阅读说明：本技术 用于过程流体压力变送器的高压封壳和集管箱 (High pressure enclosure and header for process fluid pressure transmitter ) 是由 埃里克·彼得森 尼古拉斯·E·梅耶尔 大卫·M·斯特瑞 于 2020-09-22 设计创作，主要内容包括：提供了一种用于过程流体压力变送器的压力封壳/集管箱组件。隔离体塞具有在其第一端处的隔离隔膜以及与其第一端间隔开的其第二端。隔离体塞具有将其第一端以流体方式联接到第二端的填充流体通路。集管箱具有被配置成承载压力传感器的其第一端和与其第一端间隔开的其第二端。集管箱具有从其第一端延伸到其第二端的至少一个电互连件。双轴支撑环设置在集管箱的外表面周围。双轴支撑环和集管箱在它们之间限定了锥形干涉界面。集管箱在第一焊接部处焊接到隔离体塞,并且双轴支撑环在与集管箱的第二端间隔开的位置处焊接到隔离体塞。(A pressure capsule/header assembly for a process fluid pressure transmitter is provided. The isolator plug has an isolation diaphragm at a first end thereof and a second end thereof spaced from the first end thereof. The isolator plug has a fill fluid passage fluidly coupling a first end thereof to a second end. The header tank has a first end thereof configured to carry the pressure sensor and a second end thereof spaced apart from the first end thereof. The header tank has at least one electrical interconnect extending from a first end thereof to a second end thereof. The biaxial support ring is disposed around the outer surface of the header tank. The biaxial support ring and the header define a tapered interference interface therebetween. The header tank is welded to the isolator plug at a first weld and the biaxial support ring is welded to the isolator plug at a location spaced from a second end of the header tank.)

1. A pressure capsule/header assembly for a process fluid pressure transmitter, the assembly comprising:

an isolator plug having an isolation diaphragm at a first end thereof and a second end thereof spaced apart from the first end thereof, the isolator plug having a fill fluid passage fluidly coupling the first end thereof to the second end thereof;

a header tank having a first end thereof configured to carry a pressure sensor and a second end thereof spaced apart from the first end thereof, the header tank having at least one electrical interconnect extending from the first end thereof to the second end thereof;

a dual-axis support ring disposed about an outer surface of the header tank, and the dual-axis support ring and the header tank defining a tapered interference interface therebetween; and

wherein the header tank is welded to the isolator plug at a first weld and the biaxial support ring is welded to the isolator plug at a location spaced from a second end of the header tank.

2. The pressure enclosure/header assembly of claim 1, wherein the tapered interference interface is configured to create a self-locking interface.

3. The pressure enclosure/header tank assembly of claim 1, wherein the tapered interference interface has a taper of 0.25 inches in a radial direction per 12 inches in an axial direction.

4. The pressure enclosure/header assembly of claim 1, wherein the tapered interference interface is configured to provide an interference between 0.0015 inches and 0.0024 inches.

5. The pressure enclosure/header assembly of claim 1, wherein the bi-axial weld ring is configured to provide a die pocket that isolates heat loads from the header tank when the bi-axial support ring is welded to the isolator plug.

6. The pressure enclosure/header tank assembly of claim 5, wherein the die pocket has a depth greater than 0.12 inches.

7. The pressure enclosure/header tank assembly of claim 1, wherein the bi-axial weld ring has a different material hardness as compared to a material hardness of the isolator plug.

8. The pressure enclosure/header assembly of claim 1, wherein the bi-axial weld ring comprises an edge break configured to prevent material plowing during assembly.

9. The pressure enclosure/header tank assembly of claim 8, wherein the edge break is a radius.

10. The pressure enclosure/header tank assembly of claim 1, wherein the bi-axial weld ring is configured to radially compress the header tank.

11. The pressure enclosure/header tank assembly of claim 1, wherein the dual axis support ring is formed from 17-4 PH.

12. The pressure enclosure/header assembly of claim 11, wherein the two-axis support ring is heat treated for condition H1150.

13. The pressure enclosure/header tank assembly of claim 1, wherein the header tank is constructed of 316L stainless steel.

14. The pressure enclosure/header assembly of claim 1, wherein the isolator plugs are formed from 316L stainless steel.

15. The pressure enclosure/header assembly of claim 1, wherein the isolator plugs are formed of alloy C-276.

16. A process fluid pressure transmitter comprising:

a process portion having a process fluid connector configured to couple to a source of a process fluid;

an isolator plug threaded to the process portion, the isolator plug having an isolation diaphragm at a first end thereof and a second end thereof spaced from the first end thereof, the isolator plug having a fill fluid disposed within a fill fluid passageway fluidly connecting the first end thereof to the second end thereof;

a header tank having a first end thereof configured to carry a pressure sensor and a second end thereof spaced apart from the first end thereof, the header tank having at least one electrical interconnect extending from the first end thereof to the second end thereof;

a bi-axial support ring disposed about an outer surface of the header tank and defining a tapered interference interface therebetween;

wherein the header tank is welded to the isolator plug at a first weld and the biaxial support ring is welded to the isolator plug at a location spaced from a second end of the header tank; and

a controller operably coupled to the pressure sensor and configured to provide a process fluid pressure output based on a signal from the pressure sensor.

17. The process fluid pressure transmitter of claim 16, wherein the dual-axis weld ring has an externally threaded portion configured to be within a sensor body of the process fluid pressure transmitter.

18. The process fluid pressure transmitter of claim 16, wherein the controller is operably coupled to the pressure sensor through measurement circuitry that is electrically coupled to the pressure sensor via the at least one electrical interconnect.

19. The process fluid pressure transmitter of claim 16, further comprising loop communication circuitry coupled to the controller and configured to communicate the process fluid pressure output according to a process industry communication protocol.

20. A method of manufacturing a pressure capsule/header assembly for a process fluid pressure transmitter, the method comprising:

providing a header tank carrying a pressure sensor, the header tank being formed of metal and having at least one interconnect therethrough;

providing an isolator plug having an isolator diaphragm at a first end and having a second end spaced from the first end, the isolator diaphragm including a fill fluid passage fluidly coupling the first end to the second end;

welding the header to the isolator plug proximate the second end of the isolator plug;

providing a bi-axial weld ring configured to create a tapered interference fit with an outer surface of the header tank;

placing the bi-axial weld ring around the header tank to engage the tapered interference fit; and

welding the bi-axial weld ring to the isolator plug.

21. The method of claim 20, wherein welding the header tank to the isolator plug seals the header tank to the isolator plug.

22. The method of claim 20, wherein welding the bi-axial weld ring to the separator plug occurs proximate to a second end of the separator plug.

23. The method of claim 20, further comprising checking the degree of interference of the tapered interference fit after welding the bi-axial weld ring to the separator plug.

24. The method of claim 20, wherein checking the degree of interference comprises measuring a standoff height between the bi-axial weld ring and the isolator plug.

Technical Field

Background

Industrial process fluid pressure transmitters are used to measure the pressure of industrial process fluids, such as slurries, liquids, vapors or gases in chemical processing plants, pulp processing plants, petroleum processing plants, pharmaceutical processing plants, food processing plants, and/or other fluid processing plants. Industrial process fluid pressure transmitters are often placed near process fluids or in field applications. These field applications are often subjected to harsh and varying environmental conditions, which present challenges to designers of these transmitters.

The sensing element in many process fluid pressure transmitters is typically a capacitance-based or resistance-based sensor. Isolation diaphragms are commonly used to separate process fluid from an electroactive sensing element, thereby preventing process fluid (which can sometimes be harsh, corrosive, dirty, contaminated, or at extremely high temperatures) from interacting with electrical components of the pressure transmitter.

Generally, the process fluid acts on the isolation diaphragm to produce a deflection of the isolation diaphragm that moves or otherwise displaces the substantially incompressible fill fluid behind the diaphragm, which produces an associated motion of the sensing diaphragm of the pressure sensor. The pressure sensor has an electrical characteristic, such as capacitance or resistance, that varies with the applied pressure. The electrical characteristic is measured using measurement circuitry within the process fluid pressure transmitter to provide an output signal related to process fluid pressure. The output signals may also be formatted in accordance with known industry standard communication protocols and transmitted over a process communication loop to other field devices or to a process controller.

In-line process fluid pressure transmitters typically have a single process fluid pressure inlet that can be coupled to a source of process fluid pressure and provide an indication of the process fluid pressure. Such indication may be relative to atmosphere (such as a gauge indication) or relative to vacuum (such as an absolute pressure measurement). Inline pressure transmitters that experience high maximum operating pressures (MWP) present special design challenges. A structure that provides only a single application capable of withstanding the maximum operating pressure may not be robust or robust enough to withstand fatigue in the event of repeated excursions or drifts to or beyond the maximum operating pressure. Thus, for an increasing high pressure market (such as subsea wells), it is desirable to provide an in-line process fluid pressure transmitter suitable for extended use at higher pressures in such environments.

Disclosure of Invention

A pressure capsule/header assembly for a process fluid pressure transmitter is provided. The isolator plug has an isolation diaphragm at a first end thereof and a second end spaced from the first end. The isolator plug has a fill fluid passage fluidly coupling the first end to the second end. A header or header has a first end configured to carry a pressure sensor and a second end spaced from the first end. The header tank has at least one electrical interconnect extending from a first end to a second end. The biaxial support ring is disposed around the outer surface of the header tank. The dual axis support ring and the header define a tapered interference interface therebetween. The header tank is welded to the isolator plug at a first weld and the biaxial support ring is welded to the isolator plug at a location spaced from a second end of the header tank.

Drawings

FIG. 1 is a schematic perspective view of an in-line process fluid pressure transmitter with which embodiments of the present invention are particularly useful.

FIG. 2 is a block diagram of an in-line process pressure transmitter to which embodiments of the present invention are particularly applicable.

FIG. 3 is a diagrammatic view of a portion of an in-line process fluid pressure transmitter according to the prior art.

FIG. 4 is a diagrammatic view of a high pressure enclosure and header design for an in-line process fluid pressure transmitter in accordance with an embodiment of the present invention.

Fig. 5 is a diagrammatic enlarged view in cross section of a header tank weld according to an embodiment of the invention.

FIG. 6 is a graph of temperature as a function of pocket depth according to an embodiment of the present invention.

Fig. 7 is an enlarged diagrammatic view of a header weld area showing a beneficial moment generated with respect to the header weld in accordance with an embodiment of the present invention.

FIG. 8 is a graph of predicted failure period versus capsule plug recess depth in accordance with an embodiment of the present invention.

Figure 9 is a cross-sectional view showing features of a biaxial support ring according to an embodiment of the invention.

FIG. 10 is a graph of FEA maximum principal stress versus ring interference according to an embodiment of the present invention.

FIG. 11 is a graph of predicted failure cycles for varying ring interference of welds and machined parts according to an embodiment of the present invention.

FIG. 12 is a graphical view illustrating the compressive preload resulting from annular weld contraction in accordance with an embodiment of the present invention.

FIG. 13 is a diagrammatic cross-sectional view showing standoff height as an indicator of joint interference according to an embodiment of the invention.

FIG. 14 is a table illustrating various burst ranges for the KSI aspect of interference ranging from 0.0014 "to 0.0028" in accordance with an embodiment of the invention.

FIG. 15 is a flow chart of a method of manufacturing a high pressure enclosure and a header tank according to an embodiment of the present invention.

Detailed Description

FIG. 1 is a diagrammatic perspective view of an in-line process fluid pressure transmitter with which embodiments of the present invention are particularly useful. Pressure transmitter 100 includes a process fluid connector 102 configured to couple to a source 104 of process fluid. The process fluid introduced at the connector 102 bears against an isolation diaphragm that physically isolates, i.e., physically isolates, the process fluid from the pressure sensor, but otherwise communicates the process fluid pressure to the pressure sensor disposed within the sensor body 106. The pressure sensor (shown diagrammatically in FIG. 2) has an electrical characteristic (such as capacitance or resistance) that is measured by measurement circuitry in the electronics housing 108 and converted to process fluid pressure by the controller using a suitable calculation. Process fluid pressure may be transmitted over a process communication loop via a wire coupled through conduit 110 and/or displayed locally via display 112. Further, in some embodiments, process fluid pressure may be transmitted wirelessly.

FIG. 2 is a diagrammatic view of an in-line process pressure transmitter 100 with which embodiments of the present invention are particularly well suited. Transmitter electronics are housed within electronics housing 108 and include communication circuitry 114, power circuitry 118, controller 122, display 112, and measurement circuitry 124.

Communication circuitry 114 is disposed within electronics housing 108 and can be coupled to a process communication loop via a wired or wireless connection. By coupling to the process communication loop, communication circuitry 114 allows in-line process pressure transmitter 100 to communicate in accordance with industry standard process communication protocols. Also, in some embodiments, transmitter 100 can receive all necessary power for operation via its coupling to the process communication loop. Accordingly, pressure transmitter 100 includes a power module 118 that, in some embodiments, couples to a process communication loop to supply suitable operating power to all components of transmitter 100, as indicated at reference numeral 120 labeled "to all". Examples of suitable process communication protocols include addressable remote sensor high-speed channelsProtocol, FOUNDATION^TMFieldbus protocols, etc. Furthermore, embodiments of the present invention include wireless process communication, such as according to IEC 62591 (WirelessHART).

The controller 122 is coupled to the communication circuitry 114 and the measurement circuitry 124, and is configured to cause the measurement circuitry 124 to provide a digital indication or measurement from the pressure sensor 126. This digital indication is processed or otherwise manipulated to generate a process pressure value that is communicated by controller 122 to other suitable devices via communication circuitry 114. In some embodiments, the controller 122 may be a microprocessor. A local display, such as display 112, may also display the process fluid pressure or other suitable amount.

Embodiments of the present invention generally result from a detailed analysis and insight into the prior art for high voltage applications. Before describing some of the various solutions to the identified problems, it will be useful to first describe the current structure and opportunities for improvement thereof.

FIG. 3 is a diagrammatic view of a portion of an in-line process fluid pressure transmitter according to the prior art. FIG. 3 shows a process portion 200 having a process connector 202 configured to mount to or otherwise couple to a source of process fluid entering via a process fluid inlet 204. The process fluid bears against the isolation diaphragm 206 and the pressure of the process fluid causes movement of the isolation diaphragm and thus movement of the isolation fluid within the passageway 208. Passageway 208 is fluidly coupled with a chamber 210 within which a pressure sensor 212 is located. Thus, as the process fluid bears against isolation diaphragm 206, this pressure is communicated through the fill fluid to pressure sensor 212, where it is sensed. As can be seen, isolator plug 214 is configured to be threadably engaged within process connector 202 via external threads 216.

The pressure sensor 212 is mounted to a header 218. The header 218 is mounted in the isolator plug 214 via a shrink-fit process to enclose the pressure sensor 212 within the chamber 210. Finally, welds 220 are applied around the ends of header tank 218 to bond and seal header tank 218 to upper region 215 of isolator plug 214. As will be set forth in more detail below, the prior art configuration may be improved. More specifically, it is believed that the embodiments provided herein will facilitate providing a high pressure enclosure and header design that not only provides a higher operating pressure range, but that also does so while also being easy to manufacture and having higher internal qualities. These improvements are believed to address weld fatigue and/or glass seal compression, as will be described in more detail below.

The prior art design shown with respect to fig. 3 may be a challenge when it comes to cleanability, in part due to the deeper pin traps. When the glazing, i.e. the vitrification assembly, is broken, such broken glass makes it more difficult to adequately clean contaminants from the assembly. The high thermal stresses that occur during the process used to create weld 220 (shown in FIG. 3), combined with residual stresses from the thermal shrink fit, cause surface cracks to form in the header tank material. The potential for such cracks typically requires a 100% visual inspection of all parts at the end of the capsule manufacture to prevent any severely cracked units from going further into production without being reworked or discarded. Another difficulty that may arise during the soldering process is that the solder that seals the ports (e.g. the filler tube 222 shown in fig. 3) is heated to a temperature at which the solder reflows substantially due to its proximity to the solder. This is undesirable and is not considered the best practice for brazing joints.

With the understanding of the previous designs and the challenges presented by such designs, embodiments of the present invention not only remove the thermal shrink fitting operation, but also move the header/separator plug welds to locations that are less likely to adversely affect header glazing (or vitrification assembly) and/or brazing.

FIG. 4 is a diagrammatic view of a high pressure enclosure and header design for an in-line process fluid pressure transmitter in accordance with an embodiment of the present invention. System 300 has some similarities to system 200 and like components are numbered similarly. As shown, system 300 includes a process coupling 202 having a process fluid inlet 204 and an isolation diaphragm 206. Additionally, the isolator plug 314 has a first end 315 proximate the isolation diaphragm 206 and a second end 317 spaced from the first end 315. Fill fluid passageway 319 fluidly couples first end 315 to second end 317. Isolator plug 314 is configured to threadably engage process connector 202 in substantially the same manner that isolator plug 214 (shown in fig. 3) engages process connector 202. However, the manner in which the header tank 318 is coupled to the isolator plug 314 is significantly different than the design shown in FIG. 3. In particular, header 318 is welded to insulator plug 314 at header weld 320 proximate second end 317 of insulator plug 314. In one embodiment, weld 320 is a laser weld. In another embodiment, the weld 320 may be a projection weld. In yet another embodiment, weld 320 is a combination of a laser weld and a projection weld. Preferably, the weld 320 is a full penetration weld. However, embodiments described herein may be implemented where weld 320 is a partial penetration weld.

The weld 320 surrounds the header tank 318 and seals the header tank 318 to the isolator plug 314. Thus, header weld 320 is a continuous weld that completely surrounds, i.e., circumscribes, the interface between header 318 and isolator plug 314. The weld 320 is created before the biaxial support ring 322 is placed on the assembly.

Header tank 318 is configured to carry or otherwise mount a pressure sensor such that the pressure sensor is operatively coupled to the process fluid pressure. The header tank 318 also includes one or more high voltage electrical feedthroughs that are sealed with glass or another suitable high voltage material. In addition, header tank 318 also includes a fill fluid passageway configured to allow a fill fluid to be introduced into passageway 319 during assembly of the process fluid pressure transmitter.

Once the header tank weld 320 is created, the dual-axis support ring 322 is slid over the outer diameter 324 of the header tank 318 in the direction indicated by arrow 326 and then pressed down on the header tank 318 until the dual-axis support ring 322 contacts the plug 314. Additionally, as shown by the enlarged angle 328, the interface between the outer diameter of the header tank 318 and the inner diameter of the bi-axial support ring 322 is configured to create a tapered interference fit and provide a self-locking taper angle. In one embodiment, this self-locking taper angle is about 1/4 inches in the radial direction per foot in the axial direction. When a two-axis support ring 322 is placed on the header tank 318, the support ring 322 is welded to the isolator plug 314 at an annular weld 330 proximate the weld 320 and spaced from the upper surface of the header tank 318.

Fig. 5 is a diagrammatic enlarged view of a cross section of the header tank welding part 320. The arrow 350 indicates the portion of the weld 320 where the stress is concentrated. Additionally, arrow 352 indicates the location of most weld defects. The header tank is radially welded to the closure plug and is designed such that the weld penetrates completely through the header tank and into the closure plug. By achieving this, the fatigue life of the weld is significantly improved by placing the root of the weld (where there is a high variation due to weld penetration and defects) in compression. This also benefits manufacturing by providing a greater range of acceptable weld penetration (+/-0.020 compared to +/-0.010 ") for the design shown with respect to fig. 3. Further, the design improves manufacturing by facilitating weld penetration verification, as visual inspection can easily determine whether the weld penetrates into the plug feature.

To mitigate temperature exposure during the welding process, the placement of the weld 320 and the depth of the die pocket D1 are designed such that the thermal load is substantially isolated from critical components of the system (such as sensors, solder, and glass-to-metal seals). Given the manufacturability improvements provided by the D1 die pocket, the temperature may actually vary considerably during the welding process.

FIG. 6 is a graph of temperature as a function of pocket depth according to an embodiment of the present invention. It is desirable to maintain the glass temperature below 310 degrees celsius. As can be seen, this typically means that a pocket depth of at least 0.14 "will reach the desired maximum glass temperature.

Fig. 7 is an enlarged diagrammatic view of a header weld area showing a beneficial moment generated with respect to the header weld in accordance with an embodiment of the present invention. For capsule plug designs, the geometry is modified to accommodate the header and the ring, and fatigue life is improved by placing the header plug welds in the center of the cavity between the isolator plug and the header. Placing the assembly weld in the middle of the cavity during the pressure loading process creates a compressive load at the root of the weld, thereby creating a design that works even with incomplete weld penetration or voids or other non-ideal conditions at the root of the weld. By optimizing or improving the hole diameter and depth, a beneficial moment is induced, as shown in fig. 7. The beneficial moment is indicated by arrow 370, which places the root of the weld in compression. It is believed that this will reduce the stress of the weld at location 350 (as shown in fig. 5) in the case of high pressure and further improve fatigue life.

FIG. 8 is a graph of predicted failure period versus capsule plug recess depth in accordance with an embodiment of the present invention. FIG. 8 shows fatigue life (in terms of predicted fatigue cycle) of a header weld versus capsule plug recess depth. By adjusting the capsule plug recess depth, the fatigue life of the weld joint (typically the weakest link) can be significantly improved. In addition, the machined parts may be inspected prior to assembly for the presence of defects that may reduce the fatigue life of the machined parts.

Figure 9 is a cross-sectional view showing features of a biaxial support ring according to an embodiment of the present invention. One of the important elements of embodiments of the present invention is the use of a dual axis support ring 322. As shown, the dual-axis support ring 322 is assembled to the header tank 318 via a tapered press fit at interface 327, which ensures intimate contact between the dual-axis support ring 322 and the header tank 318. This type of fit adds additional compression to the glass seal and prevents the compressed area from bending, both of which enable higher burst pressures and longer fatigue life, as indicated at arrows 329. The illustrated embodiment uses a taper angle of 1/4 inches/foot, which is a standard taper angle and provides inherent self-locking. Self-locking joints are the result of a coefficient of friction between the surfaces that is greater than the retractive force required for separation. To achieve this, any angle less than 7 degrees is considered "self-locking". For final installation into the housing, the ring 322 includes threads 331 at its outer diameter for installing the enclosure assembly into the transmitter housing. Additionally, fig. 9 shows a dual-axis weld ring 322 having an edge break or hem 333 in the form of a radius configured to prevent the material from plowing over during assembly. In addition, the weld ring 322 also includes a relief portion 335 having an inner diameter that is larger than the outer diameter of the header tank 318. Interference from the tapered press fit causes inward compressive stresses that serve to achieve high pressure capability by counteracting the pressurized chambers of the structure and providing additional support for the glass-to-metal seal, thereby allowing higher pressures to be achieved. To prevent excessive glazing or vitrification assembly stresses, the ring interference is designed to keep the tensile stress of the glass below the maximum allowable tensile limit. Due to this taper, the dual-axis support ring 322 may also carry the load of the header tank 318 in the axial direction, further reducing the stress on the weld 320. The axial load is indicated by arrow 323.

FIG. 10 is a graph of FEA maximum principal stress versus ring interference according to an embodiment of the present invention. As shown, all loop interference values ranging from pre-stress to 0.0024 result in a FEA maximum principal stress that is less than the maximum allowable glazing stress/maximum allowable vitrifying assembly stress. Thus, it is believed that a useful interference fit can be achieved without damaging or otherwise affecting the glass. It should be noted that some embodiments described herein are described with respect to particular dimensions. Such descriptions are provided only to illustrate real-world examples and the relative sizes of components. Those skilled in the art will recognize that changes may be made in size and shape without departing from the spirit and scope of the invention.

In addition to providing support for the glass-to-metal seal, the dual-collar also benefits fatigue performance by counteracting bending of the header tank against internal pressure. This reduces alternating stresses in both the header tank 318 and the header tank weld 320. For additional benefit, the taper also allows for more efficient axial load sharing between the outer annular weld and the inner header weld, further providing fatigue life as described above.

FIG. 11 is a graph of FEA predicted fatigue life versus ring interference according to an embodiment of the present invention. As can be seen, with a 0.0024 ring interference, the predicted fatigue period for the weld exceeds 800000 cycles. Accordingly, it is believed that the embodiments of the invention set forth herein will not only provide higher operating pressures, but also more robust structures with improved functional lifetimes.

FIG. 12 is a graphical view illustrating the compressive preload resulting from annular weld contraction in accordance with an embodiment of the present invention. As set forth above, the embodiments described herein generally provide a biaxial ring welded to the isolator plug. In addition to protecting the axial strain of the header tank weld from internal pressure, welding the biaxial ring also enables the header tank and header tank weld to be compressively preloaded due to thermal contraction of the weld 330 during cooling after the welding process. This compressive preload on the weld 320 provides much more additional benefit for fatigue and high pressure retention. Fig. 12 illustrates a tensile load 400 on weld 330 caused by shrinkage during cooling of weld 330. This results in a compressive load 401 on the weld 320.

Because the dual collar is not a process wetted part, it is not affected by NACE requirements. As such, this component may be made of a high strength material, such as 17-4PH or Inconel 718. If 17-4PH is to be used, it is recommended that the H1150 heat treatment be performed to provide the highest levels of corrosion resistance, stress corrosion cracking resistance, and solderability. In addition to being able to withstand the hoop stresses caused by an interference fit, this differential hardness between the two mating surfaces keeps the press fit from wearing or falling out. To further reduce the risk of material falling out during installation, an edge break or hem 333 (shown in fig. 9), such as a radius or edge taper, is machined into the dual axial ring 322. It is believed that the press fit of the two soft materials (316L-316) can be affected by severe wear, resulting in a reduced and compromised interference fit. Thus, if the taper angles are slightly mismatched, this different durometer is beneficial because the softer material will elastically conform to the contours of the harder surface.

FIG. 13 is a schematic cross-sectional view showing standoff height as an indicator of joint interference according to an embodiment of the present invention. Another benefit of embodiments of the present invention is that joint interference can be easily inferred by measuring the standoff height at the taper junction. Preferably, using a plug gauge, the seat height (clearance) between the biaxial support ring and the isolator plug at the tapered joint can be determined. FIG. 13 is a diagrammatic view of a pedestal height measured between a dual axial ring 322 and isolator plug 314. With a standard taper of 1/4 inches/foot, the travel per 0.100 "of the ring is equal to 0.002" diameter interference. This allows the effective interference to be known a priori to provide an important metric of the design that can be used to determine whether the interference is within a desired range prior to installation of the assembly.

FIG. 14 is a table illustrating various burst ranges for the KSI aspect of interference ranging from 0.0014 "to 0.0028" in accordance with an embodiment of the invention. Embodiments of the present invention were tested to determine burst pressure relative to the difference in interference. As can be seen, the burst range exceeds 50KSI even for minimal interference.

FIG. 15 is a flow chart of a method of manufacturing a high pressure enclosure and a header tank according to an embodiment of the present invention. Method 500 begins at block 502, where an isolator plug, such as isolator plug 314 (shown in FIG. 4), is placed together with a header box, such as header box 318 (shown in FIG. 4). Next, at block 504, the isolator plug and header are welded together. This welding not only mechanically secures the isolator plug and header together, but also seals the interface therebetween. Once the header tank and the isolator plugs are welded together, the method 500 continues to block 506, where a two-axis support ring, such as ring 322 (shown in FIG. 4), is slid over the outer diameter of the header tank. As explained above, this interface is tapered to facilitate self-locking. In one embodiment, the tapered interface has a radial variation of 0.25 inches per 12 inches of axial variation. However, those skilled in the art will recognize that changes may be made to the taper angle without departing from the spirit and scope of the present invention. Furthermore, the biaxial support ring and the header tank may be made (via material selection and/or heat treatment) with different hardnesses from each other. Next, at block 507, the standoff is installed to ensure the necessary amount of interference. The weld ring is then pressed onto the header tank until the stand height drops to zero.

Next, at block 508, a bi-axial weld ring is welded to the isolator plug.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As set forth above, some embodiments have been described with respect to particular dimensions. Such descriptions are provided only to illustrate real-world examples and the relative sizes of components. Those skilled in the art will recognize that changes may be made in size and shape without departing from the spirit and scope of the invention.