In a steel or aluminium boat, the welds are the structure. Weld quality is secured by three things: an approved procedure, a welder qualified for it, and inspection after welding.
Procedure and welder
- Welding procedure (WPS)
- Defines material, thickness, position, process, consumables and parameters; it rests on a procedure qualification record (WPQR).
- Welder qualification
- The certificate showing the welder is qualified for that process and position (ISO 9606).
- On aluminium
- Surface cleaning and oxide removal, a dry and clean environment; porosity is the most common defect.
- On steel
- Heat input and distortion control; welding sequence decides distortion.
Inspection methods
- Visual
- On every weld: bead profile, undercut, cracks and spatter.
- Dye penetrant
- Shows surface-breaking cracks; used on steel and aluminium.
- Magnetic particle
- Surface and near-surface cracks; steel only.
- Ultrasonic and radiographic
- Internal defects: lack of penetration, porosity, slag. On critical welds and where class requires.
Inspection plan
Which welds get which method, and at what rate, is written before work starts. Inspection is done by qualified personnel; results are recorded by weld number and every repaired defect is inspected again.
Where each method is used
Weld inspection starts by eye: bead shape, regularity, undercut, porosity and cracks are looked for. Visual inspection covers every weld. In critical areas, non-destructive methods are used: dye penetrant shows surface-breaking cracks, magnetic particle shows surface and near-surface flaws in steel, and ultrasonic and radiographic testing show flaws inside the weld. Which method applies where is set by the class rules or specification.
Welding aluminium
Aluminium welding is more demanding than steel. Surface cleanliness, shielding gas quality and shop humidity directly affect porosity. The metal loses some strength in the welded zone, so the design accounts for weld zones. Dye penetrant is a common method on aluminium.
Welder and procedure
Good welding needs an approved welding procedure and welders qualified to it. The specification states the standards for procedure and welder qualification; during the build these documents are requested and filed.
Acceptance level
Not every weld imperfection is rejected; standards define acceptance levels by type and size of imperfection. Inspection is judged against those levels. A rejected weld is marked, ground out and rewelded, then inspected again by the same method.
Timing
Inspection is done before welds are covered by paint or insulation; it is one of the build's check points and is tied to a stage payment.
Records
Inspection reports, with locations marked on drawings, go into the build file and stay with the boat for its whole life.
On steel
On steel boats, surface preparation and the paint system after welding are the first defence against corrosion. Weld areas are cleaned before painting and all slag removed. Inside the hull, areas that will be hidden behind insulation get particular attention, because corrosion there goes unseen for years.
A final check and photos before insulation goes in close the record for those areas, and give a baseline if a later inspection is ever needed.
Inspection results form part of the stage payment verification; the stage is not paid until inspection is complete. That link is what gives the inspection weight with the yard.
Where class applies, the class surveyor's own inspections run alongside; the owner's inspector does not replace them, but reports to the owner directly and independently.
Both sets of reports go into the build file together.
A weld that passes inspection today is the foundation of a hull that lasts for decades, which is why this check point is never skipped under schedule pressure.