Letter 33052

Restoring damaged pickled finish to 304 stainless steel  

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Hi,

I work for a company that manufactures stainless steel products for waste water treatment appications. All of our machines are made with 304 stainless steel and finished with a pickling method, which produces a sort of matte or dull finish. Our parent company is in Germany and we are located here in the USA. At times, we transport these machines on a flatbed, covered with a plastic tarp. While this does keep the machine dry from the elements, it causes the finish to look blotchy and dark from where the tarp would beat and flap against it. We could not find any cleaning solution that would remove the dark spots.

I would like to know it there is a method or solution of some sort the you know of, that we could use to remove these dark spots from the affected areas and restore the finish back to the original pickled or dull finish without ruining the existing finish?

Any information would be much appreciated.

Thank You,

Dave Fuller
- Huntersville, North Carolina

It sounds like you may have more things going on here. What is the pickling chemistry? (Do not use HCl.)

IF it is only a physical effect caused by flapping of the tarp covering the units it seems logical to change the type of tarp used to be something that is less "abrasive" to the finish. Is there any possibility that moisture is in contact with the units under the tarp and the tarp is chemically attacking the surface? If it is black it does not sound like a physical effect.

Once the "dark" blotches are there it is probably necessary to re-pickle or grit blast the units to get the matte finish even again.

Lee Kremer Stellar Solutions, Inc. McHenry, Illinois

Dear Sir,
I hope that you talk about the stain made by the physical beating of the ss304 material by the tarpaulin used for covering it. You can swab with Chromic/sulphuric mixture and rinse it before putting to use. You can try to coat by a thin of colourless polymer film (lacquer film)which will make a hard film on curing to keep the surface intact. Of course you should see the cost aspect on this method. But you can always try to use different material for the tarp and avoid these stains.

Ramaswami Sundar
- Al-Khobar, Saudi Arabia

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