FAILURE ANALYSIS OF THE BELLOWS EXPANSION JOINTS OF AUSTENITIC STAINLESS STEEL

According to the condition of the bellows expansion joints failures in a thermal power plant,the macroscopical 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.