Underwater Multivariable Transmitter

Abstract

A multivariable transmitter (150) is provided for measuring multiple process fluid variables. The multivariable transmitter (150) includes a metallic housing (185) constructed from a material suitable for exposure to corrosive substances such as seawater. The differential pressure sensor (166) is disposed within a metal housing (185). Line pressure sensors (187, 189) are also located within the metal housing (185). The measurement circuit (174) is operatively connected to the differential pressure sensor (166) and the line pressure sensors (187, 189) and provides differential pressure and line pressure outputs. The temperature probe (182) has a sheath (188) constructed of a material suitable for exposure to corrosive substances. The temperature probe (182) is electrically connected to the circuitry within the metal housing (185) and physically connected to the metal housing (185) via a high pressure connection (186).

Description

Technical Field

[0001] Background Industrial process control systems are used to monitor and control industrial processes that produce or transfer fluids and the like. In such systems, it is generally important to measure "process variables" such as temperature, pressure, flow rate, etc. A process variable transmitter is used to measure such a process variable and transmit information related to the measured process variable to a central location such as a central control room.

[0002] A process variable transmitter generally includes or is connected to a transducer or sensor that responds to the process variable. A process variable generally refers to a physical or chemical state of a material or a conversion of energy. Examples of process variables include pressure, temperature, flow rate, conductivity, pH, and other characteristics. Pressure is considered a basic process variable that can be used to measure flow rate, level, and even temperature.

[0003] To measure the flow of a fluid, it is often necessary to determine a number of process variables such as the process fluid temperature, the process fluid static pressure or line pressure, and the differential pressure of the process fluid passing through a partial obstruction such as an orifice plate. In such cases, a multivariable transmitter is generally used to measure and monitor multiple process variables in order to provide a calculated parameter such as the flow of the process fluid.

[0004] Multivariable process fluid transmitters generally include, in addition to a differential pressure sensor, a line pressure sensor and / or a process fluid temperature sensor. The differential pressure sensor responds to the difference in pressure between two process fluid inputs. The line pressure sensor responds to the absolute or gauge pressure of one of the fluid inputs. The process fluid temperature sensor responds to the temperature of the process fluid in terms of electrical indicators such as voltage or resistance related to the temperature of the process fluid. Multivariable process fluid transmitters are used in a variety of flow measurement applications, including, but not limited to, single-phase flow meters, multiphase flow meters, and wet gas flow meters.

[0005] Single-phase flow meters measure any type of single-fluid system, such as oil, water, chemical injection fluids, etc. Generally, these applications only include a differential pressure sensor, but by incorporating a multivariable transmitter, fully compensated flow measurement (flow measurement compensated for density differences driven by static pressure or temperature changes) becomes possible. Multiphase flow meters measure the flow rate of one or more process fluids of different phases (i.e., saturated steam / water, etc.). Wet gas flow meters are flow meters used to measure combinations of natural gas and water. These flow meters can use different primary elements from multiphase flow meters, but still use differential pressure measurements combined with static pressure and temperature measurements.

[0006] High static pressure environments, such as those in subsea applications, can pose significant challenges to process fluid transmitters. In such environments, when measuring multiphase flow or other similar measurements that require multiple process variables, multiple process fluid transmitters are needed. Providing such transmitters requires considerable cost and complexity. For example, subsea multiphase flow meters generally incorporate many sensor inputs. The three main sensor inputs for measuring the flow rate of a process fluid are differential pressure (DP), line pressure (LP), and temperature. These three sensor inputs are generally provided by two different devices: a differential pressure transmitter and a pressure-temperature (PT) transmitter. The differential pressure transmitter is generally connected to the flow meter using two flange connections, and the PT transmitter is connected to the flow meter using another flange connection. These flanges are large in order to operate under extreme process pressures or the collapse pressures of subsea environments. For example, the flanges are very large and heavy, and are a driving factor in determining the final size of the multiphase flow meter.

[0007] Since differential pressure and process temperature are important inputs for flow rate calculations, the subsea process industry has generally needed to make these redundant measurements. This is at least partially due to the cost and complexity of equipment maintenance in subsea environments. Therefore, redundant DP measurements are taken from two separate transmitters. However, PT transmitters generally have redundancy by using a pair of temperature sensors. Such a device is referred to as a dual PT device or a PTPT device. It should be noted that the embodiments are generally described with respect to subsea multiphase flow meters, but the embodiments are also applicable to other types of flow meters. SUMMARY OF THE INVENTION

[0008] Summary A multivariable transmitter is provided for measuring variables of a plurality of process fluids. The multivariable transmitter includes a metal housing constructed from a material suitable for exposure to corrosive substances. A differential pressure sensor is disposed within the metal housing. A line pressure sensor is also disposed within the metal housing. A measurement circuit is operably connected to the differential pressure sensor and the line pressure sensor and provides outputs of differential pressure and line pressure. A temperature probe has a sheath made of a material suitable for exposure to corrosive substances. The temperature probe is electrically connected to a circuit within the metal housing and physically connected to the metal housing via a high-pressure connection.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] FIG. 1 is a schematic diagram of a known subsea multiphase flowmeter system 100, which generally includes a flowmeter calculator 102 communicatively connected to a pair of differential pressure transmitters, one of which is shown as reference numeral 104, and a PT or PT / PT transmitter as shown by reference numeral 106. The flow conduit through which the process fluid flows is shown in partial cross-section as reference numeral 108. Each differential pressure transmitter 104 is connected to a pair of remote seal flanges 110, 112. Similar to the PT transmitter, each of the two differential pressure transmitters also has the necessary mounting flanges. Further, conduit 114 is used to electrically connect the differential pressure and PT transmitters to the flowmeter calculator 102. Conduit 114 generally requires shaping and welding for wiring wires to each process device. To operate at the collapse pressure of the subsea environment, the flanges required for the flowmeter 100 are relatively large. For example, each process penetration requires a large API type 6B or 6BX flange.

[0011] According to embodiments provided herein, a subsea multivariable system is provided that measures differential pressure, absolute pressure, and process temperature using two rather than three process penetrations. Reducing the number of process penetrations eliminates potential process leak paths, thereby improving the safety of the flowmeter. Further, eliminating the extra measuring devices can reduce the size and weight of the flowmeter by up to about 50 pounds. Still further, as will be described below, some embodiments provided herein can use two dual temperature elements, such as the RTD (Resistance Temperature Detector) of the same temperature sensor, to use redundant process temperature measurements, and thus can improve the redundancy and reliability of the measurements.

[0012] Some of the efforts in this field are already provided in the form of U.S. Patent No. 9,234,776, which was inherited by the assignee of the present application. This patent teaches the use of a differential pressure sensor and a line pressure sensor that combines temperature measurement capabilities in a subsea transmitter. Accordingly, at least some of the embodiments described herein can be considered improvements to the aforementioned U.S. patent. The structure described in '776 incorporates a circuit card assembly having the ability to measure a 4-wire RTD temperature sensor. In the embodiments provided herein, generally, a very robust connection between the temperature sensor and the multivariable transmitter is combined with a non-invasive process fluid temperature measurement regime.

[0013] FIG. 2 is a schematic cross-sectional view of a multivariable subsea transmitter according to an embodiment of the present invention. Transmitter 150 has many similarities to the multivariable process fluid transmitter defined in the '776 patent. In fact, the pressure sensing portion 152 of transmitter 150 can be the same as that described in the '776 patent. The corrosive substance pressure sensing module 152 includes a lower portion 158 formed of a material suitable for immersion in salt water and other corrosive substances in one embodiment. Examples of corrosive substances and other corrosive substances include, but are not limited to, oil, fresh water, and corrosive chemical materials.

[0014] Examples of materials suitable for immersion in salt water and other corrosive substances include alloy C276, available under the trade name Hastelloy C276 from Haynes International Inc., Kokomo, Indiana; Inconel Alloy 625, available from the Special Metals families of companies, New Hartford, New York; and alloy C-22, available from Haynes International. Of particular interest is alloy C276, which has the following chemical composition (weight percent). Molybdenum; 15.0 - 17.0, Chromium; 14.5 - 16.5, Iron; 4.0 - 7.0, Tungsten; 3.0 - 4.5, Cobalt; maximum 2.5, Manganese; maximum 1.0, Vanadium; maximum 0.35, Carbon; maximum 0.01, Phosphorus; maximum 0.04, Sulfur; maximum 0.03, Silicon; maximum 0.08, and the balance nickel.

[0015] The base portion 158 is connected to the side wall 160 and the end cap 162 to define a chamber 164 therewithin. The differential pressure sensor 166 is disposed within the chamber 164 and has a pair of differential pressure sensor inputs 168, 170 that communicate the process fluid pressure to a deflectable diaphragm 172, and has an electrical characteristic such as capacitance or resistance that varies with the deflection of the diaphragm. The electrical characteristic is measured or otherwise converted by a circuit 174 disposed in proximity to the sensor 166. The circuit 174 also conditions the measured value for transmission via the electrical connection point 176. The circuit 174 can include a microprocessor, similar to a process communication module for communicating via a process communication loop or segment. Examples of such process communication include the HART® (Highway Addressable Remote Transducer) protocol, or the FOUNDATION® Fieldbus protocol. The circuit 174 is connected to an output circuit board 178 mounted within a cover 180. The output circuit board 178 is configured to communicate the process measurement value to a remote circuit such as a flow calculator 102. Further, the output circuit board 178 also includes one or more inputs for connecting a multivariable transmitter to one or more temperature sensors. As shown in FIG. 2, the temperature sensor probe 182 is connected to the housing 185 via a suitable high-pressure connection such as a weld 186.

[0016] In the example shown in FIG. 2, a pair of line pressure sensors 187, 189 are provided that are operably connected to the fluid pressure and electrically connected to the circuit 174. In this way, the transmitter 150 can use the differential pressure sensor 166 to directly measure the differential pressure, as well as use one or more of the line pressure sensors 187, 189 to directly measure the line pressure. Further, any difference in the measured values of the line pressure sensors can be compared to the measured differential pressure from the differential pressure sensor 166 to provide redundancy and / or diagnostics. Each of the line pressure sensors 187, 189 can be formed of any suitable pressure sensing structure, including those disclosed in U.S. Patent No. 6,079,276.

[0017] Figure 2 is a diagram showing one aspect in which a temperature sensor is incorporated into a multivariable underwater transmitter according to an embodiment of the present invention. The temperature sensor 182 preferably comprises a mineral insulated (MI) cable 188 having a temperature sensing element 184 disposed at its distal end. The element 184 can be any suitable element having properties such as resistance or voltage that vary with temperature. For example, the element 184 can be a thermocouple, a thermistor, an RTD, or other suitable sensing element. In a preferred embodiment, the element 184 is an RTD element. The RTD element can be a two-wire, three-wire, or four-wire RTD element. The element 184 can also be of a single element type or a dual element type. Thus, if the element 184 is of a dual element, four-wire configuration, the MI cable 188 will carry eight different conductors.

[0018] Figure 2 is a diagram showing one aspect in which a temperature sensor is incorporated into a multivariable underwater transmitter according to an embodiment of the present invention. The temperature sensor 182 preferably comprises a Inorganic mineral insulated (MI) cable 188 having a temperature sensing element 184 disposed at its distal end. The element 184 can be any suitable element having properties such as resistance or voltage that vary with temperature. For example, the element 184 can be a thermocouple, a thermistor, an RTD, or other suitable sensing element. In a preferred embodiment, the element 184 is an RTD element. The RTD element can be a two-wire, three-wire, or four-wire RTD element. The element 184 can also be of a single element type or a dual element type. Thus, if the element 184 is of a dual element, four-wire configuration, the MI cable 188 will carry eight different conductors.

[0019] In the embodiments provided herein, generally, a single or dual element RTD 184 thermally coupled to the process fluid is used without the need for additional process penetrations. There are several options as to where the temperature sensor itself can be mounted. However, in such a mounting, generally, a high-pressure seal is required to mount the temperature sensor without creating a process penetration. Since no process penetration is required to measure temperature, the large flange connections used for pressure sensors are not needed, further reducing the size of the system and increasing its reliability.

[0020] Figure 3 is a schematic diagram of a subsea multiphase flowmeter using a multivariable transmitter that measures line pressure, process fluid temperature, and differential pressure, according to an embodiment of the present invention. Comparing the subsea multiphase flowmeter shown in Figure 3 with that shown in Figure 1, it is clear that the embodiments of the present invention do not use a PTPT or a dual PT transmitter. Instead, a multivariable transmitter 150 is shown. Note that the temperature sensor portion of the multivariable transmitter is not shown in Figure 3 but is illustrated in Figure 4. The MI cable portion of the temperature sensor can be of various lengths and can be bent during the installation of the temperature sensor.

[0021] Figure 4 shows a flow conduit 208 that is similar to flow conduit 108 (shown in FIG. 1), except for the way the temperature sensor is attached. As shown in FIG. 4, first and second remote seals 110, 112 are connected to flow conduit 208 at respective process fluid penetrations and transmit process pressures to process pressure inlets 210, 212 of a multivariable transmitter 150 (shown in FIG. 2). Each of remote seals 110, 112 is coupled to the process fluid pressure at a location where the diameter of the flow conduit is different from the others or at a process fluid penetration. For example, remote seal 110 is coupled to flow conduit 208 at a location having a relatively small diameter 214, while remote seal 112 is coupled to the flow conduit at a location 216 having a relatively large diameter 216. The difference in pressures measured at two locations, along with knowledge of the different flow conduit diameters, is combined with knowledge of the process fluid temperature to provide an indication of the flow of the process fluid through flow conduit 208.

[0022] As shown in FIG. 4, temperature sensor probe 182 is mounted directly within conduit 208 for the process fluid and is connected to transmitter 150 as shown in FIG. 2. For redundancy, remote seals 250, 252, and a second temperature sensor probe 254 are also shown in FIG. 4. These redundant remote seals and temperature sensor probes are preferably connected to a second subsea multivariable transmitter identical to transmitter 150 shown in FIG. 2. In this way, a fully redundant subsea multivariable transmitter system is provided that measures line pressure, differential pressure, and process fluid temperature.

[0023] As shown in FIG. 4, temperature sensor probes 182, 254 can be mounted within flow tube 208 so as to extend either directly within the conduit for the process fluid or within a thermowell that is welded, or in some embodiments, extend into the flow itself. Further, each temperature sensor probe 182, 254 can include dual RTD elements for added redundancy, where each element connected is connected to its respective subsea multivariable transmitter.

[0024] The embodiment described with respect to FIG. 4 provides a temperature probe mounted directly within a subsea flow conduit, although it is explicitly contemplated that the temperature sensing probe may be mounted or connected to a remote seal used for differential pressure / line pressure measurement.

[0025] FIG. 5 is a schematic illustration of a temperature sensor probe mounted to and disposed within a remote seal according to an embodiment of the present invention. As shown in FIG. 5, remote seal 300 has some similarities to remote seals 110, 112, 250, 252. However, remote seal 300 includes a bore 302 that receives a temperature measurement probe 304 that includes an RTD element 184. As shown in the figure, the distal end of the temperature measurement probe is disposed proximate to the isolation diaphragm 310 of the remote seal. MI cable 306 extends through a suitable metallic sheath 308 formed of a metal suitable for direct immersion in salt water, such as C276 or Inconel, towards the housing 185 (shown in FIG. 2) of the multivariable transmitter 150. This metal is welded to or otherwise connected to the housing 185 using an alternative suitable and robust connection technique. Thus, remote seal 300 is configured not only to provide an indication of process fluid pressure via a fill fluid (not shown) that transmits pressure to diaphragm 310 and the differential pressure transmitter, but seal 300 is also configured to provide an indication of process fluid temperature in accordance with an embodiment of the present invention. Thus, seal 300 can be used for differential pressure / line pressure measurement as well as process fluid temperature measurement.

[0026] Although the invention has been described with reference to preferred embodiments, those 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 multivariable transmitter for measuring variables of a plurality of process fluids, the multivariable transmitter comprising: a metal housing made of a material selected from the group consisting of C276, Inconel, and C-22 alloy; a differential pressure sensor disposed within the metal housing; a line pressure sensor disposed within the metal housing; a measurement circuit operably connected to the differential pressure sensor and the line pressure sensor to provide outputs of differential pressure and line pressure; a temperature probe having an inorganic insulation (MI) cable and an outer surface made of a material selected from the group consisting of C276, Inconel, and C-22 alloy; comprising: the MI cable extends within a metal sheath made of a material selected from the group consisting of C276, Inconel, and alloy C-22 towards the metal housing; the temperature probe is electrically connected to the measurement circuit within the metal housing and physically connected to the metal housing via a high-pressure connection; a multivariable transmitter.

2. The multivariable transmitter according to claim 1, wherein the high-pressure connection between the temperature probe and the housing is a welded joint.

3. The multivariable transmitter according to claim 1, wherein the temperature probe includes an RTD temperature sensing element.

4. The multivariable transmitter according to claim 3, wherein the RTD temperature sensing element is a 4-wire RTD.

5. The multivariable transmitter according to claim 3, wherein the RTD temperature sensing element is of a dual-element type.

6. The multivariable transmitter according to claim 1, wherein the temperature probe has a distal end connected to a structure in contact with the process fluid.

7. The multivariable transmitter according to claim 6, wherein the structure is a flow tube.

8. The multivariable transmitter according to claim 7, wherein the distal end is physically isolated from the process fluid but thermally connected thereto.

9. The multivariable transmitter according to claim 6, wherein the structure is a remote seal.

10. The multivariable transmitter according to claim 9, wherein the distal end is disposed proximate to the isolation diaphragm of the remote seal.

11. The multivariable transmitter according to claim 1, wherein the transmitter is configured to provide a flow rate output indicative of a single-phase fluid flow.

12. The multivariable transmitter according to claim 1, wherein the transmitter is configured to provide a flow rate output indicative of a multiphase fluid flow.

13. The transmitter according to claim 1, configured to provide a flow rate output indicative of the flow rate of the wet gas.

14. An underwater flow measurement system, An underwater flow conduit configured to receive a fluid flow, A first multivariable transmitter connected to the underwater flow conduit, configured to measure the differential pressure and static line pressure at a first pair of positions within the underwater flow conduit, and thermally connected to the fluid but physically isolated from the fluid, and configured to measure the fluid temperature using a first temperature probe. A second multivariable transmitter connected to the underwater flow conduit, configured to measure the differential pressure and static line pressure at a second pair of positions within the underwater flow conduit, and thermally connected to the fluid but physically isolated from the fluid, and configured to measure the fluid temperature using a second temperature probe. A flow calculator operably connected to the first and second multivariable transmitters, configured to receive each signal from the first and second multivariable transmitters and calculate a flow rate output based on each signal. The underwater flow conduit requires no more than two penetrations for the first multivariable transmitter and no more than two penetrations for the second multivariable transmitter. An underwater flow measurement system.

15. The underwater flow measurement system according to claim 14, wherein the flow calculator is configured to utilize redundant pressure and temperature measurements using signals from the first and second multivariable transmitters.

16. The underwater flow measurement system according to claim 14, wherein the flow calculator is attached to the underwater flow conduit.

17. The underwater flow measurement system according to claim 14, wherein each of the first and second multivariable transmitters is attached to the underwater flow conduit.

18. The underwater flow measurement system according to claim 17, wherein each transmitter is connected using a flange connection.

19. The underwater flow measurement system according to claim 14, wherein the flow calculator is connected to the first and second multivariable transmitters using conduits formed and welded to the first and second multivariable transmitters.

20. The underwater flow measurement system according to claim 14, wherein each multivariable transmitter is connected to the underwater flow conduit using a respective pair of remote seals.

21. The sea water flow measurement system according to claim 14, wherein each of the first and second temperature probes is disposed in each hole within the sea water conduit.

22. The sea water flow measurement system according to claim 14, wherein each of the first and second temperature probes is disposed in each remote seal.

23. A multivariable transmitter for measuring a plurality of process fluid variables, the multivariable transmitter comprising: A conduit for a process fluid constructed from a material suitable for exposure to salt water, the conduit for the process fluid having first and second process fluid penetrations; A first pressure sensor operably connected to the first process fluid penetration; A second pressure sensor operably connected to the second process fluid penetration; A measurement circuit operably connected to the first and second pressure sensors; A temperature probe having a temperature sensor therein, the temperature sensor being connected to the measurement circuit to provide an indication of the process fluid temperature, the temperature probe having an outer surface constructed from a material suitable for exposure to the salt water; comprising In attaching the temperature probe to the conduit for the process fluid, no penetration of the process fluid is created in the conduit for the process fluid. Multivariable transmitter.

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