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Passivation of 316L SS per ASTM A380

 

 

I currently need to passivate a partly electropolished 316L stainless steel process system.

The passivation procedure I intend following, in general, ASTM ASTM A380 [link is to the practice at TechStreet] -96, is Standard Recommended Practice for Cleaning and Descaling of Stainless Steel Parts, Equipment and Systems".

The passivation routine, following cleaning run is a mixture of;
4% w/w Citric acid
5% w/w Di-ammoniumhydrogencitrate
0,5% w/w Titriplex III(PH EUR, BP, USP)
90,5% Deionized water
at 80 degree C for 1 hour.

I recollect being informed that the 5% di-ammonium hydrogen citrate can effect electropolished stainless detrimentally, and that electropolished stainless should be removed from the system before running the passivating solution. Although cannot see the reason obviously myself?

Could someone confirm or deny this effect?

Regards,

Jack Lyons
- Ireland


 

Jack:

This formula should not hurt your electropolished surfaces. There are better formulations for doing what you want, however, that are available on a proprietary basis.

You should be using ASTM A967 [link is to spec at TechStreet] for passivation specification, not ASTM A380 [link is to the practice at TechStreet] is just a recommended practice. It is also quite out of date and needs to be updated. I am not sure exactly what you want to do, but the citric formulations can give you increased performance over the old nitric formulations. Let us know if we can help.

Best regards,


Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois



 

Hello Jack,

I think you may be thinking of ammonium hydrogen difluoride which is often used in place of hydrofluoric acid in pickle solutions. This would attack electro-polished surfaces and is not the kindest way to treat them. I agree with Lee that what you are proposing should not be a problem with the EP'd surfaces.

John Holroyd
- Elkhorn, Wisconsin


 

Jack:

Never use Ammonium Bifluoride on Electropolished Stainless Steel. If you let this solution inside your S.S. 316L Electropolished system it will start to get a blueish coloration, indicating the damage done to the electropolished surface. In the past we used ammonium Bifluoride flakes at 10% concentration for descaling purposes but we discontinued this practice for the same reason, it is very harmful, toxic and causes damage to this surfaces.

Hope this will help

Julio C. Nazario
- San German, Puerto Rico


sidebar August 6, 2008

INTERNAL PICKLING & PASSIVATION FOR SS SPOOLS?

DEAR SIR,

I WOULD LIKE GET CLARIFIED FROM THESE PASSIVATION METHOD AS I NEED FROM YOU IS WHAT RECOMMENDED PROPORTION OF WATER TO CHEMICAL SHOULD BE MIXED IN A BATH FOR IMMERSION TO PICKLE & PASSIVATION OF THE SPOOLS & WHICH WATER SHOULD BE USED.

TANVEER PATIL
PROJECT ENGINEER - RUWI, MUSCAT, OMAN


August 9, 2008

Hi, Tanveer. To my knowledge it is not possible to do a combination pickling and passivation. I believe you must pickle the spools with an acid which contains fluoride in some form -- often a standard nitric-hydrofluoric pickling acid or pickling paste, and follow this either with electropolishing or with nitric acid passivation or citric acid passivation to the standards discussed above. You do not need super quality water for these processes; DI or RO water will be fine.

Usually it is best to send the spools to a metal finishing shop which is already experienced in and equipped for the process. The spools are probably too expensive and important to risk to trial & error in a training program. If the piping system is already assembled, there are service companies which specialize in on-site projects of this sort, like Astropak. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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