This study was conducted to explore how varying the concentration of nano-La₂O₃ particles in the plating bath influences the morphology, constitution, and corrosion resistance of Ni-B composite coatings deposited on N80 carbon steel via electroless plating. The novelty of this work lies in the systematic investigation on the co-deposition behavior and grain refinement mechanism of nano-La₂O₃ in electroless Ni-B system, which has been rarely reported in previous studies. The microstructure and chemical composition of the coatings were characterized through a combination of SEM, EDS, XPS and XRD analyses. SEM confirmed that a dense Ni-B/La₂O₃ composite coating was formed, with a uniform thickness of approximately 10 μm, and the nano-La₂O₃ particles were evenly distributed. XPS analysis verified the presence of B, C, O, Ni and La, while XRD analysis revealed a refinement in crystalline size due to the addition of the nanoparticles. The corrosion resistance enhancement mechanism is attributed to the triple synergistic effect: nano-La₂O₃ pins grain boundaries and refines Ni-B grains to the minimum average size of 12.943 nm at the optimal concentration of 8 g·L⁻¹; the refined grain structure promotes the formation of a continuous and dense Ni(OH)₂ passive film; the uniformly dispersed nanoparticles act as physical barriers to block the penetration of corrosive media. Electrochemical measurements demonstrated that this coating exhibited outstanding anti-corrosion performance, as confirmed by a remarkably positive corrosion potential (E_corr = −0.37189 V) and a minimal corrosion current density (I_corr = 3.7524 μA/cm²). The results conclusively show that nano-La₂O₃ reinforcement effectively enhances the corrosion protection performance of electroless Ni-B alloy coatings.

The combined effect of sulfate-reducing bacteria (SRB) and a microstructure on the stress corrosion behavior of heat-affected zones (HAZs) in pipeline steel for shale gas field applications was investigated. The results show that when the peak heating temperature reached 1020 °C, a coarse microstructure formed during multiple thermal cycles (MTCs), and Widmanstätten structures appeared in the HAZ. In the simulated environment, SRB intensified localized pitting corrosion of both the base metal and the HAZ. The welding HAZ was softened by the MTCs, and significant microcrack growth was observed in the presence of SRB. Among all subzones, the coarse-grained HAZ (CGHAZ) was the most susceptible to stress corrosion cracking (SCC) under shale gas service conditions. Cracks initiated at the metal surface and propagated vertically into the material. SRB activity further increased the SCC sensitivity of the CGHAZ.

In this study, we attempted to use the response surface methodology with temperature, pH and thiourea concentration as control variables by systematically varying the experimental parameters in order to find the optimal preparation process for electroless deposition of Ni-B coatings. A mathematical model of the effect of different experimental parameters on the impedance of Ni-B coating was constructed by selecting the Box–Behnken Design (BBD) design, and the optimum plating solution temperature, pH and thiourea concentration for electroless deposition of Ni-B coating were discussed through optimization analysis. The surface microstructure of the Ni-B coating was characterized by SEM. The chemical composition of the Ni-B coating was analyzed by XRD and EDS, and the corrosion resistance of the coating was characterized by EIS and potentiodynamic polarization techniques. The results showed that the best morphology and the best corrosion resistance of the coatings were achieved when the plating solution temperature was 69.31 °C, the plating solution pH was 6.06, and the concentration of thiourea was 0.0015 g/L. The predicted impedance value was 5828.77 Ω, while the impedance value of the prepared coating based on the experimental setup parameters was 6041 Ω.

In this research, a novel polyarylene ether nitrile (PEN) coating material was fabricated through a facile stepwise polymerization method, which provides metallic substrates used in the oil industry with remarkable corrosion protection performance. A variety of characterization techniques were employed to evaluate the comprehensive properties of the PEN coating materials against a commercially established high-temperature-resistant epoxy coating. Based on the TGA curves, the PEN3 coating exhibited a T_5% value of 521 °C, which was 44.72% higher than that of the epoxy coating. According to the tensile experiment, the PEN coatings demonstrated improved mechanical performance, achieving tensile strength and breaking elongation values of 89.37 MPa and 7.14% (PEN3), respectively, while the epoxy achieved values of 18.67 MPa and 0.32%, respectively. EIS tests revealed that all the PEN coatings exhibited superior corrosion resistance compared to the epoxy coating. Among them, the PEN3 coating remained intact without failure and showed the highest impedance value (5.665 × 10⁷ Ω·cm²), which was two orders of magnitude higher than epoxy. Our research confirmed that the PEN coating material provided enhanced corrosion resistance, thermal stability and mechanical properties, positioning it as an alternative option to replace epoxy coating in prolonging the service life of steel piping in oil field applications.

A series of self-toughening benzoxazine resins containing amino-terminated polyarylene ether nitrile (APEN) segments were synthesized from bisphenol-A, paraformaldehyde, and a mixed amine source of APEN and melamine. Unlike conventional physical blending toughening, the APEN segments are covalently incorporated into the benzoxazine network via their amino end groups. This chemical integration not only significantly improves toughness but also simultaneously enhances thermal and dielectric properties, overcoming the common trade-off of “toughening without heat resistance”. Meanwhile, melamine serves as one of the amine sources; its excess amino groups can catalyze the ring-opening polymerization of benzoxazine, which helps to reduce the curing temperature. The effects of APEN content and curing temperature on the properties of the resin and glass fiber composites were studied. The incorporation of APEN optimized the crosslinked network, balancing rigid aromatic structures with flexible ether linkages. As the proportion of APEN segments increased, the thermal decomposition thresholds and char residue were notably enhanced, signifying progressively improved thermal resistance. For composite systems cured at 220 °C, flexural strength exhibited a continuous upward trend with rising APEN content, while the flexural modulus remained steadily within a range of 23–25 GPa, and the impact strength was remarkably elevated from 45 kJ/m² to values spanning 60–73 kJ/m². A further curing treatment conducted at 300 °C facilitated additional crosslinking of nitrile moieties, yielding a further enhancement in flexural strength, particularly at lower APEN contents. Fracture surface analysis confirmed the toughening effect, evidenced by the transition from smooth brittle fracture to dendritic crack patterns. In addition, the composite achieved its lowest dielectric constant of 4.2 at an APEN loading of 20 wt.% when cured at 300 °C. Overall, this investigation presented a viable and effective strategy for the design and fabrication of high-performance, self-toughened benzoxazine-based composites.

To investigate the corrosion failure of a reducing tee at a shale gas station, a failure analysis was carried out. The failed tee was made of L245N steel, with a large-diameter branch of DN 80 and a small-diameter branch of DN 25. The DN 80 branch conveyed shale gas, while the DN 25 branch served as a vent and remained closed. The tee was after approximately 20 months of service. By means of macroscopic observation, transported medium analysis, chemical composition testing of the pipe fitting, hardness testing, metallographic structure examination, and analysis of the composition and morphology of corrosion products, the corrosion failure mechanism was identified. The chemical composition and mechanical properties of the tee met the standard requirements, the inclusion content was low, and the microstructure was normal. A substantial quantity of loose, lamellar and block-like corrosion products had formed at and around the perforation. The corrosion pit regions were mainly composed of Fe, C, O, and a small amount of S. The corroded areas exhibited pitting, ring-like corrosion, and mesa attack. The corrosion products were predominantly FeCO₃, with a small amount of FeS. Comprehensive analysis indicates that the synergistic corrosion effect of carbon dioxide (CO₂) and sulfate-reducing bacteria (SRB) is the root cause of the corrosion perforation of the tee.