Maltec-T Tapered Thermowell

Dpstar Group provides top thermocouple solutions with high-quality assurance. We specialize in the design and manufacture of high-quality standard types of thermowells for various temperature sensing instruments according to our customer’s specifications. Our experienced engineer will help you to select the right product for any temperature application and offer advice on best installation practices.

Definition of Thermowell

A thermowell is a pressure-tight receptacle designed to accept a temperature sensing element and provide a means to insert that element into a vessel or pipe. The American Society for Testing and Materials (ASTM) has defined the term thermowell as a closed-end reentrant tube designed for the insertion of a temperature-sensing element and provided with means for a pressure-tight attachment to a vessel.

Principles of Operation

A thermowell acts as a barrier between a process medium and the sensing element of a temperature measuring device. It protects against corrosive process media, as well as media contained under pressure or flowing at a high velocity. A thermowell also allows the sensing element to be removed from the application while maintaining a closed system.

Why use a Thermowell?

If the measurement is not critical either to the safety of the plant or to the efficiency of the production, and if the process fluid is not particularly aggressive or dangerous, it may be possible to insert stainless steel, sheathed, industrial thermometer into the plant pipeline through a suitable compression fitting. Obviously, the thermometer could not be removed while the plant is running, and should a problem occur with the measurement, maintenance will be delayed until the process can be stopped and the line drained and made safe.

Basic components of a Thermowell

Bore Diameter (B): This is the inside diameter of the Thermowell.

Bore Depth (S): Total length of the bore.

Insertion length (U): Thermowell immersion lengths are often called the “U” length which is the measurement of the Thermowell from the bottom of the process connection to the top portion of the Thermowell.

Process Connections: This is the manner in which a Thermowell is inserted and connected into a process referring to the attachment of the element. The most popular are threaded, socket weld, and flanged connections.

Shank Construction: This is the immersion portion (shank) of the construction. The majority fall under three categories: straight, step, or tapered.

• The straight shank is the same size all along the immersion length. For general-purpose, where additional strength is not required, the straight shank or stem is used.
• The stepped shank has a larger outer diameter at the end of the immersion length in some applications for a quicker response time.
• The tapered version decreases gradually along the immersion length. Tapered thermowells are designed for use in high velocities, where extra strength is required. Special attention shall be given to the vibration effects caused by the fluid passing the thermowell.

Lagging Extension Length (T): The lagging extension commonly referred to as the “T” length is located on the cold side of the process connection and is usually an extension of the hex length.

Base diameter Dimension (Q): This is the outside dimension of the Thermowell shank and is the densest part because the outside surface area is exposed to the hazardous materials of the process.

Tip Thickness (E): The thickness of the bottom portion of thermowell.

Tip Diameter (V): Thermowell end Diameter.

What are the most common types of thermowells?

Thermowells are commonly classified according to their connection to a process. The most common types of thermowells are (1) threaded, (2) socket weld, (3) weld-in, and (4) flanged.

As the names imply, a threaded thermowell is screwed into the process either directly into the wall of a tapped pipe or into a thermowell threadolet.  A socket weld thermowell is typically welded into a weldolet socket, but the thermowell may be welded directly into the pipe wall. A weld in thermowell is welded directly into the process vessel or piping.  A flanged thermowell has a flange collar which is attached to a mating flange on a pipe nozzle.

Thermowell Applications

Thermowells find applications in many industrial sectors including petrochemical, food processing, refining, cosmetics, Chemicals, Power, pharmaceutical, and other process industries. The thermowells are designed to protect the equipment from different external forces and disturbances such as pressure, abrasion, vibration, and corrosion, which can be caused by the process medium.

A properly selected thermowell will protect the temperature instrument from damage resulting from these process variables. Additionally, a thermowell enables the removal of the temperature instrument for replacement, repair, or testing without affecting the processing system.