>>1566899take a bigger positive margin around it
there's probably rust under the paint on the weld that you didn't take off and that's the most important bit.
and for primer do a paint on rust converter. that stuff dries to black primer. if you have an auto-paint specialist store near you the paint on stuff they sell will be cheaper and better than hardware store aerosol rust converter.
clean it with a wax & grease remover before you do that
So it's ok if you leave some surface rust spots because rust converter acts on it but don't leave paint or primer layer with rust under it
and you could prime again on top with actual primer if you have some spare or it doesn't coat much or you want accurate paint because black primer will significantly darken whatever you put on top.
rust inhibitor to use inside the tubes is a different thing btw
for paint you can use an aerosol, or those little tamiya hobbyist paints hobby stores sell are pretty durable. Even nailpolish or fucking whatever would work. It's just to seal the primed layer which is porous.
