化学清洗时过热器氧化皮剥落部位基材腐蚀试验研究

摘要

锅炉过热器氧化皮发生局部剥落的部位,在进行化学清洗时会发生局部电化学快速腐蚀的情况.工程清洗后的割管和试验室的验证性模拟清洗试验,均发现了局部氧化皮剥落部位出现了深度在400 μrn以上的腐蚀坑,且这种腐蚀主要在铁索钢如T22、12Cr1MoV、T91中发生.通过电化学腐蚀试验装置,开展了对这种腐蚀的监测评价和腐蚀控制工艺研究.选取T22、12Cr1MoV、T91等3种过热器管样,进行氧化皮清洗溶解试验,测量氧化皮清洗过程中完整氧化皮管样电极和裸露金属电极之间腐蚀电流密度,并通过对比试验考察清洗液加入还原剂后的腐蚀电流密度变化情况.研究结果表明,试验所用材料氧化皮脱落部位化学清洗时的局部腐蚀速率是标准规定值的数十倍,可通过及时补加还原剂抗坏血酸的方法加以控制.%Localized electrochemical corrosion may take place at region of oxide exfoliation or cracking in the process of chemical cleaning for superheaters.After the chemical cleaning process,the corrosive pits over 400 tm deep are detected on both cut superheater samples and simulated testing tubes,especially in iron steel such as T22,12Cr1MoV and T91.The monitoring evaluation and corrosion control technology are carried out through the electrochemical corrosion test device.Three kinds of superheater tube samples are selected,such as T22,12Cr1 MoV and T91,and the corrosion current density between the intact oxidation tube electrode and the bare metal electrode during the oxidation skin cleaning process is measured.The change of corrosion current density after the addition of reductant is investigated by contrast test.It is shown that the local corrosion rate during chemical cleaning of the exfoliated parts of the materials used in the experiment is tens times of the standard values,which can be controlled by adding ascorbic acid in time.