FAQ about Pyrometric Sleeves and Silicone Sleeves for Temperature Sensors

In this guide we answer the most frequently asked questions about pyrometric and silicon thermocouple sleeves, their function, types of materials, applications and selection criteria for high temperature environments such as industrial furnaces and foundries.

Pyrometric tubes (or pyrometric sleeves) are essential to protect temperature sensors and ensure reliable readings even under severe conditions.

What is a pyrometric sleeve?

A pyrometric sheath is a protective tube designed to house a thermocouple during temperature measurements in furnaces, foundries, or other industrial thermal processes. These sheaths extend the sensor's lifespan by protecting it from corrosion, abrasion, thermal shock, and continuous exposure to high temperatures.

What is a silicone case used for?

Silicon sheaths (usually made of silicon carbide – SiC) are used to protect thermocouples in extremely hot or aggressive environments, such as metal foundries or high-temperature furnaces. They ensure durability and measurement accuracy by isolating the sensor from direct contact with molten or highly oxidizing atmospheres.

What is the difference between a pyrometric holster and a pod?

Pyrometric sleeve: usually a protective tube that is inserted directly into high-temperature processes (furnaces, foundries).
Traditional sheath: can be more robust, with fixings, designed to protect sensors in various processes.

In industrial practice, both terms can overlap, but pyrometric sleeve is more associated with direct measurement applications in furnaces and molten metal.

In what applications are pyrometric sleeves used?

They are especially useful in:

Ceramic, glass and metallurgy kilns
Ferrous and non-ferrous metal foundries
Continuous high-temperature thermal processes
Industrial ovens with aggressive atmospheres

These covers allow you to measure temperature with thermocouples without exposing the sensor directly to the process.

What materials are pyrometric sleeves made of?

The most common materials for pyrometric sheaths that house thermocouples are:

Silicon carbide (SiC) – extremely high thermal resistance
Silicon nitride – excellent mechanical and thermal resistance under aggressive conditions
Reinforced stainless steel (when internal sheaths are combined with metal structures)

The use of SiC is very common in sheaths designed for molten metal environments or extreme temperatures.

What properties does silicon carbide (SiC) offer in sheaths?

Silicon carbide sleeves offer:

High resistance to extreme temperatures
Excellent resistance to corrosion and erosion
Superior protection against thermal shock
Good thermal conductivity for more reliable measurements

This material is ideal for applications where maximum thermocouple protection is needed.

What length and dimensions can these covers have?

Pyrometric sleeves are manufactured in multiple lengths and diameters, adapting to the type of oven or industrial process. For example, dimensions can range from approximately 250 mm to over 1500 mm, with different combinations of internal and external diameters, and with threads for fixing according to standards.

How to choose a suitable pyrometric cover?

To correctly select a pyrometric sleeve, the following should be evaluated:

Maximum operating temperature
Process material (furnace charge, molten metal, etc.)
Required immersion length
Internal diameter to allow the thermocouple to be inserted correctly
Need for fixings or threads for secure mounting

Proper technical selection ensures more reliable measurements and greater sensor durability.

Can the thermocouple be replaced without removing the sheath?

Yes — pyrometric sleeves are designed to allow removal and replacement of the thermocouple without completely disassembling the sleeve from the process, reducing downtime of ovens or thermal installations.

What advantages does a high-quality pyrometric cover offer?

The main advantages of a well-selected pyrometric sleeve are:

More stable and accurate temperature readings
Greater protection and longer thermocouple lifespan
Less frequent sensor replacement
Greater safety in continuous high-temperature processes