What is unsupported length of thermowell?
A thermowell can be considered to be at negligible risk if the following criteria are met: Process fluid velocity is less than 0.64 m/s. Wall thickness is 9.55 mm or more. Unsupported length is 610 mm or less.
How is thermowell length calculated?
The standard length from the sealing face of the cap and the face of the temperature sensor end of the well is 1-3/4”. “U” is the insertion depth of the thermowell. This is how much of the thermowell will be inserted into the process, and is measured from the cap face to the tip of the well.
How do you make a thermowell?
For an acceptable thermowell design, the ratio of the Strouhal frequency and the natural frequency “shall not exceed” 0.8. The final step is an evaluation of the thermowell length based on the steady state stress. This determines the maximum length the thermowell can be in order to handle the bending stress.
What is thermowell immersion length?
Thermowell Immersion Length The immersion length of a thermowell is the distance between the tip of the thermowell and the point of immersion in the medium that is being measured. The standard symbol for the immersion length of a thermowell is “R”.
What is tip thickness in thermowell?
The most common tip outside diameter for a stepped thermowell is ½ inch, however ASME PTC 19.3-TW also allows for the use of a 7/8-inch tip for a larger root OD. The smaller tip is to provide for a faster response time to temperature changes due to less metal.
What are thermowell wake frequency calculations?
Thermowell wake frequency calculations should be conducted during thermowell specification and definately prior to thermowell manufacture. These thermowell calculations ensure that the thermowell design is robust enough to cope with the forces produced by the process media.
What is thermowell wake frequency and vortex shedding frequency?
The vortex shedding frequency (or wake frequency) is linear with fluid flow velocity and inversely proportional to thermowell tip diameter. Why is Thermowell Wake Frequency a Concern? The vortex induced forces cause the thermowell to vibrate.
What is the magnitude of a Thermowell vibration?
The magnitude of these thermowell vibrations are generally negligible. However, as the wake frequency approaches the natural frequency of the thermowell the vibrating forces increase, and when the wake frequency matches the natural frquency of the thermowell it goes into resonance.
What is the wake frequency calculation revision?
Sometimes referred to as “Wake Frequency Calculation”, the revision incorporates new elements for evaluating thermowell constructions that will reduce the chance of vibration and stress damage to the vessel, as well as avoid vibration damage to the temperature sensor it protects.