What is passivation, and why is it so essential for your stainless steel welds?
Contrary to popular belief, stainless steel can still corrode. After welders weld on stainless steel, you’ll notice that they often clean the welds with a variety of different chemicals, including nitric acid and “pickling paste” which contains hydrofluoric acid. This cleaning process, also known as “passivation”, isn’t just to enhance the looks of the welds but also prevents corrosion. In other words, passivation is the process of restoring the damaged oxide layer to prevent corrosion in stainless steel.
Once you have completed the chemical treatment, the stainless steel surface should end up with a protective oxidized layer that will be more resistant to the oxygen in the air and suffer less corrosion. Next time you see someone cleaning a weld that has recently been finished, you’ll know it is about much more than just the appearance of the weld.
While we mentioned two of the chemical solutions used to assist with passivation, there is also another method called “electrolytic weld cleaning”, which includes the TIG Brush by Ensitech. The TIG Brush is one of the most exciting new techniques being used throughout the welding industry for passivation. It’s a simple, fast, and effective way to obtain the benefits of passivation without using dangerous and complicated chemicals.
The History Behind Passivation
It was during the 1800s that chemist Christian Friedrich Schönbein discovered the effects of passivation on metal. He dipped iron in concentrated nitric acid and compared it to iron that hadn’t been treated in the nitric acid solution. The iron, which was dipped in the nitric acid, had almost no chemical reactivity compared to the iron that hadn’t been treated.
During the 1900s, as stainless steel welding and passivation became more widespread, the environmental and safety impact of using nitric acid became much more apparent.
Exposure to nitric acid can lead to hazardous damage to your respiratory condition if proper safety equipment and adequate ventilation are not used. Any exposure to nitric acid on your skin, eyes, face, or lungs can lead to permanent damage to your health. Hydrofluoric acid is even more dangerous, and can result in severe burns, osteoporosis and even death.
Why Would You Passivate Stainless Steel?
After the fabrication and welding process is complete on any stainless steel components, passivation is the next step. Some of the benefits of passivation include:
- Removes the contamination from the surface of the weld
- Extends the life of the weld and the overall life of the component
- Produces a chemical film barrier that protects against rust and corrosion
- Reduces the need for any ongoing maintenance and repairs.
How Does the Passivation Process Work?
Stainless steel is composed of iron, chromium, and nickel. It is the chromium component of stainless steel, which gives it its corrosion-resistant properties. When chromium is exposed to oxygen, a thin layer of chromium oxide forms on the stainless steel surface and protects the iron from rusting.
Without passivation, contaminants in the environment (such as chlorides) can react with free iron on the surface of the metal and start the corrosion process, which will extend into the component via the weld. Passivation is carried out to slow down or eliminate this process in two ways. Firstly, it removes free iron from the stainless steel surface, which removes the material which is most susceptible to the corrosion process. Secondly, it enhances and speeds up the oxidation of chromium to form an inert layer, which then protects the underlying component from environmental contaminants.
When Is Passivation Required and Not Required?
After grinding, welding, cutting, and any other machining operations have been completed, the passivation processes can begin. Stainless steel itself is resistant to corrosion and rust, but several different processes can introduce contaminants that will inhibit the forming of the protective oxide layer during the fabrication process.
Some of the different factors which may inhibit the forming of the oxide film include:
- Foreign materials such as dirt, dust, oils, swarf, and coating material
- Different sulfides that were added to the stainless steel to make it more machine friendly
- Iron particles are embedded into the stainless steel during the cutting process from blades, discs, and other cutting tools.
Passivation isn’t used for the following reasons:
- If the finished components are to be painted or powder-coated, passivation may not be required
Is There Only One Way to Achieve Passivation?
While the traditional nitric acid and pickling paste methods are effective ways to achieve passivation on stainless steel parts and components, they’re also dangerous and time-consuming. Another new way to achieve 100% passivation is with the TIG Brush.
You can say goodbye to hours of tedious work cleaning your welds with pickling paste forever once you start using the TIG Brush. The TIG Brush effectively bypasses the safety procedures and tedious hours of time-consuming work that pickling paste requires while delivering a much cleaner and better finish that will leave your welds looking amazing and contaminant free.
You or your team will be able to spend more time welding and preparing components and less time dealing with dangerous pickling paste. With the advances in technology we see in the TIG Brush, you’ll be able to take advantage of electrolytic weld cleaning that involves cleaning and passivating the metal surface by the application of strong electric currents and electrolytic fluids in a cost-effective and fast manner.
The TIG Brush process is much safer compared to the hazardous process of any pickling paste application. With TIG Brush’s Stainless Steel Weld Cleaning System, you can also eliminate the time-consuming extra steps of passivation and surface refinishing.
The passivation process on many stainless steel welds and components is an unavoidable yet necessary part of the process, but that doesn’t mean that you need to keep doing it the same way it’s always been done. It is time to move away from nitric acid and pickling paste, and look at the future of stainless steel passivation, the TIG Brush by Ensitech.