Pickling & Passivating

[MaxNeg63]

One of our suppliers states in his P&P procedure that duplex steel pipes can be treated for a time "up to 24 hours". Solution used is 10%-16% nitric acid + 5%-8% hydrofluoric acid in water at ambient temperature (10-25 °C)
Isn't it a very long dwell time? Is there any risk of damaging the pipe surface? And besides, are there any methods to speed up the process?
Thanks
Max

 

[EdStainless]

This is a pickle, not a passivation.
We pickle warm. 20% nitric + 5% HF at about 125-130F. Only some of the high alloy Ni-Cr-Mo grades take more than 2 hours. 304 usually thakes about 20-30 min.
At low temp you will not get much attack at all.

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