What is the lifespan of Type B and Type T thermocouples

The lifespan of kind B and Type T thermocouples varies considerably, primarily influenced by the kind of material, operating temperature, surrounding atmosphere, and protection measures employed. In general, Type B thermocouples last longer at high temperatures, while Type T thermocouples are very stable at low temperatures and in clean settings.




I. Type B Thermocouples: Long Lifespan with Precious Metals, Good for Very High Temperatures



Type B thermocouples (platinum-rhodium 30-platinum-rhodium 6) are made of precious metals and are very stable at high temperatures and resistant to oxidation. In the best circumstances, they may last more than 2000 hours.



Long-term temperature for operation: 1600℃



Temperature tolerance for a short time: 1800℃



Actual lifespan performance: Stable operation for 3-5 years in oxidizing or inert atmospheres over 1300℃; If you run it at full load at 1600°C for long periods of time, the lifespan could be cut short to 3–6 months. It also breaks down easily in sulfur-, carbon-, or reducing atmospheres, so it's not advised for usage.



Benefits: Little drift at high temperatures, strong stability, and no requirement for cold junction correction (thermoelectric potential <3μV at 0~50℃)



Limitations: prone to contamination, expensive, and not very accurate at low temperatures (<600°C)







II. Type T thermocouples: Very accurate at low temperatures, although they oxidize readily at medium and high temperatures.



Type T thermocouples, which are made of copper and constantan, are base metal thermocouples that are cheap, work well in low-temperature industrial settings, and can theoretically run for 10,000 hours straight.



Standard working temperature: -200 to 350 degrees Celsius



Temperature resistance for a short time: 400°C



Actual lifespan performance: In systems that work at low temperatures, like refrigerators and air conditioners, the lifespan is usually 3 to 5 years. Above 350°C, the copper positive electrode is likely to oxidize, which can cause thermoelectric potential drift or wire breakage. In humid or sulfur-containing environments, the constantan negative electrode is easy to corrode, which can affect long-term stability.



Pros: It's cheap, very accurate, and has good linearity. It's especially good for measuring temperatures between -200 and 0°C.



Limitations: It doesn't work well in oxidizing environments at high temperatures, thus it's not good for high-temperature readings.







III. Comparison of the Main Factors That Affect Lifespan



Table: Type B Thermocouple and Type T Thermocouple



Operating Temperature: The highest limit is substantially higher than Type T, however the lifespan is lower at higher temperatures. Above 350°C, things start to break down faster, therefore they aren't good for long-term use.



Atmosphere: Only works in situations that are oxidizing, inert, or vacuum. Can be utilized in places with low oxygen levels, but not with sulfides or heavy humidity.



Protective Measures: It is best to use 99% corundum protective tubing to make the product last longer. To stop oxidation, it is best to put metal or ceramic sheaths on.



Calibration Suggestions: Calibrate every 12 to 18 months, and if the error goes above the limitations, replace it. Change every three to five years, or calibrate often to make sure it's accurate.







IV. How to Make Thermocouples Last Longer



Don't let things get too hot: Only use them within the temperature range they are rated for.



Choose the right protective tubing:



Type B: It is best to use tubing made of high-purity alumina (corundum).



Type T: You can choose between a stainless steel or sealed sheath.



Check if the thermoelectric potential degradation is greater than the acceptable error (for example, ±3℃) during regular calibration and maintenance.



To reduce mechanical vibration and thermal shock, be careful when installing and don't let it go through hot and cold cycles too often.