Abstract

Title: Holistic Analysis of Thermocouple Sheath Failure in Cement Plant Calciner: Integrating Material Se lection, Installation Geometry, and Environmental Control. This study presents a comprehensive failure analysis of thermocouple protection sheaths within a cement plant calciner operating at approximately 850°C under a 20 mbar vacuum. The operational environment presents a unique synergy of harsh factors, including abrasive raw meal, condensing alkalis and chlorides, and reducing process gases.

The investigation reveals that the dominant failure mechanism is not merely high- temperature oxidation but a severe synergistic effect between erosive wear from particulate matter and accelerated corrosion triggered by localized thermal shock.

This shock occurs due to the ingress of cold ambient air (21% O2 at 25°C) through inadequate seals, which disrupts the stable protective oxide layer (e.g., Cr2O3).

A quantitative mathematical model was developed, integrating parabolic oxidation kinetics with linear ero sion and a synergistic damage term. Furthermore, the analysis highlights the critical impact of sensor instal lation angle. It is demonstrated that an optimal installation, minimizing the angle of impingement to =30° from the material flow direction, is essential for minimizing erosive wear fraction. Suboptimal angles (e.g., 90° impingement) can increase the erosion rate by a factor of 2-3, drastically shortening sheath life irrespective of the material chosen.

The model was solved for various materials and installation scenarios. Results demonstrate that air ingress and poor installation angle catastrophically reduce sheath lifetime. For a carbon steel sheath with a 3.5 mm wall, the model predicts failure in approximately 73 hours under combined leak and high-erosion conditions.

The conclusion emphasizes a three-fold strategy for reliability: (1) the imperative elimination of air leaks through improved mechanical sealing, (2) the optimization of sensor installation angle to =30° to minimize erosive wear, and (3) the selection of 1.4749 steel as the most cost-effective material for normal conditions, supported by a proactive maintenance schedule based on the predicted wear rates. This integrated approach is crucial for maximizing equipment lifespan, ensuring meas urement accuracy, and minimizing costly unplanned downtime in cement production processes.

DOI: doi.org/10.63721/25JPIR0112

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