Electropolishing vs. Passivation of Stainless SteelLeave a Comment
The aesthetics or physical properties of metal may often see improvement by the application of various finishing techniques. For example, in custom metal basket applications, applying an appropriate finish will impact the functionality of the basket as much as the base material does.
Two of the most popular finishing methods used for stainless steel include electropolishing and passivation. At Highland Equipment, our customers often ask: Is electropolishing the same as passivation? While both finishing methods improve the material’s durability and resistances, there are distinct differences to consider when choosing between electropolishing vs. passivation.
Electropolishing is a common finishing technique for the food and beverage, medical and dental, pharmaceutical, electrical, and semiconductor industries. The electropolishing process leaves a smooth, near-flawless finish. Manufacturers often use this method to impart non-stick qualities onto goods and components, making them easy to clean and ensuring process materials don’t stick to them during production.
The process uses a temperature-controlled chemical bath and an electric current to dissolve the metal’s outer surface layer. Electropolishing removes microscopic surface imperfections and eliminates discoloration from spot welds. It is a fast, cost-effective solution, even for parts with complex geometries.
Electropolishing is compatible with most stainless steels and a variety of other metals. Metal alloys that are good candidates for electropolishing include:
- Stainless steel: 200-300 series, 400 series, precipitating hardening grade, and unusual
- Carbon steel
- Specialty alloys
Passivation is similar to electropolishing in that it uses a chemical bath to remove contaminants acquired during the manufacturing process. However, passivation uses an acidic solution that does not require an electrical current. Passivation won’t change the material’s aesthetic appearance, but it will improve the oxide layer that protects stainless steel.
Passivation requires a thorough understanding of the type of alloy and how the chemical bath solution will interact with it. An inexperienced finisher using the wrong passivation solution could strip much more from the surface than intended and damage the workpiece beyond repair.
The passivation process provides an excellent way to remove free iron and other contaminants from the surface of many stainless steel grades. Some stainless steel materials aren’t appropriate for this finishing method, however. When the steel has low chromium and nickel levels, or if the parts have been welded or brazed, passivation is typically not the appropriate finishing method.
Choosing the Right Finishing Process
When selecting stainless steel electropolishing vs. passivation, consider the following application-specific factors:
- Offers an ideal solution for removing microscopic contaminants or imperfections
- Strips the entire outer layer of metal
- Will remove heat tinting and oxide scales
- Suitable for parts with complex geometries
- Does not require electrical current
- Removes free iron and other surface contaminants
- Won’t remove heat tinging or oxide scales but strengthens the oxide layer
- Gentler than electropolishing
The choice comes down to the application for the stainless steel. For a flawless finish or to finish components with complex shapes and angles, electropolishing offers an ideal solution. Passivation is a less complicated and gentler technique used to remove surface contaminants and enhance corrosion resistance without peeling off the material’s outermost layer.
Working with Highland for Sanitary Stainless Steel Process Equipment
At Highland Equipment, we offer passivation as one of our many value-added services. Our staff can help you to determine if passivation is the right finishing method for your project. For more information about our passivation capabilities, please contact us today.