Reducing Thermowell Dynamic Stress Forces

Reducing Thermowell Dynamic Stress Forces

by | Apr 27, 2018 | Measurement Instrumentation, Temperature |

Jim Cahill

Chief Blogger, Editor

Thermowells are traditionally a circular cylinder installed into the piping to protect the temperature sensors from the flow. From an Emerson whitepaper, Thermowell Calculations:

As a process fluid passes around the thermowell, low pressure vortices are created on the downstream side in laminar, turbulent, and transitional flow. The combination of stresses, generated by the static in-line drag forces from fluid flow and the dynamic transverse lift forces caused by the alternating vortex shedding, create the potential for fatigue-induced mechanical failures of the thermowell. Piping designers may use a variety of tools to predict and avoid thermowell failures in their systems, but ASME PTC 19.3-1974 had been the standard by which most thermowells were designed.

The standard by the American Society of Mechanical Engineers (ASME) updated the thermowell calculations from PTC 19.3 to PTC 19.3 TW. A wake frequency calculation tool is available to help perform preliminary calculations these forces.

I mention all this as background, because there is a new short 1:30 YouTube video, Rosemount Twisted Square – How It Works. This twisted square design reduces vortex induced vibrations, which are the leading cause of thermowell failure. They provide longer lasting equipment life and a solution for thermowells that don’t pass AMSE 19.3 TW calculations.

You can learn more about this design and how it eliminates over 90% of dynamic stress over traditional cylindrical thermowells on the Rosemount Twisted Square Thermowell page on Emerson.com.

You can also connect and interact with other temperature measurement experts in the Temperature group in the Emerson Exchange 365 community.

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