Expansion seal, especially for gases

A flange connection comprising:

• two flanges and a sealing ring inserted into an annular sealing space defined by radial faces and axially extending peripheral walls between the flanges;
• wherein the two flanges and the sealing ring are comprised of the same material:
• the sealing ring having an annular main body and an outer periphery with a cross-sectional shape that has legs extending outwardly from said main body;
• wherein the legs, in a condition prior to application of sealing pressure, are inclined away from each other and have rounded outer ends that abut both the radial faces and the axially extending peripheral walls defining the annular sealing space;
• wherein the legs, in a condition where the flanges are forced against each other, are axially compressed and upset at least in a radial direction by plastic flow of material on said rounded outer ends, wherein the rounded outer ends each are in sealing engagement with a first sealing point at a first contact zone with said axially extending peripheral walls and with a second sealing point at a second contact zone at one of the radial faces, respectively, wherein a free space remains between said first and second sealing points of the rounded outer ends, respectively, and in the free space the rounded outer ends have no contact with the radial faces and the axially extending peripheral walls.