The International Association of Classification Societies (IACS) has published revisions to its welding rules for marine and offshore structures, updating Unified Requirements (UR) W11, W16, and W28 to better align with international welding standards, strengthen qualification standards, and improve consistency across IACS requirements.
The amended URs harmonise high heat input welding requirements across W11, W16, and W28, while also improving alignment with ISO 15614-1 and AWS D1.1/D1.1M. The revisions include updates to welding procedure qualification requirements for marine and offshore structures.
UR W28 Rev. 3 aligns welding procedure qualification requirements with ISO 15614-1 and AWS D1.1/D1.1M, and also sets out consistency with other IACS Unified Requirements, including UR W11 (Normal and higher strength hull structural steels), UR W16 (High strength steels for welded structures), UR W23 (Approval of welding consumables for High Strength Steels for Welded Structures), and UR W31 (YP47 steels and Brittle Crack Arrest Steels).
The revised UR W28 introduces an explicit definition of high-heat-input welding, expressed as energy input per unit length (kJ/cm). The qualification range for welding procedures has been revised to provide more explicit guidance on applicable base metals, welding consumables, and welding positions. Provisions for post-weld heat treatment have also been updated to ensure compatibility with new steel grades and their mechanical properties.
Manufacturers may optionally seek approval for high-heat-input welding procedures under a structured qualification framework. A new Annex E in UR W28 introduces provisions for welding procedure qualification tests using plates with approved high heat input grade notation. At the same time, qualification for high-heat-input welding remains valid when using steels not approved explicitly for high-heat-input grades, provided the welding procedure follows the existing qualification scheme defined in UR W28.
UR W28 also clarifies the required timing for non-destructive testing (NDT) based on the specified minimum yield strength. For steels with 420 N/mm² to 690 N/mm², NDT is required at least 48 hours after welding unless post-weld heat treatment (PWHT) is applied. For steels with 890 N/mm² to 960 N/mm², NDT is required at least 72 hours after welding unless PWHT is applied.
In addition, UR W11 and UR W16 introduce an optional manufacturing approval scheme for steels intended for high-heat-input welding. The appendices in UR W11 and UR W16 set out qualification procedures, testing requirements, and acceptance criteria. Under the voluntary scheme, manufacturers may apply for certification to confirm that steel plates meet additional requirements for high-heat-input weldability. The scheme covers welding processes with heat inputs exceeding 50 kJ/cm for normal- and higher-strength steels, and 35 kJ/cm for QT steels.
Commenting on the revisions, Dr. Ajay Asok Kumar, IACS General Policy Group (GPG) Chair, said the updates were developed with feedback from steel manufacturers, shipyards, and IACS members, and are aimed at improving alignment with international standards, consistency across IACS rules, and qualification standards for welding procedures used in marine and offshore structures.
