What is the minimum number of fields to be analyzed for ferrite point count for duplex stainless steel weld metal per NACE MR0175. This specification does not indicate this in Par. A.7.3.
You can also find some good general information in MR0103 App. D. This will point you to E562 as Metengr pointed out, but has some good practices for welding Duplex as well. (D6.3 - Ferrite Testing)