US 2207005 A
Description (OCR text may contain errors)
Patented July 9, 1940k UNITED STATES PATENT OFFICE .1` claim.
This invention relates to I improvements ining `eiect of the thread when subjected to a heavy threaded joints, and it is more particularly concerned with such joints as used in oil well drilling. Persons acquainted with this art know that L the loads imposed upon pipe and tool joints in making up a casing and tool string reach tremendous proportions.
It is a common occurrence that the load on the uppermost threads will run into the hundreds of l) thousands of pounds and obviously, there is always the danger of the threads collapsing by stripping completely out of the joint. This danger is more likely to occur'in the tool string than in the casing string, and for that reason the inl-b vention is herein disclosed as related to a pin and box of a tool string. But it is to be understood that the identical principle is applicable to the joints of a casing string.
Efforts have been made heretofore to improve E upon the commonly employed V or square threads by shaping the threads so that a longitudinal section through the joint makes them look somewhat like the teeth of a saw. While the top of each modified thread has been given a downward and er, outward pitch, yet -the bottom of the thread has been made either straight (perpendicular to the axis of the pipe or tool joint) or given a slight downward pitch towards said axis. The two latter arrangements have not been found as eiectual 3f) as desired, for which reason the instant improvement has been devised with the following objects: First, to provide a thread construction for a tool joint, capable of actually drawing the pin and box together upon the ultimate tightening of the4 35 latter.
Second, to insure the sealing off of the circulation of fluid through the thread passages of the tool (or pipe) joint, said sealing off function becoming increasingly more effective as the load on 40 the thread increases.
Third, to provide a tool joint having a thread of which both sides are pitched in the same general direction toward the axis of said tool joint.
43 Other objects and advantages will appear in. the following specification, reference being had to the accompanying drawing, in which:
Figure l is a central vertical section of a tool joint, the thread on the pin and in the box being 59 constructed in accordance with the invention,
Figure 2 is an enlarged section of a portion of the thread illustrating how the top and bottom are pitched in the same general direction as the axis of the tool joint,
55 Figure 3 is a sectional view illustrating the sealj the pin is screwed in to the limit.
Figure 4 is a detail sectional view illustrating the principle of the invention embodied in a sharp thieasd rather than a blunt one, as in Figs. 1, 2v 5 an Fig. 1 the tool joint l comprises the pin 2 andbox Each of these elements is part of a rod section, only the rod section 4 of the pin` being partially shown. It is observed in Fig. 1 that the pin 2 is of tapermg form, as distinguished from the more commonly known type of straight-side pins in tool joints. This taper of the pin is known to afford a greater strength in making the joint than if 15 it were of cylindrical form. The extremity of the pin has a conical depression 5 in which a conical dependency 6 in the box 3 is seated when This interengagmg conical 4formation locks the inner end of 20 the pin against any possibility whatever of vibrating in the lateral direction and this is a large contribution toward keeping the pin and box screwed tight. If lateral vibration could occur, as it does in an instance wherein a conical for- 25 mat1on such as shown is not provided, said vibratlon even though minute will cause the threads to ultimately loosen.
At this point it is desired to state that the pin 2 is either solid in actual practice as shown, o1' 30 provided with a central, longitudinal bore in communication with a similar bore through the box.
In either case the conical configuration 5, 6, between the male and female members has the effect stated, namely, of locking the two together. 55 This is accomplished by the cam action between the confronting and contacting surfaces, which draws the box or female member in toward the pm or male member.
Another important effect of the tapering pin 2 is the provision of a wide thread base l. This aords strength where it is most needed. Particular attention is directed to the thread itself, the particular cross sectional shape shown constituting the underlying invention. The thread on the pin 2 is adapted to bescrewed into the thread passagev 9 in the box 3. The top l0 of the thread 8 is set at a pitch to the axis Il of the tool joint, said pitch being upward as denoted by the pitch line I2 (Fig. 2).
. The bottom of the thread 8 is also set at a pitch Y to the axis l`l, the direction of the pitch also being upward as denoted by the pitch line I4. But the pitch I4 is slight as comparedto the pitch l2. The crest l5 of the thread 8 is made blunt (Fig. 55
2), this particular configuration being best adapted for rough work. But in Fig. 4 the crest I6 is made sharp, the principle of pitching the top Ia and bottom I3a in the same general upward direction toward the axis of the pin being preserved.
By virtue of having the short side or bottom of the thread on the slight incline shown, there is a strong tendency to pull the pin and box together because of the interengaged hookform of the thread in the box or female member and undercut form of the thread on the pin or male member. The bottom I3, which stands onay slight upward inclination, yet considered as a" part of the thread 8, rests and ridesupon the I companion thread I'I of the box, the top I8 of which stands at an outward decline. This riding together of these matching surfaces has the -effect of drawingthe box 3 inwardly toward the pin when the two are screwed together. The action tight interconnection.
Reference is now made to Fig. 3. The direction of the load is indicated by the arrow a. The full and dotted line positions of the thread 8 are greatly exaggerated, As the load increases there is a tendency toward` a slight clockwise turning of the thread in the direction of arrow b. The crest I5 is thus projected outwardly an extremely small distance (arrow c), thus tending to flatten the bottom I3 of the thread. 'Ihe sealing function thus improves with the increase in the load, the bending of the threads resulting in their jamming together more and more tightly, progressively securing against leaks.
But by the time that this flattening has occurred the tool joint will be under an extremely heavy load. The effect of this clockwise turning of the thread is to jam the crest I5 even more tightly into the thread passage 9 than before, thus sealing thethread passage against any possibility of iiuid entering it.
A coupling for use in connecting a pair 0f members adapted to sustain a ponderous load, said coup-ling consisting of male and female members having matching threads, said threads having short sides inclined slightly downwardly from a perpendicular to the axis of the coupling, therev by to delizie a hook-form of the threads on the female member and an undercut form on the is that of a cam, and theresult is an extremely@ threads of-the male member, said thread configurations exercising a cam action under pressure of; the load sustained by the male member to draw saidinembers together and establish a sealing-oir function, thetops of the male threads and the corresponding portions of the female threads being pitched sharply downward in respect to said lperpendicular to the coupling axis to actas abrace.
, RAWLEY D. I-IAAS.