Hyperbaric wet welding: how underwater wet welding works

What wet welding is

Hyperbaric wet welding puts the welding arc straight into open water: there is no chamber, no barrier and no dry pocket around the joint — the welder-diver strikes the arc with the sea pressing directly against it. Almost every job runs on shielded metal arc welding, SMAW or welding process 111, using electrodes purpose-built to strike and burn reliably underwater rather than the rods used for welding in air.

Because there is no habitat to design, build, seal and pressurise around the joint first, a wet-welding crew can typically start cutting and welding steel sooner than a dry hyperbaric spread would even be in position. That single difference — no habitat — is also what keeps wet welding's equipment list, mobilisation time and cost below what dry hyperbaric welding requires.

Where wet welding is used

Wet welding is applied for structural work and approved repairs, wherever the technical requirements, accessibility and the chosen repair method allow it.

Because it does not require a habitat to be built and sealed around the joint, wet welding also suits time-sensitive or temporary repairs, and work where access from inside a habitat would be impractical.

None of that is determined by the welding process on its own — the applicable standard, the project specifications and the client always decide what is technically admissible and what quality level is required.

• Sheet piling and quay walls
• Harbour and hydraulic engineering structures
• Ship repairs
• Offshore structures
• Anode attachments
• Approved structural repairs

How deep can wet welding be done?

Hyperbaric wet welding is mainly used in the first tens of metres of water. The practical depth limit depends on the diving method, the qualified welding procedure and the project requirements — there is no single fixed maximum depth that applies to every job.

A qualification is not automatically limited to the exact depth at which the test was taken: the test depth and the corresponding ambient pressure help determine a defined range of qualification, set out in the applicable standard. EN ISO 15618-1 works with defined ranges of qualification, and AWS D3.6M contains explicit depth limits for this.

For deeper or more critical work, such as pipeline repairs and pressure-containing offshore structures, dry hyperbaric welding may be required, because it makes the welding environment easier to control. Whether wet welding is technically and contractually permitted is determined per project and design review.

Weld quality and metallurgy

Water conducts heat away from a weld far faster than air. In wet welding that rapid quench is the starting point for every metallurgical risk in the joint: the weld metal and the surrounding heat-affected zone (HAZ) cool so quickly that the HAZ can end up hard and brittle rather than tough.

The same arc also burns inside a vapour bubble in the water, and hydrogen from that arc and bubble can be absorbed into the weld metal. Combined with a hard HAZ, that diffusible hydrogen is a central part of the crack risk in wet welding.

Add the welding and residual stresses that are already locked into the joint, and the combination — diffusible hydrogen, a hard HAZ and stress — raises the risk of hydrogen-induced cold cracking. There is no single fixed hardness figure that marks the boundary: the actual risk depends on the combination of material, carbon equivalent, hydrogen content, heat input, welding procedure, joint design and loading.

None of that rules wet welding out. With a well-trained welder-diver, electrodes suited to the job and a correctly qualified welding procedure, the process can achieve good structural weld quality. What it cannot match is the consistency of dry hyperbaric or conventional surface welding: rapid cooling, hydrogen pickup and limited underwater visibility all place limits on what wet welding can deliver.

Standards and qualification

Two separate qualifications apply to hyperbaric wet welding: one for the welder-diver, and one for the welding procedure used by the executing company. Professional underwater welding work generally requires both — the personal welder qualification (LK) demonstrates that the welder-diver is competent within a defined range, while the welding procedure qualification (LMK/WPQR) demonstrates that the chosen procedure can produce a welded joint with the required properties under the qualified conditions.

AWS D3.6M itself does not grade the welder — Class A, Class B and Class O describe the quality and application level a weld must meet on a given project, not a ranking of the person who made it.

An additional project or class approval may also be required by a classification society such as DNV, Lloyd’s Register, ABS or Bureau Veritas, on top of the welder and procedure qualification.

• EN ISO 15618-1 — personal qualification of the welder-diver for hyperbaric wet welding
• ISO 15614-9:2025 — qualification of the welding procedure for hyperbaric wet welding
• AWS D3.6M — the American underwater welding code, where specified by the project or client

Training: how our programme covers wet welding

The Hyperbaric Welding Center trains certified professional divers to become qualified underwater welders, with the programme centred on hyperbaric wet welding. Training and testing take place in a 21-metre dive basin with a movable floor, adjustable to the centimetre, so the training and test depth can be set to match a specific range of qualification.

Admission requires a recognised professional diving certificate — the Dutch B30, B50R or B50, or an assessed equivalent such as HSE, ADAS or DCBC — plus a valid occupational diving medical. The 5-day qualification track suits divers who already have welding experience; the 11-day extended track takes divers with little or no welding background through foundational surface welding first. Both tracks conclude with a welder qualification test (LK) to the applicable standard, conducted under DNV oversight.

Wet or dry?

Wet welding is not the only underwater welding method. Dry hyperbaric welding, carried out inside a sealed habitat, may be required for pressure-containing, higher-quality joints such as pipeline tie-ins, where the extra logistics buy a more controllable welding environment. The choice between the two is driven by the required weld quality, the depth, and the project specification.

That focus is deliberate: hyperbaric wet welding underpins the large majority of Europe's civil and structural underwater welding work, and completing it gives a diver the natural foundation for specialising toward habitat work with an employer afterwards.