How to Choose the Right Thermowell

by | Jul 1, 2014 | Measurement Instrumentation, Temperature

Jim Cahill

Chief Blogger, Editor

Let’s continue our series of posts on the educational temperature measurement videos from Emerson’s team managing the Rosemount brand of products and services. You can find the complete set of videos on the Temperature Insights page.

Thermowells shield thermocouples and RTD sensors from direct contact with the process. This 4:30 YouTube video, Thermowell Selection, highlights factors that affect your choice of thermowell material, ways to avoid thermowell failures, and questions you should consider to select the best thermowell for your application.

For many industries, temperature is the most important process variable (PV) to measure, since it can have a large impact on profitability, safety, and quality of the production process. Selecting the right type of thermowell helps ensure optimal system performance, long service life, simplified maintenance, and overall integrity of the process being measured.

Three questions can help with the thermowell section process:

  1. What type of connection are you making to the process?
  2. What is the best material of construction for the application?
  3. What is the best stem profile for the application?

Thermowell-Connection-TypeThe most common types of thermowell process connections are threaded, socket welded, and flanged. For the second question—best material of construction—three factors need to be part of your consideration set. First are the temperature limits of the material. Second is the chemical compatibility with the process media being measured. And, third is compatibility with the process piping material.

Thermowell-Stem-ProfileOn the question of the best stem profile for the application, the three most common ones are tapered, straight, and stepped. Tapered stem profiles provide good response time and strength, but can induce a higher drag force on the fluid flow. Straight stem profiles are extremely strong, but provide slower response time and induce a higher drag force. Stepped stem profiles provide lower drag forces and faster response times, but are less strong than the other stem profiles.

Thermowell failures are typically caused by high drag forces, excessive static pressure, high temperature, corrosion, and/or fluid-induced vibration. To avoid these failures, it’s important to run thermowell calculations based on your application. The Rosemount Thermowell Calculations page helps you perform the calculations to comply with updated standard, performance test code, PTC 19.3TW-2010.

Rosemount-Engineers-Guide-to-Industrial-Temperature-MeasurementThe information in this educational video, as well as the complete Temperature Insights series of videos, comes from The Engineer’s Guide to Industrial Temperature Measurement. If you don’t already have your complimentary copy, order one today.

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

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.