【作者】 陈磊；

【导师】 喻健良；

【作者基本信息】 大连理工大学 ， 化工过程机械， 2024， 博士

【摘要】 通过高压管道输运超临界CO₂是碳捕集、利用与封存（简称CCUS）技术大规模应用的重要技术途径。与油气管道不同,CO₂管道一旦存在裂纹并泄漏,将因显著的焦汤效应在泄漏口形成低温,引发裂纹长程扩展。现有研究成果还无法定量描述CO₂管道裂纹扩展特性,基于天然气管道断裂试验研究得到的Battelle止裂判据也无法直接应用到超临界CO₂管道。基于此,本文通过试验、理论和数值模拟相结合的方法,研究超临界CO₂管道裂纹扩展特性,构建止裂判据及控制方法。主要工作及结论如下:（1）设计搭建了DN100、长20 m的超临界CO₂全尺寸断裂试验装置。通过加装含有预制轴向缺陷的爆破牺牲管,实现了高压CO₂管道瞬间泄漏过程裂纹扩展的实验研究。研发了裂纹尖端位置以及裂纹扩展形貌的高速测量方法,解决了裂纹扩展速度、裂纹尖端张开角等裂纹扩展特性参数难以定量表征的难题,可开展不同初始状态的CO₂管道裂纹扩展的全过程研究。（2）开展了不同初始压力、初始温度下,纯和含N₂杂质CO₂管道裂纹扩展试验,分析了影响裂纹扩展及止裂的减压波速度参数的变化规律。结果表明:在压力与减压波速度曲线上,纯和含N₂杂质CO₂的减压波速度曲线存在压力平台,导致CO₂管道相比油气管道更容易发生延性裂纹长程扩展断裂。纯和含N₂杂质的CO₂混合物的初始压力越高减压波初始传播速度越大,初始温度越高、N₂浓度越高,导致减压波速度曲线“压力平台”越高。基于等熵假设和均相流理论,建立的减压波传播速度预测模型得到的结果与实验结果一致性较好。（3）基于开展的纯和含N₂杂质的超临界CO₂管道全尺寸断裂试验结果,系统研究了不同材质、不同CO₂初始状态下管道裂口形貌、裂纹扩展速度、裂纹尖端张开角度等特性参数的量化规律。研究发现:管道裂纹起裂区受温度影响,裂纹微观形貌多为解理断裂并伴随有少量韧窝;断裂速度发展区为韧性撕裂脊形貌并形成“隧道效应”;断裂速度稳定发展区受平面应力为主导的影响,主要为解理平面、滑移带、少量浅韧窝形貌;管道裂纹停止区由于断裂控制形式不同,微观组织形貌存在差异。首次量化的CO₂管道断裂扩展速度和裂纹尖端张开角度数据表明,CO₂初始压力越大,管道初始断裂速率越大;管道裂纹尖端张开角度在断裂扩展路径上存在波动范围,平均裂纹尖端张开角度随管内CO₂泄漏量降低逐渐减小。分析管道裂纹襟翼变化过程,考虑裂纹扩展需保持能量守恒,建立了管道止裂压力计算模型,该模型对不同等级管道钢材和管道参数均适用。（4）基于ABAQUS/Explicit软件平台建立了与试验场景一致的CO₂管道流固耦合数值模拟模型。通过高低应力力学性能试验、有限元模拟迭代优化方法获得了能够反应X52钢全程变形特征的材料属性,基于GERG-2008状态方程开发了描述CO₂压力变化的子程序。形成的CO₂管道裂纹动态扩展数值模拟技术弥补了传统的以函数法或常压法代表管内介质压力的研究不足。将模拟得到的裂纹扩展速度及裂纹扩展形貌与试验对比,发现本文构建的流固耦合分析模型能够反映超临界CO₂裂纹扩展规律。模拟发现:同一管道参数、CO₂相同初始压力下,液相CO₂管道相较于超临界CO₂更容易由管道自身韧性形成止裂;超临界CO₂管道的初始温度越高,导致管道的初始断裂速率增大,稳定断裂速度增高。其它初始参数相同时,初始N₂摩尔浓度增高时,导致管道的初始断裂速率增大,稳定断裂速度增高。（5）以陆上超临界CO₂管道为研究对象,基于建立的流固耦合分析模型,系统地研究了管道参数、CO₂初始压力对管道断裂速度的影响规律。以工业最为常用的DN300（规格）超临界CO₂管道为模拟对象,研究发现管道临界裂纹尖端张开角与管道径厚比呈负指数关系。相同径厚比的DN200～DN300型管道对管道稳定断裂速度的尺寸效应并不明显,DN500型管道的尺寸效应显著。以Battelle断裂速度计算模型为基本形式,提出了以CTOA_C为关键参量的超临界CO₂管道断裂速度预测模型（MBTCM）。开展的管道断裂速度和减压波速度组成的双曲线应用研究表明MBTCM比BTCM的预测精度高,适用性更广。最后,基于速度判据和管道断裂止裂器实验建立适用于超临界CO₂管道的断裂控制方法。更多还原

【Abstract】 The transport of supercritical CO₂ through high-pressure pipelines is an important technology pathway for the large-scale application of carbon capture,utilisation and storage（CCUS）technology.Unlike oil and gas pipelines,once a crack exists in a CO₂ pipeline and leaks,a low temperature is formed at the leakage port due to the significant pyrolysis effect,which triggers the long-range crack expansion.Existing research results are not able to quantitatively describe the crack propagation characteristics of CO₂ pipelines,and the Battelle crack stopping criterion based on natural gas pipeline fracture experimental research cannot be directly applied to supercritical CO₂ pipelines.Based on this,this paper investigates the crack propagation characteristics of supercritical CO₂ pipelines and constructs fracture arrest criteria and control methods by combining experimental,theoretical and numerical simulation methods.The main work and conclusions are as follows:（1）A 20-metre-long full-size supercritical CO₂ fracture test rig of DN100 was designed and constructed.The experimental study of crack expansion during instantaneous leakage of high-pressure CO₂ pipeline was realised by installing a sacrificial pipe containing pre-fabricated axial defects.A high-speed measurement method of crack tip position and crack propagation morphology has been developed,which solves the problem of difficult quantitative characterisation of crack propagation parameters such as crack propagation velocity and crack tip opening angle,and enables the study of the whole process of CO₂ pipeline crack propagation in different initial states.（2）Based on the results of full-size fracture tests of supercritical CO₂ pipelines with pure and N₂ impurities,the quantification of crack morphology,crack expansion velocity,crack tip opening angle and other characteristics of pipelines with different materials and CO₂ initial states were systematically investigated.It is found that:the crack initiation zone of the pipe is affected by the temperature,and the microstructure of the crack is mostly deconstructed and accompanied by a small number of tough nests;the fracture speed development zone is a ductile tearing ridge shape and the formation of the"tunnel effect";the stable development zone of the fracture speed is dominated by the planar stresses,and the main deconstructed planes,slipping zones,and a small number of shallow tough nests are observed;The pipe crack stopping zone has different microstructures and morphologies due to different fracture control forms.The first quantitative data on fracture expansion velocity and crack tip opening angle of CO₂ pipeline show that the larger the initial pressure of CO₂,the larger the initial fracture velocity of the pipeline;the crack tip opening angle of pipeline fluctuates in the fracture expansion path,and the average crack tip opening angle decreases with the decrease of CO₂ leakage in the pipeline.By analysing the pipeline crack flap change process and considering that the crack expansion needs to maintain energy conservation,a pipeline stopping pressure calculation model is established,which is applicable to different grades of pipeline steel and pipeline parameters.（3）Based on the results of full-size fracture tests of supercritical CO₂ pipelines with pure and N2 impurities,the quantification of crack morphology,crack expansion velocity,crack tip opening angle and other characteristics of pipelines with different materials and CO₂ initial states were systematically investigated.It is found that:the crack initiation zone of the pipe is affected by the temperature,and the microstructure of the crack is mostly deconstructed and accompanied by a small number of tough nests;the fracture speed development zone is a ductile tearing ridge shape and the formation of the"tunnel effect";the stable development zone of the fracture speed is dominated by the planar stresses,and the main deconstructed planes,slipping zones,and a small number of shallow tough nests are observed;The pipe crack stopping zone has different microstructures and morphologies due to different fracture control forms.The first quantitative data on fracture expansion velocity and crack tip opening angle of CO₂ pipeline show that the larger the initial pressure of CO₂,the larger the initial fracture velocity of the pipeline;the crack tip opening angle of pipeline fluctuates in the fracture expansion path,and the average crack tip opening angle decreases with the decrease of CO₂ leakage in the pipeline.By analysing the pipeline crack flap change process and considering that the crack expansion needs to maintain energy conservation,a pipeline stopping pressure calculation model is established,which is applicable to different grades of pipeline steel and pipeline parameters.（4）The numerical simulation model of CO₂ pipeline fluid-solid coupling consistent with the test scenario was established based on ABAQUS/Explicit software platform.The material properties that can respond to the deformation characteristics of X52 steel throughout the whole process are obtained through high and low stress mechanical property tests,finite element simulation iterative optimisation method,and the subroutine describing the CO₂ pressure change is developed based on the GERG-2008 equation of state.The resulting numerical simulation technique for dynamic crack expansion in CO₂ pipelines makes up for the lack of the traditional study of representing the medium pressure inside the pipe by the function method or the atmospheric pressure method.Comparing the simulated crack expansion velocity and crack expansion morphology with the experiments,it is found that the fluid-solid coupling analysis model constructed in this paper can reflect the supercritical CO₂ crack expansion law.The simulation found that:under the same pipeline parameters and the same initial pressure of CO₂,the liquid-phase CO₂ pipeline is more likely to be formed by the pipeline’s own toughness to stop cracking than the supercritical CO₂;the higher the initial temperature of the supercritical CO₂ pipeline,the higher the initial fracture velocity of the pipeline,and the higher the stable fracture velocity.When other initial parameters are the same,higher initial N₂ molar concentration leads to higher initial fracture velocity and higher stable fracture velocity of the pipeline.（5）Taking the onshore supercritical CO₂ pipeline as the research object,based on the established fluid-solid coupling analysis model,the influence of pipeline parameters and CO₂initial pressure on the pipeline fracture velocity is systematically investigated.Taking DN300supercritical CO₂ pipeline,which is the most commonly used in industry,as the simulation object,it is found that the critical crack tip opening angle of the pipeline has a negative exponential relationship with the pipeline diameter-to-thickness ratio.The size effect of DN200～DN300 pipelines with the same diameter-to-thickness ratio on the stable fracture velocity of the pipeline is not obvious,and the size effect of DN500 pipelines is significant.Taking the Battelle fracture velocity calculation model as the basic form,the supercritical CO₂pipeline fracture velocity prediction model（MBTCM）with CTOA_C as the key parameter is proposed.The carried out hyperbolic application study consisting of pipeline fracture velocity and decompression wave velocity shows that MBTCM has higher prediction accuracy and wider applicability than BTCM.Finally,a fracture control method applicable to supercritical CO₂ pipelines is established based on the velocity criterion and pipeline fracture stopper experiments.更多还原