Abstract
The hydrogen desorption characteristic of Gr.122 steel welded joint was investigated to examine the applicability of hydrogen as tracer for creep damage evaluation. The thermal desorption analysis (TDA) was applied to the interrupted creep specimens with various degrees of damage. The thin plate-type specimen parallel to the loading direction was taken from the outer surface, the center of thickness and the inner surface of the welded joint. Hydrogen charging into the creep specimens was conducted by means of cathodic electrolysis. Next, the hydrogen-charged samples were subjected to the TDA for measuring the hydrogen evolution curve. The experimental results revealed that the peak height and the amount of desorbed hydrogen, CH, of the heat affected zone (HAZ) increased significantly with creep, and this increase was more pronounced at the outer surface, although that of the weld metal showed no significant change. The increase in CH with creep seemed to be attributable to the defect formation (the geometric damage) rather than the microstructural changes, because the hydrogen desorption characteristic was not significantly influenced by the mere thermal aging. In addition, there was a good correlation between the small punch (SP) creep test result and the CH, and this result indicated that the present hydrogen thermal desorption analysis could be a strong tool for detecting and evaluating the creep damage accumulated in the welded joint.
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