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海底管道阴极保护数值模拟研究

作者:润色论文网  来源:www.runselw.com  发布时间:2019/10/31 9:44:34  

摘要:随着海洋经济的快速发展,对海洋的利用开拓活动越来越频繁,海底管道作为联络海洋油气开发、运输的重要桥梁,起到的作用越来越重要,数量也日益增长。海底管道的腐蚀防护主要采用阴极保护和涂层保护联合使用。由于复杂的海底环境,对海底管道阴极保护的检测和设计一直是阴极保护工程领域的一大难点,现实操作中不仅耗财耗力耗时,而且效果并不明显。数值模拟方法是研究海底管道阴极保护的大趋势,能够在很大程度上解决实际操作中的问题。因此本文采用数值模拟方法对海底管道阴极保护的几种典型复杂情况进行研究,这对海底管线阴极保护的检测设计具有重要意义。

首先对海底管道主要的两种防腐蚀方法进行分析介绍。然后通过理论推导,基于拉普拉斯方程并结合实验所测得的动电位极化曲线获得数值模拟研究的控制方程和边界条件。并且通过测点实验所测电位和数值模拟计算所得电位进行比较,验证了用COMSOL软件研究海底管道阴极保护的有效性。

接着通过有限元方法对海底管道阴极保护的三种典型情况进行了数值模拟研究:(1)海水流速对海底管道阴极保护的影响:利用旋转圆柱电极实验装置模拟得到海水流速为0~3.5m/s的极化曲线,通过分析自腐蚀电位和腐蚀电流密度的变化评价X80钢腐蚀状况。而后利用得到的极化曲线作为边界条件,利用有限元数值模拟方法,并引入防腐层击穿系数ξ,分别研究海底管道在裸钢(ζ=1)、涂层破损严重(ζ=0.1)、涂层破损较轻(ζ=0.01)的表面电位、阳极反应电流密度、阴极反应电流密度分布情况。结果表明,X80管线钢在三种不同的表面状态下,流速对阴极保护的影响规律有很大差别;(2)交叉并行海底管道阴极保护的相互影响:以管道所在海域的天然海水为电解质测量动电位极化曲线,作为有限元数值模拟的边界条件。分别研究海底管道在裸钢、涂层破损严重、涂层破损较轻时两条交叉并行管道在不同交叉角度下的阴极保护电位。结果表明:两条交叉管道在不同的涂层质量和交叉角度下,其相互干扰规律有很大差别,且在管道交叉位置受干扰最严重。(3)海底管道腐蚀缺陷处阴极保护情况研究:利用有限元方法来模拟缺陷处的局部电位和阳极/阴极反应电流密度。结果表明在腐蚀缺陷处阴极保护电流至少被部分屏蔽,特别是在缺陷处的底部位置。缺陷处对阴极保护的屏蔽随着缺陷深度的增加和宽度的减小而越来越强且在缺陷点宽度较大时随着电解质电导率的减小而屏蔽作用变强。

基于有限元模型的数值模拟技术能够有效地利用到海底管道的阴极保护设计和腐蚀监测中,在很大程度上克服了传统检测方法的很多弱点,结合传统技术与数值模拟,不仅可以为工程实际提供理论参考,而且对现实中腐蚀状况和使用寿命的评估能起到积极的作用。

With the rapid development of Marineeconomy, the use and exploitation of Marine become more frequent. As animportant bridge that contact exploitation and transportation of Marine oil andgas , submarine pipeline plays more and more important role, and also, thenumber of pipelines is growing fast. The corrosion protection of the submarinepipeline mainly used in combination with cathodic protection and coatingprotection. Because of the complicated seabed environment, the detection anddesign of cathodic protection for submarine pipelines has been a majordifficulty in the field of cathodic protection engineering. In practice, it notonly consumes money, effort and time, but also has no obvious effect. Thenumerical simulation method is a big trend in the study of the cathodicprotection of the submarine pipeline, and can solve the problems in practicaloperation to a great extent.So this article mainly do some research aboutcomplex condition of submarine pipeline’s CP by using the numerical simulationtechnology. It has great significance for the monitoring of subsea pipelinecorrosion and the design of cathodic protection.

Firstly, the two methods of corrosionprotection of submarine pipeline are introduced. And then through theoreticalderivation, based on the Laplace's equation and combined with thepotentiodynamic polarization curves measured in laboratory to obtain thecontrol equations and boundary conditions of the numerical simulation study.The study of submarine pipeline cathodic protection by using COMSOL softwareis  effective, verified by theexperiments of measuring points is effective. Then through the finite elementmethod  on the numerical simulationsstudy the three kinds of typical case of submarine pipeline cathodic protectionstudy:

(1)The influence of seawater flow’svelocity on X80 pipeline steel’s cathodicprotection:The polarization curves ofsea water flow rate of 0 ~3.5m/s are simulated by rotating cylindricalelectrode experiment device. The X80 steel corrosion status is evaluated byanalyzing the change of corrosion potential and corrosion current density.Then, using the obtained polarization curve as the boundary condition, and withthe finite element numerical simulation method and the introduction of thecoating breakdown coefficient, respectively study the distribution of electricpotential, anode reaction current density, cathode reaction current densitywhen submarine pipeline in three different surface conditions including baresteel, seriously damaged coating, less damaged coating. The results show thatthe influence rule of the flow rate on the cathodic protection is verydifferent when X80 pipeline steel is in three different surface conditions.  (2)Numerical simulation of cathodicprotection interference in cross/parallel pipeline:As the parameters of an X80submarine oil pipeline and cathodic protection system are given, the electricpotential polarization curve of electrolyte measured by natural seawater in thearea of the pipeline is used to be boundary conditions of finite elementnumerical simulation. And the wear coefficient of anticorrosion layer(ξ) isintroduced to study submarine pipeline cathodic protection potential in thenaked steel(ξ=1), the coating damaged seriously(ξ=0.1), the coating damagedlighter(ξ=0.01) with two cross or parallel pipeline at different angles. Itturned out that in different coating quality and angles, the law of mutualinterference between two cross pipeline is greatly different. And theinterference becomes maximum in cross location. (3) In this work, theeffectiveness of cathodic protection at corrosion defects on an X80 steelsubmarine pipeline was investigated numerically. A finite element model was developed to simulate distributions of localpotential and anodic/cathodic current density inside the defect. Resultsdemonstrated that there is a non-uniform potential and current distribution atcorrosion defects. The CP is shielded,

关键词:海底管道;阴极保护;有限元法;数值模拟

submarine pipelines; cathodic protection;finite element methods; numerical simulation

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