Asked in ChemistryMechanical EngineeringElements and CompoundsMetal and Alloys
Chemistry
Mechanical Engineering
Elements and Compounds
Metal and Alloys
What is the passivation threshold of steel?
Answer

Wiki User
November 07, 2007 9:37PM
I'd think it's the limit at which there is no longer any iron that can be drawn by the passivation solution. Certain alloys have higher iron concentrations...those with high iron levels would require longer passivation times than alloys with low iron levels. Either way, there is a point reached at which no more iron can be removed. If I remember correctly, pipelines would be passivated with a hot acetic acid solution. A detector was used to measure the iron that was freed up. Once the iron levels decreased to a certain point, passivation was considered complete.
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What is steel passivation?

Passivation is removing the free iron and other exogenous
materials from the surface so that a good passive layer can be
formed. In the case of carbon steel, this is not possible. After
cleaning with a good cleaner, there are a variety of coatings that
can be used for carbon steel to provide a corrosion resistant
layer, but passivation is not the correct process. For details see
the link in the left column.
What are the mechanisms of the passivation process?

Under normal conditions of pH and oxygen concentration,
passivation is seen in such materials as aluminium, iron, zinc,
magnesium, copper, stainless steel, titanium, and silicon. Ordinary
steel can form a passivating layer in alkali environments, as rebar
does in concrete. The conditions necessary for passivation are
recorded in Pourbaix diagrams.
The Passivation process is typically an immersion process
involving nitric acid. Passivation is the process of making a
material "passive" in relation to another material prior to using
the materials together
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