During the period of preventive maintenance of the Ulsan power plant, the scale was sampled from riser pipes, sparger pipes and other important parts in the FGD facilities. Various analyses such as concentration analysis, surface morphology, and crystal structure have been performed on the scale sample. The riser pipe scale was a gypsum dihydrate form. The sparger pipe scale was different from two units, namely, gypsum dihydrate form was obtained from that of unit 6; on the other hand, 1 to 1 ratio of gypsum dihydrate form and anhydrate form was elucidated from that of unit 4. Next, the analyses of GCP spray nozzle head scale, gas-cooling zone scale, and BUF inlet duct scale were focused on the effect of base material. On the basis of the analytical results, we expect to elucidate the formation process of the scale, and finally to improve the FGD process.