 the nickel‐free DIN 1.4456 shows pitting corrosion at chloride concentrations ≥3 M. This ranking of the pitting resistance can be rationalized based on XPS surface analysis results: both the increase of the Cr(III)oxy‐hydroxide and Mo(VI) contents in the passive film and a marked nickel enrichment beneath the film improve the pitting resistance. The duplex DIN 1.4462 shows the highest pitting resistance, which can be attributed to the very high Cr(III)oxy‐hydroxide, to a medium Mo(VI) content in the film and to a nickel enrichment beneath the film. Upon time, the protective properties of the surface film improve. This beneficial effect of ageing (transformation of the passive film to a less Fe²⁺ containing, more hydrated film) will lead to higher pitting potentials. It can be concluded that short‐term solution experiments give conservative results in terms of resistance to chloride‐induced corrosion in reinforced concrete structures.