Effect of Sodium Thiosulfate on Brass L-68 Corrosion in Hydrochloric Acid.

When chemically cleaning heat exchange apparatus made of brass and other copper alloys, sodium thiosulfate is introduced into the washing solution to reduce the speed of corrosion under the action of the oxidizing ions (Fe**3** plus ). To clarify its effect on the speed of dissolution of brass L-68 in hydrochloric acid tests were conducted in which corrosion was determined gravimetrically and the methods of determination of polarization resistance and of X-ray structural analysis of the films formed on the surface of the alloy were applied. It is found that sodium thiosulfate effectively slows down the process of brass corrosion due to Fe**3** plus ions but does not ensure protection of the alloy against corrosion in the presence of copper ions (Cu**2** plus ) when their concentration exceeds 0. 25 g/l.