SA-302 Grade B: identify the manganese–molybdenum alloy correctly
Gangsteel welcomes ASME SA302 Grade B enquiries for welded boilers and pressure vessels where the project specifies manganese–molybdenum alloy plate. Establishing the alloy identity is the first procurement check: Grade B is not the nickel-bearing member simply because the family title mentions nickel. The specification, Code edition and actual test documentation must agree before material is released to fabrication.
Grade B is Mn–Mo, not a borrowed nickel grade
The official ASTM A302/A302M-17(2022) public Scope distinguishes the family clearly: Grades A and B are manganese–molybdenum; Grades C and D are manganese–molybdenum–nickel. Grade B’s official ASTM tensile range is 80–100 ksi [550–690 MPa]. This is authoritative public family information, but not an official SA-302 extract for a named Code year. The ASTM abstract also describes killed steel, fine-grain requirements and tension testing.
Nickel is not specified for Grade B in the checked public references. That does not mean an actual heat contains zero nickel, and it does not justify importing a C or D nickel range. Ask for the actual chemical report when residual elements matter. A family heading is not a chemical acceptance table, just as a commercial “alloy vessel plate” description is not a complete purchase specification.
Separate heat chemistry from the product-check range
| Element and thickness basis | Heat analysis | Product analysis |
|---|---|---|
| Carbon, ≤1 in. [25 mm], max | 0.20 | 0.20 |
| Carbon, >1–2 in. [>25–50 mm], max | 0.23 | 0.23 |
| Carbon, >2 in. [>50 mm], max | 0.25 | 0.25 |
| Manganese | 1.15–1.50 | 1.07–1.62 |
| Silicon | 0.15–0.40 | 0.13–0.45 |
| Molybdenum | 0.45–0.60 | 0.41–0.64 |
| Phosphorus, max | 0.025 | |
| Sulfur, max | 0.025 | |
| Nickel |
These are public references, not a paid official SA-302 chemistry table. The undated SHH/SteelSpecs trader compilation separates manganese, silicon and molybdenum into heat and product columns. Ferrobend’s undated family table compresses those elements into product-style ranges; it does not establish those wider ranges as heat requirements. Its carbon note applies to both analyses, and its phosphorus and sulfur figures support the reference maxima above. Product-analysis phosphorus and sulfur limits were not separately established and remain blank. Nickel’s numerical cells remain blank because no Grade B limit was established.
This distinction is practical when comparing an offer or report. A manganese result should not be judged against 1.07–1.62% without first identifying whether it is a heat result or product check. The same applies to silicon and molybdenum. Require the analysis type, material identity and applicable acceptance basis, and refer uncertain or missing information to the approved edition rather than filling a blank with an adjacent grade’s value.
Check yield and elongation without importing Grade A data
| Property | Reference value | Source boundary |
|---|---|---|
| Tensile strength | 80–100 ksi [550–690 MPa] | Official ASTM A302/A302M-17(2022) public Scope; family reference here |
| Yield strength, minimum | 50 ksi [345 MPa] | Ferrobend and trader public references; not a named-Code SA extract |
| Elongation, long gauge | 15% in 8 in. [200 mm] | Public reference; applicable A20 adjustments |
| Elongation, short gauge | 18% in 2 in. [50 mm] | Public reference; applicable A20 adjustments |
The public-reference Grade B yield is 345 MPa, not the lower Grade A figure. Elongation values belong to their gauge lengths, not to two plate-thickness bands. Check the reported specimen and applicable A20 adjustment before deciding whether a result complies. Tensile strength is a range, so checking only that the result exceeds the lower bound is incomplete.
These material acceptance figures are not design allowable stresses at service temperature. Alloy content and room-temperature tensile compliance do not establish a permitted operating temperature, resistance to every environment, or low-temperature toughness. Use the governing construction rules and engineering assessment for service selection, and identify any additional test evidence the project requires.
Define SA-302 acceptance before requesting dual marking
The order must name SA-302 or SA-302M, Grade B, the governing Code year or Section II-A edition, units, size, delivery condition, tests and certificate form. An ASTM A302 certificate is not by itself SA-302 acceptance; dual certification is not automatic. Historical ASME contents evidence confirms a family title, not a current Code adoption or Grade B nickel requirement. BPVC.II.A-2025 has not been read for this summary, so no verified current Code year is assigned.
| Hold point | Information required | Reason |
|---|---|---|
| Material identity | SA-302 or SA-302M; Grade B; Code year or Section II-A edition | Avoid accepting another family member or an ASTM-only basis |
| Plate schedule | Units, thickness, width, length, quantity and tolerances | Define geometry and the applicable carbon band |
| Delivery and testing | Condition, representative test basis and required examinations | Make mill results relevant to the approved material condition |
| Document release | Certificate form, heat and plate linkage, required witness records | Check evidence against the order before fabrication |
The two unit systems are independently standard and are not exact mathematical equivalents. Select the controlling inch-pound or SI system and use it consistently. A certificate layout showing both systems does not authorize mixing limits from different systems or replacing specified requirements with rounded conversions.
Thickness and treatment are separate acceptance questions
Official ASTM Scope limits maximum thickness by the ability of the composition to meet the mechanical requirements; it supplies no fixed numerical cap in the public text. A commercial thickness range is a supplier capability statement, not a universal SA-302 limit. Request confirmation for the actual size and do not infer availability, production route or internal soundness from a generic table.
The trader compilation restates that plate 2 in. [50 mm] and under is normally as-rolled, with normalized or stress-relieved condition available when ordered, and plate over that threshold is normalized. This is an ASTM-family compilation restatement, not a verified paid SA-302 clause. Resolve the ordered SA edition and condition before acceptance; no normalizing temperature or blanket treatment guarantee is supplied here.
Define supplementary examinations where required. An ultrasonic test request needs a method, coverage and acceptance level, not just the letters “UT”. Impact testing needs the prescribed specimen, orientation, temperature and energy criteria; no default values are assumed. Where fabrication heat treatment must be represented in testing, state the approved simulation and required results. Welding procedures likewise depend on the actual Mn–Mo material and fabrication conditions, not a carbon-plate procedure copied by strength class.
Compare material purposes without creating equivalence
For a different carbon-vessel-plate purpose, see ASTM A285 Grade C. The ASTM A516 Grade 70 page provides another carbon vessel-plate comparison. Neither is a numerical source for SA302 Grade B, an alloy substitute, or an acceptance route for this order.
SA-302 Grade B purchasing questions
Does Grade B require nickel because the specification title includes it?
No Grade B nickel limit was established in the checked references. The official ASTM Scope identifies B as manganese–molybdenum and C/D as nickel-bearing types. Not specified must not be rewritten as zero nickel.
Why are manganese heat and product limits different?
They are distinct analysis bases in the public compilation. The heat range is 1.15–1.50%; the product-style range is 1.07–1.62%. Keep the certificate result type visible and verify acceptance against the ordered edition.
Is a 345 MPa yield report enough to release material?
No. Review the full tensile range, applicable elongation, chemistry, size, condition, traceability and any required additional tests. A single passing strength value does not demonstrate the complete ASME acceptance basis.
Is ultrasonic examination included simply because this is alloy vessel plate?
Do not assume it. State the required examination method and acceptance criteria where invoked by the project or edition. Confirm the agreed scope and reporting rather than relying on a general quality claim.
Can an ASTM A302 report be relabelled as SA-302?
Not merely by changing the heading. ASME acceptance and any dual certification need a documented basis under the governing Code edition and purchase requirements. Resolve that basis before approving material documents.
Enquire for the specified Mn–Mo Grade B plate
Send the SA designation and Code edition, unit system, plate schedule, condition, required tests and certificate form. Include project acceptance criteria and relevant fabrication requirements so the offer can be reviewed without assuming stock, automatic dual certification or unspecified examinations.