Hastelloy C276® - UNS N10276

The alloy Hastelloy C276® despite being very expensive, is a nickel-molybdenum-chromium alloy with excellent corrosion resistance in severe environments (very high effectiveness). The high nickel and molybdenum contents make the nickel steel alloy especially resistant to pitting and crevice corrosion in reducing environments while chromium conveys resistance to oxidizing media. Although there are several variations of the Hastelloy nickel alloy, Hastelloy C-276 is by far the most widely used.

Hastelloy C276® Available Formats

• Bar
• Wire
• Sheet
• Plate
• Forgings
• Pipe fittings
• Flanges
• Seamless & Welded pipe
• Seamless Tube & Welded tube
• Weld Rod

 Chemical Composition  Hastelloy C276®

Applications of Hastelloy C276®

• Many parts of flue gas desulfurization systems are made with alloy C-276, including scrubbers, ducting, and stack liners. These systems control pollution from electrical plants and usually involve aggressive scrubbing with chlorides. Alloy C-276 is especially resistant to chlorides, even under scrubbing conditions.
• C-276 is excellent at handling “sour” natural gas in oilfields, which usually contains hydrogen sulfide and chlorides. This gas destroys steels by hydrogen embrittlement (sulfide stress cracking) and stress corrosion, but C-276 resists corrosion from this environment, even at high temperatures.
• C-276’s corrosion resistance also makes it the material of choice for many chemical processing plants that make products such as soap, paint, fertilizer, adhesives, and more. The alloy may be used in parts such as heat exchangers, pressure vessels or tanks, evaporators, pipes, fittings, pumps, and valves.
• The paper industry also has a unique role for C-276, because paper is bleached (bleach is a chloride). C-276 is the material of choice for bleaching vessels and digesters.
• The food industry uses C-276 because it can avoid reacting with foods. Even if the alloy did react with foods, the main alloying elements (Ni, Cr, Mo) are not especially toxic to humans.

Physical Properties

The following table discusses the physical properties of Hastelloy C276®

Corrosion Resistance Hastelloy C276®

Alloy C-276 can be used in many chemical processes with both oxidizing as well as reducing media. The high chrome and molybdenum concentrations make the alloy resistant to chloride ion attacks. The tungsten content further increases this resistance. Alloy C-276 is one of the few materials that are resistant against chlorine gas, hypochlorite and chlorine dioxide solutions. The alloy is characterized by excellent resistance against concentrated solutions of oxidizing salts (such as iron III and copper chloride)

Fabrication and Heat treatment

Heating: It is important that the workpieces are clean and free of any contaminants before and during heat treatment. Sulfur, phosphorus, lead and other low-melting-point metals can result in damage during the heat treatment of VDM® Alloy C-276. This type of contamination is also contained in marking and temperature-indicating paints or paints, and also in lubricating grease, oils, fuels and similar materials. Fuels must have as low a sulfur content as possible. Natural gas should contain less than 0.1% by weight of sulfur. Heating oil with a maximum sulfur content of 0.5% by weight is also suitable. Electrical furnaces are to be preferred due to precise temperature control and lack of contaminants due to fuel. The furnace temperature should be set between neutral and slightly oxidizing, and should not change between oxidizing and reducing. The workpieces may not come in direct contact with flames.

Hot forming: Alloy C-276 should be hot-formed in a temperature range of 950 to 1,200 °C (1,742 to 2,192 °F) with subsequent rapid cooling in water or in air. Heat treatment after hot-working is recommended in order to achieve optimal corrosion behaviour. For heating up, workpieces should be placed in a furnace that is already heated up to the target value.

Cold forming: The workpieces should be in the annealed condition for cold working. Alloy C-276 has significantly higher cold-forming properties than the widely used austenitic stainless steels. This must be taken into account during the design and selection of forming tools and equipment and during the planning of forming processes. Intermediate annealing is necessary for major cold-working treatment. When cold forming of > 15 %, final solution annealing must be conducted.

Heat treatment: Solution annealing should take place at temperatures of between 1,100 and 1,160 °C (2,012 and 2,120 °F). The retention time during annealing depends on the semi-finished product thickness and can be calculated as follows:

• For thicknesses d < 10 mm (0.4 in), the retention time is t = d ∙ 3 min/mm
• For thicknesses d = 10 to 20 mm (0.4-0.8 in), the retention time is t = 30 min + (d – 10 mm) ∙ 2 min/mm
• For thicknesses of d = 20 mm (0.8 in), the retention time is t = 50 min + (d – 20 mm) ∙ 1 min/mm

Machining

Alloy C-276 should be machined in the heat-treated condition. For reasons of the considerably increased tendency to work hardening in comparison to austenitic stainless steels, a low cut speed at a feed level that is not too high should be selected and the cutting tool should be engaged at all times. An adequate depth of cut is important in order to cut below the previously formed strain-hardened zone. Optimum heat dissipation through the use of large quantities of suitable, preferably aqueous, lubricants has considerable influence on a stable machining process.

 Conclusion

It is true the Hastelloy C276 is a very useful alloy due to its wide range of applications.

An important design factor when selecting the material can be corrosion resistance.
Corrosive conditions may be present during some fluid operations, which can cause stress corrosion cracking in components. Materials that can resist this type of mechanical breakdown can be required in corrosive environments.
Where excellent corrosion resistance is required, Nickel-based alloys are a good material choice. Nickel can increase strength and hardness while maintaining ductility. Alloys based on Nickel may be able to prevent stress corrosion cracking in heat exchangers.
For applications requiring corrosion resistance, a variety of nickel-based alloys are available.
One of the most widely used corrosion-resistant metals for the fluid processing sector is Hastelloy C276. The elements that make up the alloy are Nickel, molybdenum, chromium, and a small quantity of tungsten. Usually, the alloy has more than 50% nickel.