The removal and installation of nozzle dams (RIND) from primary water chamber of steam generator (SG) is one of the essential maintenance jobs with high radiation risk during outage in a nuclear power plant.

By the analysis of stress distortion of circular load symmetry flat plate, starting from the entire deriving course of thickness calculation formula, derives the simple formula of calculating blind flange thickness, which is fit for oral calculation of hydrostatic pressure testing of in-situ equipment and pipeline.