WIKA

Thermowells / protection tubes

For each measuring location requirement the optimum thermowell or protection tube

Thermowells or protection tubes from WIKA are used with demanding operating conditions both in one-piece versions from bar stock material and in fabricated versions with tubular design. The variants offered differ mainly in their designs; with flanges, threaded or for welding in. The connection of the protection tubes by flange is universal and is used in many processes. The compact form of the threaded connection saves space and mounting is also very easy. If the process safety and robustness is important, the thermowells can be welded into the process directly. Furthermore, all connections for sanitary applications and also thermowells in Vanstone design are available without weld seams. The selection of materials and the manufacturing of the thermowells or protection tubes in accordance with global standards or to customer specifications ensure optimal protection for the sensor.

What is a thermometer thermowell or protection tube?

As an important component of a temperature measuring location, the thermometer thermowell, also known as protection tube or pipewell, is responsible for sealing the process from the environment. Alongside the protection of the temperature sensors, thermowells also offer protection for the environment and the operating personnel. Aggressive media as well as high pressures and flow rates are kept away from the actual temperature probe, which enables the measuring insert to be changed without interrupting the process and thus during ongoing operation. Due to the wide range of possible applications for protection tubes, they are available in different designs and materials. A very decisive criterion when choosing a thermowell is the nature and type of the process connection. The thermowells and protection tubes can either be welded in, screwed in with a thread or connected to the process by means of a flange. In order to ensure accurate temperature measurement, it is necessary that the thermometer and thermowell or protection tube fit together perfectly.

What is the difference between thermowells and protection tubes?

In addition to the type of process connection, the manufacturing method is another distinguishing feature. Here one chooses between one-piece thermowell or fabricated protection tubes. Protection tubes are constructed from a tube, that is closed at the tip by a welded solid tip. Thermowells, on the other hand, are made from a single piece of solid bar stock material (round or hexagonal).

When are thermowells used?

Depending on the design, thermowells are used for high process-side loads and high chemical stresses. Thus internationally or in the petrochemical industry, thermowells are now used almost exclusively. Furthermore, flanged, weld-in and threaded thermowells are also used in process technology and in equipment manufacturing. Thermowells with flange or for welding in are also used in the petrochemical industry, onshore/offshore and in plant construction.

When are protection tubes used?

Protection tubes are generally recommended for low to medium process loads. Protection tubes with threads and flanges or for inserting/welding in are used in the chemical industry, process technology and also in equipment manufacturing. Protection tubes with flanges are used for high chemical loads. Certain protection tubes can additionally be used in the chemical industry, petrochemical industry and offshore. Here they are found in boilers, incinerators, furnaces and reactor vessels.

What should be the insertion length for thermowells or protection tubes in pipelines?

It must be ensured that the medium flows against the sensor of the thermometer. This generally occurs when the thermowell tip is located in the middle third of the pipe. The insertion length of a thermowell or protection tube depends on the thermometer used. For mechanical thermometers, a minimum insertion length of 60 ... 100 mm is assumed, whereas electrical thermometers only require an installation length of at least 35 ... 50 mm. The maximum insertion length for protection tubes is limited by the manufacturing length of the tubes (approx. 5 to 6 metres) and for thermowells by the manufacturing length of the gun drill machine (between 1,000 and 2,000 millimetres, depending on the model). However, longer thermowells can also be produced by welding individual pieces together.

What materials are thermowells or protection tubes made from?

Most thermowells and protection tubes are made from stainless steel. Special materials such as Hastelloy® and Monel®, amongst others, are used with especially demanding conditions. Depending on the application and material, a thermowell or protection tube can either be made completely of the special material or only those parts which are in contact with the process medium can be coated, e.g. with corrosion-resistant plastics.

What are the different types of thermowell stems?

As a further distinguishing feature, there are also different types of thermowell stems. A thermowell can be either tapered, straight or stepped. The tapered stem shape is the one most commonly used, guaranteeing a short response time and high strength at the same time. Protection tubes usually have the straight stem shape and thus a particularly cost-effective construction. For applications with high process-side loads with strong vibrations, we recommend the WIKA thermowell in a ScrutonWell® design.

FAQ
FAQ

What are the factors influencing the response times of thermowells and protection tubes?

Put simply, one can say that the more stable a thermowell or protection tube is constructed, the slower it reacts to temperature changes. In order to optimise the response time, there are thin wall thicknesses and low air space between sensor and the ...

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Do thermowells or protection tubes need to be CE marked?

Thermowells or protection tubes must not be CE marked, in principle. An exception as a result of its special design is the model TW61 thermowell with DN>25, suitable for orbital welding. This must be CE marked in accordance with the Pressure Equip ...

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