Yes, two sheets of metal can be butted together and butt welded. Butt welding is a joining process used to join two parts together. The work acts as the electrode and the entire cross section is welded. The parts are clamped and brought together with force and a current is applied. The intention is to create heat using Joules Law H= I2rt at the joint surface with current flow. As the joint heats up the force upsets the joint and a bulged area is formed. The current is stopped. The weld area cools under force and then the force is removed and the butt weld is complete. The limit to part size is the power and ability to clamp the part.
So two sheets of metal can be butted together or one sheet as shown on the example below can be formed into a ring and brought together to form the joint. The limits are power and the ability to hold the product and deliver the force evenly. If the machine is large enough with sufficient power you are making product. The example below illustrates a good example of a long butt joint being formed in one operation of the machine.
Reference: RWMA – Resistance Welding Manual Section 5