Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
1999-06-30
2003-02-25
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
active
06523421
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a Coriolis flowmeter. More particularly, the invention relates to a method and apparatus for a Coriolis flowmeter having bi-metallic process connections formed from two dissimilar metals that are metallurgically bonded to form a sealed process connection.
PROBLEM
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information of process materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters have one or more flow tubes of a straight or a curved configuration. Each flow tube configuration in a Coriolis flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating material filled systems are defined in part by the combined mass of the flow tubes and the process material flowing through the flow tubes. Process material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The process material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no process material flowing through the flowmeter, all points along the flow tube oscillate with an identical phase. As process material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver.
In an example of a straight tube configuration, a balance bar surrounding the flow tube balances the flow tube and isolates the sensing portion of the flow tube from external influences to provide a specific frame of reference for the sensing portion. Pick off sensors at two different points on the flow tube produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference in the two signals received from the sensors is calculated in units of time. The phase difference between the two sensor signals is proportional to the mass flow rate of the process material flowing through the flow tube or flow tubes.
The flow tube and surrounding balance bar are housed in a case. A process connection is connected to each end of the flow tube and to each end of the case. Process connections are fittings that connect the flowmeter to a pipeline or other process material delivery system. A flange is a specific example of a process connection.
In some cases, flowmeters are constructed from dissimilar metals, such as steel and titanium to improve flow meter design. The use of dissimilar metals in flowmeters permits the flowmeters to withstand harsh environments of use such as extreme temperatures, chemical attack, pipeline loading and process pressures. In the context of this application, dissimilar metals are metals that have substantially different properties including hot ductility and coefficients of thermal expansion. The substantially different properties prevent joining of the dissimilar metals by conventional welding techniques.
In one example, a flowmeter case may be constructed from carbon steel and include a stainless steel skin affixed around the exterior surface. The process connections are constructed from stainless steel. The flow tube on the other hand, may be constructed from titanium. Construction of the case from carbon steel, which costs less than stainless steel, lowers manufacturing costs. The stainless steel skin affixed around the case protects the carbon steel from rust and corrosion. The titanium flow tube provides a sanitary metallic flow path for process material.
Different metals have different corrosion tolerances and corrode at varying time intervals. Therefore, it is desirable that process material flowing through the flowmeter only contact a single metal. One prior art method of providing a flow path made of a single metal is to extend the flow tube through the process connection and terminate it flush with the outer edge of the process connection. A titanium insert configured to fit into a recessed portion on the outer face of the process connection is used to join the titanium flow tube to the end of the process connection. The flow tube is welded to the insert by conventional welding techniques. The insert is retained in the recessed portion of the process connection by the weld between the flow tube and the insert. In the prior art the titanium insert is not bonded to the stainless steel process connection. An elastomeric seal, such as an O-ring or silicone, is fitted into the joint between the insert and process connection. This seal is critical because it prevents exterior process materials from leaking into the interior case of the flowmeter.
A first problem with this prior art solution is that the joint between the insert and the process connection is a weak point in the flowmeter. The elastomeric seal breaks down at a faster rate than other surrounding welded joints. This results in a premature failure of the flowmeter because the seal cannot be replaced without destroying the entire flowmeter.
A second problem with this prior art solution is that the joint between the titanium insert and the stainless steel process connection also fails prematurely due to galvanic corrosion, resulting in premature meter failure. Furthermore, the galvanic corrosion is accelerated where the process material is corrosive.
A third problem with this prior art solution is present in applications where the flowmeter case is relied on to provide a secondary containment for the process material in the event the flow tube fails. The O-ring seal or other elastomeric seal is not designed to handle such process material, especially in large pressurized volumes present during a flow tube failure. This problem is further compounded by the fact that the need for secondary containment typically arises during applications where the process material is highly corrosive or toxic.
SOLUTION
The above and other problems are solved and an advance in the art is made by the method and apparatus of the invention wherein a bi-metallic process connection made from a first metal and a dissimilar metal that are metallurgically bonded to form a sealed process connection for a Coriolis flowmeter. A first advantage is that the need for an elastomeric seal is eliminated. A second advantage is that the bonded first metal and dissimilar metal provide superior corrosion resistance. This extends the useful life of the flowmeter in highly corrosive environments.
A Coriolis flowmeter embodying the method and apparatus of the invention includes at least one flow tube made of a first metal and a process connection made of the first metal metallurgically bonded to a dissimilar metal to form a sealed structure. A central aperture extends through the process connection and is enclosed by at least a portion of the first metal in the process connection. An end of the flow tube is affixed to the first metal in the process connection to provide a flow path enclosed by the first metal.
A first exemplary embodiment of the present invention is a stainless steel flange that includes a titanium insert metallurgically bonded to a first end of the flange. The flange includes a central recessed portion in the first and that connects to the pipeline. The central recessed portion circumscribes a central aperture passing through the main body of the flange. The recessed portion is configured to receive a cylindrical titanium insert that has a central aperture configured to mate with the central aperture of the flange. The titanium insert is metallurgically bonded into the central recessed portion of the flange to form a sealed proce
Garnett Robert Barclay
Lister Ernest Dale
Shelton Michael Benton
Tanner Terry Rock
Faegre & Benson LLP
Micro Motion Inc.
Patel Harshad
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