Patent ID: 8602249

Claim:
A pressure vessel comprising: a cylindrical metal shell; a composite reinforcement wrapped circumferentially around the cylindrical metal shell; a metal head welded to an end of the shell, the head comprising: a convex exterior wall, a concave interior wall, the interior wall spaced apart from the exterior wall by ahead thickness, and a hollow neck extruded as an integral part of the head, the neck protruding inwardly away from the concave interior wall toward an interior of the pressure vessel, the neck having a distal portion thereof spaced substantially away from the concave interior wall, the neck having a thickness that decreases towards a protruding end of the neck, the neck having internal threads, including within the distal portion; a plug having a reciprocally threaded region to engage the internal threads of the neck, including within the distal portion; wherein an internal pressure in the vessel acts on the neck to increase engagement between the neck and the plug at the distal portion of the neck.