It depends whether the sand is damp or dry.
It is easy to ride a fat bike on damp sand. No doubt, some of the previous posters are talking about damp sand. Obviously the salt water will quickly destroy the bike.
You wont successfully ride a bike on dry sand. For dry sand, you need at least 400 mm (16 inch) wide tires.
Seth, on a cheap Dolomite with dry sand, wet sand AND saltwater. Search his YouTube video: " Fatbiking in the wake of a cruise ship" HILARIOUS!