Improve reliability, extend sensor life, and reduce downtime with smarter design
Thermocouples are built to perform in some of the most demanding environments, including extreme temperatures, aggressive atmospheres, and precision-critical processes. But even the most advanced sensors can fail prematurely [MF1.1]if they’re not properly designed for the application.
The good news: most premature thermocouple failures aren’t random. They’re predictable and, more importantly, they’re preventable. By understanding the most common causes of failure, engineers can make smarter design decisions that extend sensor life, improve accuracy, and reduce costly unplanned maintenance.
Material incompatibility with the process environment
One of the most common, and costly, causes of thermocouple failure is selecting materials that aren’t suited for the operating environment.
Different sheath and thermoelement materials react very differently depending on exposure to oxygen, hydrogen, vacuum conditions, or contaminants. For example, refractory metals like tungsten and molybdenum perform well in inert or vacuum environments but can degrade rapidly in the presence of oxygen at elevated temperatures.
How to engineer it out:
Material selection should be driven by the specific environment, not just temperature range. Matching sheath and thermoelement materials to the process atmosphere helps prevent premature degradation, corrosion, and mechanical failure.
Contamination and drift
In high-temperature applications, even trace contamination can alter thermoelement chemistry, leading to calibration drift and inaccurate readings over time.
This is especially critical in semiconductor and high-purity environments, where vapor-phase transport or cross-contamination between materials can impact temperature measurement stability and, by extension, product quality.
How to engineer it out:
Design features such as high-purity insulation materials, controlled internal geometries, and protective sheath configurations help minimize contamination pathways and maintain long-term accuracy.
Thermal cycling and mechanical stress
Repeated heating and cooling cycles introduce expansion and contraction that can weaken materials, cause microfractures, and eventually lead to open circuits or other types of sensor failure.
In dynamic environments, like furnaces or turbine systems, mechanical stress is often just as damaging as temperature itself.
How to engineer it out:
Selecting materials with strong thermal shock resistance and designing for flexibility or strain relief can significantly improve durability. In some cases, adding support structures or optimizing sensor geometry can reduce mechanical fatigue and extend sensor life.
Oxidation and chemical attack
At elevated temperatures, exposure to reactive gases such as oxygen, sulfur, or carbon can rapidly degrade thermocouple components.
Certain materials are particularly vulnerable. For instance, platinum-based thermocouples can be affected by sulfur contamination, while molybdenum can oxidize above relatively moderate temperatures when exposed to air.
How to engineer it out:
Using protective sheaths, coatings, or controlled atmospheres can shield sensitive materials. In more aggressive environments, selecting inherently resistant materials is critical to maintaining performance.
Improper Installation or Mechanical Damage
Even a well-designed thermocouple can fail prematurely if it’s improperly installed or exposed to physical damage during operation.
Common issues include excessive bending, vibration, poor sealing at pressure boundaries, or inadequate support during insertion into process equipment.
How to engineer it out:
Incorporating robust mounting solutions, such as compression seal fittings and support tubes, helps protect the sensor during installation and operation while maintaining a reliable seal in pressure or vacuum environments.
Built for Your Application
For more than 75 years, Conax Technologies has worked alongside engineers to design temperature sensing solutions that perform in the most demanding environments. From semiconductor processing to aerospace and power generation, our team develops both standard and custom thermocouple assemblies tailored to each application’s unique requirements.
Backed by deep materials expertise and a commitment to precision manufacturing, Conax helps customers reduce failure rates, extend sensor life, and improve overall system performance.
To learn more about Conax temperature sensing solutions or discuss your application, contact the Conax Technologies engineering team today.