油气管道周边区域划分与距离设定研究

为合理评估并有效控制管道与周边区域的相互影响,提出1种油气管道周边区域划分与距离设定方法。通过数据统计与事故案例分析,归纳了油气管道安全运行面临的4项问题,结合管道与周边区域相互影响类型及范围,提出将周边区域沿管道中心线依次划分为管道通行区、规划控制区和应急响应区。根据法律规定、实际事故后果影响范围和典型事故后果数值计算结果,提出了上述3个区域的距离设定原则与计算方法,并针对当前油气管道周边区域管理存在的问题提出了分区域管控建议。研究结果表明:所提出的方法有助于控制管道与周边区域的相互影响,保障管道安全运行和周边区域公共安全。

Modeling and analysis of a catastrophic oil spill and vapor cloud explosion in a confined space upon oil pipeline leaking

Oil spill-induced vapor cloud explosions in a confined space can cause catastrophic consequences.In this work,investigation was conducted on the catastrophic pipeline leak,oil spill,and the resulting vapor cloud explosion accident occurring in China in 2013 by modeling analysis,field surveys,and numerical simulations.The total amount of the spilled oil was up to2044.4 m3 due to improper disposal.The long residence time of the oil remaining in a confined space permitted the formation of explosive mixtures and caused the vapor cloud explosion.A numerical model was developed to estimate the consequence of the explosion based on volatilization testing results.The results show that the death-leading zone and the glass-breaking zone could be 18 m and 92 m,respectively,which are consistent with the field investigation.The severity of the explosion is related to the amount of the oil spill,properties of oil,and volatilization time.It is recommended that a comprehensive risk assessment be conducted to analyze the possible consequences upon oil spilling into a confined space.Prompt collection and ventilation measures should be taken immediately after the spill occurs to reduce the time for oil volatilization and prevent the mixture from reaching its explosive limit.

Standards and methods for dent assessment and failure prediction of pipelines:A critical review

Dent,a common mechanical damage on pipelines,is associated with a significant local plastic deformation.Dents can cause pipeline failures,especially when they are combined with other types of defects such as gouges,fatigue,corrosion,and cracks.In this work,a systematic review of various assessment methods and standards for pipeline dents,including the combination of a dent with other defects,is conducted.Generally,the methods available today are not sufficiently accurate and reliable to assess pipeline dents,especially the dent-defect combinations.For plain dents on pipelines,both the depthbased criterion and the strain-based criterion are commonly used in engineering.Their main problems include inaccuracy and conservatism.For a dent combined with other defects,the existing assessment techniques are not mature enough to give reliable results.Both experimental testing and numerical modeling through finite element(FE)analysis are capable of investigating the influence of dents and dent-defect combinations on burst failure pressure of the pipelines,although an approximation to the reality is still the main difficulty existing in the experimental testing and FE analysis.Nowadays,relevant studies on assessment techniques for plain dents,a dent with fatigue and a dent with a single gouge have been common in literature.The combinations of a dent with corrosion or cracks have been rarely assessed due to complicated mechanisms involving a multi-physics coupling effect.Development of novel assessment methods by integrating mechanical stress and strain,electrochemical reactions and steel metallurgy will be a key topic to accurately assess the dent-defect combinations for improved pipeline integrity.

Modeling of the mechano-electrochemical effect at corrosion defect with varied inclinations on oil/gas pipelines

A 3-dimensional finite element model was built to determine the effect of inclination angle of a corro sion defect on local mechano-electrochemical(M-E)effect in a simulated soil solution.Because of the high effect of the defect inclination angle on the M-E effect,when the inclination angle is 0°(i.e.,the primary axis of the defect parallel to the longitudinal direction of the pipe),the greate st stress concentration level at the defect can be observed,which is associated with the lowest corrosion potential,the greatest anodic current density and the most serious accelerated localized corrosion.When the inclination angle is 90°,the stress concentration level reduces and the corrosion potential becomes less negative,accompanying with the decreased anodic/cathodic current densities.Besides,when the ratio(r_(ca))of the primary axial length of the defect to its secondary axial length is 1,the defect inclination does not affect the stress and the electrochemical corrosion rate at the defect.With the increase of r_(ca),the effect of the defect inclination angle is more apparent.

Molecular dynamics modeling of hydrogen-induced plastic deformation and cracking of ɑ-iron

In this work,molecular dynamics modeling was conducted to study hydrogen(H)-induced plastic deformation and cracking of polycrystalα-Fe.Under cyclic loading,the number of vacancies and the stress intensity increase with H atom concentration and the number of loading cycles.However,the effect of cyclic loading on cracking is not as significant as the increment of H concentration.As the H concentration increases,the dislocation generation and emission are enhanced in the{110}<111>slip system,but are inhibited in other slip systems.There is a critical H atom concentration,below which the plastic deformation ofα-Fe is facilitated by H atoms.When the critical H concentration is exceeded,the dislocation emission is inhibited by H atoms at grain boundaries,where the H atoms can pin dislocations,causing piling-up of the dislocations to generate a stress concentration.

Facile Li-Al layered double hydroxide films on Al alloy for enhanced hydrophobicity, anti-biofouling and anti-corrosion performance

In this work,lithium(Li)-aluminum(Al)layered double hydroxide(LDH)films modified by 4-amino-2-((hydrazine methylene)amino)-4-oxobutanoic acid(denoted as AOA acid)and/or 1H,1H,2H,2H-perfluorooctyltriethoxysilane were prepared on 6N01 Al alloy by a facile,in-situ growth method with enhanced hydrophobicity,anti-biofouling and anti-corrosion performance.The preparation is low energy consumptive and environment friendly,relying on self-assembly at ambient temperature.The structure,molecular weight and functional groups of the synthesized AOA acid were characterized by NMR spectrometer,ESI-MS spectrometer and Fourier transform infrared(FT-IR)spectroscopy.And the compositions,structure and morphology of the films were characterized by Fourier transform infrared(FT-IR)spectroscopy,glancing-angle X-ray diffraction(GA-XRD),X-ray photoelectron spectroscopy(XPS),field emission scanning electron microscopy(FE-SEM)and energy-dispersive x-ray spectrum(EDS).Water contact angle measurements(CA)and atomic force microscopy(AFM)characterization show that the films possess a micro/nanostructure with an improved hydrophobicity.Immersion test,neutral salt tests(NSS)and electrochemical impedance spectroscopy(EIS)conducted in 3.5 wt.%NaCl solutions demonstrate the improved corrosion resistance of the films over bare Al alloy.Meanwhile,the films also possess an excellent anti-bacterial property toEscherichia coli,Bacillus subtilis and sulfate-reducing bacteria.

Synergistic effects of Nb and Mo on hydrogen-induced cracking of pipeline steels:A combined experimental and numerical study

The synergistic effects of Nb and Mo on hydrogen-induced cracking(HIC)of pipeline steels were studied experimentally and numerically.The results showed that Mo was primarily segregated at grain-boundaries(GBs)or solid-dissolved in the matrix,while most Nb and a small amount of Mo formed dis-persed(Nb,Mo)C nano-precipitates and refined the microstructure.Compared with Nb alloying,the multi-ple additions of Nb-Mo played dual roles in affecting H diffusion:primarily,the H-traps densities such as GBs,precipitates,and solute Mo atoms increased,providing an advantage;however,Mo slightly reduced the H-trapping capacity of precipitates,playing an adverse role.Nonetheless,the beneficial effects far outweighed the adverse effects,thereby reducing H diffusivity and inhibiting crack initiation.Addition-ally,Nb and Mo hindered crack propagation synergistically as follows:(i)Mo enhanced GB cohesion by repelling H,impeding intergranular cracking and hydrogen-enhanced decohesion(HEDE);(ii)Nb reduced the proportion of3/high-angle grain boundaries,increasing cracking resistance;(iii)(Nb,Mo)C precip-itates impeded H-dislocation interactions,reducing the hydrogen-enhanced localized plasticity(HELP).

Numerical modeling of the critical pipeline inclination for the elimination of the water accumulation on the pipe floor in oil-water fluid flow

In this work,numerical models were developed to investigate the critical inclination of a pipeline to eliminate the water accumulation at the floor of the pipe carrying oil-water fluid.Computational fluid dynamics software was used to establish a geometric model of the pipe with various inclination angles,and a grid-independent verification was conducted to determine a reasonable meshing method.Quantitative relationships were determined between the pipe inclination angle and the affecting factors including the flow velocity,viscosity and the pipe diameter,where the water accumulation would not be able to occur.Generally,the critical inclination angle increases with the fluid flow velocity.The refluxing of water is the key mechanism causing the water accumulation at the bottom of the pipe.In addition to the fluid flow velocity,an increase in fluid viscosity and a decrease in the pipe diameter cause an increase of the critical inclination angle that the water phase can be carried away by oil.The model can be used to determine the critical inclination of pipelines carrying oil-water fluid to cause the water accumulation and the operating conditions that can eliminate the accumulation of water phase at the pipe floor.