Service intended

Thermowell is manufactured and calculated according to ASME PTC 19.3 TW-2016 to protect it from the loads of the flux. If the calculated value is not appropriate, then shorten the length of the Thermowell, and increase the root and the tip diameter of the Thermowell to change the outcome value, or try to change the structure by installing the support collar on the Thermowell. 
However, these changes have its own limits. 
A650 Series could reduce the amplitude of oscillation by 70 %, and reduce the danger of breakage of Thermowell by VIV (Vortex Induced Vibration). 
Furthermore, because it reduces the loads on the Thermowell, it makes the installation possible without installing the support collar and without the change of Nozzle.

Description

Standard Type Thermowell

The oscillation of vortices which is caused by VIV can be found around the Thermowell. If the vortex shedding frequency approaches to the natural frequency, then the resonance could  cause the breakage of the Thermowell.

A6500 Type Thermowell

By comparing the standard Thermowell with A650 Series, the noticeable decrease of the vortices could be found around the A650 Series. Furthermore, it could reduce the chance of breakage of the Thermowell which is caused by VIV.