passivating 316 s/s 3

[henegg]

HI

We are doing some custom processing of liquid egg for a bigger food company. They want any new product lines and/or tank passivated before use.

Currently, that is not our practice. We tig weld all our s/s line,with an argon purge and then polish the welds. We have never had a problem with rust or corrosion. But to keep our customer happy we passivated a new line we just installed.

The pipe was a 1/2" 316 s/s. We used a 20% citric acid solution at 120F for 40 min. then rinsed the lines with water.
The comment made after seeing our record of passivation, "you should have air dried the line after passivating, with compressed air for 30-40 minutes".

Did we passivate correctly and is the air drying step necessary ?


Thank you

Tom

 

[0707]

If the line is for food service it will be a good practice to have it dried after passivation.

luis

 

[CoryPad]

ASTM A 380 Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems, section 6.4 Final Cleaning or Passivation, or Both states:

When the stainless steel parts are to be used for applications where corrosion resistance is a prime factor to achieve satisfactory performance and service requirements, or where product contamination must be avoided, passivation followed by thorough rinsing several times with hot water and drying thoroughly after the final water rinse is recommended, whenever practical.

 

[EdStainless]

If you can show that your water had a conductivity of 4 midromohs or less then you can justify not force drying. It is usually easier to rinse with hot DI water and then just blow out with nitrogen (it is very hard to get compressed air clean enough). The nitrogen will have a dew point below -50F and combined with hot water it will all evaporate within 30 sec or so.

Passivation, yes. Anything that has been cut, formed, polished, or welded will need passivation in order to restore optimal corrosion resistance to those surfaces.

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Plymouth Tube

 

[henegg]

Thanks everyone

please educate me on how AIR DRYING insures passivation or at least that was what customer led us to believe.

Thanks

tom

 

[EdStainless]

The air drying assures that you don't have residual foreign material on the surface that can cause contamination or be a location to trap process fluid making it more difficult to clean later.
The reason that I don't like air is that it has to be very clean and very dry. Like the air used for paint systems in auto body plants. We found it easier and less expensive to use nitrogen.

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Plymouth Tube

 

[strider6]

From the articles linked below it seems that the air drying step is not necessay, i mean i've not seen this requirement.
I don't see what kind of improvement can give to the passivating process...

http://www.aws.org/w/a/wj/2002/05/feature/index.html

http://www.euro-inox.org/pdf/map/Passivating_Pickling_EN.pdf

http://www.australwright.com.au/datasheets/advice/Stainless Steels/Passivating stainless steel.pdf

http://www.bssa.org.uk/topics.php?article=68

hope this may help u

S

Corrosion Prevention & Corrosion Control