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thermowell bend

RE: thermowell bend

I have no personal experience with a bent thermowell.

The failures shown in photographs found in papers like the one at the link below (page 7) are resonance/vibration failures, not bends.
http://www.gruppofrattura.it/ocs/index.php/ICF/ICF12/paper/viewFile/1287/8989

But, the forces on a thermowell are typically shown like this:


Ironically, superimposing one photo on top of the graphic makes it look like drag force can bend a thermowell:


The original PTC 19.3 and its fairly recent revision is widely used in steam applications, which, like natural gas, has no "solids".

RE: thermowell bend

mostafa,

That's a pretty long thin tube you have there so depending on the density and actual velocity of the gas, bending is not too surprising.

Usually the thermowell vendor will do those checks so check the data sheet to see if anything has changed, e.g. gas velocity.

If the pressure has reduced, the actual velocity might be higher than was envisaged, even if the standard flowrate of the gas is lower than the design.

Most thermowells I've ever seen are tapered to give better strength and reduce vortex shedding becoming an issue, e.g. as below. Was this thermowell originally designed for a vessel or somewhere with no or low velocity?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: thermowell bend

(OP)
Dear sirs,
Thakns for your answers.Meanwhile please be warned process data such as pressure , velocity and temperature are same as data which have been considered in thermowell vendor stress calculation.Unfortunately the fact that happened for this thermowell is that during the instsllation , collar outer diameter has been reduced which could cause to thermowell resonance.Although, generaly in resonace situation thermowell will crack and break from its weak point.Nonetheless please let me know if you have any exprience about thermowell bending in resonance situation?

RE: thermowell bend

" collar outer diameter has been reduced " - hence strength of bending has been reduced. There's usually something that changed from the design....

Reduced from what to what?

Resonance is all about fatigue and cracking, not bending.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: thermowell bend

(OP)
Line diamiter:30""
U length:500
Nozzle Id.:38.1mm
Collar OD;
vendor design:37,9mm
after reducing:33mm
Collar distance from root:134mm
Please let me know how reducing of collar diamiter outcome to reduce the strange of bending?

RE: thermowell bend

Ok sorry - I missed the collar bit and thought you had machined off the taper.

Then it looks like someone got this a bit wrong.

So either:
the designer/vendor made an error (maybe put in U length of 50 instead of 500 into his designer software??)
the velocity did increase ( maybe only once for a short time) or density or something different from the data sheet
someone pigged the line without withdrawing it
The materials are not as strong as they are supposed to be ( did you get it from someone reputable?)
Someone put in the wrong one
Was it exposed to hydrotest water velocity?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: thermowell bend

Perhaps the thermowell was struck by a chunk of ice or whatever else that could possibly accumulate somewhere in the line.

RE: thermowell bend

hi mostafa
if you find a reason please share it in the group because it is my question too.
thsnks alot

RE: thermowell bend


The bending of thermowells in piping is no unusual, mainly if thermowell is installed in connections perpendicular to the main pipe. In recent piping designs, the thermowels are installed in connections with an angle of 45º to the main pipe and with the stem against the flow direction. I don´t know which is your case. Your stem bending is in the sense of the flow direction? Sometimes condensate water hammers can damage the stems of the thermocouples.

lm

RE: thermowell bend

the thermowell is too long although that my be a given.

Permanent deformation suggest line - scraper, or possible damaged during pre-commissioning.

what are the P,T, Flow and nominal sp. grav of the fluid?

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