管内流场对流动加速腐蚀的影响机理研究

Flow-accelerated corrosion (FAC) issues encountered in water and water-steam mixture piping systems can seriously affect the safety of the whole plants. Changing the water chemistry condition or using high Cr alloy pipes are currently adopted as main solution measures. In our previous works, we found that the flow field within pipes seemed to play an important role in FAC processes, and this was especially obvious for locations where flow field were strongly disturbed. In this work, we decide to firstly design a testing loop operating under the same condition of practical pipes, and then measure the local FAC rates of different locations on the test section simultaneously, through implanting the self-designed corrosion sensors into the pipe wall. The test sections employed in our testing loop include elbows and pipes equipped with orifice, valve and so on, which are typical failure components in practical plants. Through comparing the measured FAC rate data with the calculation results of computational fluid dynamics (CFD) models established to simulate the flow field within the test sections, we can consequently figure out the influence mechanism of flow field on FAC processes. Besides, it is also intended in this work to identify the indicator parameters for FAC, i.e. one or several fluid dynamics parameters capable of precisely characterizing the FAC rate and distribution. Through investigating the factors governing the indicator parameters, we will propose, with the aid of CFD simulation, several feasible measures from the aspect of fluid dynamics to decrease the FAC rate. This work can not only benefit the theoretical research on FAC mechanism, but also provide valuable guidance for determining the maintenance and inspection strategy of the water and water-steam mixture piping system, optimizing the pipe geometry, and adjusting the pipe layout.

流动加速腐蚀会造成水和汽-水输运管道壁厚不断减薄，严重影响相关系统的安全性，目前主要通过调控水化学工况和更换管材来予以缓解。前期理论建模研究和案例分析均表明，管内流场对流动加速腐蚀有非常重要的影响。本项目针对常发生严重流动加速腐蚀的典型管段，搭建能反映实际流动的高温循环回路试验系统，利用传感器阵列在线监测管段不同位置的局部腐蚀速率。在此基础上，运用计算流体力学数值模拟来计算分析典型管段内局部流场对流动加速腐蚀的影响机理，得到可以准确表征流动加速腐蚀速率及其分布的流体动力学参数——指示参数。通过分析影响指示参数的主要因素和影响机理，结合计算流体力学数值模拟和试验，提出可以有效降低典型管段流动加速腐蚀速率的方法。项目研究将在现有工作的基础上进一步揭示流动对流动加速腐蚀的影响规律，可应用于化工、核电、火电等工业的水和汽-水输运管道的设计优化、运行监测和检修维护策略制定。

世界范围内由流动加速腐蚀（Flow-accelerated corrosion，FAC）引起的输运管道破裂事故从未停止，相关研究一直在不断深入发展。本课题通过研究管内流体湍流结构演化等流动特性，从流动对传质速率的影响入手，分析流体动力学因素影响FAC的机理，采用理论与试验相结合方法，重点对弯管段和孔板下游管道在局部区域的流动形态进行研究，其主要内容如下。.（1）针对常发生严重FAC的典型管段，搭建能反映实际流动的高温循环回路试验系统和设计能够直接嵌入到管壁上的高温阵列腐蚀电极；电极表面与管壁内表面完全一致从而避免了传统的探针形传感器会干扰流场的问题；试验过程中能够在线实时地获取不同位置处的局部FAC速率，既可对比不同位置处FAC速率的差异，又可掌握某一特定位置处FAC速率随时间的变化。.（2）利用阵列腐蚀电极技术研究了不同pH、不同流速、不同温度以及不同管材弯管段FAC速率及其分布。结果表明，高温条件下阵列腐蚀电极的最小电荷转移电阻和最大腐蚀电流均位于弯管段最外侧，FAC最严重区域位于弯管最外侧，说明高温条件下弯管段阵列腐蚀电极存在电偶腐蚀效应。在电偶腐蚀系统中，弯管内弯侧阵列腐蚀电极作为阴极，腐蚀速率受到抑制；弯管外弯侧阵列腐蚀电极作为阳极，腐蚀速率被加速。.（3）结合阵列腐蚀电极技术和计算流体动力学模拟，探究高温条件下弯管段局部FAC速率与流体动力学参数相互作用的内在关系。通过将试验得到的弯管段FAC速率分布与模拟得到的流场分布作对比分析，建立流体动力学参数与FAC之间的联系，确定径向速率可以作为准确表征弯管段FAC速率及其分布的指示参数，以径向速率的大小作为衡量FAC速率的标准。.（4）利用指示参数确定降低FAC速率的可行性预测方案并进行试验验证，在此基础上结合计算流体动力学模拟提出能够表征高温条件下弯管段FAC速率及其分布的三种预测方法，并结合弯管段试验数据验证其有效性。此外，应用所提出三种预测方法来分析不同孔径比孔板下游管道腐蚀速率及其分布，验证预测方法的通用性。.本课题研究可为化工、核电、火电等工业的水和汽-水输运管道的设计优化、运行监测和检修维护策略制定提供理论依据和技术支撑。