This study investigates the effects of welding parameters and the addition of a buffer layer on the morphology, microstructure, mechanical properties, and corrosion resistance of the overlay layer during overlay welding. This paper uses Q235 steel as the base material, ER309L as the buffer layer, and ER347 as the overlay layer to conduct process experiments on overlay welding component, aiming to obtain optimal process parameters. The effects of welding line energy and weld bead overlap rate on the morphology, dimensions, and dilution rate of the overlay layer were analyzed. Furthermore, the influence of the presence or absence of the buffer layer on the microstructure, mechanical properties, and corrosion resistance of the overlay layer was investigated. The microstructure and morphology of the overlay layer were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Mechanical and electrochemical tests were also performed to evaluate the mechanical and corrosion resistance properties of ER347 stainless steel weld overlays. The results showed that the optimal process parameters were successfully obtained, which ensured sound weld bead formation while minimizing dilution. The addition of the buffer layer (ER309L) improved the bonding quality of the overlay welding component interface, reduced element dilution in the overlay layer, significantly improved hardness distribution, and reduced sudden changes in hardness in the fusion zone, thereby optimizing the mechanical properties of the ER347 stainless steel overlay layer. After adding the buffer layer, the corrosion current density decreased from 6.23 × 10⁻⁵ A·cm⁻² to 2.21 × 10⁻⁵ A·cm⁻², and the corrosion potential increased from −1.049 V to −0.973 V, effectively reducing the corrosion risk of the overlay component. This study innovatively introduced a buffer layer in the process of overlay welding austenitic stainless steel on low-carbon steel and investigated the impact of the overlay welding process on the overlay layer, thereby contributing to a comprehensive understanding of the overlay welding process from multiple perspectives.

Micro-arc oxidation (MAO) is performed on Ti-6Al-4V electron-beam-welded joints, and the microstructure, phase composition, and corrosion resistance of the joint and surface coating are investigated systematically by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), as well as electrochemical and stress corrosion analyses. SEM analyses revealed that the joint undergoes a phase transformation. The coating morphology of the joint and base materials is similar, but the joint coating is denser and thicker. XRD analyses recognize the rutile and anatase phases in the coating. Polarization and electrochemical impedance spectroscopy (EIS) corrosion tests reveal that the MAO treatment results in a decrease of two orders of magnitude in the corrosion current density of the welded joint and an increment of corrosion resistance. Stress corrosion evaluation reveals that a dense layer is exposed to protect the joint after long-term exposure to a high-stress corrosion environment. No stress corrosion-induced cracking or defects are observed in the joints, indicating the corrosion resistance of the joint has significantly improved.

Engineering practice has demonstrated that seal failure can result in severe leakage and wear, reducing the efficiency of hydraulic systems and even leading to major safety risks. Currently, analyses of the thermal aspect of seal interfaces are relatively limited, with most studies focusing on mechanical analysis. However, in actual applications, temperature has a significant impact on sealing performance. In this paper, nonlinear elastomechanics, viscous fluid mechanics, micro-contact mechanics, micro-deformation theory, and thermodynamics are coupled to establish a mixed lubrication model considering the thermal effect. The reliability of the mixed lubrication model is verified through experiments, and the temperature distribution of the oil film in the sealing area and the temperature distribution of the seal ring are simulated. Finally, the effects of the reciprocating speed, root mean square roughness, fluid medium pressure, and seal pre-compression on seal friction force and leakage are investigated. The results show that the heat generated in the sealing area accumulates at the bottom of the V-ring. Under the same conditions, compared with the instroke, the temperature-rise area of the outstroke is biased to the left and the increase in temperature is greater. In addition, the piston rod speed and the preliminary compression of the seal ring have a greater impact on the overall seal friction force and leakage. Under a lower seal pre-compression, the RMS roughness has a great influence on the leakage and friction in the outstroke, while the impact of the internal stroke is limited.

In fossil fuel and nuclear power plants, welded joints continuously experience creep-fatigue loading, which can result in premature cracking during the in-service term. To study the creep-fatigue interactive (CFI) behavior, the CFI test of P92 steel was performed with different strain rates at 823 K. Results indicate that the short cycle life is measured with the increasing strain rate. Relying on the scanning electron microscope, the fracture mechanism of P92 steel gradually changes from fatigue-dominating to creep-fatigue interactive damage with the increasing strain rate. The hardness (H), elastic modulus (E) and creep deformation were then measured by nanoindentation, and the strain rate sensitivity (m) was estimated. The relation between the degenerated mechanical properties and microstructural evaluations, i.e., enhanced grain size and nucleation of creep voids, was established, and the damage mechanism was discussed.

This study presents a systematic investigation into the influence of pulse frequency on the micro-arc oxidation (MAO) coating of AZ31B magnesium alloy following electron-beam remelting (EBR). The morphology, thickness, and corrosion resistance of the EBR-MAO composite coating were meticulously analyzed across various pulse frequencies (100 Hz, 200 Hz, 300 Hz, 400 Hz) employing scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurement techniques. The results show that as the pulse frequency escalates from 100 Hz to 400 Hz, the average thickness of the EBR-MAO composite coating diminishes from 41.1 μm to 38.5 μm, reduced by 6.7% compared to 10.4% in the MAO coating. Concurrently, the porosity exhibits a reduction from 1.93% to 1.35%, accompanied by a densification of the coating’s structure. High pulse frequencies yield coatings with enhanced smoothness and fewer defects. Notably, the corrosion resistance of the coatings demonstrates significant improvement at higher frequencies (400 Hz) compared to their lower-frequency (100 Hz) counterparts, as evidenced by a tenfold increase in corrosion current density. This research underscores the pivotal role of pulse frequency in optimizing the protective qualities of MAO coatings on magnesium alloys.

In deep oil and gas wells, sucker rod strings (SRS) frequently experience breakage and eccentric wear problems. To address this engineering challenge, this study establishes a new coupled three-dimensional (3D) mechanical-mathematical model for sucker rod strings in 3D curved wellbores. The model comprehensively considers well trajectory, rod string structure, and external excitation, analysing the influences of elastic force, inertial force, and friction force on the sucker rod micro-elements. The formulated differential equations are discretised using the central difference method to obtain the configuration of each point on SRS and the 3D distribution of stress and strain, thereby determining the eccentric wear points between the rod and tube. A numerical solution program was developed and successfully applied in the Daqing oilfield. Results from two case studies demonstrate significant improvements: for A1# well, the system efficiency increased from 16% to 20%, while for A2# well, the pump efficiency improved from 39.8% to 58.9% and system efficiency from 33.4% to 35%. The model overcomes previous limitations by considering rod torque, 3D curved tubing spatial coordinates, tubing non-anchoring effects, and forced buckling influence, providing a theoretical basis for dynamic calculations of sucker rod pumping systems in 3D curved wells.