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6 Protection tubes
6Protection tubes
Various parameters (such as temperature, pressure, and oscillations) place loads on thermometers and
their protection fittings. The protection fittings must therefore be designed accordingly. The variables in
this respect include the material, insertion length, and diameter.
DIN 43772 contains an overview of various metal protection tubes for thermocouples and RTD tempera-
ture probes. It also provides installation notes.
Protection tubes can be designed according to the following diagram. However, this information only
serves as a rough guideline. In the diagram, the maximum pressure load is listed as a function of the
wall thickness at different pipe diameters. The diagram applies to protection tubes made of stainless
steel 1.4571 and with an insertion length of 100 mm and flow velocities of 10 m/s in air and 4 m/s in water
(temperature range: -20 to +100 °C, safety factor 1.8).
The following table can be used if different materials are being used:
Thermometers manufactured according to DIN or application-specific directives require the use of vari-
ous pressure tests in accordance with the specific application in question. For this reason, specify the
necessary tests/directives when ordering the thermometers.
Data sheet 902000 for further information
Avoid internal components in areas containing a change of diameter or bends. Higher loads may be ex-
erted on the temperature probes/protection fittings in these installation locations. When performing in-
stallation work, ensure a sufficient clearance is maintained from these installation locations.
Pressure load in bar
Wall thickness in mm
Material Temperature Reduction
CrNi 1.4571 Up to 200 °C -10 %
Up to 300 °C -20 %
Up to 400 °C -25 %
Up to 500 °C -30 %
CuZn 2.0401 Up to 100 °C -15 %
Up to 175 °C -60 %
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