The China Petroleum Pipeline Engineering Co., Ltd. (CPP) is a subsidiary of the China National Petroleum Corporation and the primary builder of pipelines in China. The company has built much of the cross-country pipeline infrastructure in China and had several large-scale projects abroad.
Experimental tests and numerical simulations on tensile specimens with different geometries were carried out to investigate the ductile fracture behavior of pipeline steel under various stress states. Based on uniaxial tensile test data, the damage parameters of the MMC damage model were calibrated using a genetic-algorithm-based optimization procedure. After calibration, numerical simulations of uniaxial tensile specimens with different geometries were performed, and their fracture behavior under different stress states was studied in combination with experiments. The results show that the numerical simulations agree very well with the experimental data: the error in fracture displacement is less than 8.04%, and the average load error in the plastic regime is within 4.36%, which confirms the predictive capability of the MMC model for fracture behavior under different stress states. The significant influence of stress triaxiality and the normalized Lode angle parameter on fracture strain and failure mode is discussed. At low stress triaxiality, the material mainly exhibits shear fracture, and as the stress triaxiality increases, the fracture mode gradually transitions from shear-dominated to tension-dominated fracture. Under tension-dominated stress states, a smaller notch radius leads to higher stress triaxiality and a pronounced reduction in plastic deformation capacity. By further correlating stress paths with crack propagation trajectories and fracture morphologies, the continuous transition mechanism of X65 pipeline steel from low-triaxiality shear-dominated fracture to high-triaxiality tension-dominated fracture is revealed, demonstrating that the MMC damage model can provide a unified description of fracture modes under multiple stress paths. This study provides a reliable prediction method for the ductile fracture behavior of X65 pipeline steel and offers a reference for establishing a mapping between stress state, fracture mode, and fracture morphology of X65 pipeline steel.
Metal-organic frameworks (MOFs) are renowned for their tunable pore sizes and porosity, structural versatility, and diverse application potential. However, achieving self-supported monolithic MOFs with good crystallinity remains a significant challenge for membrane gas separation, which limits their practical applications particularly. In this study, self-supported MOFsm/polymer membranes were prepared using polymer-assisted monolithic MOFs (MOFsm), i.e., three types of self-supported MOFsm/polymer membranes-UiO-66m/PDMS, UiO-67m/PDMS and UiO-66-NH2m/PDMS were successfully prepared. A series of characterizations has demonstrated that each self-supported MOFsm/polymer membrane exhibited good crystallinity, eliminated non-selectivity defects and achieved efficient CO2/N2 separation. In addition, the self-supported MOFsm/polymer membranes still exhibit excellent gas separation performance even under high pressure conditions. This study provides a feasible new strategy for realizing monolithic MOFs in the field of membrane gas separation.
This study addresses the impact resistance design requirements for seawater and sea-sand concrete (SSC) structures in island-reef and offshore engineering. A hybrid reinforcement scheme combining glass fiber-reinforced polymer (GFRP) and stainless steel bars is investigated to leverage the corrosion resistance of FRP and the ductility of steel. Combining theoretical analysis with consideration of material strain rate effects, a tri-linear restoring force model for hybrid-reinforced beams under both static and dynamic loads was developed. Based on the experimental results, the impact process was simplified as a two-degree-of-freedom (TDOF) mass-spring model. An extensive parametric study encompassing 144 impact scenarios was conducted using the validated TDOF model. Based on the combined experimental and numerical data, empirical equations were derived for the characteristic points of the impact force time-history curve and for predicting the maximum mid-span deflection. The proposed simplified TDOF model and the associated empirical equations provide a practical and effective tool for the impact-resistant design of hybrid-reinforced SSC beams, offering significant theoretical support for the safety of marine structures.
Maintaining ultra-high vacuum (UHV) is essential for advanced technologies, where residual hydrogen can critically degrade performance. TiZrV non-evaporable getter (NEG) films are widely employed for hydrogen pumping, but require vacuum thermal activation to remove passivating surface layers and expose fresh metallic sites. However, the structural and kinetic evolution under activation and subsequent hydrogen sorption remains insufficiently understood. In this study, we combine constant-pressure hydrogen sorption measurements, multiscale surface characterization (XPS, UPS, SEM, EDS, GIXRD), and density functional theory (DFT) calculations to investigate the activation-structure-kinetics interplay in amorphous TiZrV NEG films. While the films maintain their amorphous nature post-activation, they exhibit cluster coalescence and surface carbon enrichment via thermally driven diffusion. Hydrogen sorption follows a three-stage kinetic pathway: surface-reaction-limited uptake (Stage 1), a transition regime with declining surface activity and emerging bulk diffusion (Stage 2), and bulk-diffusion-limited transport (Stage 3). DFT calculations identify Zr-Ti pairs as the most reactive dissociation sites, explaining the rapid initial uptake observed in Stage 1. These findings establish a mechanistic link between atomic-scale dissociation kinetics and macroscopic sorption behavior, providing quantitative insights and practical strategies for the design of high-performance, long-lifetime NEG coatings in UHV systems.
Mountain pipeline engineering is a critical indicator of a nation's energy infrastructure capabilities.This type of project must integrate multiple requirements, such as energy supply, engineering technology, environmental protection, and safety management, under complex geological and climatic conditions, forming a highly complex systematic engineering endeavor.Given the frequent occurrence of geological hazards in mountainous regions, pipelines are particularly vulnerable to landslides. Thus, effective disaster prevention and control measures are essential to minimize potential damage.This study investigates two landslide-induced pipeline failure events that occurred in 2017 and 2018 along the China-Myanmar natural gas pipeline (Qinglong Section, Guizhou Province). By combining geological and environmental conditions with on - site accident investigation data, and based on the finite element solid contact model, the force and deformation characteristics of the natural gas pipeline under the action of landslides are analyzed to determine the causes of the accidents. The results indicate that the deflection of the pipeline follows an approximately normal distribution when subjected to landslide forces. Stress concentrations are most pronounced in the central and boundary regions of the pipeline, making these areas highly susceptible to failure. An accumulation of soil atop the slope, where the pipeline is placed, can cause significant axial tensile stress in the pipeline. This condition can lead to brittle crack damage, especially at the pipe body or girth weld defects, resulting in gas leakage and explosion. Therefore, in subsequent maintenance operations, it is essential to prevent significant external disturbances, particularly the accumulation of large soil masses on slopes above the pipeline, to ensure long-term operational safety.
