Stainless steel is an important material for many industries and applications and is favoured for its durability, high strength and corrosion resistance. Some of the common industries that make the most of stainless steel include aerospace, automotive and construction, to name a few. Unfortunately, stainless steel can still be subjected to corrosion if it is not treated or coated adequately, and this is where passivation is essential. Passivation is a process used to improve the corrosion resistance of stainless steel, a topic we will discuss further in this blog post.
What is Passivation?
Passivation is a chemical process used on stainless steel and other alloys to enhance the corrosion-resistant properties of the material. It requires an acid-based solution to remove free irons from the service of a material in a treating or coating process, to reduce its chemical reactivity. Once the surface iron is removed from the material, the underlying components will be exposed to air, react with oxygen and form a protective layer to prevent corrosion. In the next section, we look at how it works in more detail.
How Does Passivation Work?
The chemical treatment process of passivation works removes free irons from the surface of stainless steel to create a more corrosion-resistant layer through a chemical reaction. An acid solution, such as citric or nitric acid, is used to free the irons, and the remaining layer reacts with air to create a protective oxide surface. The newly-formed passive layer is not thick but is effective in preventing rust and corrosion to the metal, which is crucial for many applications that can be impacted by environmental factors such as rain or moisture.
Several stages are involved in the passivation process, which we will outline below.
Preparation
The stainless steel’s surface must be cleaned to remove contaminants, including dirt or oil. Once cleaned, the surface is carefully washed with water and dried to remove moisture.
Acid Soaking
The second stage is soaking the steel parts in an acid solution to remove free irons from the surface and dissolve surface impurities. This stage is often called the citric or nitric acid bath. During this step, the protective oxide layer begins to form.
Rinsing
After the acid soaking, the stainless steel parts must be washed thoroughly to remove any excess acid. The surface must then be neutralised with sodium bicarbonate to stop any etching of the material.
Drying
The final stage of the passivation process is to dry the stainless steel parts, which will prevent corrosion by removing any moisture.
What are the Benefits of Passivation?
There are several benefits to passivating stainless steel components, with the primary one being to prevent corrosion and rust of parts. Other advantages include meeting regulatory compliance and improved aesthetics.
Corrosion Resistance
Although stainless steel has many outstanding qualities, increasing its corrosion and rust resistance is significant to many industries. By creating a protective oxide layer, the durability and lifespan of stainless steel products can be increased. This process is significant for companies using stainless steel in harsh environments.
Aesthetics
The passivation process can improve the look of stainless steel by removing any impurities, discolouration or stains on the surface. This is only sometimes the case, but in some industries, such as medical devices or food processing, the visual appearance of steel is essential.
Compliance
Manufacturers must adhere to industry standards when producing components. The most commonly used standards for passivating stainless steel include ASTM A967 and AMS 2700. The FDA or EPA also sets out regulatory requirements to ensure medical devices, food, or pharmaceutical processing equipment meets specific standards regarding cleanliness and safety.
Masteel: What we Offer
Masteel is a UK-based global steel supplier with a wealth of knowledge and experience in the industry. We provide a diverse range of premium products that suit our client’s needs. Understanding how significant the passivation process is, Masteel applies the process to all of our stainless steels to enhance their already outstanding properties.
To learn more about passivation and its benefits, contact a member of Masteel today.