Threaded pipe connection with a pressure energized flex-seal

A threaded connection having a central longitudinal axis and having a pressure energized flex seal region capable of sealing both liquids and gases, the connection comprising:

• a first box member having a box end, the box end having an end opening defining an interior surface with internal threads and a radially inner circumferential surface, the internal threads being defined by crests and roots and opposing flanks;
• a second, mating pin member having a pin end with a pin nose, the pin nose terminating at an outside wall region at an outer extent thereof, the pin end having an interior surface and an exterior surface, the exterior surface having 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, the outside wall region of the pin nose being located between the interior surface and the exterior surface of the pin nose;
• wherein the box member interior surface has a radially inwardly extending shoulder which is located between the internal threads and the radially inner circumferential surface and extends in a direction generally perpendicular to the central longitudinal axis of the connection, the inwardly extending shoulder having an outer surface which faces the box end opening and an oppositely arranged inner surface, the outer surface being contacted by the outside wall region of the pin nose during make up of the connection and forming a primary containment seal upon make up of the connection;
• wherein the outer surface of the box shoulder has a pair of resistive areas which are spaced apart by a recessed area, so that the outside wall region of the pin nose initially makes contact only with the resistive areas on the box shoulder during make up of the connection;
• wherein the box shoulder has a radially outward resistive area and a radially inward resistive area, with respect to the central longitudinal axis of the connection, and wherein the radially outward resistive area has a greater relative surface area than the radially inward resistive area;
• and
• wherein a concave recess comprising a machined recess is formed on the box member interior surface between the box shoulder and the radially inner circumferential surface beginning as part of the box shoulder inner surface and continuing in a direction opposite the box end opening, contact between the mating pin member pin end and the box shoulder causing the box shoulder to flex in the direction of the concave recess and form the flex-seal region upon makeup of the connection which is pressure energized during use by any fluid present in the interior of the connection.