Pipe joint

Claim 1

A pipe joint comprising, a box having a tapered thread and an annular primary seal surface, an annular seal groove in the box at the last thread, an annular seal member of compressible material in said seal groove, a step between said primary seal surface and said seal groove, an annular secondary seal surface between said step and seal groove, a pipe having a tapered thread and an annular primary seal surface for sealing engagement with the primary seal surface of the box, said pipe thread extending into said seal groove when the pipe joint is fully made up, an annular secondary seal surface on said pipe between the thread and primary seal surface for engaging said secondary seal surface in the box, a step between said primary and secondary seal surfaces on said pipe and spaced from said step in the box when the joint is fully made up to provide a space for receiving any seal material extruded past said secondary seal surfaces, said box and pipe having the following approximate relationship: tb/Db=tp/Dp wherein, tb is the thickness of the box wall at the largest diameter point of sealing engagement between said primary sealing surfaces, Db is the outer diameter of the box at the point where tb is measured, tp is the full wall thickness of the pipe, and Dp is the diameter of the pipe at the full wall thickness, said primary seal surfaces provided by frusto-conical surfaces extending at a first identical taper, said secondary seal surfaces provided by frustoconical surfaces extending at a second identical taper which is less than said first taper, said secondary seal surfaces engaging during make-up of the joint prior to the engagement of said primary seal surfaces and prior to any significant extrusion of said resilient seal.