Stainless Steel Passivation Explained

Stainless Steel Passivation Explained - KegLand

The use of high grade stainless steel is super common for brewing equipment. However, it is important to care for your stainless steel. Like any grade of steel, 304 grade stainless steel contains iron. When the iron is bonded in the stainless steel alloy it’s extremely difficult for this iron to react/rust. With that said, through the manufacturing process, bending, welding, grinding and polishing this can leave small surface imperfections and free iron which is not completely bonded to the alloy. This “free” iron can then rust. Even scrubbing your 304 grade stainless steel or using an abrasive cleaning agent can cause free iron to manually be broken out of the alloy and lead to surface rust.

How to passivate stainless steel and remove surface rust

It should also be noted that there are a wide range of oxygen based cleaning agents that are used these days that rely on peroxides such as sodium percarbonate, Oxyper, PWB, Powdered Brewery Wash, and many others. These cleaning agents are oxidising agents that will aggressively attack any free iron and accelerate the rust/oxidation process.

Luckily this surface rust is only superficial and it can easily be treated through a process called passivation.  The passivation process removes surface imperfections and surface iron and oxides.  This treatment restores the stainless properties of your 304 grade bringing it back to the bright shiny surface that brewers like to see.  Some treatments include citric acid (lemon juice), electrolysis acid baths or commercially available pickling pastes.  Most brewers normally have a phosphoric acid based sanitiser available so this is normally the easiest product to use.  The product that we sell is called StellarSan but it’s also possible to use other phosphoric based sanitisers or even straight phosphoric acid.

Pour a small amount of StellarSan onto a cloth or tissue.  Use this in it’s full concentration (do not water down).  Avoid contact with fingers, eyes and face.   Rub this into the surface of the stainless steel.

Leave the StellarSan on the surface of the stainless for 24hrs then rinse with water and your stainless will be passivated.  As you can see below this is what the stainless should looks like before and after:

Stainless steel before and after phosphoric acid or Stellarsan treatment

Regular use of StellarSan is a great way to maintain your stainless steel and will help keep your stainless steel in top condition.

As you can see below this is the difference between a passivated weld and a non-passivated weld.

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