PROTECTIVE TUBE FOR INSERTION INTO A PIPE OR VESSEL WITH REDUCED SENSITIVITY TO VORTEX INDUCED VIBRATIONS

Abstract

A protective tube for insertion into a pipe or vessel containing a medium, a measuring apparatus having such protective tube and a method for manufacturing the protective tube are disclosed, the protective tube including a tubular member having a bore extending between an upper and lower end of the tubular member and having at least one helical fin on at least a section of an outer surface of the tubular member, winding around the outer surface of the tubular member and defining a flow channel along at least a part of the tubular member. At least one geometric parameter of the at least one helical fin is configured based on at least one process condition of the medium in the vessel or pipe.

Claims

1. A protective tube introducing into a pipe or vessel containing a medium, the protective tube comprising: a tubular member including a bore extending between a proximal end and a distal end of the tubular member; and at least one helical fin on at least a section of an outer surface of the tubular member, winding around the outer surface of the tubular member and defining a flow channel extending along at least a part of the tubular member, wherein at least one geometric parameter of the at least one helical fin is configured based on at least one process condition of the medium in the vessel or pipe.

2. The protective tube of claim 1, wherein the at least one process condition is at least one of: a flow profile, a flow velocity, a pressure, a temperature, a density or a viscosity of the medium; a diameter, a volume or a roughness of the pipe or vessel; and a length or a diameter of the tubular member.

3. The protective tube of claim 1, wherein the at least one geometric parameter is at least one parameter defining the form and/or shape of the flow channel and/or the at least one helical fin.

4. The protective tube of claim 3, wherein the at least one parameter is: a height, a pitch, a width, a depth or a shape of the at least one helical fin; and/or a cross-sectional area of the flow channel.

5. The protective tube of claim 1, wherein the protective tube is a thermowell, and the tubular member is closed at the distal end.

6. The protective tube of claim 1, wherein a cross-sectional area of the flow channel has a predefined shape and/or size, which is configured based on the at least one process condition of the medium in the vessel or pipe.

7. The protective tube of claim 6, wherein the predefined shape and/or size of the cross-sectional area of the flow channel is formed by removing at least one volume section from the at least one helical fin and/or from a wall of the tubular member at least partially defining the flow channel.

8. The protective tube of claim 1, wherein a size and/or a shape of the at least one helical fin and/or a cross-sectional area of the flow channel varies along an axis of the tubular member.

9. A measuring apparatus for determining and/or monitoring a process variable of a medium, the apparatus comprising a protective tube according to claim 1.

10. The apparatus of claim 9, wherein the protective tube is configured to receive a measuring insert adapted to determine and/or monitor a process variable of a medium.

11. The apparatus of claim 10, wherein the process variable is a temperature of the medium.

12. A method of manufacturing a protective tube configured for introduction into a pipe or vessel containing a medium the protective tube comprising: a tubular member including a bore extending between a proximal end and a distal end of the tubular member; and at least one helical fin on at least a section of an outer surface of the tubular member, winding around the outer surface of the tubular member, wherein at least one geometric parameter of the at least one helical fin is configured as to depend on at least one process condition of the medium in the vessel or pipe, the method comprising: selecting at least one geometric parameter of the at least one helical fin such that the at least one geometric parameter is configured based on at least one process condition of the medium in the vessel or pipe.

13. The method of claim 12, wherein the at least one geometric parameter of the at least one helical fin is selected based on a numerical calculation of a mechanical behavior of the protective tube inside the pipe of vessel under the at least one process condition.

14. The method of claim 12, wherein the at least one geometric parameter of the at least one helical fin is selected at least in part based on an installation position and/or flow modifying elements within a pipe system.

15. The method of claim 14, wherein the flow modifying elements include at least one of a pipe corner piece, a valve, a filter, a nozzle and a separate measuring probe.

16. The method of claim 12, wherein a size of the at least one section of the outer surface of the tubular member, which comprises the at least one helical fin, is configured based on the at least one process condition.

17. The method of claim 12, wherein the at least one process condition is at least one of: a flow profile, a flow velocity, a pressure, a temperature, a density or a viscosity of the medium; a diameter, a volume or a roughness of the pipe or vessel; and a length or a diameter of the tubular member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present disclosure will now be explained in more detail by means of the following drawings:

[0029] FIG. 1 illustrates the origin of vortex shedding for an insertion body exposed to a flowing medium;

[0030] FIGS. 2a-2c show views of a thermometer having a state of the art thermowell;

[0031] FIG. 3a shows a thermowell with a plurality of helical fins according to the state of the art forming a plurality of flow channels;

[0032] FIG. 3b shows a thermowell with flow channels optimal for avoiding VIV;

[0033] FIGS. 4a-4d illustrate the influence of the flow profile and installation position on the occurrence of VIV;

[0034] FIG. 5 shows a cross-sectional view of a first embodiment according to the present disclosure with variable helical fins;

[0035] FIGS. 6a-6c show partial cross-sectional views of embodiments of a protective tube according to the present disclosure in which the area of the flow channels is optimized;

[0036] FIGS. 7a-7c show partial cross-sectional views of further embodiments according to the present disclosure having varying shapes of the helical fins; and

[0037] FIGS. 8a-8d show an exemplarily embodiment according to the present disclosure combining different optimization approaches.

[0038] In the figures, the same elements are always provided with the same reference symbols.

DETAILED DESCRIPTION

[0039] FIG. 1 illustrates the origin of vortex shedding w at a cylindrical, conically tapered protective tube 1 exposed to a flowing medium M in a pipe 2, which is indicated by one of its walls. Downstream of the protective tube 1 in the flow direction v of the medium, a ridge-like pattern develops. Depending on the flow velocity v of the medium M, this can lead to coherent vortex shedding which in turn may cause the protective tube 1 to vibrate.

[0040] The vibrations are mainly due to two forces acting on the protective tube 1, a shear force in the in y-direction and a lifting force in x-direction. The shear force causes oscillations at a frequency fs, while the lifting force causes oscillates at a frequency of 2 fs. The frequency fs now depends on the flow velocity v of the medium M, and on various physical or chemical medium properties such as its viscosity and density, as well as on the dimensions of the protective tube 1, such as its diameter and length. The closer the frequency fs is to the natural frequency of the protective tube 1 and the higher the flow velocity v of the medium M, the greater are the resulting oscillation causing forces.

[0041] As a result of the vibration causing forces, the protective tube 1 can be damaged or even break down completely. This is known as the so-called resonance condition.

[0042] FIGS. 2a-2c exemplarily and without limitation to such embodiment show a state of the art thermometer 3 having a protective tube in the form of a thermowell 4. As can be seen in FIG. 2a, the thermowell 4 comprises a tubular member 5 having a first end section 5a and a second end section 5b with a closed end. The tubular member 5 further comprises a bore 6 forming a hollow space within the tubular member 5, which is defined by an inner surface s and a predeterminable height h parallel to a longitudinal axis A of the tubular member 5, which bore 6 serves for receiving a measuring insert (not shown) for determining and/or monitoring the process variable, e.g., the temperature of the medium M.

[0043] Further, as illustrated in FIG. 2c, a process connection 8 is provided, which exemplarily is attached to the tubular member 5, here. This process connection 8 is a fastening member and serves for mounting the thermowell 4 to the pipe 2 (not shown) such that the tubular member 5 at least partially extends into an inner volume of pipe 2 and such that it is at least partially in contact with the flowing medium M.

[0044] The outer surface S the thermowell 4 of FIG. 2c has an essentially round shape as becomes visible in FIG. 2b. However, such construction can easily lead to undesired vortex induced vibrations of the thermometer 3.

[0045] To overcome the problems associated with coherent vortex shedding, protective tubes 1 with helical fins 9 which are typically arranged on the outer cross-sectional surface S of the protective tube 3 have been suggested. An exemplarily protective tube 3 having three such helical fins 9 is shown in FIG. 3a. The helical fins 9 form flow channels 10 along the tubular member 5 and thus reduce VIV of the protective tube 3. Each flow channel 10 is formed by the volume between to adjacent helical fins 9 which proceed around the tubular member 5 along its length axis A.

[0046] Ideally, such flow channels 10 should be closed channels 10′, as illustrated in FIG. 3b. Such closed channels 10′ would be able to carry medium M from the closed end section 5b towards the first end section 5a creating a suction mechanism for converting kinetic energy of the medium into pressure variations. Such variation in the flow velocity and pressure distribution would create a multidimensional motion of the medium which allows for decreasing of even suppressing VIV on the protective tube 3. Accordingly, the effectiveness of avoiding VIV is strongly related to the construction of the helical fins 9. The more the final shape resembles the ideal construction of FIG. 3b, the better the performance with respect to VIV.

[0047] A second issue is the flow profile v(x,y) of the medium M in the pipe or vessel 2. Ideally, the flow profile v(x,y) for a circular pipe has a parabolic shape, as illustrated in FIG. 4a. Accordingly, the medium M has the highest relative velocity vrel within the center region of the pipe or vessel 2. The profile slightly varies depending on the length lp of the pipe or vessel 2, as illustrated for the case of a comparably short pipe sections 2 in FIG. 4b and a comparably long pipe section 2 for FIG. 4c.

[0048] Additionally, the installation position and/or the presence of flow modifying elements 11, like the pipe corner piece shown in FIG. 4d, within a pipe/vessel 2 system may be considered as they also strongly influence the flow profile. After passing the pipe corner piece, the flow profile v(x,y) is asymmetrical (a) and only slowly transforms through several transition areas (b) to a symmetrical profile v(x,y) in a straight pipe 2 section following the pipe corner piece 11.

[0049] Since the relative velocity vrel of the medium M varies along the pipe 2 diameter d and since the installation position within a pipe system 2 highly influences the flow profile v(x,y), these quantities also strongly influence the sensitivity of a protective tube 1 regarding coherent vortex shedding.

[0050] It is an object of the present disclosure to establish an adaptive geometry which takes into account various process conditions that influence the sensitivity of a protective tube 1 towards VIV. By this procedure, the performance of a protective tube 1 subject to a flowing medium M can be highly increased. The process condition is any variable in connection with the protective tube 1, medium M properties or the geometry of the pipe or vessel 2, for example such as the flow profile v(x,y), a flow velocity v, a pressure, a temperature, a density or a viscosity of the medium M, a diameter d, volume V or roughness of the pipe or vessel 2, or a length l or diameter d of the tubular member 5.

[0051] In the following, a few examples of preferred embodiments for an optimized protective tube 1 are shown. It shall be noted that many more embodiments are possible which all do fall under the scope of the present disclosure. Additionally, the different embodiments shown can also be combined with each other.

[0052] In FIG. 5, a first embodiment of a protective tube 1 according to the present disclosure is shown. A plurality of helical fins 9 is formed on the outer surface S of a tubular member 5. The height h of the fins 9 varies with the length l of the tubular member 5. The fins 9 have the smallest height in the end section 5b which oriented towards the pipe 2 center region. In this area, the relative velocity vrel is the highest. The height h of the fins 9 continuously increases towards a section facing the pipe 2 wall, since in this area, the relative flow velocity vrel is the smallest. The height h of the fins 9 is a function of the length l of the tubular member 5 and thus, of the flow profile v(x,y). The geometric parameter height h of the helical fins 9 is chosen in dependence on the process condition flow profile v(x,y).

[0053] A second approach consists in optimizing a cross-sectional area afc of the flow channels 10, as illustrated in the second exemplary embodiment of FIG. 6a. Preferably, the cross-sectional area afc is designed such that it has a predefined shape and/or size, which is chosen depending on the at least one process condition of the medium M in the vessel or pipe 2. Different options exist for construction a certain cross-sectional area afc. It is possible to vary the dimensions and arrangement of the helical fins 9 and to add of remove a certain volume section from the fins 9 or the tubular member 5. Thereby, the cross-sectional area afc is defined as a cross-sectional area of the volume of a flow channel in a 2D cut of the protective tube.

[0054] FIG. 6a shows a partial cross-section of an embodiment of the protective tube 1 with helical fins 9 that form flow channels 10 with a cross-sectional area afc. The fins 9 are differently embodied, as exemplarily shown by the two variants 9a and 9b. That way, the cross-sectional area afc varies along the length l of the tubular member. A varying height h of the fins 9 also leads to different cross-sectional areas afc along the length l of the tubular member 5, as shown in FIG. 6b. In case of FIG. 6b, additionally volume section 12 was removed from the fins 9 in order to increase the cross-sectional area afc. As illustrated in FIG. 6c, a volume section 13 can also be removed from the tubular member 5 in the area of the respective flow channel 10

[0055] To vary this area, a volume section 12, 13 from the fins 9 or the tubular member 5 in the area of a flow channel 10 can be removed, as exemplarily illustrated in FIGS. 6b and 6c. Again, for the embodiments shown in FIGS. 6a-6c, the dimensions of the fins 9 also varies along the length of the tubular member 5. In the present case, e.g., the helical pitch p, the width t of the helical fins 9 vary along the length.

[0056] Embodiments for which the shape of the helical fins 9 varies are shown in FIGS. 7a-7c. For the protective tube 1 shown in FIG. 7a, different helical fins 9 have different shapes, as exemplarily shown for the fins 9a and 9b. FIG. 7b shows the helical fin 9b in greater detail. In contrast to the fin 9a, fin 9b has a notch 14 in its upper part. However, the shape of a specific fin 9 can also vary along the length of the tubular member 5 as shown in FIG. 7c, for which the shape of fin 9 varies from a rectangular shape 9a in a first section towards a circular shape 9b in a second section.

[0057] In FIGS. 8a-8d an advantageous embodiment of a protective tube 1 according to the present disclosure is shown, which combines different optimization approaches. As visible in FIG. 8a, the width w of the helical fin 9 varies along the length of the tubular member 5. The width decreases towards the end section 5b of the tubular member 5. As illustrated in FIG. 8b, additionally the helical pitch p and the fin width t vary along the length. Again, both quantities decrease towards the end section 5b. The resulting protective tube 1 is shown in a perspective view in FIG. 8c. The varying geometric parameters p, t and w of the helical fin 9 also lead to a varying dimensions of the flow channel 10.

[0058] To illustrate the specific choice of geometric parameters of the helical fins 9, the protective tube 1 is shown together with the respective parabolic flow profile v(x,y) inside the pipe 2 in FIG. 8d.

[0059] To manufacture a protective tube 1 according to the present disclosure, many different approaches exist, which all fall within the scope of the present disclosure. For instance, it is possible to start from a cylindrical tubular member 5, whereas the helical fins are machined on the outer surface S of the tubular member 5. The fins 9 and the tubular member 5 might further be processed by removing or adding a volume section to achieve the optimized dimensions. Alternatively, the protective tube 1 can also be formed by means of an additive manufacturing process, e.g., by means of 3D printing or the like.

[0060] In any case, at least one geometric parameter of the at least one helical fin 9 is chosen such that it depends on at least one process condition of the medium M in the vessel or pipe 2. These geometric parameters can for instance be calculated, e.g., by means of a calculation of the mechanical behavior of the protective tube 1 inside the pipe or vessel:

p,t,w,a.sub.fc=F(velocity,flow profile,density,viscosity,pressure,pipe diameter,length of the tubular member,temperature,pipe geometry)

[0061] All parameters can be used to calculate the dimensions of the flow channels 10 which depend on the choice of the geometric parameters of the helical fins. Standard values for standard situation may be derived to increase the speed of the calculation for a specific application.

[0062] In the embodiments shown, the helical fins proceed along the entire length l parallel to the length axis A of the tubular member 5. However, in other embodiments, also only a given section of the tubular member 5 might be covered by helical fins 9. In this case, the size of the section carrying the at least one helical fin 9 can also be chosen in dependence of the at least one process condition.