Alloy 825 (UNS N08825)
W.Nr. 2.4858 An Nickel-Iron-Chromium
Alloy Developed for Exceptional Corrosion Resistance In Both Oxidizing and Reducing
Environments ------------------------------------------------------------- General
Properties Alloy 825 (UNS N08825) is an austenitic nickel-iron-chromium
alloy with additions of molybdenum, copper and titanium. It was developed to provide
exceptional resistance to numerous corrosive environments, both oxidizing and
reducing. The nickel content of Alloy
825 makes it resistant to chloride stress-corrosion cracking, and combined with
molybdenum and copper, provides substantially improved corrosion resistance in
reducing environments when compared to conventional austenitic stainless steels.
The chromium and molybdenum content of Alloy 825 provides resistance to chloride
pitting, as well as resistance to a variety of oxidizing atmospheres. The addition
of titanium stabilizes the alloy against sensitization in the as-welded condition.
This stabilization makes Alloy 825 resistant to intergranular attack after exposure
in the temperature range which would typically sensitize un-stabilized stainless
steels. Alloy 825 is resistant to
corrosion in a wide variety of process environments including sulfuric, sulfurous,
phosphoric, nitric, hydrofluoric and organic acids and alkalis such as sodium
or potassium hydroxide, and acidic chloride solutions. The
fabrication of Alloy 825 is typical of nickel-base alloys, with material readily
formable and weldable by a variety of techniques. ------------------------------------------------------------- Applications Air
Pollution Control Scrubbers Chemical Processing Equipment Acids Alkalis
Food Process Equipment Nuclear Fuel Reprocessing Fuel Element
Dissolvers Waste Handling Offshore Oil and Gas Production Seawater
Heat Exchangers Piping Systems Sour Gas Components Ore Processing
Copper Refining Equipment Petroleum Refining Air-cooled Heat Exchangers
Steel Pickling Equipment ------------------------------------------------------------- Standards ASTM..........................
B 424 ASME.......................... SB 424 ------------------------------------------------------------- Alloy
825 has good mechanical properties from cryogenic to moderately high temperatures.
Exposure to temperatures above 1000F (540C) can result in changes to the microstructure
that will significantly lower ductility and impact strength. For that reason,
Alloy 825 should not be utilized at temperatures where creep-rupture properties
are design factors. The alloy can be strengthened substantially by cold work.
Alloy 825 has good impact strength at room temperature, and retains it's strength
at cryogenic temperatures. ------------------------------------------------------------- Corrosion
Resistance The most outstanding attribute of Alloy 825 is its excellent
corrosion resistance. In both oxidizing and reducing environments, the alloy resists
general corrosion, pitting, crevice corrosion, intergranular corrosion and chloride
stress-corrosion cracking. ------------------------------------------------------------- Stress-Corrosion
Cracking Resistance The high nickel content of Alloy 825 provides superb
resistance to chloride stress-corrosion cracking. However, in the extremely severe
boiling magnesium chloride test, the alloy will crack after long exposure in a
percentage of samples. Alloy 825 performs much better in less severe laboratory
tests. The following table summarizes the alloy's performance. ------------------------------------------------------------- Pitting
Resistance The chromium and molybdenum content of Alloy 825 provides a
high level of resistance to chloride pitting. For this reason the alloy can be
utilized in high chloride environments such as seawater. It can be used primarily
in applications where some pitting can be tolerated. It is superior to conventional
stainless steels such as 316L, however, in seawater applications Alloy 825 does
not provide the same levels of resistance as SSC-6MO (UNS N08367) or Alloy 625
(UNS N06625). |