Health assessment of radiant heater tube

A radiant heater tube in an oil refinery made of a particular grade of austenitic steel and service exposed for 61,000 hours was investigated for health assessment and safety. Experimentally determined yield strength and ultimate tensile strength as well as estimated 10,000 hours - 100,000 hours rupture strength as obtained from experimental data in the temperature range of 773 to 873K exhibit a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. Analysis of hot tensile and accelerated stress rupture data revealed that the service exposed radiant heater tube could remain in service for a length of more than ten years at the operating hoop stress level and maximum allowable skin temperature (158.78 MPa / 865 K), provided no localised damage in the form of cracks or dents had developed. It is recommended that a similar health check of these tubes should be carried out after 50,000 hours of service exposure at the desired operating conditions.