ASME PTC 19.3 TW:2016 pdf free download

ASME PTC 19.3 TW:2016 pdf free download.Thermowells.
6-1 GENERAL CONSIDERATiONS
6-1.1 OvervIew of Design Criteria
ThermowelLs shall be designed to withstand static pressure, steady-state fluid impingement, turbulence, and dynamic excitation due to von Karman vortices. Excitation by structure-born vibration is a possibility and should also be considered, but is not addressed by this Standard, since this type of excitation is determined by the design and support of the entire piping system. Consideration of these loads on a mechanical model of the thermowell results in pressure and velocity limits due to the combination of steady-state and oscillatory forces acting on the thermowcll. In evaluating an existing design or in designing a thermowell for given applications, the complete range of operating conditions for the thermowell, from start-up to emergency conditions, shall be considered. Factors that reduce the thermal mass of the thermowell and measurement errors are those that tend to reduce strength. Thermowell design consists of achieving accurate and reliable temperature measurement without compromising mechanical integrity or fluid containment. In all cases, the mechanical strength requirements shall control.
6-1.2 OptimIzation of Thermowell Design
Proper design ol a thermowell requires that the sensor mounted inside the thermowell attain thermal equilibrium with the process fluid. Thermal modeling of the sensor response is outside thc scope of this Standard (refer to the latest version of L’TC 19.3 for guidance). This Section briefly summarizes general design rules that will optimize the sensor performance within the constraints of the mechanical strength requirements.
A high fluid-velocity rating for the thermowell requires a sufficiently high natural frequency for the thermowell (subsection 64) and sufficiently low oscillatory stresses (subsection 6-10). Higher natural frequencies result from decreasing the unsupported length, L, increasing the support-plane diameter, A, and decreasing the tip diameter B. Lower oscillatory stresses result from decreasing length L and increasing diameter A. A higher static pressure rating (subsection 6-13) requires increasing the value of tip diameter B.
In contrast, good thermal performance favors increasing length L and decreasing diameters A and B.