A thermowell is a closed-end metal tube fitted into a pipe or vessel to protect a temperature sensor from pressure, flow, corrosion and abrasion. With a thermowell, an RTD (Pt100) or thermocouple can be replaced without shutting down or draining the process. ISE supplies custom-made thermowells following European practice: DIN 43772, EN 1092-1, PED 2014/68/EU.
What is a thermowell and why use one?
- Protects the sensor from pressure, velocity, corrosive media and solids.
- Keeps the process sealed: change sensors on line without leaks.
- Extends life and safety of temperature points in steam, hot oil, chemicals and flue gas.
Common process connections
| Type | Connection | Applications |
|---|---|---|
| Threaded | BSPP, BSPT, NPT 1/4″ – 1″ | Low – medium pressure, quick fitting |
| Flanged | EN 1092-1, ASME B16.5, JIS flanges | High pressure, removable; petrochemicals, boilers |
| Weld-in | Welded into the pipe, DIN 43772 form 4 | Very high pressure and temperature, leak-free |
| Van Stone | Lap-joint loose flange | Corrosive media, special linings |
| Limited space | Short, compact design | Small pipes, tight equipment |
Bar-stock versus fabricated
Bar-stock wells are drilled from solid bar with no welds and withstand high pressure and velocity, with straight or tapered stems. Fabricated wells are made from tube with a welded tip – economical for low pressure and velocity.
Thermowell specifications from ISE
| Parameter | Value |
|---|---|
| Design | Custom-made and to standards (DIN 43772, customer drawings) |
| Thread size | 1/4″ · 1/2″ · 3/4″ · 1″ |
| Thread type | BSPP · BSPT · NPT |
| Materials | Stainless 304, 310, 316/316L, 316Ti; Alloy C276, 400, 600, 601, 625, 800 |
| Instrument connection | BSPP · BSPT · NPT, M20×1.5 |
| Process connection | Threaded, EN 1092-1 / ASME B16.5 flange, weld-in, Van Stone |
| Documentation | EN 10204 3.1 material certificate, pressure test (on request) |
Anatomy and correct installation
- Insertion length (U): tip in the central flow region; excessive length raises vibration and breakage risk.
- Thick root, thin tip (tapered): stiffer, higher natural frequency, good thermal response.
- Tight bore and spring-loaded sensor touching the bottom for fast, stable response.
- Material chosen like the piping for medium and temperature; pressure rating matches the connection.
Thermowell wake frequency calculation
Flow past a thermowell sheds Kármán vortices; if the shedding frequency approaches the well’s natural frequency, resonance can break it. The 1995 Monju (Japan) failure from in-line resonance led to a full revision of ASME PTC 19.3 TW (2010, updated 2016) (Process Worldwide). The calculation checks frequency, dynamic stress, static stress and pressure – essential for high-velocity steam and gas. If it fails: shorten the insertion, increase root diameter, use a tapered stem or stiffer material, add a support collar or a helical-strake stem.
EU standards for thermowells
| Standard | Scope |
|---|---|
| DIN 43772 | Thermowell forms and dimensions (forms 2, 3, 4, 4F…) |
| EN 1092-1 | Steel flanges – see industrial flange standards |
| PED 2014/68/EU | Pressure equipment |
| EN 10204 3.1 | Material inspection certificate |
| EN 60751 / EN 60584-1 | Pt100 / thermocouple sensors used inside the well |
| ASME PTC 19.3 TW-2016 | Strength and wake frequency calculation |
Applications
- Steam lines and boilers – see the saturated steam temperature table.
- Thermal oil systems and thermal oil heat meters.
- Chemicals, oil and gas, food and beverage, water treatment, flue gas.
FAQ
Does a thermowell slow the response time?
Yes, because of the wall and air gap. A thin tip, close-fitting bore and spring-loaded sensor reduce the delay.
When is a wake frequency calculation needed?
For steam, gas or high-velocity liquids and long insertions; ISE supports ASME PTC 19.3 TW calculations when selecting the well.
Related products
Order custom thermowells from ISE
EQUIPMENT INDUSTRIAL SOLUTION CO., LTD (ISE) – Ho Chi Minh City, Vietnam.
Contact us: Sales +84 909 617 185 – Technical +84 979 117 185 – Email: [email protected]
