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Longevity and durability are essential erquirements for Axium Process’ stainless steel fabrications.  We understand the importance of passivation and its effect on the finished product, so much so, our inhouse “passivation service” is available for both new and pre-manufactured fabrications.  Axium engineers can help you decide if the critical role of our “post- fabrication service” is something you should consider.

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 it highlights how little is understood about the capability of stainless steel and the applications where it is used.

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.  The chemical passivation process induces formation of the protective outside layer on the metal surface, it also removes free iron trace contamination that otherwise may soon leave your shiny new stainless steel … looking rusty!

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

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