Finish the rough edge of drywall with the sharpest and cleanest L bead on the market. The Archway variety is great around duct work and piping, for finishing columns, curved walls and soffits. Archway minimum 8" inside radius or 8" outside radius. Combine this solution with the Architectural Z Shadow Bead to create a floating expansion reveal.
https://www.trim-tex.com/products/overview/commercial-beads/j-l-beads/architectural-l-bead-archway