Your client, a European shipyard, specifically requests DNV-certified angle steel. You source a great price from a mill, but they only have ABS approval. This mismatch can cancel the entire order. I’ve helped exporters navigate this exact challenge to avoid costly mistakes.

To export marine angle steel with ABS, BV, or DNV approval, you must source from mills specifically approved by that classification society, ensure the Mill Test Certificate (MTC) explicitly states the approval and grade (e.g., DNV Grade A), and often arrange for a surveyor from the society or an approved third party to witness testing or shipment. Using a mill approved for one society does not automatically qualify it for another.

For exporters and serious suppliers like us, understanding these distinctions is business-critical. Each society has its own rules and accepted mills. This guide will clarify the differences, explain the approval process, and help you ensure a smooth, compliant export. Let’s start by comparing two of the largest societies.

What is the difference between ABS and DNV?

A shipowner in Norway will likely require DNV. A shipyard in the USA will likely require ABS. While their core mission is identical, their historical roots, geographic strongholds, and some technical rules differ. A fabricator in the Philippines once ordered "classified steel" but didn’t specify the society, causing confusion with their supplier.

ABS (American Bureau of Shipping)¹ is a U.S.-based classification society² with a strong presence in the Americas and Asia, while DNV (Det Norske Veritas)³ is Norwegian with a dominant position in Europe, especially in the offshore and maritime sectors. Both set safety rules for ships and approve materials, but they are separate legal entities with their own approval lists and certificate formats. The key difference for an exporter is ensuring the steel mill is on the specific society’s approved list⁴.

A Detailed Comparison for Exporters and Buyers

Choosing between ABS and DNV is usually not the exporter’s decision; it is dictated by the end client or the ship’s flag. However, understanding their profiles helps in market positioning and client communication.

1. Historical and Geographic Focus:

• ABS: Founded in 1862 in the United States. It has deep roots in the traditional shipbuilding markets of North America, parts of Asia (like Korea, China), and certain international fleets. Its rules are widely used for tankers, bulk carriers, and container ships globally.
• DNV: Founded in 1864 in Norway. It has a very strong reputation in Europe, particularly in Scandinavia, and is a world leader in the classification of offshore oil & gas structures, complex vessels, and container ships. Its merger with Germanischer Lloyd (GL) in 2013 strengthened its position further, now operating as DNV.

2. Technical Rules and Standards:
Both societies publish exhaustive rules for materials, welding, and ship construction. The technical requirements for equivalent steel grades (e.g., ABS Grade AH36 vs. DNV NV A36) are very similar but not identical. There are subtle differences in:

• Chemical Composition Limits: Allowable ranges for elements like Carbon, Manganese, Sulfur, and Phosphorus might vary slightly.
• Testing Requirements: The frequency of testing, sample location, and specific test procedures may differ.
• Certificate Format: The layout and required statements on the MTC will be specific to each society.

3. The Critical Practical Difference for Exporters:
A mill approved by ABS is not automatically approved by DNV, and vice versa. A mill must undergo a separate audit and approval process for each society it wishes to supply. Many large, reputable mills in China and elsewhere hold multiple approvals (ABS, BV, DNV, LR, etc.). This is what you must check.

How This Affects Your Export Process:

For us as a supplier, our partner mills in Shandong hold multiple approvals. This allows us to flexibly meet the requirements of clients in Saudi Arabia (who may use ABS or BV) and clients in Romania (who may use DNV or LR). The next step is understanding what "DNV classification" means in a broader sense.

What is DNV classification¹?

When a ship is "DNV-classed," it means much more than just using DNV-approved steel. It is a comprehensive safety and environmental certification system for the entire vessel. As a steel supplier, you are a critical link in this system. A shipyard in Thailand building a DNV-classed vessel will audit their steel suppliers’ certifications carefully.

DNV classification¹ is a system where DNV, as an independent third party, sets technical standards (Rules) for the design, construction, and survey of ships and offshore structures. A vessel that is built and maintained in accordance with these Rules receives a DNV class certificate², which is a passport for insurance, operation, and port state control. It provides assurance that the vessel meets recognized safety and reliability standards.

The Role of Classification in the Maritime Ecosystem

Classification societies³ like DNV are foundational to modern maritime safety and commerce. They are not government bodies but independent organizations trusted by insurers, financiers, and port states.

The Three Pillars of DNV Classification:

1. Establishing Rules: DNV publishes detailed rules covering every aspect of a ship:

   • Hull Structure: Materials (steel grades), structural design, welding.
   • Machinery: Engines, propulsion systems, electrical systems.
   • Systems: Safety, fire protection, stability.
     These rules are based on extensive research, experience, and international conventions (like IMO SOLAS).

2. Plan Approval and Supervision⁴: Before construction, the shipyard submits detailed design plans to DNV. DNV engineers review and approve these plans to ensure they comply with the Rules. During construction, DNV surveyors visit the shipyard to witness key stages, including material tests and the installation of critical components.

3. Surveys and Maintenance of Class: After delivery, the ship must undergo regular and special surveys throughout its life to ensure it remains in compliance with the Rules. This maintains its "class" status.

Where Marine Steel⁵ Fits Into This Process:
The steel is the literal building block. The process is:

• The ship design specifies, for example, "DNV NV A36 steel" for hull frames.
• The steel mill, approved by DNV, produces the angle steel and issues a DNV MTC.
• The DNV surveyor (or an authorized representative) may review the MTCs and may witness mechanical tests at the mill or at the shipyard.
• The surveyor verifies that the steel delivered matches the MTCs and is properly marked.
• This verified steel is then used in the construction of the DNV-classed vessel.

Implications for Steel Exporters:

1. Accountability: The MTC you provide is a legal document that becomes part of the ship’s permanent record. If a problem arises years later, the steel can be traced back to the heat number on your MTC.
2. Surveyor Involvement: For some projects (especially offshore or high-value), a DNV surveyor may need to visit the loading port in China to verify the material before shipment. You must coordinate this.
3. Chain of Custody⁶: You must maintain a clear chain from the mill’s MTC to your shipping documents to prove the certified steel is what was shipped.

Understanding this big picture explains why clients are so stringent about certification. It’s not a preference; it’s a mandatory requirement of the classification process that allows the ship to operate. This leads to a key component: DNV approval for materials.

What is DNV approval¹?

For a mill, getting "DNV approval¹" is a significant achievement that opens doors to major international projects. For you as an exporter, buying from a DNV-approved mill is the only way to legitimately supply DNV-grade steel². A trading company once tried to sell us "DNV steel" from an unapproved mill; we declined because we knew it would fail our clients’ audits.

DNV approval¹ for steel mills is a formal qualification process where DNV assesses and certifies that a mill’s quality management system and production processes consistently produce steel that meets DNV’s material rules. An approved mill is listed in DNV’s database and is authorized to issue DNV-compliant Mill Test Certificates (MTCs)³. Without this mill-level approval, the steel cannot be used in DNV-classed vessels, regardless of its quality.

The Journey to Becoming a DNV-Approved Supplier

The approval is not for a single batch of steel. It is for the mill’s capability to produce steel over time.

The Approval Process Steps:

1. Application & Audit: The mill applies to DNV. DNV surveyors conduct a detailed audit of the mill’s:
   • Quality Management System⁴: ISO 9001 certification is often a baseline.
   • Production Facilities: From melting (EAF or BOF) and casting to rolling and heat treatment.
   • Testing Laboratories: Calibration of equipment, competence of personnel.
   • Traceability Systems: How they track a heat of steel from raw materials to final product.
2. Witnessed Testing: DNV typically witnesses the production and testing of one or more trial heats of steel. They verify the entire process and confirm the test results meet the rules.
3. Approval Granting: If successful, DNV grants the mill an approval certificate for specific steel grades and product forms (e.g., plates, sections, bars). The mill is added to the official list.
4. Surveillance Audits⁵: DNV conducts periodic audits (e.g., annually) to ensure the mill maintains its standards.

Types of DNV Approval Documents:

• Works Certificate: The mill’s own MTC, issued under its DNV approval¹. This is the standard document for most shipments.
• Certificate of Conformity⁶: Sometimes required, this is a certificate issued directly by DNV (for a fee) confirming a specific batch conforms. This is less common for standard materials.

What This Means for Your Export Checklist:
When preparing to export DNV steel, you must:

1. Verify Mill Approval: Check the mill’s current DNV approval¹ certificate or the online DNV database. Do not rely on a verbal claim.
2. Review the MTC: Ensure the MTC header mentions DNV, references the correct DNV rule (e.g., DNVGL-CP-0178), and has the required compliance statement.
3. Check the Grade Designation: It must use DNV’s naming system (e.g., NV A, NV D, NV A36, NV D36). Do not accept "equivalent to" statements unless explicitly agreed by the client.

Key Elements of a Valid DNV MTC:

For an exporter, your reliability hinges on your mill partners’ approvals. We only work with mills that have the necessary certifications, which allows us to offer the "SGS inspection support" and guarantee the "stable quality" our clients need. Now, let’s look at the specific grade designations under the DNV system.

What are the grades of DNV steel?

You receive a request for "DNV A36" steel. But is that the same as "NV A36"? Knowing the exact grade nomenclature is essential to avoid supplying the wrong material. A project for an offshore wind farm in Europe required "NV D36¹" angles, and we had to confirm the mill’s MTC² used precisely that designation.

DNV steel grades³ are designated with the prefix "NV" followed by a letter (A, B, D, E, F) for toughness and sometimes a number (32, 36, 40) for strength. Common grades include NV A, NV B, NV D, NV E (ordinary strength) and NV A32, NV A36, NV D32, NV D36¹, NV E36, NV F40 (high strength). For example, NV D36¹ indicates high-strength steel⁴ (355 MPa yield) with Grade D toughness tested at -20°C.

Decoding the DNV Grade Designation System

The DNV system is logical and similar to other societies but uses its own labels. Understanding it ensures you match the client’s specification exactly.

1. Ordinary Strength Grades (No number suffix):
These grades are defined by toughness level.

• NV A: Standard grade for general use. Impact testing temperature is typically 0°C or +20°C.
• NV B: Similar to NV A, with slightly different testing requirements historically. Less common in new designs.
• NV D: Improved toughness grade. Requires impact testing⁵ at -20°C. Used for structures in colder environments.
• NV E: Higher toughness grade. Requires impact testing⁵ at -40°C. For Arctic service.
• NV F: Special grade for extreme low temperatures.

2. High Strength Grades (With number suffix: 32, 36, 40):
The number indicates the minimum yield strength in kgf/mm².

• 32 = 315 MPa
• 36 = 355 MPa
• 40 = 390 MPa
  The letter prefix still indicates the toughness level.
• NV A36: High-strength (355 MPa) with standard Grade A toughness.
• NV D36¹: High-strength (355 MPa) with improved Grade D toughness (tested at -20°C). This is a very common and demanding grade for ships and offshore structures.
• NV E36/F40: Used for the most critical applications like icebreakers and Arctic offshore platforms.

Comparison with Equivalent ABS Grades:
While similar, they are not interchangeable on paperwork. A direct cross-reference is often used for understanding.

Selection and Procurement Table for Exporters:

When we prepare a shipment of DNV angles for a client in Romania or Norway, the grade on the packing list, commercial invoice, and most importantly, the MTC², must be perfectly aligned. This precision in documentation is what facilitates smooth customs clearance and final client acceptance, completing a successful export of certified marine steel.

Conclusion

Successfully exporting marine angle steel with ABS, BV, or DNV approval requires precise alignment: sourcing from society-approved mills, using correct grade nomenclature, and providing flawless certification (MTC). This ensures compliance, builds trust, and satisfies the rigorous demands of global shipbuilding and offshore projects.