Thermowells:
Thermowells are typically constructed of solid drilled-out bar stock and are designed to protect a temperature sensor from the flow, high pressure and harsh environments. A thermowell has the added advantages of allowing the removal or replacement of the sensing device without opening up the process tank or piping. Thermowells are critically important for installations where the temperature element (RTD, thermocouple, thermometer, etc.) must be replaceable without de-pressurizing the process.
Thermowells can provide added protection to the sensing equipment, and can also assist in maintenance and period calibration of equipment. Thermopaste assists in the fast and effective transfer of thermal dynamics from the process to the sensing element. Application and maintenance of this material needs to be considered. Regular maintenance and condensation can affect the operation of the paste.
Common types of thermowells:
There are mainly three types of thermowells classified based on the type of connection made with the pipeline:
- Threaded
- Socket welded
- Flanges weld
Threaded thermowell:
Threaded thermowells are used in smaller pipes to measure the temperature of the non-corrosive fluid. The thermowell is screwed into the pipe, it is used where there is no need for frequent replacement.
Thermowells are used to provide an isolation between a temperature sensor and the environment, either liquid or guide.
Flanged welded thermowell:
The flanged thermowell has the flanged top end that is connected using nuts and bolts to the pipe. Thermowell has a flange collar that is attached to a coupling flange. This type of thermowells is used when frequent replacement or removal is required.
Flanged thermowells are used for high-temperature applications.
Socket Weld Thermowell:
The thermowell is welded directly into the pipeline. As the thermowell is welded into the pipeline it only used for permanent connections.
Socket weld connection provides a permanent strong connection, hence it is used in high pressure, high temperature applications.
Application of thermowell:
Petrochemical, refining, food processing, pharmaceutical, cosmetics and other processing industries, temperature sensors and thermocouples are often subject to pressure or incompatible substance contact, therefore, a thermowell used to protect them. Aerodynamics or hydrostatic forces typically act upon the thermowells which can be designed to be low pressure depending on nature of the application.
Advantages:
- Thermowells protect the sensor from pressure, corrosion, abrasion, or vibration caused by the process medium.
- Thermowells allow the sensor to be removed and replaced without compromising either the ambient region or the process.
Disadvantages:
- Their use for temperature measurement leads to additional acquisition and installation cost.
- They offer slow and sluggish response to variations in temperature.
- Loss of heat along the entire thermowell length may result in inaccurate temperature measurements.
