INCOLOY 825 nickel-based alloy, an alternative to stainless steel
INCOLOY 825 Description
INCOLOY alloy 825 is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium. The alloy's chemical composition, given in Table 1, is designed to provide exceptional resistance to many corrosive environments. The nickel content is sufficient for resistance to chloride-ion stress-corrosion cracking. The nickel, in conjunction with the molybdenum and copper, also gives outstanding resistance to reducing environments such as those containing sulfuric and phosphoric acids. The molybdenum also aids resistance to pitting and crevice corrosion. The alloy's chromium content confers resistance to a variety of oxidizing substances such as nitric acid, nitrates and oxidizing salt. The titanium addition serves, with an appropriate heat treatment, to stabilize the alloy against sensitization to intergranular corrosion. The resistance of INCOLOY alloy 825 to general and localized corrosion under diverse conditions gives the alloy broad usefulness. Applications include chemical processing, pollution control, oil and gas recovery, acid production, pickling operations, nuclear fuel reprocessing, and handling of radioactive wastes. Applications for alloy 825 are similar to those for INCOLOY alloy 020.
Reasons why INCOLOY 825 replaces stainless steel
Nickel-iron-chromium alloys, such as Alloy 825, also known as Incoloy 825 (Specialty Metals' line of nickel-iron-chromium alloys is called Incoloy), are designed to provide more cost-effective solutions for applications requiring high temperatures and corrosion resistance - By lowering the nickel content (with more exotic alloys). Duplex stainless steel and super duplex stainless steel are quite "real" in terms of corrosion resistance and strength. However, there are certain deficiencies within the operating temperature range in which INCOLOY 825 works. The yield strength of standard super duplex alloys is greater than 80ksi, while the yield strength of INCOLOY 825 is only greater than 36ksi. Likewise, PREN (pitting resistance equivalent number) is only 31, while super duplex alloys reach >40. but: a) Alloy 825 can be used at operating temperatures up to 540°C, while super duplex stainless steel has an operating temperature of 250°C. b) INCOLOY 825 retains most of its impact strength at low temperature properties, whereas the properties of duplex and superduplex stainless steels tend to degrade at very low temperatures.The high nickel content of INCOLOY 825 ensures resistance to stress corrosion cracking. The addition of molybdenum and copper makes it resistant to reducing environments such as liuic acid and phosphoric acid. Controlling the addition of titanium can inhibit intergranular corrosion that may occur at high temperatures.
The characteristics of Incoloy 825 are
• Excellent resistance to reducing and oxidizing acids
• Good resistance to stress corrosion cracking
• Satisfactory resistance to local attacks such as pitting and crevice corrosion
• Very resistant to acid and phosphoric acid
• Good mechanical properties at room and elevated temperatures up to approximately 1000°F
• Permission to use pressure vessels with wall temperatures up to 800°F
