In modern marine engineering, the safety and structural reliability of vessels depend heavily on the quality of shipbuilding steel plates. Grades such as AH36, DH36, EH36, and other high strength structural steels are commonly used to construct hulls, decks, offshore platforms, and subsea modules. To ensure these steel plates meet the stringent demands of the marine environment, international standards define strict requirements for surface finish, flatness, and ultrasonic testing. Leading manufacturers, including sakysteel, consistently follow and exceed these standards to supply shipyards worldwide with dependable and high performance materials.
This article provides a comprehensive overview of these critical standards and explains how they influence the performance and safety of shipbuilding steel plates.
Shipbuilding plates are exposed to harsh conditions such as high dynamic loads, saltwater corrosion, vibration, and extreme temperatures. Any defect in the plate surface, flatness, or internal soundness may weaken the structure and cause significant risks for both vessels and offshore structures.
Three primary quality indicators are used globally to ensure plate reliability:
Surface finish
Plate flatness
Ultrasonic testing UT results
These factors directly affect weldability, structural integrity, and long term performance in marine applications.
Surface finish refers to the physical condition of the steel plate surface after rolling and finishing operations. A proper surface condition is essential to avoid weld defects, prevent crack initiation, and ensure efficient forming and fabrication at shipyards.
According to classification society standards, the surface must be:
Free from cracks
Free from deep pits or dents
Without sharp edges or harmful protrusions
Free of rust scale that impairs inspection
Smooth enough to allow accurate UT inspection
Minor imperfections are acceptable as long as they do not affect the plate’s functionality. Manufacturers like sakysteel use automated descaling, grinding, and conditioning machines to ensure optimal surface quality for each plate.
Rolling marks from hot rolling
Scale caused by oxidation
Surface inclusions
Handling marks during transportation
Indentations from mechanical contact
These defects are inspected visually and may undergo light grinding to meet shipbuilding standards.
Flatness is a crucial property that influences plate forming, welding, structural alignment, and hull integrity. Poor flatness can cause misalignment during construction and increase the risk of weld defects or stress concentration.
Flatness requirements are typically defined by:
EN 10029
ASTM A6
Classification society specifications
Common tolerances include:
Standard flatness
Special flatness for demanding applications
Extra strict flatness based on customer requirements
Flatness tolerances depend on thickness, width, and plate grade. For large marine plates, strict control is necessary to prevent deformation during ship assembly.
Residual stresses from rolling
Uneven cooling during production
Heat treatment distortions
Mechanical handling
Thermal deformation in storage
Manufacturers use controlled rolling, accelerated cooling, and advanced leveling equipment to ensure plates meet flatness standards.
Ultrasonic Testing UT is the most reliable method to detect internal flaws in shipbuilding plates. Internal soundness is critical because defects such as laminations or inclusions can weaken the structure and reduce fatigue resistance.
Shipbuilding plates must undergo UT according to international standards, such as:
EN 10160
ASTM A578 or A435
EN ISO 11666
ABS, DNV, LR, BV, CCS requirements
Different classes specify the level of inspection:
S0 Basic level
S1 Intermediate level
S2 Strict level
S3 Extra stringent level
For high strength plates such as DH36 and EH36 used in offshore platforms, S2 or S3 levels are often required.
UT can identify internal defects such as:
Laminations
Inclusions
Cracks
Blowholes
Disbonds
Rolling imperfections
The results must meet classification society acceptance criteria to ensure that no harmful defects remain inside the plate.
Modern steel producers use automated UT lines that scan the entire plate surface using high frequency sound waves. These systems provide:
Precise defect location
Consistent signal interpretation
Full plate coverage
Automatic recording for documentation
Such advanced inspection systems are commonly integrated into production lines at facilities managed by manufacturers like sakysteel.
These three elements work together to guarantee the reliability of shipbuilding steel plates.
Improved weld quality
Reduced risk of structural cracks
Higher fatigue resistance
Better dimensional stability during ship assembly
Longer service life in marine environments
Compliance with international safety standards
A plate that meets surface finish, flatness, and UT standards offers superior performance and safety in demanding ocean conditions.
To meet these stringent requirements, steel mills conduct multiple quality checks at different stages of production.
Visual inspection of surface condition
Plate straightness and flatness measurement
Automated UT scanning
Hardness and mechanical property testing
Dimensional accuracy verification
Documentation and traceability management
These procedures ensure that each plate meets mechanical performance, geometric precision, and structural reliability requirements.
Major marine classification societies enforce strict criteria for shipbuilding plate quality:
American Bureau of Shipping ABS
Lloyds Register LR
DNV
Bureau Veritas BV
China Classification Society CCS
Their rules specify acceptable surface conditions, maximum flatness deviation, and UT inspection levels for AH36 DH36 EH36 and similar grades.
Compliance with these standards is necessary for plates to be approved for shipbuilding use.
Steel plates that meet strict surface and NDT requirements are used in:
Hull structure plates
Deck panels
Bulkheads and stiffeners
Offshore platform modules
Subsea equipment
High strength structural members
Flatness and surface quality are especially important for curved and welded sections of a ship, while UT ensures internal reliability.
Surface finish, flatness, and ultrasonic testing standards are essential components of shipbuilding steel plate quality assurance. These standards ensure that AH36 DH36 EH36 and other marine grade plates maintain high performance under demanding conditions. By following global specifications and implementing advanced production technology, manufacturers provide shipyards with reliable materials that enhance structural safety and longevity. With extensive experience in supplying high quality shipbuilding steel, sakysteel continues to support marine and offshore industries worldwide with dependable and fully certified steel plate solutions.