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.
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.
We Type K 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.