INVESTIGATION OF ENVIRONMENTAL EFFECTS ON INTRINSIC AND GALVANIC CORROSION OF MILD STEEL WELDMENT IN CO_2 ENVIRONMENT

摘要

Localized corrosion of carbon steel welds has been thought to arise primarily from galvanic effects due to compositional differences between the deposited weld metal, the parent steel, and the heat affected zone induced by the welding process. The location and morphology of the preferential corrosion is influenced by a complex interaction of environmental parameters. The effects of salt concentration and temperature on intrinsic and galvanic corrosion of the non-alloyed standard carbon steel weldment in CO_2 environments have been investigated using different types of electrochemical techniques. Experimental results show that for the non-alloyed standard weldment, the intrinsic corrosion rates of parent metal, heat affected zone (HAZ) and weld metal are not significantly different, but the corrosion of weld metal becomes worse and the parent metal is protected due to the galvanic effects between the segments. The experimental results also show that an increase of salt concentration (1～10 wt.% NaCl) significantly affected the intrinsic corrosion rate in a nonlinear fashion. The galvanic currents were unaffected by the different salt concentrations.