Weld seam and edge of galvanneal steel.

How to protect or restore the galvanneal coat after welding. The coat must be galvanneal, not metal Zn?

Also, is there any way to minimize area of unprotected steel on the cut edge of the galvanneal sheet?

Well, galvanneal is designed to be painted, not used as a finished surface. So, are the unprotected edges, and the welded areas, really a concern if you are going to paint the object anyway?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Galvanneal is more of a process than the coating itself, the galvanized surface is a high zinc alloy that has been pickled, heated, and cooled quickly in a non-oxidizing atmosphere. To restore that, you have to repeat the process. It depends on the performance needs for your part how you repair the welded area, if you are applying zinc phosphate over it before painting then its probably OK without anything else. If the performance demands are extreme you may have to re-apply the coating, there are a few ways to do that, none of them high production. Tube mills use a spray of zinc powder onto the welded area just after welding to replace the galvanizing, you could check into something like that...