Abstract: A double-walled tube includes: 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 set to be equal to or greater than ½ of a width of a weld bead formed by the welding at the welding portion.

Abstract: A hydrogen iodide manufacturing method which includes a step of producing aqueous solution of hydrogen iodide and sulfuric acid by causing iodine-containing aqueous solution and sulfur dioxide to react with each other in a pressurized condition. The pressurized condition may be of not lower than 0.1 MPa in gauge pressure. The method may further include: a separation step of adding iodine to the aqueous solution of hydrogen iodide and separating an upper phase containing sulfuric acid relatively to a large extent and a lower phase containing hydrogen iodide relatively to a large extent; and a step of producing hydrogen iodide by adding sulfur dioxide to the upper phase in a pressurized condition and extracting the produced hydrogen iodide to the lower phase.

Abstract: A hydrogen iodide manufacturing method which includes a step of producing aqueous solution of hydrogen iodide and sulfuric acid by causing iodine-containing aqueous solution and sulfur dioxide to react with each other in a pressurized condition. The pressurized condition may be of not lower than 0.1 MPa in gauge pressure. The method may further include: a separation step of adding iodine to the aqueous solution of hydrogen iodide and separating an upper phase containing sulfuric acid relatively to a large extent and a lower phase containing hydrogen iodide relatively to a large extent; and a step of producing hydrogen iodide by adding sulfur dioxide to the upper phase in a pressurized condition and extracting the produced hydrogen iodide to the lower phase.

Abstract: A hydrogen iodide manufacturing method which includes a step of producing aqueous solution of hydrogen iodide and sulfuric acid by causing iodine-containing aqueous solution and sulfur dioxide to react with each other in a pressurized condition. The pressurized condition may be of not lower than 0.1 MPa in gauge pressure. The method may further include: a separation step of adding iodine to the aqueous solution of hydrogen iodide and separating an upper phase containing sulfuric acid relatively to a large extent and a lower phase containing hydrogen iodide relatively to a large extent; and a step of producing hydrogen iodide by adding sulfur dioxide to the upper phase in a pressurized condition and extracting the produced hydrogen iodide to the lower phase.

Abstract: A hydrogen iodide manufacturing method which includes a step of producing aqueous solution of hydrogen iodide and sulfuric acid by causing iodine-containing aqueous solution and sulfur dioxide to react with each other in a pressurized condition. The pressurized condition may be of not lower than 0.1 MPa in gauge pressure. The method may further include: a separation step of adding iodine to the aqueous solution of hydrogen iodide and separating an upper phase containing sulfuric acid relatively to a large extent and a lower phase containing hydrogen iodide relatively to a large extent; and a step of producing hydrogen iodide by adding sulfur dioxide to the upper phase in a pressurized condition and extracting the produced hydrogen iodide to the lower phase.