Is the outer diameter of the thermowell larger than the inside diameter of the nozzle?
The scary part of the site is when you try to install the thermowell inside the nozzle and you find that the outer diameter of the thermowell is larger than the inside diameter nozzle (ID)? (Thermowell specifications)
This simple point will lead to large delays because you can not enter other values of other thermowells because they go through WFC calculations, material selection, and so on. No one wants this to happen, so let’s take a look at the precautions and recommended actions. What factors are evaluated to ensure the correct placement of the thermowell in the ID nozzle?
1. Nozzle Schedule
Even 1 and 1/2 inch pipes are not always the same ID. The pipe schedule must be checked. As is logical the higher the application (such as Std, XS, XXS etc.) the smaller the ID available. Software such as Pro Tube can be used to obtain dimensions.
2. Cladding on Thermowell
Thermowell consumes a lot of materials compared to diaphragm transmitters and so on. So it’s not always a cost-effective option to upgrade thermowell materials to C-276 alloys or other exotic materials to a serious necessity. Another option that is sometimes used (depending on the application) is to prepare a metal coating on thermowood. It also consumes little space and should be considered.
3. Clearance Space
This is an important point that is overlooked. It is very easy to deal with changes in the early stages of the project, but the same changes in the next stage have a significant impact.
A classic example is the Wake frequency calculation, which increases the base O of the OD thermowell. (Maybe in the next step the modified process data or WFC will be done incorrectly, etc.) Now if we have a precise cut for the distance between the ID nozzle and the OD thermocouple, it is very difficult to tolerate such last-minute changes.
Some other examples are listed below
Thermal expansion at higher temperatures is an issue. As mentioned above, thermowell cladding may be recommended in the next step and this will save space. Also, sometimes the specifications of the pipes have a specific program, but for ease of drilling a well, a different program is chosen for the ship nozzle. Therefore, it is not preferable to remove the exact cut from it and reduce the distance.
Beware of illegal methods
Polish the thermowell to place in the nozzle
Sometimes people in the area polish the thermowell to reduce its OD to fit in the nozzle. This is an unsafe act. This is because it jeopardizes the integrity of the thermogenic design and can lead to catastrophic failure.
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