I had a steel fence that is about 150 feet long replaced at a house I just bought and where the welds were done connecting the fence pieces, the guys just hit it with some black spray paint to match the powder coating.

The spots that they didn’t spray well enough already show some very light surface rust or oxidation and some rust on the top portion of the fence where they totally forgot to spray paint. I would call them out to fix their work but figured I would just do it right myself before I plant a large privacy hedge alone the fence where it would be harder to reach.

I want this fence to last a long time so I was looking for suggestions on the best paint to use. I was planning on removing the spray paint with a light grinding wheel to give myself a clean surface and then would use a quality waterproof paint rather than spray paint. Any suggestions on best paint to use and also consideration when painting the same surface that’s already powder coated would be helpful.

I would look for a high quality epoxy paint.
Since most epoxies don't have a lot of UV protection built in, you might have to top coat it with something that has the UV protection.
Eastwood Tools Epoxy paints Check out those and see what works for you.
It sounds like you only have small areas to do, so the aerosol cans might be the right product.

Since I’m kinda a brand loyal guy, I would say Sherwin Williams KEM 400. An industrial paint that a few metal fabrications use locally for painting pole barn metal trusses, and also used by the local power company. Also the paint I plan on using for a couple of auto chassis repaints. Yes, smallest package amount is a gallon. But if you plan to do the whole fence may worth looking into.

The spec sheet:

https://www.paintdocs.com/docs/webPDF.jsp?SITEID=SWPCGIND&doctype=PDS&prodno=035777271742&lang=2

Lots of how-to on YouTube for powder coat repairs. Just need to sort thru the chaff for the practical and correct ones.

Thanks for the inputs, yes a gallon is way more than I need but want to do it right and make my expensive fence last.

Am I correct that roll/brush on paint is a much better long term solution than the Eastwood epoxy spray paint?

I don’t need to paint the whole fence, just the sections they welded together and didn’t do a great job painting the weld beads and surfaces next to the welds

I've used the Eastwood spray epoxy, and it works fine.
The most important part is preparation of the surface.
Remove all rust, rough it up, degrease several times, and then apply the epoxy.
For topcoating the epoxy, do what the manufacturer says and you'll be fine.