the ferrooxile test is just for surface iron contamination.
NEVER buy a duplex without requiring A923. Reject it. It was not annealed correctly. Use the G48 as the basis, or use poor workmanship, wrong microstructure.
Also I suggest that you switch to G48 method C, even if you have to go to a lower test temp like 45C. The test is more repeatable.
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube