The presence of welding reinforcement height (WRH) within oil and gas pipelines can lead to micro-turbulence in localized areas during transportation, resulting in corrosion failure. This study employed a modular reconstruction method to simulate and reconstruct X80 steel welded joints, and investigated the erosion-corrosion behavior at the WRH using wire beam microelectrode, electrochemical impedance spectroscopy, and computational fluid dynamics simulations. The results show that the galvanic current density (GCD) in the weld metal exhibits cathodic behavior, while the GCD in the base metal and heat-affected zone shows anodic behavior. The top of WRH is susceptible to corrosion failure. As the radius of WRH increases, the corrosion rate also increases. Additionally, the corrosion rate increases similarly with an increase in flow velocity. The galvanic corrosion intensity factor (g) is 0.24, and the local corrosion is moderate. This work has scientific significance in ensuring the long-term safe operation of pipelines and reducing the risk of corrosion failure.

PurposeThe purpose of this study is to characterize the galvanic corrosion behavior of a simulated X80 pipeline steel welded joint (PSWJ) reconstructed by the wire beam electrode (WBE) and numerical simulation methods.Design/methodology/approachThe galvanic corrosion of an X80 PSWJ was studied using WBE and numerical simulation methods. The microstructures of the coarse-grained heat affected zone, fine-grained heat affected zone and intercritical heat affected zone were simulated in X80 pipeline steel via Gleeble thermomechanical simulation processing.FindingsComparing the corrosion current density of coupled and isolated weld metal (WM), base metal (BM) and heat-affected zone (HAZ), the coupled WM exhibited a higher corrosion current density than isolated WM; the coupled BM and HAZ exhibited lower corrosion current densities than isolated BM and HAZ. The results exhibited that the maximum anodic galvanic current fitted the Gumbel distribution. Moreover, the numerical simulation results agreed well with the experimental data.Originality/valueThis study provides insight into corrosion evaluation of heterogeneous welded joints by a combination of experiment and simulation. The method of reconstruction of the welded joint has been proven to be a feasible approach for studying the corrosion behavior of the X80 PSWJ with high spatial resolution.

The internal-pipeline local corrosion in the welded joint region has been a widely concerning issue, particularly under the synergistic effect of high shear stress and electrochemical corrosion, which can easily result in pipeline rupture. Classical electrochemical testing techniques and wire beam microelectrode (WBE) are used to investigate the local corrosion behavior of X80 steel welded joints in a CO2-saturated NACE solution at different flow rates (velocities of 3 m/s, 5 m/s and 7 m/s), and the corrosion product composition and characteristics are analyzed via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and three-dimensional (3D) measuring laser microscopy. The results show that different welded joint zones exhibit different corrosion degrees. The heat-affected zone (HAZ) shows the worst corrosion resistance, whereas the base metal (BM) and weld metal (WM) show similar corrosion resistances. The HAZ is an anode that corrodes unsatisfactorily at high flow rates, and the enhanced wall shear stresses peel off part of the dense corrosion product film, promoting the development of local corrosion. Therefore, the HAZ zone is a weak link in the X80 steel welded joints. This study provides scientific guidelines for the corrosion protection of long-distance oil & gas pipelines.

The corrosion behavior of B10 copper–nickel alloy welded joints in seawater pipeline system was analyzed under local turbulence induced by weld residual height. The corrosion behavior was evaluated by array electrode technology, morphology and elemental characterization, and COMSOL Multiphysics simulation. The results provide a theoretical basis for the corrosion and leakage of B10 alloy in seawater pipeline under the action of turbulence. The results show that residual height-induced turbulence exhibits a significant effect on the corrosion behavior in different areas of welded joints in B10 alloy. Turbulence can damage some surfaces, causing polarity deflection followed by acceleration of corrosion, or it is easier to form a protective film to slow down corrosion. COMSOL Multiphysics results show that the shear rate and turbulent kinetic energy increase linearly with the increase in residual height and velocity. The corrosion behavior of alloy surface is influenced by controlling the mass transfer rate and surface state.

Liquid-solid two-phase flow erosion can lead to great economic losses and safety concerns in the oil & gas storage and transportation industry. The solid particle erosion on weld reinforcement height (WRH) in liquid-solid high shear flows were systematically investigated by coupling the computational fluid dynamics (CFD) and the discrete phase model (DPM) method. The effects of liquid velocity, WRH height, particle flow rate, and particle size on the particle erosion in the WRH region were analyzed. Increasing erosion rate was observed with increasing liquid velocity. The erosion rate first increased and then decreased with increasing WRH height. The increasing erosion rate was observed with both increasing particle flow rates and particle sizes. The existence of defects on the WRH surface significantly increased the maximum erosion rates. This work can provide scientific guidelines for the corrosion protection and safe operation of long-distance oil & gas pipelines.

Purpose - This study aims to improve the corrosion resistance of TA(2)-welded joints by superhydrophobic surface modification using micro-arc oxidation technology and low surface energy substance modification. Design/methodology/approach - The microstructure and chemical state of the superhydrophobic film layer were analyzed using scanning electron microscopy, energy dispersive X-ray spectroscopy, three-dimensional morphology, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. The influence of the superhydrophobic film layer on the corrosion resistance of TA(2)-welded joints was investigated using classical electrochemical testing methods. Findings - The characterization results showed that the super hydrophobic TiO2 ceramic membrane was successfully constructed on the surface of the TA2-welded joint, and the construction of the super hydrophobic film greatly improved the corrosion resistance of the TA(2)-welded joint. Originality/value - The superhydrophobic TiO2 ceramic membrane has excellent corrosion resistance. The micro nanostructure in the superhydrophobic film can intercept air to form an air layer to prevent the corrosion medium from contacting the surface, thus, improving the corrosion resistance of the sample.

Purpose - The corrosion behaviour of titanium alloy surface when fluid with different flow rates flows through welded joints with different residual heights was explored. Design/methodology/approach - The experiment uses a combination of array electrodes and simulation. Findings - It is found that when the weld reinforcement exists, the corrosion tendency of both ends of the weld metal is greater than that of other parts of the welded joint due to the influence of high turbulence kinetic energy and shear stress. The presence of weld reinforcement heights makes the fluid behind it fluctuate greatly. The passivation films of both the base metal (BM) at the rear and the heat-affected zone (HAZ) are more prone to corrosion than those of the front BM and HAZ, and the passivation film is rougher. Originality/value - The combination of test and simulation was used to explore the influence of electrochemical and hydrodynamic factors on the corrosion behaviour of titanium alloy-welded joints when welding residual height existed.

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation. In this study, a high wall shear stress (WSS) experimental setup was established to conduct the online electrochemical corrosion test. The corrosion behavior of welded joints in NACE solution was studied by electrochemical experimental methods such as electrochemical impedance spectroscopy (EIS) and wire harness microelectrode (WBE). The results show that different areas of the welded joint show different corrosion phenomena in NACE solution. The weld metal (WM) has the significantly better corrosion resistance, while the base metal (BM) and heat-affected zone (HAZ) have worst corrosion resistance than WM. The current of the WM surface was cathodic current, while the current of the BM and HAZ surface were anode currents.

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation. The welding reinforcement height (WRH) can induce locally micro-turbulent flow field, which aggravates local corrosion of welded joints. A high wall shear stress (WSS) experimental setup was established to conduct the online electrochemical corrosion test. The influence of WRH sizes on local corrosion of welded joints was studied at different flow rates. The electrochemical signals of the local corrosion of X80 welded joints at different flow rates were monitored in real time using electrochemical impedance spectroscopy and wire beam microelectrode. In addition, the corrosion products composition and properties were analyzed. The results show that the micro-turbulent flow fields induced by the WRHs can enhance ion mass transfer near the welded joints. The corrosion products on the WRH surface also present different microscopic morphologies at different flow rates. In strong flow fields, the locally enhanced WSS can peel off the dense corrosion product partially, leading to the electrochemical distribution of large cathode and small anode, which accelerates the occurrence and development processes of the local corrosion of welded joints. The scientific guidelines for the corrosion protection of long-distance oil and gas pipelines can be potentially provided.

A superhydrophobic Cu-Co coating is successfully applied to the surface of a B10 copper-nickel (Cu-Ni) alloy welded joint via electrodeposition and modification using a low-surface-energy material (stearic acid). The static water contact angle is measured to be 162.2 +/- 1 degrees, and the roll off angle is 2.1 degrees. Various techniques, including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared absorption spectroscopy are employed to characterize the chemical composition and phase structure of the samples before and after electrodeposition and modification. The corrosion resistance of the superhydrophobic samples is evaluated via electrochemical impedance spectroscopy, potentiodynamic polarization, and scanning Kelvin probe microelectrochemistry. The results indicate that the superhydrophobic coating exhibits greater charge transfer resistance, lower self-corrosion current density, and higher surface work function, thus effectively enhancing the corrosion resistance of the B10 Cu-Ni alloy welded joint. Furthermore, the micro-nano rough structure with low surface energy on the superhydrophobic sample surface traps air and forms an air layer, thereby reducing the contact between the corrosive medium and welded joint as well as minimizing corrosion. The superhydrophobic coating demonstrate thermal stability as well as excellent self-cleaning and mechanical properties, based on comprehensive testing and analysis.

Electrocoalescence is a time-saving and energy-efficient technology for dehydrating crude oil. The microscopic coalescence mechanism of nanoparticle-laden water droplet pair in the coupling of electric field and flow field was studied by molecular dynamics simulations. The present numerical results agreed well with the experimental work in the literature and the theoretical predictions. The effects of electric field strength and direction, flow field strength and type, droplet intersection angle, and multiple droplets on nanoparticle-laden droplet pair coalescence in the coupling fields were systematically discussed. The results illustrate that four coalescence modes occurred in the coupling of electric field and shearing flow field (E&S coupling fields), and the coalescence efficiencies ranked as: rolling coalescence mode > temporary coalescence mode > stretching mode > slipping mode. Electric fields dominate droplet coalescence, while flow fields enhance droplet coalescence in the coupling fields. Furthermore, parallel direction of electric field and flow field generally leads to high coalescence efficiencies. As to the multiple droplet systems, in the coupling of x-axis electric field and rotating flow field (E&R coupling fields), the coalescence efficiencies ranked as structure I > structure IV > structure III > structure II, whereas, in the y-axis E&R coupling fields, the coalescence efficiencies ranked as structure I > structure III > structure IV > structure II. Finally, the coalescence efficiencies of the E&R coupling fields were always higher than those of the E&S coupling fields. The results will be potentially valuable for optimizing the design of compact and efficient crude oil dehydrators.

Efficiency of energy conversion in magnetohydrodynamic (MHD) pumps is relatively lower compared with conventional mechanical pumps. The processes of energy conversion in an induction MHD pump are identified and the energy efficiencies of the processes are evaluated based on the numerical simulations. Two numerical models with different geometrical dimensions are built to simulate all involved processes. The results illustrate that vortices suddenly occur in the pump channel when the flow rate reduces below a critical value. The size and scale of the vortices are dependent on the modeling dimension. By analyzing the energy conversion among different forms of energy, it is demonstrated that the energy conversion is strongly correlated with the vortex flow. The appearing vortices at low flow rates result in both large Ohmic dissipation and negative power of Lorentz force, which are the main obstructions for energy transfer from the input power to the fluid pressure energy. In addition, the overall efficiency of this machine is estimated using the model containing external components (e.g., coils, stators and ducts). It is found that the energy dissipation in the external components plays an increasing role of reducing the energy efficiency with the increasing flow rate.

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in-oil emulsions. In this study, nanoparticle-laden droplet-droplet electrocoalescence behaviors under external electric fields were numerically investigated using molecular dynamics (MD) methods. Good agreement was obtained between numerical results and experimental validation work. The influences of electric field strength, droplet diameter, nanoparticle (NP) concentration, NP size, and electric frequency were systematically examined, analyzed, and discussed from the perspective of intermolecular interactions. The NPs migrated to the liquid bridge to form nanoparticle shell under electric fields, and the NP brown motion increased the breakup probabilities, leading to partial electrocoalescence, which is undesirable in oil-water separation process. As to unequal droplets (droplet pairs of 6&4 nm, 6&6 nm, and 6&8 nm), the daughter droplets were always ejected from the apex of the small droplet. The NP concentrations influence not only the film coalescence process but also the droplet approach process, and high concentrations (0.15, 0.22 and 0.29 mol L-1) resulted in partial coalescence. The NP size also played significant roles during electrocoalescence. At large NP sizes (0.86 & 1.16 nm), the electrostatic repulsion between NPs played the dominant roles in the overall system, accounting for the PC mode with increasing NP size. In addition, applying high frequency (10 & 40 GHz) AC electric fields was found to be a time-saving and high-efficiency method. The results of this work will be potentially useful for optimizing the design of compact and efficient oil-water separators.

Electrocoalescence is an energy-efficient and environmentally-friendly process for demulsifying water-in-oil emulsions, which has been extensively used in the oil and petroleum industries. In the present study, the electrocoalescence process of water droplet trains in sunflower oil under the coupling effect of non-uniform electric and laminar flow fields was experimentally investigated. The results showed that at high Ca (= a epsilon m epsilon E-0(2)/gamma) and Re (= 4 rho V-w(w)/pi mu(w)d(i)), the water train presented complex dynamic behaviors under the coupling of non-uniform electric and flow fields, and excessive large droplets were formed. In the presence of SDS, a long pearling water chain were easily formed and difficult to return to a spherical shape due to low surface tension. The electrocoalescence efficiency decreased with increasing particle concentrations ranging from 0 wt% to 1.5 wt%., and no short-circuiting occurred at a particle concentration of 2.0 wt%. The coupling of non-uniform electric and flow fields could be a promising method to facilitate phase separation. The rank order of the electrode performance is: the second group of the double mesh electrode > the first group of the double mesh electrode > mesh electrode > grid electrode. In addition, a large Re, i.e. large droplet velocity, gave rise to higher coalescence efficiency. The outcome of this work is potentially useful in the design of compact and efficient oil-water electro-dehydration devices. (C) 2021 Elsevier Ltd. All rights reserved.

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in -oil emulsions. In this paper, the coalescence behaviors of nanoparticle/surfactant/salt-laden water dro-plet pairs under direct current (DC) electric fields were investigated by molecular dynamics (MD) simu-lations. Good qualitative agreements of the present simulations and literature results were obtained. The effects of electric field strengths, surfactant concentrations, and surfactant types on the nanoparticle/sur factant/salt-laden water droplet pair electrocoalescence process were systematically examined, analyzed, and discussed. The results show that the nanoparticle-surfactant-salt synergistic effects mainly include two mechanisms, i.e., the electrostatic interactions of salt ions and surfactant head groups, and the hydro-gen bonds of the heteroatoms and water molecules. In addition, strong electric fields lead to high elec-trocoalescence speed, while weak electric fields result in high electrocoalescence efficiency. At high surfactant concentrations, viscoelastic rigidity of the interface can suppress coalescence, and the aggre-gations accumulated on the interface result in a significant steric hindrance effect, accounting for the shortest approaching and coalescing time at surfactant number around one single droplet SN = 30 in SDS systems. Regarding the influence of surfactant types, the coalescence efficiencies of the investigated surfactant systems ranked as SDS > Span-80 > Triton X-100 > CTAB. Regarding the nanoparticle-surfactant-salt synergistic effects, in ionic surfactant (CTAB and SDS) systems, the sum of SiO2- Surfactant and Surfactant-NaCl synergistic effects generally dominated the electrocoalescence process; in nonionic surfactant (Span-80 and Triton X-100) systems, the synergistic effects can be generally ranked as SiO2-Surfactant > SiO2-NaCl > Surfactant-NaCl. The results of this work will be potentially valu-able for optimizing the design of compact and efficient oil-water separators.(c) 2022 Elsevier B.V. All rights reserved.

Titanium alloy has been widely used in Marine pipeline system because of its excellent corrosion resistance. However, there are differences in microstructure and electrochemical properties because of the heterogeneous structure of the welded joint, the corrosion behavior is often different. In this paper, the corrosion behavior of TA2 titanium alloy welded joint in seawater at different temperatures was studied by traditional macro electrochemical test analysis combined with microelectrode array test and surface morphology analysis. Conventional macroscopic electrochemical analysis results show that the corrosion resistance of heat-affected zone is always the best, followed by the base metal and the weld. And the higher the temperature, the easier the formation of passivation film. The results of microelectrode array test show that the heat-affected zone is always the cathode region of the whole welded joint, and part of the cathode near the base metal region has the largest current density, which acts as the main cathode to slow down corrosion. At slightly higher temperatures, the polarity deflection will occur in the base metal zone and weld zone due to the different formation speeds of passivation film in early corrosion stage. With the prolongation of corrosion time, the base metal eventually becomes the cathode zone and the weld zone eventually becomes the anode zone.

依托现有的教师科研项目,设计了研究焊接接头多尺度腐蚀行为的综合性实验.该实验针对焊接接头这一非均匀结构的局部腐蚀问题,以微电极阵列为纽带,联用三种电化学测试方法,从三个不同尺度获取电化学信息,并进而对局部腐蚀过程进行准确解析.经典电化学测试结果表明,X80钢焊接接头的各组成部分若孤立存在,在CO2饱和的3％NaCl溶液环境中的腐蚀电流密度为WM

In seawater pipeline, the welding joint is a non-uniform structure composed of welding seam, base metal and heat affected zone. It has inhomogeneity in chemical composition, organizational structure, residual stress, etc. As local defects and high turbulence accelerate corrosion, the welding joint is often the weakest link in pipeline corrosion. Herein, the electrochemical corrosion behavior of B10 alloy welded joint in flowing seawater is studied from macroscopic and submicroscopic viewpoints using AC impedance, linear polarization, array electrode and morphological characterization. The results reveal that the corrosion rate of weld metal (WM), base metal (BM) and heat-affected zone (HAZ) decreased with the increase of time. Combined with SEM and EDS analysis, it can be seen that the increase in time led to the decomposition and accumulation of corrosion products, which gradually enhanced the corrosion resistance of welded joints. At the submicroscopic scale, WM acts as a cathode to mitigate corrosion during the later stages of high flow rate.

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-inoil emulsions. In this study, nanoparticle-laden drop-interface electrocoalescence behaviors under direct current (DC) and alternating current (AC) electric fields were numerically investigated using molecular dynamics methods. Good qualitative agreement was obtained between numerical results and experimental validation work. In this report, the influences of the electric field strength, nanoparticle concentration, and electric field frequency on the electrocoalescence process are systematically examined, analyzed, and discussed from the perspective of intermolecular interactions. The coupling of the hydration effect of ions and the strong interactions between silicon dioxide (SiO2) nanoparticles and water molecules was found to give rise to partial drop-interface electrocoalescence. The critical cone angle at which a transition from complete to partial electrocoalescence occurs was found to be 34.41 degrees. A larger water intermolecular distance and a greater tendency for partial coalescence was observed in the nanoparticle-laden (NP-laden) droplets than in a pure water drop. Compared to a DC electric field, an AC electric field tended to cause complete drop-interface electrocoalescence, and the efficiency of complete coalescence was found to increase with increasing frequencies ranging from 10 to 200 GHz (GHz). The results of this work will be potentially useful for optimizing the design of compact and efficient oil-water separators. (C) 2021 Elsevier B.V. All rights reserved.