The International Association of Classification Societies has adopted Revision 2 of Unified Requirement W33, “Non-destructive testing of ship hull steel welds”, with the rules applying to ships contracted for construction on or after 1 January 2028, according to Nippon Kaiji Kyokai, or ClassNK.
The 17-page requirement sets minimum standards for conventional non-destructive testing of steel welds in ship hull structures during newbuilding. It covers visual, penetrant, magnetic-particle, radiographic and ultrasonic testing, while phased-array ultrasonic testing, time-of-flight diffraction and digital radiography remain governed by UR W34.
The revision introduces detailed inspection requirements for intersections between transverse butt welds and longitudinal seam welds. At crossover points not assigned to a specific weld line, radiographic testing must cover at least 300 mm in both directions and ultrasonic testing at least 500 mm. Alternatively, testing may extend 150 mm or 250 mm, respectively, in each of four directions from the intersection.
A standard radiographic checkpoint must cover at least 300 mm and an ultrasonic checkpoint 500 mm. A non-crossover ultrasonic checkpoint must be at least 300 mm long, although the classification society may approve adjustments for restricted access, weld configuration or an acceptable shipyard welding record.
The revision replaces separate personnel-qualification provisions with a reference to UR W35, which covers non-destructive testing service suppliers. It also clarifies testing of tee, corner and cruciform joints and updates references to ISO welding and inspection standards.
Shipyards must include work by internal and external testing services in inspection reports and retain records for at least five years. Unacceptable indications require additional testing. For automatic or fully mechanised welds, testing must be extended to all affected areas of the same weld. Shipyards must also record repair rates and corrective measures within their quality-assurance systems.
IACS is an international association comprising 12 classification societies. Its Unified Requirements establish minimum standards incorporated into member rules, while allowing individual societies to impose stricter provisions. Its members’ rules and standards cover more than 90% of global cargo-carrying tonnage.
Nippon Kaiji Kyokai is an independent, non-profit Japanese ship classification society founded in 1899 and a member of IACS. At the end of June 2026, it had 9,771 ships totalling more than 285m GT under class, equivalent to approximately 20% of the world merchant fleet under class.