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

Abstract

The present disclosure includes a method of producing a protective tube for insertion into a pipe or vessel containing a medium, the protective tube including a tubular member having a bore extending between an upper and lower of the tubular member, wherein the method includes the steps of providing a preformed element comprising a coiled wire with at least one turn, arranging the preformed element around an outer surface of the tubular member, and welding the preformed element on an outer surface of the tubular member.

Claims

1. A method of producing a protective tube configured for insertion into a pipe or vessel containing a medium, the method comprising: providing a protective tube comprising a tubular member including a bore extending between a first end and a lower end within the tubular member; providing a preformed element comprising a coiled wire having at least one turn; arranging the preformed element around an outer surface of the tubular member; and welding the preformed element onto the outer surface of the tubular member.

2. The method of claim 1, wherein the preformed element is configured and/or arranged such that, after the welding onto the tubular member, the preformed element forms at least one helical fin, winding around the outer surface of the tubular member and defining a flow channel along at least a part of the tubular member.

3. The method of claim 2, wherein at least one geometrical parameter of the at least one helical fin is selected as to depend on at least one process condition of the medium in the vessel or pipe.

4. The method of claim 3, 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 diameter of the tubular member.

5. The method of claim 1, wherein the tubular member is closed at the first end or the second end such that the protective tube is configured as a thermowell.

6. The method of claim 1, wherein the welding generates a weld is produced in an upper and a lower end section of the preformed element.

7. The method of claim 1, wherein the welding generates at least one weld in a center section of the preformed element.

8. The method of claim 1, wherein the welding generates a weld along one turn of the at least one turn of the preformed element.

9. The method of claim 1, wherein an upper and/or lower end section of the preformed element are configured as a ring, and wherein a coiled section is disposed between the upper end section and the lower end section.

10. The method of claim 9, wherein the welding generates a weld at or near the ring.

11. The method of claim 1, wherein a cross-sectional area of the preformed element defines a circle, an ellipse or a square.

12. The method of claim 1, wherein a diameter of the wire of the preformed element is 5-20% of a diameter of the tubular member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present disclosure will now be explained in more detail by means of the following figures in which:

[0030] FIG. 1 illustrates vortex shedding for an insertion body exposed to a flowing medium;

[0031] FIG. 2a shows a partial cut-away view of a thermometer having a state of the art thermowell;

[0032] FIG. 2b shows a cross-sectional view at line A-A of the thermowell of FIG. 2a;

[0033] FIG. 2c shows a side view of the thermometer of FIG. 2a with a fastening unit;

[0034] FIG. 3a shows a thermowell having a plurality of helical fins according to the state of the art forming a plurality of flow channels;

[0035] FIG. 3b shows flow channels for avoiding vortex induced vibrations;

[0036] FIGS. 4a-4d illustrate the influence of the flow profile and installation position along a pipe on the occurrence of vortex induced vibrations;

[0037] FIG. 5 shows a first embodiment of a protective tube in the form of a thermowell produced by the method according to the present disclosure; and

[0038] FIG. 6 shows a second embodiment of a protective tube in the form of a thermowell produced by the method according to the present disclosure.

[0039] In the figures, the same elements are always provided with the same reference symbols.

DETAILED DESCRIPTION

[0040] 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 represented 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.

[0041] Such vibrations are mainly due to two forces acting on the protective tube 1, a shear force in the y-direction and a lifting force in the x-direction. The shear force causes oscillations at a frequency f.sub.s, while the lifting force causes oscillates at a frequency of 2f.sub.s. The frequency f.sub.s 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 f.sub.s 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.

[0042] 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.

[0043] FIG. 2a exemplarily and without limitation to such embodiment shows a state of the art thermometer 3 having a protective tube 1 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 includes 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.

[0044] Further, as illustrated in FIG. 2c, a fastening unit 8 is provided, which exemplarily is attached to the tubular member 5 as shown. The fastening unit 8 may be a process connection 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.

[0045] The outer surface S the thermowell 4 may have an essentially round shape as shown in FIG. 2b. However, such construction can easily lead to undesired vortex induced vibrations (VIV) of the thermometer 3.

[0046] 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 thermometer 3, have been suggested. An exemplarily thermometer 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 thereby reduce VIV of the protective tube 1. Each flow channel 10 is formed by the volume between two adjacent helical fins 9, which proceed around the tubular member 5 along its length axis A.

[0047] In certain embodiments, such flow channels 10 may be closed channels 10′, as illustrated in FIG. 3b. Such closed channels 10′ may be configured 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 thermometer 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.

[0048] 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 v.sub.rel within the center region of the pipe or vessel 2. The profile slightly varies depending on the length l.sub.p 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.

[0049] Additionally, the installation position and/or the presence of flow modifying elements, e.g., like the pipe corner piece 11 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 (c) in a straight pipe 2 section following the pipe corner piece 11.

[0050] The present disclosure now provides a method for producing a protective tube employing a helical structure on an outer surface of a tubular member of the protective tube in a straightforward manner. In the following, three especially preferred embodiments of thermowells produced by an inventive method, are shown. The present disclosure is, however, not limited to protective tubes in the form of a thermowell but rather is applicable to a wind range of protective tubes, in particular also to gas sampling probes and pitot tubes.

[0051] A thermowell produced according to a first preferred embodiment of the method according to the present disclosure is shown in FIG. 5. The protective tube 1 with fastening means 8 has a tubular member 5. Along a section of the tubular member 5 a preformed element 12 comprising a coiled wire with at least one turn is arranged. Note that other embodiments can also comprise arranging of the preformed element along the entire length of the tubular member 5.

[0052] The preformed element 12 shown in FIG. 5 is provided with a first ring 13a in its upper end section 12a and a second ring 13b in the second end section 12b. Between the two rings 13a, 13b a coiled section 14 is provided. The preformed element 12 is welded to the tubular member 5 by means of two welds 15a, 15b produced in the area of the rings 13a, 13b.

[0053] A second preferred embodiment is subject to FIG. 6. In contrast to the protective tube 1 shown in FIG. 5, in the embodiment of FIG. 6, the preformed element 12 has only one ring 13a in the upper end section 12a, in which a first weld 15a is produced. In the lower end section 12b, a second weld 15b is produced along one turn of the preformed element 12, here the last turn of the preformed element 12. A third weld 15c is produced in a center area of the preformed element 12. Such weld 15c serves for reinforcement of the connection between the preformed element 12 and the tubular member 5. It shall be noted, that such additional weld 15c is optional. Also, further embodiments may comprise no rings 13a,13b employed in the end sections 12a, 12b of the tubular member. Rather, any of the embodiments shown and also described previously can be combined with another.