The radiant tubes in fired heaters operating in the creep range are designed as per API 530. The typical creep design life of the heater tubes is 100,000hours. Tube sample from this 1st Inter-heater was removed after 166,500hours of operation with the process gas outlet temperature of 550oC (1022oF). The tube skin temperature was observed in the range of 600-630oC. Scale characterization using SEM/EDS, Hot and ambient tensile testing, Hardness measurement, Accelerated Creep rupture testing and creep testing was carried out as part of the assessment. This paper explains the methodology adopted for remaining life assessment and compares the results from Larson-Miller Parameter method (LMP) & MPC Omega method. The remaining life evaluation was carried out as per API 579-1/ASME FFS-1. The Creep ductility factor ?cdO and Scatter band factor ?srO was adjusted to match the Omega (?) parameter and initial strain rate (eo) derived from the creep test. As part of the metallurgical analysis damage due to carburization and metal dusting was also evaluated.