Arrangement with a metal pipe and a connecting element, as well as method of mounting the connecting element

Arrangement for a helically undulated pipe of metal and connection element, said arrangement comprising:

• A helically undulated pipe of metal which has an end face extending along a helical turn of the thread of its undulation;
• and
• a connecting element to be fastened to the pipe, said connecting element includes a pipe piece of metal which has a helically extending inner surface corresponding to the helical thread of the undulation of the pipe, and a smooth cylindrical outer surface, said connecting element when in the mounted position is arranged on the pipe by engaging in the undulation of the pipe, wherein
• in the mounted position, a metal ring is arranged on the pipe piece, with contact to the pipe piece and is welded to the pipe piece, wherein the inner surface of the pipe piece has two sections with different inner diameters arranged axially one behind the other,
• the ring rests on the pipe piece with its section having the greater inner diameter, and rests on the pipe with its section having the smaller inner diameter on the side of the pipe piece facing the end face of the pipe,
• the section of the ring with the smaller inner diameter has an end face extending along a helical line corresponding to the course of the turn of the thread of the pipe,
• the ring is welded at its helically extending end face to the end face of the pipe.