Creep Damage Evaluation on 2.25Cr-1Mo Heat Exchange Tubes by Intra-granular Distortion Analysis

摘要

Creep damages of 2.25Cr-1Mo steel heat exchange tubes used for 80.000,190,000 and 221,000 hours in fossil power plants were quantitatively evaluated in terms of intra-granular distortion by TEM. A method for calculating the average intra-granular distortion of 2.25Cr-1Mo steel developed in our previous study was applied. Average intragranular distortion used for 221,000 hours was calculated as 0.058 deg./#mu# m and estimated 2.4 percent creep strain. Relation between creep strain and creep life consumption ratio indicated more than 70 percent of creep life was consumed at service condition. Heat exchange tube used for 80,000 hours was calculated 20 percent of creep life was consumed. Among the three specimens, creep life consumption ratio was linearly increased with operation period. Near the leak portion used for 221,000 hours high creep strain rate was anticipated from the dislocation structure and non-uniform distribution of intra-granular distortion in the tube. It was concluded intra-granular distortion (IGD) analysis was applicable for the evaluation of 2.25Cr-1Mo heat exchange tube employed under and over designed period.