After thorough cleaning, the stainless steel part is ready for immersion in a passivating acid bath. Any one of three approaches can be used--nitric acid passivation, nitric acid with sodium dichromate passivation and citric acid passivation. Which approach to use depends on the grade of stainless steel and prescribed acceptance criteria.

More resistant chromium-nickel grades can be passivated in a 20 percent-by-volume nitric acid bath . As indicated in the same table, less resistant stainless grades can be passivated by adding sodium dichromate to the nitric acid bath to make the solution more oxidizing and capable of forming a passive film on the surface.

Another option, used in place of nitric acid plus sodium dichromate, is to increase the concentration of nitric acid to 50 percent-by-volume , The sodium dichromate addition and lit : higher nitric acid concentration both reduce the chance of undesirable flash attack.

APPEARANCE             :: Odourless orange crystal grain
Na2Cr2O7· 2H2O       :: 98.0% min
SULPHATES                :: 0.4% max
CHLORIDES                :: 0.2% max 

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