Thermowells - Thermowell Materials Selection Guide by Pyrosales

Background

Thermowells are recommended whenever a temperature element is to be inserted into a process where corrosion, pressure, abrasion, or shear forces may threaten the life of the element. In addition thermowells allow for a defective instrument to be removed without shutting down or draining the process.

Categories of Thermowells

Thermowells fit into 3 broad categories:

  • Screwed
  • Flanged
  • Weld-in

Thermowells can be designed to accept thermocouples, RTD’s, temperature gauges or filled systems. Thermowells can be machined from solid barstock, or fabricated from pipe.

Fabricated Thermowells

Fabricated thermowells offer a lower cost alternative where high pressure is not a design consideration. Standard thread forms are BSP and NPT (others available to order), and flange size and rating can be supplied to suit any ones requirement.

Materials Certification

Material certification, and full NDT requirements such as dye penetrant, hydrostatic pressure testing, radiography, and post weld heat treatment can all be provided. Thermowells can also be produced to satisfy the requirements of NACE MR 01 75. Stress and Frequency calculations can be performed to ensure that the thermowells design is suitable for the required process conditions.

Thermowell Material Selection Chart

Application

Protecting Tube Material

Heat Treating

Annealing

Up to 704°C

Black steel

Over 704°C

Inconel 600, Type 446 SS

Carburising hardening

Up to 816°C

Black steel, Type 446 SS

816 to 1093°C

Inconel 600, Type 446 SS

Over 1093°C

Ceramic*

Nitriding salt baths

Type 446 SS

Cyanide

Nickel (CP)

Neutral

Type 446 SS

High speed

Ceramic*

Iron and steel

Blast furnaces

Downcomer

Inconel 600, Type 446 SS

Stove dome

Silicon carbide, LT-1

Hot blast main

Inconel 600

Stove trunk

Inconel 600

Stove outlet flue

Black steel

Open hearth

Flues and stack

Inconel 600, Type 446 SS

Checkers

Inconel 600, LT-1

Waste heat boiler

Inconel 600, Type 446 SS

Billet heating slab heating and butt welding

Up to 1093°C

Inconel 600, Type 446 SS

Over 1093°C

Silicon carbide, ceramic*

Bright annealing batch

Top work temperature

Not required (use bare Type J thermocouple)

Bottom work temperature

Type 446 SS

Continuous furnace section

Inconel 600, ceramic*

Forging

Silicon carbide, ceramic*

Soaking pits

Up to 1093°C

Inconel 600

Over 1093°C

Silicon carbide, ceramic*

Nonferrous metals

Aluminum

Melting

Hexoloy®, Syalon®, 1100, Cast, Iron

Heat treating

Black steel

Brass or bronze

Not required (use dip-type thermocouple)

Lead

Type 446 SS, black steel

Magnesium

Black steel, cast iron

Tin

Extra heavy carbon steel

Zinc

Extra heavy carbon steel

Pickling tanks

Chemical lead

Cement

Exit flues

Inconel 600, Type 446 SS

Kilns, heating zone

Inconel 600

Ceramic

Kiln

Ceramic, and silicon carbide

Dryers

Silicon carbide, black steel

Vitreous enamelling

Inconel 600, Type 446 SS

Barium chloride, all concentration, 21°C

Monel®, Hastelloy C®

Barium hydroxide, all concentration, 21°C

Low carbon steels

Barium sulphite

Nichrome® Hastelloy C

Brines

Monel

Bromine

Tantalum, Monel

Butadiene

Type 304 SS

Butane

Type 304 SS

Butylacetate

Monel

Butyl alcohol

Type 304 SS

Calcium chlorate, dilute 21 to 66°C

Type 304 SS

Calcium hydroxide

10 to 20%, 100°C

Type 304 SS, Hastelloy C

50%, 100°C

Type 316 SS, Hastelloy C

Carbolic acid, all, 100°C

Type 316 SS

Carbon dioxide, wet or dry

2017-T4 aluminum, Monel, nickel

Chlorine gas

Dry, 21°C

Type 316 SS, Monel

Moist, -7 to 100°C

Hastelloy C

Chromic acid, 10 to 50% 100°C

Type 316 SS, Hastelloy C (all concentrations)

Citric acid

15%, 21°C

Type 304 SS, Hastelloy C (all concentrations)

15%, 100°C

Type 316 SS, Hastelloy C (all concentrations)

Concentrated, 100°C

Type 316 SS, Hastelloy C (all concentrations)

Copper nitrate

Types 304 SS, 316 SS

Copper sulphate

Types 304 SS, 316 SS

Cresols

Type 304 SS

Cyanogen gas

Type 304 SS

Dow therm®

Low carbon steels

Ether

Type 304 SS

Ethyl acetate

Monel, Type 304 SS

Ethyl chloride, 21°C

Type 304 SS, low carbon steel

Ethyl sulphate, 21°C

Monel

Ferric chloride, 5%, 21°C to boiling

Tantalum, Hastelloy C

Ferric sulphate, 5%, 21°C

Type 304 SS

Ferrous sulphate, dilute, 21°C

Type 304 SS

Formaldehyde

Types 304 SS, 316 SS

Formic acid, 5%, 21 to 66°C

Type 316 SS

Freon

Monel

Gallic acid, 5%,21 to 66°C

Monel

Gasoline, 21°C

Type 304 SS, low carbon steel

Glucose, 21°C

Type 304 SS

Glycerine, 21°C

Type 304 SS

Glycerol

Type 304 SS

Hydrobromic acid, 98%, 100.C°

Hastelloy B ®

Hydrochloric acid

1%, 5% 21°C

Hastelloy C

1%, 5% 100°C

Hastelloy B

25%, 21 to 100°C

Hastelloy B

Hydrofluoric acid, 60%, 100°C

Hastelloy C, Monel

Hydrogen peroxide, 21 to 100°C

Types 316 SS, 304 SS

Hydrogen sulphide, wet and dry

Type 316 SS

Paper

Digesters

Type 316 SS, Type 446S

Glass

Fore hearths and feeders

Platinum thimble

Lehrs

Black steel

Tanks

Roof and wall

Ceramic

Flues and checkers

Inconel 600, Type 446 SS

Petroleum

De-waxing

Types 304, 310, 316, 321, 347 SS, carbon steel

Towers

Types 304, 310, 316, 321, 347 SS, carbon steel

Transfer lines

Types 304, 310, 316, 321, 347 SS, carbon steel

Factioning column

Types 304, 310, 316, 321, 347 SS, carbon steel

Bridgewall

Types 304, 310, 316, 321, 347 SS, carbon steel

Power

Coal-air mixtures

304 SS

Flue gases

Black steel, Type 446 SS

Pre-heaters

Black steel, Type 446 SS

Steel lines

Types 347 or 316 SS

Water lines

Low carbon steels

Boiler tubes

Types 304, 309, or 31 0 SS

Gas producers

Producer gas

Type 446 SS

Water gas

Carburetor

Inconel 600, Type 446 SS

Superheater

Inconel 600, Type 446 SS

Tar stills

Low carbon steels

Incinerators

Up to 1093°C

Inconel 600, Type 446 SS

Over 1093°C

Ceramic (primary) Hexoloy (secondary)*

Food

Baking Ovens

Slack Steel

Charretort, Sugar

Slack Steel

Vegetables and fruit

Type 304 SS

Chemical

Acetic acid

10 to 50%, 21°C

Type 304, Hastelloy C, Monel

50%, 100°C

Type 316, Hastelloy C, Monel

99% 21 to 100°C

Type 430, Hastelloy C, Monel

Alcohol, ethyl, methyl

21 to 100°C

Type 304

Ammonia

Types 304, 316 SS

All concentration 21°C

Ammonium chloride

All concentration 100°C

Types 316 SS, Monel

Ammonium nitrate

All concentration 21 to 100°C

Type 316 SS

Ammonium sulphate, 10% to saturated

100°C

Type 316 SS

Iodine, 21°'C

Tantalum

Lactic acid

5%, 21°C

Type 304 SS, 316 SS

5%, 66°C

Type 316 SS

10%, 100°C

Tantalum

Magnesium chloride

5%, 21°C

Nickel, Monel,

5%, 100°C

Nickel

Magnesium sulphate, hot and cold

Monel

Muriatic acid, 21°C

Tantalum

Naptha, 21°C

Type 304 SS

Natural gas, 21°C

Types 304 SS, 316 SS, 317 SS

Nickel chloride, 21°C

Type 304 SS

Nickel sulphate, hot and cold

Type 304 SS

Nitric acid

5%, 21°C

Types 304 SS, 316 SS

20% 21°C

Types 304 SS, 316 SS

50% 21°C

Types 304 SS, 316 SS

50% 100°C

Types 304 SS, 316 SS

65% 100°C

Type 316 SS

Concentrated, 21°C

Types 304 SS, 316 SS

Concentrated, 100°C

Tantalum

Nitrobenzene, 21°C

Type 304 SS

Oleic acid, 21°C

Type 316 SS

Oleum, 21°C

Type 316 SS

Oxalic acid

5% hot and cold

Type 304 SS

10%, 100°C

Monel

Oxygen 21°C

Steel

Palmitic acid

Type 316 SS

Pentane

Type 340 SS

Phenol

Types 304 SS, 316 SS

Phosphoric acid

1%, 5%, 21°C

Type 304 SS

10%, 21°C

Type 316 SS

10%, 100°C

Hastelloy C

30%, 21 to 100°C

Hastelloy B

85%, 21 to 100°C

Hastelloy B

Picric acid, 21°C

Type 304 SS

Potassium bromide, 21°C

Type 316 SS

Potassium carbonate, 1%, 21°C

Types 304 SS, 316 SS

Potassium chlorate, 21°C

Type 304 SS

Potassium hydroxide

5% 21°C

Type 304 SS

25% 100°C

Type 304 SS

60% 100°C

Type 316 SS

Potassium nitrate

5%, 21°C

Type 304 SS

5%, 100°C

Type 304 SS

Potassium permanganate, 5%, 21°C

Type 304 SS

Potassium sulphate, 5%, 21°C

Types 304 SS, 316 SS

Potassium sulphide, 21°C

Types 304 SS, 316 SS

Propane

Type 304 SS, low carbon steel

Pyrogallic acid

Type 304 SS

Quinine bisulphate, dry

Type 316 SS

Quinine sulphate, dry

Type 304 SS

Seawater

Monel, Hastelloy C

Salicylic acid

Nickel

Sodium bicarbonate

All concentration, 21°C

Type 304 SS

5%, 66°C

Types 304 SS, 316 SS

Sodium carbonate, 5%, 21 to 66°C

Types 304 SS, 316 SS

Sodium chloride

5%, 21 to 66°C

Type 316 SS

Saturated, 21 to 100°C

Type 316 SS, Monel

Sodium fluoride, 5%, 21°C

Monel

Sodium hydroxide

Types 304 S, 316 SS, Hastelloy C

Sodium hypochlorite, 5% still

Type 316 SS, Hastelloy C

Sodium nitrate, fused

Type 316 SS

Sodium peroxide

Type 304 SS

Sodium sulphate, 21°C

Types 304 SS, 316 SS

Sodium sulphide, 21°C

Type 316 SS

Sodium sulphite, 30%, 66°C

Type 304 SS

Sulphur dioxide

Moist gas, 21°C

Type 316 SS

Gas, 302°C

Types 304 SS, 316 SS

Sulphur

Dry molten

Type 304 SS

Wet

Type 316 SS

Sulphuric acid

5%, 21 to 100°C)

Hastelloy B, 316 SS

10%, 21 to 100°C

Hastelloy B

90%, 21°C

Hastelloy B

Tannic acid 21°C

Type 304 SS, Hastelloy B

Tartaric acid

21°C

Type 304 SS

150°C

Type 316 SS

Toluene

2017-T4 aluminium, low carbon steel

Turpentine

Types 304 SS 316 SS

Whiskey and wine

Type 304 SS, nickel

Xylene

Copper

Zinc chloride

Monel

Zinc sulphate

5% 21°C

Types 304 SS, 316 SS

Saturated 21°C

Types 304 SS, 316 SS

25% 100°C

Types 304 SS, 316 SS

Source: Pyrosales

For more information on this source please visit Pyrosales.

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