Noel,
WELCOME TO THE AWS WELDING FORUM!!
A problem I have with your question and no sketch or picture is that the words 'flare' and 'simple fillet weld' don't go together, in most circumstances that come to mind.
A pic of the welding symbol and of the joint, either actual steel or just from the drawing, would really be great.
He Is In Control, Have a Great Day, Brent
PS: Don't forget Valentines Day!!