Passivation

“It’s Stainless Steel, It Shouldn’t Rust”

Passivation

Axium Process understands the importance of longevity and durability in all our stainless steel fabrications supplied, so much so we offer in house passivation for both new and old fabrications and our engineers fully appreciate the critical role this post fabrication process can offer customers and end users.

So, what is Chemical Passivation?  To understand this, first we need to understand the basics of Stainless steel:

It’s stainless steel, it shouldn’t rust

This is a typical statement heard when discussing failure in process piping and equipment and highlights how little is understood about the capability of stainless steel and the applications where it is used.

Understanding Corrosion

Often people are surprised to learn that 316L / 1.4404 stainless steel for example contains between 50% – 70% iron (Fe), so what is the main magic element that makes this ‘iron’ corrosion resistant ?  The answer is Chromium (Cr), In terms of 316L / 1.4404 stainless steel between 16.5 – 18.5%, the higher the Cr % the higher the corrosion resistance.

The presence of Chromium at these levels changes the corrosion barrier on the surface of stainless steel from an active film to a passive film.  This passive film / layer is extremely thin and cannot be seen by the human eye, the layer is composed mainly of Chromium Oxide and this oxide prevents further diffusion of oxygen into the base material.

New Process Parts & Equipment

Cutting, welding and mechanical polishing all damage the surface of the material breaking the passive layer.

Existing Process Parts & Equipment

Over a period of service this passive layer either dissolves or is worn away leaving free iron below the film to be exposed to the environment and in time forming rust

The Solution

Chemical Passivation is achieved by exposing the parts (new or old) to a chemical bath containing citric or nitric acid.  The carefully prepared liquid solution removes the iron and iron oxide from the surface and leaves in its place Chromium Oxide at the surface to protect the material once again.

So whether you wish to specify your Axium fabrication be completed with a passivation process or wish to send us existing equipment including pumps, valves and vessels to be passivated periodically, please do not hesitate to contact us or speak to one of our highly skilled sales engineers.

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ITCS ManagerPassivation