INCONEL alloys that can withstand excessive high temperatures

While there are a lot of considerations when it comes to material selection for a project, notably strength and corrosion resistance, the temperature of the environment that it will operate in is a key factor. A project manager needs to be able to look at each available material and find the one that offers the best performance for the individual environment.

It is a complex and involved process to select the right alloy for high-temperature situations. Distortion and cracking can occur due to thermal expansion or contraction, which increases as the temperature gets higher. You also need to consider whether the service environment will cool when it’s not in operation and if this will introduce corrosive factors at lower temperatures.

Types of corrosion

High-temperature environments put materials at risk of certain types of corrosion. One of these is oxidisation, where the metal reacts to the air to form an oxide, therefore an alloy that is oxidisation resistant is normally required.
The presence of sulphurous gases, such as in petrochemical processing, can cause extensive damage to metals, particularly in elevated temperatures. Carburisation – an issue in heat-treating facilities or gas-cracking processes – also increases at higher temperatures and these conditions, alongside oxidising ones, can weaken an alloy.

Alloys that are suitable for high temperatures are typically nickel-based and include a high chromium content. The chromium helps to form a protective oxide in these environments to protect against corrosion. These alloys will also include other elements that contribute to good corrosion resistance and high strength, such as molybdenum and iron.

INCONEL alloys

Corrotherm stocks a wide choice of INCONEL alloys, which are well suited to extreme temperatures while still offering excellent corrosion resistance. One of the most popular is INCONEL alloy 625, which is known for its resistance to many forms of corrosion, as well as its high thermal-fatigue strength. Its service temperature range goes up to a high of 982°C, and it can resist a number of specific high-temperature effects such as oxidation and carburisation. One of its applications is in advanced reactor concepts due to its high allowable design strength at elevated temperatures.

Another high-chromium nickel alloy known for its favourable properties for high-temperature use is INCONEL alloy 690. This alloy offers excellent resistance to high-temperature oxidising gases, and it also exhibits low corrosion rates and resistance to stress-corrosion cracking in high-temperature water. This makes it a popular choice for steam generator tubes, baffles and tubesheets, as well as hardware in nuclear power generation.

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