低合金鋼電縫鋼管の海水中における耐溝食性について

抄録

The grooving corrosion resistance of the ERW Cu-Sb, Cu-Ti, and Cu-Ti-Cr low alloy steel pipes were investigated. Corrosion tests carried out in artificial seawater showed that these pipes had grooving corrosion resistances four to seven times higher than that of a plain carbon steel pipe. Difference in the degree of polarization between the weld and the base metal, as determined by polarization curves in 3% NaCl solution, was large in the carbon steel pipe, the weld being less polarized and small in low alloy steel pipes. A microscopic observation of the non-metallic inclusions revealed that there was a smaller quantity of MnS inclusions, inititation sites of the grooving corrosion, in the welds of these low alloy steel pipes than in the welds of carbon steel pipe. It was considered that the good grooving corrosion resistances of the low alloy steel pipes were due to the decrease of MnS inclusions in the welds, the elimination of S^2- ion by the addition of copper, and the increase of the corrosion resistance of the base metal by the addition of chromium.