Single flare tube and joint structure of single flare tube

Abstract

A single flare tube, and a joint structure of the single flare tube makes a flare of the single flare tube hardly deformed plastically. Additionally, a tensile stress remains lower and is lower when the single flare tube is fastened. A joint structure of the single flare tube coupled with a union includes a single flare tube having a tube and a flare, a flare nut having a thread and a through-hole that receives the tube of the single flare tube, and a union having a thread for coupling with the thread of the flare nut. A width of a narrow inner circumferential groove of a radially outward extending part of the flare is substantially zero and stays substantially zero when the single flare tube is pushed against and coupled with the union by fastening the threads of the flare nut and the union together. Additionally, an internal diameter of the inner circumferential groove preferably is smaller than an external diameter of the tube. Furthermore, a curvature at a radially outer side of an outer corner of the single flare tube (where the tube is connected with the flare) is larger than a curvature at a radially inner side of the outer corner of the single flare tube along a longitudinal cut section of the single flare tube.