Which certificate do you need for underwater welding on a pipeline?
Ask three people which ‘certificate’ you need to weld on a subsea pipeline and you will probably get three different answers. That is because there is usually not one certificate, but several layers of qualification and approval.
Exactly which layers are needed is determined by the welding environment, the welding procedure applied, the executing company, the pipeline code, the project specifications and any requirements of a classification society.
The four layers
1 · The underwater welder — personal qualification
The welder-diver must be personally qualified for the work he performs:
- EN ISO 15618-1 for hyperbaric wet welding;
- EN ISO 15618-2 for dry hyperbaric welding in a habitat;
- AWS D3.6M where this American underwater welding code is contractually specified.
The qualification is tied to essential variables and a defined range of qualification. The test depth helps determine the permitted depth or pressure range; it is therefore not automatically limited to only the exact depth at which the test was taken. AWS D3.6M contains explicit depth limits for this in Table 7.3.
2 · The welding procedure — qualification of the welding method
In addition to the welder, the executing company’s welding procedure must also be qualified:
- ISO 15614-9:2025 for hyperbaric wet welding;
- ISO 15614-10:2005 for dry hyperbaric welding.
The WPQR or LMK demonstrates through testing that the proposed procedure can produce a welded joint with the required properties under the qualified conditions. The qualification applies within defined limits for, among other things, process, material, welding position and hyperbaric conditions. For dry hyperbaric welding, the pressure and the atmosphere or gas conditions applied must be controlled precisely in the WPS. ISO 15614-10 can also be used for mechanised and automated welding processes.
3 · The pipeline code — project requirements
Subsea pipelines may be governed by codes and standards such as:
- DNV-ST-F101 for submarine pipeline systems;
- API 1104 for the welding of pipelines and related facilities.
DNV-ST-F101 contains requirements and recommendations for the full life cycle of subsea pipelines. API 1104 focuses specifically on welding procedures, welders, execution, inspection and acceptance of pipeline welds. The client may also lay down project-specific requirements that are stricter than the base code.
For critical, pressure-containing or fatigue-loaded repairs, dry hyperbaric welding may be required because it makes the welding environment easier to control. Whether wet welding is technically and contractually permitted must, however, be determined per project and design review.
4 · Class approval — additional assessment or approval
For classed assets, additional requirements may apply from, for example, DNV, Lloyd’s Register, ABS or Bureau Veritas.
Depending on its rules and the project specifications, the classification society may:
- review the welding procedure and qualification documents;
- have a test witnessed by a surveyor;
- accept existing qualifications under conditions;
- require additional testing or approvals.
Physical witnessing of every test is therefore not automatically always required. ABS, for example, provides that existing welding procedures and welder qualifications may be accepted by the surveyor under certain circumstances.
The core point: for professional underwater welding work, the welder, the welding procedure and the project must demonstrably align. Any class approval forms an additional, project-bound assessment layer on top of that.
What depth changes
Hyperbaric wet welding
In wet underwater welding, the welding arc is in direct contact with the water. The surrounding water causes rapid heat extraction, while hydrogen can form in and around the arc and be absorbed into the weld metal.
The combination of diffusible hydrogen, a rapidly cooled and possibly hard heat-affected zone (HAZ) and existing stresses increases the risk of hydrogen-induced cold cracking. This risk is not determined by a single fixed hardness limit, but by the combination of material, carbon equivalent, hydrogen content, heat input, welding procedure, joint and loading.
Wet welding is mainly used for work where the technical requirements, accessibility and chosen repair method allow it, such as:
- sheet piling and quay walls;
- harbour and hydraulic engineering structures;
- ship repairs;
- temporary repairs;
- structural repairs in relatively shallow water.
A general maximum production depth of 30 or 60 metres cannot simply be established. The technical feasibility and required weld quality must be assessed per material, welding procedure, range of qualification and project.
Dry hyperbaric welding in a habitat
In dry hyperbaric welding, a sealed habitat is placed over the weld location or pipeline. The water is displaced from the work chamber and welding takes place in a controlled gas atmosphere, while the pressure in the habitat corresponds to the ambient pressure at the water depth concerned.
Because the weld zone is dry and the heat input, preheat temperature, filler materials and atmosphere can be controlled more effectively, a weld quality comparable to conventional surface welding can be achieved. Dry hyperbaric welding is therefore an established technique for high-quality joints, tie-ins and repairs to subsea pipelines.
In the North Sea, such systems have long been used for pipeline work at diver-accessible depths. SINTEF reports that existing systems have been deployed to around 250 metres and that a company-specific diving limit of 180 metres was introduced for Norwegian operations. The exact operational limit depends on the diving organisation, regulations, equipment and project requirements.
Which diving qualification matches the depth?
Within the Dutch registration scheme, the following scopes apply to heavy professional diving work:
- B30: SSE diving down to and including 30 metres;
- B50R: SSE diving down to and including 50 metres;
- B50: SSE diving, including diving from an open diving bell, down to and including 50 metres;
- C: SSE diving from a closed diving bell, with breathing gases mixed for greater depths.
For scope C, the registration scheme does not include a fixed numerical depth limit.
Beyond the usual range of surface-oriented diving, offshore work shifts to closed-bell and saturation diving. The divers then live under pressure for an extended period and are transported between the saturation system and the worksite in a closed diving bell.
Depth therefore changes not only the pressure, but also the welding process, the welding procedure qualification, the equipment, the diving technique and the required competence of the welder-diver.
Scenario table
| Scenario | Welder qualification | Welding procedure | Class, operator and witnessing | Diving qualification |
|---|---|---|---|---|
| Quay wall or sheet piling, wet, approx. 10 m | EN ISO 15618-1 or AWS D3.6M, within the qualified range | ISO 15614-9 or a WPS/PQR qualified to AWS D3.6M | Class witnessing usually not applicable; inspection or witnessing by the client may still be specified | Dutch scheme: B30 or a higher appropriate scope |
| Offshore structure, wet, approx. 25 m | EN ISO 15618-1 or AWS D3.6M. On the AWS route, the required weld class A, B or O is determined by the project | ISO 15614-9 or AWS D3.6M, depending on the standard framework specified | Document review and/or witnessing where required by the class rules, the client or the inspection plan | Dutch scheme: B30 or a higher appropriate scope |
| Pipeline repair, wet, approx. 20 m | EN ISO 15618-1 or AWS D3.6M, matching the specified repair route | Project-specifically qualified procedure. Possibly ISO 15614-9 or AWS D3.6M Class O in combination with the designated pipeline code or project specification | Only applicable where the operator and any independent verifier or class society accept the repair method; a technical integrity assessment is often required | Dutch scheme: B30 or a higher appropriate scope |
| Pipeline repair, dry habitat, approx. 60 m | EN ISO 15618-2 for the welder-diver; operator qualification where welding is mechanised or automatic | ISO 15614-10 or the specified AWS route, qualified for the relevant hyperbaric conditions | Assessment by operator and independent verifier; class witnessing where the contract specification or verification scope requires it | Dutch scheme: scope C, with a closed diving bell |
| Pipeline repair, dry hyperbaric in saturation, 100 m+ | EN ISO 15618-2 for manual welding; welding operator qualification only for mechanised or automatic welding | ISO 15614-10, qualified for the applicable pressure or depth range, the atmosphere and other essential variables | Extensive prior approval of WPS, equipment, habitat and inspection plan by operator and, where applicable, class or independent verifier; witnessing according to the project-specific scope | Scope C plus demonstrable training, experience and company authorisation for closed-bell and saturation diving |
Frequently asked
Can I weld on a pipeline with a wet-welding qualification?
A wet-welding qualification does not automatically permit welding on every pipeline. Wet welding on non-pressure-containing components around a pipeline, such as certain supports or anode structures, may be possible where the project specification, the operator and the technical assessment allow it. Welding on the pressure-containing pipe wall itself always requires a project-specific assessment and explicit acceptance. For critical pipeline repairs, dry hyperbaric welding or a mechanical repair solution is generally the usual route.
Is depth really part of my qualification?
Yes. The test depth and the corresponding ambient pressure help determine the range of qualification. You are therefore not qualified only for the exact depth tested, but for the range that follows from the test according to the standard applied. If you want to work outside that range, an additional qualification or requalification is needed. The welding procedure must also be valid for the relevant pressure and depth range and for the other essential variables. EN ISO 15618-1 works with defined ranges of qualification and AWS D3.6M contains separate depth limits for this.
That is why our dive basin has a movable floor that can be set to the centimetre. This allows the training and test conditions to be matched precisely to the intended range of qualification.
Which diving certificate do I need first?
You need a recognised professional diving registration that matches the depth and nature of the work. In the Dutch scheme, for heavy work with Surface Supplied Equipment: B30 up to and including 30 metres, B50R up to and including 50 metres and B50 up to and including 50 metres, including working from an open diving bell. For work from a closed diving bell with specially mixed breathing gases, scope C applies. Foreign professional diving qualifications are assessed individually in advance for equivalence and scope of deployment.
Who gives the final approval on a real project?
Final project acceptance rests with the client or operator, based on the applicable code, the project specifications and the inspection and verification plan. Where class approval or independent verification is specified, a body such as DNV, Lloyd’s Register, ABS or Bureau Veritas can review the qualification documents and, depending on the agreed scope, witness the test. Physical witnessing is therefore not automatically required on every project.
A valid personal welder qualification from a recognised certification body is an important basis for this, but is not in itself automatic approval for every project, every pipeline or every client. DNV offers separate approvals for underwater welders to EN ISO 15618-1 and AWS D3.6M.
Build your foundation
Welder qualification for hyperbaric wet welding, conducted under DNV oversight — the first layer of the stack.