BT - Passivation Procedure for 300-Series Stainless Steels

	Passivation Procedure for 300-Series Stainless Steels

	Step 1. Prepare a 50% (v/v) nitric acid solution by pouring an equal volume of concentrated nitric acid into an equal volume of water in a container that will not be attacked by the solution. (Nitric acid is available in 50% strength. Phosphoric acid may be used as a substitute.) Best results will be obtained if the temperature of the passivating solution is maintained at 130 °F (54 °C). Use extreme caution when using nitric acid; it is a very dangerous chemical. Step 2. Apply the passivating solution to the complete surface. Cover all areas several times. Keep the surface wet with the acid solution for about 1 h. With a small vessel (15 gal or less), it is easiest simply to fill the vessel with the passivating solution and let it soak. When dealing with larger vessels, passivation via a spray-ball system is very effective. Step 3. Rinse the vessel thoroughly with clean, warm water to remove all traces of acid. Wipe with a clean cloth (wet or dry). If no discoloration appears on the cloth, the surface is conditioned and ready to use. Passivation is not a permanent treatment. Stainless steel surfaces can become recontaminated and corroded if proper care is not taken.
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