某深度调峰锅炉水冷壁管的氧化腐蚀及其机理

针对某超超临界燃煤锅炉运行 $ 4 \times 10^{4} $ h，深度调峰（负荷 40%～45%）300 h 的 SA-213T2 钢内螺纹水冷壁管内壁产生较严重腐蚀坑的现象，文章对腐蚀产物物相、腐蚀层的结构和形貌、微区成分进行检测，分析了腐蚀坑形成及该水冷壁管的氧化腐蚀机理。结果表明：该水冷壁管内壁氧化层由细小的球形颗粒堆积而成、结构致密，但在腐蚀坑周围的颗粒状腐蚀产物尺寸较大、结构松散；腐蚀坑呈半封闭或敞开状，深度达 $ 150 \mu m $。水冷壁管内壁腐蚀坑主要发生氧腐蚀和氧浓差腐蚀，腐蚀速度快，腐蚀产物结构疏松；而水冷壁管内壁发生氧化腐蚀，腐蚀产物为 $ Fe_{3}O_{4} $ 和少量的 $ Fe_{2}O_{3} $，腐蚀层结构致密，腐蚀速率慢。该水冷壁管内壁腐蚀坑可能成为锅炉的安全隐患，须予以重视。

Aiming at serious corrosion pits in the inner walls of SA-213T2 steel rifled water wall tubes of an ultra-supercritical coal-fired boiler running for $ 4 \times 10^{4} $ h under deeply-varied load of 40%-45% for 300 h, the phases, microstructures and morphologies of corrosion layers and micro-zone compositions were tested and analyzed to clarify the formation of the corrosion pits and oxidation corrosion mechanism of the water wall tubes. The results show that the inner-wall oxidation layer has a dense structure and is piled by ultra-fine spherical particles, however, the oxide particles near the corrosion pits are coarser with a loose structure. The corrosion pits are semi-closed or completely open, having an average depth of 150 $ \mu $m. Corrosion pits in the inner-wall water wall tubes result from the oxygen corrosion and the oxygen concentration corrosion, which have a high corrosion rate and a loose corrosion product structure. On the contrary, the oxygen oxidation of the inner walls of the water wall tubes takes place to form $ Fe_{3}O_{4} $ and small amount of $ Fe_{2}O_{3} $ as the corrosion product. The corrosion layer is dense and has a small growth rate. The corrosion pits in the inner walls of the water wall tubes may be a potential safety hazard of the boiler and should be taken seriously.