Cylindro-conical pipe joint

In a separable joint for metal pipes in which a seal is formed between the end of a male member and a shoulder formed on the inside of a female member, said shoulder comprising a central frusto-conical zone the smaller end of which is directed toward the end of the female member and a frusto-conical outer zone which slopes in the opposite direction, the end of the male member having a central zone corresponding to said central zone of the female member and an outer zone having a shape which mates approximately with said outer zone of said female member, the end of said male member being provided with external threads and the end of said female member with internal threads, the improvement according to which the threads on each member lie partly on a cylindrical surface occupying the major portion of the threaded part of said member, said cylindrical surface extending from a point near said female shoulder in the case of said female member and the said end of said male member in the case of said male member, and partly on a frusto-conical surface near said end in the case of said female member and more remote from said end than said cylindrical threads in the case of said male member, wherein said frusto-conical threads occupy a surface from 15 to 25% as long as that occupied by said cylindrical threads, said threads having roots and crests substantially parallel to the geometrical axis of said joint, the axial width of said threads being substantially greater than the height of the threads, the flanks of the threads on both the male and the female members which come into contact during the make-up of the joint being substantially perpendicular to the axis of the joint, throughout the cylindrical part of the threads there being a clearance between the crests of the threads of the male member and the bottoms of threads of the female member, and between the bottoms of the threads of the male member and the crests of the threads of the female member, the rear flanks of the threads of the female member lying on said frusto-conical surface being bevelled to facilitate the insertion of said male member and the end of said female member having a conical entrance to facilitate said insertion.