A threaded pipe connection is shown which features a pressure energized flex-seal structure. The connection includes a first box member having a box end, the box end having an end opening defining an interior surface with internal threads, the internal threads being defined by crests and roots and opposing flanks. A second, mating pin member has a pin end with a pin nose, the pin end having an exterior surface with mating external threads, the external threads also having crests and roots and opposing flanks, at least selected ones of which move into engagement with the internal threads of the box when the connection is made up. A flex-seal region is located on either the box and interior surface or the pin end which forms a primary containment seal upon make up of the connection.