Electricity + Control April 2019

FLOW MEASUREMENT + INSTRUMENTATION

Stable temperature measurement in flow applications

In order to prevent any damage to a ther- mowell due to mechanical loads during operation, a thermowell calculation per ASME PTC 19.3 TW-2016 is recommended for critical process conditions. In case of a calculation with negative results, the only constructive solution until recently was to shorten the thermowell stem, or to in- crease the root and tip diameter, accepting a longer response time of the thermometer. The new ScrutonWell ® design, de- veloped by WIKA Instruments, reduces the amplitude of oscillation by more than 90% and allows for easy and fast instal- lation of the thermowell without support collar, and thus without expensive and time- consuming rework on site. This helical design has been used successfully for decades, in a variety of industrial applications, to suppress vortex- induced shrinkage excitation.

The new ScrutonWell ® design can be used for solid machined thermowells with flange connection, in Vanstone design or for weld-in or screwed process connection. Electricity + Control ’s sister publica- tion, MechChem Africa , reported in its December 2018 edition on the extensive tests performed on the ScrutonWell ® design at the National Engineering Lab- oratory’s flow test facility in Glasgow, UK. The tests confirmed that thermo- wells with a ScrutonWell ® design have no tendency to vibrate. Enquiries: Greg Rusznyak atWIKA Instruments:Tel. +27 (0)11 621 0000, or email: sales.za@wika.com

Functional principle Kai Grabenauer, Product Manager at WIKA AlexanderWiegand SE & Co, explains how the ScrutonWell ® works. With standard thermowells, in certain flow conditions, a Kármán vortex street can form behind the thermowell stem when it is subjected to a flow within a pipeline. This vortex street consists of two rows of vortices with op- posite directions of rotation, which detach themselves to the left and the right of the thermowell out of phase, and this can cause the thermowell to vibrate. With the new ScrutonWell ® design, the helical strakes arranged around the stem of the thermowell break up the flow and thus impede the formation of a clearly defined Kármán vortex street. As a result of the reduced amplitudes of the diffused vortices, vibrational excitation of the ther- mowell is avoided.

The new ScrutonWell ® thermowell is designed to break up the flow around the thermowell, preventing the formation of vortices and reducing vibration.

Electricity + Control

APRIL 2019

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