The application of thermocouples in flue gas temperature measurement
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“K-type thermocouples cannot be used directly at high temperatures in environments with sulfur, in atmospheres that are reducing or alternating between reduction and oxidation, nor in a vacuum; they are also not recommended for use in weakly oxidizing atmospheres. Then why do design firms still use K-type thermocouples to measure the temperature of flue gases in furnaces, without worrying about the impact of reducing gases such as SO2 and CO on the measurements taken by these thermocouples?
The fact that it is not recommended does not mean it cannot be used; however, errors will gradually occur during use, and the magnitude of these errors depends on various factors. If the errors are small enough to be tolerable within the context of the manufacturing process, then it can be used.
Without direct contact and protected by a sleeve, how can it be reduced or oxidized?
Some casings have molecular gaps, allowing for gradual penetration
It’s not absolute, but it’s possible. Proof method: Seal the junction box and let it operate for one and a half years or several years; check whether there is any black substance at the junction box – in most cases, this is due to the accumulation of leakage from the medium
Replacing it every one and a half years is sufficient; in many cases, it is the sleeve that wears out more quickly.
It’s amazing too that such molecules can penetrate like that!