Threaded tubular connection with outer threaded ring

A pipe union device and method in which terminal ends of well casing, well production tubing or drill pipe are connected in fluid type fashion by stressing compressively a spacer disposed between terminal ends of adjacent lengths of tubing.

BACKGROUND OF THE INVENTION 
The present invention relates to oil well production and relates in 
particular to a novel union structure between lengths of well production 
casing, tubing or drill pipe. 
Prior art unions or connections between lengths of tubing frequently 
involve internal offsets or steps which result in a discontinuity in the 
interior wall of the tubing. Such an obstruction creates a choke or 
throttling effect restricting the flow of fluid materials pumped through 
the tubing. 
This restriction results in turbulence which generates corrosion and 
erosion problems leading to weakening the union and thus creating a weak 
link in production tubing or drill pipe, as the case may be. 
The problem is magnified when the fluid flowing through the tubing contains 
sand or other finely divided abrasive material. 
In some prior art arrangements, the erosion problem is solved by 
introducing an inner tubular liner of high quality, erosion resistant 
metal wherein the liner segments abut one another to provide a straight 
through unobstructed flow path. 
U.S. Pat. No. 4,568,113, issued Feb. 4, 1986 to Axford et al., is 
representative of these prior art structures. 
SUMMARY OF THE INVENTION 
In contrast to prior art structures the present invention relates to an 
improved union or connection for lengths of well casing, well production 
tubing or drill pipe. 
In particular, the present invention provides a high strength joint which 
is of simple design, has long life and is easy to assemble. 
A further feature of the invention is the provision of pipe line union 
whose internal wall structure is "straight through", free of annular 
steps, recesses or other obstructions which would create turbulence in 
fluids flowing past the union resulting in erosion of the wall. 
A further feature of the invention is the provision of a union in a pipe 
string wherein the pipe is free of internal liners for protecting the main 
tubular structure from erosion. 
A still further feature of the invention is the provision of an inexpensive 
union for a pipe string useful in oil well production tubing and in drill 
pipe which provides a conduit for drilling mud. 
A union embracing certain features of the present invention may comprise an 
assembly of elements including opposed, spaced terminal ends of two 
lengths of tubing, a spacer disposed between said ends to create a 
continuous, straight through flow path of uniform internal diameter from 
one length of tubing to the other via said spacer, a portion of an 
external surface of said spacer and said terminal ends of said tubing 
being formed with threads and an external collar surrounding said ends and 
said spacer, said collar being formed with internal threads which 
cooperate with the threads of said spacer and said tubing to bind all 
elements of the union into a rigid fluid tight assembly. 
The invention also provides a method of effecting a high strength, tight 
seal between opposed ends of tubular members. 
Other features and advantages of the invention will become more apparent 
from an examination of the succeeding specifications when read in 
conjunction with the appended drawings in which;

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 1A, a union assembly indicated generally by the 
reference numeral 11 includes opposed tubes 12 and 13 having terminal ends 
14 and 16 spaced apart by a spacer 17. 
The internal diameters 18 and 19 of the tubes 12 and 13 and the internal 
diameter 21 of the spacer 17 are identical so that the tubes and the 
spacer form a coaxial "straight through" flow path free of obstructions, 
recesses or stepped surfaces. 
The terminal ends 14 and 16 of the tubes 12 and 13 are threaded as 
indicated at 10 and 15. In the FIG. 1 embodiment, the threads 10 and 15 
are formed on a tapered surface and are of uniform root. In some 
embodiments the threads maybe pipe threads. 
The spacer 17, having a uniform wall thickness, is formed with a continuous 
external thread 20 which is of the same "hand" as the threads 10 and 15 on 
the terminal ends 14 and 16 of the tubes 11 and 12. 
A collar 22 formed with an internal threaded contour matching and 
cooperating with the threads 10, 15 and 20. 
To accommodate the tapered surface on which the threads 10 and 15 are 
formed while insuring threaded contact with at least a portion of the 
spacer threads 20 the collar 22 is formed with converging tapers mating 
with the tapered surfaces on tube ends 14 and 16. 
As is most apparent in FIG. 1 the converging tapers on the collar 22 
creates a bulge defining a convex or thickened wall as indicated at 23 
thus insuring threaded engagement between the collar and a central portion 
of the spacer with end portions of the spacer free of threaded engagement 
as indicated at 24. 
The union arrangement of FIG. 1, as well as the alternative embodiments, to 
be described in detail hereinafter, is assembled by first threading the 
spacer 17 to a central position within the collar 22. When the spacer is 
threaded from end to end, as is apparent in FIG. 1A, threads at the 
opposed ends of the collar do not engage the adjacent threads on the 
collar. 
Thereafter the tubes 12 and 13 are threaded into opposed ends of the collar 
and "turned up" tightly to place the spacer 17 under a compressive stress 
to establish a fluid tight seal at the junctions 26 and 27 between the 
tubes and the spacer. That is, the collar 22 acts as a jackscrew to 
develop pressure. 
In the alternative, and in less expensive fashion, the spacer 17 is formed 
with threads solely in the central portion thereof as indicated by the 
reference numeral 28 in FIGS. 2 and 2A. 
Frequently it is desirable to bevel the ends of the spacer as shown in 
dashed lines in FIGS. 1A and 2A so that there is circular line contact 
with the ends of the tubes. 
Thus, when the tube ends are advanced into the collar and into contact with 
the spacer to stress the spacer compressively an "upsetting" or swaging 
action occurs greatly enhancing the integrity of the fluid tight seal as 
the beveled ends of the spacer are "cold worked". 
While a bevel angle of 20.degree. is optimum, angles ranging from 15 to 25 
degrees are satisfactory depending upon the properties of the materials 
used. 
In general, the union assembly is manufactured of metallic materials. 
However, it has been found that under certain conditions and depending upon 
the application to which the union assembly is employed the spacer can be 
manufactured from non-metallic material such as fluorocarbon polymers 
(TEFLON) and fluoroelastomer copolymers (VITON). 
FIGS. 3 and 3A show an alternative configuration of the spacer in which the 
spacer defines two elements 28 and 29 each of which is appropriately 
tapered to match the tapers of tube ends 14 and 16 and to provide full 
threaded contact with the matching threads of the collar 22. 
The dimensions of the elements of the union device are limited. The length 
S of the spacer is equal to C-2L where C is the length of the collar 22 
and L is the length of the threaded portion of a tube end. 
It is to be understood that the invention is not limited to the 
illustrations described and shown herein, which are deemed to be merely 
illustrative of the best modes of carrying out the invention, and which 
are susceptible of modification of form, size, arrangement of parts and 
details of operation. The invention rather is intended to encompass all 
such modifications which are within its spirit and scope a defined by the 
claims.