Shipbuilding welding sits at the intersection of two regulatory worlds that don’t always line up cleanly: general structural and pressure codes like AWS D1.1 and ASME Section IX, and the independent rules of whichever classification society is certifying the vessel. A weld can be perfectly compliant with AWS D1.1 and still fail a class survey if the WPS wasn’t approved under the classification society’s own scheme. Understanding how these two systems interact — and where classification society rules override general fabrication codes — is essential for any welding engineer or QA/QC professional entering shipyard work.
The Two Governing Systems
General structural welding in North American shipyards is frequently benchmarked against AWS D1.1, Structural Welding Code – Steel, particularly for shore-side structures, drydock facilities, and non-classed fabrication. But the ship itself — hull, structural members, and anything affecting seaworthiness — is built to the rules of a classification society, one of the members of the International Association of Classification Societies (IACS): ABS (American Bureau of Shipping), DNV, Lloyd’s Register, Bureau Veritas, ClassNK, and others including IRClass and RMRS regionally.
The classification society’s rules take precedence for anything tied to the ship’s class certificate. This includes material grade selection, welding procedure qualification, welder qualification, and NDT extent — all independently defined and independently surveyed, regardless of what a project’s commercial contract references from ASME or AWS.
Hull Steel Grades and Material Selection
IACS classification societies define a standardized set of hull structural steel grades — A, B, D, and E for normal-strength steel, and AH32/AH36 through EH36/EH40 for higher-strength grades. These grades differ primarily in guaranteed Charpy V-notch impact toughness at specified low temperatures, since brittle fracture resistance at sea in cold conditions is a defining structural risk for a ship hull, not just tensile strength. Grade selection depends on plate thickness and the design service temperature of the structural location — thicker plates and lower design temperatures require the tougher grades.
| Steel Grade Class | Typical Use | Key Requirement |
|---|---|---|
| Grade A / AH32-AH36 | General hull structure, moderate thickness | Standard Charpy toughness at 0°C Baseline |
| Grade D / DH32-DH36 | Thicker plating, higher-stress members | Improved toughness at −20°C Elevated |
| Grade E / EH32-EH40 | Critical structural members, thick sections, low-temperature service | Toughness guaranteed at −40°C Critical |
Welding Processes Used in Shipbuilding
Process selection in shipyards is driven by weld position, joint access, and production volume. High-volume flat and horizontal hull plating is dominated by submerged arc welding (SAW) and flux-cored arc welding (FCAW) for their high deposition rates. SMAW remains widely used for tack welding, positional work, and the awkward-access joints found inside double bottoms and confined compartments where mechanized equipment cannot be positioned. Deck plating and structural members frequently use higher-deposition electrodes such as E7024 for flat-position fill passes — see our welding rods comparison guide for electrode-specific deposition and application data.
Butt joints dominate hull plate seams for their clean load path and ease of radiographic or ultrasonic examination, while tee joints with fillet welds are the standard for stiffener and frame attachment — see our welding joint types guide for the underlying geometry.
Welder and Procedure Qualification Under Classification Society Rules
Each classification society maintains its own welder qualification and WPS/PQR approval scheme, generally aligned with ISO 9606 for welder qualification and ISO 15614 for procedure qualification, but administered independently of ASME Section IX. A WPS qualified and stamped under ASME Section IX is not automatically accepted for classed hull work — the classification society surveyor must witness or approve procedure qualification specific to their own rules before production welding of any class-certified member begins.
NDT and Inspection Requirements
Classification societies specify their own NDT extent tables based on structural criticality — typically a percentage of weld length for radiographic or ultrasonic testing on primary structural butt welds, with visual and magnetic particle testing applied more broadly. Welding inspectors on classed shipyard work are frequently required to hold recognized inspector credentials; see our comparison of CSWIP 3.1 vs AWS CWI certification for how these credentials are recognized across shipbuilding, structural, and pressure vessel sectors.
Typical Shipyard Welding Compliance Checklist
| Item | Governing Reference | Status |
|---|---|---|
| WPS/PQR approval | Classification society rules (ISO 15614-aligned) | Mandatory |
| Welder qualification | Classification society rules (ISO 9606-aligned) | Mandatory |
| Hull steel grade certification | Classification society material rules | Mandatory |
| NDT extent per structural location | Classification society NDT tables | Mandatory |
| Shore-side / non-classed structure welding | AWS D1.1 | Contract-dependent |
Recommended References on Shipbuilding Welding
AWS D1.1 Structural Welding Code
The reference structural welding code frequently used as a baseline for shore-side and non-classed shipyard fabrication.
View on AmazonShip Structural Design Reference
Covers hull steel grades, structural design principles, and classification society design philosophy.
View on AmazonWelding Inspection Handbook
NDT and inspection reference applicable to structural and shipyard welding acceptance criteria.
View on AmazonISO 15614 / ISO 9606 Reference Guide
Procedure and welder qualification standards underlying classification society approval schemes.
View on AmazonFrequently Asked Questions
Which welding code governs shipbuilding structural work?
There is no single universal shipbuilding code. AWS D1.1 Structural Welding Code – Steel is widely referenced for shipyard structural fabrication in North America, but the controlling requirement on any given vessel is the classification society whose class the ship is being built to. The classification society’s own rules for welding, materials, and NDT take precedence over AWS or ASME for anything affecting the ship’s class certificate.
Do classification societies require their own welder and WPS approval?
Yes. Each classification society maintains its own welder qualification and WPS/PQR approval scheme, generally aligned with ISO 9606 for welder qualification and ISO 15614 for procedure qualification, but administered independently. A WPS qualified under ASME Section IX is not automatically accepted for classed hull work.
What steel grades are used in ship hull construction?
IACS classification societies define hull structural steel grades A, B, D, and E (and higher-strength grades AH32/AH36 through EH). Grade selection depends on plate thickness and the design temperature the structure must resist, since grades differ primarily in guaranteed Charpy V-notch impact toughness at low temperature.
Why is SMAW still widely used in shipyards despite slower deposition than FCAW or SAW?
SMAW remains common for tack welds, positional work, and awkward-access joints inside double bottoms and confined compartments where mechanized FCAW or SAW equipment cannot be positioned. High-volume flat and horizontal hull plating, by contrast, is dominated by SAW and FCAW for their higher deposition rates.