Residual life estimation of service exposed reheater tubes in a boiler of a thermal power plant

摘要

The consequence of service failure can be tragic and expensive. There are many cases of engineering disasters resulting in loss of life and property. For boiler components the utmost attention is a must to ensure that such incidents do not take place. Life assessment exercise performed at regular intervals is a means to ensure the absence of such tragic service failure. This paper presents the high temperature tensile and the stress rupture properties of 149084 hours service-exposed reheater tubes made of 2.25Cr-1 Mo steels in a 120 MW boiler of a thermal power plant. These were used to estimate the remaining life for 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 520℃ to 580℃ exhibit a decreasing trend with increasing temperature. The effect of oxide scale deposition on the inner surface of the reheater tubes on the remaining life of the tubes has been discussed. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data reveal that the service exposed reheater tubes can remain in service for a length of more than ten years at the operating hoop stress level of 40 M Pa /540℃, provided no localised damage in the form of cracks or dents has developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 540℃.