Patent ID: 9709196
Date: 2017-07-18
CPC Classifications: E21B,F16L

Claim:
1. A threaded joint for heavy-walled oil country tubular goods comprising: a pin including an externally-threaded member formed by applying taper thread forming to an end portion of a steel pipe having a wall thickness of 18 mm or more, a nose extending toward an end side of the steel pipe from the externally-threaded member and being a non-threaded portion, and a shoulder formed at an end of the nose; and a box including an internally-threaded member threadedly joined with the externally-threaded member, an inner periphery of a seal portion of the box facing a nose outer peripheral surface of the pin in an opposed manner, and a shoulder brought into contact with the shoulder of the pin; wherein, the pin and the box are joined to each other by threaded joining so that the nose outer peripheral surface and the inner periphery of the seal portion of the box are brought into a metal contact with each other in a pipe radial direction, thereby forming a seal portion that seals a fluid at the contact portions, a pin-side surface and a box-side surface that form the seal portions are formed into a convex curved surface and a tapered surface, respectively, a seal thickness t a shape parameter t a ratio of a complete thread length L of the pin which is a length of a complete threaded portion of the externally-threaded member in a pipe axis direction to a wall thickness t of the pin raw pipe portion, the ratio which is a complete thread length ratio L/t is 4.0 or less.