Magnetic flowmeter flowtube with process fluid venting assembly

A magnetic flowmeter flowtube assembly includes a conduit having an inside diameter, a fluoropolymer liner disposed within and extending through the conduit, and a pair of electrodes mounted relative to the liner to measure a voltage induced within a process fluid flowing through the liner. A venting assembly provides a process fluid vent path from the inside diameter of the conduit to an exterior of the flowtube assembly.

BACKGROUND

Magnetic flowmeters (or mag meters) measure flow by Faraday induction, an electromagnetic effect. The magnetic flowmeter energizes one or more coils which generate a magnetic field across a section of a flowtube assembly. The magnetic field induces an electromotive force (EMF) across the flow of conductive process fluid through the flowtube assembly. The resulting potential developed across the conductive fluid is measured using a pair of electrodes that extends into the flowing process fluid. Alternatively, some magnetic flowmeters employ capacitive coupling between the electrodes and the process fluid such that the EMF can be measured without direct contact. In any event, the flow velocity is generally proportional to the induced EMF, and the volumetric flow is proportional to the flow velocity and the cross sectional area of the flowtube.

Magnetic flowmeters are useful in a variety of fluid flow measurement environments. In particular, the flow of water-based fluids, ionic solutions and other conducting fluids can all be measured using magnetic flowmeters. Thus, magnetic flowmeters can be found in water treatment facilities, beverage and hygienic food production, chemical processing, high purity pharmaceutical manufacturing, as well as hazardous and corrosive fluid processing facilities. Magnetic flow meters are often employed in the hydrocarbon fuel industry, which sometimes employs hydraulic fracturing techniques utilizing abrasive and corrosive slurries.

Magnetic flowmeters can be specified with a variety of different lining and/or electrode materials to suit the application for which the magnetic flowmeter is employed. Examples of lining materials include polytetrafluoroethylene (PTFE); ethylene tetrafluoroethylene (ETFE); PFA; polyurethane; neoprene; and linatex rubber, as well as other materials. Electrodes may be constructed from any suitable material including 316 L stainless steel; nickel alloy 276; tantalum; platinum/iridium blends; titanium; as well as other suitable materials.

Fluoropolymer lining materials such as PTFE, ETFE, and PFA are often selected for superior resistance to chemical attack and/or high temperature operation. In at least some applications, fluoropolymer-based liners are being subjected to increased application demands. For example, in the oil and gas industry, some fluoropolymer liners are being subjected to higher pressures and/or temperatures. Such conditions create a challenge in designing and manufacturing robust magnetic flowmeter devices with fluoropolymer liners. This is because at least some fluoropolymers, such as PTFE, experience “cold flow” where the lining material expands and contracts under pressure and temperature. Such expansion/contraction can cause the process fluid to leak.

The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the disclosed subject matter.

SUMMARY

In one embodiment, a magnetic flowmeter flowtube assembly includes a conduit having an inside diameter, a liner disposed within and extending through the conduit, and a pair of electrodes mounted relative to the liner to measure a voltage induced within a process fluid flowing through the liner. A venting assembly provides a process fluid vent path from the inside diameter of the conduit to an exterior of the flowtube assembly.

In one embodiment, a method of venting a magnetic flowmeter includes providing a flowtube assembly with a conduit, the conduit having an inner surface, an outer surface, and a hole formed between the inner and outer surfaces. The method also includes inserting a non-conductive liner into the conduit and providing a venting assembly in fluid communication with the hole.

In one embodiment, a magnetic flowmeter flowtube assembly includes a conduit having an inner surface, an outer surface, and a hole formed in the conduit between the inner surface and the outer surface. The assembly also includes a non-conductive liner disposed within and extending through the conduit and a pair of electrodes mounted relative to the liner to measure a voltage induced within a process fluid flowing through the liner. The assembly also includes a fitting coupled to the conduit proximate the hole formed in the conduit and a porous metal plug disposed in the fitting.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1is a diagrammatic view of a magnetic flowmeter with which embodiments described herein are useful. Magnetic flowmeter10includes flowtube assembly12coupled to transmitter electronics14. Flowtube assembly12includes a section of conduit16having ends18and20coupled to respective flanges22and24. Each of flanges22,24includes mounting holes for mounting to suitable pipe flanges such that process fluid flows through conduit16. Flanges22,24generally attach to conduit16by welding conduit16to a neck of the flange. Such coupling allows for the transfer of stress from the flange22,24to conduit16.

Flowtube assembly12also generally includes a coil/electrode portion26that contains one or more electromagnetic coils driven by transmitter electronics14to generate an electromagnetic field across conduit16. Electrodes disposed within conduit16contact the process fluid and are used to sense the electromotive force (EMF) generated across the process fluid in response to the induced magnetic field. The coil(s) and electrodes of flowtube assembly12are generally coupled to a terminal block within housing28, which is then operably coupled to transmitter electronics14. Transmitter electronics14generally includes a controller or microprocessor that is configured to provide an indication of process fluid flow based on the measured EMF. Transmitter electronics14also generally includes communication circuitry to convey such process fluid flow information to one or more remote devices as indicated by bi-directional arrow30. Such communication can be in the form of wired process communication or wireless process communication.

FIG. 2is a diagrammatic cross-sectional view illustrating a liner42disposed within a conduit16that is coupled to a pair of flanges22,24. In the illustrated embodiment, liner42is formed of a non-conductive material that insulates conduit16from the process fluid. In one example, liner42is formed of a fluoropolymer, such as, but not limited to, polytetrafluoroethylene (PTFE).

Each of flanges22,24includes a sealing face32,34, respectively, that is configured to engage a seal ring and thereby fluidically couple to an opposing pipe flange. In some cases, the seal may be a ring-type seal which is received in grooves36,38in order to generate a high-pressure metal-to-metal connection. While the utilization of an RTJ sealing ring provides a robust seal, it also creates a gap between outside diameter40of liner42and the inside diameter of the sealing ring. This gap allows the pressurized process fluid to engage or otherwise contact interface44between the fluoropolymer liner42and the flanges22,24. Generally, liner42is interference fit into the inside diameter of conduit16, and thus there is no bond between liner42and conduit16.

Embodiments of the present disclosure generally provide a venting assembly configured to vent process fluid that leaks into a space between liner42and conduit16(e.g., process fluid that breaches interfaces44, diffuses through liner42, and/or otherwise leaks between liner42and the inside diameter of conduit16). For example, under some cold flow conditions, liner42will expand or contract and can generate leak paths at the flange faces. Once process fluid breaches interfaces44, it can move along the inside diameter of conduit16to reach electrodes46very quickly. When the process fluid reaches the electrodes, electrical isolation of such electrodes is defeated and the electrodes are no longer able to carry the induced voltage from the process fluid to transmitter electronics14.

FIG. 3is a diagrammatic cross-sectional view of a portion of a flowtube having a venting assembly that provides a vent path76that drains leaking process fluid to atmosphere, in accordance with one embodiment. The flowtube has a section of conduit50, a liner52disposed within conduit50, and a flange54coupled to an end56of conduit50. The flowtube includes electrodes (not shown inFIG. 3) and a second flange (not shown inFIG. 3) that is coupled to a second end of conduit50. In one example, conduit50and liner52are similar to conduit16and liner42discussed above with respect toFIG. 2. Further, in one example, flange54is similar to flange24, shown inFIG. 2, in that it includes a raised face58and RTJ groove60. An interface62is provided between outside diameter64of liner52and face58of flange54. Accordingly, process fluid, in some situations, may breach interface62thereby moving along the inside diameter72of conduit50toward the electrodes.

As shown inFIG. 3, venting assembly68is coupled to conduit50proximate a hole70formed in conduit50, for example by a drilling process. While venting assembly68is illustrated as being coupled to a bottom of conduit50proximate end56, it is noted that venting assembly68can be positioned at any other suitable location along conduit50. Further, in one example a plurality of venting assemblies can be coupled to conduit50.

Venting assembly68provides a path for the leaked process fluid to leave the flowtube assembly, to prevent the process fluid from building up between liner52and the inside diameter of conduit50. For example, process fluid may breach interface62or diffuse through liner52into a space between liner52and the inside diameter of conduit50. In the illustrated embodiment, the leaked process fluid flows into hole70formed in conduit50and through venting assembly68. Venting assembly68includes at least one resistive flow path76that allows the process fluid to drain from hole70to atmosphere, but at a slower rate than if venting assembly68were not present at hole70. In one embodiment, venting assembly68comprises at least one tortuous flow path.

For sake of illustration, without use of venting assembly68at hole70, only the liner52would be positioned between the process fluid and the flow meter environment. Thus, in this instance, a failure of liner52could cause a release of high pressure process fluid from hole70into the environment, which could pose a risk to workers in the vicinity of the flowtube assembly, for example. In one embodiment, use of venting assembly68with the flowtube assembly satisfies industry standard pressure retention tests, such as burst testing at three times burst pressure as called out in IEC 61010.

FIG. 4is a diagrammatic cross-sectional perspective view of venting assembly68. Venting assembly68is mounted to an outer surface78of conduit50proximate the hole70formed between the inner surface (i.e., inside diameter72) and outer surface78. Liner52carries a process fluid80flowing therethrough. As similarly discussed above, during operation some of the process fluid can leak into a space between the outer diameter82of liner52and the inner diameter72of conduit50. Venting assembly68provides a venting path for the process fluid to drain into the environment or atmosphere84.

In the illustrated example, hole70is approximately one-eighth inch to one-quarter inch in diameter. However, any suitable size can be used. A fitting86is located over hole70and secured to the outer surface78of conduit50, for example by welding or any other suitable attachment. Fitting86has a corresponding bore88that is aligned with hole70.

A plug90is positioned within bore88of fitting86. Plug90is configured to provide a resistive path for the process fluid to drain into the environment84. In the illustrated example, plug90is formed of a porous metal, such as, but not limited to, stainless steel made from a powder metal process. The porous metal plug has a lower density than a corresponding non-porous plug, and is configured to allow, but provide some resistance to, a flow of process fluid through bore88.

In the example ofFIG. 4, fitting86comprises a threaded nipple, where a series of threads are disposed along surfaces of bore88. Plug90has corresponding threads along its outer surface enabling plug90to be threaded into bore88. In the illustrated example, plug90is threaded into fitting86until an end of plug90touches the outer surface82of liner52, which can provide a structural backing for liner52. To prevent plug90from backing out of the threaded engagement with fitting86(for example, due to thermal cycling and/or vibration), in one embodiment plug90is secured to fitting86by tack welding or other suitable attachment.

In another embodiment, plug90of venting assembly68is formed with a solid, non-porous material. The resistive flow path through venting assembly68is formed along the thread interface92between plug90and fitting86. In one example, the threads of fitting86and plug90can be of different sizes, thereby forming a gap therebetween that allows passage of process fluid through the thread interface92.

FIG. 5is a flow diagram of a method100of venting a magnetic flow meter. For sake of illustration, but not by limitation, method100will be described in the context of the example flow meter illustrated inFIGS. 3 and 4.

At block102, a flowtube is provided. The flowtube comprises a conduit (e.g., conduit50) having inner and outer surfaces. At block104, a hole (e.g., hole70) is provided in conduit50. For example, hole70is made by drilling through conduit50. At block106, a liner (e.g., liner52) is inserted into the conduit50. Optionally, block108can also be performed to chemically bond liner52to conduit50for additional sealing at the liner/conduit interface(s).

At block110, a fitting (e.g., fitting86) having a bore (e.g., bore88) is attached to conduit50. For example, fitting86can be welded to the outer surface78of conduit50. At block112, a plug (e.g., plug90) is inserted into fitting86. At block114, the plug90is secured to fitting86(e.g., by tack welding) to prevent plug90from backing out of bore88.

While the blocks of method100have been illustrated and discussed in a particular arrangement, the illustrated arrangement is not intended to imply any particular order of the blocks. The blocks can be performed in any suitable order. For example, in one embodiment, one or more of blocks110,112and114can be performed before blocks104and/or106.