Abstract: Using techniques like chemical composition analysis, microstructure, microhardness analysis, scanning electron microscopy, energy spectrum analysis, and nanoindentation, failure analysis was carried out in response to the cracking behavior of the furnace tube at the radiation section outlet of an ethylene cracking furnace that was in long-term service. The findings show that the combination of materials and environmental conditions (carburizing and high-temperature oxidation) resulted in the peeling of the oxide layer and the weakening of grain boundaries. This increased the brittleness and hardness of the grain boundaries and led to intergranular cracking. Recommendations and guidance were provided for the production of actual furnace tubes based on the results of the failure study.