Marine Steel Grades & Certification

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Steel Grades & Certification

Marine Structural Steel:

Ship Building Grades & IACS Certification Guide

Selecting steel for ship repair, hull renewal, or deck outfitting requires strict adherence to International Association of Classification Societies (IACS) standards. Commercial mild steel cannot substitute for class-approved shipbuilding steel due to specific yield strength, chemical composition, and low-temperature impact toughness requirements. Use this reference guide to match structural steel grades, mechanical properties, and required mill certification before placing procurement orders.

1. Shipbuilding Steel Grade Comparison

Standard vs. High-Strength Hull Structural Steel

Grade Category	Steel Grade	Min. Yield Strength (ReH)	Tensile Strength (Rm)	Charpy V-Notch Impact Temp	Typical Shipboard Application
Normal Strength	Grade A	235 N/mm²	400–520 N/mm²	+20°C (Not required for standard plates)	Superstructures, internal bulkheads, accommodation decks
Normal Strength	Grade B / D	235 N/mm²	400–520 N/mm²	Grade B: 0°C \| Grade D: -20°C	Side shell plating, deck plating, double bottom structures
Higher Strength (32 & 36)	AH32 / DH32	315 N/mm²	440–570 N/mm²	AH: 0°C \| DH: -20°C	Longitudinal framing, deck stiffeners, bottom longitudinals
	AH36 / DH36	355 N/mm²	490–630 N/mm²	AH: 0°C \| DH: -20°C	Container top decks, bulk carrier hopper tanks, sheer strakes
	EH36	355 N/mm²	490–630 N/mm²	-40°C (Severe cold environment)	Ice-class hull plating, high-stress intersection corners, bilge strakes

2. Marine Structural Profiles & Dimensions

Profile Type	Standard Specifications	Common Size Ranges	Primary Marine Function	IMPA Reference
Shipbuilding Steel Plates	Grade A, AH36, DH36 (Class Certified)	Thickness: 6 mm to 60 mm Width: 1500 mm / 2000 mm / 2500 mm	Hull plating, deck renewal, cargo hold bulkheads, cofferdams	67 01 xx
Bulb Flats (Holland Profiles)	EN 10067 / JIS G3192 (Grade A / AH36)	HP 80x5 mm to HP 430x15 mm	Primary stiffeners for hull, bottom frames, and bulkheads	67 02 xx
Equal & Unequal Angles	Marine certified structural steel	25x25x3 mm up to 200x200x20 mm	Deck outfitting, coamings, hatch support, ladder framing	67 04 xx
Seamless Marine Line Pipes	ASTM A106 Gr. B / API 5L / JIS G3454	DN 15 (1/2") to DN 600 (24") Sch 40, Sch 80, Sch 160	Ballast lines, fuel transfer piping, high-pressure fire mains	71 01 xx – 71 03 xx

3. Mill Test Certificate (MTC) Requirements: Type 3.1 vs. Type 3.2

When purchasing steel for class-surveyed ship repair, the test certificate must match the severity of the structural repair:

EN 10204 Type 3.1 (Inspection Certificate): Issued directly by the steel manufacturing mill’s authorized quality inspector. It validates chemical heat analysis and mechanical tensile/impact test values. Standard for secondary outfitting, stair towers, general machinery foundations, and non-pressure boundary fabrications.

EN 10204 Type 3.2 (Independent Third-Party Certification): Mandatory for primary hull structure, sheer strakes, keel plates, and pressure systems. Type 3.2 requires inspection, witnessing of Charpy impact/tensile tests, and physical stamp endorsement by a recognized IACS classification society surveyor (e.g., DNV, Lloyd’s Register, Bureau Veritas, ABS, or Indian Register of Shipping – IRS).

4. Steel Requisition Checklist for Ship Repairs

To avoid delays and ensure class surveyor approval during dockside delivery, provide the following details in your inquiry:

Exact Grade & Suffix: Always include strength and impact designations (e.g., specify DH36, not just 36 steel).
Standard Dimensions: Specify thickness ( $t$ ) x width ( $w$ ) $\times$ length ( $l$ ) in millimeters..
Surface Condition / Treatment: Indicate if plates require pre-blasting and shop-priming to protect against transit rust.
Required Classification Society: Name the surveyor required on the 3.2 stamp (e.g., DNV, LR, BV, ABS, or IRS)
Port / Delivery Location: Provide vessel ETA and whether delivery is needed to the shipyard quayside or local fabrication shop

Planning Hull Renewals or Structural Fabrication?

Contact NICO Marine today to discuss your requirements. Our marine metal supply desk sources class-certified shipbuilding plates, bulb flats, and seamless piping with full 3.1 / 3.2 Mill Test Certificates and expedited delivery to major ports.

Serving all major ports across India and UAE