Thermowell (process temperature sensor well)

01

Choose the mounting and process connection

REOTEMP describes thermowells as making it possible to remove an instrument without dropping pressure or losing the contents of the process, and protecting the instrument from being bent by the process media. [1] Its threaded thermowells are machined from solid bar stock, suited to infrequent replacement on smaller pipes or vessels and to non-corrosive media, with 3/4 in NPT as standard and 1/2, 1 and 1.5 in NPT options; standard stem lengths are 2.5–12 in, with lagging versions adding a "T" lag extension. [3]

Its flanged thermowells bolt to a mating flange on the process piping and are described as the preferred well where frequent removal or replacement is needed because of corrosion or other hazards, with large, high-pressure, high-corrosion pipes as typical installations. They come in 1/2–3 in flange sizes, ratings of 150#, 300#, 600#, 900–1500# and 2500# or Van Stone (lap-joint), with raised, flat or ring-type-joint faces, and full-penetration welds. [2]

Editorial note: match the flange size, rating and facing to the nozzle and piping class it mounts on, and the thread to the boss or coupling, before choosing bore and length. [2] [3]

Give the supplier the mounting style and process connection (thread size, or flange size, rating and facing), the sensor stem diameter and connection, insertion (U) length and lagging, shank style, material and any coating, process fluid, temperature, pressure and velocity for the wake frequency calculation, tests (hydrostatic, PMI), certificates (material, mill, NACE) and quantity.

02

Fit the bore, insertion length, shank and material

Both REOTEMP datasheets list a 0.260 in bore for 1/4 in sensor stems and 0.385 in for 3/8 in, with 0.515 in and internally threaded bores also offered on threaded wells; shanks are tapered, straight or stepped (stepped not with the 0.385 in bore), with flanged wells also offered with a support ring. Flanged U (insertion) dimensions run 2–22.5 in and overall lengths 4.25–24.75 in, with metric 250 and 307 mm options. [2] [3]

Materials listed include 304, 316 and 316L stainless, carbon steel, brass (threaded), Alloy 20, Hastelloy B and C, Monel, Inconel 600, titanium, F5, F11 and F22 alloys, zirconium and tantalum-lined wells, with tantalum/Halar, PTFE/PFA and tungsten carbide coatings and a 316/Stellite option. Listed options include a wake frequency calculation, external and internal pressure testing, material and mill certificates, NACE MR0175 and MR0103 approval, positive material identification, plug and chain and special surface finish (Ra 20 maximum). [2] [3]

Editorial calculation: a 0.260 in bore is 6.60 mm against a 1/4 in (6.35 mm) stem, and 0.385 in is 9.78 mm against 3/8 in (9.53 mm) — about 0.25 mm diametral clearance in both cases, so a metric 6 mm sensor will fit the smaller bore but a 10 mm sensor will not fit the larger one. [2] [3]

03

Compare what suppliers offer

No manufacturer record has been reviewed for this product yet. Send your specification and CNFX will match it against manufacturer records.

Ask each supplier for the dimensional drawing, material certificate, pressure-test record and, for flowing service, the wake frequency calculation and the method used. [2] [3]

04

Read the wake frequency report before approving the drawing

WIKA's white paper on its wake frequency calculator explains that thermowells in fast-flowing lines need the correct stem length, root diameter and tip diameter to prevent wake-induced vortices that create vibration and mechanical fatigue. Its single-calculation version checks one thermowell to ASME PTC 19.3 TW-2016: the dynamic results are the frequency ratio and the safety factor for flexural fatigue stress, the static results the safety factors for bending stress and pressure load. The downloadable PDF adds Strouhal number, Strouhal and resonant frequencies, maximum permissible pressure load, Scruton number and Reynolds number. WIKA's sample report for a TW10-F well in 316L is set out below. [4]

The full version covers tapered, straight and stepped stems with flanged, threaded, welded or Vanstone connections, holds more than 60 materials with data to ASME BPVC Section II Part D, and, when a well fails, gives a note code and recommends an optimised insertion length. WIKA states that "Responsibility for validation rests solely with the user." [4]

Editorial note: the sample's 6.6 mm bore matches the 0.260 in bore listed above [2] [3]. Ask the supplier for the report run with your own maximum velocity, density, viscosity, pressure and temperature, not sample values. [4]

05

Trace what each part controls

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your service

A thermowell quotation needs values for your service. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the connection, sensor and process data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Mounting: [threaded; flanged; weld-in; sanitary]
Connection: [NPT size; flange size/rating/face]
Sensor: [stem Ø; thread]
Length: [U; lagging; overall]
Shank/material: [style; alloy; coating]
Process: [fluid; °C; bar; velocity]
Tests/certs: [wake calc; hydro; PMI; NACE]
Quantity: [units]

See manufacturer records Send an enquiry through CNFX