The Hard Facts of Sheath Material

A Thermocouple is a versatile temperature measurement device and can be exposed to extreme environments. When this is the case, your choice of Sheath material is most important as different materials come with varied temperature ranges, melting points and chemical resistance.
This week we will look at the different sheath material available and provide you with some useful information on the 3 most common.

sheath material
310 Stainless Steel sheath material

A quick google search tells us a Thermocouple can come in a wide range of sheath materials such as Ceramic, Titanium, aluminium, Carbon Steel, copper, and a range of stainless steel. Although possible, many of these sheath materials is not common. In fact, D&N Engineering has never made an aluminium sheath in the 30 years we have been manufacturing thermocouples. So instead of giving you a brief detail on the uncommon sheath materiel, we will look in depth at our 3 most popular. Inconel 600, 310 Stainless steel and 321 stainless steel.

Most Common Sheath Material

Inconel 600:

Inconel is a family of austenite nickel-chromium-based superalloys and are the most widely used thermocouple sheath material. Resistant to oxidation and corrosion Inconel is well suited for service in extreme environments subjected to pressure and heat. Once heated the alloy forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel 600 has a maximum temperature of 1175°C
The Inconel family of alloys was first developed in the 1940’s by research teams at Wiggin Alloys.

Inconel 600 is composed of:

  • Nickel: 75%
  • Chromium: 14-17%
  • Iron: 6-10%
  • Manganese: 1%
  • Copper: 0.5%
  • Silicon: 0.5%
  • Carbon: 0.15%
  • Sulfur: 0.015%

Inconel 600 can’t be used in sulfur bearing environments but has good high temperature strength, corrosion cracking and oxidation resistance to high temperatures.

Stainless Steel:
Stainless steel doesn’t corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low- oxygen, high salinity, or poor air-circulation environments.
There are different types of stainless steels, by adding different elements such as nickel or carbon the stainless steel can be tailored to certain applications.

310 Stainless steel:
310 Stainless steel is a popular sheath material as it has excellent heat resistance with a maximum temperature of 1150°C. It boasts good mechanical and corrosion resistance.

321 Stainless Steel:
This sheath material only has a maximum temperature of 870°C and is titanium stabilised for inter granular corrosion. The alloy is designed to overcome susceptibility to carbon precipitation from 480-870°C and is most commonly used in aerospace and chemical applications.
Although this article has only touched on a few of the large range of sheath material available these are the most common materials used in D&N Engineering’s Thermocouple manufacture.
Our sales team are experts within their field and can assist you with any sheath material, thermocouple or temperature related queries you have. Head over to our contacts page to get in touch with one of our sales team.