The Difference Between Pickling and Passivation of Steel Auto Parts

When auto parts manufacturers are looking for a material that can generate maximum long-term value, stainless steel is a choice more often than not. In addition to being an inherently sustainable material, it also has high impact resistance, great strength, and is fire and heat resistant as well. It also has a sleek, sophisticated look that fits right in with the look of most modern day cars.

Having said that, stainless steel isn't perfect and even though it's extremely corrosion resistant, that doesn't mean that there isn't more that can be done to help make rust-related concerns disappear. Pickling and passivation of stainless steel auto parts are two popular techniques used to accomplish exactly that.

What is Pickling and Passivation of Stainless Steel?

Pickling and passivation of stainless steel are both chemical treatments that use acids to improve the surface of the material in question. But, they have two totally different purposes. Even though you might use both techniques within the manufacturing process of a single part, they're not the same thing and shouldn't be treated as such.

One of the major differences is that passivation can't be used on any type of steel you're working with. It's specifically designed for stainless steel, and it helps prevent corrosion and ultimately rust. Pickling can be (and often is) used for stainless steel, but it can be employed for other types of steel as well.

Other between pickling and passivation of stainless steel include the following:

• Passivation is a passive process, meaning that it works by building up the oxide layer on the surface of stainless steel. Pickling removes that layer to clean the surface.
• The types of chemicals used in passivation (citric or nitric acids) are less harsh than the ones used for pickling (hydrofluoric and nitric acids).
• Pickling can remove existing rust from the surface of a material. Passivation does not.
• Pickling can remove discoloration from the surface of the metal. Passivation does not.
• Pickling changes the properties of the metal. Passivation does not change the fundamental properties of stainless steel, although it enhances corrosion resistance.
• Pickling removes any surface iron contamination from the material it is being used on. Passivation only eliminates contamination from free iron.

So, while both techniques are intended to remove impurities from the material being worked on (in this case, stainless steel) and both are designed to protect those materials from things that can cause rust, they have two vastly different approaches.

When Is Passivation of Stainless Steel Required?

One of the many benefits of chemical passivation for stainless steel has to do with how the process helps components stand up to incredibly harsh environmental conditions. It's why you see the technique a lot in demanding fields like aerospace and the automotive industry fits in for that reason.

Your average vehicle is filled with stainless steel components — from the various elements that make up the exhaust system to hose clamps to seatbelt springs and beyond. According to one recent study, the average internal temperature of a car parked in the sun for just one hour on a mildly hot day is 116 degrees. The dashboard averaged about 157 degrees, the steering wheel hit 127 degrees, and the seats hit 123 degrees.

The seat is notable as presumably, the seatbelt springs are reaching the same high temperatures. Heat accelerates chemical reactions such as corrosion. The common guideline observed by scientists is that every 18°F increase in temperature doubles the reaction rate. Without passivation, that would make hot parts very susceptible to premature rust, meaning that they're more likely to fail. That's the last thing you want to have happen to one of your car's critical safety features.

This is just one example of a situation where passivation is not a recommendation, but a requirement.

Additional Considerations About Pickling and Passivation of Stainless Steel

Beyond that, it's important to consider that passivation doesn't just improve the safety of a car and its components — it improves its longevity as well. Once a car begins to rust, the process steadily continues if left unchecked. You may catch a critical part in time to prevent a failure, but it will still need to be replaced to maximize performance. The more often this happens, the more money you sink into a car — leading to a replacement before you may be ready.

Auto parts that are highly resistant to rust work better for longer periods of time, leading to better performance, higher customer satisfaction, and an investment that people can depend on.

If you'd like to find out more information about the difference between pickling and passivation of stainless steel auto parts, or if you have any additional questions you'd like to go over in a bit more detail, please feel free to contact us today.