Protection Tubes

Duro-Sense Protection Tube

Dur-Sense Protection Tubes

Both ceramic and metal protection tubes are used to protect the temperature sensor from harsh and/or caustic environments. Unlike thermowells, protection tubes are not primarily designed for pressure-tight applications. Protection tube construction styles are more limited than thermowells, but they tend to be more economical. They can also offer the advantages of corrosion resistance and, in some cases, higher temperature capabilities.

Protection Tube material selected for installation is governed primarily by temperature, corrosion resistance to gas or liquid and mechanical strength.

Material Composition Temperature Rating Remarks
Alumina 99.8% Recrystalized Alumina Oxide 3450°F (1899°C) Excellent electrical insulation properties. Fair resistance to thermal& mechanical shock. Impervious to gases at high temperature. Creeps (sags) at 3452°F (1900°C).
Hexoloy SA Sintered Alpha Silicon Carbide 3000°F (1650°C) Excellent corrosion resistance. High thermal conductivity. High thermal shock resistance. Good mechanical strength. Does not creep (sag). Attacked by halides, fused caustics & ferrous metals.
Mullite 63% Alumina 3100°F (1700°C) Excellent electrical insulation properties. Impervious to gases at high temperatures. Poor thermal & mechanical shock resistance. Attacked by halides. Contains silica. Creeps (sags) at 3092°F (1700°C).
Silicon Carbide 90% Silicon Carbide, 9% Silicon Dioxide, 1% Alumina Oxide 3000°F, (1650°C) Can withstand direct flame impingement. Good thermal shock resistance. Permeable. Because of it’s permeability, an inner tube of Alumina or Mullite is recommended when used in atmosphere.
Aluminum Various Grades 1000°F (538°C) Good thermal conductivity. Good mechanical strength. Oxidation can arise when not anodized or protected.
Brass Various Grades 1000°F (538°C) Good thermal conductivity. Good mechanical strength.
Carbon Steel 99% Iron, 0.8% Manganese, 0.2% Carbon, Trace amounts of Phosphorus & Sulfur 1000°F (538°C) Temperature rating based on use in non-oxidizing environments. Areas of usage include molten metals and petroleum refinery applications.
Cast Iron   1300°F (708°C) Temperature rating based on use in oxidizing environments. Can be used up to 1600°F (871°C) under reducing conditions.
Copper Various Grades 500°F (260°C) Excellent thermal conductivity. Poor mechanical strength.
Hastelloy B 67% Nickel, 28% Molybdenum, 10% Silicon, 2% Iron, 1% Cobalt, 1% Chromium, 1% Manganese, 0.02% Carbon 1500°F (815°C) - In inert or vacuum atmospheres
1000°F (538°C) - In air
Excellent resistance to pitting & stress-corrosion cracking, Suitable for most chemical applications. Excellent in Hydrochloric Acid
Hastelloy C 62.5% Nickel, 16% Chromium, 15.5% Molybdenum, 3% Iron, 2% Cobalt, 1% Manganese, .08% Silicon, .015Carbon 1900°F (1038°C) Temperature rating based on use in oxidizing environments. Exceptional resistance to a wide variety of chemical environments.
Inconel 600 76% Nickel, 16% Chromium, 8% Iron 2100°F (1149°C) under oxidizing conditions
1900°F, (1038°C) under reducing conditions
Excellent corrosion & oxidation resistance. Must not be placed in Sulfurous environments above 1000°F (538°C)
Inconel 601 61% Nickel, 23% Chromium, 14% Iron, 1.35% Aluminum 2100°F (1149°C) under oxidizing conditions
1900°F, (1038°C) under reducing conditions
Similar properties to Inconel 600, but with superior resistance to Sulphur. Also has a higher temperature oxidation resistance to 2300°F (1260°C).
Incoloy 800 46% Iron, 32.5% Nickel, 21% Chromium, .75% Manganese, .5% Silicon, .38% Aluminum, .38% Copper, .38% Titanium, .15% Carbon 1500°F (816°C) Strong resistance to oxidation & carburization at high temperatures. Resists Sulfur attack, internal oxidation & scaling in a wide variety of atmospheres.
Molybdenum 99.95% Molybdenum, .03% Tungsten 3500°F (1926°C) in inert atmospheres
3400°F (1871°C) in vacuum at 10-4 torr.
Oxidizes in air above 800°F (426°C). Poor mechanical shock resistance after being heated to 1900°F (1038°C).
Monel 66.5% Nickel, 31.5% Copper, 1.25% Iron, 1% Manganese, .25% Silicon, .15% Carbon 1000°F (538°C) Temperature rating based on use in a Sulfur-free environment. Excellent resistance to corrosion.
Platinum   2500°F (1374°C) Temperature rating based on use in continuous oxidizing conditions. Good thermal conductivity. Used in applications where high temperature but no vacuum or inert atmosphere is available.
304 Stainless Steel 19% Chromium, 10% Nickel, 2% Manganese, 1% Silicon, .08% Carbon, Trace amounts of Phosphorus & Sulfur. Balance Iron. 1650°F (899°C) Temperature rating based on use in oxidizing environments. Has good oxidation & corrosion resistance in a wide range of industrial environments. Subject to carbide precipitation, which can reduce corrosion resistance between 800°F-1000°F (427°C-538°C). Good mechanical properties from -300°F-1450°F (-184°C-788°C).
310 Stainless Steel 25% Chromium, 21% Nickel, 2% Manganese, 1.5% Silicon 2100°F (1149°C) Mechanical & corrosion resistance similar to and better than 304 stainless steel.
316 Stainless Steel 17% Chromium, 12% Nickel, 2.5% Molybdenum, 2% Manganese, 1% Silicon, .08% Carbon, Trace amounts of Phosphorus & Sulfur. Balance Iron. 1700°F (927°C) Temperature rating based on use in oxidizing environments. Similar properties as 304 stainless steel, but with improved resistance to mild acid and pitting corrosion.
321 Stainless Steel 18% Chromium, 10% Nickel, 2% Manganese, 1% Silicon, .4% Titanium, .04% Phosphorus, .03% Sulphur 1600°F (871°C) Good corrosion resistance, Used where conditions are too severe for low Carbon stainless steel.
446 Stainless Steel 27% Chromium, 1.5% Manganese, 1% Silicon, .25% Nitrogen, .2% Carbon, Trace amounts of Phosphorus & Sulfur. Balance Iron. 2000°F (1093°C) Temperature rating based on use in oxidizing environments. Excellent high temperature corrosion & oxidizing resistance. Not for use in carburizing environments.
Tantalum   4350°F (2349°C) Good resistance to corrosion. Quick heat conductivity. Good mechanical strength.
Titanium   2300°F (1260°C) Temperature rating based on use in inert or vacuum environments. Acid and chemical resistant. Oxidation resistance to 1000°F (538°C).