In this article, the research progress of the cracking mechanism of buried pipelines steel in external environment of the pipeline was firstly introduced. Then, the effect of various factors such as the material factors (alloying elements, microstructure, inclusions), environmental factors (applied potential, pH, temperature, corrosive ions), and stress factors (residual stress, load type, strain rate) on the SCC behavior and mechanism of pipeline steel was summarized in detail. After that, the development history of the relevant mechanisms of the two type pH SCC, namely high pH-SCC and near-neutral pH-SCC, have been in retrospect, it follows that the mechanism of the former is anodic dissolution (AD), but the latter is controlled by anodic dissolution and hydrogen embrittlement (AD+HE). Next, the advancement and limitations of the classical prediction model for cracks growth rate of SCC were discussed. Finally, the future research direction for SCC of buried pipelines is prospected in terms of the shortcomings related with the current research, therefore, it is expected to provide reference for the development of advanced SCC-resistant pipeline steel.
Based on the research and application of biocides in recently years, the research progress of quaternary ammonium salts biocides, guanidine biocides, heterocyclic biocides and compounds biocides used in the prevention and control of microbiologically influenced corrosion (MIC) in oil and gas fields is reviewed. The MIC induced by fungus and algae as well as the research progress of corresponding biocides are introduced. On this basis, this article summarizes the application, challenges and future development trends of biocides, providing references for the research of microbial corrosion protection and rational use of biocides.
The influence of culture medium on the growth characteristics of microorganisms and their behavior in the relevant corrosion process of materials at home and abroad was introduced in detail. First, the different types of culture media were classified. The common sources and physiological functions of the main nutrient elements were summarized. The culture media for common corrosive bacteria were also briefly described. Then, the effect of different nutrient components (such as carbon source, nitrogen source and inorganic salt components, e.g., PO43-, SO42-, Cl-, Na+, K+, Ca2+ and Fe2+) on the growth characteristics and corrosion process of bacteria was emphatically discussed. It is finally prospected that the importance of compositional optimization of culture media for the clarification of the relevant mechanism of bacteria influenced corrosion.
Zn-based materials have been adopted as candidate material of biodegradable implants and some researches give the evidence that Zn-based materials are promising as degradable scaffold. This paper will reveal the degradation behavior of Zn-xLi (x=0, 0.5%, 0.8%) alloys in artificial urine (AU). The corrosion behavior of pure Zn and Zn-xLi alloys in AU up to 28 d were investigated by means of immersion test and electrochemical approach. The results indicate that even the Zn and Zn-xLi alloys display encrustation in artificial urine, however, the encrustation degree in the present study was alleviated compared with other alloys studied previously, which seems a very encouraging phenomenon in the application for ureteral stent implantation. The corrosion products of the Zn and Zn-xLi alloys in AU was CaZn2(PO4)2·2H2O and the corresponding corrosion rate was in the range of 0.21 to 0.34 mm·a-1 for the Zn and Zn-xLi alloys after immersion for 28 d.
The 9C series Al-alloy is a kind of Al-alloy prepared by powder metallurgy technology. In order to provide a reference for the application of 9C series Al-alloy in the marine field, two grades of 9C series Al-alloy, 9C34 (extrusion forming) and 9C37 (molding forming) Al-alloy were compared with 5083 Al-alloy, especially in terms of corrosion performance. The mechanical properties of the three alloys were evaluated by tensile test and hardness test, and the effect of temperature and pH on the corrosion behavior of the alloys in different corrosive environments were comparatively investigated via salt spray tests, polarization curves measurement and electrochemical impedance spectroscopy. The results show that the strength (up to 550 MPa) and hardness (up to 130HB) of 9C Al-alloy are significantly better than that of 5083 Al-alloy. With excellent mechanical properties and high corrosion resistance, 9C series Al-alloy has obviously application prospect as corrosion-resistant structural materials.
Two Schiff base corrosion inhibitors containing phenyl groups, namely BB-S corrosion inhibitor and B-S corrosion inhibitor are synthesized, and then their corrosion inhibition behavior for the corrosion of N80 steel in 0.5% (mass fraction) HCl solution at temperatures within the range of 30~90 ℃ was assessed. The effect of temperature on the adsorption mechanism of Schiff base corrosion inhibitor was also discussed. The results show that the corrosion inhibition efficiency of corrosion inhibitors BB-S and B-S all decreases with the increasing temperature, while the corrosion inhibition efficiency of B-S is always greater than that of BB-S at different temperatures. Results of molecular dynamics and quantum chemistry calculation indicate that the decrease in corrosion inhibition efficiency of the two Schiff base corrosion inhibitors with the increasing temperature may be closely related to the larger steric hindrance of the benzene ring in the Schiff base corrosion inhibitor, molecular thermal movement, molecular adsorption configuration and frontline orbital energy. This study is of great significance for understanding the effect of temperature on the corrosion inhibition mechanism of corrosion inhibitors.
The composition and acid-solubility characteristics of corrosion products in several product oil pipelines were investigated, and the content of bacteria related to microbiologically influenced corrosion of metal materials such as sulfate reducing bacteria (SRB) and iron bacteria (IOB) in corrosion products were cultured and determined by bacterial culture method. The corrosion behavior of X60 pipeline steel in SRB-containing medium was studied by means of electrochemical polarization curve measurement, alternating impedance method, corrosion mass loss method and surface analysis technology. The results show that SRB and IOB exist in most pipeline corrosion products, and the pipeline sediments consist mainly of Fe3O4, FeS, Fe(OH)3, and Fe2O3. The results of corrosion test in a simulated solution containing product oil and SRB bacterial revealed that a large number of loose and porous corrosion products and SRB bacterial aggregation were formed on the surface of X60 steel, while the corrosion degree was more serious than that of the blank control group. Moreover, the corrosion morphology of the steel showed pitting characteristics with pit depth up to 25.1 μm/14 d.
The corrosion resistance of 304 stainless steel passivated by nitric acid in simulated concrete pore solutions was studied through the polarization curves, electrochemical impedance spectroscopy (EIS) and Mott-Schottky measurement. The results indicate that the critical Cl- concentration for the corrosion of 304 stainless steel in the simulated concrete pore solution was increased after nitric acid passivation. The bare steel and the steel subjected to passivation treatment for 0.5, 2 and 24 h presented different range of critical chloride ion concentrations, namely 0.05~0.1, 4~5, 2~4 and 1~2 mol/L, respectively. The Mott-Schottky test results show that the nitric acid passivation treatment reduces the carrier density of the passivation film and increases the stability of the film. The EIS measurement by potentiostatic polarization is suitable for detecting the critical Cl- concentration.
The stress corrosion cracking (SCC) behavior in NH4Cl solutions was studied by means of potentiodynamic polarization measurement, electrochemical impedance spectra (EIS) measurement for 316L stainless steel with microstructures corresponding with different status of the steel, including as-received, solid solution- and sensitization-treatment. The results show that 316L stainless steels exert high SCC susceptibility in NH4Cl containing environment, which increases in the order of as-received, solid solution- and sensitization-treatment. With the rising NH4Cl concentration, the stability of passive film degrades, the passive current density increases, the breakdown potential and polarization resistance decline. In particular, in the saturated NH4Cl solution, pits are prone to initiate, which leads to the occurrence of SCC. In NH4Cl solution, SCC of 316L stainless steel is dominated by anodic dissolution (AD) process, and the SCC cracks propagate transgranularly.
Walnut green husk extract (WGHE) was obtained from the raw materials of forestry and agricultural residue of walnut green husk by circulation reflux method with ethanol water solution as extractive solvent. The synergistic inhibition performance and mechanism of WGHE and potassium iodide (KI) on the corrosion of a cold rolled steel (CRS) in 1.0 mol/L citric acid (H3C6H5O7) solution were assessed by means of immersion test, potentiodynamic polarization curve measurement, and electrochemical impedance spectroscopy (EIS), as well as scanning electron microscope (SEM) and atomic force microscope (AFM). The results showed that either individual WGHE or KI was a moderate inhibitor, and the maximum inhibition efficiency was 67.4% for WGHE and 69.3% for KI respectively. When WGHE was mixed with KI, the complex could promote the inhibitive action, and the synergism parameter was higher than 1 for the solution at 20 ℃. There was a synergism between WGHE and KI, and the maximum inhibition efficiency for the mixture of 200 mg/L WGHE with 100 mg/L KI was 85.3%. No matter when WGHE was mixed with KI, the adsorption of inhibitor molecules on CRS surface obeys Langmuir isotherm. The incorporation of WGHE with KI further increases the adsorption equilibrium constant (K) up to 0.0382 L/mg，while the standard Gibbs adsorption free energy (ΔG0) shifts more negatively to -28.9 kJ/mol. Potentiodynamic curves indicate that individual WGHE or KI mainly retards the cathodic reaction, while the mixture of WGHE/KI acts as a mixed-type inhibitor. SEM and AFM microphotographs confirm that the synergistic of WGHE and KI can more efficiently alleviate the citric acid induced corrosion of the cold rolled steel.
In order to promote the application of TC4 Ti-alloy for steam turbine blades, the influence of the surface state after shot peening on the corrosion resistance of TC4 Ti-alloy was assessed. The surface morphology and roughness of the TC4 sample after shot peening were characterized by means of transmission electron microscope, energy dispersive spectrometer, laser scanning confocal microscope and X-ray diffractometer. The corrosion resistance of the bare and shot peened TC4 Ti-alloy in 3.5%NaCl solution was comparatively examined by means of potential polarization curve measurement, electrochemical impedance spectroscopy and Mott-Schottky curve measurement. The results show that the surface roughness has a greater influence on the corrosion resistance rather than the small amount of shot peening residues. The polished TC4 Ti-alloy has the lowest corrosion current density, the largest capacitive resistance arc, the least defect of passivation film and the strongest corrosion resistance. After shot peening, the passivation film formed on the surface of the TC4 Ti-alloy peened by cast steel shots is the most stable, and the corrosion resistance is relatively high. Therefore, the smooth surface helps to form a uniform passivation film and increases the corrosion resistance of the TC4 Ti-alloy in 3.5%NaCl solution.
Test pieces of 2002 duplex stainless steel composed of different proportion of phases with various amount of alloying elements were prepared by solution treatment. The effect of microstructure partition on the pitting initiation and propagation of the steel in 3.5% (mass fraction) NaCl solution were investigated by means of potentiostatic polarization, potentiodynamic scanning and surface morphology analysis. Results show that with the increase of solution treatment temperature, the main alloying elements gather to γ phase, the volume faction of α phase increases but the anti-corrosion property of the steel decreases, therewith, pitting initiates on α phase more easily. As a consequence, the pitting resistance of 2002 DSS decreases. The formed pits present lacework-like morphology, beneath the cover of a lacework there is a dish-lie pit with larger mouth opening but shallower depth. In a word, 2002 duplex stainless steel exhibits better corrosion resistance, which may be ascribed to that the formed pits on the steel surface tend preferentially to grow laterally but not deeply.
A ternary boride cermet coating was prepared on 304 stainless steel by plasma cladding technique. The microstructure and phase composition of the cladding layer were characterized by optical microscope, scanning electron microscope and X-ray diffraction. The hardness distribution of the cladding layer was measured with a micro-hardness tester, and the corrosion resistance of the cladding layer was also studied. The results showed that the boride cladding layer forms a good metallurgical bond with the 304 stainless steel, and no defects such as macro cracks and holes were found at the interface. The average microhardness of the cladding layer was 630.4 HV0.5, which was three times higher than 304 stainless steel (HV0.5≤200), effectively improving the surface hardness of 304 stainless steel. After immersion test in 10%HNO3+3%HF acidic solution for 48 h, the maximum corrosion depth ratio of the bare 304 stainless steel and the cladding layer is 77 and 9 μm respectively, so the corrosion resistance of the cladding layer is better than that of 304 stainless steel.
With the demand for continuous increment in the running speed of high-speed trains, the standards for lightweight and ride comfort requirements have also been raised. Mg-alloy has become an inevitable trend as a critical material for high-speed trains made of alloy. The effect of Ce(NO3)2 concentration as rare earth additive in silicate containing solution for sealing treatment on the performance of calcium phosphating coating of Mg-Zn-Y-Ca alloy for swing bolster were studied by means of drop test, full immersion test, electrochemical test, scanning electron microscope and XRD analysis. The results show that the sealing treatments with and without the addition of Ce(NO3)2 all can improve the structure and corrosion resistance of the coating, and the optimal addition of Ce(NO3)2 is 0.8 g/L. Correspondingly, the acquired coating has the best corrosion resistance after sealing treatment, with an average drop time of 1002 s before break down of the coating, the corrosion rate of 0.0372 mg/(cm2·h), and the corrosion current density of 4.971×10-6 A/cm2, and the coating resistance Rf is 4854 Ω·cm2. The corrosion resistance of magnesium alloy can be greatly improved through phosphating and sealing treatment, which can meet the service requirements of high-speed iron pillow beam.
The corrosion inhibition and adsorption behavior of sodium dodecyl benzene sulfonate (SDBS) in the range of 0~8.315×10-4 mol/L on Q235 steel in a simulated concrete pore fluid of 0.5 mol/L NaCl saturated Ca(OH)2 solution were studied by means of potential polarization curve measurement, Mott-Schottky curve measurement and surface morphology analysis. SDBS has a good corrosion inhibition effect on Q235 steel in the simulated concrete pore fluid, and its corrosion inhibition rate increases with the increase of SDBS concentration. The addition of 8.315×10-4 mol/L SDBS has a corrosion inhibition rate of 85.72% at room temperature, and the corrosion inhibition rate gradually decreases when the temperature rises from 298 K to 328 K.The adsorption of SDBS on the surface of Q235 steel conforms to the Langmuir adsorption isotherm. The adsorption process is a spontaneous process of exothermic and entropy increase. The adsorption of SDBS on the surface of Q235 steel is a mixed adsorption based on chemical adsorption. The adsorption film of SDBS formed on the surface of Q235 steel isolates the aggressive ions such as Cl- and inhibits the corrosion of Q235 steel.
Powders of boron nitride were non-covalently modified with dopamine, and then composite silane coatings dopped with non-covalently modified boron nitride were prepared on 40Cr alloy steel surface via socking method. The modified powder was characterized by SEM, FTIR and TGA. The corrosion resistance of silane composite film was studied by SEM, FTIR, wettability measurement and potentiodynamic polarization curve. The results showed that the polydopamine successfully coats the boron nitride particles and adheres them onto the 40Cr steel surface, the thickness of the mBN-doped silane film increased to 1.812 μm, and the surface contact angle of the mBN/BTESPT silane composite film reached 91.97°. The corrosion current density of the composite film coated steel was 9.187×10-8 A/cm2, which implies that the corrosion resistance of the composite film was about 30 times higher than that of the bare silane film, and it showed also better corrosion resistance in the neutral salt spray test. Through the physical filling and chemical bonding of silane film, mBN hindered the diffusion of corrosion medium and significantly enhanced the corrosion resistance of metal.
The atmospheric corrosion behavior of carbon steel, the main material of power transmission and transformation equipment, was studied via fled exposure in atmospheres of three different transformer substations situated at Deyang district for one year, as well as weight loss measurement, macroscopic morphology observation, SEM analysis, corrosion product analysis and electrochemical test. The results show that the average corrosion rates of carbon steel are 13.8, 23.47, and 40.18 μm/a, corresponding to the three test sites respectively. The corrosion products of carbon steel exposed in the three test sites are mainly composed of α-FeOOH, γ-FeOOH and Fe3O4, among others, the proportion of α-FeOOH is higher in the rust layer on the steel exposed in one test site，where the atmosphere is severely corrosive. The electrochemical results show that the more serious the corrosion of carbon steel is, the higher the corrosion current density and the Rct are, which indicates that the rust layer formed on the surface of carbon steel can effectively protect the steel and slow down the further corrosion of the steel substrate.
Laser remelting (LSM) was applied on cast high-Mn aluminum bronze (MAB). Then the effect of LSM on the microstructure, corrosion and cavitation erosion behavior in 3.5%NaCl solution for the cast MAB was studied via microstructure observation, electrochemical test and ultrasonic vibration cavitation test. The results showed that in comparison with the as cast bronze, the LSM bronze presents a microstructure of much finer and much homogeneously distributed crystallites, as well as a hardness of 45% higher. During electrochemical test, the LSM bronze shows more or less the same anodic and cathodic processes as that of the as cast one, however the cast bronze had a lower corrosion potential, indicating higher corrosion tendency. After cavitation erosion test in 3.5%NaCl solution for 5 h the weight loss rate of the LSM bronze was only 3/5 of that of the as cast one. Accordingly, the surface damage of the LSM bronze was much lighter with a similar damage degree everywhere, whilst the surface roughness of the LSM bronze was obviously smaller than that of the as cast one. In 3.5%NaCl solution, the synergy between corrosion and cavitation erosion deteriorated the surface damage. For both the as cast and the LSM bronze, the mechanical impact was the dominated factor for the cavitation erosion damage. For the cast bronze, the mass loss caused by the pure cavitation erosion accounted for 71.1% of the total mass loss and 50.8% for the LSM bronze.
The galvanic corrosion behavior of the couple of 5083Al-alloy and 30CrMnSiA steel in 0.05, 0.1, 0.6 and 0.85 mol/L NaCl solutions was studied by means of immersion test, corrosion morphology observation, corrosion products analysis and electrochemical measurements, while the corrosion mechanism of the galvanic couple in 0.6 mol/L NaCl solution was specially examined. The results showed that the galvanic current density of the galvanic couple in 0.1 mol/L NaCl solution was greater, while that in 0.85 mol/L NaCl solution was the lowest. In the case of 0.85 mol/L NaCl solution, the activity of Cl- was weakened and the dissolved oxygen content decreases, hence the cathode reaction rate decreases. The results of potentiodynamic polarization curve and electrochemical impedance spectroscopy measurements demonstrate that the corrosion resistance of Al-alloy decreased at first and then increased during the galvanic corrosion process, the dissolution of Al-alloy was inhibited by the corrosion products formed on its surface. The corrosion rate of the steel was low at the early stage as cathode, and then the corrosion rate increased gradually with the increase of time. After immersion for 15 d, the corrosion products of steel participated in the cathodic reaction and therewith accelerated the rate of charge transfer, resulting in a decrease in the corrosion resistance of Al-alloy and steel, while their corrosion rate increased substantially.
The corrosion characteristics of nickel-based alloys (Incoloy800, 825 and 625) in sub/supercritical water systems with the presence of sulfides were investigated using supercritical batch reactor. The surface morphology, structure and phase composition of corrosion products were characterized. The difference in corrosion behavior for the three alloys were assessed in terms of the effect of temperature and elemental composition of alloys. It is found that the nickel-based alloy with lower Ni/Cr ratio had better corrosion resistance. For Incoloy800 alloy with Ni/Cr ratio of 1.5, the Ni and Cr mainly converted into dense spinel phase NiCrO4 which could protect the substrate from corrosion. With regarding to Incoloy825 and 625 alloys, whose Ni/Cr ratios respectively were 2 and 3, the corrosion scale of Incoloy825 alloy in supercritical water was 4.26 μm in thickness, while duplex scales with outer portion of metal sulfide and inner portion of metal oxides were formed for Inconel625 alloy. However, surplus Ni generated loose NiS phase, giving rise to significant corrosion for these two alloys.
The corrosion behavior of high nitrogen austenitic stainless steel in liquid LBE saturated with oxygen at 400 ℃, by different relative flow velocity (0, 0.92, 1.27, 1.61 and 2.01 m/s) for 1000 h was studied by means of SEM with EDS and XRD. The results show that the relative flow velocity may affect the corrosion mechanism of the steel. For static samples, the initial formed oxide scale on the steel surface can effectively prevent further oxidation of high nitrogen steel; for dynamic samples, the initial oxide scale on the steel surface is destroyed, and the coexistence of oxidizing corrosion and dissolving corrosion may occur. When the relative flow velocity increases from 0 to 0.92 m/s, the damage of the initial oxide scale leads to diffusion oxidation of the steel beneath the scale, but the process is mainly oxidizing corrosion; when the relative flow rate increases from 0.92 to 2.01 m/s, alloying elements, which migrate outwards to the surface, will be removed in time at a higher relative flow velocity, thereby the proportion of dissolving corrosion increases, and the oxidizing corrosion decreases gradually. The oxidizing corrosion products composited of oxide particles with double-layered structure, the outer layer is porous Fe3O4, and the inner layer is (Fe,Cr)3O4.
MAO (Micro-arc oxidation) films on TC4 Ti-alloy was prepared, and which then subjected to different post-treatments such as silanization sealing and high temperature oxidation. The MAO/TC4 Ti-alloy before and after post-treatments was characterized by SEM and electrochemical workstation in terms of their surface morphology and performance in galvanic corrosion. The results shows that the surface morphology of the micro-arc oxide film is not significantly changed by high temperature oxidation. TC4 Ti-alloy can easily be suffered from galvanic corrosion when contacting with steel, while the galvanic current density and galvanic corrosion sensitivity of TC4 Ti-alloy couple can be reduced after micro-arc oxidation treatment. The galvanic current density of MAO/TC4 Ti-alloy couple is little affected by silanization sealing treatment, but it is obviously reduced by combined treatments of high temperature oxidation and then silanization sealing.
