| Abstract |
Eight scale samples were collected from various parts of Separator Vessel 303 in the Bacman Geothermal Production Field, Philippines during a Risk Based Inspection in December 2001. Gray to black scales having variable thickness up to ~2 mm deposited on the interior walls of the vessel, and on the surface of the steam standpipe. In those instances where thick corrosion products and scales formed, these tended to block the potentially corrosive two-phase and steam fluids from the underlying steel, and minimal corrosion was observed. Areas subject to erosion had thinner corrosion product scales, but corrosion rates were still acceptably low. Microscopic analysis of scales in the upper part of the separator vessel showed dominance of corrosion products such as magnetite (Fe3O4), hematite (Fe2O3), pyrrhotite (FeS), and pyrite (FeS2). SEM EDX analysis confirmed that Fe, S and O are the major components of these scale samples. In the middle and lower portions of the vessel where separated brine is present, scales are made up of amorphous silica (SiO2) and clay in association with corrosion products. The detection of Si, Al, and Mg by SEM EDX analysis verified the presence of silica and clay in these scale deposits. The rate of formation of the thin, adherent scales in Separator Vessel 303 is low and hence the scales do not pose any major problem in the operation of the Bacman Fluid Collection and Reinjection System (FCRS). The level of protection provided to the underlying steel by the formed scales is proposed to be dependent on the thickness and adhesion of the formed scales and the self healing characteristics of the scales. |