Calculation of thermowell strength to ASME PTC 19.3 TW-2010

By K Grabenauer, WIKA

 

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Published in:

Electricity+Control, March 2013 (pages 54 - 55)

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The safety awareness of all users has led to a continuously increasing demand for thermowell strength calculations over the last few years. The calculation of ASME PTC 19.3-1974 - based on the principles established by JW Murdock - has acquired worldwide importance.

In December 1995, a serious accident occurred in a sodium coolant circuit of the Japanese nuclear power plant in Monju. It was caused by the break of a thermowell, even though the specifications of ASME PTC 19.3-1974 had been observed. As a result, the basics of the thermowell calculation to ASME PTC 19.3-1974 were revised and brought in line with the latest state-of-the-art. Significant changes to the calculation basics have allowed a significantly improved simulation of the real operating conditions of the thermowell.

 

Take note:

  • Thermowells are tubular fittings used to protect temperature sensors, and must be designed to withstand the anticipated operating conditions.
  • ASME PTC 19.3 includes a thermowell stress calculation to prove that the materials chosen, and the mechanical design, will withstand the operating conditions.
  • Failures of thermowells have necessitated the revision of ASME PTC 19.3 to state-of-the-art, thus improving thermowell safety.