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In recent years, the demand for oil and gas pipelines has increased rapidly. Due to the restrictions of the pipeline routing, pipelines are generally laid in parallel or in the same trench, which results in stray-current interference between the independent cathodic protection (CP) systems. The purpose of this paper is to study the interference between the long-distance parallel pipelines and to obtain the optimized operation for the CP systems.

In this study, first, the numerical model of parallel pipelines was established using the boundary element analysis software (BEASY). Second, the effects of horizontal distance between parallel pipelines, coating damage rate, soil conductivity and anode output current on the interference of parallel pipelines were studied. Finally, by varying the layout or the output currents of CP stations, an optimized operation scheme osf long-distance parallel pipelines was put forward.

Simulation results showed that with a decrease in soil conductivity or coating damage rate, the interference increased. Moreover, the interference decreased with an increase in horizontal distance between two parallel pipelines or a decrease in anode output current. It was found that there are three methods to reduce the interference between long-distance parallel pipelines: to reduce the output currents of CP stations, combined protection and to close part of the CP stations. Among them, to close part of CP stations was the optimized scheme because of the lowest operating and maintenance cost.

The optimized operation scheme proposed in this study can not only solve the interference between parallel pipelines but also provide guidance for the parallel pipelines to be built in the future. Reasonably arranging the cathodic protection stations using numerical simulation can avoid the interference in the cathodic protection systems, and reduce the construction cost.

The purpose of this paper is to quantify the influence of alternating current (AC) interference on hydrogen evolution reaction of X80 steel.

The hydrogen evolution potential was obtained by cathodic potentiodynamic polarization curve. The instantaneous potential under AC interference was obtained by high-frequency acquisition with three-electrode system. Electrochemical impedance spectroscopy and Tafel polarization curves were used to study the influence mechanism of AC interference on instantaneous potential.

It was concluded that the hydrogen evolution reaction could occur on X80 steel under AC interference. There were critical AC current densities of about 100 to 200 A/m2, beyond which the cathode reaction of X80 steel changed from oxygen absorption to hydrogen evolution. Besides the pH value, the initial polarization potential EZ and impedance module of the steel/electrolyte interface under AC interference were also the factors that affected the critical AC densities in different solutions.

This research quantified the hydrogen evolution capacity of X80 steel under AC interference, which could be applied to clear the effect of AC interference on hydrogen evolution reaction.

The purpose of this paper is to study the corrosion behaviors of X70 steel under direct current (DC) interference at 0-1,200 A/m² in simulated soil solution.

The Tafel polarization curves of X70 steel under DC interference were tested using electrochemical method, the corrosion rate was calculated using weight-loss method and the change in steel surface was analyzed by optical microscopy.

The results showed that E-I polarization curves under 200-1,200 A/m² interference were linear; with an increase in the DC density, the corrosion potential of X70 steel shifted positively, solution pH after the weight-loss tests increased and corrosion rate increased linearly. A mathematical relationship between polarization resistance Rp and current density was established. Corrosion morphology indicated that pitting corrosion and crevice corrosion occurred on the X70 steel under DC interference in simulated soil solution.

All tests were conducted at a relative higher DC density (200-1,200 A/m²). The linear fitting method is proposed to fit data of Tafel polarization curves under DC interference. This study provides guidelines for safe operation of X70 steel pipelines.

Alternating current (AC) corrosion is a type of corrosion that occurs in buried pipelines under AC stray current interference, which can increase the hydrogen embrittlement sensitivity of pipelines. However, rare research works have been conducted on the hydrogen permeability characteristics of pipeline steel under AC stray current interference. The purpose of this paper is to study hydrogen permeation behavior of X80 steel under AC stray current interference.

In this paper, the hydrogen permeation behavior of X80 steel under AC interference is studied by AC hydrogen charging experiment in a dual electrolytic cell. The relationship between hydrogen evolution rate and hydrogen permeation flux is studied using the gas collection method. The difference between AC hydrogen permeability and direct current (DC) hydrogen permeability is also discussed.

The anodic dissolution caused by AC corrosion promotes the chemical desorption reaction of the adsorbed hydrogen atoms on the surface, reducing the hydrogen atom absorption ratio by 70%. When the AC is smaller than 150░ A/m², the hydrogen permeation process is controlled by the hydrogen atom generation rate, and the hydrogen permeation flux increases with the increase in hydrogen atom generation rate. When the AC exceeds 400░ A/m², the hydrogen permeation process is controlled by the absorption ratio. The hydrogen permeation flux decreases with the decrease in the absorption ratio. Under AC interference, there is a maximum hydrogen permeation flux that linearly correlates to the H⁺ concentration in the solutions.

The high-strength steel is very sensitive to hydrogen embrittlement, and X80 steel has been widely used in oil and gas pipelines. To date, no research has been conducted on the hydrogen permeation behavior of pipeline steel under AC interference, and the hydrogen permeability characteristics of pipeline steel under AC interference are not clear. The research results of this paper are of great significance for ensuring the intrinsic safety of high-strength pipelines under AC stray current interference.

The purpose of this paper is to investigate the corrosion behavior of X65 steel in the CO₂-saturated oil/water environment using mass loss method, potentiodynamic polarization technique and characterization of the corroded surface techniques.

The weight loss analysis, electrochemical study and surface investigation were carried out on X65 steel that had been immersed in the CO₂/oil/water corrosive medium to understand the corrosion behavior of gathering and transportation pipeline steel. The weight loss tests were carried out in a 3 L autoclave, and effects of water cut and temperature on the CO₂ corrosion rate of X65 steel were studied. Electrochemical studies were carried out in a three-electrode electrochemical cell with the test temperature was 60°C, and the CO₂ partial pressure was 1 atm by recording open circuit potential/time and potentiodynamic polarization characteristics. The surface and cross-sectional morphologies of corrosion product scales were characterized using scanning electron microscopy. The phases of corrosion product scales were investigated using x-ray diffraction.

The results showed that due to the wetting and adsorption of crude oil, the corrosion morphology of X65 steel changed under different water cuts. When the water cut of crude oil was 40-50 per cent, uniform corrosion occurred on the steel surface, accompanied by local pitting. While the water cut was 70-80 per cent, the resulting corrosion product scales were thick, loose and partial shedding caused platform corrosion. When the water cut was 90 per cent, the damaged area of platform corrosion was enlarged. Crude oil can hinder the corrosion scales from being dissolved by the corrosive medium, and change dimension and accumulation pattern of the crystal grain, thickness and structure of the corrosion scales. Under the corrosion inhibition effect of crude oil, the temperature sensitive point of X65 steel corrosion process moved to low temperature, appeared at about 50°C, lower corrosion rate interval was broadened and the corrosion resistance of X65 steel was enhanced.

The results can be helpful in selecting the applicable corrosion inhibitors and targeted anti-corrosion measures for CO₂-saturated oil/water corrosive environment.

The purpose of this paper was to investigate the corrosion behavior of X65 steel in the CO₂/oil/water environment using mass loss method, potentiodynamic polarization technique and characterization of the corroded surface techniques.

The weight loss analysis, electrochemical study and surface investigation were carried out on X65 steel that had been immersed in the CO₂/oil/water corrosive medium to understand the corrosion behavior of gathering pipeline steel. The weight loss tests were carried out in a 3L autoclave, and effects of flow velocity, CO₂ partial pressure and water cut on the CO₂ corrosion rate of X65 steel were studied. Electrochemical studies were carried out in a three-electrode electrochemical cell with the test temperature of 60°C and CO₂ partial pressure of 1 atm by recording open circuit potential/time and potentiodynamic polarization characteristics. The surface and cross-sectional morphologies of corrosion product scales were characterized using scanning electron microscopy. The phases of corrosion product scales were investigated using X-ray diffraction.

The results showed that corrosion rates of X65 steel both increased at first and then decreased with the increase of flow velocity and CO₂ partial pressure, and there were critical velocity and critical pressure in the simulated corrosive environment, below the critical value, the corrosion products formed on the steel surface were loose, porous and unstable, higher than the critical value, the corrosion product ?lms were dense, strong adhesion, and had a certain protective effect. Meanwhile, when the flow velocity exceeded the critical value, oil film could be adsorbed on the steel surface more evenly, corrosion reaction active points were reduced and the steel matrix was protected from being corroded and crude oil played a role of inhibitor, thus it influenced the corrosion rate. Above the critical CO₂ partial pressure, the solubility of CO₂ in crude oil increased, the viscosity of crude oil decreased and its fluidity became better, so that the probability of oil film adsorption increased, these factors led to the corrosion inhibition of X65 steel reinforced. The corrosion characteristics of gathering pipeline steel in the corrosive environment containing CO₂ would change due to the presence of crude oil.

The results can be helpful in selecting the suitable corrosion inhibitors and targeted anti-corrosion measures for CO₂/oil/water corrosive environment.

This paper aims to study the corrosion behavior of D32 steel suffered to marine splash zone. Type D32 structural steel has good mechanical properties and is commonly used for offshore oil platform construction in China. To ensure the safety of marine steel structure, it is important to study the corrosion process of D32 steel in the splash zone.

The corrosion behavior of D32 steel in splash zone environments was studied using polarization curves and electrochemical impedance spectroscopy. The electrochemical results were obtained from the corroded steel samples exposed in the splash zone of a bespoke simulate device, while corrosion morphologies and corrosion products of the steel samples were characterized using scanning electron microscopy and X-ray diffraction.

In wet–dry cyclic exposure, the reaction was a self-perpetuating process of chemical oxidation and electrochemical reduction. The rust itself took part in the reduction processes and, hence, increased the corrosion rate of the steel samples.

Finally, the corrosion process of D32 steel in splash zone is considered.

The purpose of this paper is to study some evolving mechanisms for producing weighted networks, as well as to analyze the statistical properties of the networks.

A simple one‐parameter evolution model of weighted networks is proposed, in which the topological growth combines with the variation of weights. Based on weight‐driven dynamics, the model can generate scale‐free distributions of the degree, node strength and edge weight, as confirmed in many real networks.

The exponent of the edge weight can be widely tuned. The unique parameter p controls the edge weight dynamical growth. The authors also obtain the non‐trivial weighted clustering coefficient and the weighted average to the nearest neighbors' degree.

Accessibility and availability of data are the main limitations which apply to the figures.

The new evolving networks method may be beneficial for understanding real networks.

The paper proposes a new approach of explaining the evolving mechanisms of the real networks.

This study aims to link environmental disclosure quality (EDQ) to firm performance and examine the moderating role of board independence in this relationship.

Drawing on agency theory and stakeholder theory, the authors developed and tested hypotheses using original survey data from 720 firm-year observations collected from 120 Iranian companies over six years between 2011 and 2016. In this paper, they conducted static and dynamic panel data analysis.

After correcting for endogeneity bias, the results showed that there is a significant positive relationship between EDQ and firm performance. The results also showed that board independence significantly reinforces the positive effect of EDQ on performance, and firms with more independent board members are involved environmental disclosure for improved performance. This is consistent with agency theory, which posits that a more independent board of directors can better monitor the CEO and reduce incentives for pursuing personal interests, which in turn improves performance. The results are robust after performing sensitivity tests.

This paper takes the perspective of corporate governance to empirically examine the effect of EDQ on firm performance. This study makes a contribution to the literature by showing that board independence moderates the effects of EDQ on firm performance.

The evidence supports the emphasis that recent policy statements have put on increasing the number of independent directors on corporate boards. This study offers insights to policymakers interested in enhancing the monitoring role of corporate boards.

The study adds value to the understanding of the effect of the EDQ on performance and how board independence influences this relationship, particularly in an emerging economy like Iran.