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Thermowells

Home Accessories Thermowells

0.260″ Bore, Threaded Thermowells

0.385″ Bore, Threaded Thermowells

Socket Weld, Flanged Thermowells

Mechanical Application Considerations

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Thermowells – General Information

Thermowells provide maximum protection for thermal sensors from corrosion, pressure and flow induced stresses. When selecting thermowells these parameters determine the type and material that should be used. In general, thermowells are machined from solid bar stock for “A” dimensions to 24″ but for londer lengths a built-up design is used.

Application Considerations

  • Select sensor location for representative temperature measurement.
  • Provide sufficient depth of immersion so that heat transfer along the instrument does not influence temperature measurement.
  • Select materials that are compatible with corrosive media elements.
  • Select thermowell with sufficient stiffness to resist destruction from flow induced stresses.

For Mechanical Application Considerations –Click Here!

Thermowell Materials

Strength at operating temperature and resistance to corrosion are the primary considerations in material selection.

Carbon Steels – Can be used to 1300°F (700°C) usually in oxidizing atmospheres.

Austenitic Stainless Steels (300 Series) – Can be used to 1600°F (870°C) mostly in oxidizing atmospheres although type 316 can be used in some reducing environments.

Ferritic Stainless Steels (400 Series) – Can be used to the 1800°F (982°C) – 2100°F (1149°C) range in both oxidizing and reducing atmospheres.

High Nickel Alloys – Can be used to 2100°F (1149°C) in oxidizing atmospheres.

Material CodeMATERIALMelting Point (°F)Recommended Operating AtmosphereMax. Operating Temperature in Atmosphere (°F)
304304 SS2560ORNV1650
310310 SS2560ORNV2100
316316 SS2500ORNV1700
321321 SS2550ORNV1600
347347 SS2600ORNV1600
446446 SS2700ORNV2000
CSCarbon Steel2500ON1300
INCInconelTM2550ONV2100
INXInconel XTM2620ONV1500
INYIncoloyTM2500ON1600
HTXHastelloy XTM2300O2200
HTCHastelloy CTM2310O1800
HTBHastelloy BTM2375OR1400
MONMonelTM2460OR1000
BRBrass1850O650
ALAluminum1220O700
NCKNickel2647O1400
TRNTantalum5425V5000
TITTitanium3035VN2000

O=Oxidizing, R=Reducing, N=Neutral, V=Vacuum

Velocity Rating

Once the selection of materials is made attention should be given to the parameter of flow induced stresses. Fluids flowing by a well form a turbulent wake called the Von Karman Trail. This wake has a definite frequency based on the diameter of the well and the fluid velocity. It is important to provide a well with sufficient stiffness so that the wake frequency will never exceed the natural frequency of the well itself. Should the natural frequency of the well coincide with the wake frequency, the well would vibrate to destruction. Tapered shank wells provide greater stiffness for the same sensitivity than a straight shank well. The higher strength to weight ratio gives these wells a higher natural frequency and therefore are able to operate at higher fluid velocities. Recommended maximum velocity rating can be found for every standard well length and material catalogued. Ratings are based on operating temperatures as shown in the table below.

MATERIALVelocity Rating
Operating Temperature
Carbon Steel (C1018)
304 SS
316 SS
1000°F
(538°C)
Monel900°F
(482°C)
Brass350°F
(177°C)

Single values that appear in the velocity tables may be considered safe for water, steam, air or gas. Double values distinguish between water (paranthesized) and steam, air and gases. These values are intended as general guides to selection. If you have operating conditions requiring special well designs our engineering staff is available to assist you.

Pressure Rating

The limit pressure versus temperature ratings are tabulated for various materials for each thermowell series. Here is a typical table.

LIMIT PRESSURE (lbs/in2) vs TEMPERATURE (°F)

MATERIAL

CODE
TEMPERATURE (°F)
70°200°400°600°800°1000°1200°
BrassBR500042001000----
Carbon SteelCS520050004800460035001500-
A.I.S.I. 3043047000620056005400520045001650
A.I.S.I. 3163167000700064006200610051002500
MonelMON650060005400530052001500-

NOTE: Selection of material and/or equipment is at the sole risk of the user of this site. The data presented does not and should not preclude professional engineering design and consulting for your particular application. Marlin Manufacturing Corporation, its distributors, representatives, and the contributors to this site specifically deny any warranty expressed or implied.

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  • Home
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      • Thermowells
    • Connectors and Stripanels
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    • Thermocouple Wire
    • New Products
    • Obsolete Products
  • Quality
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  • Request A Quote
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