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Passivation method of stainless steel
2022-11-28
Nitric acid solution passivation treatment
1.1 Passivation treatment
1.1.1 Stainless steel parts shall be treated in the following aqueous solutions and kept within the specified temperature range for the specified time. If immersion is not possible, other methods may be used to maintain contact between the stainless steel surface and the solution within the specified time and temperature range.
1.1.1.1 Nitric acid 1-solution shall contain 20% to 25% nitric acid by volume and 2.5% 0.5% sodium dichromate dihydrate. The parts shall be immersed at 50 to 55 ℃ [120 to 130 ° F] for at least 20 minutes.
1.1.1.2 Nitric acid 2 -- The solution shall contain 20% to 45% nitric acid by volume. Parts shall be soaked at 20 to 30 ° C [70 to 90 ° F for at least 30 minutes.
1.1.1.3 Nitric acid 3 -- The solution shall contain 20% to 25% nitric acid by volume. Parts shall be soaked at 50 to 60 ℃ [120 to 140F for at least 20 minutes.
1.1.1.4 Nitric acid 4 -- The solution shall contain 45% to 55% nitric acid by volume. Parts shall be soaked at 50 to 55 ° C [120 to 130 ° F for at least 30 minutes.
1.1.1.5 Nitric acid 5 -- Other combinations of temperature, time and nitric acid concentration, with or without other chemicals, including catalyst, inhibitor or proprietary solution, can produce parts that meet the specified test requirements.
1.2 After flushing with water removed from the passivation solution, the components shall be thoroughly flushed, using stagnant, countercurrent or sprayed cleaning solution, either alone or in combination, with or without separate. Chemical treatment to neutralize the passivation medium (see Section 9), and finally use total solids. Flush with clean water with impurity content less than 200ppm.
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