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Passivation
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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 an
nitric or citric acid based solution that will remove the surface
contamination, but will not significantly affect the stainless steel itself.
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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.
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Passivation process
forms extremely corrosion resistant Nickel-Chromium mono-oxide layer.
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The type of stainless
steel determines the most effective passivation process.
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Bath selection (time,
temperature and concentration) is a function of the type of alloy processed.
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A thorough knowledge of
the material types and passivation processes is paramount to achieving the
desired results.
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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 componen
Following represents
some of the common specifications and test certified by our organization:
Requirements of Passivate baths in-house to meet Military customers specs.
ASTM A-967
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" TRB/Andarn has
capabilty to perform and certify finishining to the following
specifications".
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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 |
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QQ-P-35-C
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Type II |
Type VI |
Type VII |
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| Nitric
Acid |
20 - 25 % |
25 - 45 % |
20
- 35 % |
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| Sodium
Dichromate |
2.0 - 3.0 % |
N/A |
N/A |
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| Temperature |
120 - 130 F |
70 - 90 F |
120 - 150 F |
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| Time |
20 Minutes |
30 Minutes |
20
Minutes |
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ASTM
A-967 (CITRIC ACID)
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Citric 1 |
Citric |
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 |
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1.8-2.2 |
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ASTM A-380
Standard practice for Cleaning, Descaling, and Passivation of
Stainless Steel Parts, Equipment, and Systems
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Code
F |
Code G |
Code H |
Code IE |
Code JE |
Code KG |
Code LE |
| Condition |
Annealed, cold-rolled, thermally hardned, dull, non-reflective surface |
Annealed, cold-rolled, thermally harden, 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. |
20-40% B.V |
20-50%
B.V |
20-25% B.V |
20-50% B.V |
1-2% B.V |
12%
B.V |
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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 |
120-130 |
70-120 |
120-140 |
120-140 |
| Time |
10-30 |
10-30 |
20-30 |
15-30 |
25-40 |
10 |
10 |
| pH |
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