The Need for Passivation in Stainless Steel Fabrication

 

 

Working with metal is a very challenging task. Just watch a Forged in Fire episode, and you will be amazed by how many different procedures it takes to complete an edged weapon. You will have processes such as cold forging, grinding, fullering, and fluxing. You will hear terminologies such as san mai, Damascus, edging, bowie, and Ricasso. Welding metal is also similar to forging as they both work with metals. Welding is even a process used in the show when contestants need to bind several pieces of metals together.

 

Like in forging blades, welding will also involve a lot of processes that will include the preparation of the metals for binding, the actual welding process, and a process that uses a stainless weld cleaner to make sure that the welds are clean and corrosion-free.

 

Cleaning the Welds

 

When you put two types of metals together, it is important to prepare both of their surfaces by ensuring they are free from any dirt, paint, rust or corrosion. Smooth and clean surfaces will create a better weld. Likewise, making sure that the surfaces are smooth will prevent weld inclusions.

 

Inclusions are defects during a welding process formed when particles get trapped within the metal or the weld interface. One type of inclusion is called the slag, which results when a faulty welding technique causes non-metallic particles to get trapped at the welding joint. Another type of inclusion is called the tungsten inclusion, which can be formed during the TIG welding process. Tungsten inclusion involves unwelded tungsten particles being trapped or deposited within the weld metal.

 

Stainless Steel Passivation

 

Stainless steel is a common metal used in construction. Engineers prefer the use of stainless steel because of its high corrosion resistance. However, this property of stainless steel does not mean that it will never rust. Stainless steel may still rust over time, especially if it reacts to different chemicals within the environment. Fortunately, you can increase the anti-corrosive property of stainless steel through a cleaning process known as passivation.

 

What is Passivation? 

 

Passivation is the process of enhancing a metal’s ability to resist corrosion. For stainless steel alloys, this process will involve rubbing the steel’s surface with a strong acid such as nitric or citric acid. The chemical compounds of the acid will bind with the free iron atoms to form a stable oxide layer. Free iron atoms are highly reactive to different environmental chemicals to form iron oxide or rust. With the passivation process, the acid will chemically react with the free irons to create an oxide layer on the steel’s surface. This oxide layer is considered “passive” and will not bind with other chemical compounds within the environment.

 

 

When Do You Need to Passivate Stainless Steel?

 

Stainless steel is highly resistant to corrosion and rust. However, the welding process may disrupt the chemical composition of the stainless-steel alloy during the fabrication process, which results in free irons that may oxidize with other chemicals to form corrosion. Therefore, it is necessary to use a stainless weld cleaner to make sure that all the welded joints are cleaned as undergoes the passivation process.

 

Before, the passivation process using nitric acid and pickling paste is very time-consuming. Likewise, handling nitric acid may be hazardous to your health, especially if you are exposed to the acid for a long time. Fortunately, the advancement in welding technology has created more modern stainless weld cleaner devices that incorporate heat, electricity, and chemistry to passivate welds in a much more convenient, safer, and more efficient way.