Metallurgical Behavior of Uniform High Tube Skin Temperature for Low Carbon Steel Tubes in Crude Distillation Furnace

Abstract A failure occurred in the fired heater tubes of the radiant section of a crude distillation furnace approximately ten months prior to the scheduled turnaround. A permanent replacement was proposed; however, this option would have resulted in an unplanned 12-day shutdown. To maintain production, the affected furnace coil comprising convection and radiant tubes fabricated from ASTM A161 Grade LC low-carbon steel was isolated. Consequently, the tubes were exposed to elevated metal temperatures in the absence of internal process flow, resulting in the loss of convective cooling and significant metallurgical changes in the microstructure and material properties. A Fitness-for-Service (FFS) creep assessment was subsequently performed to determine whether the convection tubes remained suitable for continued operation under these high-temperature conditions. Concurrently, routine thermographic scans were conducted to validate the temperature data used in the Larson–Miller Parameter (LMP) and FFS analyses. This paper presents an investigation into the corrosion and degradation mechanisms affecting ASTM A161 Grade LC low-carbon steel under prolonged exposure to elevated tube metal temperatures. The findings provide valuable insight for improving the accuracy of Fitness-for-Service evaluations and for developing more reliable approaches to assessing high-temperature degradation in fired heater components.