Metal-to-metal seals for pin and box member tubular joints are disclosed where mating annular surfaces are machined at slightly different angles such that the bearing load from initial contact is entirely on the leading edge of the pin annular surface and the trailing edge of the box annular surface....http://www.google.fr/patents/US5423579?utm_source=gb-gplus-shareBrevet US5423579 - Tubular coupling with metal to metal seal
