Hastelloy C22 UNS N06022 W. Nr. 2.4602 NiCr21Mo14W

Hastelloy C22 Alloy 22 (UNS N06022; W. Nr. 2.4602; NiCr21Mo14W) is a fully austenitic advanced corrosion-resistant alloy that offers resistance to both aqueous corrosion and attack at elevated temperatures. This alloy provides exceptional resistance to general corrosion, pitting, crevice corrosion, intergranular attack, and stress corrosion cracking. Alloy 22 is nickel-base and typically contains 22% chromium, 14% molybdenum, and 3% tungsten. Iron is normally limited to less than 3%. The alloy’s high content of chromium gives it good resistance to wet corrosion by oxidizing media.

Applications

Hastelloy 22 has found numerous applications in the chemical/petrochemical processing, pollution control (flue gas desulfurization), power, marine, pulp and paper processing, and waste disposal industries. At elevated temperatures, the high chromium level of Hastelloy C-22 Alloy helps it resist oxidation, carburization, and sulfidation. Since it is nickel-base, alloy 22 resists high temperature attack by halides (e.g., chlorides and fluorides). With these attributes, the alloy is widely used to protect steel tubes and other components in coal-fired and waste-to-energy boilers.

Specifications

Hastelloy C-22 is covered by ASME . Plate, sheet, strip, bar, tubing, and pipe are covered by ASME specifications SB-574, SB-575, SB-619, SB-622 and SB-626 and by ASTM specifications B-574, B-575, B-619, B-622 and B-626. The UNS number is NO6022.

Chemical Composition

Mechanical Properties Typical Room Temperature Tensile Properties of Annealed Material

Workability

Hastelloy C-22 can be fabricated using the same techniques as are used for alloys C-276 or C-4. It can be welded, forged, hot-upset and impact extruded. Alloy C-22 can also be successfully deep-drawn, spun, press formed or punched, although the alloy tends to work-harden.

Parts which have been hot formed or severely cold formed should be heat treated at 2050 °F and rapid quenched prior to final fabrication or installation.

Machinability

Hastelloy C-22 is considered moderate to difficult to machine, but it can still be machined using conventional production methods used for other alloys at a satisfactory rate. During machining, C-22 can harden rapidly, generate high heat, weld to the cutting tool surface, and resist metal removal, because of its high shear strength.

Fabrication of Hastelloy C-22

Although ductile enough to be formed by cold working, intermediate annealing may be necessary due to work hardening. Forging should be performed between 1750-2050° F followed by rapid cooling. Annealing can be performed at a temperature range between 2020-2150° F followed by a rapid quench. Cooling at an accelerated rate avoids the formation of detrimental phases which form between 1400-1800° F. Welding can be done by gas tungsten-arc, gas metal-arc and shielded metal-arc processes.

Corrosion Resistance in the As-Welded Condition

Hastelloy C-22 is a versatile nickel-chromium-molybdenum alloy with better overall corrosion resistance than other Ni-Cr-Mo alloys available today, including hastelloy C-276, C-4, and A625. Alloy C-22 has outstanding resistance to pitting, crevice corrosion and stress-corrosion cracking. It has excellent resistance to oxidizing aqueous media including acids with oxidizing agents, wet chlorine and mixtures containing nitric acid or oxidizing acids with chlorine ions. Hastelloy C-22 has outstanding resistance to both reducing and oxidizing media, and because of its versatility can be used where "upset" conditions are likely to occur or in multipurpose plants.

Hastelloy C-22 has exceptional resistance to a wide variety of chemical process environments, including strong oxidizers such as ferric and cupric chlorides, hot contaminated media (organic and inorganic), chlorine, formic and acetic acids, acetic anhydride, and seawater amd brine solutions.

Hastelloy C-22 resists the formation of grain boundary precipitates in the weld heat affected zone, thus making it suitable for most chemical process applications in the as-welded condition.

Welding

Any modern welding power supply with adequate output and controls can be used for common fusion welding. Generally, weld heat input is controlled in the low to moderate range.

Nickel-based alloys generally exhibit sluggish welding and shallow penetration characteristics; so, the possibility of incomplete fusion increases. Care must be used to ensure that sound welds are achieved. If orbital or automatic welding equipment is used, programs should utilize a pulsed current. Pulsed current inputs can help control weld penetration without exclusive heat input. Pulsing also helps control weld pool, improving the uniformity of weld bead appearance.

Cleanliness is critical when welding nickel-based alloys. Contamination by grease, oil, lead, sulfur, or other low melting point elements can lead to severe cracking problems. The welding surface and adjacent areas should be cleaned thoroughly with an appropriate solvent such as 99.9% isopropanol (IPA). Prior to any welding, all foreign matter—lubricates, cutting chips, burrs, crayon markings— should be removed.