Thermowell Selection Criteria
Materials the Longevity Factor
The selection of material is the most important factor for thermowell life.The material selected is based on the temperature of the application and the process medium.
Connection-The Installation Factor
All threaded well are made by easily welded or brazed materials.Welding and brazing is important for the installation requiring seal.
The pipe thread provides mechanical strength, and the weld or braze provides the seal. Flanged wells(other than van stone type) consist of a bar stocks well which is solidly welded to a top quality flange. Standard construction uses a primary “J” groove weld and a bevel groove clean fillet.
This double welded construction eliminates the possibility of crevice corrosion since no open joint are exposed from either inside or outside the installation. Socket weld well are simple to install, simply weld them into place.
Insertion Length-The Accuracy Factor
The distance from the tip of the well to the underside of the thread or other connection is defined as the insertion length (designated as “U”).
For best accuracy this length should be greater enough to permit the entire temperature sensitive part of element to project into the medium being measured.
A properly installed element: in liquid, the element should be immersed up to its sensitive length plus one inch, and in air or gas, the element should be immersed up to its sensitive length plus three inches.
Bore Size-The Interchangeability Factor
Almost all installation uses several type of temperature measuring sensor.
The selection of a standard bore diameter can produce extreme flexibility within the plant. The same well can accommodate thermocouple, resistance thermometer, and bimetal thermometer.
Tapered or Straight Well- the Velocity Rating Factor
Tapered shank provides greater stiffness with same sensitivity. The higher strength to weight ratio give these wells higher natural frequency than the equivalent length straight shank well thus permitting operation at higher fluid velocity.