Patent ID: 7997627

Claim:
A threaded joint for steel pipes comprising a pin and a box, the pin having a male thread, a metal sealing surface, and a shoulder surface, the box having a female thread, a metal sealing surface, and a shoulder surface, the male thread being interengaged with the female thread, the metal sealing surface of the pin radially interfering with the corresponding metal sealing surface of the box to form a metal to metal seal, and the shoulder surface of the pin being in axial abutment with the corresponding shoulder surface of the box, characterized in that (i) the shoulder surface of the pin in axial abutment is provided at an end face of a nose portion of the pin, (ii) the metal sealing surface of the pin is located on a pipe end side and between the male thread and the nose portion, a distance between a center of the metal sealing surface of the pin and an onset of the male thread is less than a distance between the center of the metal sealing surface of the pin and the shoulder surface of the pin, and wherein the nose portion extends from the metal sealing surface and to the end face, and further wherein an outside peripheral surface of said nose portion extending between the metal sealing surface and the end face does not contact the portion of the box facing the outside peripheral surface of the nose portion of the pin and the outside peripheral surface of the nose portion is not in prolongation of the metal sealing surface of the pin so that a thickness of the nose portion is increased over its length so that sealability with respect to external pressure and resistance to compression are improved; and further wherein a shape of the metal sealing surface of each of the pin and the box is independently selected from (i) a tapered surface resulting from rotation around a joint axis of a straight line inclined relative to the axis, wherein a taper of the metal sealing surface of the in is not less than 5 degrees, (ii) a bulged surface resulting from rotation around the joint axis of a curve, and a torical surface if the curve is a circular arc, and (iii) a torico-conical surface resulting from rotation around the joint axis of a combined line of said inclined straight line and said circular arc.