Oxide scale control is one of the critical maintenance issues in fossil fuel power plant. Hence, the water treatment of the feed water has been changed from all-volatile treatment (AVT) to oxygenated treatment (OT) by added some amount of oxygen in the system to form a stable oxide and minimize the scale growth rate. In this work, the oxide scales formed on T12 water wall tube after one cycle of chemical cleaning treatment under OT condition in a supercritical coal power plant were characterized by using various methods. It was found that the oxide scale formed on the inner surface of the tube had a multi-layer structure with a porous outer layer consisting of Fe3O4 and Cr-rich α-Fe2O3 oxides and a dense inner layer consisting of Cr-rich spinel oxide. A Cr- and Mn-enriched outermost layer was also observed. Cavities, pits, and exfoliation were observed in the oxide scales. The cavities and grain boundaries behaved as the short path of the diffusion of oxygen into the metal. Intergranular oxidation was observed between the inner layer of oxide scale and matrix. The distribution, morphology, and chemical compositional of these oxides were assessed and discussed from a point of view of the suitability of current chemical cleaning solution and procedure which has been used for AVT descaling.

中文翻译：

---

超临界电厂长期服役后T12水冷壁管形成氧化皮的表征

氧化物水垢控制是化石燃料发电厂的关键维护问题之一。因此，给水的水处理已从全挥发处理（AVT）转变为氧化处理（OT），通过在系统中添加一定量的氧气以形成稳定的氧化物并最小化水垢生长速率。本工作采用多种方法对某超临界燃煤电厂在OT条件下经过1个循环化学清洗处理后T12水冷壁管上形成的氧化皮进行表征。发现管内表面形成的氧化皮具有多层结构，外层为Fe3O4和富Cr的α-Fe2O3氧化物构成的多孔外层，内层为富Cr尖晶石氧化物构成的致密内层。还观察到富含 Cr 和 Mn 的最外层。空洞、凹坑、在氧化皮中观察到剥落。空腔和晶界表现为氧扩散到金属中的短路径。在氧化皮内层与基体之间观察到晶间氧化。从当前用于 AVT 除垢的化学清洁溶液和程序的适用性的角度评估和讨论了这些氧化物的分布、形态和化学成分。