Step 4. After-profiling composition of all elements (for quantitative comparison)
Susan Kerber of Material Interface has been actively involved with ASTM International on the development of a new stainless steel passivation standard. The new standard is currently undergoing round-robin testing. Please contact our office for additional information or for a quote.
What is Rouge and how is it removed?
Rouge is a surface deposit and discoloration on stainless steel surfaces, with various colors and textures. It generally appears after exposure of stainless to high-purity water and steam at elevated temperatures and often reappears after removal. Rouge is composed of various chromium and iron oxides. These forms are designated as Class I, Class II, and Class III Rouge. Class I Rouge is orange/reddish-brown and is primarily iron oxides and hydroxide. It is only loosely adhered to the base metal and is therefore migratory. The base alloy underneath the rouge is not affected by this deposit. It can often be removed by passivating processes. Class II Rouge is typical of rust formation, often from the presence of halides like chloride. It is active surface corrosion with a low chromium/iron ratio. Removal often requires abrasion and re-polishing. Class III Rouge forms in high temperature situations, including clean steam. It is dark blue to black in color and is chemically very stable. It contains iron oxide in magnetite form and is tightly adhered to the base alloy. In some cases, strong acids can remove this layer. In other cases, the surfaces much be mechanically repolished.