There are alternatives to nitric acid passivation of stainless steel. There is data available showing that citric acid passivation is equal to or superior to nitric acid passivation.
Citric acid has been used very successfully for years in many industries. There is test data using salt spray, copper sulfate, palladium chloride, boiling water and high humidity on many grades of stainless.
Some of the advances that have been made in the last few years are:
In all cases, it is being done successfully while saving money and providing a safer atmosphere for employees and the environment.
|Safety||Very hazardous||Very safe to use as directed|
|Air Breathing||Emits toxic gases||No toxic gases emitted|
|Ease of use||Bulky safety equipment and extreme care required||Minimum of safety equipment and caution in use|
|Passivation||Excellent passivation of most grades of stainless||Excellent passivation of nearly all grades of stainless|
|Environment||Environmentally hazardous||Environmentally friendly|
|Cost||Low cost raw material; high cost maintenance and waste disposal. High cost of safety and ventilation system||Lower overall cost to use due to lower maintenance and waste disposal costs; longer lasting solutions and lower concentration necessary|
|Speed||20 minutes to several hours required||4-20 minutes typical, depends on process and grade|
|Temperature||Elevated temperature required for many grades||Room temperature satisfactory for many grades. Elevated temperature improves speed and performance|
|Maintenance||Regular solution replacement required with removal of hazardous waste.||Solutions lasts much longer and most operations have no hazardous waste to remove at all|
|Iron Oxide removal||Removes iron oxide slowly||Readily removes iron oxide|
|Equipment||Long-term degradation of tanks and area equipment is expected||No deleterious effects on recommended tanks and equipment, or corrosion of equipment in area|
|Flexibility in use||Must control time/temperature carefully and danger of NOx emissions is always present||No hazard of leaving product in the tank too long for most products, no hazardous emissions even with poor grades of stainless steel parts|
|ASTM A-967||Meets requirements||Meets requirements|
|AMS 2700||Meets requirements||Meets requirements|