Can I re-use this gasket after welding if I remove it?

No. Once welded, the gasket bonds permanently to the flange. You'll need a fresh piece for any future disassembly. Plan your flange work carefully before committing to the weld.

Do I need to prep the flange surface before welding the gasket on?

Clean bare metal works best—remove rust, paint, and oil from both flange faces. The graphite bonds directly to steel, so surface condition directly affects seal quality.

Will this gasket work on cast iron manifolds?

Yes. Graphite bonds equally well to cast iron and steel. Verify the manifold surface is clean and flat enough to seat the gasket fully before welding.