Creep Damage Evaluation of High Cr Ferritic Steel Based on Change in Hydrogen Desorption Characteristics

The change in hydrogen desorption characteristic due to creep was investigated to examine the possibility of hydrogen as tracer for detecting and evaluating the creep damage accumulated in high Cr ferritic boiler steel, Gr.91. Hydrogen charging into the creep specimen was conducted by means of cathodic electrolysis. Next, the thermal desorption analyses (TDA) were carried out at temperature range from room temperature to 270°C for measuring the hydrogen evolution curve. The experimental results revealed that the amount of hydrogen desorbed during analysis, C_H, increased with increasing creep life fraction, although the trend of increase in C_H was strongly dependent on the stress level. Moreover, there was an almost linear correlation between the logarithm of C_H measured on the creep ruptured specimen and the Larson-Miller parameter (LMP), which was approximated by “log C_H = 0.39 LMP – 13.4”. This can be a criterion for creep rupture and means that as far as the C_H does not reach the line, the rupture never occurs.