The prestressed flanged leaktight connection device comprises a first
flange (130) presenting a first contact surface (111), a second
flange (140) presenting a second contact surface (121) situated facing the first contact surface (111), a sealing
gasket (160) received in a
gasket housing (170) formed between the first and second contact surfaces and clamping elements (150) for clamping together the first and second flanges (130, 140). The first and second contact surfaces present a localized bearing zone (Z1) forming a dog situated in the vicinity of the sealing
gasket (160). At least one (111) of the first and second contact surfaces presents, in the localized bearing zone (Z1) a surface of specified shape, e.g. conical, such that before tightening of the tightening elements (150), contact between the first and second flanges (130, 140) at the localized bearing zone (Z1) is limited to a fraction of the surface of the localized bearing zone (Z1), whereas after tightening of the tightening elements (150; 250) the contact is distributed evenly over all of the localized bearing zone (Z1).