Chitosan as a natural green polymer, which bears rich hydroxyl and free amino groups, so has attracted more and more attention in the field of anti-corrosion. In this paper, the research progress of chitosan modification, chitosan and its derivatives, as well as their application as a green corrosion inhibitor are reviewed. The developing tendencies of chitosan derivatives inhibitors are prospected.

The corrosion behavior of X70 pipeline steel in the tropical juncture area of seawater-sea mud has been studied by means of wire beam electrode technique, linear polarization, electrochemical impedance spectroscopy and other electrochemical analysis technique, coupled with the methods of corrosion morphology observation and corrosion products analysis. The results show that X70 pipeline steel has formed an oxygen concentration cell in the juncture area of seawater-sea mud, the electrodes in the sea mud and in the vicinity of interface of seawater-sea mud act as anode, and the electrodes in the seawater act as cathode. In the last stage of corrosion, the electrodes in the bottom of sea mud become cathode region where the main cathode reaction is occurred. The corrosion rate of the electrodes in the seawater is greater than the electrodes in the sea mud, and there is a peak of corrosion current in the vicinity of interface of seawater-sea mud. Dissolved oxygen promotes corrosion products gradually firmly and densely, the charge transfer resistance increased with the time, sulfate reducting bacteria in the bottom of the sea mud participate in the reaction, produced iron sulfide, the corrosion rate of the whole electrodes speed up with the cathode current density increased.

The effect of pre-strain on the hydrogen embrittlement (HE) susceptibility of DP600 steel was studied by means of slow strain-rate tensile (SSRT) test, electrochemical permeation technique and fractograph observation of fracture surface. The results indicate that the HE susceptibility of DP600 steel increases with the increasing pre-strain when the level of pre-strain is below 15%, and then tends to stable when the pre-strain exceeds 15%. The pre-strain increases dislocation density and the amount of effective hydrogen in the steel, but decreases the effective diffusivity (D_eff) of hydrogen, so that the HE susceptibility increases. However, when the pre-strain increases to above 15%, the HE susceptibility gradually becomes stable due to the decrease of diffusion and aggregation of hydrogen, which resulted from the dislocation tangle.

Atmospheric exposure of carbon steels Q235 and Q450 were conducted for 4 a in dry hot atmospheric environment at Turpan district of Xinjiang Uygur Autonomous Region. The results showed that the surface of the two steels presented obvious corrosion products scale. The average corrosion rate of Q450 and Q235 was 12 and 14 g·m^-2·a^-1 respectively. Thus, Q450 steel exhibits corrosion rate lower than Q235 steel, and while the corresponding corrosion pits were relatively shallow. The corrosion products of the two steels composed mainly of α-FeOOH, γ-FeOOH and Fe₂O₃·H₂O, while the proportion of α-FeOOH for Q450 was higher than that for Q235. The corrosion products on Q450 were relatively dense. Thereby, it hindered the absorption of water and sediment, leading to the decrease of corrosion rate. The result of EIS demonstrated that the resistance of corrosion products and surface charge transfer of Q450 was greater than that of Q235, i.e. the corrosion products of Q450 had better protectiveness.

A micro-nano superhydrophobic nickel coating was prepared on 316L stainless steel in electrolyte of NiCl₂6H₂O 1 mol/L, H₃BO₃ 0.5 mol/L and ethylenediamine dihydrochloride 0.5~2.5 mol/L via a two-step electrodeposition process, namely, the first electrodeposition was performed by current density of 5 Adm^-2 for 480 s in the electrolyte with 1.5 mol/L crystallization regulator, while the second electrodeposition was conducted by current density of 10 Adm^-2 for 60 s. The prepared micro-nano superhydrophobic coating was characterized by means of surface analysis, electrochemical tests, and contact angle measurements. Results show that the micro-nano superhydrophobic coating presents typical needle-cone array structure with preferential orientation (110) plane and well superhydrophobic performance. With the increasing current density in the second electrodeposion step, the needle-cone array structure transforms gradually in petal-shaped hierarchical structure.

According to the thermal cycle process of Q690 high strength steel by narrow-gap (NG) welding, the thermal simulated NG weldings were carried out by a Gleeble 3800 thermal simulation test machine to prepare weld joints with different HAZs of Q690 high strength steel at different peak temperature in a single thermal cycle. The parameters of thermal simulated NG welding are as follows: preheat temperature of 150 ℃, peak temperature (T_p) retention time of 1 s, t_8/5 value of 14 s, with the variation of T_p as 500, 650, 850, 950 and 1350 ℃. The effect of welding parameters on the properties of Q690 high strength steel were investigated and the relationship between the micro-structural factors, mechanical properties and electrochemical behavior were discussed. The microstructure of the thermal simulated weld Q690 HSLA steel was observed by OM and SEM. The electrochemical behavior of them in a 3.5% (mass fraction) NaCl aqueous solution at room temperature was assessed by means of open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization measurement. The mechanical properties and electrochemical behavior of the Q690 steel HAZ at different T_p show a nonlinear variation with the increasing T_p, which were mainly depended on the microstructure characteristics such as the bainite transformation and grain size. The HAZ (T_p=850 ℃) has the best low temperature impact toughness, and with similar electrochemical behavior as the bare Q690 steel.

Corrosion behavior of 304L stainless steel was investigated in the liquid and steam of 2%~20% (mass fraction) nitric acids at 80~135 ℃ by coupon immersion test. The surface morphology of specimens after corrosion test and the depth of intergranular corrosion were examined by SEM and metallographic microscope, respectively. Results showed that the corrosion rate of 304L stainless steel first increased slowly and then increased sharply with the increase of temperature or nitric acid concentration. Correspondingly, the corrosion form of the steel converted from uniform corrosion to intergranular corrosion. The influence of temperature and nitric acid concentration on the corrosion of 304L stainless steel in nitric acid steam was higher than that in nitric acid solution, while the steel is more likely suffered form intergranular corrosion in nitric acid steam. The degree of intergranular corrosion in nitric acid steam was more serious than that in nitric acid solution. With the increase of corrosion, breaking and falling off of grains on the surface of 304L stainless steel occurred, resulting in thinning in thickness of the material.

Electrochemical remediation is one important method to improve the durability of the existed reinforced concrete structural parts. However, the hydrogen evolution during the reparative process restricts the applied range of electrochemical remediation. The Nernst formula indicated that the equilibrium potential of hydrogen evolution is related to reactant concentration,product concentration and temperature. Accordingly,the equilibrium potential of hydrogen evolution of rebar as a cathode during the electrochemical remediation is related to the inner environment of the concrete under repair. The rationality of measuring current density of hydrogen evolution by potentiodynamic polarization curve is demonstrated in this paper. Then the current density of hydrogen evolution of the rebar embedded in concretes with different water-cement ratio (W /C) is measured. Results indicate that the current density of hydrogen evolution is lower for the rebar embedded in the concrete with lower W /C ratio. Therefore, it is not suitable to adopt a common current density value as a specified index for the controlling of hydrogen evolution during the electrochemical remediation of different concretes.

The corrosion rate of super 13Cr stainless steel was measured by potentiodynamic polarization curves in different environments of marine oil and gas field. Then the relationship between the corrosion behavior of super 13Cr stainless steel with the concentration of Cl^-, concentration of S^2-, pH value and temperature was evaluated by means of grey relationship analysis. Results showed that the grey correlation degree of corrosion factors in the marine oil and gas environments could be ranked with a descending sequence as follows: concentration of Cl^- (0.8223)>temperature (0.7704)>pH value (0.7646)>concentration of S^2- (0.7595). The weight of the effect of each corrosion factor on the corrosion rate of super 13Cr stainless steel was analyzed by hierarchy process, which then could be ranked with a descending sequence as follows: concentration of Cl^- (0.3905)>temperature (0.2761)>pH value (0.1953)>concentration of S^2- (0.1381). The main factors of the marine oil and gas environment, which caused the corrosion failure of super 13Cr stainless steel, were the high concentration of Cl^- and high temperature.

Using differential scanning calorimetry (DSC) with heating rate of 10 K/min, the glass transition temperature T_g and the crystallization temperature T_x of the Cu-based bulk metallic glasses (BMGs) Cu_47.5Zr_47.5-xAl₅Hf_x (x=0, 9.5) were determined to be 712~722 K and 747~766 K, respectively. X-ray diffraction (XRD) analysis confirmed that Cu-based metallic glass or metallic glass-nanocrystalline composites could be obtained throu-gh annealing. The microstructure and microhardness were affected by the annealing temperature and time. When the annealing temperature was above T_g, with the increase of annealing temperature and time, the crystallinity and the microhardness gradually increased and then leveled off. Immersion tests and potentiodynamic polarization tests were carried out to investigate the corrosion behavior of the as-cast and annealed samples in 3.5%NaCl solution. Pitting was observed on the Cu_47.5Zr_47.5-xAl₅Hf_x (x=0, 9.5) samples after immersion in 3.5%NaCl solution. Compared with the as-cast samples, the samples anneal-ed at 623 K (i.e. below T_g) or at 773 K (i.e. slightly above T_x) exhibited higher corrosion potential and slightly larger corrosion current density, indicating the similar corrosion resistance of them. The samples annealed at 923 K (i.e. much higher than T_x) for 30 min exhibited much lower corrosion potential and similar corrosion current density, indicating their poorer corrosion resistance. Hf content showed minor effect on the corrosion resistance.

Oxidation reduction potential (ORP) measurement can be an effective means for maintaining the state of feedwater for power station to be oxidizing, neutral, or reducing. In order to investigate the characteristics of ORP and its correlation with metal corrosion in high temperature water, a series of experiments including electrochemical measurement and simulated corrosion experiment were carried out. The results show that the ORP increases with the increase of dissolved oxygen content, while decreases with the increase of pH and temperature. Besides the flow rate has no effect on the ORP. It follows that ORP measurements for high-temperature and -pressure waters, as compared to the ones for low-temperature ORP waters, can act as a more sensitive and accurate method to effectively detect the trace amount of dissolved oxygen. In summary, ORP measurements can be used to understand, monitor and control the corrosion of steels in feedwater.

Hot corrosion behavior of pure nickel and its joints, which were prepared by plasma arc welding (PAW) and plasma arc welding+tungsten inert gas (PAW+TIG) respectively, in molten Na₂SO₄-K₂SO₄ salts at 900 ℃ are investigated by means of weight loss measurements, X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Experimental results show that the grain size and hot corrosion resistance of the welds obtained by the two welding methods have little difference, while the corrosion resistance of the joints is inferior to that of the base metal. The hot corrosion kinetics of the specimens follow linear power laws, and the corrosion products on the base metal and joints are mainly composed of NiO and Ni₃S₂. Cross-sectional morphologies and corresponding elemental maps indicate that corrosion product composed of an outer dense scale, beneath which there existed an internal zone of oxides and sulfides. According to these results, a mechanism of synergistic oxidation and sulfidation for hot corrosion of pure nickel is confirmed. That is, the distribution of internal oxides and sulfides, located beneath the outer oxide scale , extends to the substrate. In other words, the sulfidation-oxidation cycle process and sulfur play an important role in the process of hot corrosion. So,for pure nickel welding, PAW+TIG welding method meets the requirements of the actual industrial production and application.

The exfoliation corrosion behavior of 2A02 Al-alloy plates in a simulated marine atmospheric environment was studied by means of weight loss measurement. Namely, the plates were covered with a deposit of 4 mg/cm² solid NaCl and then tested at 60 ℃ in air with 72% humidity. The microstructure and corrosion products of the alloy were characterized by SEM, XPS, LSCM,TEM and EPMA etc. Results show that in the simulated marine atmospheric environment, the corrosion process of 2A02 Al-alloy experienced the following three successive stages, i.e. pitting corrosion, intergranular corrosion and exfoliation corrosion. It seems that the second phase particles, which situated at grain boundaries, may play a key role for the initiation of pitting corrosion, while the rapid diffusion of Cl^- along grain boundaries may act as a promoting factor for intergranular corrosion.