What is the difference between Pyrosil D® and Inconel® 600? And how to choose between then?

What is the difference between Pyrosil D® and Inconel® 600?

Inconel® 600 is a nickel-chromium-iron alloy and Pyrosil® is a nickel-chromium alloy with 1.4% silicon.

Inconel® 600  was the fore-runner of Pyrosil® and Alloy TD which were more recently developed and offer even better protection from corrosion at high temperatures. Furthermore, they have fewer contaminants than stainless steel.

Where Inconel® 600 used to be the industrial standard of choice for thermocouple sheaths in high temperature industries Pyrosil D® is increasingly taking over the market as is reflected in the fact that it is now considered standard practice for major refinery companies to use Pyrosil® sheathed thermocouples in furnace applications.

Inconel® 600 is virtually immune to chloride-ion corrosion cracking. Chloride ion stress corrosion cracking is a form of aqueous corrosion. The good resistance of alloy 600 is due to its high nickel content (~76%). Pyrosil D®also has a high nickel content (~72%) so outside of other factors it might be expected to offer a similar degree of resistance. 

Putting Pyrosil into a corrosive liquid is possibly the wrong alloy as it was developed for high temperature resistance. Alloy 600 is much better suited to aqueous corrosion resistance.

How to choose between Pyrosil D® and Inconel® 600?

Pyrosil D® is more expensive than Inconel® 600. However, if the price difference is not a limiting factor then in most high temperature applications, Pyrosil D® MI cable would be the better choice, specifically for type N and type K thermocouples due to long term stability at higher temperatures.

  1. Pyrosil D® can withstand higher temperatures: 1250°C for continuous use vs the maximum of 1150°C for Inconel® 600.
  2. Pyrosil D® has a superior high temperature stress rupture strength.
  3. Pyrosil D® is even more resistant to oxidation and nitridation than Inconel® 600, especially at higher temperatures thus ensuring a longer lifespan. 
  4. The chemistry of Pyrosil D® is very similar to that of the type N conductors which means that cross contamination is minimal and a more stable EMF output is ensured (low drift).

We stock Type K and Type N MI cables with a Pyrosil D® sheath. For situations in which  Inconel 600 is the preferred choice, we are pleased to also be able to offer you a range of Inconel® 600 stock.

You are also welcome to contact us to place an order or receive advice from our in house experts on your particular application.