Effect of Passivation Film on Stainless Steel Surface Potential

The document presents data on the influence of a passivation film on the surface potential of stainless steel. A graph shows surface potential (in millivolts) over time (minutes), comparing stainless steel exposed with a passivation film versus a reference line of cement-coated steel. The presence of chromium (Cr), iron (Fe), and oxygen (O) is noted, indicating the chemical composition of the passivation layer. The data highlight the immediate changes in surface potential following the removal of the chromium-oxide layer, emphasizing the protective role of the passivation film in maintaining surface stability.

Resistance to Crevice Corrosion

A second section details the resistance of various stainless steel grades to crevice corrosion under different chloride ion concentrations (Cl- ppm) and temperatures (°C). The steels evaluated include 316L, 17-14-4LN, 2205, 904L, 625, and 254 SMO. The temperature range spans from 0°C to 100°C, while chloride concentrations vary from 200 ppm up to 50,000 ppm.

The corrosion behavior is categorized into three stages: primary corrosion, initial pit formation, and secondary corrosion. The data imply that higher alloy grades such as 254 SMO and 625 exhibit superior resistance to crevice corrosion, especially at elevated chloride levels and temperatures, compared to lower grades like 316L.

Key Insights and Recommendations

• Passivation films significantly enhance the surface potential stability of stainless steel, reducing susceptibility to corrosion.
• Removal of the chromium-oxide layer leads to immediate changes in surface potential, underscoring the importance of maintaining this protective layer.
• Selection of stainless steel grade should consider operating temperature and chloride concentration to mitigate crevice corrosion risks.
• Higher alloyed stainless steels (e.g., 254 SMO, 625) are recommended for environments with high chloride content and elevated temperatures due to their superior corrosion resistance.