With Thermowell Assembly

Thermowells are tubular fittings used to protect temperature gauges installed in industrial processes. A thermowell consists of a tube closed at one end and mounted in the process stream. A temperature gauge or thermometer 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. Thermodynamically, the process fluid transfers heat to the thermowell wall, which in turn transfers heat to the sensor. Since more mass is present with a Temperature gauge -well assembly than with a probe directly immersed into the process, the sensor's response to process temperature changes is slowed by the addition of the well. If the temperature gauge fails, it can be easily replaced without draining the vessel or piping. Since the mass of the thermowell must be heated to the process temperature, and since the walls of the thermowell conduct heat out of the process, the temperature gauge accuracy and responsiveness is negatively impacted by the addition of a thermowell.

Traditionally the thermowell length has been based in the degree of insertion relative to pipe wall diameter. This tradition is misplaced as it can expose the thermowell to the risk of flow-induced vibration and fatigue failure.

When measurement error calculations are carried out for the installation, for insulated piping or near ambient fluid temperatures, excluding thermal radiation effects, conduction error is less than one percent as long as the tip is exposed to flow, even in flanged mounted installations.

The response time of the installed temperature gauge Thermowell assembly is largely governed by the fluid velocity and considerably greater than the response time of the temperature gauge itself. In Goa Thermostatic manufactured gauges this is generally between 6 – 8 seconds.

At Goa Thermostatic we also have longer designs which are used in low velocitiy services or in cases where historical experience justifies their usage. In modern high strength piping and elevated fluid velocities, each installation must be carefully examined especially in cases where acoustic resonances in the process are involved. At Goa Thermostatic we design the Thermowells based on PTC 19.3 standard which provides the immersion length and the vibration the thermowell can withstand in the given working conditions.

The thermowells manufactured in Goa Thermostatic are machined from drilled bar stock to ensure a proper sensor fit on state of the art CNC machines. A thermowell is typically mounted into the process stream by way of a threaded, welded, or flanged process connection. The temperature gauge is inserted in the open end of the thermowell. The use of welded sections for long designs is discouraged due to corrosion and fatigue risks.

Refer TABLES for ranges available, connection types and the various options available with the supply of Temperature gauges.


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