Threaded pipe joint having improved seal ring entrapment

The box end of a threaded joint has an interior profile of an inwardly tapered threaded section, followed by a smooth sealing surface parallel to the longitudinal axis of the threaded joint, followed by an increased diameter seal ring groove, followed by an inwardly tapered smooth sealing surface. The pin end of the joint has an external torque shoulder, followed by an inwardly tapered threaded section, followed by a reduced diameter pipe dope reservoir, followed by an extrusion hump used to extrude a deformable seal ring used in the seal ring groove, followed by an inwardly tapered smooth sealing surface. When the threaded joint is fully made up, the entrapped seal ring has a primary metal-to-metal seal on its one side, formed by the mated smooth, tapered surfaces, and a secondary metal-to-metal seal formed by the extrusion hump and the surface above the seal ring groove.

BACKGROUND OF THE INVENTION 
This invention relates generally to threaded joints, and more particularly 
to threaded connections between sections of casing, tubing or drill pipe 
used in oil and gas wells. 
In the drilling of oil, gas and like wells, it is customary to drill to the 
desired formation or formations, cement casing in place in the well bore 
and provide tubing extending downwardly in the well bore from the surface 
inside the casing, the annular space between the casing and tubing being 
packed off by a packer; although, many wells are produced without a 
packer. Ordinarily, the casing is perforated at the face of the formation 
or is set above the formation traversed by the well bore and a section of 
tail pipe is provided below the packer. The tail pipe may be perforated or 
slotted or open-ended so that, ordinarily, pore fluid from the formation 
flows into the well bore, such as through the perforations in the casing 
or below the casing and into the interior of the well bore into tubing or 
casing up to the surface or is pumped therethrough. In some instances, the 
flow is in the annular space between the tubing and the casing such, as 
for example, in the case of dual or multiple completions where one 
formation is being produced in the tubing and another formation is being 
produced in the annular space between the tubing and the casing. 
In producing oil, gas and like wells, particularly in those wells under 
high pressure, joints in the tubing sometimes fail and permit oil, gas and 
the like to leak through the tubing into the annular space which provides 
a high pressure on the casing at the surface, which is the weakest point 
of the various strings of pipe positioned in the well bore. These leaking 
joints are ordinarily caused due to the failure to obtain a satisfactory 
seal, such as caused by normal wear and tear, improper machining and, in 
those joints utilizing packing, by the corrosive action of the fluid in 
the well bore. 
It is well known in the tubing and casing arts to use a polymerized 
tetrafluoroethylene packing or sealing ring to assist in the sealing off 
of the high pressures encountered in oil and gas wells. 
For example, U.S. Pat. No. 3,054,628, assigned to the assignee of the 
present application, shows such a ring slipped over the lower end of the 
pin member, and which is deformed against the tapered surface of the box 
member. 
U.S. Pat. No. 3,047,316, assigned to the assignee of the present 
application, shows a seal ring engaged by the threads of the pin member, 
causing a portion of the seal ring to be forced into the entrance between 
the first two full height threads to seal the passage. 
U.S. Pat. No. 2,980,451, assigned to the assignee of the present 
application, shows an annular groove intermediate the thread ends on 
either the pin member or the box member, with the seal member seated in 
the groove. As the threads are made up, the seal member is extruded into 
the threaded section adjacent the annular groove. 
Although each of the foregoing prior art designs has enjoyed considerable 
commercial success, there has arisen the need for more uniform sealing 
when extruding the seal ring. The designs using the seal entrapped within 
the threads, in particular, sometimes experience non-uniform extrusion, 
and, thus, non-uniform sealing. 
These same designs having the seal ring extruding into the threads also 
have had only a single metal-to-metal seal on one end of the entrapped 
seal, with the thread form on the other end of the entrapped seal ring. 
It is therefore the primary object of the present invention to provide a 
new and improved threaded pipe joint having improved uniformity of seal 
ring entrapment. 
It is yet another object of the present invention to provide a new and 
improved threaded pipe joint having the extruded seal ring completely 
entrapped by two metal-to-metal seals. 
It is still another object of the invention to provide a new and improved 
threaded pipe joint which includes engagement means designed to decrease 
the likelihood of seal damage during makeup of the threaded joint. 
SUMMARY OF THE INVENTION 
The primary object of the invention is accomplished, generally, by the 
provision of a box member having an inwardly tapered threaded section on 
its inner periphery and an enlarged diameter, seal ring entrapment area 
below said inwardly tapered threaded section, a deformable seal ring in 
said entrapment area, a pin member having an inwardly tapered threaded 
section on its outer periphery adapted to threadably engage the threaded 
section of said box member, and having an enlarged diameter, extrusion 
hump sized to engage and deform the deformable seal ring, thereby creating 
a uniform, high pressure seal between the box member and the pin member. 
Another object of the invention is accomplished, generally, by the 
provision of the extrusion hump being sized to provide a first 
metal-to-metal seal on one side of the entrapped seal, while the primary 
metal-to-metal seal is located on the other side of the entrapped seal. 
Yet another object of the invention is accomplished, generally, by the 
extrusion hump being sized to contact the inner periphery of the box 
member prior to the engagement of the primary metal-to-metal seal, thereby 
aligning the primary metal-to-metal sealing surfaces and decreasing the 
aspect of seal damage otherwise resulting from misalignment. 
These and other objects, features and advantages will become apparent from 
the following detailed description taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings in more detail, especially to FIG. 1, there 
is illustrated an elevational view, partly in cross-section, of a threaded 
joint 10 according to the present invention, comprised of a pin member 11 
and a box member 12. The pin member 11 has an extrusion hump 13 which has 
caused the deformable seal ring 14 to be deformed into a sealing 
arrangement between the pin member 11 and the box member 12, all of which 
is described in greater detail hereinafter. 
Referring now to FIG. 2, the pin member 11 of FIG. 1 is illustrated and 
described in greater detail. The pin member 11 includes an inwardly 
tapered thread 20 on its outer periphery having a reduced diameter section 
21 below the end of the thread 20 which is used as a dope reservoir. 
Immediately adjacent the dope reservoir 21 is an extrusion hump 22 having 
an increased diameter as compared to the diameter of the dope reservoir 
21. Immediately below the extrusion hump 22 is a pin end 23 whose outer 
surface serves as the primary metal-to-metal seal when engaged with the 
surface 33 of box member 12. 
FIG. 2 also illustrates a deformable seal ring 25 which is formed, in a 
preferred embodiment, of polymerized tetrafluoroethylene. The manufacturer 
of this material is E.I. DuPont Nemours and Co. under the trade name 
"Teflon". 
Referring further to FIG. 2, the box member 12 is illustrated in greater 
detail. The box member 12 has an inwardly tapered thread 30 on its inner 
periphery designed to match the thread 20 on the outer periphery of the 
pin member 11. Immediately below the lower end of the threaded section 30 
is a smooth surface 31 sized and positioned to form a secondary 
metal-to-metal seal with the outer surface 26 of the extrusion hump 22. 
Below the surface 31 of the inner periphery of the box member 12 is an 
enlarged diameter section 32 for retaining the deformable seal member 25 
as is illustrated in greater detail in FIG. 3 hereinafter. Still further 
below the sealing ring retention portion 32 is a smooth surface 33 which 
forms the primary metal-to-metal seal when engaged with the surface of the 
lower pin member 23. 
Referring now to FIG. 3, the pin member 11 is illustrated as being 
partially madeup with the box member 12 such that the threaded section 20 
of the pin member 11 has engaged some of the threads 30 of the box member 
12. As illustrated, the extrusion hump 22 at this stage in the makeup 
process has engaged the sealing surface 31, but has yet to engage the 
deformable sealing ring 25. At this point in the process, the surface of 
pin end 23 and surface 33 have not yet engaged to form the primary 
metal-to-metal seal. The manufacturing process in accordance with the 
preferred embodiment of the present invention contemplates the extrusion 
hump 22 being machined on an axis parallel to the longitudinal axis of the 
threaded joint while the primary metal-to-metal seal is machined on a 
taper to the longitudinal axis of the threaded joint. By machining the 
extrusion hump parallel to the threaded joint axis, this necessarily 
allows the extrusion hump 22 to make contact with the surface 31 before 
the primary metal-to-metal surfaces are engaged. This then allows the 
primary metal-to-metal surfaces to be guided together without damage which 
can occur due to misalignment of the pin member with the box member. By 
having the extrusion hump 22 contact the surface 31 prior to the primary 
metal-to-metal surfaces coming together, there is a decrease of the the 
probability of high angle cocking of the pin member 11. As another way of 
expressing this relationship, the initial contact of the extrusion hump 22 
with the surface 31 does not prevent cocking of the pin member, but 
lessens the angle of cocking to thus reduce the probabililty of damage to 
the primary metal-to-metal seal. If it were not for this feature, the pin 
member 11 can easily become cocked such that the point 28 of the pin 
member can dig into the surface 33 and cause damage to the seal. 
Referring now to FIG. 4, following additional makeup of the joint, the 
extrusion hump 22 is illustrated as having now contacted the seal ring 25 
which causes a partial deformation of the seal ring 25. 
FIG. 5 illustrates the complete makeup of the threaded joint such that the 
seal ring 25 is completely deformed in accordance with the present 
invention and the primary metal-to-metal sealing surfaces 23, 33 are 
engaged. It should also be appreciated that the surface 26 of extrusion 
hump 22 forms a secondary metal-to-metal seal with the surface 31 of the 
box member. Thus, there is a primary metal-to-metal seal on one side of 
the deformed seal ring 25 and a secondary metal-to-metal seal on the upper 
side of the deformed seal ring 25. 
In order to improve the control of the machining of the seal ring 
entrapment area 32, the extrusion hump 22 and the seal ring retention 
groove 32, with its two adjacent sealing surfaces 31, 33, are machined 
with the same tool. Although the dimensions will vary with different size 
casing, tubing, drill pipe, or the like, in a 5" casing made in accordance 
with the present invention, the dope reservoir 21 is cut to a diameter of 
4.264". The extrusion hump 22 is cut to a diameter of 4.362" and has a 
length between points 53 and 54, as illustrated in FIG. 3, of 0.300". The 
seal ring groove 32 has a diameter of 4.402" and has a length between 
points 50 and 51, also illustrated in FIG. 3, of 0.250". The surface 31, 
also machined parallel to the longitudinal axis of the threaded joint, has 
a diameter of 4.356". Thus, the extrusion hump 22, with its diameter of 
4.362", forms an interference fit with the surface 31, helping to prevent 
cocking of the pin member 11. The surface 33, having a length of 0.400", 
has a taper of 11/8" per foot and has a diameter at point 52 of 4.244". 
The surface of pin end 23 has a matching taper. 
The groove 21 above the extrusion hump 22, having a reduced diameter, acts 
as a resevoir to allow entrapped thread lubricants to flow therein. In 
typical prior art threaded connections, the thread lubricants would be 
trapped between the external torque shoulder and the primary 
metal-to-metal seal with no place to flow, resulting in an increase of the 
stresses in the connection. 
Referring again to FIG. 1, it should be appreciated that in the preferred 
embodiment of the present invention, the torque shoulder is comprised of 
the upper surface 15 of the box member 12 being torqued against the 
shoulder 16 of the pin member. As an alternative embodiment, if desired, 
the lower end 17 of pin member 11 can be torqued against the shoulder 18 
within the interior of the box member 12. 
In view of the foregoing, it will be seen that by this invention a threaded 
joint has been produced which has greatly improved sealing characteristics 
for operations in high pressure oil and gas wells, or the like. The 
features of this invention can be used with casing, tubing, drill pipe, 
and the like, although the preferred embodiment contemplates manufacture 
and utilization of well casing.