Wet welding vs dry hyperbaric welding
Both happen under water, but they are fundamentally different processes with different quality levels, costs and applications. Understanding the difference is the first step in understanding the trade — and in reading project specifications correctly.
Wet welding
In hyperbaric wet welding the arc burns directly in the surrounding water. The process most commonly used is shielded metal arc welding — SMAW, or process 111 — with electrodes developed specifically for underwater use.
The welder-diver works without a dry habitat around the weld location. That makes wet welding flexible, relatively quick to mobilise and generally less equipment- and cost-intensive than dry hyperbaric welding.
The biggest challenge lies in the metallurgy. The surrounding water causes very rapid cooling of the welded joint. At the same time, hydrogen from the arc and the surrounding vapour bubble can be absorbed into the weld metal. The combination of diffusible hydrogen, a potentially hard and brittle heat-affected zone (HAZ) and existing welding and residual stresses increases the risk of hydrogen-induced cold cracking.
With a well-trained welder-diver, suitable electrodes and a correctly qualified welding procedure, wet welding can be applied effectively for structural work and approved repairs — for example on sheet piling, quay walls, harbour structures, offshore structures and anode attachments. The technical admissibility and the required quality level are always determined by the applicable standard, the project specifications and the client.
Welder qualification
- EN ISO 15618-1 for the personal qualification of the welder-diver for hyperbaric wet welding;
- AWS D3.6M where the American underwater welding code is specified.
Within AWS D3.6M, Class A, Class B and Class O indicate the required quality and application level of the weld. They are not separate qualification levels of the welder.
Welding procedure qualification
- ISO 15614-9:2025 for the qualification of welding procedures for hyperbaric wet welding;
- AWS D3.6M for procedure qualification where the project is executed entirely to the American code.
Dry hyperbaric (habitat) welding
In dry hyperbaric welding a sealed chamber — the habitat — is placed around the workpiece or pipeline. The water is displaced from the working space, after which the welder works in a dry, controlled gas atmosphere at a pressure corresponding to the water depth.
Because the weld zone is dry and the atmosphere, preheat temperature, heat input and welding parameters can be controlled more precisely, a weld quality comparable to conventional surface welding can be achieved. Dry hyperbaric welding is therefore an established method for high-quality joints, tie-ins and repairs to subsea pipelines. In the North Sea the technique has been in use since the 1980s. Existing systems have been deployed successfully at depths down to approximately 250 metres.
The downside is the extensive logistics. Execution requires, among other things, a habitat, sealing and positioning systems, gas management, pressure control, communications and inspection provisions. At greater depths the work is usually carried out by closed-bell and saturation divers.
The welding procedure is qualified to ISO 15614-10 for dry hyperbaric welding. This standard describes the qualification of the WPS and the minimum testing requirements, and can also be applied to mechanised and automated welding processes. The procedure must be valid for the hyperbaric conditions applied and the other essential variables.
Personnel qualification
- EN ISO 15618-2 for the welder-diver in manual or partly mechanised dry hyperbaric welding;
- EN ISO 15618-2 for the welding operator in fully mechanised or automated welding.
Welding procedure qualification
- ISO 15614-10 for the qualification of the welding procedure for dry hyperbaric welding;
- an additional project or class approval where this is required by the operator, client or classification society.
Side by side
| Subject | Wet welding | Dry hyperbaric welding |
|---|---|---|
| Environment | Open water; the arc and the welded joint are in direct contact with the water | Sealed, dry habitat around the workpiece, at a pressure corresponding to the water depth |
| Typical application | Structural work, such as sheet piling, quay walls, harbour structures, ship repairs, anodes and approved structural repairs | High-quality and critical joints, such as pipeline repairs, tie-ins and pressure-containing offshore work |
| Typical depth range | Mainly in the first tens of metres; the practical limit depends on the diving method, welding procedure and project requirements | Can be applied down to several hundred metres using closed-bell and saturation diving |
| Quality level | Good structural weld quality is achievable, but rapid cooling, hydrogen absorption and limited visibility set limits on the process | A weld quality comparable to conventional surface welding is achievable thanks to the controlled, dry welding environment |
| AWS weld class | Depends on the qualified procedure and project requirements; Class B is common, but Class A or O may be possible on a project-specific basis | Class A or Class O may be achievable depending on the procedure, the applicable code and the project requirements |
| Welder qualification | EN ISO 15618-1 or AWS D3.6M | EN ISO 15618-2, or AWS D3.6M where the American code is applied |
| Welding procedure qualification | ISO 15614-9 or AWS D3.6M | ISO 15614-10 or AWS D3.6M |
| Cost and mobilisation | Relatively quick to mobilise and generally less equipment- and cost-intensive | Considerably more complex and costly due to the habitat, positioning, gas and pressure management and, where applicable, saturation diving |
Our training and qualification focus on hyperbaric wet welding — the method behind the vast majority of civil and structural underwater welding work in Europe. It is also the natural foundation before specialising towards habitat work with an employer.
Learn the trade where it starts
Hyperbaric wet welding, trained and qualified under the DNV flag in Enkhuizen.