Abstract:
A pressure relief valve for cryogenic service includes: a fluid inlet and a fluid outlet; a nozzle disposed within the fluid inlet, said nozzle having a nozzle groove radially formed on an exterior cylindrical surface of the nozzle and an outwardly disposed ledge having a lower ledge surface comprising a portion of an exterior surface of the nozzle groove and an upper ledge surface comprising a seat; a substantially cylindrical closure disc with a lower portion including a groove formed on an exterior radial surface of the cylindrical body, an outwardly disposed lip having an upper surface comprising a portion of an interior surface of the groove, said lip of the closure disc having a lower closure surface. The lip of the closure disc being adapted to deflect downward and inward in response to a cryogenic thermal gradient applied across the lip.

Description:
TECHNICAL BACKGROUND 
       [0001]    This disclosure relates to pressure relief valves, and more particularly, to pressure relief valves suitable for use in cryogenic applications. 
       BACKGROUND 
       [0002]    Typically, a pressure relief valve may be used to control or limit pressure in a system or vessel, which can build up by, for example, a process upset, instrument or equipment failure, or fire. In some instances, pressure relief valves may be used in a chemical processing plant that distills natural gas into pure methane, e.g., a “methanizer.” The process eliminates impurities like toluene and ethane from the natural gas to provide pure methane. The distillation is done by the adiabatic expansion of natural gas. Pressurized natural gas is made to work on compressors. The reduction in pressure to perform work is reflected by a drop in temperature. At different stages of temperature drops, the different compounds, such as toluene and ethane, start distilling and are collected in separate containers. Since methane has the lowest atomic weight in the gases comprising natural gas, pure methane results at the final stage of distillation. 
         [0003]    The process fluid coming out of the methanizer (e.g., methane) is in liquid form and may also be used elsewhere in the plant or sold as liquefied natural gas (“LNG”). A safety, or pressure, relief valve may be used to protect against overpressures at the methanizer output, or any other location within the piping system. LNG facilities may operate in the range of −150 degrees F. to −450 degrees F. 
         [0004]    In some instances, premature and/or undesirable leaks from prior art pressure relief valves may occur due in part to a difference in temperature between a fluid flowing to an inlet of the pressure relief valve and an ambient condition within the valve. Such a leak may begin as a microleak but, without attention, may increase in flow to a macroleak, thereby preventing the valve from maintaining a desired pressure-seal in the system. Very large temperature differences may occur with valves in cryogenic service. In some instances, the temperature differences between the fluid flowing to the valve inlet and the ambient valve condition may be in the range of 250 degrees F. Referring briefly to  FIGS. 7A and 7B , sectional views of a conventional prior art disc  700  of a prior art pressure relief valve used in a high temperature (e.g., steam) application is illustrated. Such prior art discs have been used in high temperature applications for over 50 years. The disc  700  includes lips  705  extending from a bottom surface of the disc  700  and directed towards a centerline of the disc  700 .  FIG. 6  shows the disc  700  in a non-operational state, i.e., with no high temperature fluid flowing through the valve in which the disc  700  is placed. Upon introduction of the high temperature fluid to the valve and opening of the valve, a temperature gradient occurs across the lips  705  (e.g., high temperature at an inlet of the valve compared to ambient temperature at an outlet of the valve).  FIG. 7B  illustrates a deflection of the lips  705  due to the temperature gradient and thermal characteristics of the disc  700 . As illustrated, due to a high temperature fluid, the lips  705  deflect in the direction “X.” Such deflection may help seal the valve (i.e., cause the disc to seat on a nozzle in the valve) to leaks, such as microleaks and/or macroleaks. 
         [0005]    In some instances, a prior art pressure relief valve disc such as disc  135  (as shown in  FIGS. 1A ,  1 B and  1 C) experiences micro or macroleaks when such a valve is placed in cryogenic service. Such prior art valve discs may also experience galling. In some cases, galling is a form of surface damage on an interior surface of the pressure relief valve arising between sliding solids. Galling is, typically, distinct from damage caused by microscopic (usually localized) roughening and creation of protrusions (i.e., lumps) above the interior surface. Galling may contribute or exacerbate the leaks experienced by the pressure relief valve due to the temperature difference experienced in cryogenic service. 
         [0006]    Therefore, there has been long felt and unmet need for a unique design for discs for relief valves used in cryogenic service that solve the problems discussed above. 
       SUMMARY 
       [0007]    In some implementations, the PRV of the present disclosure includes a disc-nozzle combination that minimizes and/or prevents process fluid leakage therethrough by deflection of portions of the disc and/or nozzle due to a thermal gradient between the process fluid temperature and the ambient condition. For example, in some implementations, the disc of the PRV may include a groove disposed on an outer circumferential surface of the disc, thereby forming a protrusion (e.g., a lip) that deflects axially (rather than or in addition to radially) in order to sealingly contact the nozzle (as explained more fully below). Further, in some implementations, the nozzle may include a notch disposed in an exterior circumferential surface of the nozzle to form a protrusion (e.g., a ledge) that, in response to a thermal gradient between the process fluid and the ambient condition on the outlet of the PRV, said ledge deflects to sealingly contact the disc and minimize and/or prevent leaks. 
         [0008]    Various implementations of a pressure relief valve (PRV) according to the present disclosure meet long felt but unmet needs for valves in cryogenic service. PRVs of the present disclosure may include one or more of the following features. For example, the PRV may help prevent or minimize leaks during cryogenic service of the valve. In some implementations, the PRV may help prevent or minimize such leaks subsequent to a first opening (or “pop”) of the valve in use in cryogenic service. As another example, the PRV may be used in a wide variety of cryogenic services and fluid temperatures while minimizing and/or preventing leaks through the valve caused at least in part by a temperature difference between the process fluid circulating through the valve and an ambient temperature condition in the valve (e.g., temperature on an outlet side of the PRV). As another example, the PRV may maximize set tightness during cryogenic service of the valve. The PRV may also utilize thermal characteristics of a material used for a valve disk and/or nozzle to minimize and/or prevent leaks of the valve during cryogenic service. For instance, the PRV may utilize a material deflection caused by a thermal gradient across the disc and/or nozzle to minimize and/or prevent leaks between the disk and nozzle. In sonic cases, the PRV may utilize the thermal characteristics with a geometry of the disc and/or nozzle in order to minimize and/or prevent leaks between the disc and nozzle. For example, one or more components of the PRV may axially deflect, rather than radially deflect, to sealingly contact and close the PRV to fluid flow therethrough in order to minimize and/or prevent leaks of the process fluid through the PRV. 
         [0009]    These general and specific aspects may be implemented using a device, system or method, or any combinations of devices, systems, or methods. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1A  illustrates a sectional view of a prior art pressure relief valve (PRV) with a prior art cryogenic disc; 
           [0011]      FIG. 1B  illustrates a perspective cross-sectional view of the PRV of  FIG. 1A ; 
           [0012]      FIG. 1C  illustrates an alternate embodiment of the PRV of  FIG. 1A , wherein the nozzle of the PRV is integral with a base of the PRV; 
           [0013]      FIG. 2  illustrates an enlarged cross-sectional view of the prior art disc of  FIGS. 1A ,  1 B and  1 C used for cryogenic service; 
           [0014]      FIGS. 3A and 3B  illustrate a cross-sectional view of a disc used in one implementation of a PRV in accordance with the present disclosure; 
           [0015]      FIG. 4  illustrates an enlarged sectional view of the disc of  FIGS. 3A and 3B  and a nozzle combination used in one implementation of a PRV in accordance with the present disclosure; 
           [0016]      FIGS. 5A and 5B  illustrate a cross-sectional view of another embodiment of a disc used in one implementation of a PRV in accordance with the present disclosure; 
           [0017]      FIG. 6  illustrates an enlarged sectional view of prior art thermodisc and a nozzle combination used in a PRV for a high temperature fluid (e.g., steam) service; and 
           [0018]      FIGS. 7A and 7B  illustrate a prior art thermodisc used in the PRV of  FIGS. 1A ,  1 B and  1 C for a high temperature fluid (e.g., steam) service. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Reference is now made to the drawings wherein like reference characters indicate like or similar parts through the figures. 
         [0020]    A pressure relief valve (PRV) according to the present disclosure may include a disc, a disc holder, a nozzle, and a mass-spring-damper system that allows for a fluid (e.g., gas, liquid, or multiphase fluid) within a system, such as a piping system or pressure vessel, to be relieved by operation of the PRV when the fluidic, pressure of the fluid exceeds a predetermined threshold. In some embodiments, the PRV may be used for cryogenic service, where a process fluid circulated to the PRV is at a lower temperature than an ambient condition at an outlet of the PRV. “Cryogenic service,” when used in the present disclosure, refers to applications in which a temperature of the process fluid circulated to the PRV is within one of the following temperature ranges: −21 to −75 F (e.g., propane as the process fluid); −76 to −150 F (e.g., ethylene as the process fluid); and −151 to −450 F (e.g., liquefied natural gas “LNG”, liquid nitrogen, liquid hydrogen or liquid helium as the process fluid). Alternatively, the term “cryogenic service” may refer to other temperature ranges for a combination of the aforementioned process fluids and other process fluid, such as: 0 to −50° F.; −50 to −150° F.; and −150 to −450° F. 
         [0021]      FIGS. 1A-B  illustrate sectional views of one implementation of a prior art pressure relief valve (PRV)  100 .  FIG. 1C  illustrates a sectional view of another implementation of a pressure relief valve (PRV)  1000  having an alternative nozzle  121  integral with the base  105 . Referring now to  FIGS. 1A ,  1 B and  1 C, PRV  100  (and  1000 ; hereinafter referred to for convenience as PRV  100 ) receives a fluid  101  (e.g., gas or liquid or a multiphase fluid) at and through an inlet  110  and directs the fluid  101  to and through an outlet  115  of the PRV  100  in order to relieve a pressure within a system. For example, the PRV  100  is typically in fluid communication with components, such as pressure vessels, heat exchangers, mechanical equipment (e.g., compressors, turbines, and others) within a piping or conduit system and may be used to control or limit a pressure in such a system, including such vessels, heat exchangers, and/or equipment, which can build up by a process upset, instrument or equipment failure, fire, or other incident. Pressure is relieved through the operation of PRV  100  by allowing the pressurized fluid to flow from the inlet  110  through the outlet  115  at a predetermined pressure set point. For instance, the PRV  100  may be designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. 
         [0022]    The process fluid  101  may he one of a number of fluids utilized in cryogenic service. For example, the fluid  101  may be methane, propane, ethylene, LNG, liquid nitrogen, or any combination thereof or other fluid. In any event, a temperature of the fluid  101  flowing through the inlet  110  may be substantially lower than an ambient temperature condition at the outlet  115 . The ambient temperature, typically, is between 50-90° F. 
         [0023]    PRV  100  includes a base  105  at least partially enclosing a nozzle  120  (or, alternatively, PRV  1000  includes a base  105  with an integral nozzle  121  (see FIG.  1 C)), and enclosing a disc  135 , and a disc holder  140 , and optionally an adjusting ring  125 . The base  105  receives (e.g., threadingly or welded or integral) the nozzle  120  at the inlet  110  of the PRV  100  and, in the illustrated embodiment  FIGS. 1A and 1B , includes a flanged connection at the outlet  115 . The nozzle  120  (or  121 ), generally, may be a pressure containing component in constant contact with the fluid  101  in both the open and closed positions of PRV  100 . (Note: The nozzle  120  or  121  may sometimes be referred to in the art as a seat or seat bushing.) 
         [0024]    The base  105  may also include a flanged connection at the inlet  110  or, alternatively, may include other connection mechanisms (e.g., grooved pipe connection, butt weld, or otherwise) at one or both of the inlet  110  and outlet  115 . In some embodiments, a portion of the base  105  adjacent the outlet  115  may have a lower pressure rating than a portion of the base  105  adjacent the inlet  110  of, for example, a decrease in fluidic pressure of the fluid  101  at the outlet  115  relative to the inlet  110 . 
         [0025]    PRV  100  also includes a cap  180  and a bonnet  145  enclosing (at least partially) a spindle  160 , which is threadingly engaged through one or more of a lock nut  185 , an adjusting screw  175 , spring washers  170 , a spring  165 , and a spindle head  155 . Generally, the bonnet  145  is mechanically coupled (e.g., by one or more bolts and locking nuts or by threading) at one end to the base  105  while the cap  180  is mechanically coupled (e.g., threadingly) to the bonnet  145  at a second end. The adjusting screw  175 , rigidly coupled to the bonnet  145  via the lock nut  185 , guidingly allows the spindle  160  to oscillate vertically within the cap  180  and bonnet  145  during operation of the PRV  100 . 
         [0026]    The PRV  100  also includes a guide  150  that receives at least a portion of the disc holder  140  therethrough. Typically, the disc  135 , disc holder  140 , spring washer (or washers)  170 , spindle  160 , spindle head  155 , and spring  165  comprise a “mass-spring-damper” system that works to respond to fluidic forces applied by the fluid  101  as it contacts the disc  135  through the nozzle  120 . The disc holder  140  includes a receiving aperture at a top end to receivingly engage the spindle head  155  such that force may be transmitted from the disc holder  140  to the spindle head  155  and, thus, to the spring washers  170  and spring  165 . For example, when an upward fluidic force greater than the spring force of the spring  165  is applied to the disc  135  (and is thus transmitted through the disc holder  140 , the spindle head  155 , and the spring washer  170  to the spring  165 ), the spring  165  may be compressed, thereby urging the spindle  160  upward through the adjusting screw  175 . Likewise, as the spring force of the spring  165  is greater than the fluidic force, the spring  165  expands, thereby urging the spindle  160  (and spindle head  155 , disc holder  140 , and disc  135 ) downward. 
         [0027]    In the embodiment of the PRV  100  illustrated in  FIGS. 1A and 1B , an adjusting ring  125  is engaged (e.g., threadingly) with a top portion of the nozzle  120 . Typically, adjusting ring  125  may be adjusted upward and/or downward on the nozzle  120  by threading or unthreading the ring  125  on the nozzle  120 . By adjusting the location (i.e., height) of the adjusting ring  125  relative to a top end of the nozzle  120 , blowdown, or reseating pressure, may also be adjusted. For example, when the adjusting ring  125  is moved upward, blowdown is increased thereby lowering the reseating pressure. Alternatively, when the adjusting ring  125  is moved downward, the blowdown is decreased, thereby raising the reseating pressure. In some embodiments, the adjusting ring  125 , and therefore the PRV  100 , may be preset at a predetermined position prior to putting the PRV  100  in service. In such embodiments, presetting may reduce the necessity of “popping” (i.e., applying the set pressure to the PRV  100 , such that significant lift of the disc and/or disc holder is obtained) the PRV  100  in service to ascertain that the adjusting ring  125  has been set properly for attaining the necessary lift and relieving capacity. 
         [0028]    In the embodiment illustrated in  FIGS. 1A and 1B , a ring pin  130  extends from a location external to the base  105 , through the base  105 , and operates to secure the adjusting ring  125  at a certain location (e.g., vertical position) on the nozzle  120 . When the ring pin  130  is rotatably removed or partially removed from the base  105 , the adjusting ring  125  may he adjusted (i.e., moved upward or downward). For example, the adjusting ring  125  may have multiple vertical grooves arranged circumferentially around an outer surface of the ring  125 . In some embodiments, the adjusting ring  125  has 30 grooves; alternatively, the adjusting ring  125  may have fewer or more grooves (e.g., 16, 42, or other number of grooves). The ring pin  130  includes a pointed tip configured to fit within a groove (e.g., approximately halfway between peaks and a valley between two grooves) and substantially prevents the adjusting ring  125  from vertical movement along the nozzle  120  through rotation of the adjusting ring  125  around the nozzle  120 . For example, in one implementation of the adjusting ring  125  including 30 grooves, adjusting the ring pin  130  between adjacent grooves may allow for approximately 12 degrees of rotation of the adjusting ring  125 , which translates to approximately 2/1000 inch vertical movement of the adjusting ring  125  along the nozzle  120 . 
         [0029]    As illustrated in  FIGS. 1A and 1B , the PRV  100  is in a “closed” state, where the disc  135  is “seated” on the nozzle  120 . (In a like manner, PRV  1000  is illustrated in a closed state in FIG:  1 C.) In the closed state, flow of the fluid  101  may be prevented or substantially prevented from the inlet  110  to the outlet  115  of the PRV  100 . In some instances, however, such as when the PRV  100  is urged from an open state to the closed state (e.g., shown in  FIG. 2 ), the PRV  100  may experience a leak such that a small flow of fluid  101  occurs from the inlet  110  to the outlet  115 . In certain instances, such as during cryogenic service of the PRV  100 , a thermal gradient may occur across the disc  135  and/or nozzle  120 . For example, the thermal gradient may occur across a portion of the disc  135  that contacts the nozzle  120 , e.g., a “seat.” Such a thermal gradient across a disc and/or nozzle may cause a thermal deflection of one or both of these components, thereby exacerbating the leak (or preventing the disc from seating on the nozzle). This thermal deflection may, for example, cause a radial deflection of the disc (e.g., radially outward from a vertical centerline of the valve), thereby increasing a gap between the disc and nozzle. The gap may allow fluid  101  to flow to the outlet  115  during a leak. 
         [0030]    In order to solve problems with leakage in PRVs which use prior art discs, applicant has invented and discloses herein a disc  200  and/or nozzle  300  for use in the prior art PRV  100  to thermally deflect in an axial direction toward each other (i.e., vertically in parallel with a centerline  10  defined through the PRV  100  as shown in  FIG. 4 ). For example, in some embodiments, as explained below, at least a portion of the disc  200  may axially deflect towards a seat  119  of the nozzle  300 , thereby closing or substantially closing the PRV  100  to prevent or substantially prevent flow of the fluid  101  from the inlet  110  to the outlet  115  in cryogenic service. Further, in some embodiments, a portion of the nozzle  300  may deflect axially towards the disc  300  to assist in closing the PRV  100 . 
         [0031]      FIGS. 3A and 3B  illustrate a sectional view of the disc  200  that may be used in the PRV  100  of the present disclosure. The disc  200  has a body  210 , a lip  215 , a groove ring  220 , and a groove cut  225 . As shown particularly in  FIG. 3B , in some embodiments, at least a portion of the disc  200  may axially deflect in the illustrated direction “Z” in response to a thermal gradient across the lip  215 . For example, when the disc  200  is utilized in the PRV  100  during cryogenic service, a thermal gradient between the inlet  110  and the outlet  120  of the PRV  100  may occur across the lip  215  of the disc  200 . The thermal gradient may, in some embodiments, be dependent on the difference between a temperature of the fluid  101  at the inlet  110  of the PRV and an ambient temperature at the outlet  115  of the PRV. As illustrated in  FIG. 3B , position P 1  illustrates the configuration of an embodiment of the disc  200  when not deflected due to a thermal gradient. Position P 2  illustrates a deflected position due to a thermal gradient across the disc  200 . Dotted lines illustrate the approximated deflected position P 2 . The amount of deflection will vary depending on the thermal gradient and the configuration of the disc  200 . 
         [0032]    In the illustrated embodiment, the groove ring  220  may be a circumferential recess in the body  210  around an exterior, radial surface  230  of the disc  200 . Further, in the illustrated embodiment of the disc  200 , the groove cut  225  may be formed in a bottom surface of the body  210 . In forming the groove ring  220  and the groove cut  225  in the body  210  of the disc  200 , the lip  215  may be configured to extend away from the body  210  in response to the thermal gradient. 
         [0033]    In the illustrated embodiment of the disc  200 , the groove ring  220  and groove cut  225  may minimize and/or reduce a thermal mass of the body  210  of the disc  200 . For instance, by forming the groove ring  220  and groove cut  225  in the body  210  of the disc  200 , thermal mass may be removed in order to minimize thermal mass around the lip  215 . In some embodiments, this minimization of thermal mass may direct and/or confine the thermal gradient across the lip  215  rather than, for example, other portions of the body  210 . Due to the reduction of thermal mass by the groove ring  220  and/or groove cut  225 , thermal deflection in a radial direction (e.g., radially towards the exterior surface  230 ) of the body  215  may be minimized and/or prevented. The groove cut  225  also reduces the section modulus of the disc at the lip which increases the thermally induced deflection in the axial direction. Thermal deflection, as shown in  FIG. 3B , may therefore be confined or directed in the “Z” direction, deflecting the lip  215  substantially axially toward the nozzle (not shown here). By confining and/or directing the thermal deflection of the disc  200  due to the thermal gradient in a substantially axial direction, “Z,” the lip  215  may be urged into contact with the nozzle to close or substantially close the PRV  100  against leaks of the fluid  101  from the inlet  110  to the outlet  115 . 
         [0034]    In some embodiments, all or a portion of the disc  200  may be manufactured from a material with a relatively high coefficient of thermal expansion. For example, in some embodiments, the disc  200  may be made from  316  stainless steel. Alternatively, in other embodiments, the disc  200  may be made from Inconel X-750, or another alloy, such as Incoloy 903, Incoloy 907, Incoloy 909, Inconel X-783, or other alloy(s) suitable for cryogenic applications with a relatively high coefficient of thermal expansion. 
         [0035]      FIG. 4  illustrates a sectional view of a disc and a nozzle combination used in one implementation of the PRV  100 . As illustrated, disc  200  may be used in combination with a nozzle  300  in the PRV  100  to regulate flow of the fluid  101  from the inlet  110  to the outlet  115  of the PRV  100 . In the illustrated embodiment, the nozzle  300  includes a ledge  305  formed at a top surface of the nozzle  300  (i.e., seat  119 ). The ledge  305  may be formed in the nozzle  300  to protrude radially towards the centerline  10  of the PRV  100  by, for example, formation of a recess in an exterior surface  315  of the nozzle  300  to form a radial notch  310 . 
         [0036]    In some embodiments of the nozzle  300  including the ledge  305 , the thermal gradient between the inlet  110  and the outlet  120  of the PRV  100  may be experienced across the ledge  305 . The radial notch  310  may minimize and/or reduce a thermal mass of the nozzle  300  at the seat  119 . For instance, by forming the radial notch  310 , thermal mass may be removed in order to minimize thermal mass around the ledge  305 . In some embodiments, this minimization of thermal mass may direct and/or confine the thermal gradient across the ledge  310  rather than, for example, a full thickness of the seat  119  between the interior surface  315  and an exterior surface  320 . Due to the reduction of thermal mass and section modulus by the radial notch  310 , thermal deflection in a radial direction (e.g., towards the interior surface  315 ) of the seat  119  may be minimized and/or prevented. Thermal deflection may therefore be confined to or directed in an axial direction, deflecting the ledge  305  toward the disc  200 . By confining and/or directing the thermal deflection of the ledge  305  due to the thermal gradient in an axial direction, the ledge  305  may be urged into contact with the disc  200  to close or substantially close the PRV  100  against leaks of the fluid  101  from the inlet  110  to the outlet  115 . 
         [0037]    In some embodiments, the nozzle  300  may be manufactured from a material with a relatively high coefficient of thermal expansion. For example, in some embodiments, the nozzle  300  may he made from  316  stainless steel. Alternatively, in other embodiments, the nozzle  300  may be made from Inconel X-750, or another alloy, such as Incoloy 903, Incoloy 907, Incoloy 909, Inconel X-783, or other alloy(s) suitable for cryogenic application with a relatively high coefficient of thermal expansion. 
         [0038]      FIGS. 5A and 5B  illustrate a sectional view of a disc  400  that may be used in the PRV  100  of the present disclosure. The disc  400  has a body  410 , a lip  415 , and a groove ring  420 . As shown particularly in  FIG. 5B , in some embodiments, at least a portion of the disc  400  may axially deflect in the illustrated direction “Z” in response to a thermal gradient across the lip  415 . For example, when the disc  400  is utilized in the PRV  100  during cryogenic service, a thermal gradient between the inlet  110  and the outlet  120  of the PRV  100  may he experienced across the lip  415  of the disc  400 . The thermal gradient may, in some embodiments, be a difference between a temperature of the fluid  101  at the inlet  110  of the PRV and an ambient temperature at the outlet  115  of the PRV. As illustrated in  FIG. 5B , position P 1  illustrates the configuration of an embodiment of the disc  400  when not deflected due to a thermal gradient. Position P 2  illustrates a deflected position due to a thermal gradient across the disc  400 . Dotted lines illustrate the approximated deflected position P 2 . The amount of deflection will vary depending on the thermal gradient and the configuration of the disc  400 . 
         [0039]    In the illustrated embodiment, the groove ring  420  may be a circumferential recess in the body  410  around an exterior, radial surface  430  of the disc  400 . As compared to the disc  200  (shown in  FIG. 3A ), the disc  400  may not have a groove cut formed in a bottom surface of the disc  400 . In forming the groove ring  420  in the body  410  of the disc  400 , the lip  415  may be formed to deflect away from the body  410  in response to the thermal gradient. 
         [0040]    In the illustrated embodiment of the disc  400 , the groove ring  420  may minimize and/or reduce a thermal mass of the body  410  of the disc  400 . For instance, by forming the groove ring  420  in the body  410  of the disc  400 , thermal mass may be removed in order to minimize thermal mass around the lip  415 . In some embodiments, this minimization of thermal mass may direct and/or confine the thermal gradient across the lip  415  rather than, for example, other portions of the body  410  (e.g., the full radial thickness of the body  410 ). Due to the reduction of thermal mass by the groove ring  420 , thermal deflection in a radial direction (e.g., radially towards the exterior surface  430 ) of the body  415  may be minimized and/or prevented. Thermal deflection, as shown in  FIG. 5B , may therefore be confined or directed in the “Z” direction, deflecting the lip  415  substantially axially toward the nozzle (not shown here). By confining and/or directing the thermal deflection of the disc  400  due to the thermal gradient in a substantially axial direction, “Z,” the lip  415  may be urged into contact with the nozzle to close or substantially close the PRV  100  against leaks of the fluid  101  from the inlet  110  to the outlet  115 . 
         [0041]    Applicant&#39;s test data regarding the disc  200  of  FIGS. 3A and 3B  as a % improvement over a conventional prior art disc is summarized below: 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Test fluid: Liquid Nitrogen: Fluid Temperature: −305 F. to −285 F. 
               
             
          
           
               
                   
                 Standard Trim 
                 Cryogenic Trim 
                   
               
             
          
           
               
                   
                 Set 
                   
                 % set 
                 Set 
                   
                 % set 
                   
               
               
                   
                 Pres- 
                 Leak 
                 pres- 
                 pres- 
                 Leak 
                 pres- 
                 % improve- 
               
               
                   
                 sure 
                 stop 
                 sure 
                 sure 
                 stop 
                 sure 
                 ment 
               
               
                   
                   
               
             
          
           
               
                 1900J 
                 97.1 
                 38.6 
                 39.7% 
                 95 
                 76.4 
                 79.8% 
                 201% 
               
               
                 1900F 
                 107 
                 39.6 
                 37.0% 
                 108 
                 75.4 
                 69.8% 
                 189% 
               
               
                   
               
               
                 The percentage improvement is calculated as the improvement in the leak pressure/set pressure ratio of the cryogenic trim over the standard trim. 
               
             
          
         
       
     
         [0042]    Various embodiments of the PRV  100  may include varying disc-nozzle combinations. For example, the disc  200  may be combined with the nozzle  300  as shown in  FIG. 4 . Further, the disc  400  may be combined with the nozzle  300 . As another example, the disc  200  may be combined with a conventional nozzle, such as the nozzle  120 , which, in some embodiments, may not include the radial notch  310  and/or ledge  305 . As another example, the disc  400  may be combined with the nozzle  120 . As yet another example, the nozzle  300  may be combined with a conventional disc, which may not include a groove cut, a groove ring, or a lip as those components of the disc are illustrated in the present disclosure. 
         [0043]    Different combinations may provide for varying operation of the PRV  100 . For instance, combining the disc  200  with the nozzle  300  may provide for maximal sealing contact between the lip  215  and the ledge  305 , as axial thermal deflection due to a thermal gradient across the lip  215  and ledge  305  may urge the disc  200  and nozzle  300  into sealing contact. Accordingly, the present disclosure contemplates many different embodiments with varying combinations of the disc, nozzle, and other components of the PRV depending on, for example, a temperature of the fluid  101  and/or cryogenic service in which the PRV  100  is used. 
         [0044]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, the recess of the groove ring  220  and/or  420  in an outer surface of the disc  200  and/or  420  may have a cross sectional profile that is hemispherical, square, or v-shaped. Accordingly, other implementations are within the scope of the following claims.