Fisuración en tubos de refrigeración del horno cuchara de aceria de Ternium Siderar

J. USART; O. BIGA; R. LÓPEZ; J. INES; I. BOCCANERA; J. BOOMAN; J,L. OTEGUI

San Nicolás

Conferencia; 5° Conf. Usos del Acero, Instit. Argentino de Siderurgia; 2009

This article analyses repeated failures in refrigeration tubes of the Ladle Furnace, and mitigation alternatives. Failure mode was identified as circumferential crack growth from the tube outer surface exposed to heat, associated with previous damage due to cyclic plasticity or low cycle thermal fatigue. This damage is caused by heating and cooling of the tubes during service, and to the differences in temperature between hot and cold surfaces. Heat cycles are related to the batch nature of the Ladle Furnace process, and to the formation and loosening of slag build up at the refrigerating tube walls. Through the thickness temperatures gradients also cause high stress cycles that can surpass twice the tensile strength of the material at that temperature, and generate thermal fatigue damage. No other degradation mechanisms, such as loss of thickness, severe corrosion, and creep or fabrication defects were likely to contribute significantly to the observed failures. Mitigation alternatives involve changing the tubes material by one of better fatigue resistance at process temperature, reducing temperature gradients on the tubes wall and making heat transfer more uniform. It is then suggested to add slag trappers at tube surfaces, and booster pumps to increase pressure and flow rate of cooling water.