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.
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.
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.
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.
An independent agency confirms the authenticity of test results and material performance, eliminating concerns about internal testing errors or inconsistencies.
Using non-compliant steel can cause project delays, classification society rejections, and expensive re-fabrication.
International shipbuilding buyers benefit from a transparent, verifiable quality-control system that safeguards their projects.
Third-party inspection covers a broad range of tests, both destructive and non-destructive, ensuring compliance at every stage.
Inspectors check:
Steel grade (AH36, DH36, EH36, S355G10, etc.)
Heat number
Dimensional accuracy
Visual surface quality
Marking and traceability
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.
To verify tensile properties:
Yield strength
Tensile strength
Elongation
These determine the structural performance of the steel in shipbuilding applications.
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.
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.
Inspectors verify:
Flatness
Thickness tolerance
Edge quality
Rolling direction
For normalized or TMCP plates, inspectors may witness:
Heating cycle
Cooling process
Grain refinement controls
This ensures microstructural stability.
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.
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.
A standard shipbuilding steel MTC includes:
Heat number
Steel grade
Plate dimensions
Quantity
Standard (ASTM A131, EN 10025, etc.)
Full ladle analysis of key elements:
C, Mn, Si
P, S
Al, Nb, V, Ti
Other micro-alloys
Yield strength
Tensile strength
Elongation
Hardness (if required)
Charpy V-Notch values at specified temperatures.
As-rolled
Normalized
TMCP
Normalized-rolled
If UT or Z-direction tests are conducted, results are included.
The certificate is stamped by the relevant society:
ABS
LR
DNV
BV
CCS
This stamp confirms that steel meets marine-grade requirements.
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.
Shipyards can trust that the steel meets the exact toughness, strength, and weldability requirements for their project.
Certified steel speeds up technical review, inspection, and installation permissions.
Non-certified materials may be rejected during construction, causing delays and financial loss.
When steel properties are clearly documented, welders, engineers, and inspectors work faster and more accurately.
If future repairs or upgrades are needed, MTCs provide essential data on the original material.
Suppliers like sakysteel play a central role in the quality assurance pipeline:
Coordination with ABS, LR, DNV, BV and other societies
Providing 3.1 or 3.2 MTCs for every heat number
Supporting UT, impact tests, tensile tests, and chemical analysis
Maintaining full traceability from steelmaking to delivery
Offering pre-shipment inspection services for international buyers
This ensures that steel plates are ready for use in demanding marine and offshore environments.
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.
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.