DH36 and EH36 Steel Plates for Offshore Platforms and Subsea Equipment

In the offshore and subsea engineering sectors, structural materials must perform flawlessly under extreme conditions — from high mechanical stress to low temperatures and aggressive saltwater environments. Among the most reliable materials for these demanding applications are DH36 and EH36 steel plates, high-strength marine steels designed to withstand dynamic loads, impacts, and harsh marine corrosion. These steels are indispensable in the construction of offshore platforms, oil rigs, wind turbine foundations, and subsea equipment where safety, durability, and performance are non-negotiable.

At sakysteel, we provide certified DH36 and EH36 steel plates that meet international classification standards (ABS, LR, DNV, BV, and others) to support the structural integrity of marine and offshore engineering projects worldwide.

1. Introduction to DH36 and EH36 Steel Grades

DH36 and EH36 are part of the ASTM A131 family of high-strength marine structural steels. While both grades offer similar strength and mechanical characteristics, their difference lies in impact toughness — the temperature at which the steel can absorb energy without fracturing.

• DH36: Impact tested at -20°C, suitable for moderately cold marine environments.

• EH36: Impact tested at -40°C, designed for extreme low-temperature conditions such as Arctic and deep-sea operations.

These grades exhibit high tensile and yield strengths, exceptional toughness, and excellent weldability, making them perfect for both surface and subsea structures.

2. Chemical Composition and Mechanical Properties

The composition of DH36 and EH36 steel plates is carefully balanced to achieve strength and toughness without compromising weldability.

Typical Chemical Composition:

• Carbon (C): ≤ 0.18%

• Manganese (Mn): 0.90–1.60%

• Silicon (Si): 0.10–0.50%

• Phosphorus (P): ≤ 0.035%

• Sulfur (S): ≤ 0.035%

• Microalloying elements: Nb, Ti, V (for grain refinement and toughness)

Mechanical Properties:

• Yield Strength: ≥ 355 MPa

• Tensile Strength: 490–620 MPa

• Elongation: ≥ 21%

• Impact Toughness:

  • DH36: ≥ 34 J at -20°C

  • EH36: ≥ 34 J at -40°C

This combination ensures superior resistance to cracking and deformation, even under fluctuating stresses and low-temperature exposure.

3. Importance of High-Strength Steel in Offshore Platforms

Offshore oil and gas platforms face some of the harshest environmental and operational challenges. They must withstand powerful waves, wind loads, and the corrosive effects of seawater, all while supporting heavy equipment and pipelines.

DH36 and EH36 steel plates are widely used because they provide:

• High load-bearing capacity for deck and leg structures.

• Excellent resistance to fatigue in cyclic loading conditions.

• Superior impact strength to prevent brittle failure.

• Consistent performance in low temperatures found in deep waters and cold regions.

These characteristics make them the foundation materials for jack-up rigs, semi-submersible platforms, and fixed offshore installations.

4. Application in Offshore Structures

a. Topsides and Deck Structures

DH36 and EH36 plates are used for decks and support beams that carry heavy machinery, drilling equipment, and living quarters. Their high strength-to-weight ratio enhances structural stability without increasing platform weight.

b. Jacket and Leg Components

In fixed offshore platforms, the legs and jacket frames must resist both compressive and bending forces from waves and wind. The toughness of EH36 ensures reliable performance even when exposed to sub-zero water temperatures and constant vibration.

c. Floating Production Systems (FPSO, Semi-Submersible Rigs)

Floating structures face continuous motion and fatigue stress. EH36’s high impact resistance provides long-term safety for hulls, pontoons, and column structures.

5. Subsea Equipment Applications

a. Subsea Manifolds and Structures

Subsea manifolds distribute oil and gas flow at great depths. EH36’s excellent low-temperature impact strength ensures these structures remain safe under hydrostatic pressure and cold seawater conditions.

b. Pressure Vessels and Subsea Pipelines

DH36 and EH36 are used to build subsea pressure vessels, risers, and pipe supports, ensuring mechanical integrity under fluctuating internal pressures and thermal stresses.

c. Umbilical Frames and Anchoring Systems

The toughness and weldability of EH36 make it ideal for subsea anchoring systems and umbilical support frames that must operate reliably in deep-sea environments.

6. Fabrication and Welding Performance

DH36 and EH36 steel plates are favored for their excellent weldability. They can be fabricated using common techniques such as:

• Shielded Metal Arc Welding (SMAW)

• Submerged Arc Welding (SAW)

• Gas Metal Arc Welding (GMAW)

• Flux-Cored Arc Welding (FCAW)

Their low carbon equivalent (CEV) ensures minimal preheat requirements and reduces the risk of hydrogen-induced cracking. This makes them suitable for large-scale welded structures found in offshore and subsea engineering.

At sakysteel, all plates undergo ultrasonic testing (UT), Charpy impact testing, and dimensional verification to guarantee flawless weldability and mechanical uniformity.

7. Corrosion Resistance and Protective Coatings

Offshore and subsea structures are constantly exposed to saltwater corrosion, high humidity, and microbial activity. To enhance corrosion resistance, DH36 and EH36 steel plates are often:

• Shot-blasted and shop primed before delivery.

• Coated with marine epoxy or zinc-rich primers.

• Protected using cathodic systems to prevent galvanic corrosion.

These treatments ensure long service life and reduce maintenance costs over time.

8. Performance in Low-Temperature Environments

One of the most notable features of DH36 and EH36 steel plates is their exceptional low-temperature toughness. EH36, in particular, maintains ductility and impact resistance at temperatures as low as -40°C, making it ideal for Arctic operations, ice-breaking vessels, and deepwater subsea structures.

This capability prevents brittle fractures — a major concern in cold environments — ensuring operational safety and structural longevity.

9. Classification Society Certifications

DH36 and EH36 steel plates supplied by sakysteel meet or exceed the requirements of major classification societies, including:

• ABS (American Bureau of Shipping)

• DNV (Det Norske Veritas)

• Lloyd’s Register (LR)

• Bureau Veritas (BV)

• RINA, NK, and GL

Such certifications confirm compliance with international marine and offshore construction standards, ensuring that each plate can be confidently used in critical load-bearing applications.

10. Advantages of DH36 and EH36 for Offshore and Subsea Projects