Vanstone type thermowell is produced without any welding process by processing the whole round bar. Since it does not involve any welding process, it is used when high pressure, high velocity fluid and corrosive process media such as penetrating gas exist, and serving to isolate and protect from any leakage. The required flange is not standard and can be provided as an optional extra.
Selection of thermowell
In general, the thermowell material chosen for the installation is governed mainly by the corrosion condition the thermowell will face. Recommended material for various services are given in the corrosion table. Occasionally, the material consideration is one of strength rather than corrosion. For example, a stainless steel thermowell may be required for a high pressure water service where otherwise a brass thermowell woule be satisfactory from a corrosion standpoint.
The distance from the end of the well to the underside of the thread or other connection means (Designated as "U") is the insertion length.
■ Bore size
Almost any installation uses several type of temperature measuring instruments. The selection of a standard bore diameter can produce extreme flexibility within the plant.
■ Tapered or straight type
Tapered type thermowells provide greater stiffness for the same sensitivity. The higher strength to weight ratio gives these thermowells higher natural frequency than for equivalent length straight type thermowells, thus permitting operation at higher fluid velocity.
Wake frequency calculations in accordance with ASME PTC 19.3
WISE Inc. offers this as an engineering service.
■ Standard "T" length
Well size 1½" or DN40 : 40 mm
2" or DN50 : 45 mm