Passivation ASTM A967 Type II leaves yellow or brown spots on 304(2005)
We manufactured some parts made from 304 stainless steel and according to the print had them passivated per ASTM A967 [link by ed. to spec at TechStreet] Type II. Our customer has rejected the parts saying that they are rusted. Our passivater says that they are not rusted but have sodium dichromate on them from the passivation type II. He says the proper type of passivation would be type VI, VII or VIII which does not have the sodium dichromate additive which is only needed for 400 series stainless. Is he correct?James Kjorsvig
Machine Shop - Minneapolis, MN, USA
First of two simultaneous responses -- (2005)
It is not nice to throw stones at another plater/passivator, but we always used a dual counterflow rinse and ended with a warm DI rinse and blow down to avoid spotting. Darn few customers will accept spotted SS parts, and I do not see why you should have to unless you beat up the passivator on price.James Watts
- Navarre, Florida
Second of two simultaneous responses -- (2005)
Sounds like your passivator has given you a big clue as to the problem, the solution should be obvious and doesn't have to involve a change in process. All you need to do is instruct your passivator to rinse your components properly to ensure all traces of sodium dichromate are removed.
When you are supplied a part with sodium dichromate on, you have a Health, Safety and Environmental nightmare on your hands! Especially as the proposed exposure limits for hex chrome in the USA are extremely small.
As for using one of the other types, the best bet is to carry out some small scale trials before committing to a change. The other options will give you less of a Health and Safety problem, but check compatibility first.
Aerospace - Yeovil, Somerset, UK
Yes he is.
Bangalore, Karnataka, India
ASTM A 967 type II is not the same as QQ-P-35 [link is to free spec at Defense Logistics Agency, dla.mil] in that in the ASTM standard there are Citric and Nitric passivate processes and you do not indicate which one is called for.
Even if processed per the Military standard there should be no visible staining of the parts, no dichromate residue would remain. Sounds like poor rinsing or other issues exist.
- San Jose
I would advise you to double check the spec. ASTM A967 Nitric 2 method does not allow sodium dichromate. Nitric 1 method does. Parts may be passivated to the incorrect spec..?Chris Hemann
- Minneapolis, MN, USA
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