Making the grade

News and developments in the world of corrosion resistant alloys through the eyes of Corrotherm International

Product focus – INCONEL alloy 690

20 July 2021

Product focus – INCONEL alloy 690

This high-chromium alloy in the INCONEL series of superior nickel-based materials offers excellent resistance against some of the most corrosive acids in industrial use

INCONEL is the go-to series of high-performance nickel alloys for a wide range of industrial applications. Each Grade offers specifications and characteristics to enable design engineers to select the right material for each job.

Each Grade develops over time, creating new versions, enhanced or evolved in some way to offer different properties. INCONEL alloy 690, for example, is a version of INCONEL alloy 600, but with a different balance of nickel and chromium. While INCONEL alloy 600 has a minimum of 72% nickel and around 14-17% chromium, making it perfect as a standard material of use in the chemical industry, there are some corrosive environments that require a higher level of chromium.

This is where INCONEL alloy 690 builds on the INCONEL alloy 600 base. There is a much higher chromium content, up to 31%, and a minimum of 58% nickel. Both versions of the alloy also contain iron, as well as controlled amounts of other key chemical elements.

Corrosion resistance and applications

The higher chromium content lends INCONEL alloy 690 excellent resistance to a large number of oxidising acids and salts. Its resistance to particular acids means that it has a number of common applications.

For instance, its ability to resist nitric acid and hydrofluoric acid means that it can be employed in pickling operations, such as the pickling of stainless steels, and the reprocessing of nuclear fuels. It’s used for various components including tail-gas reheaters, heating coils and tanks in these environments.

The material also offers exceptional resistance to sulfuric gases, which means that it can be used for coal-gasification units, burners and ducts in petrochemical processing and waste processing.

One of its other key properties is its ability to resist both corrosive aqueous and high-temperature environments. In hot-water situations, it is shown to have low corrosion rates and an excellent resistance to stress-corrosion cracking. This is thanks to the high levels of nickel in the alloy’s composition, which protect it against stress-corrosion cracking in environments with chloride or sodium hydroxide.

Due to these desirable characteristics, INCONEL alloy 690 can also be used for steam generator tubes, baffles, tube sheets and components for nuclear power generation.

Other attributes

While its key selling point might be its high corrosion resistance, INCONEL alloy 690 has other properties that make it such a popular choice of material. For example, it exhibits high strength over a broad range of temperatures, normally in annealed condition.

It is often chosen for its longevity, perfect for extended use in applications at elevated temperatures. It has good creep-rupture strength and metallurgical stability.

It’s also easy to handle, being readily fabricated, welded and joined using conventional methods. In most cases, it can be worked in the same way as INCONEL alloy 600, with similar characteristics.

If you’d like to find out more about INCONEL alloy 690 or discuss its potential for your next project, please get in touch with a member of our Sales team.

Published in Corrotherm News