Letter 20041

Nitric acid to strip EN plated stainless steel parts  

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We strip EN plated stainless steel parts using 42 Baume nitric acid. When immersed in the tank some parts react rapidly and stripped in less than 5 minutes. Other parts don't appear to be reacting at all. On the difficult to strip parts we put into B-9 and they strip over time. B-9 is a good product but nitric is much faster and cheaper for stainless steel. Why do some EN plated parts strip faster than other in the nitric acid?

Doug Goedecke
- North Kansas City, MissouRhode Island

The simple answer is that some strip fast and others not. One simple thing to try is to put the parts in wet. Neat nitric can try to passivate rather than strip, dilute nitric is more of a stripper. By puting the parts in wet you form a small layer of dilute nitric and once the stripping starts it goes on.

Martin Trigg
surface treatment shop - Stroud, Glos, England

Putting parts in wet can cause an erratic stripping some of the time. I normally used a 50% mixture with water and increased the percentage of acid as the nickel content went up, finally sending it to the wastewater facility as it will quit stripping or get too slow for commercial applications.

James Watts
- Navarre, Florida

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