2000 Volume 40 Issue Suppl Pages S54-S58
A majority of cooling system failures in many corrosion resistant alloys is around weldments. Weld regions are particularly attractive to microbes as welding alters the material surface characteristics. Hence, it is presumed that there is a correlation between the susceptibility to this type of corrosion and the microstructure. Existing literature hardly mentions anything about the preferential adhesion of bacteria on areas of varying microstructures. One of the important characteristics of weld is its microstructure. A study involving both microstructure and bioadhesion would reveal the reason why welds suffer preferential MIC attack. Experiments were carried out to study the effect of microstructure on adhesion of a corrosive bacterial strain Bacillus sp. isolated from the residual water of an MIC affected effluent treatment plant on weld samples (weld metal, HAZ and base metal separately) of two different materials viz. 316L and 304L stainless steel.
Base metal, HAZ and weld metal of both the material tested, showed difference in area of adhesion. Weld metal or HAZ harboured more bacteria in both the materials tested, with base metal showing the lowest. A difference in percentage area of adhesion was observed between as welded and polished coupons of the same material. Since base metal, HAZ and weld metal of both the materials showed difference in area of adhesion in spite of the uniform surface condition, the influence of microstructure gathers significance. This preferential adhesion contributes very much to corrosion and can be considered as one of the factors causing MIC attack on welds.