A drilling flange and an independent screwed wellhead provides a metal-to-metal seal that supplements the traditional elastomeric O-rings for providing a fluid seal between the drilling flange and the wellhead. The metal-to-metal seal may be achieved using a metal ring gasket or two contacting metal...http://www.google.com/patents/US7650936?utm_source=gb-gplus-sharePatent US7650936 - Drilling flange and independent screwed wellhead with metal-to-metal seal and method of use
