ASTM A387 Grade 11 Class 2: specify the complete plate requirement
ASTM A387 Grade 11 Class 2 combines a chromium-molybdenum grade identity with a particular tensile class. For a Gangsteel enquiry, both parts belong on the purchase line. Ordering only “1.25Cr-0.5Mo plate” identifies the nominal alloy family but leaves the class, specification edition, delivery condition and acceptance documents unresolved. Start with the project material schedule, then make those requirements visible in the request for quotation.
The current official public listing used here is A387/A387M-25. Its Scope covers chromium-molybdenum plates intended primarily for welded boilers and pressure vessels designed for elevated-temperature service. Grade 11 is listed at nominal 1.25% chromium and 0.50% molybdenum. These nominal figures identify the grade; they are not exact chemical targets or a replacement for the heat-analysis ranges shown later.
Build a Grade 11 Class 2 purchase line
| Order item | Purchaser input | Reason to resolve it |
|---|---|---|
| Specification identity | A387 or A387M, Grade 11, Class 2, required edition | Avoid an alloy-only or class-unspecified offer |
| Dimensions | Thickness, width, length, quantity and unit system | Keep size and material requirements connected |
| Delivery condition | Required thermally treated state and supporting records | Confirm the condition represented by testing |
| Inspection | Required tests, criteria and any purchaser additions | Do not assume an additional examination package |
| Documentation | Required certificate form and plate/heat identification | Provide an agreed basis for receiving review |
The official Scope makes two tensile classes available for Grade 11. Class 2 therefore needs to remain explicit when documents are exchanged, including any revised offer. A change of class is a technical deviation, not a harmless shortening of the material name. When several sizes are requested, keep the class and condition on each line rather than relying on a heading that can become detached from the size list.
Use the Grade 11 silicon range, with analysis type identified
| Element | Heat analysis | Product analysis |
|---|---|---|
| Carbon | 0.05–0.17 | 0.04–0.17 |
| Manganese | 0.40–0.65 | 0.35–0.73 |
| Silicon | 0.50–0.80 | 0.44–0.86 |
| Chromium | 1.00–1.50 | 0.94–1.56 |
| Molybdenum | 0.45–0.65 | 0.40–0.70 |
| Phosphorus, max | 0.025 | 0.025 |
| Sulfur, max | 0.025 | 0.025 |
| Ni, V, Nb, B, N, Al, W |
Source limits: these heat/product splits are public compilation restatements, independently checked in an older stockist compilation and a dated September 2026 compilation. Official A387/A387M-25 Table 1 was not inspected. In particular, the phosphorus and sulfur maxima are compilation figures to confirm in the ordered edition, not a claimed quotation of the current official table. Blank element cells indicate no limit established here; they do not mean zero content.
Silicon deserves a separate check on Grade 11: the labelled heat range is 0.50–0.80%, while the product range is 0.44–0.86%. The analysis type must travel with the result. A list of percentages headed only “chemical composition” leaves the reviewer to guess which limits were intended. Compare heat results against the applicable heat requirements and identify any product-analysis evidence separately, using the ordered specification rather than an unexplained combined range.
Chromium and molybdenum also have distinct heat and product bands. A quotation repeating only the nominal 1.25Cr-0.50Mo description does not supply that distinction. Where the project requests restricted chemistry, write the proposed element limit and analysis basis explicitly for review. Such a purchaser restriction should not be represented as a standard Grade 11 property merely because it appears on an enquiry attachment.
Class 2 mechanical reference: keep both elongation gauges
| Property | Reference value | Reporting basis |
|---|---|---|
| Tensile strength | 75–100 ksi [515–690 MPa] | Class 2 range |
| Yield strength, minimum | 45 ksi [310 MPa] | Class 2 minimum |
| Elongation, minimum; 8 in. [200 mm] gauge | 18% | Gauge length, not plate thickness |
| Elongation, minimum; 2 in. [50 mm] gauge | 22% | Gauge length, not plate thickness |
The mechanical values were independently confirmed on the Grade 11 mill reference, including its 2017 datasheet, and on public compilations. They are not reproduced from the official Tensile Requirements tables: those paid tables were not read. The mill reference also directs elongation adjustments to the applicable general requirements. Use the complete ordered documents for specimen and adjustment details instead of assuming that one website row settles every acceptance question.
The two elongation entries refer to different specimen gauge lengths, not two thickness bands. Keep the gauge on the report comparison; selecting the more convenient percentage without its specimen basis is not a valid review. Likewise, ksi and MPa are independent unit systems in the specification. State the governing system and use it consistently, rather than calculating new rounded values and combining them with the other system’s requirements.
Confirm thermal condition without inventing a treatment recipe
The official abstract states that the steel is killed and thermally treated. Public compilations describe usual Class 2 delivery as normalized and tempered, or accelerated cooling followed by tempering; they also state that Class 2 tensile requirements are not applicable to annealed plate. This delivery description is a labelled compilation restatement, not the paid official heat-treatment clause. Confirm the exact route in the ordered edition and record the agreed condition.
No quenching, normalizing or tempering temperature is prescribed here. Raise any subsequent fabrication condition that the purchaser needs represented in testing during contract review, rather than treating a supplier description as a welding procedure. The grade name alone does not establish an impact requirement, examination schedule or certificate form. Those items need the project’s explicit criteria and agreement.
Official Scope limits maximum thickness only by the composition’s capacity to meet the specified mechanical properties. That is a specification principle, not a promise of rolling capability or a numerical size cap. For family comparisons, see Grade 12 Class 2 plate and Grade 22 Class 2 plate. These are related-topic links, not numerical sources or substitution approvals.
Buyer questions
Does “1.25Cr-0.5Mo” fully specify Grade 11 Class 2?
No. It is the official Scope’s nominal alloy description. Name A387 or A387M, Grade 11, Class 2, the required edition and delivery condition, together with dimensions, tests and certificate requirements. Nominal alloy content does not replace detailed chemistry or class requirements.
Which silicon values should a preliminary chemistry comparison use?
The labelled public reference is heat 0.50–0.80% and product 0.44–0.86%. Keep the analysis type identified. These are independently checked compilation ranges, not an official Table 1 extract; the ordered edition remains the acceptance reference.
Why are there two elongation percentages?
The public-reference minima are 18% in 8 in. [200 mm] and 22% in 2 in. [50 mm]. They describe gauge lengths, not thickness categories. Review the specimen basis and any applicable adjustment requirements with the test result.
Can annealed plate be assumed to satisfy this Class 2 request?
No. The labelled compilations exclude annealed plate from the Class 2 tensile basis and describe usual normalized-and-tempered or accelerated-cooling-plus-temper delivery. Confirm the required route and its supporting evidence against the ordered edition rather than assuming a condition from the alloy name.
Does an A387 document automatically establish ASME acceptance?
No. An ASTM certificate is not by itself SA-387 acceptance, and the reverse is not automatic. Dual certification requires agreement and evidence for both requirements. Establish the governing Code edition when relevant; no current Code year is assigned here.
Request a Grade 11 Class 2 plate review
Send the designation and edition, dimensions, quantity, unit system and required thermal condition. Include inspection criteria, certificate requirements and any proposed deviations so the enquiry can be compared with the project material schedule.