Measuring and controlling temperature can the most important parameter in many production processes. It’s not only the temperature sensors that are important, but how they are protected by thermowells.
Thermowells are tubular fittings used to protect temperature sensors installed in industrial processes. A thermowell consists of a tube closed at one end and mounted in the process stream. A temperature sensor such as a thermometer, thermocouple or resistance temperature detector is inserted in the open end of the tube, which is usually in the open air outside the process piping or vessel and any thermal insulation. The process fluid transfers heat to the thermowell wall, which in turn transfers heat to the sensor. Since more mass is present, the sensor’s response to process temperature changes is delayed. If the sensor fails, it can be easily replaced without draining the vessel or piping. To be representative of the average temperature of fluid, the thermowell must extend a few per cent of the inside diameter of the process pipe or vessel.
In a prior post we’ve shared how to choose the right thermowell for your temperature measurement application. Selection is based on answering three basic questions:
- What type of connection are you making to the process?
- What is the best material of construction for the application?
- What is the best stem profile for the application?
This post includes an embedded YouTube video on the thermowell selection process.
Since thermowells penetrate into piping with fluids flowing by, understanding the mechanical impact of vibration and resonant frequencies is important. In a post, Online Calculation Tool for Thermowell Installations, we discuss the ASME temperature measurement best practice standard, PTC 19.3 TW-2010 and point to an online tool for performing preliminary calculations to see how your design meets the ASME standard requirements. The calculations are based upon process fluid properties, piping specifications and thermowell dimensions.This online calculation tool site also includes an educational video, whitepaper and a request for help for an official calculation to be performed. In the video, Emerson’s Dirk Bauschke explains the key improvements in the PTC 19.3 TW thermowell calculation standard.
One of the things that triggered me to do this post was a cool new video on the manufacturing process for thermowells. This video is from the Emerson facility in Karlstein, Germany shows the production processes including automated cutting, CNC-controlled gun drilling, ultrasonic cleaning, pressure testing and finally pin stamping. The 2:35 YouTube video, Rosemount Thermowell Manufacturing Site does not include any narration but shows the process from raw material to finished product.
You can connect and interact with other temperature measurement experts in the Temperature group in the Emerson Exchange 365 community.