Multiple seal, double shoulder joint for tubular products

Claim 1

A joint for metallic tubular elements embodying male and female members having engageable threads of relatively long pitch disposed on a relatively steep taper, the said female member having full threads and the said male member having vanishing threads, the threads on said male member, when said joint is maDe up, being engaged throughout their length, and said male and female members having complementary conical sealing surfaces axially displaced and radially offset from said threads to make full conical surface contact throughout substantially their overlapped length with only surface deformation of the complementary sealing surfaces; said male member having an internal annular shoulder, said female member having an internal annular shoulder, the end of said female member abutting the external annular shoulder, said female member having an internal annular shoulder, the end of said female member abutting the external annular shoulder of said male member to prevent overtightening, and the end of said male member abutting the internal annular shoulder of said female member, when said joint is made up, to provide a leak-proof seal, the end of said female member and said external annular shoulder of said male member being undercut at an angle from about 5* to about 10* with respect to the radius of said joint, and the end of said male member and said internal annular shoulder being undercut at an angle from about 5* to about 20* with respect to the radius of said joint.