Is AH36 the same as DH36?

No. Both are high-strength shipbuilding plate grades used in marine and offshore work, but they are not automatic substitutes. Impact test temperature and project class rules can differ, so the purchase order must name the exact grade required by the design or classification package.

Which grade should a buyer choose for a ship or offshore project?

Choose the grade written on the drawing, material list, or classification-approved specification. Do not accept an AH36 for DH36 substitution, or the reverse, without written engineer or class approval.

What must an RFQ include for AH36 or DH36 plate?

State the exact grade, product form, thickness range, dimensions, quantity, classification or project document requirements, impact testing scope, surface condition, dimensional tolerance, packing, MTC or EN 10204 3.1 document needs, and inspection plan.

Does an MTC alone prove the plate is ready for shipment?

Not by itself. Review heat number traceability, required mechanical and impact results, product form, marks, packing list match, and any class-related document scope before shipment release.

AH36 vs DH36 Shipbuilding Steel Plate: Buyer Guide for Grade Selection and RFQs

Introduction

Shipbuilding and offshore buyers often see AH36 and DH36 quoted as if they were interchangeable high-strength hull plates. Both grades are widely used for marine structural plate. The commercial risk appears when a quotation treats them as automatic substitutes without matching the project grade callout, thickness range, impact testing requirement, classification document scope, and certificate language.

AH36 and DH36 belong to the high-strength shipbuilding steel family used for hull and marine structure plate supply. Approximate strength levels can look similar in a sales table, but acceptance is not decided by a single yield number. Buyers must confirm the exact grade named by the project, the impact test temperature or toughness option required by the material specification package, the product form, and the inspection documents that will be audited before loading.

This guide compares AH36 vs DH36 from a procurement perspective. It is written for importers, shipyards, fabricators, and project buyers who need RFQ language that prevents silent grade substitution and shipment disputes.

Quick Decision Table: AH36 or DH36?

Buyer decision point	AH36	DH36
Typical buyer reason	Drawing or class package names AH36	Drawing or class package names DH36
Strength positioning	High-strength shipbuilding plate family	High-strength shipbuilding plate family
What not to assume	Automatic replacement for every DH36 callout	Automatic replacement for every AH36 callout
Common RFQ risk	Impact option, thickness, or class document scope omitted	Impact option, thickness, or class document scope omitted
Documentation risk	Certificate lists a neighboring grade or different toughness option	Certificate lists a neighboring grade or different toughness option

Use the table as a first filter only. Exact mechanical properties, chemistry, thickness rules, and impact temperatures must come from the applicable current material standard package, the classification society or project specification, and the purchase order. Do not invent a universal conversion table from marketing sheets.

For commercial product context, buyers can review AH36 carbon steel plate. That page helps frame supply options; it does not replace the project grade callout.

Why Name Matching Is Not Enough

A buyer may see that AH36 and DH36 are both discussed as high-strength ship plate grades with similar headline yield classes. That proximity is why false substitutions enter quotations.

Procurement still has to answer:

Which exact grade string is named on the drawing or approved material list?
Is the order plate, cut piece, or another form the mill can certify?
What impact test temperature or toughness option does the project require?
Are there thickness-dependent property or testing rules that change acceptance?
Must certificates support a classification society package, an owner standard, or both?
Will the yard, third-party inspector, or class surveyor accept a substitute?

If any of those answers is unclear, do not approve a grade swap on price alone.

Standards Context Without Over-Claiming Equivalence

AH36 in buyer language

AH36 is commonly ordered for high-strength shipbuilding plate when the project material list names AH36. Buyers should still confirm the full designation, thickness range, and testing options because neighboring grades in the same family are not automatically interchangeable.

When ordering, write:

Exact grade string: AH36.
Product form: plate or cut piece as required.
Thickness, width, length, and quantity.
Surface condition if the fabrication route requires blasted, primed, or other agreed finish.
Impact testing scope if required by the drawing or class package.
Certificate type, often including MTC and EN 10204 3.1 when project QA requires inspection documents.

DH36 in buyer language

DH36 is commonly ordered when the project names DH36 rather than AH36. Buyers should treat the letter designation as a controlled callout, not a free commercial upgrade or downgrade path.

When ordering, write:

Exact grade string: DH36.
Product form and size range.
Any thickness-dependent testing notes from the project package.
Mechanical and impact acceptance basis required by the PO.
Heat number marking and document list, including EN 10204 3.1 when required.

Related structural comparisons on this site, such as S355JR vs ASTM A572 Grade 50, follow the same rule: compare decision points, do not invent a universal conversion table.

Practical Inspection Notes Before Shipment

A correct grade name on a quotation can still fail at receiving if inspection is vague. Align the mill, inspector, and buyer on the same checkpoints.

Check these points before release:

Plate marking matches the packing list and MTC heat number.
Ordered grade appears on the certificate without silent substitution.
Thickness, width, and length measurements follow the agreed method and sampling plan.
Surface condition is acceptable for the fabrication or coating route.
Impact results appear when the order requires them; absence is a nonconformance if the PO required the test.
Document type is correct. Many importers request EN 10204 3.1 inspection documents for overseas marine projects.

For certificate workflow detail, pair this guide with how to verify a steel mill test certificate before shipment and the EN 10204 3.1 certificate checklist.

RFQ Checklist: What To Put In Writing

Use this checklist as the minimum commercial text for either grade.

RFQ field	What to state	Why it matters
Standard and grade	AH36 or DH36 exactly as named by the project	Prevents “equivalent grade” quoting
Product form	Plate or cut piece	Certificate scope follows product form
Dimensions	Thickness, width, length	Controls fabrication fit and mass
Quantity	Pieces, tons, or both with tolerance basis	Avoids shortage or over-delivery disputes
Impact / toughness scope	Required test temperature or option if applicable	Strength and toughness are not the same request
Surface / delivery condition	Mill finish, blasted, primed, or other agreed state	Affects welding prep and coating
Dimensional tolerance	Thickness, flatness, edge rules if critical	Prevents rework after nesting or assembly
Documents	MTC, `EN 10204 3.1` if required, packing list, photos	Separates material evidence from logistics evidence
Inspection	Mill inspection, third-party witness, sampling plan	Makes acceptance reproducible
Packing	Bundling, edge protection, seaworthy wrap, labels	Protects traceability during sea freight

Use the broader steel RFQ checklist to add destination, Incoterms, port, quantity, and delivery fields.

Common Buyer Mistakes

Accepting “AH36 / DH36 equivalent” language without engineer or class approval.
Ordering by strength class only and omitting the full grade designation.
Forgetting impact requirements that appear in the design notes but not in the commercial email.
Approving an MTC that lists a neighboring grade or a different toughness option.
Skipping mark-to-certificate reconciliation until cargo arrives at the yard.
Leaving packing and label requirements verbal so heat numbers cannot be traced after loading.

First-Hand Procurement Notes

On export ship plate orders, the expensive failure is rarely the headline yield figure. It is the missing acceptance rule. A mill can supply strong plate that still fails project QA because the certificate, impact option, thickness range, or marking method does not match the purchase order.

Before confirming production, send one concise RFQ package that includes the drawing grade callout, the thickness list, the document list, and the inspection plan. Ask the supplier to repeat those fields in the proforma invoice and packing specification. If the supplier answers with a broad “equivalent available,” request a written deviation approval path instead of silent substitution.

Conclusion

AH36 and DH36 can both serve marine structural plate needs when the project names them correctly. They are not automatic commercial equivalents. Choose the grade named by the project, write the grade and product form into the RFQ, and require certificates and measurements that can be checked before shipment.

If you are preparing a shipbuilding plate inquiry, share the grade callout, thickness list, product form, destination packing needs, and document requirements, including any MTC or EN 10204 3.1 needs. A clear RFQ is the fastest way to compare mill options without rework risk. You can also request a quote with those fields attached.

Buyer tip: freeze the project grade letter and impact option in the RFQ subject line so quotations cannot silently swap AH36 and DH36.