350MW超临界锅炉水冷壁管表面网状裂纹失效分析

Failure Analysis on Surface Net Cracks of Water Wall Tubes for 350 MW Supercritical Boiler

为了保证超临界锅炉的安全稳定运行,文中借助OM、SEM、EDS、XRD等手段对350 MW超临界锅炉水冷壁管基体成分、物相构成和表面网状裂纹的形貌、物相构成等进行分析。试验结果表明:该电厂锅炉水冷壁管壁表面网状裂纹位于水冷壁管与其鳍片之间的焊缝区,起裂源为焊缝中靠近熔合线的柱状晶晶界,裂纹沿柱状晶晶界扩展,裂纹界面有S元素富集,属于典型的焊接热裂纹;起裂原因主要是焊接内应力较高,应在焊接过程中应采取适当工艺措施降低焊接应力,防止焊接热裂纹的产生。

In order to ensure supercritical boiler operating safely and stably,morphology and phase composition of matrix element,physical structure and surface net cracks for 350 MW supercritical oiler were analyzed and researched by OM,SEM,EDS and XRD. The results show that surface net cracks of power plant boiler water wall tube wall lie in the welding zone between water wall tube and rectangular fin. Columnar grain boundaries in the welding zone near the fusion zone are the cleavage initiation sites and the cracks along the grain boundary of the columnar crystal expand. S enriches on the crack interfaces. The surface net cracks belong to welding hot cracking. The cracking mainly reason is high internal stress. So the proper technological measures would be taken to decrease the welding stress in the welding process and prevent the production of welding hot cracking.