AH36 vs DH36 vs EH36: How to select the right marine steel plate according to ABS standards?

1. Key difference: Impact test temperature

AH36, DH36 and EH36 all fall under the ABS specification for high-strength marine steels (all with a minimum yield strength of 355 MPa). The most fundamental difference between them lies in the minimum temperature for the Charpy V-notch impact test.

AH36: Impact test temperature is 0°C

DH36: Impact test temperature is -20°C

EH36: Impact test temperature is -40°C

This difference directly determines the operational regions for which each steel grade is suitable. For vessels operating year-round in tropical or temperate waters, AH36 fully meets the requirements; however, if the route involves the North Atlantic in winter or waters near the polar regions, DH36 or even EH36 must be selected. For icebreakers or polar transport vessels operating on Arctic routes, the EH36 grade within the ABS Grade Shipbuilding Steel Plate range is virtually mandatory.

2. Impact Energy Absorption Requirements

In addition to differences in test temperature, the ABS Code specifies subtle variations in the impact energy absorption requirements for these grades of ABS Grade Shipbuilding Steel Plate. The following are typical requirements (10×10 mm specimen, longitudinal):

AH36: Average ≥ 34 J at 0°C

DH36: Average ≥ 34 J at -20°C

EH36: Average ≥ 34 J at -40°C

It is worth noting that AH36 typically retains a certain level of impact toughness at lower temperatures (such as -20°C), but the ABS Code only certifies its performance at 0°C. If your ship design documentation requires the steel plate to provide guaranteed values at -20°C, you must select DH36 and cannot substitute it with AH36.

3. Differences in Chemical Composition and Carbon Equivalent

To achieve lower impact test temperatures, the chemical compositions of DH36 and EH36 have been optimised. This is primarily reflected in:

Manganese (Mn) content: EH36 typically contains a higher manganese content (up to 1.70%) to enhance low-temperature toughness.

Microalloying elements: The addition of niobium (Nb), vanadium (V) and titanium (Ti) is more finely controlled in EH36 to refine the grain structure.

Carbon equivalent (CEV): As the strength is maintained at 355 MPa whilst the impact temperature is reduced, the carbon equivalent of EH36 is often slightly higher than that of AH36, which places slightly higher demands on the welding process.

However, the carbon equivalent of all three ABS Grade Shipbuilding Steel Plates is controlled within a range suitable for conventional welding processes (typically CEV ≤ 0.38%), meaning shipyards do not need to make significant changes to their existing welding procedure specifications (WPS).

4. How to select based on ship type and route?

The following are specific recommendations for selection:

Note: In practice, many large vessels do not utilise a single grade of ABS Grade Shipbuilding Steel Plate throughout the entire ship. The hull is designed using a 'mixed design' approach based on the risk levels of different sections: for example, DH36 may be selected for the deck plating and main deck, whilst AH36 is used for the bottom plating and internal longitudinal frames. This graded material selection strategy balances safety and economy.

5. Special considerations regarding Z-direction properties (Z35)

When ABS Grade Shipbuilding Steel Plate is used in joints subjected to tensile stress in the thickness direction (such as connection areas for cast steel components or T-joints in thick plates), the ABS Code may require additional Z-direction properties. AH36, DH36 and EH36 are all available with Z15, Z25 or Z35 suffixes, indicating the required reduction of area in the thickness direction (short transverse direction). This is a key indicator for preventing laminar tearing and is particularly important in critical joints on offshore platforms and large container ships.

6. Risks of Incorrect Material Selection

Selecting an ABS Grade Shipbuilding Steel Plate grade that falls short of design requirements may lead to catastrophic consequences. Historically, several incidents of structural failure in vessels operating in cold waters have been partly attributed to the use of steel with insufficient impact temperature. Conversely, over-specifying EH36 in place of AH36 will significantly increase material costs (EH36 is typically 15–25% more expensive than AH36) and may introduce unnecessary welding difficulties. Therefore, accurately assessing the vessel’s operating temperature range and strictly selecting steel grades in accordance with ABS specifications are fundamental principles during the design and procurement phases.

Conclusion

AH36, DH36 and EH36 form the core range of ABS high-strength shipbuilding steels. The choice between them is not a matter of ‘which is better’, but rather ‘which is more suitable’. The impact test temperature is the primary indicator distinguishing them, whilst the operating environment, structural stress levels and shipbuilding costs collectively determine the final selection. Understanding the differences between these three ABS Grade Shipbuilding Steel Plates helps design teams optimise material costs whilst ensuring safety.