UREA 25.22.2 chemical composition has been optimized for specific uses in Urea plants.
It is a 310L modified austenitic stainless steel with low carbon, low silicon and high nitrogen additions in order to stabilize and strengthen the austenitic phase. The alloy is particularly designed for improved corrosion resistance properties in
Ammonium carbamate environments including strippers. The grade is also well designed for resistance in wet corrosive conditions due to its high contents of chromium, molybdenum and nitrogen (PREN > 33). UREA 25.22.2 is designed for the fabrication of lining interiors in Urea units or complementary products (pipes, fittings…). The grade can be used for urea strippers.
Liner strip UREA 25.22.2 -310MoLN – UNS S31050 for relining Urea reactor in Fertilizer Plants
Mechanical Properties
|
Tensile strength: |
540-740 |
N/mm² |
|
Yield strength 0,2% : |
250 |
≥ N/mm² |
|
Elongation: |
35/30 |
≥ % |
|
Hardness Brinell: |
240 |
≤ HB |
Chemical Composition
Carbon C 0,020% max
Silicon Si 0,40% max
Manganese Mn 2% max
Phosphorus P 0,020%max
Sulphur S 0,010% max
Chromium Cr 24-26%
Molybdenum Mo 2,0-2,6%Nickel Ni 21-23,5%
Nitrogen N 0,10-0,15%
Heat Treatment
heat treatment (1140°-1180°C –2084-2156°F) and water quenching
Corrosion testing
The corrosion resistance properties are enhanced thanks to the low carbon level, low silicon level and complementary additions of nitrogen.
Typical maximum corrosion results required following different specifications for the 25.22.2 grade after 5 periods of 48 h following ASTM A 262-C practice are:
maximum general corrosion: 1,6 μm/48 h or 65 mg/dm² per hour with a maximum depth of microcracks of 100 μm in the long direction of rolling.
Non destructive testing
- Ferrite check 100% (less than 0,5%)
- Measurement location chosen by Inspector
Welding
UREA 25.22.2 can be welded with most of the welding processes : TIG, Plasma, MIG welding, as well as SMAW, SAW or FCAW processes. The alloy is sensitive to hot cracking phenomenon due to its fully austenitic microstructure. Weld should be performed in order to obtain extra-low ferrite contents, no carbide or nitride precipitations, low silicon contents as well as no intermetallic phase precipitations. Higher manganese content products should be considered.
Source: https://www.gemaco-piping.com/materials/urea-grades/1-4466-urea-25-22-2-310moln-uns-s31050/
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