超超临界塔式炉T23水冷壁早期失效分析

Analysis on Early Stage Failure of Welded T23 Steel Waterwall in USC Tower Boilers

对国内多台超超临界塔式炉T23水冷壁早期失效案例进行了统计,对典型失效管样进行宏观和微观分析,测试接头的力学性能,在此基础上分析失效机理及主要影响因素。研究结果表明,失效是由于焊缝产生横向裂纹,裂纹沿晶界扩展。初步判断裂纹性质为楔形蠕变裂纹。合金过饱和固溶使焊缝处于高硬度水平是产生楔形蠕变裂纹的内因,水冷壁密集焊缝结构使接头部位的拉伸应力增大,它与内压应力叠加提供了裂纹形成和扩展的力学条件。降低焊缝硬度和细化晶粒有利于避免失效。

The statistical analysis on causes of early stage failure of T23 steel waterwall in USC tower boilers is conducted. Macroscopic and microscopic examinations on the typical failured specimens are performed and the mechanical properties of the welded joints are tested to determine the mechanism and main factors for the failures. The results show that the failure are due to the traversing cracking occurred in the butt weld of pipes and propagated along its grain boundaries, which is regarded as wedge creep cracking. The high hardness of the weld is the internal cause for wedge creep cracking. The great tensile stress prodcued by the horizontal shrinking of dense fin welds in the waterwall, is the mechanical reason for the cracking formation and extension. Therefore, reducing the hardness and grain size of weld are helpful to aviod cracking.