Abstract:
An apparatus for enclosing a flow tube of a device for measuring properties of a material flowing through the flow tube having a casing and a veneer. The casing substantially encloses flow tube from inlet end to outlet end and withstands the structural load of the flow tube. The veneer encloses the casing and provides a sanitary surface for said casing.

Description:
FIELD OF THE INVENTION 
     This invention relates to a casing enclosing a Coriolis flowmeter. More particularly, the present invention relates to a veneer on the outside of the casing that allows the casing to be used in sanitary applications. Still more particularly, the present invention relates to a veneer that encloses a casing and that provides a sanitary and/or corrosion proof surface for the casing. 
     PROBLEM 
     It is known to use Coriolis effect mass flowmeters to measure mass flow and other information of 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 curved or a straight configuration. Each flow tube configuration in a Coriolis mass 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 material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The 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 material flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As a 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. 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 of 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 material flowing through the flow tube or flow tubes. 
     The flow tubes are typically enclosed in a casing. The casing prevents damage to the flow tubes from outside forces. The casing may also be used to contain material when a flow tube ruptures and may also be used as a spacer to maintain the distance between flanges connecting the flow tube to a pipeline. 
     It is a problem that customers sometimes require the casing to be made out of sanitary or corrosion resistant material. The casing must be made out of sanitary material that is easy to clean when the flowmeter is used in a system, such as an ingredient delivery system in food processing. The casing must be made of a corrosion resistant material when the flowmeter is inserted into an environment that may contain a corrosive material such as an acid. 
     In a conventional dual loop Coriolis flowmeter, it is not a problem to make a casing of sanitary or corrosion resistant material. A spacer bears the structural load of the flowmeter to reduce external vibrations and maintains proper spacing between the inlet and the outlet. The loop configuration of the flow tubes allows the middle section of the flow tube to expand outward and inward to account for expansion and contraction. Thus, the casing must have enough space between the casing and the tube to allow expansion and contraction of the flow tube. For these reasons, the casing and spacer may be made from or coated with a sanitary material in order to provide a sanitary surface for the flowmeter. 
     However, it is a problem to make a casing out of sanitary or corrosion resistant material for a straight tube Coriolis flowmeter. In a straight tube flowmeter, the casing and spacer are combined and provide the same function of bearing the structural load of the flowmeter. As the flow tube heats up and expands, the length of the flow tube increases because the straight tube must expand radially and axially. 
     The casing will be subjected to the same net axial loading of the flow tube, although the axial loading of the casing will be opposite in sign to that of the flow tube. However, the stress on the flow tubes will be much greater than the casing due to its smaller cross section. Therefore, the axial expansion of the flow tube is a problem because the casing is affixed to the flow tube at the ends of the flow tube and if the casing does not expand at the same rate as the tube, the flow tube will be subjected to stresses that will damage the integrity of the flow tube. 
     One solution may be to make the casing and the flow tube out of the same sanitary and corrosion resistant material. However, the cost of a corrosion resistant material such as titanium is prohibitive. Therefore, there is a need to make a casing that can withstand the stress applied by the thermal expansion of dissimilar metals while being cost efficient to produce. This will allow less expensive straight flow tube Coriolis flowmeters to be produced. 
     SOLUTION 
     The above and other problems are solved and an advance in the art is made by the provision of a casing for a Coriolis flowmeter enclosed in a veneer of sanitary or corrosion resistant material. For purposes of this invention, a veneer is a layer of material that encloses or is layered onto a surface of a casing to cover the material of the surface. The veneer of this invention allows a casing to carry the structural load of a flowmeter while a function of providing a sanitary surface is accomplished by the veneer. 
     A first advantage of this invention is that the use of a veneer of sanitary or corrosion resistant material to enclose the casing reduces the amount of sanitary or corrosion resistant material needed to produce a Coriolis flowmeter which reduces the cost of production. The amount of sanitary material needed is reduced because the casing does not have to be made of sanitary or corrosion resistant material. A second advantage is that the casing material may have a coefficient of thermal expansion that is substantially equal to the flow tube. Therefore, expansion and contraction of the casing and flow tube occur at substantially the same rate which reduces structural stress caused by thermal expansion. 
     The casing of this invention is constructed in the following manner to provide the above advantages. A casing encloses a flow tube of a Coriolis flowmeter. The casing is affixed to the opposing ends of the flow tube. The outer surface of the casing is enclosed by a veneer. The veneer is affixed to case ends made of a material having substantially the same properties as the veneer material to allow affixing. Further expansion and contraction of the veneer may be independent of the expansion and contraction of the casing. 
     In order for the expansion and contraction of the veneer to be independent of the expansion and contraction of the casing, there may be a space defined by a gap between an inner surface of the veneer and an outer surface of the casing. The space allows the casing to expand and contract freely inside the veneer. 
     Alternatively or in conjunction with the gap, a veneer may have bellows around the perimeters of opposing ends of the veneer. Bellows are bends in the surface veneer which may bent as the material of the veneer expands and may be pulled straight as the veneer contracts. 
     The gap between the veneer and the outer surface of the casing may be filled with insulation. The insulation keeps the temperature of the flow tube more uniform. The gap could also house heating elements that provide a heating jacket for the flow tube. Another possibility is that steam or other fluid could flow through the gap to regulate the temperature of the flow tube. All of these alternatives could be used to reduce axial stress on the flow tube due temperature gradients through the flow tube. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The above and other features of this invention can be understood from the Detailed Description as well as the following drawings: 
     FIG. 1 illustrating a cross section of a veneer enclosing an outer surface of a casing that is enclosing a straight tube Coriolis flowmeter; 
     FIG. 2 illustrating a view of a casing having a veneer enclosing a flowmeter; 
     FIG. 3 illustrating a cross sectional view of the Coriolis flowmeter showing insulation in a gap between a casing and a veneer; 
     FIG. 4 illustrating a cross sectional view of the Coriolis Flowmeter showing heating elements in a gap between a casing and a veneer; and 
     FIG. 5 illustrating a cross sectional view of a Coriolis flowmeter showing fluid flowing in a gap between a casing and a veneer. 
    
    
     DETAILED DESCRIPTION 
     The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. Those skilled in the art will appreciate that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure is thorough and complete, and conveys the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout. 
     FIG. 1 discloses a straight tube Coriolis flowmeter  5 . Although shown in conjunction with a straight tube Coriolis flowmeter  5 , those skilled in the art will recognize that this invention may also be used to house flow tubes having a curved or looped configuration. Coriolis flowmeter  5  is comprised of Coriolis sensor  10  and associated meter electronics  20 . 
     Coriolis sensor  10  has casing  103  which encloses flow tube  101  and surrounding balance bar  102 . The flow tube  101  includes a left end portion thereof designated  101 L and a right end portion thereof designated  101 R. Flow tube  101  and its ends portions extend the entire length of the flowmeter from the input end  107  of flow tube  101  to the output end  108  of the flow tube. The balance bar  102  is connected at its ends to flow tube  101  by brace bar  121 . 
     Left end portion  101 L of flow tube  101  is affixed to inlet flange  122  and right end portion  101 R is affixed to outlet flange  122 ′. Casing  103  has end portions  128  extending axially out from each end of the casing and connecting casing  103  to inlet flange  122  and outlet flange  122 ′. Inlet flange  122  and outlet flange  122 ′ connect Coriolis sensor  10  to a pipeline. 
     In a well known conventional manner, a driver  104  and a left pick off  105  and a right pick off  105 ′ are coupled to flow tube  101  and balance bar  102 . Driver  104  receives signals over path  110  from meter electronics  20  to cause driver  104  to vibrate flow tube  101  and balance bar  102  in phase opposition at the resonant frequency of the material filled flow tube  101 . The oscillation of vibrating flow tube  101  together with the material flow therein induces Coriolis deflections in the flow tube in a well known manner. These Coriolis deflections are detected by pick offs  105  and  105 ′ with the outputs of these pick offs being transmitted over conductors  111  and  111 ′ to meter electronics  20 . In a well known manner, the phase difference between the output signals of these pick offs represents information pertaining to the material flow within flow tube  101 . The pick offs signals are received over conductors  111  and  111 ′ by meter electronics  20  which in a well known manner processes these signals to generate output information that is applied to conductor  26  representing the various parameters of the material flow. These parameters may include density, viscosity, mass flow rate and other information regarding material flow. 
     The present invention as described herein, can produce multiple drive signals for multiple drivers. Meter electronics  20  processes left and right velocity signals to compute mass flow rate. Path  26  provides an input and an output means that allows meter electronics  20  to interface with an operator. An explanation of the circuitry of meter electronics  20  is unneeded to understand the casing  103  and veneer  150  of the present invention and is omitted for brevity of this description. 
     The present invention relates to casing  103  having a veneer  150  that encloses outer surface  151  of casing  103 . In the present invention, casing  103  bears the structural load of casing and a separate veneer  150  provides a sanitary or corrosion proof surface for casing  103 . Casing  103  is made of a first material. In the preferred embodiment, the first material is not sanitary and is not corrosion resistant. 
     In the preferred embodiment, veneer  150  is made of a second material that is dissimilar from the first material. For purposes of this discussion, dissimilar means that the two material have different properties, such as different coefficients of thermal expansion. In a preferred embodiment, the second material is a corrosion resistant material, such as stainless steel. Veneer  150  encloses the outer surface  151  and provides a sanitary and/or corrosive covering for sensor  10 . 
     As seen in FIG. 2, veneer  150  is affixed to outer surface  151  of casing  103  (FIG. 1) in the following manner. Veneer  150  is affixed to ends  103 L and  103 R of casing  103  by orbital weld  201 . Longitudinal weld  202  is used to seal overlapping sides veneer of  150  after veneer  150  is wrapped around casing  103 . It is also possible to plate veneer  150  to outer surface  151 , paint veneer  150  on outer surface  151 , or to coat outer surface  151  with veneer  150  in some other manner. 
     In a preferred exemplary embodiment, casing  103  is made of a material that has a coefficient of thermal expansion that is substantially equal to the material from which flow tube  101  is made. For example, flow tube  101  may be made of titanium which has a coefficient of thermal expansion that is 4.6e −6  per degree Fahrenheit and casing  103  is composed of carbon steel which has a coefficient of 6.5e −6  per degree Fahrenheit which is sufficiently equal for most operations. 
     However, if the corrosion proof veneer  150  is made of a material such as stainless steel which has a coefficient of thermal expansion that is 6.5e −6  per degree Fahrenheit, the disparity between the thermal coefficients for veneer  150  and flow tube  101  or casing  103  can be too great. In order to prevent undo stress caused by the disparity in thermal coefficients, veneer  150  may be a separate structure having an inner surface and an outer surface. Veneer  150  may have ends that affix veneer  150  to a right end  103 R of casing  103  and a left end  103 L of casing  103 . 
     Gap  170  may be formed between inner surface of veneer  150  and outer surface  151  of casing  103 . The gap  170  allows casing  103  to expand and contract inside veneer  150  without applying any stress to veneer  150 . Alternatively or in conjunction with gap  170 , veneer  150  may have bellows  191  (Shown on FIGS. 3-5) at opposing ends of casing  150 . Bellows  191  are bends in the surface of veneer  150  that can expand and contract so that as the underlying casing  103  expands and contracts bellows  191  bend and unbend to prevent stress on veneer  150 . 
     In some embodiments, gap  170  may contain insulation  300  as shown in FIG.  3 . Insulation  300  keeps the temperature more uniform inside veneer  150 . Insulation  300  may be used to retain heat in casing  103 . This heat retention reduces axial stress due to temperature gradients inside Coriolis sensor  10 . Heating elements  400  (Shown in FIG. 4) may also be mounted inside gap  170 . Heating elements  400  provide a heat jacket that heats casing  103  to reduce axial stress in Coriolis sensor  10  caused by expansion and contraction of flow tube  101 . In a third alternative, a fluid  500  (Shown by arrows in FIG. 5) may flow through gap  170  to regulate the temperature of Coriolis sensor  10 . 
     The above is a description of a casing having a veneer made of sanitary or non-corrosive material. It is envisioned that those skilled the art can and will design alternative casings for Coriolis flowmeters that infringe on the casing having a veneer as set forth in the claims below either literally or through the Doctrine of Equivalents.