Stainless Steel 310MoLN
Stainless Steel 310MoLN (UNS S31050) is a low-carbon, molybdenum- and nitrogen-alloyed variant of the 310 series. It contains Mo (2-2.5%) and N (0.10-0.16%) in a high Cr-Ni base, giving it strong resistance to concentrated nitric acid and urea process environments. Standard 310 or 316L grades would corrode rapidly under the same conditions.
1. Chemical Composition
The table below lists the elemental composition for Stainless Steel 310MoLN. The molybdenum and nitrogen additions, paired with a very low carbon ceiling, give this grade its corrosion performance in aggressive oxidising acid environments.
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo | N | Other |
| 310MoLN | ≤ 0.020 | ≤ 2.00 | ≤ 0.030 | ≤ 0.010 | ≤ 0.75 | 24.00–26.00 | 19.00–22.00 | 6.00–7.00 | 0.18–0.25 | Cu ≤ 0.75 |
2. Mechanical Properties
The following table shows the minimum ambient-temperature mechanical properties for Stainless Steel 310MoLN in the solution-annealed condition. The nitrogen addition noticeably increases yield strength compared to Mo-free 310S.
| Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HB) |
| 310MoLN | ≥ 650 | ≥ 300 | ≥ 35 | ≤ 220 |
3. Equivalent Grade
This table maps Stainless Steel 310MoLN across international standard designations. It is mainly referenced in European and process industry specifications for urea and nitric acid plant construction.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 310MoLN | S31050 | S31053 | 022Cr25Ni22Mo2N | - | X1CrNiMoN25-22-2 | 1.4466 | - |
4. Key Technical Advantages
- Resistance to Nitric Acid Corrosion: High Cr (24-26%), very low carbon (<=0.020%), and controlled nitrogen together produce corrosion rates in concentrated nitric acid (HNO3) that meet the strict ASTM A262 Practice C (Huey Test) criteria. These criteria are mandatory for urea and nitric acid plant qualification.
- Urea Plant Carbamate Resistance: The 2-2.5% molybdenum content greatly improves resistance to ammonium carbamate, the main corrodent in urea synthesis loops. This makes 310MoLN one of the few austenitic grades accepted for stripper and carbamate condenser service.
- Nitrogen-Boosted Strength and Pitting Resistance: The 0.10-0.16% N range strengthens the austenitic structure through interstitial solid solution hardening. It also raises the pitting resistance equivalent number (PREN), which improves resistance to localised attack in mixed acid-chloride environments.
- Very Low Impurity Ceiling: Tightly controlled phosphorus (<=0.020%) and sulfur (<=0.010%) limits reduce grain boundary segregation. This is a critical factor for maintaining intergranular corrosion resistance in highly oxidising nitric acid service.
Technical Note: 310MoLN is typically specified to ASTM A240 or EN 10028-7 for plate and sheet forms. Pipe and tube supply in this grade is primarily governed by EN standards (1.4466). Procurement should confirm applicable test requirements, including the Huey Test (ASTM A262 Practice C) for urea service qualification.
5. Common Manufacturing Standards
Stainless Steel 310MoLN is mostly produced under European and process-industry standards. ASTM coverage is limited for this specialised grade:
ASTM A213: Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — referenced for chemical and mechanical verification where UNS S31050 is specified.
ASTM A312: Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes — applicable when UNS S31050 designation is specified by purchaser.
ASTM A262: Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels — Practice C (Huey Test) mandatory for urea plant qualification.
DIN EN 10216-5: Seamless steel tubes for pressure purposes — Technical delivery conditions for stainless steel (1.4466).
DIN EN 10028-7: Flat products made of steels for pressure purposes — stainless steels (1.4466).
Standards Comparison Table:
| Standard | ASTM | EN/DIN | JIS | GB/T | GOST |
| Seamless Tube | A213 (S31050) | EN 10216-5 (1.4466) | - | - | - |
| Seamless Pipe | A312 (S31050) | EN 10216-5 (1.4466) | - | - | - |
| Welded Pipe | A312 (S31050) | EN 10217-7 (1.4466) | - | - | - |
| Plate / Sheet | A240 (S31050) | EN 10028-7 (1.4466) | - | - | - |
6. Primary Applications
- Urea Synthesis Stripper and Condenser: High-pressure tubing and vessel components in urea plants that contact ammonium carbamate solutions. Resistance to both general and intergranular corrosion is necessary for long plant life.
- Nitric Acid Production Plants: Heat exchanger tubes and piping in HNO3 absorbers and concentrators, where standard 304L or 310S corrode at unacceptable rates in concentrated oxidising acid.
- Fertiliser Processing Equipment: Pressure vessels, pipelines, and heat exchangers in ammonium nitrate and mixed fertiliser synthesis that involve nitric acid and ammonia environments.
- Speciality Chemical Reactors: Reactor internals and transfer piping in processes that use concentrated oxidising acids or mixed nitric-sulfuric acid streams.
- Nuclear Fuel Reprocessing: Evaporator tubes and dissolvers in spent fuel reprocessing facilities, where boiling concentrated nitric acid is the primary process fluid.