topic 57523
Rinsing after Passivation
A discussion started in 2011 but continuing through 2019
August 3, 2011Q. I am currently working on Chemical cleaning services at Saudi Arabia. We observed staining of passivating solution on pipelines/vessels after passivation using ammoniated citric acid with sodium nitrite (as oxidizer to form gamma iron oxide layer). Here are my questions:
1. Is it possible to rinse after passivation ? (Our worry that passivation may strip-off after rinsing).
2. What is the life of iron oxide and other passivation chemistry when it is in process water line? when it is in oxygen line?
Chemical Engineer - Saudi Arabia
August 16, 2011
A. Dom,
Assuming you are talking about stainless steel passivation here, since pipelines are generally stainless. Yes, you can rinse, in fact, you NEED to rinse. The passivation treatment with acid removes free iron from the surface, but most or all of the formation of the passive chromium oxide layer takes place when the iron-depleted surface comes into contact with air. Any stainless surface being passivated must be rinsed, dried or allow to dry, and left in contact with air for at least a few hours if possible before entering service.
The passivation will not strip off via rinsing because stainless passivation is a treatment, not a coating. The passive layer is formed from the metal itself.
August 28, 2011
Q. Thanks a lot Mr. Ray. Is this standard practice in industry? or you tested in your lab? How about if it is citric based passivated carbon steel, is there any issue if we will do the post rinsing?
Dom Marcos [returning]Chemical cleaning - Saudi Arabia
September 2, 2011
A. Is rinsing after acid treatment standard practice in industry for stainless steel passivation? It's a required step, if you look at the passivation standards (ASTM A967 [link by ed. to spec at TechStreet]
, AMS2700 [link by ed. to spec at TechStreet], even the now defunct QQ-P-35C [link is to free spec at Defense Logistics Agency, dla.mil]).
Carbon steel cannot be passivated by acid treatment. If you use citric acid on carbon steel you had better rinse it off or you may not have much steel left.
July 2, 2019
Q. Hi I'm currently working on a passivation set up and I encounter myself with a question regarding post treatment and neutralization processes after passivation of stainless steel in accordance with AMS2700 [link by ed. to spec at TechStreet] F.
my question is: how necessary is neutralization needed after the parts have been passivated?
- Anaheim California USA
July 16, 2019
A. Hassan,
With citric acid, a water rinse is all you need. With nitric acid, a water rinse should be sufficient in most cases, but many people go with an alkaline neutralizing bath first just to make sure, especially if the parts have blind holes or other types of nooks and crannies where acid residue may become trapped.
July 17, 2019
A. We use a Ion exchange system for our final rinse. a two tank counterflow.
If you check your pH of the last tank often you should have no issue with a 3 to 5 minute rinse.
Edwards Interiors - Rincon, Georgia
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