[Objective]Girth 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.[Methods]The 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.[Results]SSRT 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.[Conclusion]The 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.(8 Figures,3 Tables,31 References)
[Objective]When 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.[Methods]Taking 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.[Results]Canada'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.[Conclusion]Drawing 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.(1 Figure,3 Tables,35 References)
[Objective]Long-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.[Methods]A 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.[Results]Pipeline 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.[Conclusion]The 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.(21 Figures,4 Tables,28 References)
[Objective]As 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.[Methods]To 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.[Results]Following 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.[Conclusion]The 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.(6 Figures,3 Tables,25 References)
[Objective]Repurposing 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.[Methods]Utilizing 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.[Results]For 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.[Conclusion]For 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.(7 Figures,4 Tables,30 References)
