In this study, the failure of the central thermocouple protection tube, as the main temperature-monitoring instrument in direct-reduction furnaces, has been investigated. The failure of this critical component causes disturbances in the production process and increases maintenance costs. The aim of this research is to identify the mechanisms affecting failure and to present a scientific framework for optimizing the design and increasing the service life of the tube. For this purpose, using the finite element method and the coupled Eulerian–Lagrangian approach in the ABAQUS software, the dynamic flow of granular materials and the pressure distribution along the central axis of the furnace, at the location of the thermocouple protection tube, were simulated. The developed numerical model was compared and validated with conventional analytical models, including the Janssen model and the Eurocode design standard. Then, different failure mechanisms, including yielding, fatigue, creep, and their combined effect, were examined. The results showed that at the operating temperature of 800 °C, the creep mechanism is the main factor reducing the durability and service life of the tube. In addition, the geometry and material of the tube play a decisive role in its stress behavior and operational life. The proposed model, by combining numerical analyses and classical relations, provides a reliable framework for predicting the service life and optimal design of the tube, which can increase reliability