Pickling of Duplex Stainless Steel

We picklie Duplex stainless steel with Nitric and HF. The solution is supplied to us as 26wt%HNO3 and 7wt%HF solution mixed in water.

We then further dilute the the above liquor 2 to 1 with water.

I am trying to calculate the pH and the chemical reactions but the combination of the acids is confusing me!

Can I do a simple titration on the above? Or is the effect of two acids going to screw it up?

I thought there would be some good info on the web, like an idiots guide. But it seems like a black art!