The present invention relates to a pressure tank in stainless steel to be used as a water heater. The tank is provided by two identical tank halves (12a, 12b; 14a, 14b). The two tank halves are joined about a common dividing plane (7) and have a longitudinal axis (26) that lies in the dividing plane (7) so that an extended tank is provided. The tank halves have welding flanges (22a, 22b) that are placed against each other in the joint dividing plane (7) and are joined together by welding or melting of the flanges (22a,22b) to a watertight tank. The plate thickness is calculated according to the maximum test pressure of the tank and not limited by the welding. An efficient welding of the internal welding seam (24), by placing the tank in a rig and rotating the tank, provides safe protection against corrosion in the weld.
