Process pressure transmitter with polymer seals

Abstract

The process pressure transmitter system includes a process pressure transmitter housing (14) and a process pressure sensor (28) within the process pressure transmitter housing (14). A metal flange (17) is configured to be mounted to a process vessel (10) carrying a process fluid (16). An isolation diaphragm (25) is attached to the metal flange (17) and exposed to the process fluid (16) through an opening in the process vessel (10). The isolation diaphragm (25) comprises a polymer diaphragm bonded to the metal surface of the metal flange (17). A capillary passage carries filling fluid from the isolation diaphragm, thereby transmitting the process pressure to the pressure sensor (28).

Description

Technical Field

[0001] This invention relates to the process control industry. More specifically, this invention relates to a type of diaphragm or seal for connecting process control instruments to industrial processes. Background Technology

[0002] Some types of process control instruments, such as pressure transmitters, have pressure sensors fluidly connected to an isolation diaphragm via a filling fluid. The isolation diaphragm comprises components called a "remote seal" or "diaphragm seal" and isolates the pressure sensor from the corrosive process fluid being sensed. Pressure is transmitted from the isolation diaphragm to the sensor via the filling fluid, which is essentially incompressible and fills the cavities and capillaries on both sides (or through-holes in the case where the seal is directly mounted to the instrument). For remote seals, the tubing is typically flexible and can extend several meters. The process medium contacts the remote isolation diaphragm, which transmits the applied pressure to the pressure sensor housed within the transmitter housing.

[0003] Typically, any process-wetting portions of the diaphragm and remote seal are made of corrosion-resistant materials so that the process medium does not damage the diaphragm. It is also known in the art to provide a coating on the diaphragm to protect it from corrosion due to contact with the process fluid. However, there is a persistent need for improved diaphragm protection. Summary of the Invention

[0004] A process pressure transmitter system includes a process pressure transmitter housing and a process pressure sensor housed within the housing. A metal flange is configured to be mounted to a process vessel carrying a process fluid. An isolation diaphragm is attached to the metal flange and exposed to the process fluid through an opening in the process vessel. The isolation diaphragm comprises a polymer diaphragm bonded to the metal facet of the metal flange. A capillary passage carries filler fluid from the isolation diaphragm, thereby transmitting the process pressure to the pressure sensor.

[0005] The summary and abstract of this invention are provided in a simplified form to introduce the selection of concepts further described in the detailed embodiments below. The summary and abstract are not intended to identify key or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter. Attached Figure Description

[0006] Figure 1 This is a simplified schematic diagram illustrating a transmitter with a remote seal according to the present invention.

[0007] Figure 2 This is a simplified schematic diagram showing a pressure transmitter system including a pressure transmitter connected to a remote seal.

[0008] Figure 3A It is the existing technology of remote sealing components along the line in Figure 3B The side sectional view is taken from the line marked 3A-3A in the figure.

[0009] Figure 3B Is Figure 3A Bottom plan view of existing remote seal technology.

[0010] Figure 3C yes Figure 3A A top view of existing remote sealing technology.

[0011] Figure 4a and Figure 4b This is a side cross-sectional view showing a polymer film bonded to a metal flange.

[0012] Figure 5 This is a side sectional view showing the construction of a metal flange using a laser beam.

[0013] Figure 6 It is a side cross-sectional view of the polymer film connected to the metal flange.

[0014] Figure 7 It is a side sectional view of the extended flange seal (EFW) including the polymer protective element. Detailed Implementation

[0015] The present invention includes a polymer diaphragm for connecting a pressure transmitter to a process fluid. In a particular configuration, the polymer diaphragm is bonded to a metal flange that is connected to a process vessel, process piping, or other process component including the process fluid, such as a tank.

[0016] Figure 1 A remote seal 12 of a process variable transmitter 11 is shown. The remote seal 12 is connected to the transmitter diaphragm in a housing 14. The remote seal 12 includes a housing (metal flange) 17 and is configured to connect to the process fluid through an opening in the process vessel.

[0017] According to one embodiment, transmitter 11 measures the pressure of process medium 16. A remote seal 12 includes a thin, flexible diaphragm 18 that contacts the process medium 16. Seal 12 also includes a backplate 19, which, together with the diaphragm 18, defines a cavity 20. A capillary 22 connects the cavity 20 to a pressure sensor 28 disposed within transmitter housing 14, the connection being formed via a diaphragm 25 in the transmitter housing, and a sealed fluid system connecting the diaphragm 25 to the sensor 28. The sealed fluid system, as well as the cavity 20 and capillary 22, are filled with a suitable fluid for transmitting process pressure to the sensor 28. The fluid may include silicone, oil, glycerin and water, propylene glycol and water, or preferably any other suitable fluid that is substantially incompressible.

[0018] When process pressure is applied from process medium 16, diaphragm 18 moves fluid, thereby transmitting the measured pressure from remote seal 12 to pressure sensor 28 through a passage in plate 19 and through tube 22. The resulting pressure is applied to pressure sensor 28, which can be based on any pressure sensing technology including a capacitive pressure-sensitive element. For a capacitive sensor, the applied pressure causes the capacitance to change according to the pressure at medium 16. Sensor 28 can also operate on other known sensing principles, such as strain gauge technology, etc. In this embodiment, circuitry in transmitter housing 14 electronically converts the capacitance into a linear 4mA-20mA transmitter output signal on lead pair 30 relating to process pressure. Any suitable communication protocol can be used, including those in which digital information is modulated into a 4mA-20mA current. Communication protocols, Foundation Fieldbus, or Process Fieldbus communication protocols, etc. Process control loop 30 can also be implemented using wireless communication technology. An example of wireless communication technology is based on IEC 62591. Communication protocol.

[0019] Figure 2 This is a simplified block diagram showing a pressure transmitter system 10, in which a process pressure sensor 28 is positioned within a process pressure transmitter housing 14. Figure 2 As shown, an isolating diaphragm 25 is carried on the flange surface 80 of the housing 14. A first capillary passage 82 carries an isolating filler fluid and extends from the diaphragm 25 to the pressure sensor 28. A process diaphragm seal 18 is connected to the process fluid, and a second capillary passage 22 carries a second filler fluid and extends from the process seal diaphragm 18 to the isolating diaphragm 25. As pressure is applied to the diaphragm 18, the diaphragm 18 flexes. This causes pressure to be transmitted to the isolating diaphragm 25 via the second filler fluid. The isolating diaphragm 25 then flexes again, causing pressure to be transmitted to the filler fluid in the capillary passage 82. This can be sensed by the pressure sensor 28 according to known techniques. Transmitter electronics 88 are used to sense the applied pressure and communicate information relating to the applied pressure to another location.

[0020] Figure 3A This is a side sectional view of the remote seal 12. Figure 3B This is a bottom plan view of the remote seal 12 and Figure 3C This is a top view of the remote seal 12. The remote seal 12, referred to as a "flange-type flush design," includes a sealing housing (metal flange) 17. The remote seal 12 also includes a hydraulic fluid (filling fluid) filling port 54, an instrument connection 56, and a flexible diaphragm 18 joined by a coupling 60, described in more detail below. An annular surface 62 extending around the diaphragm 18 is provided. Bolt holes 64 are used to connect the housing 17 to, for example, a tank for filling process fluid or some other process vessel.

[0021] Typically, the housing 17 is made of stainless steel and has a thickness of approximately 1 inch. The housing 17 is machined in a manner to bond to a circular polymer diaphragm 18. The gasket surface 62 is also machined onto the housing 17.

[0022] As described in the background section, certain process fluids can damage isolation diaphragms such as diaphragm 18. For example, hydrofluoric acid (HF) and sodium hydroxide (NaOH) can cause corrosion of metal diaphragms commonly used in remote sealing applications. These diaphragms are typically made of sheet metal bonded to a metal body (or flange) by TIG welding, RSEW (resistance seam welding), or sintering. Many different types of metals are available, and the metal can be selected based on the specific process medium. However, many metals that are highly corrosion-resistant also exhibit reduced performance and continue to corrode over time. For example, Alloy 400 (an alloy of approximately 67% Ni and 23% Cu) is a cheaper metal resistant to hydrofluoric acid. However, even Alloy 400 will corrode, especially at higher temperatures, after extended corrosion. Other more expensive options include gold and platinum.

[0023] One existing technique for dealing with this corrosion is to use a polymer diaphragm assembly. The polymer diaphragm is sandwiched between two metal flanges and sealed with two O-rings. Bolts are then used to attach the flanges together and reinforce the O-ring seal. Oil is then filled into the area behind the diaphragm. However, the system is not removable, and the mechanical fastening and sealing structure is less reliable than welding techniques used with metal diaphragms.

[0024] Another existing technique uses a diaphragm cap made of a corrosion-resistant material placed above a metal diaphragm. The cap can be made of a fluoropolymer, such as PFA (perfluoroalkoxyalkane) or FEP (fluorinated ethylene propylene). The cap can be bonded to the metal diaphragm, for example, using grease. The cap serves to protect the metal diaphragm from corrosion by the process fluid. However, the cap reduces the diaphragm's sensitivity to pressure applied by the process fluid, which can lead to inaccurate measurements. Furthermore, the construction is unsuitable for vacuum measurements.

[0025] In one exemplary configuration, the present invention overcomes the disadvantages of the prior art described above by using a polymer diaphragm directly bonded to the metal flange of the seal. The polymer diaphragm can be attached to the metal housing using any suitable technique.

[0026] Figure 4a and Figure 4bThis is a cross-sectional view illustrating an exemplary technique for bonding a polymer sheet 18 to a metal flange 17. Because polymers have lower melting points than common metals, conventional welding techniques cannot be used to bond polymers to metals. Welding temperatures cause thermal decomposition of the polymer material. However, laser bonding methods can be performed. Figure 4a The illustration depicts a laser transmission method in which a laser beam 100 is guided through a polymer diaphragm 18 and toward a metal flange 17. In this configuration, the polymer diaphragm must be optically transparent enough to the wavelength of the applied laser beam 100 so that the metal flange 17 absorbs a significant amount of energy from the laser beam 100. The laser beam 100 thus passes through the polymer diaphragm and heats the metal flange 17. The polymer diaphragm 18 is therefore heated and melted in the region where the laser beam 100 is guided, resulting in the formation of a weld or joint 102. Figure 4b The illustration shows the relevant configuration of laser beam 100 applied to metal flange 17. This provides a thermally conductive connection for the laser beam 100 to heat the rear side of metal flange 17. The polymer film 18 is heated and melted by means of the thermal conduction that leads to the formation of bonding member 102. This bonding method is suitable for polymer film 18 that is opaque to laser beam 100. Additionally, flange 17 should be thin enough to allow for more precise heating ("focusing" of the heating) of the interface between flange 17 and film 18.

[0027] To facilitate the bonding of the polymer film 18 to the metal flange 17, the surface of the metal flange 17 can undergo surface fabrication. Studies have shown that appropriate microfabrication of the metal surface can lead to improved shear strength when the metal surface is bonded to the polymer material. Furthermore, polymer-to-metal overlay bonding is typically impossible without any surface treatment. Lasers can be used to generate microstructures on the metal surface.

[0028] Figure 5 This is a side cross-sectional view of a metal flange 17 pre-constructed by a laser beam 106 applied to its surface 108. The applied laser beam 106 causes sublimation and melting of surface 108, resulting in material removal and the formation of a hole 110 in surface 108. This process is repeated in the bonding area on surface 108. This pre-construction allows the bonding to form with a bonding strength within the strength range of the polymer material used to form the diaphragm 18. With this construction performed on the surface 108 of the metal flange 17, the polymer diaphragm 18 can be bonded by means of laser bonding, such as described above. Other bonding techniques can also be used, such as ultrasonic-based bonding and induction-based bonding techniques. For example, this pre-construction can be performed using a TruMicro 7050 or 7240 available from CT Farmington's TruMicro 7050 or 7240.

[0029] Figure 6This is a side sectional view showing the connection between the polymer diaphragm 18 and the metal flange 17, representing the remote seal 12. Figure 6 As shown, a polymer film 18 extends over a metal flange 17 and forms a pad surface region 120. A laser-formed and connected region 122 is formed on the surface of the metal flange 17. In this region, the polymer film 18 is bonded to the metal flange 17.

[0030] The polymer diaphragm 18 can be formed using any forming technique, including vacuum forming and injection molding. This is in contrast to metal diaphragms, which can require complex forming dyes and applied mechanical forming pressures. This can lead to stress concentration and cause metal diaphragms to rupture. Additionally, in one configuration, the polymer diaphragm 18 has a thickness that varies throughout its diameter; for example, the diaphragm 18 can be configured to be thinner in a central region to increase sensitivity to applied pressure and thicker in the pad surface region 120 to provide additional strength. This configuration is difficult to manufacture using techniques used to form metal diaphragms.

[0031] In one configuration, diaphragm 18 is formed of multiple layers. These layers can be used to reduce corrosion and prevent process fluids from penetrating the diaphragm or to provide other desired properties. Exemplary barrier polymers include EVOH (vinyl alcohol), LCP (liquid crystal polymer), PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PVDC (polyvinylidene chloride), etc. These materials can be laminated onto the raw polymer / plastic material, giving diaphragm 18 a multilayer composite.

[0032] In another exemplary configuration, membrane 18 includes a lower metal layer bonded to the polymer layer. For example, the lower metal layer may include gold or other metals and may be used to reduce hydrogen permeation through the membrane. Any suitable bonding technique may be used in this configuration, including, for example, sputtering the metal layer onto the polymer layer.

[0033] This invention is also applicable to other sealing structures. For example, Figure 7 An extended flange seal (EFS) 150 is shown, having a flange 152 carrying an extension portion 154. A diaphragm 156 is positioned at the distal end of the extension portion and applies pressure via a filling fluid carried in a capillary 158. This can be applied to a pressure sensor as described above. In this configuration, a polymer guard 160 can be bonded to the metal forming the extended flange seal 150. This bonding can occur anywhere along the inner surfaces of the extension portion 154 and the flange 152. In one configuration, a polymer diaphragm 156 as described above is used. In another exemplary configuration, a metal diaphragm 156 with a polymer coating bonded thereon is used.

[0034] While the invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the invention. The remote seal can be any construction other than those specifically illustrated herein. Examples include flange seal types such as flush flange seals, extended flange seals, or disc seals. Other constructions include threaded seals (RTW), pipe fitting seals, chemical T-shaped seals, threaded pipe mounting seals, saddle and overflow seals, etc. The capillary passage 22 can be extended, such as... Figure 1 As shown, or in another exemplary configuration, it can be relatively short, thereby allowing the transmitter to be directly mounted to the seal. The polymer diaphragm improves the seal's corrosion resistance. In one configuration, a remote seal with a polymer diaphragm welded thereon can be mounted as a single component, eliminating the need for internal mechanical fastening and sealing structures. This configuration also improves sensitivity to applied pressure signals and can be used for vacuum measurements. In one configuration, the metal flange is formed of stainless steel. The polymer diaphragm may include coatings on one or both of its sides. Depending on desired characteristics, such as providing a barrier or additional protection for process fluids, the coating may be on either side. The coating may be metallic or non-metallic. In one configuration, a diamond-like carbon (DLC) coating is disposed on the polymer diaphragm. The diaphragm configurations discussed herein can be used in remote sealing configurations or can be used to provide an isolating diaphragm on a pressure transmitter.

Claims

1. A process pressure transmitter system, comprising: Process pressure transmitter housing; A process pressure sensor housed within a process pressure transmitter. A metal flange, the metal flange being configured to be mounted on a process vessel carrying process fluid; and An isolation diaphragm is attached to a metal flange and exposed to process fluid through an opening in a process vessel. The isolation diaphragm includes a polymer diaphragm pad surface area on a constructed connection region bonded to the metal surface of the metal flange. A capillary passage carrying filling fluid from a diaphragm to transmit process pressure to a pressure sensor. The metal flange is pre-constructed using a laser beam applied to its metal surface, and a hole is formed in the metal surface through sublimation and melting of the metal surface and the resulting material removal. In the case of the pre-construction process, the polymer film is bonded to the metal surface of the metal flange, and the bonding strength between the polymer film and the metal surface is within the strength range of the polymer material used to form the polymer film.

2. The process pressure transmitter system according to claim 1, wherein: The metal flange includes a remote seal.

3. The process pressure transmitter system according to claim 1, wherein: The polymer film is welded to the metal surface of the metal flange.

4. The process pressure transmitter system according to claim 1, wherein: The polymer film is bonded to the metal surface using laser bonding.

5. The process pressure transmitter system according to claim 4, wherein: Laser bonding includes laser transmission bonding.

6. The process pressure transmitter system according to claim 4, wherein: Laser bonding includes laser thermal conduction bonding.

7. The process pressure transmitter system according to claim 1, wherein: The polymer film is bonded to the metal surface of the metal flange by ultrasonic bonding.

8. The process pressure transmitter system according to claim 1, wherein: The polymer film is bonded to the metal surface of the metal flange through inductive bonding.

9. The process pressure transmitter system according to claim 1, wherein: The metal facet of the metal flange includes a structural region configured to promote bonding between the polymer film and the metal facet.

10. The process pressure transmitter system according to claim 9, wherein: The constructed regions are created through microstructural processing.

11. The process pressure transmitter system according to claim 10, wherein: Microstructure processing includes laser processing.

12. The process pressure transmitter system according to claim 9, wherein: The constructed region includes the laser constructed region.

13. The process pressure transmitter system according to claim 12, wherein: Laser structures include microstructures.

14. The process pressure transmitter system according to claim 1, wherein: The polymer film includes a liner surface area.

15. The process pressure transmitter system according to claim 1, wherein: The polymer film has a varying thickness.

16. The process pressure transmitter system according to claim 15, wherein: The polymer membrane is thinner near the central region and thicker near the edge region.

17. The process pressure transmitter system according to claim 16, wherein: Polymer films include laminated polymer films.

18. The process pressure transmitter system according to claim 17, wherein: Polymer films include multilayer composite films.

19. The process pressure transmitter system according to claim 1, wherein: The polymer film is coated with a metal film.

20. The process pressure transmitter system according to claim 1, wherein: A metal film is coated onto at least one side of a polymer film.

21. The process pressure transmitter system according to claim 19, wherein: The metal film includes a sputtered layer.

22. The process pressure transmitter system according to claim 19, wherein: Metal films include gold.

23. The process pressure transmitter system according to claim 1, wherein: The polymer film includes a barrier layer.

24. The process pressure transmitter system according to claim 1, wherein: The filling fluid transmits process pressure to a second diaphragm connected to a pressure sensor via a second filling fluid.

25. A method for connecting a process pressure transmitter to the pressure of an industrial process fluid, comprising: A metal flange is obtained that is configured to be attached to a process container, the metal flange including a configured connection region; Obtain a polymer film with a padding surface area; The pad surface region of the polymer film is connected to the constructed connection region of the metal flange by bonding the polymer film to the metal surface of the metal flange; The pressure of the process fluid carried in the process vessel is applied to the polymer membrane; The pressure applied to the polymer diaphragm is connected to a pressure sensor using a capillary pathway; and Process pressure is measured using a pressure sensor. The metal flange is pre-constructed using a laser beam applied to its metal surface, and a hole is formed in the metal surface through sublimation and melting of the metal surface and the resulting material removal. In the case of the pre-construction process, the polymer film is bonded to the metal surface of the metal flange, and the bonding strength between the polymer film and the metal surface is within the strength range of the polymer material used to form the polymer film.

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