Folic acid (FA), a non-toxic organic compound, is introduced as a synergist to the combination of nitrilotris(methylenephosphonic acid) (NTMP) and zinc ions. Results of gravimetric studies on the protective nature of surface film produced by the new ternary formulation, NTMP, zinc ions and folic acid on carbon steel in low chloride aqueous environment are presented. The surface film could be produced at relatively low concentrations of both NTMP and Zn2+ in presence of folic acid, when compared with the binary system containing only NTMP and Zn2+. The required minimum concentration of Zn2+ for maintenance of the protective film is found to be only 15 ppm. The new ternary inhibitor formulation is effective in the pH range 5 to 9. The protective nature of the surface film is retained for longer immersion periods as well as in hydrodynamic Key words: conditions.
