How is stainless steel passivated? The passivation process used to involve dipping a stainless steel part in a nitric acid solution, but in the 1930s the Department of Defense developed a new standard. What was originally called QQP 35 eventually became QQP 35C. In 1998, the Defense Department withdrew the standard in favor of a new one called ASTM A967, which today is the most widely accepted general industry standard. A second standard, AMS 2700 C, is accepted in the aerospace industry.

The two standards are virtually identical in regards to the what is required in the passivation process. They both allow for the use of nitric acid and citric acid solutions, the latter of which is the newer, more effective method. More specifically, the standards prescribe the concentrations, temperatures, times and water quality required for passivating stainless steel.

Stainless steel parts that are to be passivated must be clean, including immediately prior to the passivation process. Though this is generally accepted as a best practice, it is not specifically required in the standards mentioned above. The parts are then placed in a solution where they remain for a predetermined amount of time. From there, the parts are double-rinsed using clean water and then dried thoroughly.

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