注多元热流体环境下流速对N80钢腐蚀行为的影响研究

目的 研究不同流速条件下N80钢在注多元热流体环境中的腐蚀特征，探究流速变化对N80钢腐蚀行为的影响规律及机理。方法 利用自制高温高压多相流冲刷腐蚀环路装置模拟不同流速(0、0.5、1.0、2.0 m/s)的注多元热流体环境，采用失重法计算不同流速下N80钢的平均腐蚀速率，并同时进行原位电化学测试。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对不同流速条件下N80钢腐蚀后的腐蚀产物物相组成和表面微观形貌进行分析。结果 N80钢在注多元热流体环境中的平均腐蚀速率随着流速增加而增大。流速增加影响O2的扩散传质过程、近表面离子分布和壁面剪切力的大小，使腐蚀产物膜特征发生变化。0 m/s时，腐蚀产物主要由FeCO3和少量Fe2O3组成，为单层膜结构，腐蚀形态为均匀腐蚀。0.5~2.0 m/s范围内，腐蚀产物种类增加，主要由FeCO3、Fe2O3和少量FeO(OH)组成，呈双层膜结构，同时N80钢表面腐蚀产物膜出现鼓泡，且随流速增加鼓泡数量增加，去除腐蚀产物膜后发现鼓泡下方存在局部腐蚀。原位电化学测试结果表明:随着流速增加，塔菲尔极化曲线的阳极斜率增大，阴极斜率减小。电化学阻抗谱测试结果表明，N80钢表面外层腐蚀产物膜电阻Rf1、电荷转移电阻Rct和扩散电阻W随流速增加而减小。结论 流速增大加快了O2的扩散传质过程，使得腐蚀电化学控制步骤由阴极氧扩散过程转变为阳极溶解过程，且试样表面保护性FeCO3膜厚度减小，导致产物膜保护性降低。另外，Fe²⁺更容易被氧化形成Fe³⁺，局部FeCO3被氧化成为Fe2O3，破坏了内层膜的完整性，导致局部腐蚀发生。

Effect of Flow Rate on Corrosion Behavior of N80 Steel in a Multivariate Thermal Fluid Environment

In order to study the corrosion characteristics of N80 steel under different flow rate conditions in the environment of injecting multiple thermal fluids, and to explore the influence and mechanism of flow rate changes on the corrosion behavior of N80 steel, this article used a self-made high-temperature and high-pressure multiphase flow erosion corrosion loop device to simulate the environment of injecting multiple thermal fluids with different flow rates (0, 0.5, 1.0, 2.0 m/s). The corrosion simulation experiment was conducted in a corrosion testing section, and the average corrosion rate of N80 steel at different flow rates was measured by the weightlessness method. At the same time, in-situ electrochemical testing was conducted under the same conditions in the electrochemical testing section. Scanning electron microscope (SEM) and diffraction of X-rays (XRD) were used to analyze the phase composition and surface morphology of corrosion products of N80 steel after corrosion at different flow rates. The results indicated that the average corrosion rate of N80 steel in the multi element hot fluid environment increased with the increase of flow rate. The flow rate affected the diffusion and mass transfer of O2, the distribution of near surface ions, and the magnitude of wall shear force, leading to changes in the characteristics of the corrosion product film and inducing varying degrees of corrosion of the substrate. At 0 m/s, the corrosion product was composed of FeCO3 and a small amount of Fe2O3, which was a single-layer film structure, and the bond between it and the steel substrate was relatively tight, and the corrosion was uniform. Within the range of 0.5-2.0 m/s, the types of corrosion products increased, which mainly composed of FeCO3, Fe2O3, and small amounts of FeO (OH). The film layer showed a double-layer structure. The outer layer was an iron oxide film, which was reddish brown in color and had weak binding force with the inner layer film, making it easy to be detached. The inner layer was similar to the product film at 0 m/s. The macroscopic morphology showed that there were bubbles in the gaps between the inner and outer film layers, and the number of bubbles increased with the increase of the flow rate. After removing surface corrosion products, it was found that local corrosion occurred below the bubbles. In addition, the in-situ electrochemical results showed that as the flow rate increased, the anode slope increased, while the cathode slope decreased. The outer corrosion product film resistance Rf1, charge transfer resistance Rct, and diffusion resistance W showed a decreasing trend. Therefore, the above experimental results indicate that the increase in flow velocity accelerates the diffusion and mass transfer process of O2, causing the corrosion electrochemical control step to change from cathodic oxygen diffusion process to anodic dissolution process. Additionally, the protective FeCO3 film thickness on the sample surface decreases, leading to a decrease in the protective properties of the product film. Furthermore, Fe2+ is more easily oxidized to form Fe3+, and local FeCO3 is oxidized to Fe2O3, thus damaging the integrity of the inner film and causing localized corrosion.