A method for joining a tube and tube plate for use in a tube-and-shell heat exchanger is disclosed. The method enables a joint between the tube and tube plate that is substantially hermetic and substantially corrosion-resistant. The method comprises providing an anvil inside the tube, wherein the anvil supports the tube wall during a friction-stir welding process used to join the tube and tube plate. The anvil facilitates formation of a reliable weld region and enables faster friction-stir welding.