304 vs 310S Stainless Steel Pipe: Key Differences
Two Austenitic Grades for Different Jobs
Both 304 and 310S are austenitic stainless steels, non-magnetic in the annealed condition and weldable by standard procedures. The difference is alloy loading. 304 (UNS S30400, EN 1.4301) is the world's most common stainless grade, balanced for corrosion resistance, formability and cost in general service. 310S (UNS S31008, EN 1.4845, JIS SUS310S) is a heat-resistant grade whose 25-20 composition (24-26% chromium, 19-22% nickel) is chosen for one purpose: to keep its strength and its oxide scale at furnace temperatures where 304 would oxidize and sag within months. Choosing between them is not about which is "better" but about the metal temperature of the application.
Chemical Composition Comparison
| Element (weight %) | 310S (S31008) | 304 (S30400) |
|---|---|---|
| Chromium | 24.0-26.0 | 18.0-20.0 |
| Nickel | 19.0-22.0 | 8.0-10.5 |
| Carbon (max) | 0.08 | 0.08 |
| Manganese (max) | 2.00 | 2.00 |
| Silicon (max) | 1.50 | 0.75 |
| Phosphorus (max) | 0.045 | 0.045 |
| Sulfur (max) | 0.030 | 0.030 |
Room-Temperature Mechanical Properties
| Property (min) | 310S | 304 |
|---|---|---|
| Tensile strength | 515 MPa | 515 MPa |
| Yield strength 0.2% offset | 205 MPa | 205 MPa |
| Elongation in 50 mm | 40% | 40% |
| Hardness | 217 HB max | 201 HB max |
At room temperature the two grades are near-equivalent in strength. The separation appears above roughly 500°C, where 304 loses strength rapidly and 310S retains useful creep resistance.
High-Temperature Resistance and Oxidation
310S resists oxidation in continuous service up to about 1050-1100°C, with good resistance to thermal cycling, spalling and sulfur-bearing furnace atmospheres; intermittent exposure can be somewhat lower.
304 is rated for continuous oxidation resistance to roughly 870°C, but its creep strength falls off above 500-600°C, so structural and pressure service is normally limited well below that.
The high chromium and nickel of 310S form a dense, adherent chromium oxide scale that re-forms quickly if damaged, which is what protects furnace pipe from burn-through and scaling.
Neither grade resists molten salts, strong reducing atmospheres or sulfur-rich combustion gases without additional alloying; always confirm the actual atmosphere with the mill or a materials engineer.
Applications
310S pipe: radiant tubes and furnace rolls in heat-treatment furnaces, kiln and combustion-chamber internals, muffles, annealing furnace components, heat-exchanger piping in high-temperature processes, burner nozzles and support structures above 800°C.
304 pipe: chemical and food processing lines, brewery and dairy piping, architectural handrails and cladding, water treatment, cryogenic service down to -196°C, and general process piping per ASTM A312/A269.
Where both temperature and pressure combine (superheaters, reformer piping), evaluate 310S or 304H/321H/347H against the design code's allowable stresses rather than guessing.
Cost and Selection Guidance
Material cost: 310S typically costs 1.8-2.5 times as much as 304 because of the doubled nickel and chromium content; only specify it where the metal temperature demands it.
Continuous metal temperature below 500°C: 304 is the economical and correct choice.
Continuous metal temperature 500-800°C: consider 304H, 321H or 347H first; they are cheaper than 310S and cover much of this band.
Continuous metal temperature above 800°C: 310S (or higher-alloy 330/333-type grades) is the standard choice for oxidation and creep resistance.
Fabrication: both grades weld with austenitic procedures; 310S requires controlled heat input to avoid sigma-phase embrittlement in heavy sections, so welding procedure qualification is recommended.
Common Misconceptions
"310S is just a stronger 304." It is not stronger at room temperature; its value is elevated-temperature oxidation and creep resistance.
"304 works fine in furnaces." Above about 550-600°C sustained, 304 loses strength and its scale spalls; furnace service needs 310S or stabilized heat-resistant grades.
"Higher nickel always means better pipe." Alloying is application-driven; paying for 310S nickel in a room-temperature water line wastes budget with no benefit.
"310S cannot be welded." It welds well with matching austenitic filler; heavy sections just need heat-input control to avoid sigma phase.
"Both grades have the same carbon, so they behave alike in service." The chromium-nickel balance, not carbon, drives the high-temperature difference between them.
FAQ
What is the maximum service temperature of 310S pipe?
Continuous service in air is commonly rated to about 1050-1100°C for oxidation resistance; for pressurized piping, the design code allowable stress at temperature must be checked, which will reduce the usable maximum.
Is 310S more corrosion resistant than 304 at room temperature?
Not necessarily. Its higher chromium helps in some oxidizing acids, but 310S has no molybdenum, so in chloride pitting service 316 outperforms it. 310S is specified for heat, not for chlorides.
What is the difference between 310 and 310S?
310S is the low-carbon version (0.08% carbon max versus 0.25% for 310), which reduces carbide precipitation at grain boundaries during welding and service, improving ductility; 310S is the pipe grade normally specified today.
Can 310S pipe be used in reducing atmospheres?
In strongly reducing or sulfur-rich atmospheres, 310S can suffer accelerated attack; high-temperature alloys with chromium plus aluminum or silicon are evaluated for such service. Confirm the atmosphere composition with the supplier.
Which standard covers 310S pipe?
ASTM A312 for seamless and welded pipe, with grade TP310S/UNS S31008; equivalent EN designation is 1.4845, and JIS is SUS310S. Tube products follow A213 or A269 where applicable.
Why is 310S pipe so much more expensive?
Nickel and chromium content roughly double that of 304, and both are costly alloying elements whose prices are volatile; the alloy surcharge alone accounts for most of the premium.
