Objective To find out the causes for corrosion cracks by failure analysis in the condition that the bellows subassembly made of 06Cr19Ni10 stainless steel in the sealed valves cracked which resulted in the failure of sealed valves. Methods The appearance of the failed bellows subassembly was examined by naked eyes, the metallographic structure and the chemical components were analyzed respectively by the metallographic microscope and direct reading spectrometer; the morphology and fracture of the failed subassembly were observed by SEM. Results Cleavage plane, cleavage steps and corrosion products were seen on the fracture of the outer wall, which was the typical feature for stress corrosion cracking of austenitic stainless steel. Some dimples were observed on the inner wall fracture, which indicated that the inner wall had ductile fracture. The analysis showed that the quality of microstructure and chemical composition of the bellows subassembly met the requirements on design and usage. The medium test results showed that the content of harmful ions was relatively high in the heat transfer fluid (HTF) which contained 55 mg / kg chloride ion and over 350 mg / kg sulfur. Conclusion The main fracture causes of outer and inner wall of the double-layer bellows subassembly were different; the failure of outer wall was due to the stress corrosion related to the high content of chloride ion, while the fracture of inner wall was ductile fracture,which was due to the significant decrease in compressive strength in the result of the plane instability cause by the failure of outer wall. It is proposed that the content of harmful ions should be reduced in HTF and the stainless steel with better corrosion resistance should be used.