Reference
Standards & terms explained
Grade tables, certificates and shipping documents use terms that are standard across the shipbuilding steel trade but not always explained. Below are plain-language definitions — reference material, not marketing copy.
Standards & approval
- IACS
- The International Association of Classification Societies. Its Unified Requirements — including UR W11 for hull structural steel — set common minimum standards that member classification societies (CCS, ABS, DNV, BV, LR, RINA, KR, NK and others) build their own rules on. AH32 and higher grades are defined to UR W11.
- Classification society / class
- An independent body that sets construction and material rules for ships and surveys compliance with them. "In class" is a condition insurers, flag states and port authorities rely on. A classification society approves both the shipyard's design and, separately, the steel mills allowed to supply material for classed vessels — see "works approval" below.
- Normal strength vs higher strength steel
- Under IACS UR W11, grades A, B, D and E have a minimum yield strength of 235 MPa ("normal strength"). AH32/DH32/EH32 step up to 315 MPa and AH36/DH36/EH36 to 355 MPa ("higher strength"). The letter (A/B/D/E) sets the required impact test temperature; the number (32/36) sets the minimum yield.
Mechanical properties & process
- TMCP (Thermo-Mechanical Controlled Processing)
- A rolling process that combines controlled deformation with controlled cooling to refine the steel's grain structure without a separate reheating step afterwards. It is one of the delivery conditions classification societies approve for hull plate; the alternative is normalizing, a separate reheat-and-air-cool step after rolling. Both appear on the mill certificates published on the certifications page.
- EN 10204 3.1 vs 3.2
- Both are types of mill test certificate defined by EN 10204. A 3.1 certificate is issued and validated by the manufacturer's own authorized quality department. A 3.2 certificate additionally requires countersignature by an independent inspector — typically the classification society surveyor — making it the stronger form for classed vessels.
- ReH, Rm, A5
- Standard symbols on a mill test certificate: ReH is the upper yield strength, Rm is the tensile strength, and A5 is elongation after fracture measured over a gauge length of five times the specimen diameter. These are the values a grade table's "min. yield" and "tensile" columns refer to.
- Impact test temperature (Charpy V-notch)
- A Charpy V-notch test measures how much energy a small notched specimen absorbs before fracturing at a specified low temperature — a proxy for resistance to brittle fracture. Grades D and E, and the corresponding DH/EH series, require testing at progressively lower temperatures (0°C, −20°C, −40°C) because they are intended for colder or more highly stressed structural locations.
- Killed steel / deoxidation practice
- "Killed" describes steel fully deoxidized during steelmaking — commonly with aluminium or silicon — to stop gas evolving as it solidifies, giving more uniform internal structure and properties. It appears on manufacturer approval certificates as the deoxidation practice for a given grade.
- Continuous casting (CC)
- The standard modern steelmaking step where molten steel is poured directly into a continuously withdrawn strand and cut to length, rather than cast into individual ingots. It appears on every mill certificate as the casting process, alongside the steelmaking method (typically basic oxygen furnace).
- Grain refining elements (Al, Nb)
- Small additions of aluminium or niobium made during steelmaking to refine the size of the steel's grain structure, improving strength and low-temperature toughness. Higher-strength grades (AH32 and up) typically require grain refinement; normal-strength A and B typically do not.
Documents & traceability
- Heat number
- A traceability number assigned to one specific melt of steel. Every mill test certificate, and the markings on the plate itself, are tied to a heat number, so a buyer or surveyor can trace a specific plate back to the exact chemistry and test results for the batch it came from.
- Mill test certificate vs works approval
- These are two different documents. A mill test certificate (MTC) reports the actual chemistry and mechanical test results for one specific heat, issued with each shipment. A works or manufacturer approval certificate — the certificates published on the certifications page — is a separate, prior approval confirming that a factory is capable of producing a given product to a given standard at all, independent of any specific shipment.
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