Metallic seal for use in highly-corrosive oil and gas environments

Abstract

A metal seal assembly to seal components in highly corrosive environments, such as a sour well environment. The seal assembly is comprised of a base metal structural component with a softer metal layer applied onto its surface. The purpose of the soft metal layer is to locally deform and, thereby, form a seal against a surface of an opposing component. The base metal structure of the seal may be comprised of a corrosion-resistant alloy. In addition, the soft metal layer may be comprised of a corrosion-resistant alloy, such as a refractory metal like tantalum.

1 . A seal assembly for a wellhead assembly, comprising:
 a metal seal structural body having at least one surface area adapted to form a seal against an opposing surface; and   a metal layer disposed over at least one of the metal seal structural body or the opposing seal structure to form a metal-to-metal seal, wherein the metal layer comprises tantalum.   
   
   
       2 . The seal assembly as recited in  claim 1 , wherein the metal layer comprises an alloy corresponding to UNS (Unified Numbering System) R05200. 
   
   
       3 . The seal assembly as recited in  claim 1 , wherein the metal layer comprises an alloy corresponding to UNS (Unified Numbering System) R05210. 
   
   
       4 . The seal assembly as recited in  claim 1 , wherein the metal seal structural body comprises a corrosion-resistant alloy (CRA). 
   
   
       5 . The seal assembly as recited in  claim 4 , wherein the CRA is an alloy intended to be resistant to general and localized corrosion of oilfield environments that are corrosive to carbon steels. 
   
   
       6 . The seal assembly as recited in  claim 4 , wherein the CRA is a nonferrous-based alloy in which any one or the sum of the specified amount of the elements titanium, nickel, cobalt, chromium, and molybdenum exceeds 50% (mass fraction). 
   
   
       7 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises a precipitation-hardened nickel-based alloy. 
   
   
       8 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N07718. 
   
   
       9 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N07725. 
   
   
       10 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N07716. 
   
   
       11 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N09925. 
   
   
       12 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises a precipitation-hardened cobalt-based alloy. 
   
   
       13 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy R31233. 
   
   
       14 . The seal assembly as recited in  claim 6 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy R30006. 
   
   
       15 . A seal assembly for a wellhead assembly, comprising:
 a metal seal structural body having at least one surface area adapted to form a seal against an opposing surface, wherein the metal body comprises a first corrosion-resistant alloy; and   a metal layer disposed over at least one of the at least one surface area adapted to form a seal against an opposing surface or the opposing surface, wherein the metal layer comprises a second corrosion-resistant alloy, the second corrosion-resistant alloy having a greater ductility than the first corrosion-resistant alloy.   
   
   
       16 . The seal assembly as recited in  claim 15 , wherein the second corrosion-resistant alloy comprises a refractory metal. 
   
   
       17 . The seal assembly as recited in  claim 16 , wherein the second corrosion-resistant alloy comprises tantalum. 
   
   
       18 . The seal assembly as recited in  claim 17 , wherein the second corrosion-resistant alloy comprises an alloy corresponding to UNS (Unified Numbering System) alloy R05200. 
   
   
       19 . The seal assembly as recited in  claim 17 , wherein the second corrosion-resistant alloy comprises an alloy corresponding to UNS (Unified Numbering System) alloy R05210. 
   
   
       20 . The seal assembly as recited in  claim 16 , wherein the first corrosion-resistant alloy is an alloy intended to be resistant to general and localized corrosion of oilfield environments that are corrosive to carbon steels. 
   
   
       21 . The seal assembly as recited in  claim 16 , wherein the first corrosion-resistant alloy is a nonferrous-based alloy in which any one or the sum of the specified amount of the elements titanium, nickel, cobalt, chromium, and molybdenum exceeds 50% (mass fraction). 
   
   
       22 . The seal assembly as recited in  claim 21 , wherein the first corrosion-resistant alloy comprises a precipitation-hardened nickel-based alloy. 
   
   
       23 . The seal assembly as recited in  claim 21 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N07716. 
   
   
       24 . The seal assembly as recited in  claim 21 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N07718. 
   
   
       25 . The seal assembly as recited in  claim 21 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N07725. 
   
   
       26 . The seal assembly as recited in  claim 21 , wherein the metal seal structural body comprises an alloy corresponding to UNS (Unified Numbering System) alloy N09925. 
   
   
       27 . A method of manufacturing a seal, comprising:
 machining a metal to form a base seal structure having at least one surface configured to form a seal against an opposing surface; and   disposing a layer comprising tantalum over at least one of the at least one surface configured to form a seal against an opposing surface of the base seal structure or the opposing surface.   
   
   
       28 . The method as recited in  claim 27 , wherein disposing a layer comprising tantalum comprises disposing a layer of tantalum over the at least one surface configured to form a seal against an opposing surface. 
   
   
       29 . The method as recited in  claim 27 , wherein machining a metal to form a base seal structure having at least one surface configured to form a seal against an opposing surface comprises machining a corrosion-resistant alloy to form a base seal structure having at least one surface configured to form a seal against an opposing surface. 
   
   
       30 . A method of manufacturing a seal, comprising:
 machining a first corrosion-resistant alloy to form a base seal structure having at least one surface configured to form a seal against an opposing surface; and   disposing a layer of a second corrosion-resistant alloy having a greater ductility than the first corrosion-resistant alloy on at least one of the at least one surface configured to form a seal against an opposing surface of the base seal structure or the opposing surface.   
   
   
       31 . The method of manufacturing a seal as recited in  claim 30 , wherein disposing a layer of a second corrosion-resistant alloy having a greater ductility than the first corrosion-resistant alloy on the base seal structure comprises disposing a layer comprising tantalum on the at least one surface configured to form a seal against an opposing surface of the base seal structure or the opposing surface. 
   
   
       32 . The method of manufacturing a seal as recited in  claim 30 , wherein machining a first corrosion-resistant alloy to form a base seal structure having at least one surface configured to form a seal against an opposing surface comprises machining a nickel or cobalt-based alloy to form a base seal structure having at least one surface configured to form a seal against an opposing surface.