In order to investigate the applicability of hydrogen as a tracer for detecting Type IV creep damage, the hydrogen thermal desorption analysis (TDA) was applied to the small plate-type specimen (10×6×0.5 mm) containing weld metal (WM), heat affected zone (HAZ) and base metal (BM). The specimens were taken from the large cross weld specimens of ASME Gr.122 steel with various degrees of creep damage. Hydrogen charging was carried out by means of cathodic electrolysis, and the hydrogen-charged specimen was subjected to the TDA for measuring the hydrogen evolution curve. Experimental results revealed that the hydrogen desorption characteristic was changed depending on not only the degree of creep damage but also the distance from outer surface. The amount of desorbed hydrogen, CH, increased with consuming creep life from the early stage of creep damage, and this increase was more pronounced at the distances of around 5.5 and 20 mm from the surface. This result indicated that the creep damage was preferentially initiated and accumulated at those regions. From the individual analyses of WM, HAZ and BM specimens, it was also found that the increase in CH was caused principally by the creep damage accumulated in HAZ, especially, FGHAZ and ICHAZ. Additionally, the change in hydrogen thermal desorption characteristic was well correlated with the area fraction of creep voids and the small punch creep strength.
