NDT and Class Requirements in the Marine Industry
Whether a ship can keep sailing depends on approval from its classification society, and that approval rests on measured thickness data. Seawater, humid ballast tanks, cargo-induced fatigue and cavitation keep a hull in a constant state of degradation. Periodic surveys show how fast that degradation is progressing, and decisions on steel renewal are made from this data.
Shipyards run two different kinds of work side by side. New construction requires verifying weld quality against class rules, while repair and maintenance require measuring the remaining section of the existing structure. Dry-dock time is expensive, so inspection speed and preparation time are decisive on both sides.
Hull Thickness Gauging
Hull plate thickness gauging is at the heart of every class survey. Readings taken at thousands of points show the percentage loss against original thickness, which is then compared with the limits in the relevant class rules. Probe technologies that measure through coatings reduce the need to grind off paint, shortening survey time and preserving coating integrity. Decks, holds, bulkheads and ballast tanks are where readings concentrate.
New-Build and Repair Weld Inspection
New-build and repair welds require detection and sizing of volumetric flaws. Because ultrasonic array methods need no radiation exclusion zone, they offer a real operational advantage in a shipyard where many crews work at the same time. In high-stress connections, the rudder stock area, shaft bearings and deck fittings, the priority is detecting surface-breaking cracks. Electromagnetic methods that work through paint shorten preparation time and contribute directly to dry-dock economics.
Protective Coatings and Tank Inspection
At sea, coating integrity is the first and most economical line of defense against corrosion. Dry film thickness measurement verifies that protective paint meets specification, while holidays and discontinuities in the coating are detected with high-voltage methods. Inspecting ballast tanks, double-hull voids and inaccessible engine room spaces visually, without human entry, saves time and improves safety. Confined space entry is one of the highest-risk tasks in any shipyard.
Standards in the Marine Industry
Hull thickness measurements are carried out under the unified requirements of the International Association of Classification Societies (IACS) and the rules of individual class societies. Turkish-flagged vessels follow the rules of Turkish Lloyd. Weld inspection follows EN ISO 17640 and EN ISO 17636, and dry film thickness measurement follows ASTM D7091. Weld quality requirements in new construction are defined by EN ISO 3834.
Common NDT Methods in Marine and Shipbuilding
Ultrasonic Testing. The core method for thickness gauging of hulls, decks and tanks in class surveys. Through-coating probes shorten preparation time.
Phased Array & TOFD. Detect and size volumetric flaws in new-build and repair welds. No radiation zone is required, so work in the yard continues uninterrupted.
Magnetic Particle & Penetrant Testing. Detect surface cracks around the rudder stock, shaft bearings, deck fittings and high-stress connections.
Eddy Current. Scans for surface cracks without paint removal and is widely preferred at the welded nodes of offshore structures.
Coating Thickness Measurement. Verifies protective coatings against specification, checking the first line of defense against corrosion at sea.
Videoscopes. Allow inspection of ballast tanks, double-hull voids and inaccessible spaces without human entry.
Industrial Radiography, Holiday Detectors, XRF Analyzers and Hardness Testers are also widely used in marine and shipyard applications.
