Metal seal for a tubular connection

A metal seal for sealing the male end of a tube into the female end of another tube, particularly in a subsea well installation. An annular metal lip is located on the exterior of the male end of the tube. The lip has a free end with a radially protruding metal band. The band has an outer diameter greater than the inner diameter of the female tube bore, providing an interference fit. An annular recess is located inward from the lip, allowing the lip to deflect and exposing the inner portions of the lip to pressure in the bore to act outwardly on the lip.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to subsea well assemblies, and in 
particular to a metal seal for a tubular connection, such as a stinger in 
a subsea wellhead. 
2. Description of the Prior Art 
In subsea well installations, there are instances where tubes interconnect 
telescopingly but stationarily and provide sealing against high pressure 
for a long duration. One instance would be a stinger, which is a tube that 
has a lower end that inserts into a female end or bore of a lower tubular 
member. The upper end is secured to an upper tubular member. The upper 
member may be a Christmas tree assembly, and the lower tubular member 
might be a tubing hanger which is connected to tubing extending into the 
well. Normally, elastomeric seals are located on the lower end of the 
stinger for sealing against the bore of the lower tubular member. 
The seals must withstand high pressure, and in some cases may be located in 
place for several years. There is some danger of deterioration and leakage 
with time. Also, some chemicals may damage elastomeric seals. Metal seals 
are used at times in various places of the subsea wellhead in place of 
elastomeric seals, or used with elastomeric seals as a backup. Normally 
these metal seals require two sealing surfaces. There are also other 
applications currently using elastomeric seals that preferably could be 
replaced with metal seals of an improved design. 
SUMMARY OF THE INVENTION 
In this invention, the tube, which could be a stinger, has an annular metal 
lip located on the exterior near one end. The lip has a free end with a 
radially protruding metal band. The band has an outer diameter that is 
slightly greater than the inner diameter of the bore, providing an 
interference fit. An annular recess is located radially inward from the 
lip. The recess allows the lip to deflect slightly when the tube is 
inserted into the female bore. Also, the recess exposes the inner surface 
of the lip to the high pressure in the bore, which acts outwardly on the 
lip to enhance sealing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the components are conventional, except for the seal 
on the stinger and will not be described in detail. Briefly, the subsea 
wellhead assembly includes a wellhead 11 located on the sea floor. The 
wellhead connector 13 is mounted over the wellhead 11. The connector 13 is 
secured by dogs 15 to the wellhead 11 in a conventional manner. The 
Christmas tree assembly 17 is mounted to the top of the connector 13 and 
extends upwardly. A metal seal 19 of conventional nature is located 
between the upper end of the wellhead 11 and the lower end of the 
Christmas tree assembly 17. 
A tubing hanger 21 is mounted inside the wellhead 11. A tubular member 23, 
which forms a part of the tubing hanger 21, is located inside. Tubular 
member 23 has a bore 25. A stinger 27 is rigidly mounted to the lower end 
of the Christmas tree assembly 17 by a retainer 29. The upper end of the 
stinger 27 extends into a bore 31 of the Christmas tree assembly 17. The 
lower end of the stinger 27 is inserted into the bore 25 of the tubular 
member 23 when the Christmas tree assembly 17 is lowered over the wellhead 
11. 
A seal 33 is located a short distance above the lower end 35 of the stinger 
27. A metal seal 34 of the same structure, but slightly larger diameter is 
located above metal seal 33, and also seals in bore 25. In addition, there 
are two metal seals 36 and 38 of similar structure that are received 
within bore 31. The metal seals 34, 36 and 38 will not be described in 
detail because of the similarity in structure to seal 33. 
Referring to FIG. 2, which shows seal 33 in more detail, the lower end 35 
has an outer diameter that is only slightly less than the inner diameter 
of bore 25, however, it does not perform sealing. The lower end 35 is an 
insertion end and is frusto-conical or bevelled. An annular recess 37 is 
formed in the sidewall of the stinger 27 above the lower end 35. Recess 
37, in cross-section, is generally rectangular, having upper and lower 
shoulders 39 and 41, which face each other and are located in planes 
perpendicular to the axis of the stinger 27. Shoulder 41 is located a 
short distance above lower end 35 and has an outer diameter only slightly 
less than the bore 25. A lip 43 depends downwardly from the upper shoulder 
39. Lip 43 is a cylindrical member that has an outer sidewall that is only 
slightly less in diameter than the inner diameter of the bore 25 for a 
close sliding fit and is substantially the same diameter as the outer 
diameter of shoulder 41. Lip 43 has an inner sidewall 47, that is 
concentric with the outer sidewall 45, and also with the cylindrical 
surface of the recess 37. The inner sidewall 47 is spaced from the 
sidewall of recess 37 by a distance that is approximately equal to the 
cross-sectional thickness of the lip 43. 
An integral annular band 49 is formed on the sidewall 45 of the lip 43 at 
the lower end of the lip, as shown in FIG. 3. The lower end of lip 43 is 
spaced above shoulder 41 a short distance. Band 49 is coated with an 
annular deposit of a softer metal than the lip 43 for lubrication. Lip 43 
will be integral with the stinger 27, and thus will normally be of steel. 
The coating is preferably of cadmium and is about 0.0005 inches thick. The 
radial thickness of the band 49 is preferably about 0.007 inch. This 
results in an interference fit with the bore 25. For example, in a bore 25 
of 5.125 inch diameter, the outer diameter of the band 49 is preferably 
about 5.137 inch. The cadmium is deposited on the lip 43 in a conventional 
manner. In the prior art, cadmium has been deposited on the metal seal 19 
(FIG. 1) for lubrication to enhance sealing, and the same technique may be 
used herein to apply the cadmium. Seals 34, 36 and 38 are constructed in 
the same manner and will not be described in further detail. 
In operation, when the Christmas tree assembly 17 is lowered onto the 
wellhead 11, the stinger 27 will insert into the bore 25. The lip 43 will 
deflect inwardly a slight amount as it enters the bore 25. The deflection 
is not enough to permanently deform the lip 43, rather the deflection is 
within the elastic limits of the lip 43. Some of the cadmium coating on 
band 49 will deposit on the bore 25 as the stinger 27 is inserted, forming 
smooth sealing surfaces. Once the pressure is applied to the bore 25 and 
bore 31, the fluid will enter the recess 37 and act outwardly on the inner 
sidewall 47 of the lip 43. This pressure will press the lip 43 against the 
bore 25 for a tighter seal. 
The invention has significant advantages. The metal seal needs only one 
sealing surface to seal against. The seal, being an integral part of the 
tube, does not require a retaining ring. This allows several seals of 
different diameters to be placed on the same tube and backed up with 
elastomeric seals. 
While the invention has been shown in only one of its forms, it should be 
apparent to those skilled in the art that it is not so limited but is 
susceptible to various changes without departing from the scope of the 
invention.