Classification of shipbuilding plates

Shipbuilding steel plate refers to the carbon steel and alloy steel plate used in offshore and Marine engineering, and its classification is mainly based on its strength grade, toughness grade, and the relevant classification society certification standards. Common grades are A, B, D, E, AH32/36/40, DH32/36/40, EH32/36/40.

1. Divide by intensity level

Marine steel plates can be divided into the following three categories according to yield strength:

(1) Normal Strength Steel Plates
Yield strength: not less than 235 MPa.
Common brands: A, B, D, E.
A: Suitable for zero environment, general minimum requirements;
B: Slightly higher than grade A, slightly more widely used;
D/E: Used in low temperature environment, higher toughness requirements.
(2) High Strength Steel Plates
Yield strength: 315 MPa, 355 MPa, 390 MPa, 460 MPa, etc.
Common brand: AH32, AH36, DH36, EH36, FH36, etc.
A/D/E/F: indicates the toughness level of the steel plate (grade F has the highest toughness).
Number: Indicates the yield strength (for example, AH36 indicates a yield strength of 36 ksi, that is, about 355 MPa).
(3) Ultra High Strength Steel Plates
Yield strength: higher than 460 MPa.
Common brand: EH40, FH40, EH47, FH47, etc.

2. According to the toughness level

According to the ambient temperature, Marine steel plates are divided into different toughness levels:

Grade A steel plate: suitable for normal temperature environment, minimum toughness requirements.
Grade B steel plate: toughness is slightly higher than grade A, can be used for slightly low temperature environment.
Grade D steel plate: suitable for use at -20°C.
Grade E steel plate: suitable for use at -40°C, with good low temperature toughness.
Grade F steel: The highest toughness, suitable for use in lower temperatures and more harsh environments, such as polar environments.

3. Classification by classification society certification

Marine steel plates need to meet different international classification society standards, usually certified by the following authorities:

American Bureau of Shipping (ABS) : such as ABS A and ABS AH36.
DNV (Det Norske Veritas) : such as DNV AH36 and DNV EH40.
LR (Lloyd's Register) : for example, LR DH36, LR EH32.
Bureau Veritas (BV) : such as BV AH36 and BV DH40.
China Classification Society (CCS) : such as CCS A and CCS EH36.
GL, NK, KR and other classification society certification.

4. Chemical composition

（1）Common strength grade (ABS A/B/D/E)
Generally, the upper limit of carbon content is approximately 0.21%, manganese is about ≤1.3%, silicon is 0.10-0.50%, and phosphorus and sulfur are strictly controlled at ≤0.035%. Some high-toughness grades (such as D and E) also add ≥0.015% aluminium for deoxidation and grain refinement.

（2）High-strength grades (such as AH36 / DH36 / EH36)

Elements	C	Mn	Al	Si	P	S
AH32	≤0.18	0.7~1.60	≥0.015	0.10~0.50	≤0.04	≤0.04
DH32	≤0.18	0.90~1.60	≥0.015	0.10~0.50	≤0.04	≤0.04
EH32	≤0.18	0.90~1.60	≥0.015	0.10~0.50	≤0.04	≤0.04
AH36	≤0.18	0.7~1.60	≥0.015	0.10~0.50	≤0.04	≤0.04
DH36	≤0.18	0.90~1.60	≥0.015	0.10~0.50	≤0.04	≤0.04
EH36	≤0.18	0.90~1.60	≥0.015	0.10~0.50	≤0.04	≤0.04

5. Mechanical properties

Mechanical Properties
Steel Grade	Thickness/mm	Yield point/ MPa	Tensile strength/ MPa	Elongation/ %	V-type impact test
					Temperature/  ℃	Average impact absorption workAkv/J
						Vertical	Horizontal
A	≤50	≥235	400~490	≥22	-	-	-
B	≤50	≥235	400~490	≥22	0	≥27	≥20
D	≤50	≥235	400~490	≥22	-10	≥27	≥20
E	≤50	≥235	400~490	≥22	-40	≥27	≥20
AH32	≤50	≥315	440~590	≥22	0	≥31	≥22
DH32	≤50	≥315	440~590	≥22	-20	≥31	≥22
EH32	≤50	≥315	440~590	≥22	-40	≥31	≥22
AH36	≤50	≥355	490~620	≥22	0	≥34	≥24
DH36	≤50	≥355	490~620	≥22	-20	≥34	≥24
EH36	≤50	≥355	490~620	≥22	-40	≥34	≥24

6. Supplement and Explanation

The meanings of the letters in the grades: The letters A/B/D/E/F represent the minimum test temperature, which determines the applicable environment for toughness. The numbers (32/36/40) represent the yield strength class (corresponding to approximately 32, 36, and 40Ksi respectively).
Delivery status process: Low-toughness steels (such as D/E/F, etc.) are usually treated with TMCP, controlled rolling or normalizing to ensure high toughness at low temperatures. F-grade materials (such as FH36) are typically quenched and tempered (QT) to meet the requirements of extreme low-temperature toughness.
The corresponding relationship of classification society certification: Generally, the same grade of steel can be recognized by multiple classification societies, but production, testing and certification must be carried out in accordance with the rules of each institution. For example, "CCS EH36" and "ABS EH36" have the same principle, but the certification process and report format are different.

Summary

Mainstream classification: Structural steel grades are divided into general strength (A/B/D/E) and high strength (AH/DH/EH/FH) based on strength and impact toughness.
The material selection basis for each grade: environmental temperature (especially in low-temperature icy sea areas), stress requirements of structural parts, thickness range, welding and processing methods, etc.
Standards and processes: Usually in accordance with the norms of classification societies such as CCS, ABS, DNV, and GL, the blanking needs to indicate the delivery status and performance requirements. Generally, processes such as TMCP or controlled rolling are used.

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