Thermowells subjected to external pressure
Thermowells subjected to external pressure
(OP)
Would the external pressure calculations of UG-28 apply to thermowells? I am concerned with ones that are essentially suspended (hung) inside a pressure vessel with one side free while the other side is part of a pressure retaining seal.
As I read through the "Basis for external pressure calculation charts" given in Section II Part D, I understand that it assumes that both the ends are simply supported (and therefore suggests could therefore lead to buckling failure). This is clearly not the case for the case of a thermowell whose one side is completely free to undergo any longitudinal dimensional changes.
As I read through the "Basis for external pressure calculation charts" given in Section II Part D, I understand that it assumes that both the ends are simply supported (and therefore suggests could therefore lead to buckling failure). This is clearly not the case for the case of a thermowell whose one side is completely free to undergo any longitudinal dimensional changes.





RE: Thermowells subjected to external pressure
I think you are getting in a tizzy here. UG28 is for radial bucklin of shells whereby the shells buckle radially. UG 28 does not check for Euler type buckling. Why are you concerned about a thermowell? Normally thermowells have a low D/t ratio and checking for external pressure is not performed. (i.e. to buckle a thermowell you would need a very very high pressure)
RE: Thermowells subjected to external pressure
UG-31 specifically does say that UG-28 is to be used for external pressure calculations when tubes and pipes are used as tubes or shells. Agreed that t/w bucking or failure under external pressure would be highly unlikely. However, how else would one calculate their external pressure ratings? Also, please state a quantitative value for "very very high pressure" (and temperature?).
RE: Thermowells subjected to external pressure
thermowells do collapse though it is usually the fabricated tube design not the drilled barstock type
good luck
RE: Thermowells subjected to external pressure
RE: Thermowells subjected to external pressure
The thermowell is closed on the end so that provides one support for the "shell", in a similar way that a dished end of a pressure vessel shell provides support. Check out FIG UG-28.1(d).
Many pressure vessels are free to extend in a longitudinal direction, when fitted with a sliding support, so I'm not sure what your concern is.
Cheers,
John
RE: Thermowells subjected to external pressure
RE: Thermowells subjected to external pressure
there is design guidance specific to thermowells, that relies on UG-28 for the pressure rating and otherwise covered by the performance test codes(ASME).
are you attempting to redefine available design criteria or develop a new one?