Alloy C-276 (UNS N10276) is generally considered the most versatile heat resistant and corrosion resistant alloy available. A Ni-Cr-Mo-W alloy, C-276 offers excellent resistance to pitting, stress-corrosion cracking and high temperature atmospheres. Additionally, due to its low carbon content, C-276 resists the formation of grain boundary precipitates in the weld-affected zone making it useful for applications in the as-welded condition.

C-276 exhibits excellent resistance in a wide variety of chemical processing environments including those with ferric and cupric chlorides, hot contaminated organic and inorganic media, chlorine, formic and acetic acids and acetic anhydride. C-276 is one of the few materials capable of withstanding the corrosive attack of wet chlorine gas, hypochlorite, and chlorine dioxide solutions. C-276 is also very useful in seawater applications.

Alloy C-276 is used in pollution control, chemical processing, pulp and paper production, waste treatment, marine seawater applications, etc. It is specified in sour gas applications and is commonly implemented in applications for flue gas scrubbers, dampers and ducts.  C-276 has high temperature applications to 1500°F.

Alloy C-22 (UNS N06022) is very similar to Alloy C-276 (UNS N10276) and is also a good heat resistant and corrosion resistant alloy. A Ni-Cr-Mo-W alloy, C-22 offers resistance to pitting, stress-corrosion cracking and crevice corrosion. 

Hastelloy C-22, (like C-276) is used in pollution control, chemical processing, pulp and paper production, waste treatment, marine seawater applications, etc. When comparing the two alloys, there is little difference in corrosion resistant performance with one exception;  C-22 shows an improvement over C-276 when used in certain saturated wet chlorine environments. However, in most cases because of its supply/availability, C-276 is a more cost-effective option. 

Alloy B2 (UNS N10665) is a nickel base wrought alloy with excellent resistance to reducing environments like hydrogen chloride gas and sulfuric, acetic and phosphoric acids. Molybdenum is the primary alloying element. This nickel alloy can be used in the as-welded condition because it resists the formation of grain-boundary carbide precipitates in the weld heat-affected zone.

This nickel alloy provides excellent resistance to hydrochloric acid at all concentrations and temperatures. Additionally, alloy B2 has excellent resistance to pitting, stress corrosion cracking and to knife-line and heat-affected zone attack. Hastelloy B2 provides resistance to pure sulfuric acid and a number of non-oxidizing acids.

Alloy B2 has poor corrosion resistance to oxidizing environments, therefore, it is not recommended for use in oxidizing media or in the presence of ferric or cupric salts because they may cause rapid premature corrosion failure. These salts may develop when hydrochloric acid comes in contact with iron and copper. Therefore, if this alloy is used in conjunction with iron or copper piping in a system containing hydrochloric acid, the presence of these salts could cause the alloy to fail prematurely. In addition, this nickel steel alloy should not be used at temperatures between 1000° F and 1600° F because of a reduction in the ductility in the alloy.

Alloy 600 (UNS N06600) is a nickel-chromium alloy with good oxidation resistance at high temperatures and resistance to chloride-ion stress-corrosion cracking, corrosion by high-purity water and caustic corrosion. Alloy 600 is used for furnace components, in chemical and food processing, in nuclear engineering and for sparking electrodes.

Alloy 625 (UNS N06625) is a nickel-chromium-molybdenum alloy with excellent strength from room temperature up to about 1500°F. It maintains good oxidation resistance up to 1800°F and provides good resistance to aqueous corrosion. Some of the applications of this alloy are in chemical processing, aerospace and marine engineering, pollution-control equipment and nuclear reactors.

Depending on customer requirements, alloy 625 may also be supplied in the solution heat-treated condition.

Alloy 686 (UNS N06686) is a single-phase, nickel-chromium-molybdenum, tungsten alloy designed for outstanding corrosion resistance in a wide range of environments. This alloy is used in the most severe environments encountered in chemical processing, pollution control, pulp and paper production, marine (seawater) and treatment of industrial and municipal wastes. Chemical processing uses include heat exchangers, reaction vessels, evaporators and transfer piping. Air pollution control applications are stack liners, ducts, dampers, scrubbers, stack-gas re-heaters, fans and housings.

Development for Navy Applications:

Alloy 686 has been tested and qualified for manufacture of fasteners for service in aggressive marine environments. By cold working, fasteners with yield strength levels up to 150 ksi can be made. The resulting products exhibit excellent resistance to corrosion by seawater and hydrogen embrittlement. Alloy 686 fasteners are galvanically compatible with the common materials of marine construction. The high strength fasteners exhibit good ductility and fracture toughness. Thus, alloy 686 fasteners are expected to solve many of the problems encountered with existing grades of corrosion-resistant marine fasteners.

Fasteners of three grades of alloy 686 can be specified by ASTM F467 (nuts) and ASTM F468 (bolts). Each grade offers differing mechanical properties but maintains the same chemistry.

A precipitation-hardenable nickel-chromium alloy, Alloy 718 offers excellent strength and corrosion resistance with good fabrication characteristics in the annealed condition. Alloy 718 is normally only used for component applications up to 1200°F. It is used in gas turbines, rocket motors, spacecraft, nuclear reactors, pumps, naval ships, etc.

Alloy 718 should be used in the aged condition for stability of mechanical properties. Two standard heat treat conditions exist, AMS 5662 and AMS 5664. AMS 5662 is the standard lower temperature solution treat and offers slightly more strength. The latter, AMS 5664, specifies a higher solution treating temperature which when subsequently age-hardened provides enhanced ductility and fracture toughness. The latter is commonly specified in naval applications.

Alloy 825 (UNS N08825) is a nickel-iron-chromium alloy with additions of molybdenum and copper. It has excellent resistance to both reducing and oxidizing acids, stress-corrosion cracking and to localized attack such as pitting and crevice corrosion. The alloy is especially resistant to sulfuric and phosphoric acids. This nickel alloy is used for chemical processing, pollution-control equipment, oil and gas piping, nuclear fuel reprocessing, acid production and pickling equipment.