Securing and Optimizing Industrial Thermocouple Extraction Using Vibratory Methods

The issue

A major player in the energy sector approached Metravib Engineering to optimize its thermocouple extraction methods using vibratory techniques during on-site maintenance operations. The existing extraction system showed limitations in vibration propagation when navigating the bends of the thermocouple duct, requiring a technical upgrade to ensure better performance and improved ergonomics. The overall objective for the client was clear: to secure maintenance operations by optimizing this maneuver, thereby minimizing the risk of damaging critical installations.

The challenge: overcoming friction

Extracting tapered thermocouples from sinuous industrial ducts poses serious contact mechanics challenges:

• Friction and galling: Tests revealed that the minimum forces required to extract the thermocouples increase significantly with repeated friction cycles. This galling phenomenon degrades the thermocouple’s surface finish and heavily alters the friction coefficient.
• Risk of plastic deformation: The tensile forces involved during extraction from a highly bent duct can exceed the thermocouple’s yield strength or even its ultimate tensile strength, leading to plastic deformation or break before it is fully withdrawn.
• Limitations of analytical models: The extraction force varies greatly depending on the specific geometry of each duct. The discrepancy observed between analytical extrapolations (bend-by-bend calculations) and physical tests proves that a simplified prediction model cannot accurately estimate the actual forces involved due to the highly non-linear nature of the phenomenon.

The solution: dynamic characterization and experimental validation

To meet this need while bypassing overly simplistic theoretical models, our engineers deployed a rigorous methodology:

• Design of a representative test bench: We built a mockup accurately reproducing the actual mounting conditions of two industrial duct configurations: one “easy” and one “difficult” (featuring multiple bends).
• Experimental Modal Analysis: Using a laser vibrometer to guarantee non-contact measurement (without adding mass), we characterized the dynamic behavior of the ducts to accurately identify their natural modes and resonance frequencies.
• Multiparametric test campaign: We evaluated the effectiveness of various complex dynamic excitations, such as sine sweeps, shocks, and random vibrations. Simultaneously, we tested and quantified the benefits of an industrial lubricant applied using several methods.

Conclusion: reliable maintenance and optimized efforts

Through our cross-testing approach, we were able to identify the safest intervention strategy for technical directors and on-site operators:

• The proven effectiveness of random vibrations: Unlike a standard signal, applying a random vibration excitation, filtered on the duct’s first lightly damped natural modes, emerged as the most effective vibratory strategy. This method generates continuous micro-shocks between the thermocouple and the duct, reducing extraction forces by up to approximately 30%.
• The decisive impact of lubrication: The addition of a lubricant drastically reduces result dispersion by eliminating the galling phenomenon. On its own, the lubricant manages to reduce extraction forces by up to approximately 45%.
• Peak performance of the combined solution: Maximum efficiency was achieved by combining the application of lubricant with random vibration excitation, successfully reducing the extraction force by approximately 55%.

Are you facing delicate extraction issues, risks of galling, or premature sensor wear in your facilities? Theoretical models are not enough to guarantee the integrity of your critical equipment.

Benefit from our unique expertise in dynamic characterization and vibratory engineering to design a custom extraction or maintenance solution, validated through physical testing.