The service life of thermocouples

Thermocouple is a commonly used temperature instrument with a wide range of applications. Because armored thermocouples have sleeves for maintenance and isolation from external conditions, the material of the sleeves has a significant impact on the lifespan of armored thermocouples. It is necessary to choose thermocouple wires and metal sleeves based on their use. Below is a detailed introduction to the application lifespan of thermocouples.

The lifespan of detachable thermocouples

Only the stability of thermocouples is required at the scale of our country. Namely, the change in thermoelectric potential before and after application at a certain temperature for 200 hours. However, there is no established definition for the lifespan of applications yet. The request for the service life of thermocouples in Japan is based on the continuous application time of thermocouples specified in the Japanese JIS (C-1602-1995) standard. For type B, R, and S thermocouples, it is 2000h, while for type K, E, J, and T thermocouples, it is 10000h.

In practical applications, detachable thermocouples usually have maintenance tubes and are only used with bare wires in special circumstances. Therefore, in a few places, the lifespan of the maintenance tube determines the lifespan of the thermocouple. The determination of the practical application life of thermocouples requires the use of temporary networks and the accumulation of data under actual application conditions in order to provide accurate results.

Degradation of thermocouples

The application life of thermocouples is closely related to long-term tasks. The degradation of thermocouples refers to the phenomenon of aging and degeneration after application. Thermocouples formed from metals or alloys have external grains that gradually grow overnight at low temperatures. At the same time, the alloy contains a large number of impurities, which will cause changes in its position or shape, and will also have a reaction to the recovery or oxidizing gases in the surrounding conditions. Along with the above changes, the thermoelectric potential of the thermocouple will also be sensitive to changes. Therefore, the deterioration of thermocouples is preventable.