Thermowell forms to DIN 43772

The thermowell separates the measuring insert from the process. It takes up pressure, flow and corrosion, makes the sensor replaceable during operation — and at the same time decides the response time.

DIN 43772 sorts the forms by mounting and tube geometry. The choice follows from the installation situation, the pressure and the flow velocity.

The forms at a glance

The G stands for the screw-in boss, the F for the flange connection. Without a suffix, mounting is by compression fitting and the immersion depth stays adjustable.

The four forms in longitudinal section, process side on the right. The process connection is marked blue.

Which form when

• Form 2 — vessels and pipelines at moderate pressures, general process engineering. The most common form.
• Form 3 — where a fast response matters: the tapered tip has less mass and a shorter response time, at the same strength at the root.
• Form 4 — steam, gas, high pressures and flow velocities. Drilled from solid, considerably more robust.
• Form 8 — where little installation space is available: the shortest form, without a neck tube.
• Neck tube — keeps the connection head at a distance from the hot process; mandatory at high medium temperatures or with insulation.

Spare thermowells on their own

We also supply the thermowells without a measuring insert — as a replacement for existing measuring points, with a 3.1 material test certificate to EN 10204 and dye-penetrant, pressure and X-ray testing on request. In addition the tubes to DIN EN 50446 for straight thermocouples, in form A with a rounded bottom and form C with a welded-in bottom; the standard regards both as equivalent and interchangeable in operation.

Strength verification

Whether a thermowell withstands the flow is not decided by the form alone. From around 10 m/s in liquids and 40 m/s in gases a verification is part of it — see Thermowell calculation to ASME PTC 19.3.