In this paper, the test methods, evaluation indexes, influencing factors and initiation mechanism related with the stress corrosion cracking in high temperature and high pressure water for structural materials such as stainless steels and nickel-based alloys commonly used in nuclear power plants are reviewed, and the shortcomings of current research and the future research trends are also pointed out.

Halloysite nanotubes (HNTs) are natural aluminosilicate nanomaterials with unique hollow tubular structure, large specific surface area and high reactivity. They exhibit more and more significant application value as a nano-carrier in the field of intelligent anti-corrosion coatings. In this paper, the structure, and properties of HNTs are briefly described, the feasibility of application of HNTs for intelligent coatings is analyzed, the mechanism of surface modification of HNTs and the factors affecting the carrying capacity of corrosion inhibitor are described, the application research progress of the modified HNTs as self-repairing unit for intelligent anticorrosion coating is also analyzed. Simultaneously, the functional improvement of HNTs modified intelligent coating is prospected.

This paper sums up the influencing factors and test methods of galvanic corrosion, which is widely existing in marine engineering. Galvanic corrosion is mainly affected by metal itself and environmental factors. And the paper summarizes the research on galvanic corrosion in marine environment at home and abroad in recent years. The application of various test methods and characterization methods for galvanic corrosion in marine environment and the latest progress are introduced. Finally, the research direction in this field is prospected, which provides new ideas for researchers in related fields.

The initial atmospheric corrosion behavior of Cu foils induced by co-depositioned with of particulates with different proportions of (NH₄)₂SO₄ and NaCl particles in a weathering chamber was assessed via electrochemical impedance (EIS), quartz crystal microbalance (QCM) and thin foil electrical resistance probe (TER). The results show that the mixed salt particles of (NH₄)₂SO₄ and NaCl promote the initial atmospheric corrosion of PCB-Cu compared with sole NaCl salt particles in the initial 30 h when the total deposition amount is equal. However, after 30 h, the atmospheric corrosion rate of PCB-Cu beneath the mixed salts is significantly lower than that beneath the sole NaCl particles when the mixing ratio of (NH₄)₂SO₄ to NaCl is 1:1, and the inhibition ratio of Cu corrosion can reach 84%, indicating that the (NH₄)₂SO₄ can refrain the corrosion of PCB-Cu beneath induced by NaCl particles. According to the SEM, XRD and XPS analysis of corrosion products, in the early stage of corrosion, due to the catalytic effect of NH4⁺ on the corrosion of Cu, dense Cu₂O corrosion products quickly formed on the copper surface, which dramatically refrains the corrosion of Cu substrate. Although Cu₂O corrosion products are also generated on PCB-Cu surface where NaCl particles are deposited, they are relatively loose and porous, which could accelerate the corrosion of Cu beneath porous Cu₂O layer due to the cathodic depolarization of the corrosion product layer.

The electrochemical corrosion behavior of 2Cr-1Ni-1.2Mo-0.2V steel in NH₄H₂PO₄ solutions was investigated by means of open circuit potential measurement, polarization curve measurement, electrochemical impedance spectroscopy, laser scanning confocal microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray polycrystalline diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that with the increase of NH₄H₂PO₄ concentration, the corrosion rate of 2Cr-1Ni-1.2Mo-0.2V steel was increased rapidly at first and then slowly. Pitting corrosion occurred when the 2Cr-1Ni-1.2Mo-0.2V steel immersed in solutions of 0~1 mmol/L NH₄H₂PO₄ for 20 h. But only uniform corrosion might occur when the steel immersed in solutions of 30-120 mmol/L NH₄H₂PO₄ for 20 h. The corrosion product of 2Cr-1Ni-1.2Mo-0.2V steel was a two layered scale, the outer layer composed mainly of Fe₃(PO₄)₂ and FePO₄, and the inner layer composed mainly of Fe₃O₄. With the increase of NH₄H₂PO₄ concentration, the coverage and compactness of the outer corrosion product layer increased, and Cr, Mo enriched in the inner corrosion product layer, thereby the corrosion resistance of 2Cr-1Ni-1.2Mo-0.2V steel was increased.

The corrosion behavior of 690 MPa high performance weathering bridge steel in a laboratory simulated industrial atmosphere was investigated by means of cyclically alternative immersion-drying accelerated corrosion test, electrochemical test, scanning electron microscopy (SEM), X-ray diffractometer (XRD), electron probe (EPMA) and other surface testing techniques. The results show that the corrosion resistance of Q690qENH steel composed mainly of bainite is better than that of Q235 steel composed of ferrite and pearlite at the early stage of corrosion. At the later stage of corrosion, the corrosion rate of Q690qENH steel decreases gradually and which is much lower than that of Q235 steel. The enrichment of alloying elements Cu, Cr and Ni in the rust layer of Q690qENH steel improves the denseness and stability of the rust layer, which has stronger resistance to corrosive medium, and higher α/γ* ratio of the so-called rust layer protectiveness. The electrochemical test results also show that the rust resistance and linear polarization resistance of Q690qENH steel are larger and the protective effect is stronger. Therefore, the corrosion resistance of Q690qENH steel is obviously better than that of Q235 steel in simulated industrial atmospheric environment.

The plasma electrolytic oxidation (PEO) coating is a ceramic-like coating without catalytic activity of its surface, thus which should be activated with noble metal Pd before an electroless nickel (EN) plating process can be conducted. To replace the expensive Pd-activation process, Cu-activation and Ag-activation methods were developed. A field emission-scanning electron microscopy was employed to characterize the surface morphology and cross-section morphology of EN films on the Cu- and Ag-activated PEO coatings. In comparison with the Cu-activated PEO coating, a thicker, compact and more uniform EN layer film was formed on the Ag-activated PEO coating. Moreover, the results of electrochemical tests shown that the EN film plated on Ag-activated coating presents more or less the same corrosion resistance as the EN film plated on Pd-activated PEO coating, and better than the EN film plated on Cu-activated PEO coating. Hence, the Ag-activation method significantly reduce the cost, and best of all, it guaranteed the corrosion resistance of the composite coating.

The evolution of micro-morphology for the couple of NiCrAlY coating/N5 high-temperature alloy system during service at high temperature, namely the precipitated TCP-phases within the substrate, the interface of coating/substrate, and the formed oxide scale etc., was studied by means of image processing technology, aiming to acquire the information related with their characteristics for the identification and retrieval of the relevant features of coating/alloy systems. Based on the acquired date-sets from 3600 frames of cross-sectional feature images of 64×64 pixels, a convolutional neural network (CNN) was established for classification and identification of the TCP phase, the interface of coating/substrate, and the oxide scale via a deep learning technique. The convolutional neural networks with two or three convolutional layers were respectively trained, so that the classification and identification of these three kinds of features, as well as the sliding window retrieval positioning are realized, thereby, the test set accuracy was 98% or 90.67%, respectively, for the neural network of two or three convolution layers coupled with the RMSProp optimizer. The test set accuracy for the convolutional neural network with three convolutional layers coupled with the Adam optimizer was 99.17%. This network performs best in retrieving the desired three features for images of 1024×943 pixel, correspondingly, the retrieval accuracy even can reach 100%.

Epoxy resin (E-20) was co-modified by silane coupling agent (KH550) and hydroxyl silicone oil through a two-step reaction process. The ethoxy group (coming from KH550) was introduced into E-20 by addition reaction of primary amine to increase the activity, thereby the grafting efficiency of E-20 with hydroxyl silicone oil was improved. The mechanism of two-step reaction process and the effect of reactant ratio on properties of modified resin were studied in detail through IR, GPC test, stability analysis and DSC test so that to optimize modification parameters. The results show that the appropriate ratio of reactants was E-20: hydroxyl silicone oil: KH550=10:1.5:0.5 (mass ratio). Further, the Mg-rich primer made of the modified resin was prepared and then applied on Al-alloy, afterwards the protective performance for the Mg-rich primer coated Al-alloy was assessed through salt spray testing and aging testing. The results show that this coating has high adhesion and good flexibility, as well as excellent salt spray resistance and aging resistance.

A polymethyl methacrylate coating (PMMA) containing particles of basalt/cerium oxide composite was applied on X70 steel, then the effect of the addition amount of basalt/cerium oxide composite on the corrosion- and wear-resistance of the coating was studied. The synthesized basalt/cerium oxide composite material was characterized by X-ray diffractometer. The surface morphology, composition, hydrophilicity, and hydrophobicity of the coating before and after the addition of basalt/cerium oxide particles were assessed comparatively by scanning electron microscope with energy dispersive spectroscope and contact angle tester. At the same time, the anti-corrosion and friction behavior of the modified coating were studied by means of electrochemical impedance spectroscope, polarization curve measurement, friction- and wear-tester. The results show that the modified coating with basalt/cerium oxide composite exhibits much obvious hydrophobicity and better corrosion resistance and friction resistance.

The influence of sodium benzoate (SB) concentration of acid Zn-Ni plating bath (AZNB) at room temperature on the dissolution behavior of Zn and corrosion inhibition effect on Zn anode was assessed by means of static corrosion mass loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve measurement. The results show that the addition of SB to AZNB has a good inhibitory effect on the dissolution of Zn. With the increase of SB concentration within the range of 30-120 mg/L, the corrosion inhibition efficiency for Zn gradually increases. Therefore, SB is an anode type corrosion inhibitor. When the SB concentration of AZNB is the same, the corrosion inhibition efficiency for Zn decreases with the increasing temperature. The adsorption isotherm curve revealed that SB satisfies the Langmuir isotherm adsorption model on the surface of the Zn anode. The increase in temperature reduces the adsorption equilibrium constant of the corrosion inhibitor molecules on the Zn surface, resulting in a decrease in its adsorption capacity. The changes of thermodynamic parameters when SB adsorbed on Zn surface at different temperature show that the entropy increase process of SB corrosion inhibitor molecules on the Zn surface is controlled spontaneously by a mixture of physical adsorption and chemical adsorption.

Corrosion behavior of Sanicro 25 austenitic steel, HR230 and 740H Ni-based alloys in CO₂ environment at 800, 900 and 1000 ℃ was studied by means of weight gain measurement, scanning electron microscope with energy dispersive X-ray spectroscopy and X-ray diffractometer. The results showed that the corrosion kinetic curves of the three alloys in the high-temperature CO₂ environment conformed to the parabolic law. The reaction rates of the three alloys all increased with the temperature, and the thickness of surface corrosion products also increased with the temperature. The corrosion products generated on the surface of the three alloys were mainly Cr-rich oxides, which were caused by the high content of Cr. However,the structure of the surface corrosion products of Sanicro 25 steel and HR230 and 740H alloys was different. Sanicro 25 steel was a composite layer type, HR230 and 740H alloys was a single-layer type; both HR230 and 740H alloys had internal oxidation, and the high content of Al and Ti in 740H alloy made internal oxidation more serious, therewith degraded its corrosion resistance. According to the corrosion mass gain measurement results and the occurrence of internal oxidation phenomenon, the nickel-based alloy HR230 has superior corrosion resistance in high temperature CO₂ environment.

The microstructure and corrosion behaviour of the wire arc additive manufactured (WAAM) thin wall structure of AA2024 Al-alloy are investigated by means of scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive X-ray spectrometer (EDX), as well as immersion test in 3.5%NaCl solution. Three distinctive areas, including melt pool zone (MPZ), melt pool border (MPB) and heat affected zone (HAZ), were formed in the WAAM structure. S-phase, θ-phase and α-phase are present in all three zones, which could exist individually or in cluster. Localized corrosion tends to initiate at MPB rather than HAZ and MPZ, which is closely associated with the de-alloying behaviour of intermetallic (IM) particles.

In order to develop new environment-friendly corrosion inhibitors of high corrosion inhibition efficiency, longan shell carbon dots (ls-CDs) and nitrogen doped longan shell carbon dots (N-lsCDs) were synthesized by calcination and one-pot hydrothermal methods, respectively. Meantime, the structural, composition, optical property, and corrosion inhibition performance of ls-CDs and N-lsCDs were assessed by means of FT-IR, FL, XPS, TEM, electrochemical method, and static mass loss method. Results showed that when the concentration of ls-CDs and N-lsCDs was 100 and 20 mg·L^-1 in 1 mol·L^-1 HCl solution, the corresponding corrosion inhibition efficiency for Q235 steel reaches 89.49% and 92.41% respectively. Besides, the N-lsCDs present advantages, such as excellent corrosion inhibition performance in low dosage etc., and it is especially noticeable that the N-lsCDs could be produced from the longan shell as waste. The polarization curve test results showed that N-lsCDs is a mixed inhibitor, and the adsorption of N-lsCDs on the surface of carbon steel conforms to the Langmuir adsorption isotherm. Using biomass as raw material to prepare new environment-friendly corrosion inhibitor can turn waste into resources, which has attractive potential application prospects.

In order to enhance the corrosion resistance of Cu alloy to meet the requirements for their application in marine engineering equipment and facilities, a gradient composite coatings Ni/Ni-Cr/Ni-Cr-Al-Si were prepared on Cu plate by step-wise processes, i.e. firstly electrodeposited Ni film and then magnetron sputtered Ni-Cr alloy films and Ni-Cr-Al-Si alloy films in sequence. The structure and corrosion characteristics of the Ni/Ni-Cr/Ni-Cr-Al-Si gradient composite coatings with different Cr contents were characterized by means of X-ray diffractometer and electrochemical impedance spectroscope (EIS). The results show that among others, the gradient composite coating (S2 sample) with Cr content of 43.05% has the highest corrosion resistance, namely the highest low frequency impedance, capacitance arc radius, maximum phase angle, charge transfer resistance R_f and corrosion potential. The higher the atomic ratio of Al/Cr in the deposited Ni-Cr-Al-Si films is, the better the corrosive resistance of the deposited composite coating is. The corrosion process of the deposited gradient composite coating is mainly pitting corrosion, and the interface of the clusters on the surface of the films is the center of pitting corrosion. The Ni/Ni-Cr/Ni-Cr-Al-Si gradient composite coating with appropriate Cr content has good corrosion resistance in seawater and thermal conductivity, thus it is suitable as a protective coating for heat exchangers made of Cu alloys used in seawater.

The stress corrosion cracking (SCC) susceptibility of a new type of 2.25Cr1Mo steel and its weld joints was studied by means of slow strain rate tensile (SSRT) tests at a constant strain rate of 1×10^-6/s in air and steam at 0.1 MPa/500 ℃ respectively, in order to evaluate its suitability for heat exchanging pipes. The morphology of fracture surface, gage surface and cross-section were analyzed by scanning electron microscopy (SEM). The element composition of oxide scales was determined by energy spectrum analysis (EDS). Experimental results showed that the tensile strength and elongation at break of weld joints were lower than that of base metal in steam at 500 ℃, whilst the elongation at break of which in high temperature steam was higher than that in air. All specimens exhibited features of simple ductile fracture and low SCC susceptibility, cracking occurred only in the oxide scale which was near the fracture, without extending to the matrix. In addition, cracking did not occur near the fusion boundary after SSRT. In conclusion, welding had little effect on SCC susceptibility.

Oxidation behavior of nickel-based alloy Inconel617B in 700 ℃/25 MPa supercritical water was studied by means of electron balance, SEM, XRD, XPS and AFM. The results show that the oxidation kinetics of Inconel617B at 700 ℃ obeys regulation in between parabolic and straight-line law, the formed oxide scales are composed mainly of NiO, NiCr₂O₄ and Cr₂O₃, and a small amount of Ni(OH)₂, CoO and TiO₂ are also detected. The phase constituents of the formed oxide scales varied with oxidation time. The three-dimensional morphology shows that the growth of the oxide scale can be attributed to the outward diffusion of metal ions. The growth mechanism of the oxide scale of Inconel617B in supercritical water was further discussed.

This paper puts forward a mathematical model for corrosion of steel made sea-going ships that takes the effect of marine environment temperature, seawater oxygen content and relative humidity into account. The effect of random corrosion on the local bearing capacity of stiffened plate structure of the ship and the longitudinal ultimate bearing capacity of ship hull girder is analyzed by finite element analysis. The distribution of ultimate bearing capacity of ship structure after being subjected from random corrosion is summarized. Compared with the nominal marine environment, the temperature, relative humidity and seawater oxygen content in marine environment have a significant impact on the ultimate bearing capacity of the ship structure. However, the ultimate bearing capacity of the stiffened plates and hull girder obeys a normal distribution after service for the same period of years.

Corrosion behavior of high-strength Q690qE bridge steel was investigated by means of immersion-drying cyclical corrosion test (CCT) method coupled with characterization of the morphology and composition of rust, cross sectional morphology of the corroded steels and corrosion depth measurement. The results revealed that a compact rust layer can easily form in this simulated humid coastal-industrial environment, and which presents certain protection ability for the steel substrate. However, there was no enrichment of Ni/Cr and other alloy elements in the rust. Besides, there was apparent concentration of Cl^- and FeSO₄ underneath the rust layer, which may contribute to the high corrosion rate and evident corrosion pits on the steel surface. The results of power exponent fitting display that the corrosion depth (mm) and time (d) exhibits a well power function of D=0.019·t^0.7.

The corrosion characteristics of butt welds of Q690 high strength steel in the ocean splash zone was studied via laboratory simulation with a desired accelerated corrosion scheme of cyclic immersion in artificial seawater and maintenance in hot and humid chamber, in terms of the macroscopic and microscopic corrosion morphology, mass loss, pit size, and corrosion depth etc., so that to acquire the corrosion regulation of the steel. The results show that as the corrosion cycle increases, the metal luster gradually darkens, more rusts emerge on the weld joints, the formed rust rather loose with pelling off can be seen at local areas. After 100 d of corrosion, the mass loss rate of the steel is 8.46%. The observation results of laser scanning confocal microscope (LSCM) show that surface deposits can inhibit corrosion from extending along the depth direction. The corrosion process gradually transforms from needle-like corrosion spots to corrosion pits, the average depths of pits in the weld zone and heat affected zone are about 311.01 and 333.24 μm, respectively. The research results are of great significance for the durability evaluation of domestic high strength steel in marine environment.

The high temperature corrosion behavior of Sanicro 25 steel beneath deposition of artificial high-sulfur coal ash in an simulated boiler atmosphere was studied at 650 and 700 ℃ for 2000 h. Meanwhile, samples were taken out at certain intervals, cleaned and weighed, to obtain corrosion kinetics data. Further, the microstructure, element distribution and phase composition of the corrosion products were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results indicate that the corrosion rate of Sanicro 25 steel accelerated with the increasing temperature. A relative complete and dense protective oxide scale was formed on the surface of the alloy at 650 ℃, thus the alloy had good corrosion resistance. The corrosion products were composed mainly of Cr₂O₃ and Fe₂O₃. A certain degree of hot corrosion occurred at 700 ℃. The corrosion process could be divided into high temperature oxidation stage and molten sulfate accelerated corrosion stage, the later stage corresponds to molten salts induced destroy of the oxide scale, while a number of corrosion products peeled off and the alloy had obvious mass loss.

The Gd₂Zr₂O₇ ceramics, as a candidate material for making thermal barrier coating, was subjected firstly to pre-corrosion beneath deposits of CaO-MgO-Al₂O₃-SiO₂ (CMAS) powders in temperature range of 900-1300 ℃ for 0.5 h, afterwards, the pre-corroded Gd₂Zr₂O₇ ceramics were subjected to CMAS induced hot corrosion at 1250 ℃ for 3 h. Then the corroded ceramics were characterized by means of XRD, SEM and EDS in terms of the composition and phase constituent of corrosion products and cross-sectional morphology of the corroded ceramics. Results reveal that after being pre-corroded beneath CMAS deposits at 1100 ℃, the ceramics present better corrosion resistance rather than the blank ceramics during the post-corrosion beneath CMAS deposits at 1250 ℃. Which presented corrosion depth of 39.46 and 70.49 μm after CMAS induced hot corrosion at 1250 ℃ for 3 and 10 h respectively. It is proposed that during the pre-corrosion, the Gd₂Zr₂O₇ could react with the melt CMAS at 1250 ℃ to form a dense top reaction scale riched in apatite (Ca₂Gd₈(SiO₄)₆O₂), which can effectively inhibit the further penetration of CMAS during the post corrosion process induced by CMAS deposits.

The effect of RE content and cold rolling plus annealing on the microstructure and corrosion resistance of Al-Mn-RE alloy were studied by means of metallographic microscope, scanning electron microscope and electrochemical workstation. The results show that the eutectic phases with different sizes and irregular shapes can be seen in Al-Mn-xRE alloys. With the addition of different RE content, the amount of Si containing eutectic increases, the long strip-like eutectic structure was refined and gradually transformed into spherical or short rod-like structure. When RE content reaches 0.25% or more, the eutectic structure begins to coarsen. With the increase of RE content, the corrosion potential and pore size of Al-Mn-xRE alloys increase, however, the corrosion potential of Al-Mn-0.18RE alloy shifts positively and then negatively, whilst the corrosion current density decreases first and then increases. In fact, the alloy with 0.18% RE presents the maximum corrosion resistance. The corrosion potential and pitting corrosion potential of the Al-Mn-0.18RE alloys subjected to different treatments may be ranked the following order: homogenization>cold rolling+325 ℃ annealing>rolling>cold rolling +475 ℃ annealing. With the increase of RE content, the corrosion rate of the Al-Mn-xRE alloys subjected to cold rolling and annealing at 325 ℃ decreases first and then increases, and reaches the minimum value when the RE content is 0.18%. The corrosion resistance of the rolled Al-Mn-0.18RE alloy is lower than that of homogenized Al-Mn-0.18RE alloy, but the corrosion resistance can be improved by subsequent stabilization annealing at 325 ℃.

Regeneration tower bottom reboiler is the key equipment for the desulfurization and decarbonization process of sour natural gas purification unit. With the incearsing tendency in processing raw gases of inferior quality, the corrosion of the reboiler and relevant parts is becoming more serious, which not only affects the normal operation of natural gas purification plant, but also has a great safety hidden danger. In this paper, aiming at the serious leakage of tube bundles and plates of regeneration tower bottom reboiler in natural gas purification unit, the inducement mechanism and influencing factors of corrosion in reboiler were clarified through comprehensive investigation of field service conditions and information about the production process, and assissted with proper electrochemical assessment. Moreover, the feasible countermeasures were put forward to ensure long-term safe operation of the equipment to the greatest extent.

Halloysite nanotubes were modified by microwave heating, and then charged with metal corrosion inhibitor benzotriazole, while dispersed via ultrasonic vibration in a solution containing tetraethyl orthosilicate and silane coupling agent. Finally, the self-healing coating made of epoxy resin and the prepared halloysite nanotubes was applied on brass plate. The charging capacity of inhibitor into halloysite nanotubes is measured by differential thermal analysis, and the corrosion performance of the coating is assessed by electrochemical impedance method. SEM observation revealed that the surface morphology of nano halloysite nanotubes after microwave heating presented as a broken tubular structure like aggregates. The charging amount of corrosion inhibitor varied with the charging time during ultrasonic vibration. The charging efficiency of corrosion inhibitor benzotriazole for halloysite nanotubes may reach the best by ultrasonic vibration for 8 h. The electrochemical impedance increases with time for the coating/brass plate, which implies that the epoxy coating coupled with halloysite nanotubes charged with benzotriazole inhibitor has a good protective effectiveness for metal materials.