Nitric vs Citric Acid Passivation

Nitric vs Citric Passivation Methods

Stainless steel is an inherently corrosion resistant material, however when stainless steel is machined, formed or fabricated free iron can be introduced to the surface that can corrode independent of the base material.  Proper passivation of stainless steel with an oxidizing acid such as nitric or citric acid removes this free iron and promotes the growth of a thin, dense protective oxide layer which maximizes the corrosion resistance of the stainless steel. Depending on the type of stainless steel and end application certain passivation processes may perform better at passivating than others. In this article we will compare nitric vs citric acid passivation which are the two primary chemistries specified in ASTM A967 and AMS 2700.

Nitric Acid Passivation

Passivation Specifications

When comparing nitric vs citric passivation, the most common method used throughout industry is nitric acid passivation. The Nitric acid passivation processes was the original passivation processed specified in QQ-P-35, the first military specification covering passivation, revision A being released in the 1960s.  Nitric acid passivation offers a range of options to customize the oxidizing potential of the acid to suit a specific grade of stainless steel. The various methods and types of nitric acid passivation include several heated options as well as options that include a sodium dichromate.

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Passivation of Stainless Steel for Critical Applications

By S Patel

passivated metal springsPassivation is a critical processing step in the manufacturing of stainless steel components to enhance the corrosion resistance and make stainless steel parts truly “stain-less.” Proper passivation of stainless steel components can make the difference between satisfactory field performance and premature corrosion failures.  If performed improperly, the passivation process can actually attack and etch the stainless surface or induce corrosion. Passivation is often misunderstood to be a scale removal or bright dipping process when in fact it is fully removed from either of these processes.  The information within the blog serves to detail some of the key principles of passivation of stainless steel offered by Advanced Plating Technologies. Continue reading