With the development of modern industrial technology, there is an increasingly urgent need for the preparation of high-strength and high-performance coatings on the surface of traditional metal materials

High-velocity oxygen fuel (HVOF)-sprayed amorphous alloy coatings usually have advantages of a dense structure that improve their resistance to corrosion, wear, and fatigue in the substrate. The flame flow characteristics and particle behaviors during the spray process have a significant influence on the amorphous coating structure and properties. In this study, a computational fluid dynamics model is enforced to analyze the flame flow and Fe-based amorphous alloy particle behavior in an HVOF spray process. The flame flow temperature, velocity characteristics, and the Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ Fe-based amorphous alloy particles’ velocities, temperatures, flight trajectories, and mass concentration distribution characteristics are simulated. Moreover, the effects of the oxygen/fuel ratio, particle morphology parameter, particle-injection rate, and angle on the particle behavior are also investigated. Judging from the simulation results, the optimum amorphous alloy particle size varies between 20 and 30 μm, the shape factor is within the range of 0.9–1, the optimum O/F ratio is 3.4, the optimum injection angle is 45°, and the optimum injection rate is 10 m/s. With these conditions, most of the particles settled toward the centerline of the spray gun and are in a semisolid or solid state before affecting the substrate, giving the materials optimal coating structure and performance.

This paper presents a full-scale deep-water steel catenary riser fatigue test system. The proposed system can carry out fatigue tests on steel catenary risers, hoses, and subsea pipelines up to 21 m in length, ranging from 8 to 24 inches in diameter. The test system was realized by mechanical loading with loading control systems, and could carry out axial tension and compression, bending moment, torsion, and internal pressure to simulate all load types on deep-water steel catenary risers or subsea pipelines. The counterforce was sustained by a counterforce frame. Through mechanical simulation analysis, the authors determined the size of the counterforce frame and designed the connection form of the counterforce frame and loading system. According to the required loading capacity, the appropriate cylinder thickness and diameter were obtained through calculation. After the design and construction of the test system, the authors designed a fatigue test to confirm the loading capacity and accuracy of the test system. The authors performed full-scale testing to assess the fatigue performance of pipe-to-pipe mainline 5G girth welds fabricated to BS 7608. This test was designed according to the stress level of pipelines in the Lingshui 17-2 gas field, and the test results were compared with the calculation results of the S–N curve.

This study proposed a novel experimental platform to conduct dynamic loading tests of a truncated model steel catenary riser (SCR) within the touchdown zone (TDZ). The facilities of the platform, including a soil tank, a loading system, and a soil stirring system, were introduced in detail. The parameters of the test were determined through the simulation of an in situ riser. A steel pipe was adopted as the model riser, with its outer diameter equaling that of the prototype SCR. Before executing the dynamic loadings, the model riser developed its static configuration under the submerged weight and applied bending moment. Subsequently, cyclic vertical and lateral displacement loads were applied to the truncated point. The test results showed that when the vertical loading amplitude increased from 200 mm to 300 mm, the stress ranges at the front of the model riser increased by more than 100%, whereas the stress range only differed by less than 5% under different loading periods. Numerical models of the SCR were built based on the vector form intrinsic finite element (VFIFE) method. High similarities between the test and simulation results proved the reliability of the nonlinear soil model and the numerical model. During the test, a seabed trench was developed with a depth of 0.71 D and a width of 0.48 D, and its shape was similar to the in situ trench.

The applications and studies of gravity anchors in the ocean are becoming more and more extensive. Most of the research, however, has been directed toward the bearing properties of sand. Relatively less attention has been paid to the bearing properties of gravity anchors in clay. Clay is widely distributed on the seabed. The research on the bearing capacity of gravity anchors in clay is of great significance for offshore oil exploitation. Therefore, the gravity anchor was investigated by conducting reduced-scale model tests, and the bearing process of gravity anchors in clay was simulated through a 3D finite element method. Model tests and numerical simulations were used to determine the capacity curve and the V-H failure envelope of gravity anchors in clay. The simulation results and the test results are in good agreement. The failure form of the gravity anchor in clay was revealed by 3D finite element analysis. The effect of cohesion, internal friction angle, and mooring point height on bearing capacity have been studied. The influence of the height of the mooring point on the V-H failure envelope curve was explored by changing the height of the mooring point. The formula of the V-H failure envelope curve suitable for different mooring point heights was obtained.