Marine structures – such as offshore cranes – and cargo ships must be able to endure extreme conditions without fracturing or corroding. Materials used to build these structures – including steel plate – are highly regulated and standardized to ensure the structures can withstand maritime conditions. Steel plate materials used in these capacities are known as marine and offshore steel plate.

This article will look in-depth at the properties and applications of primary offshore and marine steel plate grades. Steel plate suppliers that service the marine industry, such as Leeco® Steel, typically stock these specialized grades in large quantities, especially in coastal regions such as Houston and Florida, where these structures are often assembled.

What is Offshore & Marine Steel Plate?

Offshore and marine steel plate is specifically certified for use in maritime projects by regulatory organizations, including the American Bureau of Shipbuilding (ABS), which regulates materials used in building structural parts of ships, and the American Petroleum Institute (API), which regulates materials used in the construction of offshore oil rigs or cranes.

Specifications established by these organizations ensure offshore and marine steel plate has the necessary mechanical and chemical properties to resist corrosion, decrease brittleness – especially in colder climates – and increase strength and toughness. These properties play a key role in allowing plate to withstand the vibration and force trauma present in marine conditions.

Before taking a deeper look at the properties and applications of specific offshore and marine plate grades, it is important to understand the key mechanical properties present in these grades:

Strength: The load a material can bear, measured by yield point and tensile strength. Yield point is the maximum point of stress at which a material will permanently change shape, and tensile strength is the point at which a bent material will break.

Toughness: The ability of a material to absorb impact without breaking.

Hardness: The wear-resistance ability of a material, usually measured by a Brinell test.

Machinability: How easily a material can be welded, bolted, drilled or machined.

Each of these mechanical properties are crucial in ensuring primary offshore and marine steel plate grades are equipped for use in maritime applications.

Properties & Applications of Offshore & Marine Steel Plate Grades

There are two primary organizations for offshore and marine plate: ABS and API. Each organization has its own specifications and various grades that are used in maritime applications.

ABS Steel Plate

ABS steel plate is certified for use in shipbuilding capabilities by the American Bureau of Shipbuilding and is comprised of several high strength grades.

ABS grades are divided into two categories based on their yield points and tensile strength: ordinary strength and higher strength, both of which are readily stocked by Leeco. Ordinary strength ABS plate includes four grades: grades A, B, D and E. While there are 12 grades of higher strength ABS plate, grades AH36, DH36, EH36 and FH36 are most common.

In comparison to higher strength ABS grades, ordinary strength ABS grades have a relatively lower yield point and tensile strength, shown in the chart below.

ABS Grade

Yield Point

Tensile

A

34 ksi

58-75 ksi

B

34 ksi

58-75 ksi

D

34 ksi

58-75 ksi

E

34 ksi

58-75 ksi

AH36

51 ksi

71-90 ksi

DH36

51 ksi

71-90 ksi

EH36

51 ksi

71-90 ksi

FH36

51 ksi

71-90 ksi

 

With their great strength and toughness, both ordinary and higher strength ABS grades are ideal for use in the building of structural parts of ships, barges and other marine equipment. These properties allow plate to absorb the stress and energy of powerful waves without breaking, which is crucial in ensuring key structural parts of ships stay intact.

While shipbuilding applications primarily use ABS steel plate, other grades – such as ASTM A131 – may also meet the regulatory standards required for shipbuilding use. These grades are typically ordered with ASTM specifications that are certified by ABS, meaning the plate is produced by an ABS approved mill and has mill test reports stamped by ABS. This process ensures that non-ABS grades meet all the necessary regulatory standards for use in constructing marine vessels.

API 2H Steel Plate

API 2H steel plate is certified by API for use in the construction of marine structures and offers intermediate strength similar to other structural steel grades.

API 2H steel plate has two grades: 42 and 50, which are both stocked by Leeco. These grades have high impact toughness and resistance-to-fatigue-loading due to their chemical and mechanical properties.

Chemicals that increase strength, toughness and machinability – including manganese, phosphorus and silicon – are present in API 2H grades to ensure the plate is strong enough to endure harsh marine conditions.

API 2H

Grade 42

Grade 50

Carbon

0.18%

0.18%

Manganese

0.90-1.35%

1.15-1.60%

Phosphorus Max

0.030%

0.030%

Sulfur Max

0.010%

0.010%

Silicon

0.05-0.40%

0.05-0.40%

Colombium

0.04% Max

0.01-0.04%

Titanium

0.020% Max

0.020% Max

Aluminum Total

0.02-0.06%

0.02-0.06%

Nitrogen Max

0.012%

0.012%

 

Chemical alloys give API 2H grades 42 and 50 relatively strong mechanical properties, detailed in the chart below, along with a balance of toughness and machinability. With these properties, API 2H grades are ideal for use in applications that require welding – such as marine wind turbines or offshore cranes – without sacrificing the strength and hardness necessary for marine conditions.

API 2H

Yield Point

Tensile

Grade 42

62-82 ksi

18 ksi

Grade 50 ≤2.5” thick

70-90 ksi

16 ksi

Grade 50 > 2.5” thick

70-90 ksi

16 ksi

 

 Because marine applications require greater strength and toughness, API 2H grades receive a heat treatment, known as normalizing, to enhance these properties.

The normalizing process involves heating plate within a furnace to an extremely high temperature, holding the plate at that temperature for a sufficient time – typically an hour per inch of thickness – and then allowing plate to air cool. This process changes the grain structure of plate to increase strength and toughness.

Related: Learn more about heat treatment processes.

API 2H grades may also require a Charpy impact test if used to construct offshore structures in particularly harsh climates. Charpy impact tests use a pendulum hammer to measure steel’s ability to absorb energy at a variety of temperatures without becoming brittle. This test is important for ensuring API 2H plate can face frigid winters or extreme temperature changes without fracturing or becoming brittle, as this could damage or destroy offshore structures.

Sourcing Offshore & Marine Steel Plate

When considering a steel plate supplier for offshore and marine steel plate, it is important to look for a supplier with a large product inventory, quality control processes and locations in close proximity to your delivery destination to reduce freight costs.

With 11 strategically-located distribution centers throughout North America, Leeco Steel stocks ABS and API 2H steel plate in large quantities and can get you the plate you need, when you need it. Leeco is also ISO 9001 certified in quality management to ensure customers receive the highest quality steel plate products. Contact us or request a quote today to discuss your offshore and marine steel plate needs.