Process pressure transmitter for hydrogen applications

Abstract

The process fluid pressure transmitter (100) includes a pressure sensor body (102) which includes a pressure sensor (140) having electrical properties that change in response to the applied pressure. An isolation diaphragm (110) is configured to be exposed to the process fluid. The filling fluid fluidically couples the isolation diaphragm (110) to the pressure sensor (140). A welding ring (202) is welded to the isolation diaphragm (110) at a first weld (205). The barrier metals (206, 208) are positioned on at least one surface of the isolation diaphragm (110) such that they extend across the first weld (205). The welding ring (202) is welded to the pressure sensor body (102) at a second weld (230) spaced apart from the barrier metals (206, 208).

Description

Background Art

[0003]

[0001] In many industrial processes such as papermaking, petroleum refining, and coal processing, it may be desirable to measure process parameters, such as the level or pressure of a process fluid within a vessel, in order to control the process. A process pressure transmitter is generally configured to be exposed to a source of process fluid and includes a structure such as a sensing diaphragm that deforms in response to the pressure of the process fluid. The deformation of the diaphragm is measured by a measurement circuit. This can be done by evaluating strain gauges attached to the diaphragm, by sensing a change in capacitance from the diaphragm to the wall of the sensing chamber, or by any other suitable technique.

[0002] The process fluid to which a process pressure transmitter is exposed can be corrosive and / or at a high temperature. For such applications, many process pressure transmitters include a deflectable isolation diaphragm configured to be directly exposed to the process fluid. On the opposite side of the deflectable isolation diaphragm, a substantially incompressible filling fluid transmits the movement of the deflectable isolation diaphragm to another sensing diaphragm.

[0003] One problem with process pressure transmitters occurs when the process fluid contains hydrogen or is hydrogen. Due to the size of hydrogen molecules, hydrogen molecules can diffuse through thin metal films such as isolation diaphragms, causing the accumulation of hydrogen entrained in the filling fluid of the process fluid pressure transmitter. When the process pressure is released, the gas dissolved in the filling fluid comes out of solution, creating observable shifts or errors in the output of the process fluid pressure transmitter.

[0004] Several attempts have been made to reduce hydrogen diffusion across isolation diaphragms by providing gold plating to the surface of the diaphragm, but these attempts have only achieved limited success. As process industries begin to offer solutions for the hydrogen industry where hydrogen pressures can reach 10,000 psi, better solutions are needed. [Overview of the project]

[0005] The process pressure transmitter includes a pressure sensor body containing a pressure sensor having electrical properties that change in response to the applied pressure. An isolation diaphragm is configured to be exposed to a process fluid. The filling fluid fluidically couples the isolation diaphragm to the pressure sensor. A welding ring is welded to the isolation diaphragm at a first weld. A barrier metal is placed on at least one surface of the isolation diaphragm such that the barrier metal extends across the first weld. The welding ring is welded to the pressure sensor body at a second weld spaced apart from the barrier metal. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a schematic diagram of a process pressure transmitter in which the embodiments described herein are particularly useful. [Figure 2] Figure 2 is a schematic cross-sectional view of a pressure sensor housing of a process pressure transmitter in which the embodiments described herein are useful. [Figure 3] Figure 3 is a schematic diagram of an isolation diaphragm coupled to a welding ring according to one embodiment. [Figure 4] Figure 4 is a schematic diagram showing an isolator / welding ring subassembly after gold plating has been applied, according to one embodiment of the present invention. [Figure 5] Figure 5 is a schematic diagram of an improved gold-plated isolator assembly welded to a pressure sensor module housing according to one embodiment of the present invention. [Figure 6] Figure 6 is a flowchart illustrating a method for constructing a process pressure transmitter according to one embodiment of the present invention. [Modes for carrying out the invention]

[0007] Detailed description of exemplary embodiments As mentioned above, the emerging hydrogen market is creating a need for new process measurement solutions that are more robust against hydrogen intrusion. At high hydrogen pressures, any area of ​​an isolation diaphragm that does not contain gold plating becomes susceptible to hydrogen intrusion. However, the manufacturing process for process pressure transmitters using isolation diaphragms generally requires welding to seal and bond the isolation diaphragm to the transmitter. When welding is performed on a structure that is already gold-plated, the weld may become a mixed-metal weld. Gold contamination in welding is undesirable for several reasons. For example, a gold-contaminated weld will not meet NACE standards and may therefore not meet ISO standards.

[0008] The Materials Protection and Performance Association provides standards and certifications for corrosion-resistant structures and methods. The relevant corrosion standards are NACE MR0103 and NACE MR0175. "NACE" compliance is generally considered to be compliance with these two standards. Regarding welding, NACE compliance generally excludes mixed-metal welding. However, providing a process pressure transmitter that is NACE compliant and capable of operating at high hydrogen pressures would offer significant advantages in the emerging hydrogen process market.

[0009] The embodiments described herein generally provide process pressure transmitters suitable for high-pressure hydrogen applications. Furthermore, in various embodiments herein, gold plating is used while maintaining NACE compliance. Although the embodiments described herein generally relate to coplane process pressure transmitters, the embodiments are applicable to any process pressure transmitter that may be exposed to hydrogen.

[0010] Figure 1 shows a front view of an exemplary coplanar process pressure transmitter 100. The pressure transmitter 100 includes an electronic housing 101 that encloses electronic circuitry and a pressure sensor module housing 102 that houses an isolator diaphragm, a pressure sensor and associated sensor circuitry. The pressure sensor module housing 102 is bolted to a pressure flange 104 by bolts 105. The bolts 105 also pass through a flange adapter union 118. The flange adapter union 118 has a threaded inlet that can be connected to a threaded process pipe (not shown). The pressure flange 104 provides one or more process fluid pressures to the transmitter 100 for pressure measurement. The pressure transmitter 100 is energized and connected to a process loop 103 that provides communication (preferably bidirectional communication) for use in a process control system.

[0011] Figure 2 is a schematic cross-sectional view of a pressure sensor housing of a process pressure transmitter in which the embodiments described herein are useful. The pressure sensor module housing 102 includes an isolator diaphragm 110 welded directly to the pressure sensor module housing 102. The housing 102 also includes threaded bolt holes 112 in a standard pattern around the isolator diaphragm 110. A differential pressure sensor 140 is located inside the pressure sensor module housing 102 and connected to the isolator diaphragm 110 via a substantially incompressible filling fluid in tubes 142, 144. While a differential pressure sensor 140 is shown in Figure 2, it should be noted that other types of pressure sensors, including absolute pressure sensors or gauge pressure sensors, may be used according to the embodiments described herein. The isolator diaphragm 110 is welded directly to the pressure sensor module housing 102. A circuit board 146 provides the circuitry related to processing the electrical signal from the differential pressure sensor 140. The flat cable reel 148 houses a flat cable that provides an electrical connection from the circuit board 146 to the circuit in the electronic housing (for example, the housing 101 shown in Figure 1).

[0012] In embodiments of the present invention, the design constraints of each part of the coplanar pressure sensor module are considered individually and adjusted to specific needs. While the overall assembly of the coplanar pressure sensor module according to embodiments of the present invention may be more complex than conventional designs, such embodiments add greater structural integrity to other components, while allowing for flexibility to different applications and enabling the reduction of the cost of certain components.

[0013] Figure 3 is a schematic diagram of an isolation diaphragm coupled to a weld ring according to one embodiment. The isolation diaphragm 110 can be made of any suitable material and is coupled to the weld ring 202 at a weld 205. Generally, the isolation diaphragm 110 is a metal diaphragm formed of stainless steel or some other suitable alloy. Similarly, the weld ring 202 is also formed of metal and is suitable for welding the isolation diaphragm. In some embodiments, the weld ring 202 is also formed of stainless steel. The weld ring 202 generally includes an O-ring recess 204 configured to receive an elastic O-ring when the pressure sensor module housing 102 is coupled to the pressure flange 104. In the example shown in Figure 3, the weld 204 is a continuous ring having a diameter of approximately 1.035 inches. While specific dimensions are shown to illustrate embodiments of the present invention, those skilled in the art will recognize that embodiments can be similarly implemented with other dimensions. By providing a continuous ring, the isolator diaphragm 110 is not only mechanically coupled to the weld ring 202 but is also fluidly sealed to them. When the isolator diaphragm 110 is coupled to the welding ring 202 in this manner, the isolator / welding ring subassembly is completed.

[0014] Figure 4 is a schematic diagram showing the isolator / weld ring subassembly after a barrier material such as gold has been applied. While the embodiment describes the barrier material to be plated onto the isolation diaphragm, it is explicitly intended that other techniques for depositing the barrier material, such as physical vapor deposition or ion beam deposition, may be used. In the illustrated example, the gold plating is represented by dashed lines 206, 208. As shown, the gold plating is applied to all process wet surfaces. Furthermore, in the illustrated example, the gold plating has a diameter of approximately 1.075 inches. As can be seen, the gold plating extends beyond the diameter of the weld 205. However, the gold plating 206, 208 does not extend across the entire surface of the isolator diaphragm 110. The gold plating 206, 208 is applied to substantially cover the entire isolator surface and, preferably, to cover its mounting weld both internally and externally. It should be noted that this structure is relatively easy to mask and plate.

[0015] Furthermore, the gold plating on both the inside and outside of the isolation diaphragm provides improved scratch resistance and enhanced wear resistance, and even reduces costs by plating both sides of the isolation diaphragm simultaneously. This offers advantages in both cost and performance. Because both sides of the isolation diaphragm are plated simultaneously, the overall plating thickness grows at twice the rate of single-sided plating. This allows for the growth of plating of equivalent thickness in half the time, reducing costs by limiting the plating bath time. In addition, the plated structure provides improved resistance to scratches and wear because the inner plating (i.e., the surface exposed to the filling fluid) is not directly exposed to the process fluid. Finally, as shown, the gold plating 206, 208 extends across the entire process wet surface of the isolation diaphragm 110, including the inner and outer mounting welds 205. The plating on these mounting welds 205 effectively reduces the susceptibility to hydrogen embrittlement and hydrogen permeation of the mounting welds. Once plated, the isolator assembly is then welded to the pressure sensor module housing 102.

[0016] Figure 5 is a schematic diagram of an improved gold-plated isolator assembly welded to a pressure sensor module housing according to one embodiment of the present invention. As shown, the weld ring 202 is welded to the pressure sensor module housing 102 at the weld 230. As shown in Figure 5, the inner diameter of the ring constituting the weld 230 is approximately 1.115 inches. In contrast to the maximum diameter of the gold plating shown in Figure 4 (1.075 inches), it can be seen that the weld 230 contains no gold at all that is applied during the gold plating process. Thus, the only materials welded to the weld 230 are the material of the weld ring 202, the material of the isolation diaphragm 110, and the material of the pressure sensor module housing 102. All of these materials can be specified so that the resulting weld is not a mixed-metal weld. Thus, even with a strong welded structure, NACE compliance can be maintained, while the use of gold plating still allows for significant hydrogen ingress resistance.

[0017] Figure 6 is a flowchart of a method for constructing a process pressure transmitter according to one embodiment of the present invention. Method 300 begins in block 302, where a weld ring is provided. Next, in block 304, an isolation diaphragm is provided. In block 306, the isolation diaphragm is welded to the weld ring to form a continuous sealed interface between the isolation diaphragm and the weld ring. Next, in block 308, a barrier metal such as gold is plated over the weld ring / isolation diaphragm subassembly. This plating should preferably not extend over the entire weld ring / isolation diaphragm assembly but over the isolation diaphragm weld (such as the weld 205 shown in Figure 3). The plating may be on one side, as shown in block 310, or on both sides for special protection against hydrogen ingress, as shown in block 312. Next, in block 314, the plated isolation diaphragm / weld ring subassembly is welded to the pressure sensor module housing. This weld is performed so that there is a homogeneous metal weld in the areas where no plating material is present. Therefore, welding does not introduce mixed metals, thus facilitating NACE compliance. Furthermore, in embodiments where the pressure transmitter is a coplanar pressure transmitter, method 300 may be repeated for a second isolator assembly for a process pressure transmitter.

Claims

1. A pressure sensor body including a pressure sensor having electrical properties that change in response to applied pressure, An isolation diaphragm configured to be exposed to process fluid, The isolation diaphragm is fluidically coupled to the pressure sensor with a filling fluid, A welding ring welded to the isolation diaphragm at the first weld, The isolation diaphragm includes a barrier metal disposed on at least one surface and extending across the first weld, A process pressure transmitter in which the welding ring is welded to the pressure sensor body at a second weld spaced apart from the barrier metal.

2. The process pressure transmitter according to claim 1, wherein the barrier metal is gold.

3. The process pressure transmitter according to claim 1, wherein the barrier metal is plated onto the isolation diaphragm.

4. The process pressure transmitter according to claim 1, wherein the barrier metal is arranged on both sides of the isolation diaphragm.

5. The process pressure transmitter according to claim 4, wherein the barrier metal is gold.

6. The process pressure transmitter according to claim 1, wherein the second welded portion is formed from a homogeneous metal.

7. The process pressure transmitter according to claim 6, wherein the homogeneous metal is different from the barrier metal.

8. The process pressure transmitter according to claim 6, wherein the homogeneous metal is the same metal used for the pressure sensor body, the isolation diaphragm, and the welding ring.

9. The process pressure transmitter according to claim 1, wherein the pressure sensor is an absolute pressure sensor.

10. The process pressure transmitter according to claim 1, wherein the pressure sensor is a gauge pressure sensor.

11. An additional isolation diaphragm configured to be exposed to the process fluid, The additional volume of the filling fluid that fluidly connects the additional isolation diaphragm to the pressure sensor, An additional welded ring is welded to the additional isolation diaphragm at the third weld, A barrier metal plated on at least one surface of the additional isolation diaphragm and extending across the third welded portion The process pressure transmitter according to claim 1, further comprising the additional welding ring being welded to the pressure sensor body at a fourth weld spaced apart from the barrier metal.

12. The process pressure transmitter according to claim 11, wherein the pressure sensor is a differential pressure sensor.

13. The process pressure transmitter according to claim 12, wherein the process fluid pressure transmitter is a coplanar process fluid pressure transmitter.

14. The process fluid pressure transmitter according to claim 1, wherein the process fluid pressure transmitter is NACE compliant.

15. The process pressure transmitter according to claim 1, wherein the barrier metal is selected based on the process fluid to which the isolation diaphragm is exposed.

16. A method for manufacturing a process pressure transmitter useful for process fluids containing hydrogen, wherein the method is: To provide a welded ring, To provide an isolator diaphragm configured to be exposed to the aforementioned process fluid, The isolator diaphragm is welded to the welding ring at the first position, The barrier metal is covered over the isolator diaphragm such that the barrier metal extends over the first position, A method comprising welding the welding ring to the pressure sensor body of the process transmitter at a second position spaced apart from the barrier metal.

17. The method according to claim 16, wherein coating the isolator diaphragm with the barrier metal includes gold plating the isolator diaphragm.

18. The method according to claim 17, further comprising gold plating both sides of the isolator diaphragm.

19. The method according to claim 18, wherein both sides are plated simultaneously.

20. To provide additional welding rings, To provide an additional isolator diaphragm configured to be exposed to the process fluid, The additional isolator diaphragm is welded to the additional welding ring at the third position, The barrier metal is covered over the additional isolator diaphragm such that the barrier metal extends over the third position, The method according to claim 16, further comprising welding the additional welding ring to the pressure sensor body of the process fluid transmitter at a fourth position spaced apart from the barrier metal.

21. The method according to claim 20, wherein the process transmitter is a coplanar process fluid transmitter.

22. A pressure sensor having electrical properties that change in response to the applied pressure, An isolation diaphragm configured to be exposed to process fluid, A welding ring welded to the isolation diaphragm at the first weld, A barrier metal disposed on at least one surface of the isolation diaphragm and extending across the first weld, The welding ring is welded to the pressure sensor body at a second weld spaced apart from the barrier metal. A pressure transmitter in which the isolation diaphragm is operably coupled to the pressure sensor.

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