Surface Finish Flatness and Ultrasonic Testing Standards for Shipbuilding Plates

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.

Importance of Quality Standards in 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 Requirements for Shipbuilding Plates

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.

Acceptable Surface Condition

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.

Common Surface Defects and Their Causes

• 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.

Plate Flatness Standards for Marine Grade Steel

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.

International Flatness Criteria

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.

Factors Affecting Plate Flatness

• 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 Standards for Internal Plate Soundness

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.

UT Standards for Shipbuilding Steel

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.

What UT Detects

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.

UT Equipment and Test Procedures

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.

Combined Importance of Surface Finish Flatness and UT Results

These three elements work together to guarantee the reliability of shipbuilding steel plates.

Benefits Include

• 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.

Inspection and Quality Control During Production

To meet these stringent requirements, steel mills conduct multiple quality checks at different stages of production.

Key Quality Control Steps

• 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.

Standards from Classification Societies

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.

Applications of Plates Meeting These Standards

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.

Conclusion

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.