A threaded joint which economically imparts effective sealing properties to a metal-to-metal seal portion and which can prevent seizing at the time of make-up comprises a steel pipe 1 having at its tip a male thread 1b and an unthreaded sealing surface 1a, and a coupling 2 having on its inner surface...http://www.google.fr/patents/US6957834?utm_source=gb-gplus-shareBrevet US6957834 - Threaded joint for pipes
