Welding on a subsea pipeline is not something a single course, or a single certificate, qualifies you for. It rests on four separate layers. The welder-diver holds a personnel qualification — EN ISO 15618-1 for wet welding, EN ISO 15618-2 for dry habitat welding, or AWS D3.6M. The contractor qualifies the welding procedure for the job’s depth window, under ISO 15614-9 (wet) or ISO 15614-10 (dry). On top of those sit the pipeline code — DNV-ST-F101 or API 1104 — and, on most real projects, witnessing by a classification society. Depth is an essential variable at every one of those layers, which is why a qualification earned for one scenario rarely transfers cleanly to another.
The four layers, in plain terms
The first layer is the welder-diver’s own qualification. EN ISO 15618-1 covers hyperbaric wet welding, EN ISO 15618-2 covers hyperbaric dry (habitat) welding, and AWS D3.6M — the American standard, with weld classes A, B and O — covers either. In every one of these standards, depth is an essential variable: your qualification is valid for the depth range you were actually tested at, not for “underwater welding” as a general skill. This personnel qualification is the layer a training provider delivers.
The second layer is procedure qualification: proving that a specific welding procedure, at a specific depth window, produces welds that meet the required quality level. For wet welding that runs through ISO 15614-9; for dry hyperbaric welding it runs through ISO 15614-10. That work is project- and contractor-specific — it is qualified for the job in hand, not delivered as part of a training course.
The third layer is the pipeline code itself, which decides what is allowed on the structure: DNV-ST-F101 for submarine pipeline systems, and API 1104 in a US context. The fourth layer is class witnessing — a surveyor from a classification society such as DNV, Lloyd’s, ABS or Bureau Veritas attending the qualification test and issuing project-specific approval. Both of these sit with the contractor and the client, on a project-by-project basis.
Why “pipeline-certified” is not a real qualification
No training provider can hand you a certificate that makes you “pipeline-certified”. What a provider delivers is the first layer above: a personnel welding qualification. The procedure qualification, pipeline-code compliance and class witnessing are arranged separately, project by project, by the contractor and the client — they cannot be pre-packaged into a course. Any provider claiming otherwise is overstating what a personnel qualification actually covers.
That layering is not a technicality — it is how the industry checks that a weld on a live pipeline is fit for purpose. Understanding it is more useful to a working diver-welder than any single certificate name.
Why depth matters at every layer
Because depth is an essential variable throughout this system, both the welder’s qualification and the procedure qualification are tied to a depth window, not to a single pass/fail. As a general picture — an indicative band rather than a fixed figure — wet welding is used for production work mostly up to roughly 30–60 metres; it has been done technically at greater depths, but weld quality becomes harder to control as pressure and gas conditions change. For deeper or more critical work, hyperbaric dry (habitat) welding, combined with saturation diving, is the established route.
That is also why wet welding is almost never accepted for the pipeline itself: it typically cannot meet workmanship requirements such as those in API 1104. Where wet welding is used at all near a pipeline, it is through project-specific fitness-for-service acceptance granted by the operator — not a standard, repeatable route — and is generally limited to structural work rather than the pipeline wall.
What this looks like at different depths
Shallow civil or harbour work, around 10 metres: typically wet welding, and a personnel qualification under EN ISO 15618-1 (or AWS D3.6M Class B, sometimes A) is usually the base requirement, without a pipeline-specific procedure or class witnessing attached.
Offshore structural work, around 25–30 metres: still wet welding in many cases, but class witnessing becomes usual for structural components, alongside the same personnel qualification tested at the relevant depth range.
Pipeline repair around 60 metres: this typically moves into hyperbaric dry habitat welding, needing an EN ISO 15618-2 personnel qualification and an ISO 15614-10 procedure qualified for that depth window, plus class witnessing under the applicable pipeline code.
Saturation work at 100+ metres: habitat welding with saturation or closed-bell divers, a procedure qualified per depth window (including the gas mixture as a variable), and full class and client witnessing. Hyperbaric pipeline repairs at this kind of depth are a documented part of North Sea practice, with cases carried out well beyond 100 metres.
Who actually signs off welding on a subsea pipeline
No single party does. The welder-diver’s personnel qualification confirms they can weld to standard. The contractor’s qualified procedure confirms that specific method works at that depth. The pipeline code sets what is permitted on the structure. And a classification-society surveyor — DNV, Lloyd’s, ABS or Bureau Veritas, depending on the project — witnesses the qualification test and issues approval under their own rules. Sign-off on a live pipeline weld is the sum of all four, arranged and owned by the contractor and the operator, not by any single training provider.
Frequently asked
Can I get pipeline-certified from a welding course?
No — “pipeline-certified” is not a real qualification. A course can give you a personnel welding qualification (such as EN ISO 15618-1 or -2, or AWS D3.6M). Welding on an actual pipeline additionally requires a project-specific procedure qualification and, usually, classification-society witnessing — both arranged by the contractor and client, not by a training provider.
What is the difference between welder qualification and procedure qualification?
Welder (personnel) qualification proves that a specific welder-diver can produce sound welds, tested at a given depth. Procedure qualification proves that a specific welding procedure — the method, consumables and parameters — produces sound welds at a given depth window. A project needs both, and they are qualified separately.
At what depth does wet welding stop being used on pipelines?
There is no single cut-off depth. As a general, hedged picture, wet welding is used for production work mostly up to roughly 30–60 metres, and is essentially never accepted on the pipeline wall itself at any depth — except through project-specific fitness-for-service acceptance by the operator. Hyperbaric dry welding is the established route for deeper or more critical pipeline work.
Who signs off welding on a subsea pipeline?
No single party. Sign-off combines the welder’s personnel qualification, a contractor-qualified welding procedure for that depth, compliance with the applicable pipeline code, and — on most projects — witnessing and approval by a classification society such as DNV, Lloyd’s, ABS or Bureau Veritas.
Does EN ISO 15618-1 cover pipeline welding directly?
EN ISO 15618-1 qualifies a welder-diver for hyperbaric wet welding — it is a personnel qualification, not a pipeline-welding certificate. Whether wet welding under that qualification is acceptable on a specific pipeline is a separate question, decided project by project against the applicable pipeline code and the operator’s fitness-for-service acceptance.