SMO 254

What is SMO 254 stainless steel?

SMO 254 is a high-performance austenitic stainless steel known for its excellent corrosion resistance, especially in environments with high chloride levels like seawater and brackish water. It contains high amounts of chromium, molybdenum, and nitrogen, which give it protection against pitting, crevice corrosion, and stress corrosion cracking.

Alloy 254 SMO is substantially stronger than the common austenitic grades, with strength nearly twice that of 300 series stainless steel. It also has a low carbon content which helps prevent carbide precipitation during welding. In some applications it has even been found to be a more cost effective substitute for high nickel and titanium alloys.

Chemical composition of Stainless steel SMO 254

%	C	Cr	Mn	Mo	N	Ni	P	Si	S
254 SMO	0.02 max	min: 19.5 max: 20.0	1.00 max	min: 6.0 max: 6.5	min: 0.18 max: 0.20	min: 17.5 max: 18.0	0.03 max	0.80 max	1.01 max

C (Carbon): Max 0.02%: Low carbon content minimizes carbide precipitation during welding, which enhances corrosion resistance, especially intergranular corrosion.

Cr (Chromium): 19.5–20.0%: Chromium is vital for forming a passive oxide layer that gives stainless steel its corrosion resistance, especially against oxidizing agents.

Mn (Manganese): Max 1.00%: Manganese improves hot working properties and contributes to strength, though its role is less significant compared to other elements here.

Mo (Molybdenum): 254 SMO is perfect for chemical and marine applications because of its high molybdenum concentration which provides remarkable resistance to pitting and crevice corrosion in chloride conditions.

N (Nitrogen): 0.18–0.20%: Nitrogen increases strength and improves resistance to localized corrosion without compromising ductility.

Ni (Nickel): 17.5–18.0%: Nickel stabilizes the austenitic structure, enhancing toughness, formability, and resistance to stress corrosion cracking.

P (Phosphorus): Max 0.03%: Kept low to prevent embrittlement and maintain corrosion resistance, especially in welded components.

Si (Silicon): Max 0.80%: Silicon improves oxidation resistance and acts as a deoxidizer during steelmaking.

S (Sulfur): Max 1.01%: Normally sulfur is kept low to maintain ductility, but if close to 1.01%, it might be a typo or unusual. Typically, sulfur in stainless steel is < 0.03% to avoid brittleness.

Mechanical properties of Stainless steel SMO 254

Grade	Tensile Strength ksi (MPa) min	Yield Strength 0.2% Offset ksi (MPa) min	Elongation - % in 50 mm (min.)	Hardness (Brinell) MAX	Hardness (Rockwell B) MAX
254 SMO Sheet & Strip	100 (690)	45 (310)	35	223	96

Tensile Strength: 100 ksi (690 MPa) min: This high tensile strength ensures the material can withstand significant stress before breaking, making it ideal for demanding structural and marine applications.

Yield Strength (0.2% Offset): 45 ksi (310 MPa) min: A high yield strength is essential for pipe systems and pressure vessels because it shows a good load-bearing capacity before plastic deformation.

Elongation: 35% in 50 mm (min): A high elongation percentage signifies excellent ductility, allowing the material to bend and stretch without cracking, essential for forming and welding.

Hardness (Brinell): MAX 223: Moderate Brinell hardness ensures a good balance between strength and machinability, resisting surface wear without becoming too brittle.

Hardness (Rockwell B): MAX 96: This confirms the Brinell rating, ensuring consistent mechanical performance and ease of fabrication.

Physical properties of Stainless steel SMO 254

Grade:	Alloy 254
Density	8.0 kg/dm³
Modulus of Elasticity	195 GPa
Linear Expansion at 68 to 212°F (20 to 100°C)	16.5 × 10^-6/°C
Thermal Conductivity	14 W/m°C
Thermal Capacity	500 J/kg°C
Electrical Resistivity	0.85 µΩ·m

Density – 8.0 kg/dm³: A relatively high density indicates a solid, compact structure, contributing to the alloy’s strength and durability in pressure-bearing and structural applications.

Modulus of Elasticity : 195 GPa: A high modulus means the material is stiff and resists deformation under stress, important for maintaining structural integrity in mechanical components.

Linear Expansion (20–1000°C): 16.5 x 10⁻⁶ /°C: Moderate thermal expansion ensures dimensional stability across wide temperature ranges, critical for heat exchangers and flanges under thermal cycling.

Thermal Conductivity : 14 W/m·°C: Lower thermal conductivity than carbon steel, but adequate for high-performance environments; helps control heat flow in reactors and condensers.

Thermal Capacity : 500 J/kg·°C: Good heat retention allows the material to absorb and withstand temperature changes without degrading, supporting energy efficiency in thermal processes.

0.85 µΩ·m Electrical Resistivity: 254 SMO has a higher resistivity than copper or aluminum which makes it less appropriate for electrical conduction but advantageous in corrosive conditions where current insulation is important.

Fabrications and Welding

Weldability

Stainless steel 254 SMO exhibits good weldability despite its high alloy content. It can be welded using most conventional techniques such as GTAW (TIG), GMAW (MIG) and SMAW (stick). However, distortion during welding may occur if improperly regulated because of the alloy's limited heat conductivity and excessive thermal expansion.

Machinability

Stainless steel 254 SMO is quite tough to machine due to the extremely high work hardening rate and lack of sulfur content; however, using sharp tools, overpowered machine tools, positive feeds, a good amount of lubrication, and slow speeds tends to provide good machining results.

Annealing

To prevent the precipitation of intermetallic phases, the alloy should be heated to a temperature between 1149 and 1204°C (2100 and 2200°F) and then quickly cooled, to avoid precipitation of intermetallic phases.

Hot Working

254 SMO can be hot worked efficiently, provided it is done at the correct temperature range. The alloy should be heated uniformly to 982–1149°C (1800–2100°F). It is important to avoid working below 982°C (1800°F) to prevent strain hardening.

Cold Working

254 SMO responds well to cold working, though it requires more force than lower alloyed stainless steels. Operations like bending, drawing, or rolling result in increased strength and hardness due to strain hardening.

Hardening

Unlike carbon steels, 254 SMO cannot be hardened by heat treatment. Its strength is improved primarily through cold working. Heat treatment like annealing is used only for softening or stress relieving purposes.

Corrosion Resistance of SMO 254

Stainless Steel SMO254 offers exceptional corrosion resistance in harsh environments, including seawater, chlorides, and acidic solutions. Its high molybdenum content ensures superior durability against chemical attack.

General Corrosion

SMO254 resists general corrosion effectively in a wide range of acids and alkaline solutions, outperforming standard austenitic stainless steels in harsh industrial settings.

Cracking from Stress Corrosion (SCC)

With high nickel and molybdenum content, SMO254 provides excellent resistance to stress corrosion cracking, especially in chloride-rich and high-temperature environments.

Intergranular Corrosion

Because of its stable microstructure and low carbon content SMO254 maintains its resistance to intergranular corrosion even after heat treatment or welding.

Pitting Corrosion

The high molybdenum and chromium levels offer outstanding resistance to localized pitting corrosion, making it ideal for use in saltwater and chemical processing environments.

Crevice Corrosion

The weak point of conventional stainless steels is their limited resistance to crevice corrosion. SMO254 performs exceptionally well in crevice corrosion prone areas, maintaining integrity in tight spaces and stagnant conditions where other alloys may fail.

Applications of Stainless Steel 254 SMO

Because of its remarkable corrosion resistance, high strength, and endurance under challenging conditions, stainless steel 254 SMO is widely used in a variety of industries.

Petroleum Production: Because of its resistance to sulfide stress corrosion and chloride corrosion stainless steel 254 SMO is used in the petroleum industry. It performs well in challenging conditions such as sour wells and offshore platforms.

Saltwater Handling: With excellent resistance to pitting and crevice corrosion, SMO 254 is ideal for saltwater applications such as seawater piping, heat exchangers and marine hardware, where conventional stainless steels may fail.

Food and Chemical Processing Equipment: It is a preferred material for food and chemical processing industries, because of its high corrosion resistance and cleanability. It ensures hygiene and durability in acidic, caustic or saline processing conditions.

Pulp Mill Bleach Systems: It is a reliable option for bleach washers, towers and storage tanks in tough bleaching settings because it can withstand the corrosive impacts of chlorine dioxide and other bleaching agents in pulp mills.

Flue Gas Desulphurization Scrubbers: SS SMO254 performs exceptionally in flue gas desulfurization systems, where it withstands acidic condensates, and high chloride content.

Tall Oil Distillation Columns: SMO254 is utilized in tall oil distillation columns because of its exceptional resistance to organic acids and high-temperature corrosion, which prolongs equipment life and reduces maintenance in chemical recovery operations.

Offshore Oil and Gas Production Equipment: These are utilized on offshore platforms for structural components, pipelines and valves that are exposed to seawater and salty air. Long-term performance in a harsh environment, guaranteed by its robustness and resistance to chlorine.

Desalination Equipment: SMO254 is utilized in evaporators, pipes, and heat exchangers in desalination facilities. It provides lifespan and minimizes downtime caused by corrosion, and withstanding harsh brine solution.