Technical Brief

Natural Frequencies of Plate Supported Thermowells

[+] Author and Article Information
David S. Bartran

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 January 30, 2014; final manuscript received September 27, 2014; published online December 4, 2014. Assoc. Editor: Chong-Shien Tsai.

J. Pressure Vessel Technol 137(2), 024502 (Apr 01, 2015) (5 pages) Paper No: PVT-14-1013; doi: 10.1115/1.4028703 History: Received January 30, 2014; Revised September 27, 2014; Online December 04, 2014

An idealized model of a welded-flange thermowell is used to establish the role of flange thickness in natural frequency estimates. It is found that for thermowell diameters comparable to flange thickness, the support compliance of the thermowell/flange interface approaches that expected for a semi-infinite support. This allows the interface to be treated as a boundary condition rather than requiring a detailed deflection analysis of the flange. This finding is supported by published measurement data and independent finite element calculations for rigidly supported, welded-flange thermowells.

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Grahic Jump Location
Fig. 1

A representative thermowell installation showing thermowell, connection head, and flanged nozzle. The unsupported length of the thermowell and flange projection is also shown.

Grahic Jump Location
Fig. 2

Coordinates at the thermowell flange interface showing the load and response coordinates as described in the text

Grahic Jump Location
Fig. 3

Thin-plate compliance integral F(b¯) (Eq. (9)) plotted as a function of the normalized beam radius b/a. For b/a→1, the thin-plate model ceases to be an adequate description.

Grahic Jump Location
Fig. 4

Minimum plate thickness h/a as a function of beam b/a radius with the percentage frequency reduction, relative to the thick-plate limit, as a parameter. Cantilever length is L = 250 mm and plate radius is a = 100 mm.

Grahic Jump Location
Fig. 5

Normalized natural frequencies of a plate mounted cylindrical beam as a function of the plate thickness ratio h/d relative to the cylinder diameter d. The beam 250 mm in length and 20 mm in diameter affixed to a clamped plate 200 mm diameter.



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