2004 Hyundai Santro Fuel pressurization and tank rupture

My wifes car has been throwing a fuel system code for a few weeks. Initially, I suspected a simple gas cap replacement or hose leak somewhere. Then the gas tank started leaking. I dropped the tank and sure enough there is a ruputure type crack in a formed ridge on top top of the tank (nowhere near a contact area or area I would believe to be subject to fatigue stress).

I can fix/repair the tank but something else is happening to cause excess tank pressure (IMO). Could a faulty vapor canister valve cause the tank to build up too much pressure or is there something else I should look at?

Thanks,

Michael