ASTM A240 Stainless Steel Plate, Sheet and Strip Specification
What Is ASTM A240?
ASTM A240/A240M is the Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications. It defines, for each covered grade, the required chemical composition, tensile and yield strength, elongation, hardness, grain size where applicable, heat-treatment condition, surface finish and the sampling and certification procedures. Because the same standard covers plate from 4.76 mm upward and sheet and strip below that thickness, it is the single most cited document when buying stainless flat products in China, Europe, the Middle East and the Americas. The metric edition, A240M, uses SI units and is the version most suppliers quote.
Grades Covered by ASTM A240
The standard groups grades by alloy family. The most frequently purchased include:
| Grade | Material description |
|---|---|
| 304 / 304L (S30400 / S30403) | 18-8 chromium-nickel austenitic; general-purpose and low-carbon weldable version |
| 316 / 316L (S31600 / S31603) | Chromium-nickel-molybdenum austenitic; chloride-resistant, low-carbon version |
| 321 (S32100) | Titanium-stabilized 18-8 for elevated-temperature service |
| 410 (S41000) | 12% straight-chromium martensitic; hardenable, wear-resistant |
| 904L (N08904) | High-nickel, high-molybdenum super-austenitic for sulfuric and phosphoric acid service |
| UNS S31803 / S32205 | Duplex ferritic-austenitic; high strength plus chloride stress-corrosion resistance |
| UNS S32750 / S32760 | Super duplex; for offshore and desalination service |
| UNS S31254 | 6% molybdenum super-austenitic (254 SMO type) for seawater and bleach service |
Chemical Composition and Mechanical Requirements
Representative composition limits (weight %, maximum unless shown as a range):
| Element | 304 | 316 | 321 | 410 | 904L | S31803 | S32750 |
|---|---|---|---|---|---|---|---|
| Carbon | 0.07 | 0.08 | 0.08 | 0.08-0.15 | 0.02 | 0.03 | 0.03 |
| Manganese | 2.00 | 2.00 | 2.00 | 1.00 | 2.00 | 2.00 | 1.20 |
| Silicon | 0.75 | 0.75 | 0.75 | 1.00 | 1.00 | 1.00 | 0.80 |
| Chromium | 17.5-19.5 | 16.0-18.0 | 17.0-19.0 | 11.5-13.5 | 19.0-23.0 | 21.0-23.0 | 24.0-26.0 |
| Nickel | 8.0-10.5 | 10.0-14.0 | 9.0-12.0 | 0.75 | 23.0-28.0 | 4.5-6.5 | 6.0-8.0 |
| Molybdenum | - | 2.0-3.0 | - | - | 4.0-5.0 | 2.5-3.5 | 3.0-5.0 |
| Nitrogen | 0.10 | 0.10 | 0.10 | - | 0.10 | 0.08-0.20 | 0.24-0.32 |
Minimum mechanical properties for annealed plate:
| Grade | Tensile strength | Yield strength | Elongation | Hardness (max) |
|---|---|---|---|---|
| 304 | 75 ksi (515 MPa) | 30 ksi (205 MPa) | 40% | 201 HBW / 92 HRB |
| 316 | 75 ksi (515 MPa) | 30 ksi (205 MPa) | 40% | 217 HBW / 95 HRB |
| 321 | 75 ksi (515 MPa) | 30 ksi (205 MPa) | 40% | 217 HBW / 95 HRB |
| 410 | 65 ksi (450 MPa) | 30 ksi (205 MPa) | 20% | 217 HBW / 96 HRB |
| 904L | 71 ksi (490 MPa) | 31 ksi (220 MPa) | 35% | 95 HRB |
| S31803 | 90 ksi (620 MPa) | 65 ksi (450 MPa) | 25% | 293 HBW / 31 HRC |
| S32750 | 116 ksi (800 MPa) | 80 ksi (550 MPa) | 15% | 310 HBW / 32 HRC |
| S31254 | 100 ksi (690 MPa) | 45 ksi (310 MPa) | 35% | 223 HBW / 96 HRB |
Equivalent Standards Around the World
ASME SA-240: the code-adopted version of A240 for pressure-vessel construction under ASME Boiler and Pressure Vessel Code Section VIII.
EN 10088-2: European specification for stainless flat products; grade numbers such as 1.4301 (304) and 1.4404 (316L) map directly to A240 chemistry.
JIS G4304 (hot-rolled plate/sheet) and G4305 (cold-rolled): Japanese equivalents using SUS designations, e.g., SUS304, SUS316L.
GB/T 24511: Chinese standard for stainless steel plate and strip for pressure equipment; GB/T 3280 covers general flat products.
IS 6911: Indian standard for stainless steel plate, sheet and strip. Note that IS 2062 is a carbon-steel structural standard and is not a valid equivalent for stainless grades; always compare grade to grade, not standard to standard.
A240 vs SS304 vs A666
ASTM A240 is a specification, not a material. "SS304" is a shorthand name for grade 304 stainless steel, which in plate form must be manufactured and tested to A240 if purchased to that standard. In other words, SS304 is the product, A240 is the rulebook the product follows. ASTM A666, by contrast, is a separate specification for austenitic stainless steel sheet, strip and plate in the annealed and cold-worked conditions, used mainly for structural and architectural applications where higher cold-worked strength is desired; it does not carry the pressure-vessel pedigree of A240. If the end use is a pressure vessel or heat exchanger, A240 (or SA-240) is the correct call; for general structural cold-worked material, A666 may apply.
Common Misconceptions
"A240 is only for 304 and 316." A240 covers more than 40 grades across austenitic, ferritic, martensitic, duplex and super-austenitic families.
"SA-240 is a different material." SA-240 is the same specification adopted by ASME; the material, test requirements and certificates are aligned.
"Any mill can issue an A240 certificate without testing." A240 requires heat analysis, mechanical testing per heat and thickness, and marking; buyers should verify that the mill certificate references the current A240 edition and heat numbers.
"Hardness and tensile tests are interchangeable." Some A240 grades allow either hardness or tensile verification as a supplemental requirement, but for pressure service the tensile values in the standard remain the governing acceptance criteria.
"Equivalent standards mean identical tolerance." Chemistry limits map across EN, JIS and GB standards, but dimensional tolerances, test frequencies and marking rules differ; confirm the governing standard in the purchase order.
FAQ
What thickness range does ASTM A240 cover?
A240 covers plate from 4.76 mm (3/16 in) in thickness and sheet and strip below that. Plate up to several hundred millimeters can be supplied, subject to the mill's rolling capability and the mechanical-test requirements of the specific grade.
Is ASTM A240 the same as ASME SA-240?
Substantially yes. SA-240 is the ASME Boiler and Pressure Vessel Code version of A240, with identical composition and mechanical limits. Pressure-vessel fabricators must order to SA-240 when the vessel is built to ASME code.
Which A240 grade should I choose for seawater service?
For mild or intermittent seawater exposure, 316L is the entry point. For permanent immersion, high chloride content or stagnant conditions, super-austenitic UNS S31254 or super duplex UNS S32750 is normally specified.
How do I verify a plate certificate?
Check that the certificate lists the grade, UNS number, heat number, chemical heat analysis, mechanical test results with the required elongation and hardness, the A240 edition and year, and that the plate markings match the heat number on the certificate.
Does A240 allow cold-worked plate?
A240 specifies annealed (or, for some grades, normalized and tempered) conditions. If higher strength through cold work is needed, ASTM A666 covers austenitic stainless sheet and strip in cold-worked tempers for structural applications.
Can 410 plate be supplied to A240 and hardened afterwards?
Yes. 410 is covered by A240 in the annealed condition for pressure service, and it can be subsequently heat treated to higher hardness for components such as valve trim, as long as the final condition meets the applicable product requirement.
