What is the difference between alloy 825 and super duplex?
Alloy 825 can perhaps be considered the entry point from stainless steel to more expensive nickel alloys. With >40% nickel and >20% chromium, it certainly represents a step up in price compared to super duplex alloys.
Why specify Alloy 825?
Nickel-iron-chromium alloys such as Alloy 825 (also known as Incoloy 825 because Special Metals Corporation's line of nickel-iron-chromium alloys is known as Incoloy®) are designed to provide a more cost-effective solution for applications that require high temperature resistance and corrosion resistance. This corrosion resistance is achieved by reducing the nickel content compared to more exotic alloys.
Duplex and super duplex stainless steels both offer considerable bang for the buck in terms of corrosion resistance and strength. However, there are practical limits to the operating temperature range that need to be considered. This is where Alloy 825 comes into play. While standard super duplex alloys have a yield strength of >80ksi, Alloy 825 only has a yield strength of >36ksi. Likewise, the PREN (pitting resistance equivalent number) is only 31, while super duplex alloys can achieve >40.
Other considerations for using Alloy 825
However, there are other considerations. These are:
Alloy 825 can be used at service temperatures up to 540 degrees Celsius, while super duplex stainless steels are limited to 250 degrees Celsius.
Alloy 825 retains much of its impact strength at low temperature properties, while duplex and super duplex stainless steels tend to lose performance at very low temperatures.
The high nickel content of Alloy 825 ensures resistance to stress corrosion cracking. The addition of molybdenum and copper enables it to resist reducing environments such as sulfuric and phosphoric acids. The controlled addition of titanium inhibits intergranular corrosion that can occur at high temperatures.
With the expansion of the stock range, the order volume has increased. Alloy 825 is commonly used by our customers to manufacture valve and pump components for the chemical processing industry and downhole equipment for corrosive services. We stock a variety of solid bar sizes, ranging from 3/4 inch to 10 inches in diameter.
