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复杂环境下长输管道阴极保护数值模拟研究

作者:完美论文网  来源:www.wmlunwen.com  发布时间:2019/10/8 9:16:01  

摘要:长输管道是当下实现石油与天然气资源远距离高效配置的一个主要方式,阴极保护技术作为管道腐蚀防护的一个主要手段,对于保障管道的安全运行具有重大意义。但是随着我国近些年能源与交通运输业的快速发展,油气长输管道规模不断扩大,地下管道系统所处的大环境也因此变得更加复杂,随之而来的外界干扰会对阴极保护效果产生严重影响,甚至可能导致阴极保护系统过早失效。传统的阴极保护设计与优化方法已经难以满足这些新问题带来的新要求。因此利用数值模拟技术研究不同电解质环境下不同管道结构、以及直流杂散电流干扰对阴极保护电位和电流密度分布产生的影响、评估预测牺牲阳极的使用寿命,对阴极保护系统的优化设计和日常维护有着重要意义。

通过实验和理论计算获取X80管线钢在均一海水和土壤中的电化学特性参数,作为研究中数学模型的阴极边界条件。建立埋地金属管道阴极保护系统的简化模型,利用数值模拟软件求解获取管道表面阴极保护电位数据;自行搭建埋地管道腐蚀实验装置,通过实验验证了数值模拟的有效性。

分析了管道铺设于均一的海水和土壤中时阴极保护的电位分布情况,研究不同电解质电阻率对阴极保护电位分布的影响规律。基于管道表面防腐蚀涂层的破损程度,研究海底管道系统中存在弯管和分支管时阴极保护电位的分布情况,同时研究了弯管转过的角度不同时阴极保护电位的分布规律。在此基础上,研究了牺牲阳极不同布置形式对阴极保护电位的影响。结果表明,不同角度弯管和分支管对管道阴极保护影响较大,且在管道转弯处与出现分支处这种影响最为明显,可采用分布式阳极加强对这部分管道的保护。

以地铁牵引电压造成的直流杂散电流干扰为例,研究直流杂散电流干扰下埋地管道阴极保护电位和电流密度的分布规律,同时研究了地铁轨道与金属管道两种不同铺设形式下(并行铺设和交叉铺设),阴极保护电位和电流密度的分布情况。和管轨并行铺设相比,管轨交叉铺设时杂散电流干扰对阴极保护的影响相对较小;随着地铁线路牵引电压的增大、与管道距离的减小,阴极保护系统中牺牲阳极的损耗量也会越来越大,及时采取排流等措施对管道加以额外的保护就显得尤为重要。

建立埋地管道阴极保护系统时变型模型,基于管道表面防腐涂层的破损情况和牺牲阳极的性能参数,通过数值模拟技术对牺牲阳极的使用寿命做出评估预测。结果表明,牺牲阳极的实际使用寿命要短于其设计使用寿命,且在系统达到预期使用寿命前的4~5年,应当加强对管道沿线电位分布情况的实时监测,以便及时更换阳极从而保障管道系统的安全运行。

Long-distance pipeline is a major method torealize efficient allocation of oil and gas resources. As an importantanti-corrosion means, cathodic protection is of great significance for ensuringthe safety and stability of pipeline system. Whereas, with the rapiddevelopment of China's energy, power and transportation industries, the scaleof oil and gas long distance pipeline is expanding and the underground pipelinesystem is becoming more and more complicated. These external disturbances maycause a serious impact on the cathodic protection system, such as leading topremature failure. Using traditional methods to design and optimize thecathodic protection system is difficult to meet the new requirements brought bythese new problems, so it is meaningful to study the influence of differentpipeline structures in various electrolyte environments, and DC stray currentinterference on distribution of cathodic protection, and evaluate the servicelife of cathodic protection system by using numerical simulation technology.

By experiment and theoretical calculations,the boundary conditions of X80 pipeline steel in uniform seawater and soil wereobtained in the model built in this study. Simulation software was adopted to obtainthe potential distribution of cathodic protection on pipeline surface.Effectiveness of numerical simulation was verified by comparison withexperimental data achieved by building a buried pipeline corrosion experimentdevice.

The distribution of cathodic protectionpotential in uniform seawater and soil was analyzed, and the influence ofvarious electrolyte resistivity on potential distribution was also studied.Based on the damage of anti-corrosion coating on pipeline surface, thedistribution of cathodic protection potential in the presence of elbow andbranch pipe in the pipeline system was researched. Furthermore, when the angleof the bend was different, the potential distribution law was also studied. Onthis basis, the influence of different arrangements of sacrificial anodes oncathodic protection potential was studied. The results shows that differentangles of bend and branch pipe have a great influence on the cathodicprotection system, and this effect is most obvious at the turn and branch ofthe pipeline. The distributed anode ought to be applied to strengthen theprotection of this part.

Taking the dynamic DC stray currentinterference of subway as an example, the influence of DC stray currentinterference on cathodic protection potential and current density distributionwere investigated. As to two different laying conditions for tracks andpipelines (parallel-laying and cross-laying), when the rails and pipelines arelaid across, the influence of DC stray current is relatively small. With theincrease of traction voltage of subway rails and the decrease of the distancefrom pipelines, the loss amount of sacrificial anode in cathodic protectionwill also become larger and larger. It is especially significant to takemeasures such as drainage in time to provide additional protection.

The time-varying model of the cathodicprotection system for buried pipeline was established. Comprehensively takinginto account the damage condition of anti-corrosion coating on pipeline surfaceand the performance parameters of the sacrificial anode, the service life ofsacrificial anode was evaluated and predicated by numerical simulation. Theresults indicates that the actual service life of sacrificial anode is shorterthan its design service life. In order to ensure the safe operation of pipesystem, it is necessary to enhance real-time monitoring of potentialdistribution along the pipeline to replace sacrificial anode in time about 4~5years before the system reaches its expected life.

关键词:阴极保护;数值模拟;电解质环境;杂散电流干扰;使用寿命

cathodic protection; numerical simulation;electrolyte environment; stray current interference; service life

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