Thermally-sensitive triggering mechanism for selective mechanical energization of annular seal element

Abstract

A seal assembly for use in a valve that maintains a seal during operational excursions of high temperature, such as during a fire. The seal assembly includes a eutectic material that retains an energizing element in place during normal conditions, which in turn keeps a secondary seal spaced axially away from a sealing position. During high temperature excursions, the eutectic material degrades and releases the energizing element. When released, the energizing element energizes a secondary seal that is in an annular space between a valve stem and valve housing.

What is claimed is: 
     
         1 . A valve assembly for use with a wellhead member comprising:
 a valve housing having a bore;   a valve stem inserted into the bore; and   a packing assembly for sealing an annulus between the valve stem and valve housing comprising,
 primary stem packing in the annulus; 
 a secondary stem packing in the annulus that is selectively compressed into sealing contact with the valve stem, 
 a resilient element in the annulus that selectively expands from a compressed configuration to an expanded configuration to exert a compressive force onto the secondary stem packing, 
 a eutectic element that degrades at a specified temperature other than an expected operating temperature of the valve assembly, and 
 a compressive stack comprising the eutectic element and that retains the resilient element in the compressed configuration, and releases the resilient element when the eutectic element is exposed to a temperature at which the eutectic element degrades. 
   
     
     
         2 . The valve assembly of  claim 1 , wherein the compressive stack projects radially through a sidewall of the valve housing and into contact with an energizing element that is axially disposed between the resilient element and the secondary stem packing. 
     
     
         3 . The valve assembly of  claim 1 , wherein the eutectic element degrades at a temperature that is less than a temperature at which the primary stem packing degrades 
     
     
         4 . The valve assembly of  claim 1 , wherein the compressive stack further comprises a plug on an outer radial side of the eutectic element and a retention element on an inner radial side of the eutectic element. 
     
     
         5 . The valve assembly of  claim 1 , further comprising an annular cartridge in the axial bore having an annular space in which circumscribes the secondary stem packing and resilient member, wherein a lower terminal end of the annular space forms a ledge, and wherein the resilient member is supported on the ledge. 
     
     
         6 . The valve assembly of  claim 5 , further comprising a metal to metal seal formed on an outer periphery of the annular cartridge that sealingly engages an inner surface of the bore. 
     
     
         7 . The valve assembly of  claim 1 , wherein the compressive stack comprises the eutectic element and a retention element that impinges against an energizing element. 
     
     
         8 . The valve assembly of  claim 7 , wherein the eutectic element and an outer radial portion of the retention element are in a groove formed on an inner surface of the axial bore. 
     
     
         9 . The valve assembly of  claim 1 , wherein the compressive stack comprises a retention nut that mounts into a side of the valve housing, the retention nut having a bore in which the eutectic member is disposed, the compressive stack further comprising a retention element that inserts into an end of the bore in the retention nut, the retention element having an end distal from the retention nut that selectively compresses a retention element against the stem. 
     
     
         10 . The valve assembly of  claim 9 , further comprising a port in an end of the retention nut that intersects with the bore in the retention nut, so that when the eutectic element degrades to a flowable substance, the flowable substance can flow from the bore in the retention nut through the port. 
     
     
         11 . The valve assembly of  claim 1 , further comprising an annular packing gland for retaining the packing assembly in the valve housing. 
     
     
         12 . A valve assembly for use with a wellhead member comprising:
 a valve housing having a bore;   a valve stem inserted into the bore; and   a packing assembly for sealing an annulus between the valve stem and valve housing comprising,
 a secondary stem packing in the annulus that is selectively compressed into sealing contact with the valve stem, 
 a resilient element in the annulus that selectively expands from a compressed configuration to an expanded configuration to exert a compressive force onto the secondary stem packing, 
 a retention element axially adjacent the resilient element and selectively coupled to the valve stem when the resilient element is in the compressed configuration and slidable with respect to the valve stem when the resilient element is in the expanded configuration, 
 a eutectic element that degrades at a temperature greater than an expected operating temperature of the valve assembly, and 
 a compressive stack comprising the eutectic element and that exerts a compressive force to couple together the retention element and valve stem, and that releases the compressive force when the eutectic element is exposed to a temperature at which the eutectic element degrades. 
   
     
     
         13 . The valve assembly of  claim 12 , further comprising an annular cartridge that circumscribes the valve stem, and has an upper portion that is spaced radially outward from the valve stem, so that an annular space is formed between the valve stem and annular cartridge for receiving the secondary stem packing, energizing element, and resilient element, and wherein the primary stem packing is in the annulus and below a lower portion of the annular cartridge. 
     
     
         14 . The valve assembly of  claim 13 , further comprising a retaining element for axially retaining the annular cartridge within the axial bore, wherein inner and outer radial edges of the retaining element project into grooves formed respectively on outer and inner surfaces of the annular cartridge and axial bore. 
     
     
         15 . The valve assembly of  claim 12 , further comprising a gate on an end of the stem for controlling well fluid. 
     
     
         16 . The valve assembly of  claim 12 , wherein the eutectic element degrades at a temperature less than a temperature at which the primary stem packing degrades. 
     
     
         17 . A valve assembly for use with a wellhead member comprising:
 a valve housing having an axial bore;   a valve stem in the axial bore that defines an annulus in the valve housing;   a primary stem packing;   a packing assembly in the annulus that comprises a secondary stem packing, a resilient member that selectively expands axially into compressive engagement with the secondary stem packing so that the stem packing radially expands into sealing engagement with radial surfaces in the annulus, and a means for retaining the resilient member in a compressed configuration until the valve housing is exposed to a temperature that exceeds a design temperature of the valve assembly by a designated amount.