Abstract
Commercial power generation plants often experience corrosion problems within their service water systems. The corrosion mechanism in untreated natural water is typically identified as a combination of both general and microbiologically influenced corrosion (MIC). An appropriate solution to this problem is the substitution of more corrosion resistant material in place of the frequently applied steel piping. The focus of this research is to evaluate such a solution, in this case a carbon steel with an internal cladding of alloy 625. Of particular interest was the behavior of the material around weldments throughout the system. Due to the non-equilibrium solidification nature of weldments, the electrochemical properties of the weld may be different than those of the surrounding base material due to changes in surface texture, solute segregation, second phase precipitation, or, in the case of a clad material, dilution of the weld root by the carbon steel substrate. This study presents initial results from an ongoing long term investigation which seeks to establish the MIC susceptibility of alloy 625 weldments. Susceptibility was assessed via an array of AC and DC techniques in an ex situ environment consisting of lake water inoculated with a mixed culture of anaerobic bacteria containing primarily sulfate reducing bacteria. In addition to weldments of alloy 625, other base metal/weld metal combinations examined include 304 SS/308 SS, 316L SS/alloy 625, 316L SS/316L SS, 317L SS/alloy 625, and A36/A36 (carbon steel).
