In the nuclear power plants (NPPs), wall thinning of the piping materials is generally caused by a
flow-accelerated corrosion (FAC) and leads to a rupture with no warning unless it is detected and
repaired in a timely manner. To reduce the FAC, it is better to use low-alloy steels, such as 1Cr-½Mo
and 2¼Cr-1Mo, having higher FAC-resistance than carbon steel. Meanwhile, in the secondary water
chemistry at the NPPs in Korea, hydrazine concentration is maintained within the range of 100~150
ppb. For applying these low-alloys to a piping material, we investigated the influence of hydrazine
concentration on their FAC. An experiment was carried out at pH25°C of 9 controlled with ammonia in
a deoxygenated aqueous solution containing 0~250 ppb-hydrazine by using a FAC test loop at 250°C
for 300 hours. Experimental weight loss showed a hydrazine concentration dependency of the FAC in
this concentration range, giving minimum at 150 ppb.
