Passivation

  • Passivation is “the removal of exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution, most typically by a treatment with a nitric or citric acid-based solution that will remove the surface contamination but will not significantly affect the stainless steel itself.
  • Passivation process removes “free iron” contamination left behind on the surface of the stainless steel from machining and fabricating. These contaminants are potential corrosion sites that result in premature corrosion and ultimately result in deterioration of the component if not removed.
  • Passivation process forms an extremely corrosion-resistant Nickel-Chromium mono-oxide layer.
  • The type of stainless steel determines the most effective passivation process.
  • Bath selection (time, temperature and concentration) is a function of the type of alloy processed.
  • A thorough knowledge of the material types and passivation processes is paramount to achieving the desired results.
  • Improper bath and process selection and/or process control will produce unacceptable results. In extreme cases, this can lead to catastrophic failure, including extreme pitting, etching and/or total dissolution of the entire component.

Following represents some of the common specifications and test certified by our organization:

Requirements of Passivate baths in-house to meet Military customer’s specs.
ASTM A-967

Andarn has capability to perform and certify finishing to the following specifications.

Nitric 1 Nitric 2 Nitric 3 Nitric 4 Nitric 5
Nitric Acid 20 - 25 % 20 - 45 % 20 - 25 % 45 - 55 % Other Combinations
Sodium Dichromate 2.0 - 3.0 % N/A N/A N/A Other Combinations
Temperature 120 - 130o F 70 - 90o F 120 140 o F 120 - 130 oF Other Combinations
Time 20 Min. minimum 30 Min. minimum 20 Min. minimum 30 Min. minimum Other Combinations
QQ-P-35-C
Type II Type VI Type VII
Nitric Acid 20 - 25 % 20 - 45 % 20 - 35 %
Sodium Dichromate 2.0 - 3.0 % N/A N/A
Temperature 120 - 130 F F 70 - 90 F F 120 150 F
Time 20 Min. minimum 30 Min. minimum 20 Min. minimum
ASTM A-967 (CITRIC ACID)
Citric 1 Citric 2 Citric 3 Citric 4 Citric 5
CITRIC ACID 4-10% B.W 4-10% B.W 4-10% B.W Other combinations Other combinations
Temperature 140-160 F 120-140 F 70-120 F Other combinations Other combinations
Time 4 Min. Minimum 10 Min. Minimum 20 Min. Minimum Other combinations Other combinations
pH 1.8-2.2
ASTM A-380 Standard practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems
Code F Code G Code H Code IE Code JE Code KG Code LE
Condition Annealed, cold-rolled, thermally hardened, dull, non-reflective surface Annealed, cold-rolled, thermally hardened, bright polished surface Annealed or hardened dull or non-reflective surfaces Annealed hardened with bright machined or polished surfaces Annealed or hardened, with bright machined or polished surfaces Same as JE Same as JE
Nitric Acid 20-50% B.V.e 20-40% B.V 20-50% B.V. 20-25% B.V 20-50% B.V. 1-2% B.V 12% B.V
Sodium Dichromate 2-6% B.W 2-6% B.W 2-6% B.W 1-5% B.W 4% B.W Cu SO4.5H2O
Temperature 120-160 120-155 110-130 120-130V 70-120 120-140 120-140
Time 10-30 10-30 20-30 15-30 25-40 10 10
pH