Continually increasing energy cost is an impetus to increasing the operating temperatures in industrial recuperators. However, higher service temperatures increase the risk of thermal fatigue failures. This paper presents a case study involving thermal fatigue analysis of a recuperator in an integrated steel plant.
The paper first describes the background and the rationale for a proposal to operate recuperators at the Inland 80" Hot Strip Mill at a higher than normal temperature for the purpose of fuel savings. A quick engineering analysis identified thermal fatigue as a high risk item that needed to be analyzed before deciding to operate the recuperators at a higher temperature. To quantify the resulting thermal effects, temperature profiles were recorded on an experimental basis for one furnace run at both the normal and higher operating temperatures. The paper describes the steps and assumptions involved in analyzing the data and estimating the thermal fatigue life. The calculations indicate that increasing the operating temperature from 1100° to 1250°F (593 to 677°C) may reduce the thermal fatigue life of the recuperator by as much as 637%. Based on these calculations and practical difficulties in achieving higher degree of skin temperature regulation, the option of operating recuperators at a higher temperature was considered unattractive.