Can I weld an air compressor tank?

Please no, an air tank is a bomb when filled with air.If the repaired area failed during service it could potentially hurt or even kill anyone within the area that projectiles could be blown to.If you would like to repair it must be a full penatration weld with NDE done after. Best bet is to repair using a approved procedure as the can could be any type of material grade.Then fill with water and then test the vessel to 1 1/2 times the design working pressure (which will be stamped on a nameplate somewhere on the vessel).All pressure vessels fabrication , repair and testing are done under ASME code.