PURPOSE: To protect devices, pipings, etc. from damage in a power generating plant or the like, by lowering the concentration of an oxide scale-dissolving agent without lowering the dissolving speed of the oxide scale.
CONSTITUTION: An object 1 from which oxide scale is to be separated, is dipped in a solution 2 containing an organic acid and a reducing agent in a dissolving vessel 3. The solution is circulated through a conduit 6 by a circulating pump 5, while light having a wave length in a range of from ultraviolet to near infrared is radiated from a xenon lamp 4. Thus, oxide scale is separated from the object 1. In the light source of the xenon lamp 4, a luminosity is large especially in a range of from near ultraviolet to ultraviolet where the light-absorbing intensity of the scale is large and the light absorption by the reducing agent itself is effected, so that the oxide scale is converted into an easily soluble excited state by absorption of the light energy. Consequently, a higher dissolving speed can be obtained even when the concentration of the dissolving agent and a temperature in the dissolving step are low, as compared with that in a conventional method.
SAITOU MASAYUKI
ITOU HISAO
FURUYA YASUMASA
HITACHI ENG CO LTD