Marine corrosion tests of electroplates for ship instruments: V. Electroplates of Sn-Pb and Sn-Bi alloys on carbon steel

Electroplates of Sn-40Pb and Sn-1Bi alloys of a thickness of 9 and 3 mu m, respectively, on carbon steel 10 were tested for 14-20 years in containers, which simulate the instrumental cases of watertight and splashproof types, at corrosion stations in Murmansk, Vladivostok, and Batumi in cold, temperate humid, and warm humid (subtropical) zones, respectively. The corrosion-induced changes and the appearance of the electroplates were assessed visually and, in the end of the tests, gravimetrically. After 20 years, the electroplate thickness decreased by 0.2-4.4 mu m (or on average by 0.01-0.22 mu m yearly). The Sn-1Bi alloy corrodes, as a rule, twice as quickly as the Sn-40Pb alloy. The decisive factor that affects the corrosion of Sn-1Bi electroplates is the salt content, and the factor affecting the corrosion of Sn-40Pb alloys is sulfur contaminants in air. The useful life of tin electroplates in ship equipment is assessed.