QQ-P-35

Stainless Steel Passivation Specification

Coating Weight Testing

Certain coatings are qualified by physically weighing deposit as opposed to measuring the thickness. Type I and II anodize and phosphate coatings fall in this category. Although there is some actual buildup of these coatings the industry uses the weight as the acceptance criteria for validating these coatings.

24-hour Immersion Testing

This test involves a one hour immersion of a sample in distilled water, at room temperature, followed by a one hour drying cycle. This is then repeated for 12 cycles. If there is any evidence of staining or rust on the part the lot would be rejected.

Copper Sulfate Testing

This test is referenced in ASTM A967 as a way of detecting free iron on the surface of certain grades of stainless steel. The presence of copper on the surface of the part post-test indicates the presence of free iron, and is cause for rejection.

Salt Fog Testing

Also called Salt Spray Testing, is described in ASTM B117. The test provides a controlled corrosive environment which is used to generate resistance information for metals and coated metals exposed in the test chamber.

AMS QQ-P-35

This has been canceled and is superseded by AMS 2700

AMS 2700

The specification document AMS 2700 offers norms and recommendations for the passivation of stainless steel alloys. Stainless steel can be made more corrosion-resistant by using a chemical process called passivation, which cleans the metal’s surface of impurities. The specifications, testing protocols, and processes for passivating stainless steel parts used in manufacturing and aerospace are outlined in AMS 2700.

440C Stainless Steel

This particular grade of stainless steel is susceptible to intergranular attack by nitric acid. In some of the older specifications it was recommended that this particular alloy not be processed through passivation.

Citric Acid Passivation

Meets AMS 2700, ASTM A967, QQ-P-35, AMS QQ-P-35. This is one form of passivating stainless steel. There are various bath concentrations and temperatures that can be used, typically determined by the alloy of the stainless steel.