Expandable lubricating packing assembly for wellheads

A packing assembly (10) for sealing the annulus between concentric tubular members (12, 14). The assembly (10) includes upper and lower sealing ring assemblies (31, 32) on each side of a lantern ring (33), and upper and lower retainer rings (36, 35) located atop and below the sealing ring assemblies and bolted together to maintain the rings in stacked concentric relation. Each sealing ring assembly (31, 32) includes a central lubricating packing ring (34) having inner and outer lubricating surfaces of graphite material; an inner pair of upper and lower metal seal rings (69, 70) seated in annular grooves in the central lubricating packing ring (34); and an outer pair of upper and lower metal seal rings (83, 84) located in annular grooves in the outer periphery of the lubricating packing ring (34). The metal seal rings and the packing ring are each provided with cooperative camming surfaces (72 and 41; 76 and 46; 85 and 61; 88 and 66) which interact when an axial compressive force is applied to the assembly (10) to thereby effect a controlled radial expansion of the sealing ring assemblies (31, 32) and establishing metal-to-metal seals (81, 82) and a lubricating packing seal with the annulus walls (11, 13). The axial compressive force is mechanically applied by the camming action of holddown screws (100) with a camming surface (102) on the upper retainer ring (36) and the outer tubular member is provided with an aperture (110) to permit injection of lubricant into the lantern ring for energizing the seals in emergency situations.

BACKGROUND OF THE INVENTION 
The invention relates to a packing assembly for sealing the annulus between 
the inside wall of a hollow cylindrical member and the outside wall of a 
second cylindrical member disposed therein and more particularly, it 
relates to a packing assembly for sealing the annulus between the inside 
wall of a wellhead and the outside wall of a casing or tubing hanger which 
is supported therein. 
Heretofore, a great variety of packing assemblies have been used for 
sealing in wellheads and these generally employ elastomeric materials in 
the sealing elements. Such packing assemblies are susceptible to 
destruction by fire and at elevated temperatures short of fire conditions 
tend to deteriorate to such degree that their sealing capabilities are 
seriously impaired. Metal packing rings, on the other hand, have the 
advantage of holding up well under high pressure and temperatures but do 
not seal effectively where the coacting sealing surface has been galled or 
otherwise damaged. 
Accordingly, it is a general object of the invention to provide an improved 
packing assembly for sealing an annulus as in a wellhead assembly, which 
is effective for sealing under high pressure and high temperature 
conditions and wherein the packing assembly can be mechanically activated. 
Another object is to provide a packing assembly for sealing an annulus 
which includes the combination of metal-to-metal seals and lubricating 
packing seals and which can be reinforced in emergency conditions by the 
injection of a sealing plastic or fluid. 
A further object is to provide a packing assembly which provides the 
combination of metal-to-metal seals and lubricating packing seals and 
which can be mechanically activated by the application of a carefully 
controlled axial compression force. 
A still further object is to provide a packing assembly with both metal 
seal rings and lubricating packing rings which can be mechanically 
activated by the application of an axial compressive force to achieve a 
controlled radial expansion of the metal and lubricating packing seal 
rings. 
SUMMARY OF THE INVENTION 
The invention is directed to a packing assembly for sealing an annulus 
between cylindrical surfaces of cylindrical members in concentric 
relationship as between a casing hanger and casing head. The assembly 
includes upper and lower sealing ring assemblies disposed on each side of 
a lantern ring in stacked concentric relation. A pair of retainer rings, 
one atop and one below the respective sealing ring assemblies, are bolted 
together to maintain the ring assemblies in their stacked concentric 
relation. Each sealing ring assembly includes a lubricating packing ring 
and inner and outer pairs of metal seal rings which are nested in inner 
and outer pairs of annular grooves in the packing ring. The metal seal 
rings are provided with camming surfaces adapted to interact with camming 
surfaces on the packing ring to effect a radial expansion of the rings 
when an axial compressive force is applied to the packing assembly thereby 
effecting metal-to-metal seals and a lubricating packing seal with the 
concentric surfaces defining the annulus. The axial compression force for 
loading the packing assembly is achieved by mechanical means, such as 
holddown screws which extend through the outer cylindrical member and are 
used to cam the upper retainer ring downwardly against a shoulder of one 
of the cylindrical members and thereby compress the packing assembly. In 
addition, an aperture is provided through the wall of the outer 
cylindrical member adjacent the lantern ring whereby in the event of seal 
failure injectible sealing fluid may be injected into the annulus through 
the lantern ring to reinforce the seals. In a modification of the 
invention, instead of a single lubricating packing ring a pair of 
lubricating packing rings are disposed on the respective inner and outer 
surfaces of a metal camming ring which is provided with camming surfaces 
for interacting with the camming surfaces of the metal seal rings when an 
axial load is applied to activate the packing assembly.

Referring more particularly to the drawings, a packing assembly 10 
representing a preferred embodiment of the invention is shown installed in 
a wellhead for sealing the annulus between the outside wall 11 of a casing 
hanger 12 and the inside wall 13 of a casing head 14. The casing head 14 
is provided with an internal upward facing annular shoulder 15 formed by a 
reduced diameter portion of the casing head bore. The shoulder 15 supports 
the casing hanger 12, which is provided with an annular flange 16, the 
underside of which forms a downward facing shoulder 17 for seating against 
a metallic seal ring 18 positioned on the shoulder 15. The metallic seal 
ring 18 may be formed of stainless steel or a material having similar 
properties and may be slightly deformed by the weight of the casing 
suspended from the hanger 12 to thereby form a tight metal-to-metal seal 
between the shoulders 15 and 17. 
Atop the casing head 14 is installed another wellhead component such as a 
tubing head 20 which is secured to the casing head by bolts or studs 21 
extending upwards through an annular flange 22 provided at the top of the 
casing head. An annular seal 23 located in accommodating annular grooves 
formed in the top of the casing head and the bottom of the tubing head 
seals the junction therebetween. 
The packing assembly 10 is seated on a horizontal shoulder 26 provided by 
the upper annular face of the casing hanger flange 16 and, when an axial 
load is applied thereto, seals between the cylindrical walls 13 and 11 of 
the casing head and casing hanger respectively. The packing assembly 10 
comprises upper and lower sealing ring assemblies 31 and 32 separated by a 
lantern ring 33. It also includes a lower retainer ring 35 and an upper 
retainer or adapter ring 36. 
Details of a preferred embodiment of the packing assembly 10 are shown in 
FIGS. 2 and 3 which illustrate sealing elements of the lower sealing ring 
assembly 32 when in the unloaded and loaded states, respectively. The 
sealing ring assembly 32 comprises a central lubricating packing ring 34 
which is fabricated from a high temperature resistant and lubricating 
material such as graphite. One such product which satisfies the 
requirements for the lubricating packing ring 34 is "Grafoil" which has 
the unique combination of high temperature stability, resiliency and 
lubricity. For its application herein as a packing material for sealing 
under high pressure it is necessary to use a very high density "Grafoil" 
which can be formed by compaction. 
The lubricating packing ring 34 is provided with upper and lower annular 
grooves 37 and 38, respectively, in its inner peripheral surface. The 
groove 37 is defined by a central bottom surface 41 and vertical and 
horizontal sides 42, 43, respectively. The groove bottom 41 is of 
frusto-conical configuration and serves as a camming surface for purposes 
hereinafter described. The lower annular groove 38 is formed with a 
similar configuration, comprising a central frusto-conical camming surface 
46 and vertical and horizontal sides 47, 48, respectively. 
The lubricating packing ring 34 is also provided on its outer peripheral 
surface with upper and lower annular grooves 51, 52 of cross-sectional 
configuration similar to the grooves 38 and 37, respectively. However, in 
the outer grooves 51 and 52, the central frusto-conical camming surfaces 
face outwardly of the packing assembly 10. The groove 51 comprises a 
central camming surface 61 and vertical and horizontal sides 62, 63. The 
groove 52 comprises a central camming surface 66 and vertical and 
horizontal sides 67, 68. 
Seated within the inner annular grooves 37 and 38 of the lubricating 
packing ring 34 are a pair of metal seal rings 69 and 70, respectively. 
The metal ring 69 is provided with an outer frusto-conical camming surface 
72 of corresponding configuration with the camming surface 41 of the 
lubricating ring 34 against which it is seated. The metal ring is also 
formed with a lower annular surface 73 which is of like configuration with 
the horizontal groove side 43 against which it is seated. It is also 
provided with a vertical inner peripheral surface 74 which engages the 
vertical side 42 of the groove 37. As shown in FIG. 2, the vertical side 
74 of the metal ring 69 is of greater height than the vertical side 42 of 
the "Grafoil" ring 36 so that the top surface 75 of the metal ring is 
slightly higher than the top surface 35 of the "Grafoil" ring 34. 
The lower inner metal seal ring 70 is of corresponding configuration to the 
groove 38 being provided with an outer frusto-conical camming surface 76, 
an annular top surface 77, and an outer vertical surface 78 which seat 
respectively against the camming surface 46 and walls 48 and 47 of the 
"Grafoil" ring 34. 
Each of the metal seal rings 69 and 70 is formed with an annular groove 80 
in its interior peripheral surface which forms upper and lower annular 
lands 81, 82. The lands 81, 82 provide sealing surfaces for sealing 
against the outer cylindrical surface of the casing hanger 12. 
The sealing ring assembly 32 also includes a pair of outer metal seal rings 
83, 84 which are seated in the outer annular grooves 51 and 52, 
respectively, of the "Grafoil" ring 34. The upper metal seal ring 83 is 
provided with an inner frusto-conical camming surface 85, a vertical 
annular surface 86, and a bottom surface 87 which engage respectively the 
camming surface 61, and walls 62 and 63 of the upper outer groove 51 of 
the "Grafoil" ring 34. 
The lower metal seal ring 84 seats in the lower outer groove 52 of the 
"Grafoil" ring 34 and is similarly configured. The metal seal ring 84 is 
provided with an inner frusto-conical camming surface 88, a top surface 
89, and an inner annular surface 90 which engage the respective surfaces 
66, 68 and 67 of the groove 52. As seen in FIG. 2, the height of the 
vertical walls 90 and 78 of the lower metal seal rings 70 and 84 is 
greater than the vertical side walls 67 and 47 of the grooves 52 and 38, 
respectively, so that the bottom surfaces of the metal rings 70 and 84 
extend below the bottom of the "Grafoil" ring 34. The outer metal seal 
rings 83, 84 are also grooved in their outer peripheral surfaces to form 
upper and lower lands 91, 92, respectively, similar to the lands 81 and 82 
which are formed in the inner peripheral surfaces of the inner metal seal 
rings 69 and 70. The lands 91, 92 provide sealing surfaces for sealing 
against the inner cylindrical wall of the casing head 14. 
As shown in FIG. 1, the sealing ring assembly 32 rests on the lower metal 
retainer ring 35 which is seated on the annular shoulder 26 of the casing 
hanger. The upper sealing ring assembly 31 is identical to the lower 
sealing ring assembly 32 and rests on the top surface of the lantern ring 
33 which, in turn, rests on the top surfaces of the sealing ring assembly 
32. The lantern ring 33 is of conventional type having annular recesses in 
its exterior and interior peripheral surfaces and provided with a 
plurality of inlet openings 94 extending transversely therethrough. In 
addition, a plurality of longitudinal passageways 95 extend from the top 
end of the lantern ring to the bottom thereof and communicate with the 
transverse openings 94. 
The packing assembly 10 is held together by a plurality of bolts 95, only 
two of which are shown in FIG. 1. Each bolt 95 extends through vertically 
aligned openings 96 in the lubricating packing rings of the sealing ring 
assembly 31, 32 and a vertical passageway 97 of the lantern ring 33. The 
bottom of the retainer ring 35 is provided with an annular groove 98 and 
vertical openings 99 extending from the groove and aligned with the 
vertical openings through the lubricating packing rings 34. The groove 
accommodates the heads of the bolts 95 which seat against the shoulder 
provided by the central wall of the groove 98 when the packing assembly 10 
is bolted together. The ends of the bolts 95 are threaded into threaded 
bores in the bottom side of the upper retainer ring 36. 
In order to activate the packing assembly 10 and seal the annulus between 
the casing hanger 12 and the casing head 14, an axial load is mechanically 
applied to the packing assembly 10. The load is applied by means of a 
plurality of holddown screws 100 which are threaded through lateral 
openings provided in the flange 22 at the top of the casing head 14 and 
are angularly spaced about the circumference thereof. The holddown screws 
100 are formed with generally conical tips 101 and are of sufficient 
length to extend into the central bore of the casing head where they 
engage the bottom upward facing wall 102 of an annular groove which is 
formed circumferentially about the exterior of the upper retainer ring and 
adapter 36. As the holddown screws 100 enter the bore of the casing head, 
their conical tips 101 engage the tapered groove wall 102 and cam the 
retainer ring 36 downwardly. By suitably dimensioning the size of the 
bolts 100 and the groove in the retainer ring 36, as much as one million 
pounds force may be applied in the axial direction of the packing assembly 
10. 
When such an axial force is applied, the packing assembly 10 is compressed 
and the sealing ring assemblies 31 and 32 radially expand to seal against 
the cylindrical walls of the casing hanger and the casing head. The 
configuration of the sealing ring assembly 32 after an axial load is 
applied is illustrated in FIG. 3. It will be seen from FIG. 3, that the 
lubricating packing ring 34 is axially compressed and expanded radially 
outward to form lubricating seals with the casing hanger and casing head. 
At the same time, the inner metal seal rings 69 and 70 are cammed radially 
inward by the interaction of their respective camming surfaces, such as 
exemplified by the camming action on the upper inner metal seal ring 69 
applied by the camming surfaces 41 and 72. The radial forces applied to 
the metal seal rings 69 and 70 are concentrated in their sealing surfaces 
81, 82, respectively and thus effect very tight metal-to-metal seals. 
In similar fashion, the axial compression of the sealing ring assembly 32 
urges the outer metal seal rings 83, 84 in the radially outward direction 
to establish tight metal-to-metal seals with the inner wall of the casing 
head. The lubricating packing ring 34 is also axially compressed and 
expanded radially outward to establish a lubricating packing seal with the 
casing head, and radially inward to seal against the hanger 12. 
It is to be understood that the upper sealing ring assembly 31 is identical 
to the lower sealing ring assembly 32 and the axial compression of the 
packing assembly 10 activates the upper sealing ring assembly 31 in the 
same manner as the lower sealing ring assembly 32. 
For emergency purposes, in the event of a seal leak, an injectible sealing 
fluid can be injected into the packing assembly through a port 110 
provided in the wall of the casing head adjacent the lantern ring 33. A 
removable plug 111 is normally installed in the threaded port 110 but can 
be replaced with a suitable fitting for accommodating a means for 
injecting a pressurized sealant fluid or plastic material into the annulus 
about the lantern ring and the passageway thereof to thereby enhance the 
seals between the sealing ring assemblies and the walls of the casing 
hanger and casing head. A suitable injectible material for this purpose is 
W-K-M No. 109 TFE/Asbestos, a product of the W-K-M Division of ACF 
Industries, Incorporated. This is a flexible, plastic material which 
consists of a chemical and solvent resistant acid, Teflon, binders, wood 
chips and a friction-reducing aggregate. 
A modified form of the packing assembly of this invention is illustrated in 
FIGS. 4 and 5. In this modified form, the packing assembly is 
substantially identical to the packing assembly 10 of FIGS. 2 and 3 except 
that the central lubricating ring in each sealing ring assembly is 
fabricated in three parts with a central metal camming ring 34a, an 
internal lubricating packing ring 34b and an external lubricating packing 
ring 34c. When assembled the three parts represent a ring which has the 
same configuration as the lubricating packing ring 34 in the packing 
assembly of FIG. 2. An upper sealing ring assembly 31a is illustrated in 
FIGS. 4 and 5 with the parts thereof corresponding to the parts of the 
sealing ring assemblies of FIG. 2 having similar numbers. 
When the packing assembly is placed under axial compression, as shown in 
FIG. 5, the inner metal seal rings 69a, 70a of the sealing ring assemblies 
are cammed radially inward and the outer metal seal rings 83a and 84a are 
cammed radially outward in the same manner as demonstrated for the sealing 
ring assemblies in the packing assembly 10 of FIG. 2. In addition, the two 
lubricating packing rings 34b, 34c are compressed and expanded radially by 
their interacting camming surfaces in the same manner as the lubricating 
ring 34 of FIG. 3 to thereby establish lubricating packing seals with the 
casing hanger and casing head, respectively. 
In this second embodiment, the degree of compaction of the packing assembly 
is greater controlled. For instance, the metal seal rings move downwardly 
and outwardly but only along the direction of slope of their camming 
surfaces and the coacting camming surfaces of the camming ring 34a. In the 
packing assembly 10 of FIGS. 2 and 3, there is some increased compaction 
and densification of the graphite material in the lubricating packing ring 
34 which displaces the camming surfaces of the ring 34 in the downward 
direction and the metal seal rings are subjected to a complex movement 
which does not occur in this second embodiment. Accordingly, the vertical 
shrinkage or vertical dimension of the sealing ring assemblies in the 
modification illustrated in FIGS. 4 and 5 can be precisely determined, and 
this can be advantageous when there are restrictions in the degree of 
camming action to be applied by the holddown screws 100 on the upper 
retainer ring 36. 
A third embodiment of the invention is shown in FIG. 6. In this embodiment, 
the central lubricating packing ring in both the upper and lower sealing 
ring assemblies is fabricated in two parts 34d and 34e which are separated 
by a downwardly extending cylindrical extension 36a of the upper retainer 
ring 36. In addition, two lantern rings 33a and 33b are separated by the 
cylindrical extension 36a which is also provided with a transverse 
aperture 112 therethrough to establish fluid communication between the two 
lantern rings. In this third embodiment of the packing assembly of this 
invention, the assembly is clamped together by bolts (not shown) which 
extend from the bottom retainer ring 35 to threaded bores in the bottom of 
the cylindrical extension 36a. The metal seal rings 69b, 70b, 83b and 84b 
are identical to the metal seal rings of the packing assemblies shown in 
FIGS. 2 and 4. 
The principle of operation of this embodiment is identical to that for the 
packing assemblies illustrated in FIGS. 2 and 4. However, in this third 
modification, the axial compression forces applied to the sealing ring 
assemblies act on smaller areas as represented by the smaller top surface 
35c of the sealing ring assembly 31c. Accordingly, the axial compressive 
force applied by the upper retainer ring 36 is, in effect, multiplied and 
would be comparably greater than that applied to the sealing ring 
assemblies in the embodiments of the invention illustrated in FIGS. 3 and 
5. 
It will therefore be seen that a new packing assembly for a wellhead is 
disclosed herein which is fire-resistant and is suitable for operation in 
high temperature and high pressure conditions since the only materials 
used in its fabrication are metal and graphite. It is also activated and 
energized by the mechanical application of an axial load which can be 
carefully controlled and whereby its sealing capabilities are independent 
of fluid pressures such as varying well pressures. In addition to 
metal-to-metal seals and lubricating seals, the assembly includes 
provision of a lantern ring for emergency sealing by the injection of an 
injectible pressurized sealant fluid. While the packing assembly has been 
particularly illustrated in the application of sealing between a casing 
head and casing hanger, it could easily be applied to sealing between 
other wellhead components such as a tubing hanger and tubing head or in 
many other applications. 
The foregoing description of the invention has been presented for purposes 
of illustration and explanation and is not intended to be exhaustive or to 
limit the invention to the precise form disclosed. It was chosen and 
described in order to best explain the principles of the invention and 
their practical application to enable others skilled in the art to best 
utilize the invention in various embodiments and with various 
modifications as are suited to the particular use contemplated. For 
example, the packing assembly can be adapted for use as a valve stem 
packing wherein the axial load can be applied by any of a variety of well 
known means, such as an outside packing gland. 
It is intended that the scope of the invention be defined by the claims 
appended hereto.