ObjectiveTraditional rapid evaluation methods for small-hole leakage on the sidewall of cylindrical tanks often assume a constant discharge coefficient. This leads to significant deviations under small-aperture and low-Reynolds-number conditions. To improve the evaluation accuracy of leakage flow rate, drainage duration and liquid level state, this study develops an evaluation method for leakage parameters to support emergency rapid assessment during the initial stage of accidents. MethodsAn experimental apparatus was set up to simulate small-hole leakage on the sidewall of atmospheric cylindrical tanks. Using tap water as the test medium, variable liquid-level leakage experiments were systematically conducted across eight different aperture sizes. Key data—including leakage flow rate, drainage duration, and jet range—were acquired, with the experimental Reynolds number ranging from 4.0×103 to 2.5×104. On this basis, the dynamic variations of the discharge coefficient with respect to aperture size and Reynolds number were analyzed, and a discharge coefficient correction model was established and integrated into the drainage process calculations. Finally, a Multilayer Perceptron (MLP)-based jet range prediction model and a liquid level inversion model were constructed using aperture size, liquid level, and effective head as input variables. Cross-validation was adopted to verify the generalization ability of the models, enabling rapid inversion of the internal tank state based on external leakage characteristics. ResultsWithin the 3–10 mm aperture range, the discharge coefficient was not constant but was jointly influenced by orifice geometric features and the Reynolds number. For small apertures (3–4 mm), the mean discharge coefficient was approximately 0.885, which was 36％–45％ higher than the mean value (0.61–0.65) of the classic sharp-edged orifice theory. After adopting the corrected discharge coefficient, the prediction error for drainage duration within the effective inversion interval (liquid level: 200–500 mm) for small apertures (3–4 mm) decreased from roughly 33％–37％ to less than 2％. Throughout the entire drainage process, drainage duration decreased following a power-law trend as aperture size increased, yielding a fitting exponent of −1.954 and a coefficient of determination R2 of 0.999 8. The R2 of the jet range prediction model reached 0.983. In the small-aperture sensitive region, the Mean Absolute Percentage Error (MAPE) was reduced from the traditional theoretical range of 11％–18％ to 1.5％–3.5％. The overall MAPE of the liquid level inversion model was 1.91％. ConclusionThis study develops a rapid evaluation framework for small-hole leakage on the sidewall of cylindrical tanks, comprising three modules: discharge coefficient correction, jet range prediction, and liquid level inversion. The framework collaboratively outputs key parameters including leakage flow rate, residual liquid level, drainage duration, and impact distance. Applicable to low-viscosity, single-phase liquid leakage under atmospheric pressure, this method provides a technical reference for rapid emergency decision-making and digital safety assessments during the initial stage of leakage accidents.
ObjectiveThe formation of hydrogen atoms on the surface of hydrogen pipeline steel serves as the critical link between the external hydrogen environment and internal hydrogen-induced damage. While existing research predominantly concentrate on hydrogen diffusion, hydrogen trapping, and macroscopic mechanical property degradation, systematic reviews regarding the dissociative adsorption of hydrogen on pipeline steel surfaces remain insufficient, which fails to supply direct theoretical basis for safety assessment of operational hydrogen pipelines. MethodsCentering on of the dissociative adsorption of hydrogen, recent research regarding gaseous hydrogen embrittlement and hydrogen behavior in pipeline steel was summarized across three dimensions: theoretical foundations, experimental testing, and numerical simulations. The application scopes of multiple methodologies were systematically compared, including surface characterization, hydrogen permeation testing, densityfunctional theory, ab initio molecular dynamics, and the finite element method. Furthermore, influencing factors such as surface states, corrosion product films and passive films, impurity gases, alloying elements, temperature, and stress were integrated into a unified analytical framework. ResultsStatistical analysis indicated that in the field of gaseous hydrogen embrittlement, studies on macroscopic mechanical properties and hydrogen embrittlement mechanisms accounted for approximately 72％, those on hydrogen diffusion in steel accounted for roughly 15％, and only around 8％ directly addressed surface dissociative adsorption—revealing insufficient research on this initial process. Comparative analysis of typical numerical simulation methods revealed that density functional theory was applicable to analyzing stable adsorption sites, adsorption energy, and dissociation energy barriers at a scale of 0.1–10.0 nm. Ab initio molecular dynamics described dynamic interfacial processes at finite temperatures for scales of 0.1–20.0 nm, though it was limited by system size and time scale. The finite element method could reach micrometer scales and even component scales, but it relied on atomic-scale input parameters. Experimental results further demonstrated that surface roughness, grain boundaries, dislocation emergences, and inclusion interfaces increased local active site density. The integrity and compactness of corrosion product films/passive films significantly affect hydrogen ingress, and compact films generally show a hydrogen-barrier effect, gas impurities introduced distinct chemical behaviors: O2 and CO primarily induced competitive adsorption and surface poisoning, CO2 exhibited environment-dependent characteristics, and H2S tended to facilitate the ingress of atomic hydrogen into the steel matrix. ConclusionThe dissociative adsorption of hydrogen on pipeline steel surfaces should not be regarded as an isolated surface reaction, but rather as the starting point of the entire degradation sequence: surface hydrogen generation – interfacial hydrogen ingress – bulk hydrogen diffusion – hydrogen trapping and enrichment – damage evolution. Future research should focus on in-situ characterization under high-pressure gas phases, standardized gaseous hydrogen permeation testing, and multi-scale coupling models to provide quantitative benchmarks for material selection, gas quality management, and the safety evaluation of in-service hydrogen pipelines.
ObjectiveDriven by the accelerating global transition toward a diversified, low-carbon energy structure, the need for intensive pipeline utilization continues to rise. Pipeline engineering is consequently shifting from traditional oil and gas transportation to a new paradigm involving various media, including carbon- and hydrogen-based energy, chemicals, pastes, slurries, and capsules (collectively termed “novel media”). These systems operate under complex conditions spanning onshore areas, deep-sea and extraterrestrial environments. In turn, the unique physicochemical properties of novel media, paired with harsh operating environments, pose major challenges to pipeline design, material selection, operational control, and safety assurance. MethodsThis paper systematically reviews the development status of key pipeline transportation technologies under complex operating conditions in China from both internal conditions (e.g., temperature and pressure) and external service environments. The review aligns with national strategies of building “a country with strong transportation network” and ensuring national energy security. Representative technical routes and engineering practices are summarized across multiple domains. These include thermal insulation for extreme-temperature pipelines, material development and fracture control for supercritical/dense-phase CO2 pipelines, material compatibility for high-pressure hydrogen pipelines, and corrosion protection and integrity management for deep-sea and deep underground pipelines. They also cover the pipeline transportation of pastes, slurries, hydrogen-based energy, and capsules. ResultsDeficiencies are identified in existing studies regarding the modeling of multi-physics coupling mechanisms, the evolution of material degradation and failure, and the adaptability of current standard systems. ConclusionGoing foward, it is essential to establish a comprehensive standard system covering the entire lifecycle of pipelines (planning, design, operation, and maintenance), to develop pipeline operation and control technologies based on multi-physics coupling modeling, and to refine pipeline integrity management frameworks tailored to complex operating conditions. Simultaneously, the research, development and application of novel materials and equipment should be accelerated. These efforts aim to construct an intelligent operational management system characterized by coordinated substance-energy transmission, extreme-environment accessibility, security resilience, and multi-network integration. This system will support the safe, efficient, and large-scale development of pipelines for novel media, safeguard national energy and strategic material transportation, facilitate the establishment of a modern energy system, and advance national maritime and aerospace strategies.
ObjectivePermanent ground displacement from strike-slip faults poses a serious threat to buried oil and gas pipelines. It can induce local plastic deformation that leads to tensile fracture or buckling failure, thereby compromising pipeline structural integrity. Accurate prediction of pipeline deformation under strike-slip fault displacement is therefore essential. Existing analytical methods struggle to capture the nonlinear interaction between pipelines and surrounding soil and the elastic–plastic behavior of the pipes. Finite element modeling (FEM) is complex and often fails to strike an effective balance between computational accuracy and efficiency. MethodsTaking into account shortcomings of previous research, a method for solving pipeline deformation under strike-slip fault displacement based on a Physics-Informed Neural Network (PINN) is proposed. A Deep Neural Network (DNN) is constructed to map axial and lateral pipeline displacements within the axial spatial coordinates of pipelines. Using the principle of virtual work and the Green–Lagrange strain measure, a nonlinear soilspring model simulates axial and lateral nonlinear interactions between pipelines and the surrounding soil, while a linear-hardening constitutive model characterizes the pipe’s nonlinear material behavior. A physics-informed loss function is formulated to express pipeline deformation under strike-slip fault displacement. A boundary condition loss function is established, further integrating mechanical characteristics of pipelines under fault displacement and enforcing Dirichlet boundary conditions. The combined formulation enables high-precision prediction of pipeline deformation under strike-slip fault displacement. ResultsIn a case study based on a 1,016 mm pipeline section crossing a strike-slip fault zone, the PINN calculation results for crossing angles of 30°, 45°, 60°, 75°, and 90° under a fault displacement of 2.5 m were compared with the reference values from FEM calculations and found to be closely aligned. Subsequent quantitative error analysis yielded the following ranges of mean squared errors (MSE) for the PINN calculations: 3.82×10−7–1.85×10−6 for axial displacement and 1.73×10−6–6.18×10−6 for lateral displacement. For strain metrics derived from the PINN results, the axial tensile-strain MSE ranged from 1.20×10−10–6.06×10−9, and axial bending-strain MSE ranged from 8.01×10−10–2.73×10−8. To broaden the comparison conditions, comparisons were also made with international representative methods for solving peak pipeline strain under strike-slip fault displacement. Results showed that the PINN results remained consistent with the FEM results under different load conditions, with an average relative error of 2.88％, demonstrating its significant superiority to other methods for solving peak strain. ConclusionThe proposed PINN method exhibits significant advantages in computational efficiency and accuracy, providing a new approach to maintaining pipeline structural integrity under fault displacement.
ObjectiveAgainst the backdrop of the “dual carbon” goals, methanol holds significant potential as a clean liquid fuel and hydrogen carrierfor large-scale pipeline transport. Given the high investment costs and long construction cycles of dedicated pipelines, batch transportation of methanol via existing product oil pipelines offers a practical alternative. Nevertheless, methanol differs substantially from gasoline and diesel in physical properties and miscibility, and its mixing dynamics during batch transportation remain unclear, necessitating systematic research under engineering-scale conditions. MethodsWith reference to mixing dynamics in conventional gasoline and diesel batch transportation, this research was conducted through miscibility tests and pilot-scale flow experiments. The miscibility characteristics between methanol and gasoline/diesel, alongside their effects on product oil quality, were analyzed. A self-built pilot-scale test loop was adopted to carry out batch transportation tests for methanol-gasoline and methanol-diesel under turbulent flow. Tests were performed across different flow velocities, transportation sequences, and transportation distances. Combined with visual observations through transparent pipeline segments and data from online densimeters, the mixed oil concentration distribution and axial development of mixed oil length were quantitatively characterized. ResultsThe test results indicated that methanol and gasoline exhibited good miscibility. During batch transportation, the mixed oil section maintained high transparency, and the concentration changed continuously along the pipeline axis, showing marked similarities with traditional gasoline-diesel mixing dynamics. Within the investigated operating conditions, the mixed oil length of the methanol-gasoline system decreased with increasing flow velocity, whereas the transportation sequence exerted only a minor influence. In contrast, methanol and diesel exhibited poor miscibility and distinct physical properties. Longer mixed oil sections and pronounced tailing characteristics were observed during their batch transportation, making the mixed oil length more sensitive to the transportation sequence. Although increasing the flow velocity suppressed the mixed oil growth rate, it failed to completely eliminate the mixed oil expansion caused by poor miscibility and viscosity differences. ConclusionThe mixing dynamics of methanol-gasoline batch transportation can draw on the operational experience of traditional gasoline-diesel systems, rendering this mode technically feasible for engineering applications under properly controlled flow velocities. Conversely, the batch transportation of methanol and diesel involves a more complex mixing process. Consequently, process design should prioritize the selection of the transportation sequence, optimization of operating parameters, and formulation of mixed oil cutting strategies. These research findings provide a valuable reference for engineering tests and operational optimization of methanol batch transportation in existing product oil pipelines.
ObjectiveNatural gas pipeline networks serve as the core hubs of the natural gas supply chain, and their operational objective is to ensure safe, stable, and efficient transmission while meeting established gas delivery targets. While complex network topologies offer multiple feasible routing and flow allocation schemes, current research focuses heavily on economic optimization. Consequently, there remains a critical gap in evaluating system reliability—the network’s capacity to consistently fulfill transmission requirements. MethodsTo address the aforementioned issue, an optimization method for flow allocation in natural gas pipeline networks considering system reliability was proposed. First, a system reliability evaluation method for flow allocation schemes was established. At the unit level, a reliability model for pipeline segments was constructed based on operating pressure variations to quantitatively assess reliability under different schemes. At the system level, the reliability block diagram method was adopted to characterize overall network reliability, establishing an evaluation model spanning operating states, unit reliability, and system reliability. Second, a flow allocation optimization model was developed to maximize system reliability. Within a unified framework—constrained by flow conservation, pressure boundaries, hydraulic conditions, and operational limits—pipeline flow rates, flow directions, node pressures, and delivery tasks were integrated to achieve coupled optimization of operating variables and system reliability. Finally, to address the model’s high nonlinearity, non-convexity, and implicit objective function, a staged decoupling solution method was introduced. Model solution was achieved through candidate scheme generation, reliability evaluation, and ranking optimization. ResultsThe method was verified using an in-service natural gas pipeline network in China. Results demonstrated that the optimal flow allocation scheme achieved a system reliability of 0.998 9, outperforming conventional operational schemes. The proposed scheme exhibited a higher safety margin and enhanced supply security, achieving superior reliability-oriented flow allocation while satisfying all injection-production tasks and operational constraints. ConclusionIntegrating system reliability theory into the operational scheduling of natural gas pipeline networks provides a robust framework for safety-oriented decision-making, offering both theoretical support and practical engineering value.
ObjectiveWith the large-scale deployment of Carbon Capture, Utilization, and Storage (CCUS), hydrogen energy, and cryogenic oil and gas transportation technologies, long-distance pipelines are exposed to increasingly complex service conditions that complicate structural integrity assessments. Rolling and manufacturing processes cause the evolution of grain textures in pipeline steel, leading to distinct mechanical anisotropy. Consequently, conventional isotropic constitutive models fail to accurately describe these direction-dependent plastic behaviorsand can not meet engineering requirements for precise failure and fracture prediction. MethodsX52 seamless pipeline steel for CO2 transportation is selected as the research material. Circumferential (0°), diagonal (45°), and axial (90°) tensile specimens are prepared via in-situ sampling to eliminate the extra pre-strain induced by conventional flattening-based sampling method. Combined with the Digital Image Correlation (DIC) technology, multi-orientation in-situ tensile tests are carried out to obtain material stress-strain curves, mechanical properties, and plastic strain ratio parameters. ResultsX52 seamless pipeline steel exhibits significant strength anisotropy. As the specimen orientation shifts from circumferential to axial, the yield strength and ultimate tensile strength increase by 48％ and 14％, respectively, accompanied by a 36％ drop in uniform elongation. In contrast, the anisotropy of plastic flow is relatively mild. Circumferential specimens feature obvious thickness reduction, while plastic deformation in axial specimens mainly occurs along the width direction, and the two anisotropic features evolve asynchronously. Five commonly used hardening models are compared in terms of fitting accuracy, and the Multi-Voce model proves capable of accurately capturing hardening evolution across the entire plastic regime. A non-associated flow anisotropic constitutive framework is established by combining the Hill48 yield function, independent plastic potential function and Multi-Voce hardening model, followed by full parameter calibration. A user material subroutine is developed in ABAQUS to implement numerical calculations for the proposed model. Both the proposed anisotropic constitutive framework and the classic Mises isotropic model yield satisfactory predictions of specimen load-displacement responses. Nevertheless, the new anisotropic framework characterizes the plastic behavior of specimens with different orientations using one unified set of parameters, featuring better physical consistency and higher parameter transferability. ConclusionThis study reveals the anisotropic plastic deformation behavior of X52 seamless pipeline steel. The developed framework provides a theoretical basis for plastic failure assessment, ductile fracture prediction, and structural integrity analysis of oil and gas pipelines. It also serves as a reference for the mechanical characterization and engineering applications of similar pipeline steels.
ObjectiveThe large-scale deployment of Carbon Capture, Utilization, and Storage (CCUS) technology drives the research, development and engineering implementation of supercritical CO2 pipeline transport. However, conventional crack arrest models fail to accurately predict the crack arrest toughness of these pipelines. Furthermore, existing stress correction formulas yield highly inconsistent results that deviate significantly from current CO2 pipeline design standards. Consequently, the lack of an established crack arrest control system presents a major barrier to widespread CCUS adoption, highlighting an urgent need for a more cost-effective, engineering-applicable crack arrest evaluation model. MethodsTo address the above issue, full-scale burst test data of CO2 pipelines publicly available worldwide were adopted in this study, covering different pipe diameters, wall thicknesses, steel grades, and test conditions. Existing resistance-driving force curves were modified via the crack arrest toughness parameter correction method, based on the crack arrest criteria of dynamic fracture mechanics and relevant CO2 pipeline design standards. The crack arrest evaluation performances of different correction coefficients were compared, and the optimal correction coefficient k was obtained by fitting the measured data. Meanwhile, a novel crack arrest evaluation model for supercritical CO2 pipelines was established by replacing the crack tip pressure with the fluid saturation pressure. ResultsThe research results indicated that existing crack arrest evaluation models were not fully applicable to CO2 pipelines, as traditional crack arrest stress formulas led to large calculation errors and a remarkable overestimation of pipeline crack arrest capacity. When the fitted correction coefficient of the crack arrest toughness parameter (k) was set to 3.09, the proposed model demonstrated high stability and optimal crack arrest evaluation performance within the sample range. This modified model eliminated the non-conservative prediction bias of traditional prediction models and broadened the application scope of crack arrest evaluation diagrams. Additionally, a crack arrest evaluation scheme was formulated for the design of Pipeline L22 in the Phase II CCUS Project of Yanchang Oilfield. Corresponding crack arrest control recommendations were put forward, including increasing wall thickness to enhance material crack arrest toughness and installing external crack arresters. ConclusionThe crack arrest evaluation model developed in this study demonstrates high accuracy and engineering applicability. To accommodate variations in pipeline material and diameter resulting from large-scale CCUS deployment, future research should utilize finite element simulation technology with two-way fluid-structure interaction in conjunction with existing full-scale burst test data.
ObjectiveThe 15th Five-Year Plan period is a crucial stage for China to accelerate the development of a new energy system and fulfill its carbon peaking commitments. It also represents a strategic turning point for oil and gas pipeline networks to upgrade from conventional single-purpose oil and gas transportation corridors to multi-energy integrated new energy infrastructure. There is an urgent need to clarify the impacts of evolving energy supply-demand patterns on oil and gas pipeline networks and identify the core directions for their high-quality development during this period, thereby provide a reference for decision-making regarding the scientific planning, forward-looking deployment and transformative development of China’s oil and gas pipeline networks. MethodsTo achieve carbon peaking and carbon neutrality goals and build a strong energy nation, this paper systematically evaluates the consumption trends and features of petroleum, natural gas, hydrogen, green methanol, green ammonia and other novel energy carriers. Combined with the practical operation of China's oil & gas pipeline networks, it further elaborates the core opportunities and major challenges facing pipeline construction. ResultsPetroleum consumption is expected to reach a peak and plateau, with a growing share shifting toward petrochemical feedstock, thereby increasing spare capacity in refined oil pipelines. Meanwhile, natural gas continues to grow steadily as a critical transitional fuel. However, surging peak-shaving demand from gas-fired power plants has introduced severe diurnal and weekly consumption fluctuations, requiring far more stringent real-time pipeline dispatching. Concurrently, emerging energy carriers—such as green hydrogen, green methanol, and green ammonia—are poised for large-scale industrialization. A stark spatial mismatch between their supply and demand opens vital opportunities to upgrade existing pipeline assets. Consequently, China’s pipeline networks face three major opportunities: expanding infrastructure driven by natural gas demand, developing multi-medium storage and transport businesses fostered by the energy transition, and advancing smart pipeline construction empowered by digitalization and intellectualization. Conversely, the sector faces compounding challenges: declining utilization and rising strandedasset risks for legacy pipelines, rising construction and operational costs, the delicate balance between energy security and decarbonization, and an ongoing reliance on foreign core equipment and proprietary technologies.ConclusionDuring the 15th Five-Year Plan, China should focus on three priorities in developing its oil and gas pipeline networks. First, optimize infrastructure layouts to strengthen the entire production, supply, storage, transport, and sales chain. Second, drive low-carbon transformation and multi-energy integration by scaling up hydrogen-blending in natural gas pipelines, repurposing idle refined oil pipelines, and expanding transport capacity for liquid carriers like green ammonia and green methanol. Third, overcome bottlenecks in core equipment and technologies to build a self-reliant domestic technical ecosystem and advance full-scale smart pipeline construction. Additionally, China must deepen pipeline operational reforms, refine market-based trading and pricing mechanisms, standardize multi-medium pipeline transport specifications, and introduce targeted supportive policies to provide robust institutional safeguards for the transformative upgrade of oil and gas pipeline networks.
ObjectiveGirth welds are critical joints in long-distance liquid ammonia pipelines. However, complex microstructures and residual stress distributions render these welds highly susceptible to Stress Corrosion Cracking (SCC) in impure liquid ammonia environments, posing a severe threat to pipeline integrity. Consequently, it is imperative to determine the SCC susceptibility of X52 seamless steel pipe girth weld microstructures under liquid ammonia service conditions. MethodsThe base metal, heat-affected zone, and weld center of X52 seamless steel pipe girth welds were selected as the primary research subjects. Slow Strain Rate Tensile (SSRT) tests were conducted in air and two distinct impure liquid ammonia environments. Through metallographic observation, fracture surface scanning electron microscopy, electron backscatter diffraction analysis, and surface residual stress testing, the stress corrosion susceptibility indices were systematically evaluated based on tensile strength and elongation after fracture. The results were correlated with microstructural characteristics, and the mechanisms underlying variations of SCC susceptibility in liquid ammonia environments were elucidated. ResultsSSRT test results demonstrated that susceptibility indices based on tensile strength and elongation after fracture followed a consistent trend, with elongation after fracture exhibiting higher susceptibility to SCC in liquid ammonia environments. The SCC susceptibility of the girth weld regions decreased in the following order: weld center ＞ heat-affected zone ＞ base metal. Microstructural analysis indicated that the weld center exhibited grain refinement, non-uniform size distribution, the highest kernel average misorientation, and a peak surface residual tensile stress of 54 MPa. These characteristics increased the electrochemical activity of the weld center. Under the coupled influence of impure liquid ammonia and tensile stress, pitting corrosion initiated preferentially, inducing brittle cleavage fracture and distinct brittle fracture surface features. Conversely, the base metal exhibited superior SCC resistance, characterized by a uniform microstructure and low residual stress of only 5 MPa. ConclusionThe SCC susceptibility of X52 seamless steel pipe girth welds in liquid ammonia environments is primarily governed by microstructural inhomogeneity and subsequent residual stress concentration. To ensure the operational safety of liquid ammonia pipelines, welding procedures must be strictly controlled during fabrication and construction. Post-weld heat treatment should be performed when necessary to reduce the microstructural gradient and residual stress—particularly within the weld center and heat-affected zone—thereby effectively mitigating SCC risk.
ObjectiveWhen engaging in overseas Carbon Capture, Utilization, and Storage (CCUS) projects, Chinese oil and gas enterprises frequently encounter complex, multi-level regulatory systems and friction between engineering requirements and institutional boundaries. Consequently, it is vital to systematically identify how these regulatory regimes constrain the project lifecycle and to establish clear compliance pathways and key control points within these intricate institutional environments. MethodsTaking the integrated CCUS project of Canada’s L Oilfield as the research object, relevant policies and regulations were synthesized, including federal carbon credit and tax incentive policies, provincial resource ownership and environmental approval systems, and Alberta Energy Regulator directives. Centering on the end-to-end CCUS process, the technical standards and licensing boundaries of each phase were clarified. In conjunction with project implementation practice, a full-lifecycle framework centered on proactive compliance was constructed, and key compliance interfaces and risk control nodes were identified. ResultsCanada’s CCUS regulatory framework is characterized by the legalization of technical standards, the pre-positioning of administrative licensing, and the institutionalization of long-term liabilities. Regulatory requirements are deeply integrated across all project phases, shifting the approval focus forward to the feasibility study and engineering design stages while extending oversight to post-injection monitoring. Critical technical parameters—including capture measurement boundaries, pipeline phase control, crack arrest design, injection well integrity, and Measurement, Monitoring, and Verification (MMV) systems—directly impact carbon credit accounting, licensing, and project economics. Furthermore, the interplay of federal and provincial policies reinforces constraints on technical selection and investment decisions. ConclusionDrawing on the characteristics of Canada’s CCUS regulatory framework, the following compliance and implementation guidelines for Chinese engineering practices are proposed: (1) Implement a “Compliance-by-Design” approach: Integrate regulatory requirements directly into engineering design parameters and boundary conditions. (2) Establish an integrated Monitoring, Reporting, and Verification (MRV) system: Develop a comprehensive MRV framework that bridges physical engineering with carbon reduction accounting to ensure seamless data alignment. (3) Strengthen differentiated facility compliance management: Coordinate registration requirements for in-service pressure equipment with safety specifications for long-distance pipelines. (4) Enhance lifecycle techno-economic evaluations: Incorporate post-injection monitoring, liability transfer, and associated costs into evaluations to mitigate project compliance and investment risks.
ObjectiveLong-term service of oil and gas pipelines often leads to interacting corrosion defects, which significantly degrade structural integrity and elevate the risk of leakage or rupture. This study elucidates the interaction mechanisms between multiple defects and their specific effects on failure pressure. MethodsA three-dimensional (3D) nonlinear finite element model was established in ABAQUS to numerically simulate the failure pressure of pipelines with multiple corrosion defects. The influence mechanisms of relative position, geometric size and spatial spacing of defects on failure pressure were systematically analyzed. Three typical pipeline steels including X46, X60 and X80 were selected, with model reliability validated against physical burst test data from existing literature. ResultsPipeline failure pressure decreased progressively as the interaction between multiple defects intensified. Relative position, geometric shape, and spacing were identified as the primary controlling factors. In a tangential state, adjacent defects triggered stress field superposition at their edges, reducing the effective cross-sectional net bearing area to its minimum and maximizing interaction. These mechanisms varied with defect overlap or spacing. Specifically, overlapping defects caused local stress concentration zones to merge, leading to a more uniform stress distribution and a paradoxical reduction in peak local stress. Conversely, increasing defect spacing weakened the interference effect. Axial spacing was found to exert a greater influence on failure pressure than circumferential spacing. When normalized circumferential and axial spacings are no less than 0.6 and 0.8, respectively, defect interaction was effectively eliminated, allowing for evaluation via single-defect standards. Furthermore, failure pressure declined with increasing defect size, with depth significantly amplifying interaction effects. High-strength X80 steel exhibited higher sensitivity to defect parameters and more pronounced degradation in bearing capacity. Based on parametric simulation results, a critical spacing criterion and a failure pressure prediction formula that accounted for defect interaction were established. ConclusionThe 3D finite element model and critical spacing criterion successfully elucidate the interaction mechanisms between multiple corrosion defects, enabling accurate prediction of pipeline failure pressure. These results are applicable to steel grades X46 through X80, with depth-to-wall-thickness ratio up to 0.7 and normalized lengths up to 1.2. This study serves as a theoretical foundation for pipeline integrity assessment and risk management in the presence of complex corrosion features.
ObjectiveAccurate quantification of metal-loss defects in oil and gas pipelines lays an essential foundation for ensuring pipeline structural integrity and operational safety. However, existing magnetic flux leakage (MFL) analysis methods are insufficient in characterizing subtle local geometric features, hindering high-precision estimation of complex defect profiles and limiting the refinement of pipeline integrity assessment. MethodsAccordingly, a defect profile estimation model based on dual-component MFL image fusion, termed MFL-SPN, was proposed. First, the Adaptive Dirichlet Function (ADF) was employed to encode one-dimensional axial and radial MFL signals into two-dimensional autocorrelation matrix images, and a weighted fusion scheme was applied to achieve complementary enhancement of dual-component information, generating a unified image representation with higher information density and improved anti-interference performance. Second, a Dynamic-Enhanced Multiscale Backbone (DEMB) was developed to adaptively highlight local geometric features at defect edges, slope transitions, and weak-response regions via dynamic convolution. Finally, a Parallel Alignment Feature Pyramid Network (PAFPN) was constructed, where a Context Feature Calibration (CFC) module and a Spatial Feature Calibration (SFC) module were embedded into the shallow and deep layers of the pyramid network, respectively. Bidirectional alignment of cross-scale features was implemented using attention mechanisms and deformable convolution, mitigating spatial misalignment and detail degradation during feature fusion. The model output defect length and a sequence of profile depths sampled at equal axial intervals to enable parametric estimation of defect profiles. ResultsOn a hybrid dataset combining simulated and real-world scenarios, MFL-SPN outperformed mainstream models on key metrics, reducing defect length error and comprehensive profile-depth error by 13.0％ and 11.2％, respectively. The ablation study and visualization analysis confirmed the effectiveness of the dual-component fusion strategy and feature calibration modules, demonstrating superior profile reconstruction capability and robustness against complex defect morphologies. ConclusionBy integrating dual-component MFL image fusion and multi-scale feature calibration, MFL-SPN enables high-precision parametric estimation of defect profiles, providing technical support for critical tasks in pipeline integrity management, including risk assessment and maintenance decision-making.
ObjectiveAs a clean secondary energy source with zero emissions upon combustion, hydrogen plays a pivotal role in the global energy transition. While liquefaction is one of the most effective methods for improving hydrogen storage and transportation efficiency, it remains a highly energy-intensive process characterized by high specific energy consumption and low exergy efficiency.MethodsTo mitigate energy consumption and enhance liquefaction efficiency, a novel hydrogen liquefaction process integrating LNG cold energy precooling and deep cryogenic refrigeration with a helium Brayton cycle was designed based on an LNG terminal in China, with a liquid hydrogen capacity of 300 t/d. In this process, natural gas obtained from LNG gasification was adopted as feedstock to produce hydrogen via steam methane reforming. By-product CO2 was recovered through liquefaction to serve as raw material for dry ice production. Process modeling and parameter optimization were conducted using HYSYS software and a particle swarm optimization algorithm. Finally, energy analysis, heat exchange analysis, exergy analysis, and thermodynamic analysis were performed on the established system. ResultsFollowing optimization, the specific energy consumption, exergy efficiency, and coefficient of performance of the proposed process reached 4.797 kW·h/kg, 65.44％, and 0.276, respectively, reflecting superior liquefaction performance. Exergy analysis indicated a total process exergy loss of 58 589.63 kW, primarily attributed to ortho-para hydrogen reactors and heat exchangers, which accounted for 56.27％ of the total. Among the major equipment, heat exchangers and compressors exhibited the highest exergy efficiencies, whereas expanders exhibited relatively low exergy efficiency due to low expansion temperatures. Additionally, the deep cryogenic heat exchangers achieved excellent heat exchange efficiency. ConclusionThe proposed process simultaneously achieves hydrogen production and high-efficiency liquefaction while satisfying the operational gas delivery pressure requirements of LNG gasification. Consequently, it provides a pivotal reference for future LNG cold energy utilization and the development of high-performance hydrogen liquefaction processes.
ObjectiveLong-distance oil and gas pipelines are critical components of global energy infrastructure. However, complex operating environments frequently induce surface defects that jeopardize structural integrity. As a non-destructive technology, Magnetic Flux Leakage (MFL) detection identifies defect-induced signal anomalies without interrupting pipeline operations, providing vital data for comprehensive integrity assessments. MethodsTo address baseline drift and high-frequency noise in ultra-high-definition MFL in-line inspection signals, a base value calibration method was adopted to eliminate signal offsets from sensor variations and environmental disturbances. Simultaneously, a Gaussian denoising algorithm was integrated to suppress random noise and enhance signal quality. Through image mapping, the preprocessed one-dimensional MFL signals were converted into two-dimensional pseudo-color images, mapping defect features to locally salient regions. Consequently, a pipeline defect identification dataset containing spatial semantic information was constructed. Finally, the Detection Transformer (DETR) model was implemented, leveraging its global modeling and end-to-end detection mechanism to achieve intelligent identification and precise localization of pipeline defects. ResultsTo verify the effectiveness of the proposed method, pull-through tests using ultra-high-definition MFL in-line inspection tools were conducted under multi-diameter conditions. MFL signals from various defect types, sizes, and positions were systematically collected, establishing a dataset of 341 valid samples. Evaluation on the test set indicated that the DETR model achieved an mAP50 of 92.5％, a precision of 90.3％, a recall of 86.3％, and an F1-score of 88.3％, demonstrating superior comprehensive performance in pipeline defect identification. Notably, the model significantly outperformed the You Only Look Once (YOLO) model in identifying small-size and low-contrast defects with inconspicuous edge features. To further validate engineering applicability, the method was deployed for the ultra-high-definition MFL in-line inspection of an in-service crude oil pipeline. The results confirmed that defects of diverse geometric morphologies and spatial positions were accurately identified with an mAP50 of 84.9％, reflecting robust engineering adaptability and stability. ConclusionThe proposed identification method exhibits excellent robustness and generalization ability in both multi-diameter pipeline pull-through tests and practical engineering applications, providing an important reference for the accurate evaluation of residual strength and reliable prediction of residual life for defective pipelines.
ObjectiveTo solve the key sequential decision-making problem of rapid and optimal selection of control stations during natural gas pipeline network fault handling, traditional experience-based dispatching modes face critical bottlenecks, including delayed responses, highly subjective decision-making, and underutilized historical data. MethodsAn optimal selection method for natural gas pipeline network control stations during fault handling was proposed, leveraging Domain Expert Knowledge (DEK) and Deep Reinforcement Learning (DRL). First, a structured processing workflow for historical dispatching experience was designed. Through action semantic analysis, state space construction, and reward value calculation, unstructured fault-handling cases were converted into standardized datasets suitable for reinforcement learning training, achieving the externalization of implicit expert knowledge. Second, the optimal control station selection was formalized as a Markov decision process. A state space containing fault types, locations, and selected station information was constructed, a discrete action space for station selection was defined, and a three-stage reward function based on expert solution consistency was designed to guide the model in learning high-quality decision strategies. Third, the Double Deep Q-Network (DDQN) algorithm was adopted to solve this decision-making problem. Decoupling action selection from value evaluation effectively alleviated the Q-value overestimation inherent in standard Deep Q-Networks (DQN), greatly improving the stability and reliability of decision-making. Finally, experimental verification was conducted on 1,847 actual fault-handling records collected from a natural gas pipeline network between 2020 and 2024. ResultsExperimental results demonstrated that the proposed method achieved a precision of 94.8％, a recall of 95.2％, and an exact match rate of 82.3％ on the test set, with an average inference time of just 12.5 ms. This approach outperformed standard DQN, Random Forest, and rule-based methods in both decision quality and response efficiency. Furthermore, the ablation study confirmed that the Double mechanism, experience replay, and three-stage reward design all contributed significantly to boosting model performance. ConclusionThe proposed method seamlessly integrates data-driven and knowledge-driven approaches, providing rapid, reliable intelligent decision-making support for natural gas pipeline network emergency responses. Consequently, it holds substantial theoretical and practical value for enhancing the operational safety and intelligence level of pipeline networks.
ObjectiveRepurposing in-service refined oil pipelines for gaseous CO2 transport is a highly efficient strategy for large-scale CO2 delivery. However, its economic viability depends on variables such as repurposing schemes and carbon subsidies, yet a reliable method for economic evaluation and operational optimization remains unavailable. This study proposes an integrated evaluation and optimization framework that accounts for retrofitting costs, carbon subsidies, and phase-behavior constraints to support the economic evaluation of pipeline repurposing projects. MethodsUtilizing the Net Present Value (NPV) method, a comprehensive economic evaluation and optimization model was established for repurposing in-service refined oil pipelines for gaseous CO2 transport. The maximum annual net cash flow was defined as the objective function, with pipeline throughput, outlet pressure and temperature at the initial station serving as optimization variables. The framework fully incorporated costs for pipeline and station retrofitting, operation and maintenance, and energy consumption, alongside CO2 pipeline transportation revenue. An adaptive genetic algorithm was employed for model solution and parameter optimization. Taking a refined oil pipeline in Eastern China as a case study, key operational parameters were optimized, and the impacts of pipeline throughput, service life after repurposing, and subsidy mechanism on annual net cash flow were systematically analyzed. ResultsFor the case pipeline, a transportation tariff of CNY 0.5/(t·km) and a carbon sequestration subsidy of CNY 65/t yielded an optimal pipeline throughput of 1 383 t/day, with an initial station outlet pressure of 5 MPa at 292 K, resulting in an annual profit of CNY 3.386 million. The factors influencing project profitability, in descending order of influence, were as follows: pipeline throughput, carbon subsidy mechanism, and service life after repurposing. Under a fixed subsidy mechanism, total costs—including retrofitting, energy consumption, and maintenance—exceeded revenues when the subsidy fell below a CNY 57/t threshold. Increasing the sequestration subsidy from CNY 60/t to CNY 80/t reduced the payback period from 11 years to 4 years. Under a floating subsidy mechanism, the repurposing project achieved break-even status with initial carbon sequestration subsidies of CNY 54/t, 52/t, and 50/t paired with annual growth rates of 1％, 1.5％, and 2％, respectively. ConclusionFor the studied pipeline, a carbon sequestration subsidy range of CNY 57–80/t yields an optimal daily throughput of 1 127–1 581 t, with an initial station outlet pressure of 4–5 MPa and an operating temperature stabilized near 295 K. It is recommended that the fixed carbon subsidy be set at a minimum of CNY 57/t, while the floor value for floating subsidies should remain no less than CNY 47/t. These findings serve as robust technical and economic benchmarks for the retrofitting design and economic evaluation of repurposing refined oil pipelines for CO2 transport.
ObjectiveAmid the ongoing emphasis on the “dual-carbon” goals and energy security, natural gas consumption in China continues to grow, with external import dependence remaining high. However, gas storage capacity development lags significantly, and insufficient storage and peak-shaving capabilities have become critical constraints on supply security and market stability. To ensure national energy security while balancing market efficiency and sustainable enterprise development, this study draws on the European Union’s natural gas storage experience to propose a modern storage development path tailored to China’s national conditions. MethodsComparative institutional analysis and policy text deconstruction methods were employed. The European Union’s natural gas market reform process and gas storage regulatory framework were systematically reviewed. By integrating European Union gas storage operation data, regulations, and member states’ implementation rules, the dual-track mechanism of “mandatory dominance + market supplement” was summarized. Simultaneously, China’s gas storage facility scale, market structure, and recent policy developments were compared, and recommendations for optimizing China’s natural gas storage mechanism were proposed. ResultsThrough institutional measures such as phased filling targets, the “use-it-or-lose-it” rule, and the combined use of subsidies and fines, the European Union significantly improved the security resilience of its natural gas supply while maintaining market participation. Key issues in China’s natural gas storage mechanism were identified, including unclear storage classifications and responsibility boundaries, poor transmission of price-differential signals and peak-shaving cost pass-through, limited independent operation and service capabilities, and inadequate cross-regional coordination. Based on these findings, three optimization strategies were proposed: (1) Establish a framework for four storage types—strategic, mandatory, emergency, and market-based; (2) Develop a peak-valley gas pricing mechanism linked to electricity prices and design a pricing model for gas storage operations to support pipeline transmission balance; (3) Implement fiscal support strategies, issue special storage bonds, and establish regional coordination and storage linkage mechanisms to enhance resource allocation. ConclusionThe market-oriented development of China’s gas storage facilities is best supported by a dual-track mechanism combining strict liability constraints with market-based regulatory incentives. This approach can ensure basic supply security capacity through legislation and regulation, stimulate market vitality through price differential and cost pass-through mechanisms, and improve resource allocation efficiency through regional coordination. These research findings provide valuable references for optimizing China’s gas storage policies and market mechanisms.
ObjectiveWater flooding is a primary method for maintaining and enhancing oilfield production. However, seawater—one of the predominant injection source—is highly corrosive to transportation pipelines. Current corrosion control relies primarily on seawater deoxygenation treatments. This study investigates the influence and underlying mechanisms of varying Dissolved Oxygen (DO) levels on the corrosion behavior of X65 pipeline steel in deaerated seawater. By establishing deaeration technical indicators for effective corrosion control, this study provides a framework to ensure the operational safety of seawater transportation pipelines and treatment facilities. MethodsSimulated seawater corrosion experiments on X65 steel were conducted across varying DO concentrations using a high-temperature, high-pressure autoclave, and average corrosion rates were measured. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) were employed to analyze the phase composition and surface micromorphology of X65 pipeline steel corrosion products. In conjunction with electrochemical polarization curves, the influence and mechanisms of different DO levels on the corrosion behavior of X65 pipeline steel in simulated seawater were investigated. ResultsThe corrosion rate of X65 steel increased progressively with rising DO levels. At a DO concentration of 10 ppb, X65 pipeline steel exhibited slight corrosion, which escalated to moderate levels as concentrations rose from 50 ppb to 500 ppb. The corrosion product film on the surface of the specimen was primarily composed of Fe3O4 and γ-FeOOH, with minor amounts of granular Fe2O3 adhering to the surface. Higher DO content increased the proportion of γ-FeOOH within the film; the resulting structural defects served as diffusion channels for corrosive media, thereby compromising the film’s protective integrity. Furthermore, potentiodynamic polarization curves indicated that at DO levels below 200 ppb, the cathode experienced both hydrogen evolution and oxygen reduction, with the oxygen reduction process being inhibited. Once the DO content reached 500 ppb, the cathodic process was dominated by oxygen reduction, with the overall corrosion rate governed by electrochemically controlled oxygen reduction.ConclusionThe threshold value for DO content to ensure the corrosion safety of X65 pipeline steel in 60 °C simulated seawater has been determined. The research results provide essential data support for establishing deaeration control indicators in seawater transportation and oilfield water injection systems. By optimizing anticorrosion costs while ensuring long-term pipeline integrity, this method achieves a critical balance between corrosion mitigation and engineering investment, offering significant guiding value for practical engineering applications.
ObjectiveGiven the challenges of reverse distribution and inefficient high-carbon logistics for green methanol in China, coupled with the risk of idle and stranded assets in existing oil pipelines amid peak oil consumption, it is crucial to revitalize existing oil pipeline infrastructure to develop an efficient, low-carbon methanol transportation system. MethodsBased on system theory, a construction path for a methanol pipeline transportation system was proposed from the perspectives of multi-energy integration and revitalization of stock assets. At the physical facility level, technical challenges were analyzed, including methanol-induced stress corrosion cracking, seal swelling, mixing control during batch transportation, and gas lock oscillation in high-drop pipeline segments. An adaptive renovation path was put forward based on material compatibility evaluation and precise tracking of mixed oil interfaces. At the logistics network level, a three-dimensional logistics architecture of “long-distance trunk lines + regional microgrids + hub peak shaving” was established to address the flow mismatch between continuous pipeline transportation and terminal pulsed consumption, and to smooth “last-mile” delivery. For safety assurance, a risk prevention and control system for methanol pipeline transportation was proposed, incorporating a phase separation monitoring mechanism, leakage early-warning lines, and full-life-cycle integrity management. ResultsThe results indicated that: (1) The stock asset revitalization strategy, combined with a “marginal cost + green premium” pricing model and flexible pipeline capacity trading, effectively unlocked idle pipeline capacity and enabled seamless integration of “production, supply, storage, and refueling” infrastructure. (2) A full-life-cycle digital carbon passport traceability system was established to address international non-tariff barriers. (3) A market-oriented operation mechanism, deeply coupling carbon, energy, price, and benefit, facilitated the redistribution of regional economic benefits through spatial reallocation of energy resources. ConclusionThe use of stock assets for methanol transportation represents a Pareto improvement approach that addresses logistics challenges and revitalizes idle assets. This approach transforms traditional oil pipeline networks into integrated energy systems coupling hydrogen, carbon, and methanol, bridges the theoretical gap in reconstructing long-distance methanol pipeline networks in China, strengthens the “liquid defense line” for national energy security, and offers a Chinese model for the green transformation of global fossil energy infrastructure.
