Creep Deformation and Rupture Properties of Long-term Used Super 304H Steel Boiler Tubes

Creep deformation and rupture properties of several long-term used Super 304H steel boiler tubes were presented in this paper. The aged superheater tubes that have been in service for about 140,000 hours at the approximate metal temperature ranged from 550°C to 640°C, have been investigated. Creep tests were conducted at 650°C and 700°C using standard and miniature specimens taken from the axial and circumferential directions of tubes, and effects of specimen size, sampling direction and position on creep properties were discussed. Creep deformation of long-term used materials with significant microstructural degradation accelerated earlier than that of virgin material, and the time to rupture and the fracture ductility were also smaller. The degradation of the rupture properties of the long-term used material was discussed in relation with microstructural analyses. In addition, there was little effects of specimen size and sampling direction on creep deformation and rupture time, whereas the creep rupture time changed significantly due to the sampling position.