Thermocouple Application Note 4

Why can’t chemical analysis alone always solve failure problems?

Chemical analysis of a failed thermocouple is often an important step in determining the cause of failure. Analysis of the wire, insulators and sheath can identify contaminants that may cause changes in the emf vs. temperature response of the thermocouple. However, it is possible for contaminants to be present without affecting accuracy. Some contaminants simply do not affect the wires thermoelectric response sufficiently to cause an error. Also, even contaminants that affect the response of the wire may not cause an apparent failure if they are not present in a temperature gradient.

Chemical analysis is an important tool in failure analysis but it must be properly interpreted. Knowledge of the effects of the specific contaminants is important. It is one component in understanding the failure mechanism.

Concept Alloys has extensive experience in evaluating the possible effects of contamination as well as other failure mechanisms.

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Figure 1 : Chemical analysis spectra

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