Cleaning

Cleaning and Passivation

There are alternatives to nitric acid passivation of stainless steel. There is data available showing that stainless steel citric acid passivation is equal to or superior to nitric acid passivation.

Citric acid has been used very successfully for years in many industries, so it has many advantages. 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 in the citric acid passivation concentration realm that have been made in the last few years are:

  • Elimination of rust and corrosion problems on 410 ss that has been a problem for many years with nitric acid passivation (surgical industry).
  • Chrome oxide : Iron Oxide ratios on the surface of 316 stainless steel that are higher than ever obtained with nitric acid (semiconductor industry). Ratios as high as 12.7 to 1 have been obtained!!!
  • Complete elimination of passivation problems on orthodontic devices made of 316 stainless steel brazed with gold/palladium (orthodontics industry).
  • Cleaning and passivation of heat treated 455 stainless steel to pass water immersion tests and eliminate oxide coating to look like electropolished material (surgical industry).
  • Elimination of the need for Hydrochloric acid to remove heat treat oxides on 440C stainless steel (controls industry).
  • Improved corrosion resistance compared to nitric acid on 302 and 316 stainless steel. Elimination of rejects that were plaguing the customer (spring industry).

In all cases, it is being done successfully while saving money and providing a safer atmosphere for employees and the environment, making this one of the advantages of citric acid.

Comparison of CitriSurf and Nitric Acid Passivation

PROPERTY NITRIC ACID CITRISURF
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

Environmental Information

General:

The CitriSurf line of products has specifically been formulated to eliminate the safety and environmental problems of nitric acid and other mineral acids used in the cleaning and passivation of stainless steel. When used as directed, CitriSurf products yield excellent results without producing hazardous waste or NOx pollution in the air.

Waste water:

CitriSurf products are a high quality blend of chemicals formulated for the cleaning and passivation of stainless steel products normally without producing hazardous rinse solutions which require waste treatment prior to drain. Because the EM>CitriSurf products do not strip the nickel or chromium from the surface, the rinse water can normally be put directly to drain as long as the pH falls within local guidelines (normally 5.0-9.0, but local areas vary!). CitriSurf products are excellent at selectively removing the iron and iron oxides from the surface, yielding rinse water that can easily be drained.

When the master bath requires replacement, which is seldom, the bath can be treated easily to remove all possible contaminants that may be in the bath, so that the requirements of local, state and Federal regulations are all met. Consult our technical experts if you have any questions in this area.

Air cleanliness:

There are no NOx fumes emitted from the CitriSurf products. It is not necessary to scrub the air over the CitriSurf bath as required with nitric acid. When used as directed, the CitriSurf products do not produce fumes which are hazardous to individuals or to the environment as with nitric acid.

While the company believes that the information contained herein is factual and the opinions expressed are based on tests and data believed to be reliable, it is the user’s responsibility to determine the safety, toxicity and suitability for his own use of the product described herein. Since the actual use by others is beyond our control, no guarantee, expressed or implied, is made by this company as to the effects of such use, the results to be obtained, or the safety and toxicity of the product, nor does this company assume any liability arising out of the use, by others, of the products referred to herein. Nor is the information herein to be construed as absolutely complete since additional information may be necessary or desirable when particular or exceptional conditions or circumstances exist or because of applicable laws or governmental regulations.

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