Letter 39032

Pickling and Passivation bath for stainless steel 316Ti  

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We are stainless steel vessel manufacturer. We have a nitric acid bath with heating facility to pickle stainless steel 316/316Ti. We find recently the pickling result deteriorate. Please explain
1.what is wrong
2.how we can monitor the concentration of the acid
3.how metal content in the bath affects the pickling result
4.how the metal content can be removed from the bath.
Thank you.

Alfred B. S. Lee
Stainless steel vessel manufacturer - Hong Kong, China

I SUGGEST IF YOU CAN USE 3 TO 5 % HF YOU WILL GET BETTER PERFOMANCE
THANKS,

THOTE SHESHRAO
- AURANGABAD, INDIA

As the bath slowly removes metal from the parts that you are pickling, it will lose its effectiveness.
The concentration of the HNO3 can be determined by titration.
Yes, the metals in the bath will slowly reduce the effectiveness. They can be removed by precipitation, but you will have to add fresh HNO3 to make the solution work again. Best is to scrap the solution (legally) and start with fresh solution.
As stated, there are better pickling solutions. You can go online at this site and learn more about how to do this.

Lee Kremer Stellar Solutions, Inc. McHenry, Illinois

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