P A S S I V A T I O N   An Aid for the Enhancement of Your Parts

Do you supply or work with stainless steel parts that have gone through processes such as machining, blasting, or shot peening, and will be subjected to extreme environments that require corrosion resistance? Did your parts come back from the heat treater looking like blackened catfish? Will your parts receive a coating application? If so, MIL performs Passivation which is a process that through chemical dissolution and use of mild acids such as nitric acid, a “passive film” is formed that acts to protect the surface from oxidizing environments and increases adhesion for optimal coating performance. The first part of the process is the removal of contamination and imbedded material which would interfere with the creation of the film. When parts cannot be cleaned of heavy contaminants such as heat treat scale, MIL can add a descale step to more effectively facilitate the spontaneous formation of the “passive film.” Next, with the use of mild acids such as nitric acid, the “film” or protective layer is created to prevent corrosion and the formation of corrosion sites with the onset of foreign particles during future use. The part also has an enhanced surface cleanliness that offers increased adhesion properties for extended life of coating applications. Additionally, the film created is only a few microns thick, making it negligible as a coating and does not require dimensional allowance.

In accordance with many specification requirements, MIL ensures that the surface has been made passive and resistant to corrosion through the use of various tests. The lot acceptance test most commonly specified, and the one that MIL defaults to is the humidity test, in which we place the parts in a controlled environment that is kept at 95-100% relative humidity and 95-105 degrees Fahrenheit. The test parts are removed from this environment after 23-25 hours so that they can be inspected for evidence of rust or corrosion. Parts that show tell-tale discoloration are rejected and with your authorization, MIL can process the parts again through the passivation steps, as it is a process that does not change the dimension or material of the parts. Other tests that MIL can perform by request or specification requirement are copper sulfate, and salt spray testing. These tests also subject the parts to exaggerated environmental conditions in order to determine performance when out in the field.

Once the parts have passed the testing, they are ready to be shipped back to the you to be put into action, or moved onto coating processes, where the passivated surface provides a more reliable and adhesive surface for various topcoats.

• Contaminants may be present due to prior processing or environmental conditions
• Passivation cleans parts of surface contaminants
• Enhanced surface cleanliness provides ideal surface for coating application
• Tests ensure a “passive” or clean surface as required perspecification
• 23-25 hour Humidity test is most commonly performed test

MIL’s new passivation lines