Basic Guidelines for Passivation of Stainless Steel Lines and Tanks

  1. After thoroughly rinsing the tank or lines after welding and installation of new equipment, and confirming that there are no leaks, proceed with cleaning and passivating.
  2. Check system to make sure there are no metals other than stainless steel in the system.
  3. Acid resistant gaskets such as EPDM are best, but if using buna gaskets, check condition before and after passivation.
  4. Start with a chelated caustic compound, and add 100 ppm of chlorine if there is no chlorine in the caustic compound.  Use 1 to 2% caustic solution, and refer to manufacturers directions for time and temperatures, usually longer the better, but at least for 1 hour.
  5. Rinse the caustic solution out thoroughly until rinse water ph is close to plant water ph.
  6. If using Nitric acid, add enough gallons to system to reach ph of 1.5 to 2.  Use warm tepid water, and circulate for 45 minutes.
  7. Rinse thoroughly with fresh water, and open tank lines to air dry.
  8. Air dry as long as possible, possibly two days if possible to achieve maximum chromium oxide reaction that occurs.  If time is a problem, install circulation fans in tank doorways, or route air through lines to speed up the process.
  9. If using citric acid, add sufficient pounds of citric acid to achieve ph of 1.5 to 2 ph, and follow same guidelines as for the nitric passivation.
  10. Combinations of nitric-phosphoric acid blends may be used and follow the above time temperature guidelines and ph levels.