254 SMO is a high-alloy austenitic stainless steel developed for use in seawater and other aggressive chloride-bearing media. The steel is characterized by the following properties:
- Excellent resistance to pitting and crevice corrosion, PRE = ≥42.5*
- High resistance to general corrosion
- High resistance to stress corrosion cracking
- Higher strength than conventional austenitic stainless steels
- Good weldability
*The PRE is defined as, in weight-%, PRE = %Cr + 3.3 x %Mo + 16 x %N
Trademark information: 254 SMO is a trademark owned by Outokumpu OY.
Standards
- UNS: S31254
- EN Number: 1.4547
- EN Name: X1CrNiMoCuN20-18-7
- W.Nr.: 1.4529**
- AFNOR: Z1 CNDU 20.18.06AZ*
Product standards
- Seamless tube and pipe: ASTM A269, A213, A312, NFA 49-217, EN 10216-5
- Norsok MDS R11/R18, IOGP S-563 MDS IR111/111S/IR118/IR118S
- Welded tube and pipe: ASTM A249, A269 , A312, A358, A409
- Fittings: ASTM A182
- Bar: ASTM A276, A479, EN 10088-3
- Forged products: ASTM A473
Approvals
- UNS S31254 (Alleima® 254 SMO) in the form of seamless pipe has been approved by the American Society of Mechanical Engineers (ASME) for use according to ASME Boiler and Pressure Vessel Code section VIII, div. 1. However, there is no approval for UNS S31254 in the form of seamless tube, but according to the ASME paragraph UG-15 it is allowed to use the design values for seamless pipe according to ASME section VIII, div. 1 also for seamless tube.
- NACE MR 0175 (sulphide stress cracking resistant material for oil field equipment).
Chemical composition (nominal)
Chemical composition (nominal) % | C | Si | Mn | P | S | Cr | Ni | Mo | N | Cu |
| ≤0.020 | ≤0.80 | ≤1.00 | ≤0.030 | ≤0.010 | 20 | 18 | 6.1 | 0.20 | 0.7 |
Applications
Alleima 254 SMO is used in the following applications:
- Equipment for handling of seawater, such as seawater cooling, cooling water pipes, ballast water systems, firefighting systems etc.
- Hydraulic and instrumentation tubing
- Equipment in pulp bleaching plants
- Components in gas cleaning systems
- Tanks and pipelines for chemicals with high halide contents
Trademark information: 254 SMO is a trademark owned by Outokumpu OY.
Corrosion resistance
In solutions containing halides such as chloride and bromide ions, conventional stainless steels can be readily attacked by local corrosion in the form of pitting corrosion, crevice corrosion or stress corrosion cracking (SCC). In acid environments, the presence of halides also accelerates general corrosion.
Mechanical properties
The following figures apply to solution annealed condition seamless tube and pipe.
Metric units, at 20°C | Wall thickness | Proof strength | Tensile strength | Elong. | Hardness |
| | Rp0.2a) | Rp1.0a) | Rm | Ab) | A2" | HRB |
| mm | MPa | MPa | MPa | % | % | |
| <5 | ≥310 | ≥340 | 675-850 | ≥35 | ≥35 | ≤96 |
| >5 | ≥310 | ≥340 | 655-850 | ≥35 | ≥35 | ≤96 |
1 MPa = 1 N/mm2
Imperial units, at 68°F | Wall thickness | Proof strength | Tensile strength | Elong. | Hardness |
| | Rp0.2a) | Rp1.0a) | Rm | Ab) | A2" | HRB |
| inch | ksi | ksi | ksi | % | % | |
| <0.187 | ≥45 | ≥49 | 98-123 | ≥35 | ≥35 | ≤96 |
| >0.187 | ≥45 | ≥49 | 98-123 | ≥35 | ≥35 | ≤96 |
a) Rp0.2 and Rp1.0 correspond to 0.2% offset and 1.0% offset yield strength, respectively.
b) Based on L0 = 5.65 √S0 where L0 is the original gauge length and S0 the original cross-section area.
Impact strength
Due to its austenitic microstructure, Alleima 254 SMO has very good impact strength both at room temperature and at cryogenic temperatures.
Tests have demonstrated that the steel fulfils the requirements (60 J (44 ft-lb) at -196 oC (-320 oF)) according to the European standards EN 13445-2 (UFPV-2) and EN 10216-5.
At high temperatures
Intermetallic phases are precipitated within the temperature range of 600–1000°C (1110–1830°F). Therefore, the steel should not be exposed to these temperatures for prolonged periods.
Metric units | Temperature | Proof strength |
| °C | Rp0.2 | Rp1.0 |
| | MPa | MPa |
| | min. | min. |
| 100 | 230 | 270 |
| 200 | 190 | 225 |
| 300 | 170 | 200 |
| 400 | 160 | 190 |
| 500 | 148 | 180 |
Imperial units
| Temperature | Proof strength |
| °F | Rp0.2 | Rp1.0 |
| | ksi | ksi |
| | min. | min. |
| 200 | 34 | 40 |
| 400 | 27 | 32 |
| 600 | 24 | 29 |
| 700 | 24 | 28 |
| 900 | 22 | 26 |
