Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

Impact of corrosion on low-cycle fatigue degradation of reinforcing bars with the effect of inelastic buckling

The combined effect of inelastic buckling and chloride induced corrosion damage on low-cycle high amplitude fatigue life of embedded reinforcing bars in concrete is investigated experimentally. A total of forty-eight low-cycle fatigue tests on corroded reinforcing bars varied in percentage mass loss, strain amplitudes and buckling lengths are conducted. The failure modes and crack propagation are investigated by fractography of fracture surfaces using scanning electron microscope. The results show that the inelastic buckling, percentage mass loss and nonuniform corrosion pattern are the main parameters affecting the low-cycle fatigue life of reinforcing bars. It was found that the fatigue life of corroded reinforcing bars combined with inelastic buckling has a significant path dependency. The results show that in some cases the number of cycles to failure of corroded bars under constant amplitude fatigue test is increased.     

Study on corrosion simulation device for marine structural steel

A corrosion simulation device was studied using offshore long scale hanging specimens. An Ni-Cu-P steel specimen was studied by analysing its corrosion products and corrosion types. The appearance of the samples and the surface of the metallic substrate after the removal of the rust layer produced by these two methods were observed and compared after 470 days of exposure. The phase structure of the corrosion products under different marine environments were analysed and compared. It further indicated good correlation between the electrically connected hanging specimen method and the long scale hanging specimen method.     

Significance of oxygen concentration on the quality of passive film formation for steel reinforced concrete structures during the initial curing of concrete

Reinforced concrete prisms with varying surface conditions (sealed, partially sealed, and unsealed) and curing environments (in air and submerged in water) were used to vary the oxygen concentration in laboratory experiments. The experiment results (current rate and half-cell potential) of these tests were used to establish the time-dependent influence of oxygen concentration on passive film formation and corrosion of the reinforcement steel embedded in concrete under various defined conditions. It was found that the adequate availability of free oxygen during the initial curing stage is crucial for the proper formation of the passive layer. This suggests ways to improve passive layer development, and thus the durability of reinforced concrete structures, through the use of curing procedures that control both moisture and oxygen availability.     

Effects of bentonite content on the corrosion evolution of low carbon steel in simulated geological disposal environment

The effects of bentonite content on the corrosion behavior of low carbon steel in 5 mM NaHCO3+ 1 mM NaCl + 1 mM Na2SO4 solution were investigated by electrochemical measurements combined with X-ray diffraction(XRD) and scanning electron microscopy(SEM). In the initial immersion stage, the cathodic process of low carbon steel corrosion was dominated by the reduction of dissolved oxygen, while it transformed to the reduction of ferric corrosion products with the immersion time. The presence of bentonite colloids could suppress the cathodic reduction of oxygen due to their barrier effect on the diffusion of oxygen. However, the barrier performance of bentonite layer was gradually deteriorated due to the coagulation and separation of bentonite colloids caused by the charge neutralization of iron corrosion products dissolved from the steel substrate. More bentonite colloids could maintain the barrier effect for a long time before it was deteriorated by the accumulation of corrosion products. Conversely,it could lose the performance completely, and the corrosion behavior of low carbon steel reverted to the same as that in the blank solution.     

Correlation of surface features with corrosion behaviors of interstitial free steel processed by temper rolling

Temper rolling,as a final manufacturing procedure,brings the change of surface features and hence affects the corrosion behaviors of interstitial-free(IF)steel.This study investigates changes in residual stress,microstructure,and surface topography of IF steel using X-ray diffraction,electron backscatter diffraction,and optical interferometric microscopy.And the synthetic influence of surface features on the corrosion process of the steel was evaluated by damp heat tests and electrochemical measurements.Results showed that low tensile and compressive residual stresses are introduced to the surface of the IF steel.Some grains had a grain orientation spread(GOS)value greater than 0.50 after temper rolling.Moreover,temper rolling caused a slight change in the surface profile of the IF steel.The compressive residual stress had an overwhelming role at the macroscopic level,in retarding the corrosion evolution process of IF steel,as well as in decreasing the average corrosion rate.And corrosion was more likely to initiate and propagate in matrices with a high GOS value,which played the determinant role at the microscopic level.Moreover,the depth of valley in the surface profile could affect the diffusion process involved in the electrode reactions,which was more likely to exert an extra influence on the corrosion rate of IF steel.     

Effect of tannic acid on corrosion behavior of carbon steel in NaCl solution

Corrosion behavior of unrusted Q235 carbon steel was investigated in 3.5% NaCl solutions with 1–5 wt%tannic acid addition, using electrochemical methods including electrochemical impedance spectra(EIS),potentiodynamic polarization and scanning vibrating electrode technique(SVET) combined with surface analysis. Results show that the corrosion rate decreases with increasing tannic acid concentration. As compared with tannic acid-free solution, 1% tannic acid does not provide inhibition effect during the whole immersion, while inhibition effect is observed for 3% tannic acid after 8 h and for 5% tannic acid after 4 h. The inhibition efficiency by weight loss measurements(áw) for 1%, 3%, and 5% tannic is around-17.2%, 40.3%, and 51.5%, respectively. Corrosion of unrusted carbon steel in the presence of tannic acid is attributed to the joint effect of tannic acid adsorption and pH decrease. Formation of ferric-tannates is verified by X-ray photoelectron spectroscopy(XPS) and Raman spectra. The reaction mechanism between tannic acid and unrusted carbon steel is proposed.     

Effects of chromium(VI) reducing agents in cement on corrosion of reinforcing steel

During the production of cement it is necessary to add a reducing agent that converts soluble hexavalent chromium into trivalent chromium. This paper explores effects of iron(II) sulphate reducing agents, namely monosulphate and heptahydrate, as cement admixtures, on corrosion of concrete reinforcement. Accelerated corrosion tests of reinforcing steel have been performed in pore solutions simulating concrete prepared using either CEM I or CEM II type cement, with addition of various concentrations of iron(II) sulphate reducing agent. All of the test results indicate corresponding tendencies and point towards the potential for iron(II) sulphate to foster or accelerate corrosion of the reinforcement. The results of this study indicate an immediate need for a more detailed research, especially in concrete as a more realistic corrosion environment, of the application of iron(II) sulphate as a reducing agent in cement.     

Distinct beneficial effect of Sn on the corrosion resistance of Cr-Mo low alloy steel

In this work,the beneficial effect of Sn addition on the corrosion resistance mechanism of Cr-Mo low alloy steel was studied.Results demonstrated that Sn improves the corrosion resistance of the steel matrix mainly by influencing the microstructural transformation.Sn addition and the synergistic effect of Sn,Cr,and Mo promote the formation of α-FeOOH,SnO2,SnO,Cr(OH)3,and molybdates,lead to the improved protection and stability of the rust layer.This synergistic effect also endows the inner rust layer with cation selectivity,preventing the further penetration of Cl-and inhibiting the localized corrosion of steel.     

An study on accelerated corrosion testing of weathering steel

This paper assesses the use of wet/dry cyclic laboratory corrosion tests that can provide information on the protective capacity of weathering steels in short times. Two steels were considered, a weathering steel ASTM A 242 Type 1 and a plain carbon steel (as reference), that were exposed in the atmosphere of Madrid (3 years) and in the following laboratory wet/dry cyclic tests: Cebelcor (10⁻⁴ M Na₂SO₄) (945 h), Kesternich (0.2 L SO₂) (2160 h) and Prohesion (2160 h). Characterisation of rust layers was done by XRD, FTIR, SEM, SKP and EIS. Wet/dry cyclic tests make it possible to shorten the testing time to assess in laboratory the protective capacity of rusts formed on weathering steels in the atmosphere. Some analogies between experimentation in the field and in the laboratory have been established.     

Effect of high temperature post-oxidizing on tribological and corrosion behavior of plasma nitrided AISI 316 austenitic stainless steel

In this research, the microstructure, tribological and corrosion properties of plasma nitrided-oxidized AISI 316 austenitic stainless steel at high oxidation temperature were studied and compared with conventional plasma nitride. The structural, tribological and corrosion properties were analyzed using XRD, SEM, microhardness testing, pin-on-disk tribotesting and electrochemical polarization. Plasma nitriding was conducted for 5 h at 450 °C with gas mixture of N₂/H₂ = 1/3 to produce the S-phase. The nitrided samples were post-oxidized at 500 °C with gas mixture of O₂/H₂ = 1/5 for 15, 30 and 60 min. X-ray diffraction confirmed the development of CrN, ? and γ′ nitride phases and magnetite (Fe₃O₄) oxide phase under plasma nitriding-oxidizing process. In addition, it was found that oxidation treatment after plasma nitriding provides an important improvement in the friction coefficient and the corrosion resistance. The optimized wear and corrosion resistance of post-oxidized samples were obtained after 15 min of oxidation.     

The study of the inhibitory properties of benzoin, benzil, benzoin-(4-phenylthiosemicarbazone) and benzil-(4-phenylthiosemicarbazone) on the corrosion of mild steel in hydrochloric acid

The effects of benzoin (BN), benzil (BL), benzoin-(4-phenylthiosemicarbazone) (BN4PTSC) and benzil-(4-phenylthiosemicarbazone) (BL4PTSC) on the corrosion of mild steel in hydrochloric acid have been studied. Weight loss and hydrogen evolution measurements reveal that BN exhibit a higher maximum inhibition efficiency than BN4PTSC, BL and BL4PTSC. Generally, inhibition was found to increase with increase in inhibitor concentration and temperature. Chemical adsorption mechanism has been proposed for the inhibitors and the difference in the inhibition behaviour of the compounds has been explained in terms of the solubility of the compounds as well as the strength of the inhibitor–metal bond.     

Detection and analysis of microbiologically influenced corrosion of 316 L stainless steel with electrochemical noise technique

Microbiologically Influenced Corrosion (MIC) is a specific type of corrosion caused or promoted by microorganisms usually chemoautotrophs. In recent years, there has been growing interest in the exploitation of electrochemical noise technique to investigate and monitor biocorrosion. The advantages of Electrochemical Noise (EN) technique includes the possibility to detect and study the early stages of localized corrosion; however the comprehension of EN signals still remains very limited. In the present work an attempt has been made to analyze the current and potential noise records for type 316 L stainless steel (SS) specimen immersed in Iron oxidizing bacteria inoculated medium amended with different concentrations of NaCl. All the potential and current noise data collected in the time domain were transformed in the frequency domain, using MATLAB software. Shot noise parameters like frequency of corrosion events (f_n), average charge in each event (q), true coefficient of variation and noise resistance (R_N) were analyzed. Low frequency events and high charge were observed for the specimen after the exposure of 3 weeks in microbial medium with 1% NaCl when compared to control. It indicates that microbes can influence the pitting corrosion over the specimen which was also evidenced by Scanning Electron Microscope (SEM). In addition to this, the probabilistic failure model for MIC on 316 L SS was predicted using Weibull distribution.     

Synergistic inhibition between OP and NaCl on the corrosion of cold-rolled steel in phosphoric acid

The effects of single OP and the mixture of various concentrations of OP and 0.1 M NaCl on the corrosion of cold-rolled steel in 1.0–3.5 M phosphoric acid have been investigated by using weight loss method and polarization method. This study revealed that cold-rolled steel in phosphoric acid has been more efficiently inhibited by OP in the presence of NaCl than single OP, and inhibition efficiency increases with increasing concentration of OP at the same temperature, but decreases with increasing temperature studied. A synergistic effect exists when OP and chloride ion are used together to prevent cold-rolled steel corrosion in 1.0–3.5 M phosphoric acid at every experimental temperature. The polarization curves showed that OP is a cathodic inhibitor, while the complex of OP and NaCl is a mixed-type inhibitor that mainly inhibits the cathodic corrosion of the steel. The experimental results suggested that the presence of chloride ion in the solution stabilized the adsorption of OP molecules on the metal surface and improved the inhibition efficiency of OP. The adsorption of single OP follows the Langmuir adsorption isotherm, and the adsorption of the complex accords with the Langmuir adsorption isotherm too. Some thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy have been calculated by employing thermodynamic equations. Kinetic parameters such as apparent activation energy and pre-exponential factor have been calculated and discussed. In 1.5–3.5 M phosphoric acid, the concentration pre-exponential factor and acid concentration constant have been calculated, and the synergistic effect has been observed too.     

Study of phosphonate addition and hydrodynamic conditions on ordinary steel corrosion inhibition in simulated cooling water

The effect of phosphonate anion (PHOS) on the corrosion of ordinary steel in simulated cooling water has been studied using weight loss, polarization curves and electrochemical impedance spectroscopy measurements. PHOS was studied in the concentration range from 7.5 × 10⁻⁵ to 10⁻³ M. The results obtained reveal that PHOS perform excellently as corrosion inhibitor for ordinary steel in simulated cooling water. The inhibition efficiency of PHOS was increased with increasing both its concentration and water circulation velocity. These two factors seem to promote the adsorption of phosphorus and oxygen ions on the metal surface, leading to the formation of a protective layer with a greater charge transfer resistance and lower permeability.     

Effect of heat-input on pitting corrosion behavior of friction stir welded high nitrogen stainless steel

In this study, different welding parameters were selected to investigate the effects of heat-input on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results showed that, the welding speed had major influence on the duration at elevated temperature rather than the peak temperature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail.     

The study of tribological and corrosion behavior of plasma nitrided 34CrNiMo6 steel under hot and cold wall conditions

This paper reports on a comparative study of tribological and corrosion behavior of plasma nitrided 34CrNiMo6 low alloy steel under modern hot wall condition and conventional cold wall condition. Plasma nitriding was carried out at 500 °C and 550 °C with a 25% N₂ + 75% H₂ gas mixture for 8 h. The wall temperature of the chamber in hot wall condition was set to 400 °C. The treated specimens were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness and surface roughness techniques. The wear test was performed by pin-on-disc method. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were also used to evaluate the corrosion resistance of the samples. The results demonstrated that in both nitriding conditions, wear and corrosion resistance of the treated samples decrease with increasing temperature from 500 °C to 550 °C. Moreover, nitriding under hot wall condition at the same temperature provided slightly better tribological and corrosion behavior in comparison with cold wall condition. In consequence, the lowest friction coefficient, and highest wear and corrosion resistance were found on the sample treated under hot wall condition at 500 °C, which had the maximum surface hardness and ε-Fe_2–3N phase.     

The effect of repeated repair welding on mechanical and corrosion properties of stainless steel 316L

The purpose of this study is to evaluate changes in the mechanical, micro structural and the corrosion properties of stainless steel 316L under repeated repair welding. The welding and the repair welding were conducted by shielded metal arc welding (SMAW). The SMAW welding process was performed using E316L filler metals. Specimen of the base metal and different conditions of shielded metal arc welding repairs were studied by looking in the micro structural changes, the chemical composition of the phases, the grain size (in the heat affected zone) and the effect on the mechanical and corrosion properties. The microstructure was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical composition of the phases was determined using energy dispersive spectrometry (EDS). The corrosion behavior in 1 M H₂SO₄ + 3.5% NaCl solution was evaluated using a potentiodynamic polarization method. Tensile tests, Charpy-V impact resistance and Brinell hardness tests were conducted. Hardness of the heat affected zone decreased as the number of repairs increased. Generally an increase in the yield strength (YS) and the ultimate tensile strength (UTS) occurred with welding. After the first repair, a gradual decrease in YS and UTS occurred but the values of YS and UTS were not less than values of the base metal. Significant reduction in Charpy-V impact resistance with the number of weld repairs were observed when the notch location was in the HAZ. The HAZ of welding repair specimen is more sensitive to pitting corrosion. The sensitivity of HAZ to pitting corrosion was increased by increasing the number of welding repair.     

Experimental investigation on corrosion and hardness of ion implanted AISI 316L stainless steel

The AISI 316L stainless steel has been widely used both in artificial knee and hip joints in bio-medical applications. In the present study AISI 316L SS was implanted with two different ions: nitrogen and helium at 100 keV with a dose of 1 × 10¹⁷ ions/cm² at room temperature. The crystallographic orientation and surface morphology were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The effects of ion implantation on the corrosion performance of AISI 316L stainless steel was evaluated in 0.9% NaCl solution using electro chemical test both on the virgin and implanted samples. The subsequent Tafel analysis shows that the ion implanted specimens were more corrosion resistant when compared to the bare specimens. Microhardness was also measured by Vickers method by varying the loads. The results of the studies indicated that there was a significant improvement in both corrosion resistance and hardness of implanted samples.     

Effect of cold deformation on corrosion fatigue behavior of nickel-free high nitrogen austenitic stainless steel for coronary stent application

Due to the excellent mechanical properties, good corrosion resistance, high biocompatibility and nickel-free character, the high nitrogen nickel-free austenitic stainless steel (HNASS) becomes an ideally alternative material for coronary stents. Stent implantation works in harsh blood environment after a balloon dilatation, i.e., the material is used in a corrosive environment with a permanent deformation. The present study attempts to investigate effects of pre-straining on high-cycle fatigue behavior and corrosion fatigue behavior of HNASS in Hank’s solution and the relevant mechanism for coronary stents application. It is found that higher pre-straining on HNASS results in higher strength and maintains almost same corrosion resistance. Fatigue limit of 0% HNASS is 550 MPa, while corrosion fatigue limit is 475 MPa. And improvement in fatigue limit of 20% and 35% pre-strained HNASS is in comparison with the 0% HNASS, while corrosion would undermine the fatigue behavior of HNASS. In a suitable range, the pre-straining had a beneficial effect on corrosion fatigue strength of HNASS, such as nearly 300 MPa improved with 20% cold deformation. This result provides a good reference for predicting the life of HNASS stent and as well its design.