核电环境下流体加速腐蚀行为及其研究进展

 多年来流体加速腐蚀问题一直困扰着核电工业。在核电环境下，流体加速腐蚀是碳钢或低合金钢表面保护性的氧化膜在水流或多相混合物液流冲刷作用下发生溶解、破坏，从而引起管壁减薄的过程。流体加速腐蚀主要发生在管形装置中有强烈湍流的部位，减薄区域在工作压力、水流突然冲击或启动加载等冲击力的作用下发生破坏，对于大型装置可能发生突然爆裂，流体加速腐蚀特征是大面积的壁厚减薄而非局部腐蚀。在单相流体条件下，当腐蚀速率较高时，金属表面出现马蹄形、扇贝形、桔子瓣形的腐蚀形貌；在两相流条件下，管道的腐蚀形貌是“虎皮纹”。本文针对与核安全密切相关的流体加速腐蚀问题，从流体加速腐蚀的行为、机制和主要影响因素方面进行综述。在流体加速腐蚀过程中，其主要影响因素是通过改变金属表面氧化膜性能、离子扩散状态等过程，影响流体加速腐蚀速率。尽管流体加速腐蚀是造成核电设备损坏的主要问题之一，但在已有经验和研究的基础上，采用合理的防护方法可以提高设备可靠性，如改良水化学成分可降低腐蚀速率，可以更换敏感区和损坏区的材料等。

A Review of Flow-Accelerated Corrosion in Nuclear Power Industry

Flow-accelerated corrosion has plagued the nuclear power industry for years. In the nuclear environment, the protective oxide film of carbon steel or low alloy steel may experience dissolution and destruction under the action of water flow and multi-phase and liquid materials flow, which would lead to a wall thinning process. Flow-accelerated corrosion occurs mainly in the tube-shaped parts, where are strong turbulent flows, under the action of working pressure, sudden shock or impact or the boot loader, damage may be produced in the thinning region, and sudden burst may happen in large devices. The characterization of flow-accelerated corrosion concerns a large area of wall thinning rather than a localized part. In single-phase fluid conditions, when the corrosion rate is high, the corrosion of the metal surface has morphology of U-shaped, scallop-shaped, orange-shaped flaps; while in the two-phase flow conditions, the pipe corrosion has the morphology of the tiger pattern. This paper reviews the flow-accelerated corrosion (FAC), as an important issue related with nuclear safety. The corrosion behavior, mechanism, and key parameters of FAC are outlined. The FAC process in nuclear power plants is characterized. Many influencing factors of FAC processes are analyzed in terms of surface corrosion film, diffusion rate and FAC rate. Although FAC remains a major problem in nuclear power plants, properly designed protection methods, based on the experience and studies of FAC, will improve plant reliability, such as by adjusting water chemical composition to reduce the corrosion rate and by replacing the materials of damaged and sensitive areas.