The current status of research on irradiation assisted stress corrosion cracking (IASCC) of core structural materials for light water reactors was reviewed with focuses on influencing factors and mechanism of IASCC. Challenges and perspectives for the research of IASCC in the future were also briefly addressed.
Effect of post solution- and stress relief-treatment on the stress corrosion cracking (SCC) resistance via U-bend specimens test in 42% boiling MgCl2 solution, as well as the microstructure, residual strain and mechanical properties of the forged 316LN stainless steel was studied. Results showed that the yield stress was reduced and the residual strain was eliminated through post solution-treatment for the forged steel. After immersion in boiling MgCl2 solution for 24, 48 and 72 h, respectively, all the U-bend specimens of either the solution-treated or the stress relief-treated steels suffered from clearly transgranular stress corrosion cracking (TGSCC). Furthermore, of which all the stress relief-treated specimens were entirly cracked, while the solution-treated specimens were only locally cracked after immersion for 72 h, suggesting higher SCC resistance for the forged steel after a proper post solution-treatment. Finally, the mechanism of the effect of post-heat treatments on the SCC resistance was discussed in terms of the residual strain and yield stress of the forged steel.
： The synergistic inhibition effect of imidazoline ammonium salt (IAS) and three anionic surfactants on corrosion of Q235 carbon steel in CO2 saturated brine solution was studied by using mass loss method, potentiodynamic polarization measurements and molecular dynamics (MD) simulation. It is found that in CO2 saturated brine solution, there exists a good synergistic inhibition effect between IAS and sodium dodecyl sulfonate (SDSH), and the most significant synergistic inhibition with an inhibition efficiency of 88.5% occurs when the concentration ratio of them is 1:1. The synergism also occurs when using IAS together with sodium dodecyl benzene sulfonate (SDBS). However the antagonism occurs between IAS and sodium dodecyl sulfate (SDSL). Good corrosion inhibition on Q235 carbon steel is also found when only one of the three anionic surfactants is used. The factors affecting the synergism between IAS and the three surfactants were conjectured using molecular simulation.
Four imidazoline derivates were synthesized using diethylenetriamine with stearic acid, oleic acid, n-docosanoic acid and erucic acid respectively as raw materials. Then the inhibition performance and adsorption capacity on the carbon steel surface and the ability of hydrophobic of the prepared derivates were studied in dynamic H2S/CO2 environment by means of dynamic weight loss test, SEM, AFM, contact angle measurement and molecular dynamics simulation. The measurememnt results for contact angle and AFM force showed that the hydrophobic effect is better and the adhesion force is bigger respectively for imidazoline derivatives with double bonds in their hydrophobic chains. The surface adsorption energy of the four imidazoline derivatives on the face of Fe (001) were calculated by using molecular dynamic simulation, the results indicated that the surface adsorption energy of imidazoline which has double bonds in hydrophobic chain was larger than that one without double bonds. The theoretical evaluation of corrosion inhibition performance of four imidazoline derivates accorded well with the experiment results.
Epoxy based conductive anti-corrosion coatings were prepared on the surface of grounding grid Q235 carbon steel with graphite, carbon fiber andaluminum tripolyphosphateas pigments. The influence of the pigment/binder ratio (PBR) on the properties of the coatings was investigated such as the morphology and the electric conductivity of the coatings as well the corrosion behavior of Q235 carbon steel coated by coatings with an optimal PBR by immersion in salt solutions and burying in a selected soil from Shenyang test site. The results indicated that after buried in the soil, the bare Q235 steel suffered from serious corrosion and bubbles occurred on the E44 lacquer coating on the steel, in the contrast, the coatings with the optimal PBR showed excellent protectiveness for the steel even after buried for up to 1000 h in the soil. The volume resistivity and surface contact resistivity of the coatings are 0.65 Ω·cm and 8.72 Ω/cm2 respectively. The coatings exhibited excellent with standing capacity to high current impulse, such as their electrical resistance decreased by 5.95% and 11.09% for the ones suffered from a high current impulse of 1 kA for 20 times and a power frequency current of 10 A for 5 times respectively, while the surface of the coatings maintained unchanged without any destruction.
Polyatyrolsulfon acid doped polyaniline (PSSA-PANI) was synthesized by emulsion polymerization method, and then was characterized by IR spectra and XPS. The synthesized PSSA-PANI exhibited good solubility in water. The corrosion inhibition performance of the PSSA-PANI on mild steel was examined in acidic NaCl solutions by means of electrochemical impedance spectroscopy (EIS). The results revealed that PSSA-PANI had a high conductivity. In the synthesized PSSA-PANI, PSSA existed in two states, namely doped-state and free-state, PSSA can improve not only the conductivity but also the water solubility of PANI. The PSSA-PANI showed good corrosion inhibition for 20# steel in acidic NaCl media with an inhibition efficiency over 80%.
A complex chemical conversion film of CeO2-siloxane was prepared on AA6063 aluminum alloy by successively dipping the alloy in CeCl3 aqueous solution and then in bis-[triethoxysilypropyl] tetra-sulfide (BTST) alcohol solution. Electrochemical tests show that the polarization resistance of the bare Al alloy in 3%NaCl solution can be enhanced by an order of magnitude with the CeO2 conversion film alone. But the complex film can rise both the polarization resistance by two orders of magnitude and the pitting potential by ca 400 mV. The enhancement of corrosion resistance of the alloy is limited by applying either CeO2 conversion film or BTST film alone, while a lot of pits can be observed on the Al electrode surface after immersed in 3%NaCl for 300 h. However, after the CeO2/BTST complex film was formed, no noise peaks can be found from the ECN curves when Al electrode immersed in 3%NaCl for 168 h, indicating that the complex film has a strong inhibition effect on the propagation of metastable- and steady-pits on the aluminium alloy. Since CeO2 can be absorbed preferentially on the second phase (AlFeSi), it can inhibit the growth of metastable pits; and the siloxane has a high binding energy with Al—O bond, therefore, the synergistic effect of CeO2 and siloxane may be beneficial to the excellent protectiveness of the complex film.
Calcareous deposit was formed on Q235 carbon steel surface in nature seawater by applying cathodic protection, afterwards, the corrosion test of the steel covered with and without calcareous deposit was carried out in f/2 culture medium containing Amphora. Then the morphology and chemical composition of corrosion products were characterized by means of XRD, SEM, FTIR and EIS. The result revealed that the calcareous deposit prepared by a current density of -30 µA/cm2 showed an even- and uniform-surface morphology composed of nice crystalline phase. The Amphora and its metabolite could adhere to the steel surface forming a biofilm, which could suppress the mass transfer of corrosive species from the medium to the steel surface to some extent, but not obviously that of the oxygen. Calcareous deposit was apt to combine with Amphora forming a composite film on the steel surface, which then could rather effectively suppress the migration of oxygen. The corrosion process of Q235 steel beneath the composite film can be described as the following three stages: as the corrosive media penetrated the composite film on to the steel surface, the steel is corroded leading to the formation of corrosion products, while, with which the combination of the existed biofilm, thus the composite film could act as barrier enabling the corrosion rate to be decreased to some extent; later as damages occurred within the composite film, thereby its protectiveness deteriorated, the corrosion rate of the steel increased again.
The corrosion behavior of Hastelloy N and 316L stainless steel (316L) in molten eutectic LiF-KF-NaF (FLiNaK) salt at 700 ℃ for 1000 h was investigated by means of static corrosion tests, while the corroded alloys were examined by SEM and EPMA. It was found that Hastelloy N and 316L all suffered from steady corrosion, while the corrosion resistance of Hastelloy N was superior to that of 316L. Hastelloy N experienced slight uniform corrosion, which was mainly due to the outward diffusion of Cr from the alloy. While 316L suffered from significant intergranular corrosion, which was related to the outward diffusion of Cr along grain boundaries. In addition, the mass loss of Hastelloy N firstly increased, and then degraded slowly with exposure time, which was mainly attributed to the re-deposition of Ni and Fe from the molten salt on the surface of Hastelloy N. The mass loss of 316L increased obviously for the first 400 h, and then became stable. The different in corrosion behavior of the two alloys in molten fluoride salt was mainly associated with their difference in chemical composition.
Effect of an applied alternating electric field on the oxygen diffusion coefficient in thin electrolyte layers on an electrode of stainless steel was investigated by chronoamperometry. The results show that the oxygen diffusion coefficient increased with the decrease in TEL thickness, as well as the increase in AEF strength. The effect of AEF on the oxygen diffusion coefficient is found to be due to that the migration of oxygen form the gas/liquid interface to electrode surface was accelerated by the applied electric field. For a thinner electrolyte layer by a stronger applied electric field, the cathodic process of the electrode would be more intensive,which corresponds to higher corrosion rate of metal.
The effect of particle-parameters of a liquid-solid two phase flow on the erosion rate of different sections for pipebends was analyzed by means of computational fluid dynamics (CFD) in terms of flow rate, particle size and particle velocity etc., while the trajectories of particles were calculated by Lagrange method. Then the relevant erosion mechanism of pipe wall may be acquired by considering the known particle collision model. The results show that: (1) the vulnerable areas mainly exist on the sidewall, as well as the outermost side of the junction of downstream straight pipe and elbow; (2) the change of Stokes number can cause shift of the serious erosion area, whilst not the entire sidewall of the junction of downstream straight pipe and elbow will be subjected to serious erosion.
As one type of typical nondestructive technique of life extension, bi-directional electro-migration (BIEM) can enhance the durability of concrete structures, which suffered from chloride attack. During the BIEM process, rust-inhibitor can be migrated inward to the surface of steel bar while the chloride can be extracted out of the concrete cover. This paper applied the BIEM technique to reinforced concrete slabs poured with sea sand and seawater. The results showed that the migration of rust-inhibitor and the extraction of chloride could be realized for the reinforcing bars located within a range of 12 cm from the lateral side of an electrolyte maintaining device. In accordance with the electron flux equivalent principle, the needed time and current density for realizing the practical engineering applications could be calculated from the measured voltage and safety voltage of concrete. A trial application of BIEM to several engineering concrete structures with sea sand proved that the ratio of organics content to the chloride concentration was far above 1.0. Consequently, both of the laboratory experiment and the engineering applicant indicated that BIEM technique could play an excellent role in chloride extraction and rust resistance, thus could act as an effective method for enhancing the durability of the existed sea sand containing structures.
An intelligent method based on fuzzy neural network and grey correlation analysis was proposed to predict the corrosion rate of oil and gas pipelines in marine environment. Through correlation analysis, the correlation between the corrosion rate of pipelines and environmental factors was built, and from which then the appropriate factors with high correlation could be picked out. Finally, the mapping relationship between the corrosion rate of pipelines and environmental factors could be figured out through fuzzy neural network. The validity and reliability of the results predicted by the proposed method were tested with statistic data which involved different environmental factors, it follows that the average relative error of the predicted corrosion rate was 5.96%, in other words, the present method exhibited a good accuracy in prediction even that less environmental factors were involved during the analysis process. Therefore, the method based on fuzzy neural network and grey correlation analysis, can predict the corrosion rate of pipelines rapidly and accurately with the known environmental factors.
