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Research Papers: Design and Analysis

Support Flexibility and Natural Frequencies of Pipe Mounted Thermowells

[+] Author and Article Information
David S. Bartran

Mem. ASME
Exothermics, Inc.,
14 Columbia Drive,
Amherst, NH 03031
e-mail: dbartran@yahoo.com

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received February 5, 2014; final manuscript received October 17, 2014; published online February 20, 2015. Assoc. Editor: Chong-Shien Tsai.

J. Pressure Vessel Technol 137(4), 041201 (Aug 01, 2015) (6 pages) Paper No: PVT-14-1016; doi: 10.1115/1.4028863 History: Received February 05, 2014; Revised October 17, 2014; Online February 20, 2015

A simplified model of a pipe mounted thermowell provides a measure of insight into the design and application of intrusive pipe fittings. A combination of Fourier and Green’s function methods together with a distributed load model of the thermowell/pipe wall interface are used to calculate the support compliance and subsequently the natural frequencies of the thermowell. These are compared with limited though independent calculations. This comparison confirms a profound reduction in natural frequencies for commonly encountered thermowell installations, reductions that should not be ignored where the risk of flow-induced resonance is high.

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References

Figures

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Fig. 2

Relationship between the differential load at B, a distance yB from the neutral axis, and the deformation at point N, a distance yN from the neutral axis of the beam, after [12]

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Fig. 3

Natural frequency of a pipe-mounted thermowell versus wall thickness for NPS10 pipe, with thermowell dimensions listed in Table 1

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Fig. 4

Natural frequency of pipe-mounted thermowell versus wall thickness for NPS18 pipe with thermowell dimensions listed in Table 1

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Fig. 5

Natural frequency of a pipe-mounted thermowell versus wall thickness for NPS24 pipe with thermowell dimensions listed in Table 1

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Fig. 6

Support compliance for the pipe-mounted thermowell in Fig. 4 versus wall thickness for NPS10 pipe. Note that the finite element data, in this case, do not exhibit a limiting condition as pipe wall thickness is increased. This appears to be an artifact of the meshing protocols used.

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Fig. 7

Support compliance for the pipe-mounted thermowell in Fig. 5 versus wall thickness for NPS18 pipe

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Fig. 8

Support compliance for the pipe-mounted thermowell in Fig. 6 versus wall thickness for NPS24 pipe

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Fig. 1

Shell mounted cantilevers of length L and diameter d for isolated and opposed load distributions. The midsurface diameter of the shell is 2a with thickness h. Out-of-plane bending is shown in the figures, while in-plane bending refers to loads directed along the shell axis.

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