Fe content in Nitric Passivation solution

[jarrell13]

Is there a spec somewhere or a good rule of thumb on how much iron (in ppm) is ok in a 45% Nitric acid passivating bath, before the tank should be purged? I am trying to write an internal company spec and this question has come up.

 

[EdStainless]

How high have you ever gotten it?
I think that the tank looks very bad long before it causes process issues
I am out of the office so I can't check out spec.
I only recall the pickle numbers.

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Plymouth Tube

 

[jarrell13]

We don't have any historical data around iron content, and yes, when they look bad the acid is still doing its' job. Our process defines some very specific things, but our Quality Eng. is looking for something they can test to. If you come up with something when you are back in the office, let me know.

 

[SJones]

How are you confirming that passivation is of the correct quality after treatment? Would it not be just a case of regarding that as soon as there is a quality control test rejection then the determined iron content is the absolute maximum followed by the setting of a tighter 'safety margin' for future operations?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EdStainless]

The only reliable test for passivation is an electrochemical corrosion test. Not very practical in production.
So people rely on process control. If we got good results with 10 min bath time then we use 15 or 20 in production to assure passivation.

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Plymouth Tube

 

[jarrell13]

Ed, you are spot on about the use of process control. We run four passivation lines, and it would be impossible to test for passivation level on the finished product at our production rates.

Were you able to find anything about iron levels?