Temperature Measurement · Glossary

What is a Thermowell?

protective pressure tubeTemperature Measurement

A thermowell is a closed end tube fitted into the process that protects a temperature sensor and allows it to be removed under pressure.

Thermowell Explained

The well takes the process pressure, flow and corrosion, while the sensor sits inside. Sensors can be replaced without opening the process.

Thermowells slow the response and must be designed against flow induced vibration. ASME PTC 19.3 TW gives the calculation method.

Types	threaded, socket weld, flanged, Van Stone
Shapes	straight, tapered, stepped

What is a Thermowell?

A thermowell is a closed end tube fitted into the process that protects a temperature sensor and allows it to be removed under pressure.

Why do thermowells break?

Mostly from vortex induced vibration at high velocity, when the shedding frequency approaches the well natural frequency.

How do I improve response in a well?

Use a spring loaded sensor touching the bottom, a close fitting bore and, if allowed, a heat transfer paste.

Thermocouple and RTD installation precautions

A practical guide on instrumentationblog.in with more detail on thermowell and how it is applied on real plants.