Third-Party Inspection and Mill Certificates for Shipbuilding Steel Plates

In the global shipbuilding and offshore engineering sectors, the demand for reliable, high-performance steel plates continues to rise as vessels grow larger, offshore structures operate in deeper waters, and maritime regulations become increasingly rigorous. To ensure that every steel plate used in these demanding environments meets strict performance requirements, third-party inspection and mill certificates (MTCs) have become indispensable elements of the marine material supply chain.

These quality assurance mechanisms provide verifiable proof that shipbuilding steel plates comply with international standards such as ASTM A131, EN 10025, and classification society rules from ABS, LR, DNV, BV, CCS, and others. Leading suppliers like sakysteel consistently integrate third-party inspection services and complete MTC documentation into their delivery process, enabling global shipyards to build vessels and offshore structures with absolute confidence.

This article explores the purpose, process, standards, and advantages of third-party inspection and mill certificates for shipbuilding steel plates. It also explains why these quality controls have become an essential component in modern maritime engineering.

Why Third-Party Inspection Matters in Shipbuilding Steel Procurement

Third-party inspection (TPI) refers to independent verification by accredited agencies or classification societies to ensure that steel plates meet technical, chemical, and mechanical requirements.

1. Ensures Compliance With Classification Societies

Most shipbuilding projects require certification from:

  • ABS American Bureau of Shipping

  • LR Lloyd’s Register

  • DNV Det Norske Veritas

  • BV Bureau Veritas

  • CCS China Classification Society

  • NK Nippon Kaiji Kyokai

  • RINA Registro Italiano Navale

  • KR Korean Register

TPI verifies that steel plates meet the rules set by these organizations.

2. Eliminates Quality Risks in Critical Marine Structures

Marine steel plates are used in:

  • Hull structures

  • Decks and superstructures

  • Bulkheads

  • Offshore platforms

  • Jack-up legs and foundations

  • Floating production units

These components face high stress, corrosion, and fatigue. Third-party inspection ensures that materials are safe, durable, and suitable for long-term service.

3. Provides Independent, Unbiased Verification

An independent agency confirms the authenticity of test results and material performance, eliminating concerns about internal testing errors or inconsistencies.

4. Prevents Costly Delays and Rework

Using non-compliant steel can cause project delays, classification society rejections, and expensive re-fabrication.

5. Enhances Confidence in Global Supply Chain Transactions

International shipbuilding buyers benefit from a transparent, verifiable quality-control system that safeguards their projects.

Types of Third-Party Inspections for Shipbuilding Steel Plates

Third-party inspection covers a broad range of tests, both destructive and non-destructive, ensuring compliance at every stage.

1. Material Verification

Inspectors check:

  • Steel grade (AH36, DH36, EH36, S355G10, etc.)

  • Heat number

  • Dimensional accuracy

  • Visual surface quality

  • Marking and traceability

2. Chemical Composition Testing

Samples are tested using spectrometers to confirm compliance with:

  • Carbon limits

  • Manganese content

  • Silicon

  • Sulfur and phosphorus

  • Alloying elements such as Nb, V, Ti

These ensure weldability, toughness, and corrosion resistance.

3. Mechanical Property Testing

To verify tensile properties:

  • Yield strength

  • Tensile strength

  • Elongation

These determine the structural performance of the steel in shipbuilding applications.

4. Impact Toughness Testing (Charpy V-Notch)

For marine-grade steels, toughness is essential:

  • AH36 tested at 0°C

  • DH36 tested at -20°C

  • EH36 tested at -40°C

TPI confirms that plates meet minimum absorbed energy requirements.

5. Ultrasonic Testing (UT)

UT ensures plates are free of internal defects such as:

  • Laminations

  • Voids

  • Inclusions

  • Cracks

Depending on project needs, inspectors evaluate levels A, B, or C.

6. Surface and Dimensional Inspection

Inspectors verify:

  • Flatness

  • Thickness tolerance

  • Edge quality

  • Rolling direction

7. Witnessing Heat Treatment or TMCP Processes

For normalized or TMCP plates, inspectors may witness:

  • Heating cycle

  • Cooling process

  • Grain refinement controls

This ensures microstructural stability.

What Is a Mill Test Certificate (MTC)

A Mill Test Certificate is an official document issued by the steel manufacturer. It provides complete verification of the steel plate’s chemical and mechanical properties and processing history.

MTC Types Under EN 10204

  • 2.2 Factory Test Report
    Basic information but not sufficient for shipbuilding.

  • 3.1 Mill Test Certificate
    Issued by the mill’s quality department and approved by inspectors.

  • 3.2 Certificate
    Verified by independent classification society surveyors.
    Required for critical offshore or military applications.

Shipbuilding steel plates typically require 3.1 or 3.2 certificates.

What Information Is Included in a Mill Test Certificate

A standard shipbuilding steel MTC includes:

1. Basic Identification Data

  • Heat number

  • Steel grade

  • Plate dimensions

  • Quantity

  • Standard (ASTM A131, EN 10025, etc.)

2. Chemical Composition

Full ladle analysis of key elements:

  • C, Mn, Si

  • P, S

  • Al, Nb, V, Ti

  • Other micro-alloys

3. Mechanical Properties

  • Yield strength

  • Tensile strength

  • Elongation

  • Hardness (if required)

4. Impact Test Results

Charpy V-Notch values at specified temperatures.

5. Heat Treatment Condition

  • As-rolled

  • Normalized

  • TMCP

  • Normalized-rolled

6. Non-Destructive Testing Results

If UT or Z-direction tests are conducted, results are included.

7. Classification Society Approval Stamp

The certificate is stamped by the relevant society:

  • ABS

  • LR

  • DNV

  • BV

  • CCS

This stamp confirms that steel meets marine-grade requirements.

The Relationship Between Third-Party Inspection and Mill Certificates

Third-party inspection and mill certificates work together to ensure steel plate authenticity and compliance:

  • The mill certifies the steel through an MTC.

  • The third-party agency verifies the mill’s data through independent testing.

  • Both documents are combined in the final quality package for shipyard submission.

Together, they form a complete traceability system recognized by the maritime industry.

How TPI and MTCs Support Shipyards and Marine Engineers

1. Guarantees Material Reliability

Shipyards can trust that the steel meets the exact toughness, strength, and weldability requirements for their project.

2. Facilitates Classification Society Approval

Certified steel speeds up technical review, inspection, and installation permissions.

3. Reduces Risk of Rejection

Non-certified materials may be rejected during construction, causing delays and financial loss.

4. Improves Fabrication Efficiency

When steel properties are clearly documented, welders, engineers, and inspectors work faster and more accurately.

5. Enables Long-Term Traceability

If future repairs or upgrades are needed, MTCs provide essential data on the original material.

The Role of Reliable Suppliers in TPI and Documentation

Suppliers like sakysteel play a central role in the quality assurance pipeline:

  1. Coordination with ABS, LR, DNV, BV and other societies

  2. Providing 3.1 or 3.2 MTCs for every heat number

  3. Supporting UT, impact tests, tensile tests, and chemical analysis

  4. Maintaining full traceability from steelmaking to delivery

  5. Offering pre-shipment inspection services for international buyers

This ensures that steel plates are ready for use in demanding marine and offshore environments.

Digitalization in TPI and MTC Management

Modern shipyards increasingly adopt digital quality systems:

  • QR-coded traceability

  • Digital certificate databases

  • Cloud-based inspection reports

  • Automated verification matching heat numbers with plates

These tools reduce human error and accelerate certification processes.

Conclusion

Third-party inspection and mill certificates are essential components of the shipbuilding supply chain. They ensure that marine-grade steel plates meet the strict standards required by classification societies and international regulations, providing shipyards with reliable, high-quality materials for hulls, decks, offshore platforms, and critical marine structures.

By combining independent verification with thorough documentation, TPI and MTCs enhance safety, reduce project risk, support compliance, and guarantee long-term traceability. As the marine industry continues to advance, the importance of rigorous inspection and certification practices will only increase. Through strong technical capability and consistent documentation support, suppliers like sakysteel help the global shipbuilding market maintain the highest standards of quality and reliability.

Post time: Nov-14-2025