Double-walled tube, method of manufacturing double-walled tube and steam generator

A method of manufacturing a double-walled tube including a plurality of double-walled tube forming members, each having an inner tube and an outer tube, connected by welding at welding portions of axis direction end portions thereof,

• the method comprising:
• in each of the welding portions of the double-walled tube forming members, providing a groove having a length in an axis direction being equal to or greater than ½ of a width of a weld bead formed by the welding at the welding portions;
• welding the inner tube s from the inside of the inner tubes;
• and
• welding the outer tubes from the outside of the outer tubes.

A steam generator, comprising:

• a vessel through which liquid metal flows;
• and
• a heat transformer tube that is housed in the vessel and through which water and steam flow;
• the heat transformer tube being a double-walled tube including:
• a plurality of double-walled tube forming members, each having an inner tube and an outer tube, connected by welding at welding portions of axis direction end portions thereof;
• and
• each of the welding portions of the double-walled tube forming members including a groove having a length in an axis direction being equal to or greater than ½ of a width of a weld bead formed by the welding at the welding portion.