Tianping Gu

This study focused on burn-through leakage at girth welds of mechanically lined pipe (MLP) during field service. Field failure analysis, experimental tests, and numerical simulation were combined to investigate the process parameters of seal welding and multi-pass girth butt welding. Macroscopic metallography and energy dispersive spectroscopy (EDS) of failed specimens showed that excessive welding heat input (high current) caused severe expansion of the heat-affected zone (HAZ) and significant element dilution. The results indicated that the HAZ width of the solid-wire girth weld increased markedly from 1.312 mm to 2.247 mm under high-current conditions. Meanwhile, the Fe mass fraction in the root pass sharply increased to 33.66%, while key corrosion-resistant elements such as Cr and Ni were greatly reduced, which directly led to local pitting corrosion and perforation leakage. In addition, a moving heat source model was established in Abaqus 2024 to simulate the multi-pass welding process. The results showed that strong stress concentration developed at the groove root and the interface between the backing steel pipe and corrosion-resistant liner during repeated thermal cycles. The maximum von Mises stress reached 686.56 MPa during the second butt welding pass. After final cooling, the residual hoop tensile stress and axial tensile stress at the center of the inner surface reached 500–550 MPa and 480–510 MPa, respectively. By correlating microscopic compositional evolution with the macroscopic residual stress field, this study revealed the weld failure mechanism of MLP joints. The proposed finite element method can also be used as an efficient tool to predict the effects of welding speed, current, and voltage on residual stress, providing guidance for field welding procedure optimization and pipeline structural integrity assessment.

This study investigates the thermal and residual stress development in multi-layer lined pipe welding through numerical simulation and experimental validation. The focus is on the weld overlay/liner transition region, a critical area prone to stress concentrations and fatigue crack initiation. Using finite element analysis (FEA) with the Goldak double-ellipsoidal heat source model, the research examines the temperature evolution, residual stress distribution, and deformation characteristics during the welding process. Key findings reveal that the peak temperature in the weld overlay region reaches 3045.2 °C, ensuring complete metallurgical bonding. Residual stresses are predominantly tensile near the three-phase boundary, with maximum von Mises stress observed in the base pipe at 359.30 MPa. This study also employs Response Surface Methodology (RSM) to optimize welding parameters, achieving a 20.5% reduction in residual axial stress and a 58.1% reduction in residual circumferential stress. These results provide valuable insights for optimizing welding processes, improving quality control, and enhancing the long-term reliability of bimetallic composite pipelines.

Lined pipes are widely used in oil and gas transportation systems due to their excellent corrosion resistance and cost-effectiveness. However, current design codes often oversimplify their mechanical behavior by treating them as single-layer systems, neglecting the complex interactions between the liner and outer pipes under temperature–pressure coupling. To address this gap, this study develops a finite element model for a Φ323.8 × (10 + 3) mm X60-825 lined pipe under elastic laying conditions. The model evaluates stress distribution, bonding strength, and liner deformation under varying operational conditions, including temperatures ranging from 20 °C to 80 °C and internal pressures from 0 MPa to 14 MPa. Key findings reveal that the liner pipe approaches its yield strength (241 MPa) under high-pressure conditions, with a maximum Tresca stress of 238.81 MPa, while the outer pipe reaches 286.51 MPa. Internal pressure significantly enhances bonding strength, increasing it from an initial 0.85 MPa to 11.86 MPa at 14 MPa, thereby reducing the risk of delamination. Simplified single-layer models, which ignore the liner’s pressure-bearing effect, underestimate stress interactions, resulting in a 16.63% error in outer pipe stress under extreme conditions. These results underscore the limitations of simplified models and highlight the importance of considering multi-field coupling effects in pipeline design. This study provides critical insights for optimizing laying radii and ensuring the long-term integrity of lined pipe systems. Future work should focus on experimental validation and microstructural analysis to further refine the design guidelines.

Titanium alloys are crucial in precision manufacturing due to their exceptional properties, but traditional machining methods lead to tool wear, deformation, and high costs. Conventional cooling fluids reduce heat but cause environmental issues, necessitating more sustainable solutions. Cryogenic Minimum Quantity Lubrication (CMQL) technology, using liquid nitrogen or carbon dioxide with minimal amounts of cutting fluid, offers an eco-friendly alternative that reduces machining temperatures and friction. This study tested the TC6 titanium alloy under conventional and CMQL conditions, focusing on tool wear, surface quality, and machining efficiency. Results showed that CMQL significantly decreased tool wear and surface roughness, with a 42% reduction in surface roughness during drilling and a 20–30% efficiency increase. The findings highlight CMQL’s potential to improve machining quality and efficiency while promoting environmentally friendly practices in the industry.