A STUDY OF THE CORROSION OF CARBON-STEEL BY ALKALINE CHLORIDE SOLUTIONS CONTAINING, EITHER OR BOTH HYDROGEN-PEROXIDE AND SODIUM THIOSULFATE

The aim of this experimental work was to compare the relative effects on the corrosion of carbon steel of Na2S2O3.5H(2)O, Na2S2O5, H2O2 and NaCl in caustic solutions. Bore steel specimens and specimens coated w ith two different cootings were examined in these solutions. The corro sivity was evaluated by carrying out corrosion potential, potentiodyna mic polarization and mass loss measurements. The results indicate that Na2S2O3.5H(2)O ond Na2S2O5 have no significant effect on the corrosio n rate of bore steel, but which increases fourfold when these sulphur compounds ore both present in the caustic solutions. H2O2 is a corrosi on activator only in solutions of sulphur salts or in solutions which contain chloride ions. Thiosulphate ions, In the presence of chlorides , impair steel passivation especially at high concentrations of chlori de. This combination is the most harmful. The coating systems provided protection in all cases. Both had a two component epoxy system finish ing coat and a different primer. One, comprising a water-based primer with dispersed tonnin, gave higher protection than the other in which the primer was a two-compound acrylic system containing a chromate pig ment.