What are the grades of DNV steel?

In shipbuilding and offshore engineering, selecting the right material is the key to ensuring safety, compliance, and cost-effectiveness. DNV (Det Norske Veritas), as one of the world's leading classification societies, sets the gold standard for steel used in marine applications. Whether you are building ocean-going vessels, offshore drilling platforms, or other marine structures, understanding the DNV steel grading system is the first and most critical step.

This article provides a comprehensive breakdown of DNV steel grades-from general strength to ultra-high strength-along with key performance parameters to help you make informed procurement decisions.

DNV steel designations follow a clear logic, primarily reflecting two properties: Strength and Toughness (impact resistance).

First, DNV steels are divided into two main categories based on Strength:

Mild Steel (General Strength): These are fundamental grades that offer adequate strength and good weldability, suitable for less critical structural parts.

High-Tensile Steel (HT Steel): Enhanced with alloying elements (such as niobium, vanadium, and titanium) and produced through controlled rolling and cooling processes, these steels achieve higher yield strength. This allows for greater load-bearing capacity without increasing weight-essential for lightweight design.

Second, based on Toughness (impact energy at specific temperatures), steels are classified into grades A, B, D, E, and F. This letter indicates the minimum Charpy V-notch impact energy at a specified test temperature, directly relating to a vessel's safety when navigating in cold or polar waters.

Below are the most common DNV steel grades and their core performance parameters.

1. General Strength Steels (Yield Strength ≥ 235 MPa)

These are the most widely used carbon steel plates. The main DNV general strength grades are A, B, D, and E, with key differences in impact test temperature and delivery condition.

2. High-Tensile Steels (Yield Strength ≥ 315 MPa)

High-tensile steel grades include numbers in their designation to indicate the minimum yield strength. For example, 32 means a minimum yield strength of 315 MPa, 36 means 355 MPa, and 40 means 390 MPa.

These grades are combined with toughness letters (A, D, E, F) to form designations such as:

NV A32 / NV D32 / NV E32 / NV F32

NV A36 / NV D36 / NV E36 / NV F36

NV A40 / NV D40 / NV E40 / NV F40

Among these, NV E36 is a highly sought-after combination of high strength and toughness. It offers a minimum yield strength of 355 MPa and an impact test temperature of -40°C, making it a popular choice for large vessel hull structures and critical offshore engineering joints.

3. Higher-Strength & Special Application Grades (≥ 420 MPa)

As vessels grow larger and more advanced, the demand for higher-strength materials increases. DNV specifications cover grades up to 960 MPa. These ultra-high-strength steels are typically used in weight-sensitive specialty vessels or deep-sea equipment.

Common higher-strength grades include:

NV A420 / NV D420 / NV E420 / NV F420: Minimum yield strength of 420 MPa.

NV A460 / NV D460 / NV E460 / NV F460: Minimum yield strength of 460 MPa.

Even Higher Strengths: Grades up to A500, A550, A620, A690, and even A960 are available for special design requirements.

4. Special-Purpose DNV Steels: Stainless Steels & Low-Temperature Steels

Beyond conventional carbon steels, DNV also certifies stainless steels and nickel-alloy steels for specialized environments.

Austenitic & Duplex Stainless Steels: Primarily used in piping, valves, ballast tanks, and other areas demanding high corrosion resistance. Common DNV-certified grades include NV 304L, NV 316L, and duplex grades such as UNS S31803 and UNS S32205.

Low-Temperature Nickel Steels: Used in LNG (Liquefied Natural Gas) storage tanks and equipment operating at temperatures as low as -100°C or even lower. DNV-certified grades include NV 5Ni (5% nickel steel) and NV 9Ni (9% nickel steel) .

Follow Design Specifications: Your engineering drawings or classification society rules will explicitly state the required steel grades.

Assess the Operating Environment: If the vessel will navigate high-latitude or polar waters, you must select Grade D, E, or even F steels with high impact toughness to avoid brittle fracture risks.

Consider Cost-Effectiveness: While high-tensile steels have a higher unit price, they can reduce the total weight and volume of steel required. A balanced combination of different strength grades can significantly optimize overall project costs.

Get DNV-Certified Steel for Your Next Project

 

Whether you need the most common NV A/B/D/E, the high-strength and high-toughness NV E36, or specialty stainless and low-temperature steels, we offer complete DNV-certified steel solutions.

We maintain extensive inventory and have strong partnerships with major mills, enabling us to supply a full range of DNV shipbuilding plates. We can also provide additional requirements such as through-thickness properties (Z15, Z25, Z35) . All materials come with official DNV mill test certificates, ensuring full traceability and quality assurance.

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FAQ

 

 

01.What is DNV-approved steel, and why is it so important for shipbuilding?

DNV-approved steel refers to steel products that have undergone rigorous testing and approval by Det Norske Veritas. It is not just a certificate; it signifies that the steel meets strict international maritime standards in chemical composition, mechanical properties, dimensional tolerances, and internal quality (such as ultrasonic testing). Using DNV-approved steel is a legal and safety prerequisite for vessels to obtain classification certificates and sail safely in global waters.

02.What do the letters (A, B, D, E) and numbers (32, 36, 40) in DNV steel grades stand for?

That is an excellent technical question. The letter indicates the steel's toughness grade, specifically referring to the test temperature for the Charpy V-notch impact test. For instance, Grade A is tested at +20°C, Grade D at -20°C, and Grade E at -40°C. Lower temperatures signify greater resistance to brittle fracture in cold environments. The numbers represent the minimum yield strength (in ksi or approximate MPa). For example, 32 means a minimum yield strength of 315 MPa, and 36 means 355 MPa. Combined, such as NV E36, this indicates a high-toughness steel that maintains a yield strength of 355 MPa even at -40°C.

03.What is the main difference between NV E36 and regular NV A36 steel plates, and how do I choose between them?

The primary difference lies in their low-temperature impact toughness. While both are high-tensile steels (yield strength ≥ 355 MPa), NV A36 is impact-tested at +20°C, whereas NV E36 must pass the impact test at a much lower temperature of -40°C. This means NV E36 offers a higher safety margin in cold waters or severe sea conditions. If your project involves Arctic routes, winter trans-oceanic voyages, or critical load-bearing structures, NV E36 is the preferred choice. If the vessel operates only in tropical or temperate waters with no special design requirements, NV A36 is a more cost-effective option.

04.Besides the grade, what other key parameters should I pay attention to when purchasing DNV-approved steel plates?

Apart from the grade (e.g., NV E36), you must pay close attention to the following core parameters to ensure correct procurement:

Dimensional Tolerances: Confirm that the allowable deviations in thickness, width, and length meet your cutting or fabrication requirements.

Through-Thickness Properties (Z-properties): If the plate will endure tensile stress in the thickness direction (e.g., at nodal joints), you should specify Z15, Z25, or Z35 grades to prevent lamellar tearing.

Delivery Condition: Clarify whether it is As-Rolled (AR), Controlled-Rolled (CR), Normalized (N), or Quenched & Tempered (QT), as this directly affects the final microstructure and weldability.

Certification & Traceability: Always request the official DNV Mill Test Certificate to ensure that the heat number and batch number correspond with the actual material, providing full traceability throughout the supply chain.

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