What is the Difference Between Passivation & Pickling?

Two popular methods of metal finishing include pickling and passivation, both of which provide protective properties in metal to guard against rust corrosion. They also remove imperfections from the surface of the metal for improved functionality.

How the Two are Different

Superficially, there may not seem to be a lot of differences between pickling and passivation, but there are several key distinctions to make.

Pickling uses acids to remove the surface of the metal to treat sublevel imperfections, causing a bigger change in the metal. Passivation, on the other hand, uses less aggressive citric or nitric acid, and doesn’t go below the surface of the metal to change its properties.

Advantages of Passivation and Pickling

There are advantages to both types of treatments, which include:

  • Increased protection from pollutants that can cause rust and damage over time
  • Removal of impurities left following manufacturing
  • Smoother metal surface without imperfections
  • Increased durability of the metal

What is Electropolishing?

Another popular metal finishing process is electropolishing, which is used to effectively remove imperfections like passivation and pickling. It’s basically a “reverse plating” technique that is suitable for nearly any metal alloy.

Unlike passivation and pickling, however, electropolishing uses a combination of chemicals and electrical current to remove surface imperfections while eliminating contaminants. It’s more aggressive than passivation and doesn’t require a separate treatment. Following electropolishing, metal parts are left in a homogenous state that offers maximum corrosion resistance.

Keep in mind which process is ideal for your metal parts, as passivation isn’t compatible with parts that are made of certain types of stainless steel that don’t contain sufficient nickel and chromium. Passivation is also not recommended for brazed or welded parts.

However, electropolishing is ideal for all grades of stainless steel, including heavily contaminated parts such as machined parts, brazed, or welded assemblies. It’s also more efficient than passivation, taking less time to complete compared to other metal finishing methods.

How Do I Choose the Right Metal Finishing Process?

If you’re unsure about which metal finishing process is appropriate for your application, you can consult with a professional who can help you determine which one will work best for your metal parts. There are several factors that can influence the metal finishing process chosen, and an expert in the industry will be able to help you select the right one that will give you the best results.

For some applications, you may require aggressive pickling, while others may need to undergo passivation or electropolishing. The best way to determine which will give you the results you want is to work with experts who have performed them, or learn about the different grades that are suitable for these processes.

Ultimately, passivation may be the right process in many cases, but it isn’t always the best choice depending on the metal parts that require finishing. Some processes will take longer than others and remove more of the surface metal, but an experienced specialist will help ensure you choose the right service.