This is for the Thermowell Specialists.. Need a bit of Advice.. I am in the process of updating the Specs for an end user regarding ASME PTC 19.3 TW. Some of us are aware that PTC 19.3 methodology required the user to calculate the natural frequency through a simple formula that did not account for pipe wall flexibility. The user calculated the ratio of vortex shedding frequency about the tip of the thermowell (wake frequency) to the natural frequency of the thermowell. This design was acceptable if the frequency ratio was less than 0.8 to guard against vortex induced vibrations.A number of thermowells designed in accordance to ASME PTC 19.3 have failed in non-steam service leading to catastrophic consequences. Subsequently ASME issued PTC19.3 TW and updated in 2016, I would like to add the following criteria in the Specs, Pl confirm this approach is good enough for a robust design.
Calculated wake frequency shall not exceed the number in Table below based on information on pipe schedule in data sheets.
Table - Limits of thermowell frequency ratio
Parent pipe schedule (Note 1)
Schedule 160 or greater
Schedule 80 to less than Schedule 160
Schedule 40 to less than Schedule 80
Less than Schedule 40
1. Treat stainless and non-stainless pipe the same (i.e. Schedule 40S and 40 have the same limit)
In reply to timchan bonkat:
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