Microscopic analysis of the destruction of passive film on stainless steel caused by sulfide in simulated cooling water

Abstract Sulfide often appears in circulating cooling water due to the presence of sulfate reducing bacteria and could affect corrosion behavior of cooling pipe metals such as stainless steel. Scanning Kelvin probe and scanning electrochemical microscope measurements, combined with electrochemical testing, were used to investigate the micro-electrochemical information of passive film and analyzed the influence of sulfide in simulated cooling water on corrosion resistance of stainless steel. Results showed that the presence of sulfide in water caused a negative shift in surface potential of stainless steel, an increase in surface potential difference, and an increase in local response current on the surface, resulting in a current peak that gradually increased over time. The analysis results of passive film composition showed that the presence of sulfide caused increase in the ratio of Fe/Cr and OH − /O 2− , as well as the content of Cr(OH) 3 and Fe(OH) 3 in passive film, whereas caused a decrease of Cr 2 O 3 content, and led to the formation of FeS 2 in the passive film. These changes in the composition of the passive film made it easier for active sites to appear on the surface of stainless steel and enhanced the conductivity of the passive film and significantly reducing its protective performance.