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topic 57523

Rinsing after Passivation

Current question and answers:

December 4, 2020

Q. Hello,
When passivating with Citric acid, do you rinse immediately after the bath and then let 24 hour dry with air, or do you let it dry first just after the bath, and rinse 24 hours after?
Thank you

Jay Bee
- Grasse, France
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simultaneous December 4, 2020

You should thoroughly rinse your parts immediately after the passivation step before the chemistry dries on the parts.

Jon Hickman
Best Technology Inc.
supporting advertiser
Plymouth, Minnesota
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December 4, 2020

You generally want to follow the citric passivation with a RO water or DI water rinse right after the citric solution, which 3 to 5 minutes is generally enough for time and you can use a conductivity meter for verification that parts are full rinsed.

mark battles
Mark Battles
Best Technology Inc.
supporting advertiser
Plymouth, Minnesota
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February 4, 2021

Rinse first, dry after.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

Previous closely related Q&A's starting in:

August 3, 2011

Q. 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?

Dom Marcos
Chemical Engineer - Saudi Arabia
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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.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
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McHenry, Illinois
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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
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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 / A967M [affil. link to spec at Techstreet] , AMS2700 [affil. link 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.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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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 [affil. link to spec at Techstreet] F.
my question is: how necessary is neutralization needed after the parts have been passivated?

Hassan Tello
- Anaheim California USA
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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.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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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.

Micheline Forth
Edwards Interiors - Rincon, Georgia

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