subject: Using Protection Tubes With A Thermocouple [print this page] Thermocouples have come down in price since the first bulky platinum thermocouple was invented, but can still be pricey pieces of equipment and worth protecting. Protection tubes, thermowells, and other accessories can protect your process measuring device from corrosion and oxidation due to harsh chemicals and harsh environmental conditions.
Protection tubes are made from a variety of materials, and are designed to be used similarly to a thermowell. These tubes are protective sheaths made of ceramic or metal that are made to hold a thermowell or RTD sensor inside of them. They are designed to prevent corrosive chemicals and extreme environments (such as high pressure, high velocity, and corrosive atmospheric gasses) from damaging a thermocouple or RTD sensor. The tubes also prevent contamination and physical damage to the temperature measurement device. They are manufactured in three sizes generally (12 inch, 18 inch, and 24 inch), and can be sold with or without fittings.
Protective tubes come in many materials, including: cast iron, metal ceramic, silicon carbide, alumina, mullite, tercod, ceramic bore insulator, drilled protection well, and metal. Metal protection tubes come in the more commonly used metal alloys.
Cast iron tubes are used to protect thermowells that are used in non-oxidizing atmospheres. They are effective at protecting equipment up to 2000 degrees Fahrenheit.
Metal ceramic tubes perform better than ceramic tubes at protecting thermocouples from physical damage due to impact, and from damage caused by thermal shock and mechanical shock. However, metal alloy protective tubes generally perform better at resisting these hazards. They are effective up to temperatures of 220 degrees Fahrenheit.
Silicon carbide tubes are used often to erase the possibility of contamination from other types of tubes (such as cast iron). They are effective at protecting a thermocouple in an environment experiencing large temperature changes.
Alumina tubes are effectively used at temperatures up to 3200 degrees Fahrenheit. They perform better if they are preheated and are resistant to corrosive factors of many chemicals.
Tercod tubes are used for non-ferrous metals. A tercod tube is effective at protecting a thermocouple at temperatures up to 2300 degrees Fahrenheit.
Metal tubes are the most common type of protective tube. You can find metal tubes in a variety of alloys and in most sizes. Metal alloy tubes are among the most highly resistant to impact, thermal shock, and mechanical shock.
