INCONEL? 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 has found numerous applications in the chemical/petrochemical processing, pollution control (flue gas desulfurization), power, marine, pulp and paper processing, and waste disposal industries. 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 (e.g., nitric acid and ferric and cupric salts). Its contents of molybdenum and tungsten give the alloy resistance to wet reducing media (e.g., sulfuric and hydrochloric acids). Alloy 22 exhibits excellent resistance to corrosive attack by seawater under stagnant and flowing conditions. At elevated temperatures, the high chromium level of INCONEL alloy 22 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. INCONEL alloy 22 products are covered by ASTM, ASME and ISO specifications. Alloy 22 is approved for construction of pressure vessels and components under the ASME Boiler and Pressure Vessel Code Section VIII, Division 1 for service up to 1250°F (677°C). The alloy is also approved by VdTüV under Werkstoffblatt 479. The alloy is equivalent to and directly competes with Hastelloy? C-22? and Nicrofer? 5621hMoW alloys. The limiting chemical composition ranges for alloy 22 are presented in Table 1. Table 2 compares the combined alloying content (Cr+Mo+W+Nb) of INCONEL alloy 22 with other similarly alloyed materials. Physical properties are presented in Table 3; mechanical properties at room temperature are found in Table 4; thermal conductivity in Table 5. Mechanical properties at elevated temperatures are seen in Figure 1. Table 1 - Limiting Chemical Composition, %, of INCONEL alloy 22 (ASTM B 574, B 575, etc.) Nickel............................................................................Balance* Chromium....................................................................20.0-22.5 Molybdenum ...............................................................12.5-14.5 Iron ..................................................................................2.0-6.0 Tungsten..........................................................................2.5-3.5 Cobalt ...........................................................................2.5 max. Vanadium....................................................................0.35 max. Carbon......................................................................0.015 max. Manganese .................................................................0.50 max. Sulfur ..........................................................................0.02 max. Silicon .........................................................................0.08 max. Phosphorus ................................................................0.02 max. *Reference to the ‘balance’ of a composition does not guarantee this is exclusively of the element mentioned but that it predominates and others are present only in minimal quantities. Table 2- Typical Compositions of the Ni-Cr-Mo-W corrosion resistant alloys Alloy UNS Werkstoff Fe Ni Cr Mo W or PREN* Number Number Nb 686 N06686 2.4606 1 57 20.5 16.3 3.9 50.8 22 N06022 2.4602 2.5 59 21.5 14.1 3.1 47.3 C-276 N10276 2.4819 6 57 15.5 16 3.9 45.4 625 N06625 2.4856 3 62 22 9 3.6Nb 40.8 C-4 N06455 2.4611 2 66 16 16 - 40.0 *PREN= %Cr + 1.5(%Mo + %W + %Nb)
