We can use a variety of materials in our sheaths:
Mild Steel
These protection sheaths are rarely used because of their low temperature limit.
Basic Composition: Iron and Carbon (Fe,C)
Temperature Limit: +550°C
International Standard: Seamless Pipe
Density: 7.9g/cm³
446, 4C54, Ferritic
Ferritic provides resistance to oxidation in air and is a very good material to use when it comes to resisting sulfurous gases and salts.
446 performs better than austenitic steels in sulfurous reducing atmospheres but nitrogen concentrations can result in early failure. Hot gases containing hydrocarbons and carbon monoxide can cause carburisation. 446 requires oxygen to be present in order to form an oxide layer, otherwise failure occurs quickly.
Basic Composition: Cr 26.5%, Mn 0.8%, Si 0.5%, N 0.2%, C 0.2%, P 0.03%, S 0.15%, Bal Fe
Temperature Limit: +1100°C in oxidising conditions
International Standards: 1.4749, 446-1
Density: 7.9g/cm³
Specific Heat: 460 – 670 J/Kg°C
Thermal Conductivity: 17 – 28 W/m°C
Kanthal AF, Kanthal APM
Kanthal provides great sulphur resistance and can resist carburisation at higher temperatures than most materials. It also gives better heat transfer than ceramic.
Basic Composition: Cr 22%, Al 4-6%, Fe Balance
Temperature Limit: 1400°C
Density: 7.1g/cm³
Specific Heat: 460 – 670 J/Kg°C
Thermal Conductivity: 12-32 W/m°C
321 SS
Often used for MI sheathing on type J and Pt 100 sensor assemblies, 321 SS, also called 18/8, is corrosion resistance and remains ductile.
Basic Composition: Cr 18%, Ni 9%, Mn 2%, Si 1%, C 0.1%, Bal Fe
Temperature Limit: 800°C
International Standards: BS 970 321 S31, W No 1.4541
Density: 7.9 g/cm³
Melting Range: Approx 1400°C
Specific Heat: 500 J/Kg°C
Thermal Conductivity: 14.7 W/m°C
310 SS
Commonly known as 25/20, 310 SS displays good oxidation resistance and resistance to sulphur and reducing atmospheres. It is used as a high temperature sheathing material and is not recommended for use continuously between 550°C and 850°C.
Basic Composition: Cr 25%, Ni 20%, Mn 2%, Si 2%, C 0.02%, Bal Fe
Temperature Limit: 1100°C
International Standards: BS 970 Grade 310 S31, W No 1.4841
Density: 7.9 g/cm³
Melting Range: Approx 1400°C
Specific Heat: 500 J/Kg°C
Thermal Conductivity: 14.7 W/m°C
316 SS
This is one of our most popular sheath material choices and is commonly found in chemical plant temperature sensor applications. It has very similar characteristics to 321 SS but provides better acid resistance and effective corrosion and pitting resistance.
Basic Composition: Cr 17.5%, Ni 12.5%, Mn 2%, Si 1%, Mo 2-2.5%, C 0.03%, Bal Fe.
Temperature Limit: 800°C
International Standards: BS 970 Grade 316, W No 1.4401
Density: 7.9 g/cm³
Melting Range: Approx 1400°C
Specific Heat: 500 J/Kg°C
Thermal Conductivity: 14.7 W/m°C
353 MA ®
Often used in the PetroChemical industry, during the ammonia cracking process, 353 MA displays good resistance to most combustion gases and carburisation, in particular nitriding gases.
Basic Composition: Cr 25%, Ni 35%, Si 1.6%, Mn 1.5% Max, N 0.16%, C 0.05, P 0.04 Max, S 0.03 Max, Ce 0.05, Bal Fe
Temperature Limit: 1175°C
International Standards: UNS S 35315
Density: 7.89 g/cm³
Specific Heat: 450 – 670 J/Kg°C
Thermal Conductivity: 11-28 W/m°C
253 MA ®
This is similar to 353 MA and displays good oxidation resistance as well as protecting vital components effectively against carburisation.
Basic Composition: Cr 21%, Ni 11%, Si 1.7%, Mn 0.8% Max, N 0.17%, C 0.08, P 0.04, S 0.03, Ce 0.05, Bal Fe
Temperature Limit: 1150°C in air, oxidation and carburisation.
International Standards: 1.4835, S 30815, W Nr 1.4893
Density: 7.8 g/cm³
Specific Heat: 440-690 J/Kg°C
Thermal Conductivity: 14.5-29 W/m°C
Alloy 600 (Inconel®)
Alloy 600 Inconel is a strong oxidation resistant material at high temperatures, particularly with cycling, and resists sulphur compounds and carbon dioxide at moderate temperatures.
Basic Composition: Ni 72% Min, Cr 14-17%, Fe 6-10
Temperature Limit: 1100°C
International Standards: W No 2.4816, UNS N06600
Density: 8.472 g/cm³
Melting Range: 1354-1413°C
Specific Heat: 444 J/Kg°C
Thermal Conductivity: 15-27 W/m°C
Alloy 800 HT (Incoloy®)
Alloy 800 HT displays good resistance to high temperature corrosion with reasonable effectiveness against sulphur resistance at moderate temperatures.
Basic Composition: Ni 30-35%, Cr 19-23%, Fe 39.5%
Temperature Limit: 1100°C
International Standards: W No 1.4876, UNS N08811
Density: 7.945 g/cm³
Melting Range: 1357-1385°C
Specific Heat: 460 J/Kg°C
Thermal Conductivity: 11-32 W/m°C
Pyrosil
Pyrosil is commonly used in mineral insulated thermocouple sheathing, especially in Type K and N sensor assemblies.
Basic Composition: Ni Cr Si
Temperature Limit: 1250°C
Hastelloy C276
This can be an effective material to use in severe environments and displays good corrosion resistance in reducing and oxidising atmospheres.
Basic Composition: Ni 57%, Mo 16%, Cr 15.5%, Fe 5.5%, W 3.8%
Temperature Limit: 1040 ° C
International Standards: UNS N10276
Density: 8.9g/cm³
Melting Range: 1325-1370°C
Syalon 101
This is a strong and thermal shock resistant material for use in molten metals with little wetting or dross build up.
Basic Composition: Silicon Nitride, Aluminium Oxide
Temperature Limit: 1000°C (1250°C in controlled conditions)
Density: 3.26 g/cm³
Thermal Conductivity: 16.7 W/m°C
Quartz
Quartz provides good high shock resistance.
Basic Composition: SiO 2
Temperature Limit: 1500°C (Then flows under own weight)
Density: 2.2 g/cm³
Melting Range: 1683°C
Specific Heat: 670 J/Kg°C
Thermal Conductivity: 1.4 W/m°C
Silicon Carbide (Clay Bonded)
Clay Bonded Silicon Carbide tends to have a thick wall to improve strength. It displays good thermal shock resistance and high thermal conductivity.
Basic Composition: SiC 70 – 90%
Temperature Limit: 1400°C
Density: 2.4 g/cm³
Thermal Conductivity: 28.0 W/m°C
Silicon Carbide (Recrystalised)
Recrystalised Silicon Carbide has great thermal shock resistance.
Basic Composition: SiC 99%
Temperature Limit: 1600-2000°C dependant on atmosphere
Density: 2.6 to 2.7 g/cm³
Thermal Conductivity: 30.0 W/m°C
Sillimanite 60
Sillimanite 60 is a porous material with good thermal shock resistance.
Basic Composition: Al 2O 3 73 to 75%
Temperature Limit: 1600°C
International Standards: DIN VDE 0335 C530
Density: 2.35 g/cm³
Thermal Conductivity: 1.4 W/m°C
Recrystalised Alumina (Alsint)
Used with R, S and B thermocouples, Recrystalised Alumina is a pure and tough ceramic exhibiting hardness and vacuum tightness.
Basic Composition: Al 2O 3 99.7%
Temperature Limit: 1750°C
International Standards: DIN VDE 0335 C799
Density: 3.9 g/cm³
Melting Range: 2072°C
Aluminous Porcelain (Pythagoras)
Pythagoras Porcelain is commonly used with J, K, N and E conductors.
Basic Composition: Al 2O 3 60%
Temperature Limit: 1500°C
International Standards: DIN VDE 0335 C799
Density: 2.6 g/cm³
Platinum
Platinum is commonly used in glass manufacturing processes.
Basic Composition: Pt
Density: 21.45 g/cm³
Melting Range: 1769°C
Thermal Conductivity: 74 W/m°C at 20°C
Platinum 10% Rhodium
This platinum alloy gains strength at higher temperatures and is therefore used in molten glass processes and heat treatment.
Basic Composition: Pt 90%, Rh 10%
Temperature Limit: 1700°C
Density: 20.00 g/cm³
Melting Range: 1840-1870°C
Thermal Conductivity: 31 W/m°C at 20°C
At Electroserv our platinum materials are available with grain stabilisation to reduce degradation at higher temperatures