Steam generator tubes in nuclear power plants are continuously exposed to harsh environmental conditions including high temperatures, pressures, fluid flow rates and material interactions resulting in various types of degradation mechanisms. Consequently they need to be inspected periodically for cracks and leaks. Multi-frequency eddy current technique is one of the widely used Non-Destructive Evaluation (NDE) techniques for steam generator tube inspection in nuclear power industry. The multi-frequency technique enables nullifying the effect of extraneous discontinuities via multi-frequency mixing and improves defect identification, classification and characterization of the eddy current data. In this paper, different defect characterization algorithms developed for the multi-frequency eddy current data obtained from the heat exchange tubes is discussed. A comprehensive comparison of the performance of the different characterization algorithms is also presented.