Thermowells
Thermowells which are made of solid bar stock of various heat and corrosion resistant alloys by drilling are usually preferred over the tip welded protection tubes for critical applications where high mechanical strength and longer service life are required. If the alloy bar material is correctly selected and designed properly, the Thermowell lasts long against corrosives, high pressure, high temperature, mechanical shock and vibration that may result from high velocity of fluids. In order to offer the best and safest. A specially developed computer programme as based upon operating conditions at the site makes Thermowells against Ka’rma’n’s Turbulence and other stresses, automatic calculations of mechanical strength to fluid pressure and flow velocity to estimate frequency of critical resonance. At TECHNO, a genuine Two Shaft Gun Drilling Machine of two-metre max manufactures Thermowells.

Thermowells are ideal where a sensor is required to be inserted into a process where external elements such as pressure, corrosion, or abrasion affect the life of the sensor. . Techno has been manufacturing solid barstock type Thermowells to accommodate applications in the petrochemical, chemical, refining, power and other process industries for many years. Threaded, flanged, weld-in, socket, Van Stone and other styles are custom made to your specs or available from our large inventory for immediate shipment. Optional coatings and sprays are also offered.

The thermowell wall must be thin enough to minimize sensor error caused by thermal conduction and slow sensor response, but thick enough to withstand collapse from process pressure, erosion from abrasive media and bending from the process flow. Spring-load mounting styles are recommended to ensure positive contact to maximize thermal transfer and minimize sensor vibration within a thermowell.

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Insertion Length
The insertion length or 'U' length is the distance from the end of the well to the underside of the thermowell thread or other connection device. For maximum accuracy, this length must be long enough to permit the temperature sensor to be fully immersed in the media to be measured and minimize sensor error caused by thermal conduction, But short enough to withstand damage caused by process flow vibration. As a general rule of thumb, the thermowell should extend into the process a minimum of 10 times the sensor diameter or, in the case of RTDs, 10 times the sensor diameter plus one inch. This should extend the sensor into the process between 1/3 and 1/2 the diameter of the process pipe. The insertion length must also take into consideration any dead length required to pass through walls, pipe fittings and insulation.

Velocity
The most common cause of well failure is the vibration effect caused by fluid forming a turbulent wake as it flows past the well. This turbulence has a definite vibration frequency based on the diameter of the well and the velocity of the fluid. The well must have sufficient stiffness to ensure that the wake frequency will never equal the natural frequency of the well. If the natural frequency of the well coincides with the wake frequency, the well will potentially vibrate to destruction. To be in compliance with the ASME Performance Test Code, the thermowell should have a natural frequency a minimum of 125% of the wake frequency. Tapered shank wells (heavy duty - Type H) have a high strength-to-weight ratio with a resultant higher natural resonant frequency than the equivalent length straight shank well. Tapered shank wells are preferred for operation at higher fluid velocities.

Process Connection
Techno Instruments Technologies provides standardized wells in most of the common connection types, including threaded, flanged and socket weld types with standard bore sizes. Threaded wells are available in materials that can be readily welded. Flanged wells are manufactured by welding a bar stock well to the specified flange style. Doubled-welded construction reduces crevice corrosion and stress problems by ensuring that no open joints are exposed inside or outside the installation.

Bore Size
Selection of a standard bore size throughout the plant permits the use of several types of temperature measuring instruments in the same wells. Techno standard bore sizes fit most commonly used temperature sensing devices. Most applications use 0.260" or 0.385" diameter bores. This number represents the inside diameter of the well, expressed in thousandths of an inch.

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Standard Bores and Depths

Standard
Sizes of Solid Bar Materials