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The purpose of this paper is to research whether microstructure varieties of zones at welded joints pose a tremendous effect on its corrosion in SC-CO₂.

The interrelation between the corrosion and microstructure of base metal (BM), fine grain heat affected zone (FHAZ), coarse grain heat affected zone and weld metal (WM) in welded of X80 steel in water saturated supercritical CO₂ was studied by using optical microscope, weight loss test, electrochemical measurements and surface analytical techniques.

The all subzones of X80 weld joints were attacked by SC-CO₂ corrosion and showed flower-like corrosion scale spots consisted of granular FeCO₃. The most severe corrosion appeared at WM due to lower proportion of ferrite to pearlite, but the slightest corrosion displayed at BM. GHAZ with larger grains and more polygonal ferrite exhibited more severe corrosion than that at BM. Due to its smaller grain, FHAZ displayed comparatively more severe corrosion to that at BM.

There exists close interrelation between the corrosion and microstructure of the welded carbon steel in water saturated supercritical CO₂.

The aims are to investigate the influence of different environmental parameters on atmospheric corrosion of carbon steel and to further emphasize the feasibility and importance of atmospheric corrosion monitor (ACM).

The experiment includes outdoor exposure test and laboratory simulation test. ACM as an electrochemical method was adopted in order to research the effects of the environmental parameters on the atmospheric corrosion of carbon steel.

The corrosion current of ACM can respond satisfactorily to the corrosion of carbon steel caused by different environmental factors, especially relative humidity. Sulfur dioxide can greatly accelerate the corrosion of carbon steel and the importance of sulfur dioxide is closely related to its concentration and relative humidity. Copper‐accelerated acetic acid salt solution is more aggressive than neutral salt solution, which may be due to sub acidity and copper ion in the former solution.

Recently, ACM seems to be ignored in the research of atmospheric corrosion when some new methods come up, but in practical applications it is a simple, direct and effective method that should be attached importance. This paper further verified the feasibility and effectiveness of ACM used in monitoring atmospheric corrosion and exploring the relationship between corrosion rate and environmental parameters.

The purpose of this study was to evaluate the grey relational analysis method as a way of determining quickly the important factors affecting the atmospheric corrosion of Q235 carbon steel in one year.

Atmospheric corrosion exposure tests on Q235 steel were carried out at seven typical test sites in China. The test period lasted one year. The corrosion rate of the Q235 test panels was determined using the weight-loss method and environmental factors were monitored and recorded by standard methods. The importance of the various environmental factors was evaluated using the grey relational analysis method.

The results obtained by the grey relational analysis method showed that the ranking order of factors affecting the corrosion of Q235 carbon steel from “slightly” to “severely” was as follows: relative humidity > dew days > SO₃ > pH value of rain > rain precipitation > temperature > rainy days > Cl− > H₂S > NO₂. Furthermore, the initial atmospheric corrosion of Q235 carbon steel was recognized as being the corrosion of the smooth surface by water medium, or acidic aqueous solution.

Materials corrosion can be defined as a grey system because corrosion has a clear outcome and complex but uncertain characteristics. The grey relational analysis method, a part of grey system theory, is an effective and quick data processing method that can be used to sort out the degree of correlation of environmental factors affecting atmospheric corrosion in terms of it being a grey system with a lot uncertain information.

The present work primarily aims to study the corrosion characterization of tubular steel API‐P110 in high H₂S containing solution with or without CO₂.

Corrosion behaviors of steel in buffered solutions containing 50 percent H₂S and various levels of CO₂ concentration were investigated via weight‐loss method, SEM and EDS. The effects of CO₂ on corrosion occurred on the metal were analyzed by electrochemical techniques.

Corrosion rates of steel decreased as the CO₂ content in H₂S/CO₂ solution increased. It was observed for the tubular steel to experience an increase in corrosion rate at concentrations 17 percent CO₂ or 34 percent CO₂ in 50 percent H₂S while when further increasing concentration of CO₂ to 50 percent the corrosion rate decreases. Increased CO₂ content in H₂S/CO₂ led to fewer anions desorbing and fewer reactants adsorbing, e.g. H+, H₂CO₃. As a result, cathodic reaction rate decreased and the amount of hydrogen absorbed decreased.

The experimental results showed that corrosion alleviated when increasing CO₂ content in high H₂S and CO₂ containing environment.

The purpose of this paper is to obtain the environmental factor, which has the greatest effect on the corrosion rate of Q235 carbon steel under thin electrolyte layer, and to analyze the effect of this factor on the corrosion morphology, corrosion products and polarization process of Q235 carbon steel.

An electrochemical device, which can be used under thin electrolyte layer is designed to measure the corrosion current in different environments. Response surface methodology (RSM) is introduced to analyze the effect of environmental factors on corrosion rate. Scanning electron microscope (SEM) and X-ray diffraction (XRD) technique are used to analyze the results. The Tafel slopes of anode and cathode in different humidity and solution are calculated by least square method.

The three environmental factors are ranked according to importance, namely, humidity, temperature and chloride ion deposition rate. In a high humidity environment, the relative content of α-FeOOH in the corrosion product is high and the relative content of β-FeOOH is low. The higher the humidity, the lower the degree of anodic blockage, whereas the degree of cathodic blockage is independent of humidity. The above experiments confirm the effectiveness and efficiency of the device, indicating it can be used for the screening of corrosive environmental factors.

In this paper, an electrochemical device under thin film is designed, which can simulate atmospheric corrosion well. Subsequent SEM and XRD confirmed the reliability of the data measured by this device. The introduction of a scientific RSM can overcome the limitations of orthogonal experiments and more specifically and intuitively analyze the effects of environmental factors on corrosion rates.

The great magnitude differences between the integral tunnel and its structure details make it impossible to numerically model and analyze the global and local seismic behavior of large-scale shield tunnels using a unified spatial scale, even with the help of supercomputers. The paper aims to present a combined equivalent & multi-scale simulation method, by which the tunnel's major mechanical properties under seismic loads can be represented by the equivalent model, and the seismic responses of the interested details can be studied efficiently by the coupled multi-scale model.

The nominal orthotropic material constants of the equivalent tunnel model are inversely determined by fitting the modal characteristics of the equivalent model with the corresponding segmental lining model. The critical sections are selected by comprehensive analyzing of the integral compression/extension and bending loads in the equivalent lining under the seismic shaking and the coupled multi-scale model containing the details of interest is solved by the mixed time explicit integration algorithm.

The combined equivalent & multi-scale simulation method is an effective and efficient way for seismic analyses of large-scale tunnels. The response of each flexible joint is related to its polar location on the lining ring, and the mixed time integration method can speed-up the calculation process for hybrid FE model with great differences in element sizes.

The orthotropic equivalent assumption is, to the best of the authors’ knowledge, for the first time, used in the 3D simulation of the shield tunnel lining, representing the rigidity discrepancies caused by the structural property.