Aimed at the corrosion failure of the flat nozzle at the connection of the inlet expansion pipe of an oxygen concentrator,by using macroscopic and microscopic methods and combining with EDS analyses,it was determined that the corrosion penetrated into the metal matrix of flat nozzle and the rust product was mainly Fe2O3.The possible sources of corrosive medium were analyzed by logical derivation.Through finite element modeling,the Mises stress and CPRESS contact pressure distribution on the sealing surface of flared tube under the most common assembly condition with deflection angle in actual assembly were analyzed.It is concluded that the cause of corrosion failure of flat nozzle is that because the expansion pipe connection needs periodic and repeated disassembly,the assembly of different shaft deflection angles is easy to occur in the disassembly operation,resulting in uneven contact and abnormal deformation of the inner surface of the tube flare,which destroys the integrity of the sealing surface and forms a communication channel between the tube inside and the sleeve nut/flat nozzle gap.Condensed moisture or corrosive medium can gradually leak through these channels and accumulate at the gap,resulting in crevice corrosion.