GB786652A - Improvements in or relating to tapering box-and-pin-type threaded couplings - Google Patents

Abstract

786,652. Pipe couplings. NAAMLOOZE VENNOOTSCHAP DE BATAAFSCHE PETROLEUM MAATSCHAPPIJ. March 14, 1955 [March 16, 1954], No. 7378/55. Class 99(1). [Also in Group XXIV] In a tapering pin-and-box type threaded coupling the two members, the pin and the box are provided with tapering threaded surfaces, such that when the pin has been screwed tight into the box the outer flanks (as defined) of the pin threads and the inner flanks (as defined) of the box threads are loaded more heavily than the other flanks. A small number of the outer flanks of the pin threads and the inner flanks of the box threads at or near the middle of the screwed threads may remain unloaded. The couplings may be used at many points in welldrilling apparatus such as tool joints casing collars, subs, drill collar joints and drill bit joints. In Fig. 4, the pitch of the thread of the pin 1 is bigger and that of the box 3 smaller at the middle part of the thread. Thus the outer flanks of the pin thread press against the inner flanks of the box thread. The threaded part of the pin is under compression. The pitch variation may be provided in only one of the screw threads. In Fig. 5 the pitch P2 at the right hand side of the thread is smaller than P1. The thread may be interrupted at a point where the pitch is varied. In Fig. 6 the pitch P2 is greater than P1. The difference between the pitch diameters of the pin and box threads near the mid point of their length is smaller than at either end. In a modification of Fig. 6 the box pitch diameter line is straight. The pin of the screw thread is divided into two parts having tapers which differ from each other and also from the taper of the box thread 4. The transition between the two tapering parts of the pin is designed to take place more or loss gradually. In another modification, the taper of the pin may be constant and the box may have two parts with different tapers such that the taper of the part near the open end of the box is larger and the taper of the part near the inside of the box is smaller than the taper of the pin. In addition the pitch of the pin screw thread may be made different on two parts of the pin, it may, for example, be made equal to the pitch of the box thread over the left hand part of the thread. Couplings of the kind shown in Fig. 6 and in Fig. 7 (not shown) in which there is a small difference in pitch between the pin and box threads may in addition be provided with local pitch variations such as those provided on the threads of the couplings shown in Figs. 4 and 5. Sealing, instead of being by means of shoulders 5, 6, may be provided by engaging tapering faces. The box may be preheated and cooled after the pin has been screwed into it. The threads of both the pin and box may comprise two parts with different tapers or a cylindrical part and a tapering part. Dimensions of a coupling according to the invention are quoted and results of a test thereon. A coupling with threads 1 in. longer than the standard length was also tested.