Precaution :- Thermowell interface with Nozzle
A scary part on site is when you try to install the Thermowell inside the Nozzle and you realize the Thermowell O.D is larger than I.D of nozzle.
This simple thing will lead to great delays since you can’t just insert some other thermowell as they go through W.F.C calculations, material selection etc.
Nobody would want this to happen, so Let’s explore the precautions and recommended practices.
What factors are to be evaluated for ensuring the Thermowell gets properly inserted in Nozzle I.D
This simple thing will lead to great delays since you can’t just insert some other thermowell as they go through W.F.C calculations, material selection etc.
Nobody would want this to happen, so Let’s explore the precautions and recommended practices.
What factors are to be evaluated for ensuring the Thermowell gets properly inserted in Nozzle I.D
1.Nozzle Schedule
Even 1&1/2 inch pipe wont have the same I.D all the time.
The schedule of the pipe needs to be checked.
As it is logical the Higher the schedule (like Std, XS, XXS etc) the smaller the I.D available.
Software’s like pipe pro can be used to get dimensions.
The schedule of the pipe needs to be checked.
As it is logical the Higher the schedule (like Std, XS, XXS etc) the smaller the I.D available.
Software’s like pipe pro can be used to get dimensions.
2.Cladding on Thermowell
Thermowell consume a lot of material as compared to diaphragm of transmitters etc.
So always it is not a cost effective option to upgrade thermowell material to Alloy C-276 or other exotic material until it’s a dire necessity.
Another option sometimes used (depends on application) is to provide cladding on thermowell.
This also consumes little space and must be accounted for.
So always it is not a cost effective option to upgrade thermowell material to Alloy C-276 or other exotic material until it’s a dire necessity.
Another option sometimes used (depends on application) is to provide cladding on thermowell.
This also consumes little space and must be accounted for.
3. Clearance space
This one important consideration that gets overlooked.
Handling changes at initial stages of project is very easy, but the very same changes at later stage have a significant impact.
Classic example is Wake frequency calculation that caused the Thermowell base O.D to increase.(Maybe in the later stage process data got revised or WFC was incorrectly done etc)
Now if we have exact cut to cut distance between nozzle I.D and Thermowell O.D then it is very difficult to accommodate such last minute changes.
A Few more examples are listed below :-
Thermal expansion at higher temperatures is an issue.
As indicated above maybe at a later stage cladding of thermowell is recommended and this will consume some space.
Also sometimes the Pipe spec has a certain schedule but for ease of welling a different schedule is selected for vessel nozzle.
Hence it is preferred not to take exact cut to cut distance and keep some clearance.
Handling changes at initial stages of project is very easy, but the very same changes at later stage have a significant impact.
Classic example is Wake frequency calculation that caused the Thermowell base O.D to increase.(Maybe in the later stage process data got revised or WFC was incorrectly done etc)
Now if we have exact cut to cut distance between nozzle I.D and Thermowell O.D then it is very difficult to accommodate such last minute changes.
A Few more examples are listed below :-
Thermal expansion at higher temperatures is an issue.
As indicated above maybe at a later stage cladding of thermowell is recommended and this will consume some space.
Also sometimes the Pipe spec has a certain schedule but for ease of welling a different schedule is selected for vessel nozzle.
Hence it is preferred not to take exact cut to cut distance and keep some clearance.
Beware of unsafe Ways
Polishing of thermowell to fit into the Nozzle :-
Sometimes on site people polish the thermowell to reduce its O.D so that it fits in the nozzle.
This is as unsafe practice. As this risks the integrity of thermowell design and can lead to catastrophic failure.
Thanks for reading.
Hope it has been of value to you.
PS: This is as per best of my current understanding
Sometimes on site people polish the thermowell to reduce its O.D so that it fits in the nozzle.
This is as unsafe practice. As this risks the integrity of thermowell design and can lead to catastrophic failure.
Thanks for reading.
Hope it has been of value to you.
PS: This is as per best of my current understanding
