- 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.
- Check system to make sure there are no metals other than stainless steel in the system.
- Acid resistant gaskets such as EPDM are best, but if using buna gaskets, check condition before and after passivation.
- 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.
- Rinse the caustic solution out thoroughly until rinse water ph is close to plant water ph.
- 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.
- Rinse thoroughly with fresh water, and open tank lines to air dry.
- 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.
- 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.
- Combinations of nitric-phosphoric acid blends may be used and follow the above time temperature guidelines and ph levels.