ASTM A387 Grade 11 Class 1 plate: retain the specified tensile class
Gangsteel welcomes enquiries for ASTM A387 Grade 11 Class 1 chromium-molybdenum pressure-vessel plate. The starting point is the material selected by the purchaser, not an assumption that a higher tensile class would be a better purchase. A useful enquiry keeps the grade, Class 1 strength level and required delivery condition together, so that commercial comparisons do not conceal a material change.
The current official public edition identified here is A387/A387M-25. Its Scope describes chromium-molybdenum alloy plates intended primarily for welded boilers and pressure vessels designed for elevated-temperature service. Grade 11 has nominal chromium of 1.25% and molybdenum of 0.50%. These figures explain the familiar 1.25Cr-0.5Mo description; they do not define a complete purchase specification or exact analysis targets.
What the Class 1 selection means for a quotation
Grade 11 is offered in two tensile classes within the specification framework. A quotation that omits the class leaves an important requirement unanswered, even when its alloy description is correct. If the drawing calls for Class 1, retain that selection in the size schedule and ask for a separate deviation statement whenever another class or grade is proposed. An unsolicited strength increase should not silently replace the engineering selection.
| Decision | Information to provide | Review objective |
|---|---|---|
| Material line | A387 or A387M, Grade 11, Class 1; ordered edition | Retain the specified tensile class |
| Size schedule | Thickness, width, length, quantity and units per item | Keep material identity attached to every size |
| Thermal state | Required delivery condition and any purchaser conditions | Agree what condition the results represent |
| Inspection basis | Tests, specimen requirements and acceptance criteria | Separate standard requirements from purchaser additions |
| Documents | Requested certificate form and plate/heat identification | Define the evidence needed at receiving |
A quotation can be commercially attractive yet technically incomplete if the treatment condition or reporting basis is absent. Gangsteel enquiry review should therefore begin with the material schedule and any project notes that qualify it. Where attachments conflict, identify the controlling revision before comparing offers. Recording that decision early is more useful than trying to resolve different interpretations after plate has been ordered.
Chemistry belongs to Grade 11, not to the tensile-class label
| 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 |
This is a public compilation reference, not official Table 1. The grade-specific analysis columns were checked against independently reviewed Class 1 compilations, including a September 2026 compilation and an older stockist table. Official Table 1 was not inspected. Confirm the limits in the ordered edition, especially the compilation phosphorus and sulfur maxima. Empty cells are deliberately unassigned; they do not certify that those elements are absent.
The silicon split is particularly useful when an enquiry includes a chemical-analysis attachment. Heat analysis is shown at 0.50–0.80%, while product analysis is shown at 0.44–0.86%. A result cannot be assessed responsibly without knowing which analysis it represents. Similarly, the broader product chromium and molybdenum bands must not be presented as heat limits. Keep the analysis heading, element name and range on the same comparison sheet.
Changing from one tensile class to another does not create a different grade chemistry table. Conversely, matching chromium and molybdenum percentages alone does not establish the ordered class. Review the chemistry and mechanical evidence as connected but distinct parts of acceptance. If the purchaser requires a tighter element limit, state it as an additional requirement for agreement rather than implying that every Grade 11 plate has that restriction.
The independently checked Class 1 mechanical reference
| Property | Reference value | Basis |
|---|---|---|
| Tensile strength | 60–85 ksi [415–585 MPa] | Class 1 range |
| Yield strength, minimum | 35 ksi [240 MPa] | Class 1 minimum |
| Elongation, minimum; 8 in. [200 mm] gauge | 19% | Specimen gauge length |
| Elongation, minimum; 2 in. [50 mm] gauge | 22% | Specimen gauge length |
The Class 1 row is supported by the independently checked mill reference and its 2017 datasheet, together with the reviewed compilations. The official Tensile Requirements tables were not read, so these values are not labelled as an official table extract. Establish the complete specimen and adjustment rules from the ordered documents before using a report for acceptance. Elongation entries describe gauge lengths, not thickness bands.
Treat ksi and MPa as independent unit systems, with the selected system governing the comparison. Recalculating one column and substituting a newly rounded value into the other can obscure the actual requirement. Identify the governing system on the order, and retain the original specimen basis when reviewing test results. The class name should still be visible beside the result, not inferred from a strength number alone.
Agree delivery condition rather than prescribing a web-based recipe
Official abstract describes killed and thermally treated steel. For Class 1, the reviewed public compilation describes usual delivery as annealed, or normalized and tempered, or accelerated cooling followed by tempering. That is a compilation restatement, not the official heat-treatment clause. Agree the required route against the ordered edition; this page does not set treatment temperatures or establish fabrication procedures.
The official Scope limits thickness by the composition’s capacity to meet specified mechanical properties, rather than a universal numerical maximum. This is not a statement of available rolling sizes. Send the requested dimensions for review together with the material condition. Impact testing, additional examination and documentation must be specified where needed; none should be inferred from the alloy name or the elevated-temperature application description.
For related alloy topics, compare Grade 12 Class 1 plate and Grade 22 Class 1 plate. These pages provide navigation within the family, not technical evidence or permission to substitute another grade. Material selection remains with the project’s engineering and purchasing requirements.
Buyer questions
Can an offer for a higher class be accepted without changing the order?
Do not treat it as an automatic upgrade. The selected class is part of the material requirement, and a proposed alternative needs an explicit technical review. Keep Class 1 on the purchase line until an authorized change is agreed.
Does the nominal 1.25Cr-0.5Mo description establish compliance?
No. It identifies Grade 11 in official Scope, but does not replace analysis limits, mechanical requirements, delivery condition or document review. The percentage ranges above distinguish heat from product analysis and remain labelled public references.
Is the 19% elongation figure a thick-plate requirement?
No. It is the labelled Class 1 reference for an 8 in. [200 mm] gauge. The separate 22% entry uses a 2 in. [50 mm] gauge. Preserve the gauge and applicable specimen rules when checking a report.
Must every Class 1 enquiry demand normalized-and-tempered plate?
Not solely because of this grade name. The reviewed Class 1 compilation includes annealed and accelerated-cooling-plus-temper routes as well. Resolve the required delivery condition using the ordered specification and project needs, rather than assuming one universal route.
Will an ASTM certificate also satisfy an ASME material request?
An ASTM certificate alone is not SA-387 acceptance, and the reverse is not automatic. Any dual requirement needs separate agreement and evidence against both governing documents. Identify the applicable Code edition when relevant; no current Code year is assigned here.
Discuss a Grade 11 Class 1 purchase requirement
Send your material schedule, ordered edition, unit system, dimensions and quantity. Add the required delivery condition, test criteria and certificate form so Gangsteel can review the enquiry on a clear, consistent basis.