Finned tubes are widely used in the convection sections of industrial furnaces to enhance heat transfer efficiency. However, their service life can be limited by thermal, mechanical, and chemical degradation mechanisms, particularly in high-temperature environments where dissimilar materials are employed. This paper focuses on the investigation of finned tube failures observed in the convection section of the dehydration furnace (Unit 104). The tubes were manufactured from ASTM A106 Grade B carbon steel, and the fins from AISI 304 stainless steel. To identify the root causes of failure, several experimental techniques were employed, including optical microscopy, Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and corrosion testing in accordance with ASTM A262-15 (2021) Practice A. Visual inspections revealed multiple cracks on both tube and fin surfaces. The analyses indicated that sulfide formation on fin surfaces, welding imperfections at the fin–tube interface, and differences in heat transfer coefficients between the two materials contributed to uneven thermal distribution and crack initiation. Furthermore, microstructural examination revealed chromium carbide precipitation and sensitization along grain boundaries in the fin material. The combined effects of these factors promoted crack propagation from the fins into the tube wall, ultimately leading to leakage and fire hazards.