【作者】 崔铭伟；

【导师】 曹学文；

【作者基本信息】 中国石油大学(华东) ， 油气储运工程， 2014， 博士

【摘要】 海底多相流混输工艺越来越多的应用到海上油气开采中,含CO₂多相流内腐蚀,尤其是段塞流内腐蚀成为影响海管安全的重大隐患。由于石油管道输送介质成分十分复杂,加之段塞流的复杂性,为含CO₂多相流管材内腐蚀以及腐蚀管道剩余强度的分析评价提出了新的课题,论文针对多相流CO₂腐蚀和腐蚀管道剩余强度这两个问题展开,分别采用数值仿真、实验研究、理论分析等方法开展研究,分析了含CO₂多相流管道内腐蚀影响因素、腐蚀机理;建立了轴向均匀腐蚀和点腐蚀管道剩余强度评价方法,提出了腐蚀管道中双轴向腐蚀、双点腐蚀相互作用规律以及相互作用系数的计算方法。论文上述研究方法与成果的建立为排除海底多相流混输内腐蚀安全隐患提供了有效的技术支持。论文研究内容和研究成果如下:（1）应用全瞬态多相流仿真软件OLGA,采用数值仿真的研究方法,结合OLGA的管道多相流流动仿真功能,选择不同的CO₂腐蚀速率预测模型,分析了管线操作条件,如CO₂分压、出口压力、入口温度、处理量、含水率;路由条件,如管线倾角和立管高度;腐蚀介质条件,如Cl^-浓度、HCO₃^-浓度以及缓蚀剂浓度等因素对输送含CO₂油水混输管道和输送含CO₂湿气管道内腐蚀的影响规律。结果表明:由于管内气液两相流动状态的不同,输送湿气管道和油水混输管道内腐蚀速率变化规律是不同的。输送湿气管道,可能出现的段塞流通过影响管线持液率、壁面剪切力以及管壁润湿性等因素,控制管内腐蚀速率,而油水混输管线中一直都是满管流,管线持液率、壁面剪切力以及管壁润湿性变化不大。（2）研制了高压起伏管路模拟实验装置,应用实验研究方法,采用挂片失重、线性极化和电感的腐蚀速率检测手段,分别定量分析了管道运行压力、CO₂分压、管道运行温度、管内气液比、管内油水比、缓蚀剂浓度、Cl^-浓度、HCO₃^-浓度等因素对输送含CO₂多相流管道内腐蚀速率的影响规律。结果表明:在60oC-80oC之间时,材质均匀腐蚀速率和局部腐蚀速率均达到最高值,具体温度与CO₂分压有关,而非文献介绍的60oC;CO₂分压一方面提高了阴极反应,导致腐蚀速率加快,另一方面产生的腐蚀产物膜保护挂片基体,且随着温度的变化,影响的两面性表现出不同的影响规律;气液比主要通过影响壁面剪切力和壁面润湿度两个因素来影响CO₂腐蚀速率;原油含量主要通过壁面润湿度来影响CO₂腐蚀速率;Cl^-浓度对局部腐蚀速率的影响非常大,极易引起腐蚀穿孔;随着HCO₃^-浓度的增加,均匀腐蚀速率先增大后减小;缓蚀剂浓度对CO₂均匀腐蚀速率影响存在一临界值,超过临界值,腐蚀速率很小,即使再增加缓蚀剂浓度也对CO₂均匀腐蚀速率影响不大。低于临界值腐蚀速率均较高。（3）采用修正的B31G、BS7910、DNV-RP-F101和PCORRC等腐蚀管道评价规范,分别分析了中高强度单轴向腐蚀和单点腐蚀管道剩余强度,发现现有腐蚀管道评价规范存在很大的保守性。应用大型有限元软件ANSYS,采用非线性数值仿真的研究方法,定量分析了单轴向腐蚀中轴向腐蚀长度、轴向腐蚀深度、轴向腐蚀宽度、轴向腐蚀形貌、轴向腐蚀位置等因素,以及单点腐蚀中点腐蚀直径、点腐蚀深度等因素对腐蚀管道失效压力的影响,并以此为依据,应用应力集中理论分别建立了单轴向腐蚀管道剩余强度计算方法和单点腐蚀管道剩余强度计算方法。结果表明:与现有标准提供的计算方法相比,论文建立的计算方法计算误差小,可以满足X60以上中高强度单轴向腐蚀管道和单点腐蚀管道剩余强度的预测。（4）当前修正的B31G、BS7910和PCORRC等应用广泛的评价规范均为给出双腐蚀管道评价方法或准则,只有DNV-RP-F101给出了简单的评价准则,但存在较大保守性。论文应用软件ANSYS,采用非线性数值仿真的研究方法,分别定量分析了双轴向腐蚀轴向间距、双轴向腐蚀环向间距、相同轴向腐蚀深度、相同轴向腐蚀长度、不同轴向腐蚀深度、不同轴向腐蚀长度、交叉腐蚀对双轴向腐蚀剩余强度的影响,以及双点腐蚀轴向间距、双点腐蚀环向间距、相同双点腐蚀直径、相同双点腐蚀深度、不同双点腐蚀直径、不同双点腐蚀深度对双点腐蚀管道剩余强度的影响,分别提出双轴向腐蚀和双点腐蚀相互作用规律,并依次建立了双轴向腐蚀相互作用系数和双点腐蚀相互作用系数计算方法。更多还原

【Abstract】 With the increasing application of offshore multiphase transportation technology in the exploitation of offshore oil and gas fields, multiphase internal corrosion containing CO₂, especially slug flow internal corrosion has become a serious potential safety hazard affecting subsea pipelines. Because of the complication of the medium composition transported in oil pipeline and the complexity of slug flow, new task is proposed for multiphase flow internal corrosion containing CO₂ and residual strength analysis evaluation of corroded pipeline. This paper aims at two problems which are multiphase flow CO₂ corrosion and corrosion pipeline residual strength. Using numerical simulation, experimental research and theoretical analysis method respectively, influence factor and corrosion mechanism are analyzed in multiphase flow internal corrosion containing CO₂. Axial uniform corrosion and pitting pipeline residual evaluation method is established. Interaction law and computing method of interaction coefficient between biaxial corrosion and double pitting are proposed in corrosion pipeline. With the above research methods and results, effective technical support is provided to eliminate subsea multiphase flow transportation internal corrosion security hidden danger. Research contents and research results are as follows:Applying transient multiphase flow simulation software OLGA and the numerical simulation method, combining the multiphase flow pipeline simulation functions in OLGA, selecting different CO₂ corrosion rate prediction models, the effect of different pipeline operation conditions, routing conditions and corrosive medium conditions on the oil water mixed pipeline containing CO₂ and wet gas pipeline containing CO₂ is qualitatively analyzed. The operation conditions include CO₂ pressure, outlet pressure, inlet temperature, capacity, moisture content. The routing conditions are pipeline angle and the height of the riser. The corrosive medium conditions include Cl^- concentration, HCO₃^- concentration and corrosion inhibitors concentration.The result demonstrates that, the corrosion rate change rule of wet gas pipeline and oil and gas mixed pipeline is various on account of different two-phase flow conditions. In wet gas pipeline, the slug that may occur can control the pipeline corrosive rate through influencing liquid holdup, wall shear rate and wall wettability. While in the oil water mixed pipeline the liquid holdup, wall shear rate and wall wettability show little change because it is full pipe flow.Combining the features of loop-line test, autoclave experiment and electrochemical experiment, the high-pressure rectilinear oscillation experiment facility is developed. Referring to the quantitative analysis result of numerical stimulation, applying experimental research method and adopting weight-loss test, linear polarization technique and inductance as corrosion rate testing methods, the influences of pipeline operation pressure, CO₂ pressure, pipeline temperature, gas-liquid ratio, oil-water ratio, corrosive inhibitor concentration, Clconcentration, HCO₃^- concentration on the corrosion rate in wet gas pipeline containing CO₂ are quantitatively analyzed. The results show that the material uniform corrosion rate and localized corrosion rate reach the maximum between 60oC-80 oC instead of 60 oC in former papers. The relationship of CO₂ pressure and CO₂ corrosion rate is exponent sign. Gas-oil ratio influences CO₂ corrosion rate by effecting wall shear rate and wall wettability. Content of crude oil affects CO₂ corrosion rate by changing wall wettability. As the concentration of HCO₃^- increases, the uniform corrosion rate increases first and then decreases. There is a critical value of corrosive inhibitor concentration. When the concentration exceeds the critical value, the corrosion rate is small and increasing the concentration has little impact on the uniform corrosion rate. When the concentration is lower than the critical value, the corrosion rate is higher.According to emendatory pipeline corrosion evaluation specifications B31G、BS7910、DNV-RP-F101 and PCORRC, residual intensity of high uniaxial corrosion and pitting pipeline is analyzed. It shows that the current pipeline corrosion evaluation specifications are conservative.Utilizing finite element software ANSYS, nonlinear numerical simulation is carried out to analyze the effect of factors such as axial corrosion length, depth, width, morphology and location in uniaxial corrosion, pitting diameter and depth in pitting corrosion, on the pipeline failure stress. Based on the results, residual strength calculation method of uniaxial corrosion pipeline and single pitting pipeline is developed according to the stress concentration theory. It turns out that the new method can predict the residual strength of X60 high uniaxial corrosion pipeline and single pitting pipeline with little errors and lower conservation, when compared with the current calculation method proposed by the specifications.Utilizing ANSYS and nonlinear numerical simulation, this paper quantitatively analyzes the influence of biaxial corrosion axial spacing, biaxial corrosion ring spacing, the same axial corrosion depth, the same axial corrosion length, biaxial corrosion depth, biaxial corrosion length and cross corrosion, on the residual strength of biaxial corrosion. This paper also analyzes the influence of double pitting axial spacing, double pitting ring spacing, same double pitting diameter, same double pitting depth, different double pitting diameters and different double pitting depth on the residual strength of double pitting pipelines. The interaction laws of biaxial corrosion and double pitting are put forward respectively. And the interaction coefficient calculation methods of biaxial corrosion and double pitting are established respectively.更多还原