The effects of cold working on sensitization and intergranular corrosion behavior of AISI 304 stainless steel

The effects of prior cold rolling of up to an 80 pct reduction in thickness on the sensitization-desensitization behavior of Type AISI 304 stainless steel and its susceptibility to intergranular corrosion have been studied by electrochemical potentiokinetic reactivation (EPR) and Strauss-test methods. The results indicate that the prior deformation accelerated the sensitization as compared to the undeformed stainless steel. The deformed Type 304 stainless steel experienced desensitization at higher temperatures and times, and it was found to be enhanced by increased cold deformation. This could be attributed to the increased long-range chromium diffusion, possibly brought on by increasing pipe diffusion and vacancies. The role of the deformation-induced martensite (DIM) and texture, introduced by uniaxial cold rolling, on the sensitization-desensitization kinetics has also been discussed. This study could not reveal any systematic relationship between texture and the degree of sensitization (DOS) obtained. The effect of DIM on DOS seems to be pronounced at 500 °C when the steel retained significant amounts of DIM; however, the retained DIM is insignificant at higher sensitization times and temperatures

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Studies on enhancement of biofilm formation and adherence due to mechanical treatment of titanium surfaces in cooling-water systems

Titanium has proven to be the heat exchanger material of choice for seawater- cooled power plants owing to its outstanding resistance to pitting and crevice corrosion in a wide range of aggressive media. However, the inertness of the titanium surface makes it highly susceptible to biofilm formation and subsequent biofouling. This can hinder the heat transfer properties and flow of water. Fouling control strategies in condensers include a combination of mechanical, chemical and thermal treatments. However, reports from various industrial situations suggest that mechanical treatment may not have long-term effects. This study aimed to find out whether mechanical cleaning eventually enhances biofilm formation and increases the adherence of biofilm. In our studies epifluorescence micrographs of biofilms on control and mechanically treated titanium surfaces clearly showed accelerated biofilm formation as well as increased adherence on themechanically cleaned surface. Total counts of viable bacteria acquired by culturing technique, and biofilm thickness measurements made using microscopic techniques, confirmed this observation. Surface profilometry showed increased roughness of the titanium surface, facilitating adherence of biofilm. The number of microbial species was higher on mechanically cleaned and re-exposed surfaces than on fresh titanium. Thus we concluded that mechanical cleaning can increase biofilm formation and adherence of biofilm, thereby increasing the potential of biofouling in the long term

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