奥氏体不锈钢波纹膨胀节失效分析

FAILURE ANALYSIS OF THE BELLOWS EXPANSION JOINTS OF AUSTENITIC STAINLESS STEEL

采用化学成分分析、硬度测试和金相检验等方法对某电厂多次发生泄漏的膨胀节进行了检测,对其形成原因进行分析。结果表明:膨胀节在服役环境下,其内侧蒸汽中携带的氯化钠,在膨胀节的波峰内侧部位发生富集和浓缩,并在工作条件下,腐蚀裂纹从膨胀节内侧启裂,以沿晶状特征逐渐向外壁延伸穿透,最终形成穿透裂纹和点蚀坑,使波峰处材质发生应力腐蚀开裂而导致泄漏。

According to the condition of the bellows expansion joints failures in a thermal power plant, the rnacroscopical and microcosmic cracking character, metallographic examination, fracture appearance and mechanical property on the failure specimens were tested and evaluated by means of optical microscopy, scanning electron microscopy and energy disperse spectroscopy and X-ray diffraction. The results shows that, the character of the expansion joints failure is stress corrosion cracking; The failure reason is that, there is some concentration NaCl steam at the inner side of joints operating on the high temperature, especially NaCl steam enriched and concentrated at the wave ridge on the opeartion condition. So the SCC took place at the joints wave ridge from the inner side to out side by means of intergranular crack. Gradually the pitting corrosion and penetrable crack came into being.