It is a common misconception that stainless steels resists all forms of corrosion. The ‘stainless’ nature of stainless steels is as a result of the chemical composition of the alloy. Stainless steels typically contain in excess of approximately 12% chromium. This induces the formation of a passive chromium oxide barrier at the external surface. Under certain conditions the protective barrier coating can be compromised, permitting corrosion of the underlying steel substrate. One such condition being when free iron is present. In the presence of an electrolyte, the free iron fluxes the chromium oxide barrier, enabling corrosion of the underlying substrate. Where stainless steel has been selected for an application based on its appearance, free iron staining can create an eye sore.

Passivation of the stainless steels components in order to remove free iron can be a costly exercise that can delay projects. It is essential that carbon steel and stainless steel items are segregated during fabrication in order to prevent contamination. Upon arrival at the installation site it is important to ensure that carbon steel fabrication activities in the areas have been completed. Having scaffolding over head is not ideal since it can result in free iron dropping onto stainless steel surfaces during break down. Should this be the case, stainless steel fabrications would need to be passivated on site. This can be achieved in a number of ways, but that most commonly used is pickling with a suitable acid.

In order to verify that all free iron has been removed from the stainless steel surface, it is necessary to conduct a suitable method of testing. R-TECH Materials have extensive experience of testing to ASTM A380 in order to verify that free iron is not present on the stainless steel surface, whether it be in the fabrication shop or at the installation site. For more information please contact us at info@r-techmaterials.com