Alloy 825, also known as UNS N08825 or Incoloy 825, is a remarkable alloy that belongs to the Ni-Cr-Fe-Mo family. It was developed in the 1950s and boasts a unique composition that provides exceptional resistance to a broad spectrum of corrosive settings, as well as sensitization that has intergranular character. Comprising 42% nickel, 32% iron, 22% chromium, 2.5% molybdenum, and 2% copper, this alloy is further stabilized with 0.8% titanium, making it particularly adept at withstanding the following acids: phosphoric and sulfuric.
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Where Is It Used?
The versatility of Alloy 825 for chemical industry is evident in its various applications. It finds utility in chemical and petrochemical processing, oil and gas extraction, pollution control, waste processing, and pickling applications. Alloy 825 can be delivered in various forms, including plates, pipes, bars, and sheets. Its characteristics and remarkable ability to withstand a broad spectrum of corrosive conditions make it a valuable material in numerous industrial applications.
Alloy 825 demonstrates excellent corrosion resistance. It excels in seawater and is well-suited for applications involving the following acids: phosphoric and sulfuric. It resists corrosion that has intergranular character due to its titanium stabilization. It can also withstand corrosion cracking caused by chloride stress thanks to its high nickel content, and pitting because of its molybdenum content. It is also resistant to media that cause oxidation.
The Influence of Hydrochloric Acid and High Temperature
Despite its impressive corrosion resistance, Alloy 825 does exhibit some susceptibility to hydrochloric acid, especially in stagnant, unaerated solutions. The corrosion rates in hydrochloric acid vary with acid concentration and temperature. The alloy’s performance is also influenced by temperature. For instance, the tensile strength and yield strength both decrease as the temperature rises, and the elongation increases at higher temperatures.
How It Performs in Phosphoric Acid?
In phosphoric acid applications, Alloy 825 performs exceptionally well. It showcases minimal corrosion rates in various phosphoric acid solutions under different conditions. When exposed to atmospheric corrosion, Alloy 825 maintains its integrity, as demonstrated by a 20-year exposure study near the ocean. The alloy is also notable for its resistance to stress-corrosion cracking, sulfide stress cracking, and weldability. It belongs to the 45th weldability group according to ISO 15608 and is suitable for brazing.