Process pressure transmitter for hydrogen applications

Abstract

A process fluid pressure transmitter includes a pressure sensor body housing a pressure sensor having an electrical characteristic that varies in response to an applied pressure. The isolation membrane is configured to be exposed to a process fluid. A fill fluid fluidly couples the isolation membrane to the pressure sensor. The weld ring is welded to the isolation membrane at a first weld seam. A barrier metal is disposed on at least one surface of the barrier membrane such that the barrier metal extends over the first weld. The weld ring is welded to the pressure sensor body at a second weld spaced from the barrier metal.

Description

Technical Field

[0001] The present invention relates to a process pressure transmitter for hydrogen applications. Background Art

[0002] In many industrial processes, such as paper processing, petroleum refining, and coal processing, it is sometimes desirable to measure a parameter of the process, such as the pressure or level of a process fluid in a vessel, in order to control the process. A process pressure transmitter is typically configured to be exposed to a process fluid source and includes a structure, such as a sensing membrane, that deforms in response to the process fluid pressure. The deformation of the membrane is measured by a measurement circuit. This can be accomplished by evaluating a strain gauge mounted to the membrane, by sensing a change in capacitance from the membrane to the wall of the sensing chamber, or any other suitable technique.

[0003] The process fluid (to which the process pressure transmitter is exposed) may be corrosive and / or at high temperatures. For such applications, many process pressure transmitters include a deflectable isolation diaphragm that is configured to be directly exposed to the process fluid. On the opposite side of the deflectable isolation diaphragm, a substantially incompressible fill fluid transmits the movement of the deflectable isolation diaphragm to a discrete sensing diaphragm.

[0004] Process pressure transmitters face a challenge when the process fluid contains or is hydrogen. The size of the hydrogen molecule allows it to diffuse through thin metal membranes, such as isolation diaphragms, and can result in the accumulation of entrained hydrogen in the fill fluid of a process fluid pressure transmitter. When the process pressure is released, the gas dissolved in the fill fluid escapes from the solution and creates an observable offset or error in the process fluid pressure transmitter output.

[0005] Although some attempts have been made to reduce hydrogen diffusion through the isolation membrane by providing a gold plated portion on the surface of the membrane, such attempts have only achieved some success. As the process industry begins to provide solutions for the hydrogen industry where hydrogen pressures may be as high as 10,000 psi, a better solution is needed. Summary of the invention

[0006] A process pressure transmitter includes a pressure sensor body housing a pressure sensor having an electrical characteristic that changes in response to an applied pressure. An isolation diaphragm is configured to be exposed to a process fluid. A fill fluid fluidically couples the isolation diaphragm to the pressure sensor. A weld ring is welded to the isolation diaphragm at a first weld. A barrier metal is disposed on at least one surface of the isolation diaphragm such that the barrier metal extends over the first weld. The weld ring is welded to the pressure sensor body at a second weld spaced from the barrier metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1is a schematic diagram of a process pressure transmitter with which the embodiments described herein are particularly useful.

[0008] Figure 2 is a schematic cross-sectional view of a pressure sensor housing for a process pressure transmitter for which the embodiments described herein are particularly useful.

[0009] Figure 3 is a schematic diagram of an isolation diaphragm coupled to a weld ring according to one embodiment.

[0010] Figure 4 is a schematic diagram showing a spacer / solder ring subassembly after gold plating has been applied in accordance with an embodiment of the present invention.

[0011] Figure 5 is a schematic diagram of an improved gold plated isolator assembly welded to a pressure sensor module housing according to an embodiment of the present invention.

[0012] Figure 6 is a flow chart of a method of constructing a process pressure transmitter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] As described above, the emerging hydrogen market is creating a need for new process measurement solutions that are more robust to hydrogen intrusion. Under high hydrogen pressures, any area of ​​the diaphragm that does not include the gold plated portion becomes susceptible to hydrogen intrusion. However, the manufacturing process of process pressure transmitters using diaphragms typically requires welds to seal the diaphragm and connect the diaphragm to the transmitter. When welding is performed on a structure that has been gold plated, the weld may become a mixed metal weld. Gold contamination in the weld is undesirable for a variety of reasons. For example, a gold-contaminated weld will not meet NACE standards and may not meet ISO standards.

[0014] The Materials Protection and Performance Association provides standards and certifications for corrosion resistant structures and methods. The relevant standards for corrosion are NACE MR0103 and NACE MR0175. "NACE" compliance generally refers to compliance with these two standards. In terms of welding, NACE compliance does not generally include mixed metal welds. However, providing a process pressure transmitter that complies with NACE and can operate at high hydrogen pressures will provide significant benefits to the emerging hydrogen process market.

[0015] The embodiments described herein generally provide a process pressure transmitter suitable for high pressure hydrogen applications. In addition, although gold plating is used in various embodiments herein, NACE compliance is still maintained. Although the embodiments described herein will generally be described with reference to a coplanar process pressure transmitter, the embodiments are applicable to any process pressure transmitter that may be exposed to hydrogen.

[0016] Figure 1 A front view of an exemplary coplanar process pressure transmitter 100 is shown. The pressure transmitter 100 includes an electronics housing 101 that encloses electronic circuitry and a pressure sensor module housing 102 that houses an isolation 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 fitting 118. The flange adapter fitting 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 connected to a process loop 103 that powers the pressure transmitter 100 and provides communications (preferably bidirectional communications) for use in a process control system.

[0017] Figure 2 1 is a schematic cross-sectional view of a pressure sensor housing of a process pressure transmitter for which the embodiments described herein may be used. The pressure sensor module housing 102 includes an isolation diaphragm 110 that is welded directly to the pressure sensor module housing 102. The housing 102 also includes threaded bolt holes 112 in a standard pattern surrounding the isolation diaphragm 110. A differential pressure sensor 140 is located inside the pressure sensor module housing 102 and is connected to the isolation diaphragm 110 via a substantially incompressible fill fluid within tubes 142, 144. Note that although Figure 2 1, but other types of pressure sensors, including absolute pressure sensors or instrument pressure sensors, may be used in accordance with the embodiments described herein. The isolation diaphragm 110 is welded directly to the pressure sensor module housing 102. The circuit board 146 provides the circuitry associated with processing the electrical signals from the differential pressure sensor 140. The flat cable drum 148 contains a flat cable that provides electrical connections from the circuit board 146 to an electronics housing such as a Figure 1 Electrical connections for circuits in the housing 101) shown.

[0018] According to an embodiment of the present invention, the design constraints of each part of the coplanar pressure sensor module are considered separately and customized for specific needs. Although the overall assembly of the coplanar pressure sensor module according to an embodiment of the present invention may become more complex than existing designs, such an embodiment allows flexibility for different applications and the ability to reduce the cost of certain components while potentially adding greater structural integrity to other components.

[0019] Figure 3 205 is a schematic diagram of an isolation diaphragm coupled to a weld ring according to one embodiment. The isolation diaphragm 110, which may be constructed of any suitable material, is coupled to the weld ring 202 at a weld 205. Typically, 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 compatible with welding of the isolation diaphragm. In some embodiments, the weld ring 202 is also formed of stainless steel. The weld ring 202 typically includes an O-ring recess 204 that is configured to receive an elastomeric O-ring when the pressure sensor module housing 102 is coupled to the pressure flange 104. Figure 3 In the example shown, weld 204 is a continuous ring having a diameter of approximately 1.035 inches. Although specific dimensions are shown for the purpose of illustrating embodiments of the present invention, those skilled in the art will recognize that embodiments may be practiced with other dimensions. By providing a continuous ring, isolation diaphragm 110 is not only mechanically coupled to weld ring 202, but is also fluidically sealed with weld ring 202. When isolation diaphragm 110 is so coupled to weld ring 202, the isolator / weld ring subassembly is complete.

[0020] Figure 4is a schematic diagram showing an isolator / welding ring subassembly after a barrier material such as gold is applied. Although embodiments will be described with respect to barrier materials plated to the isolating membrane, it is clearly contemplated that other techniques for depositing barrier materials, such as physical vapor deposition or ion beam deposition, may be used. In the example shown, the gold-plated portion is represented by dashed lines 206, 208. As shown, the gold-plated portion is disposed on all process-wetted surfaces. In addition, in the example shown, the gold-plated portion has a diameter of about 1.075 inches. It can be seen that the gold-plated portion extends beyond the diameter of the weld 205. However, the gold-plated portions 206, 208 do not extend across the entire surface of the isolating membrane 110. The gold-plated portions 206, 208 are applied to substantially cover the entire isolator surface, and its attached welds are preferably on the inside and outside. Note that this structure is relatively easy to mask and plate. In addition, the gold coverage on the inside and outside of the isolating membrane provides improved scratch resistance, enhanced wear resistance, and can even reduce costs to a certain extent because the two surfaces of the isolating membrane are plated synchronously. This provides cost and performance advantages. Since both sides of the isolation diaphragm are plated synchronously, the growth rate of the overall plating thickness is twice that of the single-sided plating. This allows the coating of equal thickness to grow in half the time, thereby reducing costs by limiting the time in the plating bath. In addition, since the internal coating (i.e., the surface exposed to the filling fluid) is not directly exposed to the process fluid, the coating structure provides improved anti-scratch and anti-wear robustness. Finally, as shown in the figure, the gold-plated parts 206, 208 extend on the entire process wetted surface of the isolation diaphragm 110 (including the attachment weld 205 on its inner and outer sides). This coating on the attachment weld 205 effectively reduces the sensitivity of hydrogen embrittlement and the permeability of the attachment weld to hydrogen. Once the isolator assembly is plated, it is then welded to the pressure sensor module housing 102.

[0021] Figure 5 FIG. 2 is a schematic diagram of an improved gold-plated isolator assembly welded to a pressure sensor module housing according to an embodiment of the present invention. As shown, the welding ring 202 is welded to the pressure sensor module housing 102 at the weld 230. Figure 5 As shown, the inner diameter of the ring including weld 230 is approximately 1.115 inches. Figure 4 Compared to the maximum diameter of the gold plated portion shown (1.075 inches), it can be seen that weld 230 does not include any gold applied during the gold plating process. As such, the only materials melted in weld 230 are the material of weld ring 202, the material of isolation diaphragm 110, and the material of pressure sensor module housing 102. All of these materials can be specified so that the resulting weld is not a mixed metal weld. Therefore, even with a robust welded construction, NACE compliance can be maintained while still achieving significant hydrogen intrusion resistance by utilizing gold plating.

[0022] Figure 6 3 is a flow chart of a method of constructing a process pressure transmitter according to an embodiment of the present invention. Method 300 begins at block 302, where a weld ring is provided. Next, at block 304, an isolation diaphragm is provided. At block 306, the isolation diaphragm is welded to the weld ring to form a continuous sealing interface between the isolation diaphragm and the weld ring. Next, at block 308, a barrier metal such as gold is plated on the weld ring / isolator diaphragm subassembly. The plating preferably does not extend over the entire weld ring / isolator assembly, but must be applied to the isolation diaphragm weld (such as Figure 3 The process pressure transmitter is provided with a plurality of isolator assemblies, each of which ...

[0023] 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.

Claims

1. A process pressure transmitter, comprising: a pressure sensor body housing a pressure sensor having an electrical characteristic that changes in response to an applied pressure; an isolation diaphragm configured to be exposed to a process fluid; a fill fluid fluidly coupling the isolation diaphragm to the pressure sensor; a weld ring welded to the isolation diaphragm at a first weld; a barrier metal disposed on at least one surface of the isolation film, the barrier metal extending over the first weld; and Wherein the weld ring is welded to the pressure sensor body at a second weld seam spaced apart from the barrier metal.

2. The process pressure transmitter of claim 1, wherein: The barrier metal is gold.

3. The process pressure transmitter of claim 1, wherein: The barrier metal is plated on the isolation film.

4. The process pressure transmitter of claim 1, wherein: The barrier metal is disposed on both sides of the isolation film.

5. The process pressure transmitter of claim 4, wherein: The barrier metal is gold.

6. The process pressure transmitter of claim 1, wherein: The second weld is formed from a homogeneous metal.

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

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

9. The process pressure transmitter of claim 1, wherein: The pressure sensor is an absolute pressure sensor.

10. The process pressure transmitter of claim 1, wherein: The pressure sensor is an instrument pressure sensor.

11. The process pressure transmitter of claim 1 further comprising: an additional isolation diaphragm configured to be exposed to the process fluid; an additional volume of fill fluid fluidly coupling the additional isolation diaphragm to the pressure sensor; an additional weld ring welded to the additional isolation diaphragm at a third weld; a barrier metal plated to at least one surface of the additional isolation film, the barrier metal extending over the third weld; and Wherein, the additional weld ring is welded to the pressure sensor body at a fourth weld seam spaced apart from the barrier metal.

12. The process pressure transmitter of claim 11, wherein: The pressure sensor is a differential pressure sensor.

13. The process pressure transmitter of claim 12, wherein: The process fluid pressure transmitter is a co-planar process fluid pressure transmitter.

14. The process pressure transmitter of claim 1, wherein: The process fluid pressure transmitter complies with NACE standards.

15. The process pressure transmitter of claim 1, wherein: The barrier metal is selected based on the process fluid to which the isolation membrane is configured to be exposed.

16. A method of manufacturing a process pressure transmitter for servicing a process fluid containing hydrogen, the method comprising: Provide welding ring; providing an isolation diaphragm configured to be exposed to the process fluid; welding the isolation membrane to the weld ring at a first location; coating a barrier metal on the isolation film so that the barrier metal extends over the first position; and The weld ring is welded to a pressure sensor body of the process transmitter at a second location spaced apart from the barrier metal.

17. The method of claim 16, wherein: Coating the barrier metal on the isolation film includes plating gold onto the isolation film.

18. The method of claim 17, further comprising: Gold was plated onto both sides of the isolation membrane.

19. The method of claim 18, wherein: Both sides are plated simultaneously.

20. The method of claim 16, further comprising: Additional welding rings are provided; providing an additional isolation membrane configured to be exposed to the process fluid; welding the additional isolation membrane to the additional welding ring at a third location; coating a barrier metal on the additional isolation film so that the barrier metal extends over the third position; and The additional weld ring is welded to the pressure sensor body of the process fluid transmitter at a fourth location spaced apart from the barrier metal.

21. The method of claim 20, wherein: The process transmitter is a co-planar process fluid transmitter.

22. A pressure transducer, comprising: a pressure sensor having an electrical characteristic that changes in response to applied pressure; an isolation diaphragm configured to be exposed to a process fluid; a weld ring welded to the isolation diaphragm at a first weld; a barrier metal disposed on at least one surface of the isolation film, the barrier metal extending over the first weld; wherein the weld ring is welded to the pressure sensor body at a second weld spaced apart from the barrier metal; and Wherein, the isolation diaphragm is operably coupled to the pressure sensor.

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