Industrial thermowells fail for several reasons. The four main factors are:
MECHANICAL - Bending or breakage caused by an applied force in excess of the thermowell yield strength.
CORROSION - Induced by chemicals and/or elevated temperatures.
EROSION - Resulting from high-speed particle impingement on the thermowell
VIBRATIONAL - Failure due to Von Karmen Trail Effect
The above failure modes can be minimized through proper engineering and material selection. However, vibrational fatigue failure is less familiar and often overlooked in thermowell design. Vibrational fatigue occurs as a stream of product passes the thermowell, creating a wake on the downstream side. When this wake oscillates at a frequency that is equal to the natural frequency of the thermowell, a resonance is created, which can cause thermowell failure.
The phenomenon is known as the Von Karman Trail Effect, and has a defined frequency that is based upon the well configuration and the velocity of the flow. Given reliable process information, the suitability of a thermowell can be determined. As in other engineering calculations, safety factors should be employed to compensate for unforeseen process variables.
Consideration of these factors and proper calculations of the results can eliminate all but the most unusual thermowell failures.
GAYESCO can assist you in designing a thermowell that can meet your operating conditions and design criteria.