Shipbuilding

Shipbuilding welds fast and in volume, often in sections built by different companies and joined later. Quality assurance therefore revolves around two things: procedures approved by the classification society, and dimensional stability of sections that must fit elsewhere.

Procedure approval by the classification society
Shipbuilding steel grade A to EH36 and above
Controlling distortion and section dimensions
Inspection at the yard and at section builders

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DEHAAS supports yards, section builders and suppliers with qualification, welding quality assurance and inspection, and acts as the welding technology contact towards the surveyor.

Classification society and material

Shipbuilding steel is supplied in grades approved by the classification society: A, B, D and E for normal strength, AH to EH36 and above for higher strength. The letter indicates the impact toughness requirement, the number the yield strength. Those grades may only come from certified mills, with a certificate accepted by the society.

The same applies to consumables: they must be approved by the society for the relevant steel grade and used within the conditions of that approval. An otherwise excellent wire without class approval is unusable in this context.

Procedures and welders

Welding procedures are qualified to the society's rules, which largely follow ISO 15614-1 but with their own additions, for example on testing and on the range a qualification covers. The surveyor usually has to witness the coupon or approve the report.

Welder qualifications normally run through ISO 9606-1 with class endorsement. Where work is subcontracted to section builders, a common failing is that the subcontractor's qualifications were not verified beforehand, putting entire sections in question afterwards.

Distortion and dimensions

Thin stiffened panels are highly prone to distortion: weld shrinkage pulls the panel out of flat and causes buckling between stiffeners. Classification societies apply flatness tolerances, and exceeding them means flame straightening, which brings its own risks.

Control lies in welding sequence, in choosing one sided welding with backing or mechanised welding, and in a throat thickness no larger than required. See controlling weld distortion.

Inspection across the chain

Because sections arise at different parties, inspection at source is the only way to prevent assembly problems. That means verifying procedures and qualifications beforehand, visits during construction and dimensional checks before a section is shipped.

DEHAAS performs those inspections on behalf of the yard or the client, including at foreign section builders, reporting in English. See vendor inspection.

Frequently asked questions

In the Netherlands and northwest Europe mainly Lloyd's Register, Bureau Veritas, DNV and ABS. Each has its own rules for material, procedures and welders. If you work for several, track per society which qualifications are recognised.

E is the highest impact toughness class in the series A, B, D, E; H stands for higher strength and 36 for a minimum yield strength of 355 N/mm2. It is higher strength shipbuilding steel with good low temperature toughness.

No. Societies prescribe percentages per weld type and location in the vessel, with more examination on critical seams such as deck and shell and less on secondary structure. That is captured in an NDT plan approved by the society.

Yes. We inspect at suppliers at home and abroad, review their procedures and qualifications beforehand and attend hold points according to the inspection plan.