5 Essential Underwater Welding Techniques Explained
Wet SMAW, dry hyperbaric welding, mechanized FCAW, friction-based repair and robotic subsea welding solve different access, quality and risk problems. The right choice starts with the required weld class—not with the process name.
A 60-second selection rule
Do not ask “Which underwater welding process is best?” until the owner, engineer and diving contractor agree on acceptance class, access, inspection and operational risk.
AWS D3.6 distinguishes weld classes, including Class A, Class B and Class O. The required class changes procedure qualification, testing and repair strategy.
Open-water access favors mobility. A sealed habitat offers much better control of shielding, heat treatment, visibility and consumables.
Water accelerates heat loss and the arc bubble changes stability. Material chemistry, restraint, electrodes and bead sequence require qualification together.
Electrical isolation, communications, gas hazards, decompression, entrapment and emergency response are system-level controls—not operator improvisations.
What are the main underwater welding techniques?
The first practical distinction is the environment around the molten pool. In wet welding, the arc burns inside a transient gas bubble created by electrode decomposition and water vapor. The diver has direct access to the structure, but visibility, arc stability and heat flow are difficult to control. In dry hyperbaric welding, a chamber excludes water from the weld area while maintaining pressure close to the surrounding water. This controlled space makes familiar processes—such as SMAW, GTAW, GMAW and FCAW—more practical and improves the ability to inspect and manage the joint.
The American Welding Society’s AWS D3.6M Underwater Welding Code covers welding below the water surface in both wet and dry environments. It defines general requirements and separate weld classes. That matters because a temporary attachment, a low-consequence repair and a critical pressure-containing tie-in should not be selected or qualified in the same way.
Why the five techniques overlap
Process names alone can be misleading. FCAW, for example, describes the consumable and arc process; it does not tell you whether welding occurs wet, inside a full habitat or behind a local dry shroud. “Robotic underwater welding” may mean a teleoperated arm working in water, a mechanized head inside a dry chamber, or a research platform using laser-assisted or hybrid joining. This guide therefore treats each technique as an engineering route rather than a universal recipe.
- Wet SMAW optimizes access and deployment speed.
- Dry hyperbaric welding optimizes process and quality control.
- Mechanized FCAW optimizes wire delivery and deposition in a qualified setup.
- Friction-based methods avoid a conventional open arc and target specialized repairs or attachments.
- Robotic/local-dry systems optimize remote access, repeatability and reduced diver exposure where the project supports the tooling.
Five routes, five different decision windows
The table is a planning map. Actual suitability must be demonstrated by a qualified procedure, representative test assembly and the governing owner or classification requirements.
| Technique | Working environment | Best fit | Primary strength | Main engineering constraint |
|---|---|---|---|---|
| Wet SMAW | Arc and joint directly exposed to water | Accessible steel repairs, attachments and urgent intervention where the specified class permits | Mobility and relatively simple deployment | Rapid cooling, hydrogen, visibility, porosity, slag and difficult inspection |
| Dry hyperbaric welding | Pressurized gas-filled habitat around the joint | Critical repairs, pipeline work and joints needing better process control | Dry joint, better visibility and broader process options | Habitat engineering, sealing, gas management, logistics and pressure effects |
| Mechanized FCAW / wire process | Usually dry hyperbaric or local-dry; some wet variants are specialized | Long seams or repeatable deposition where a feed system and guidance can be controlled | Continuous wire and production consistency | Wire-feed reliability, arc behavior under pressure and access for mechanized tooling |
| Friction stud / friction stitch | Immersed tooling or controlled subsea repair system | Attachments, anode connections, plugs and overlapping crack-repair features | Solid-state joining without a conventional open arc | High axial force, specialized machine, hole preparation and geometry limits |
| Robotic / local-dry welding | ROV, manipulator or autonomous platform, often with a local dry enclosure | Repeatable remote tasks, deep or hazardous access and high-value assets | Reduced diver exposure and programmable motion | Sensing, seam tracking, communication latency, tool integration and qualification |
Classification framework: AWS D3.6M:2017. Wet/dry process overview: TWI, What is Underwater Welding?
From direct diver access to remote repair cells
Each route shifts the balance among deployment complexity, control of the weld pool, repeatability and human exposure.
Wet SMAW
A waterproof coated electrode creates the arc and shielding bubble while the diver manipulates the weld directly in water.
Dry hyperbaric
A sealed chamber displaces water from the joint and supports more controlled arc welding, consumables and inspection.
Mechanized FCAW
Wire feeding and guided travel can raise consistency, especially inside a habitat or purpose-built local-dry enclosure.
Friction joining
Rotating studs or tapered plugs create heat and plastic flow under force for specialized subsea attachments and repairs.
Robotic systems
Manipulators combine sensing, motion and process tooling, frequently with local water exclusion around the seam.
Wet SMAW: fast access, harder metallurgy
Wet shielded metal arc welding—also called wet manual metal arc welding—places the electrode, arc and workpiece directly in the surrounding water. The waterproof electrode coating decomposes to create shielding gases and slag. This makes the process portable and adaptable to irregular structures, but the arc bubble is dynamic and the water extracts heat rapidly.
Its value is operational. A trained diver-welder can reach joints that would be expensive to enclose. That can be decisive for temporary reinforcement, attachments and qualified repairs where the design authority permits wet welding. Its limitation is not simply “lower quality”; it is a narrower, more sensitive process window. Material carbon equivalent, restraint, electrode classification, polarity, current, bead placement, joint preparation and water conditions interact.
Photo: U.S. Navy / Shane Tuck, public domain, via Wikimedia Commons. Technical context: TWI wet welding repairs.
Dry hyperbaric welding: control around the joint
Dry hyperbaric welding seals a gas-filled habitat around the work area. Water is displaced, the joint becomes visible and consumables can be handled in a controlled environment. Depending on the repair design and qualification, the habitat may support SMAW, GTAW, GMAW or FCAW. The central advantage is not that pressure disappears—it does not—but that water no longer contacts the weld pool directly.
This opens the door to better surface preparation, controlled shielding, interpass cleaning, preheat or post-weld heat treatment when the engineering plan allows it, and more conventional inspection access. It is often considered where the weld must approach above-water structural performance or where the consequences of failure justify the habitat and support system.
Dry hyperbaric welding still needs specialized procedure development. Elevated pressure influences arc voltage, heat transfer, shielding behavior and equipment. The chamber must be sealed to the actual geometry, continuously managed and integrated with the commercial diving plan. Habitat selection therefore belongs to the project design—not to a welder’s field preference.
Photo: U.S. Navy, public domain, via Wikimedia Commons. Process overview: TWI.
Mechanized FCAW: continuous wire is only half the system
Flux-cored arc welding can improve deposition continuity, but an underwater project must also control the environment, feed path, torch position, shielding and inspection.
Continuous electrode feed
Compared with manually replacing stick electrodes, a wire process can support longer runs and more repeatable deposition. Mechanization can also stabilize travel speed and torch angle.
- Useful for repetitive or extended seams
- Compatible with guided or robotic motion
- Consumable formulation can support the targeted metallurgy
Dry or locally dry tooling
FCAW is most straightforward when the wire drive, contact tip and arc operate in a dry hyperbaric or engineered local-dry environment. Fully wet variants are specialized and must not be assumed equivalent.
- Habitat welding with controlled access
- Mechanized repair heads
- Project-specific wet or water-exclusion systems
Feed and pressure interactions
A wire process adds moving parts and interfaces. Long liners, bends, moisture, contact-tip condition, pressure and torch alignment can disturb feed stability before the arc problem is even considered.
- Bird-nesting, slip or inconsistent feed
- Arc behavior changes under pressure
- Seam-tracking error becomes a weld defect
Specialized repair machines and remote intervention
These methods can solve problems that arc welding cannot, but they are engineered systems—not universal substitutes for wet SMAW or a dry habitat.
Friction stud welding for subsea attachments
A rotating stud is pressed against the component. Friction generates heat, the interface plasticizes and axial force consolidates the joint. Because the method is solid-state, it avoids a conventional open arc and molten weld pool. TWI has investigated underwater friction stud welding for electrical couplings and sacrificial-anode take-off connections under immersed and pressurized conditions.
Friction taper plug and friction stitch repair
A tapered plug is rotated and forced into a prepared hole. Overlapping plugs can form a “stitch” along a defect or crack path. Research on DH36 steel shows that bonding, heat treatment and plug overlap require careful control; the method is promising for repair, but it demands heavy purpose-built tooling, drilling accuracy and a qualified sequence.
Sources: TWI underwater friction welding study; Materials & Design study on underwater friction stitch repair.
Robotic welding: repeatability without easy conditions
ROVs and robotic manipulators can reduce diver exposure and reach deeper or more hazardous locations. A practical system may carry a camera, structured-light or sonar sensors, a preparation tool, a local dry chamber, the welding head and inspection instruments. The weld process is only one subsystem.
Seam tracking is difficult because turbidity, bubbles, marine growth, reflections and vehicle motion degrade the sensor signal. Forces at the torch can disturb a free-swimming vehicle. Communication latency and limited operator depth perception further complicate teleoperation. For these reasons, many successful concepts clamp to the structure or create a mechanically referenced local work cell before welding.
Underwater laser and laser-assisted processes continue to be researched, but they should not be presented as a drop-in replacement for conventional offshore repair. Laser transmission through water, plume and bubble behavior, optical protection, path stability and local water exclusion all require engineered solutions.
Photo: NOAA Fisheries, public domain, via Wikimedia Commons. The vehicle is shown as an example of subsea robotic access, not as a welding machine.
The weld pool is fighting water, pressure and time
A visually smooth bead does not prove that the heat-affected zone, hydrogen level or internal soundness meets the engineering requirement.
Arc bubble forms
Electrode coating and vapor create a temporary gas cavity. Bubble growth and collapse affect arc length, metal transfer and visibility.
Hydrogen enters
Moisture and arc reactions can introduce diffusible hydrogen. Susceptible steel, high restraint and a hard microstructure raise cracking risk.
Heat leaves rapidly
The surrounding water extracts heat, accelerating cooling compared with air welding and encouraging hard transformation products in the HAZ.
Defects can hide
Porosity, slag, lack of fusion and subsurface cracking may not be visible through a helmet or on the finished bead surface.
Research basis: Mechanisms of rapid cooling in underwater welding and The State of the Art of Underwater Wet Welding Practice.
Match the repair route to the dominant constraint
These routes are starting points for an engineering review, not automatic approvals.
ACCESS
Local steel repair with open diver access
Review wet SMAW if the material, joint, weld class and inspection plan allow it. Qualify on a representative assembly and water condition.
CLASS
Critical load path, pressure boundary or demanding acceptance
Begin with dry hyperbaric or a purpose-built local-dry concept. The habitat creates a better route to controlled welding and inspection.
SEAM
Repeatable geometry with sustained deposition
Evaluate mechanized FCAW or another wire process inside the selected dry/local-dry environment. Design the feed system and seam reference together.
JOINT
Stud, anode connection, plug or localized defect
Consider friction-based tooling where geometry and axial reaction can be accommodated. Confirm material flow, bonding and inspection access.
ZONE
Deep, hazardous or repetitive intervention
Study a clamped robotic or ROV-supported local work cell. Treat sensing, preparation, water exclusion, welding and NDT as one integrated system.
Underwater welding is a commercial diving operation.
The welding procedure cannot substitute for a dive plan, operational manual, designated person in charge, qualified team, emergency capability and jurisdiction-specific compliance.
Surface-tended current interruption
Under OSHA 29 CFR 1910.422(g), a surface team member in voice communication with the diver must tend the switch that interrupts welding current and keep it open except while welding or burning. The machine frame must be grounded, and cables, holders and connections must be properly insulated and rated.
Communications, gas and decompression
Operational two-way communications, depth-time profiles, breathing-gas planning, reserve supply and decompression procedures belong to the dive system. Loss of communication or reserve-gas use can trigger dive termination requirements.
Entrapment, differential pressure and stored energy
Water flow, suction, moving equipment, unstable members, enclosed spaces and suspended loads can dominate the risk assessment. Isolate energy sources and verify the physical worksite before hot work begins.
Flammable or explosive gas pockets
Welding or burning on closed compartments, structures or piping requires control of vapors that may already exist or may be generated. OSHA specifies venting, flooding or purging with a non-combustible mixture for relevant closed spaces.
Cold, visibility and workload
Commercial divers face drowning, respiratory and circulatory hazards, hypothermia and strenuous work in restricted visibility. Welding adds electrical, thermal, fume and structural hazards to that baseline.
Prove the weld before it carries real consequence
Appearance is one data point. A defensible underwater repair links design, procedure qualification, diver-welder or operator qualification, production controls and inspection records.
Define the weld class
Record the governing code, owner specification, service consequence and acceptance class before procedure development.
Qualify the procedure
Replicate material, thickness, joint, position, water environment or pressure, consumable and essential process variables.
Qualify personnel
Confirm commercial diving competency and the applicable wet or dry diver-welder or welding-operator qualification.
Inspect the production weld
Use the approved visual and nondestructive examination plan, with traceable records and a defined disposition for indications.
Confirm grade, carbon equivalent, coatings, corrosion loss, prior repairs and remaining section.
Match restraint, orientation, joint access and environmental conditions closely enough to expose real risks.
Plan cleaning, lighting, dimensional checks and NDT access before adding a habitat, clamp or reinforcement.
Define when to stop, remove, rework, reinforce or switch to a dry method before the operation begins.
Specify pressure, load, leak or functional testing and the engineering authorization needed for return to service.
Retain WPS/PQR, qualifications, dive logs, consumable control, inspection results and as-built location data.
Qualification references include AWS D3.6M and, where adopted, the wet and dry diver-welder qualification parts summarized under ISO 15618. Always use the edition and jurisdiction named by the project.
Underwater welders are divers first—and qualified welders within a team.
A credible pathway combines commercial diver training, surface welding fundamentals, underwater welding instruction, emergency response, equipment competence and supervised field experience. The order and credentials depend on the country, employer, diving mode, offshore sector and governing contract. No single short course makes a person ready for every underwater welding task.
Employers typically need evidence that the individual can work safely as part of a commercial dive team and can meet the welding qualification required for the specific procedure. Dry hyperbaric work may also involve chamber operations, atmosphere management and process-specific operator qualifications. Robotic work shifts part of the competence toward controls, sensing, tooling and remote intervention while retaining welding engineering oversight.
Need a controlled laser welding process above water?
Oceanplayer handheld and robotic laser welding systems are designed for controlled industrial fabrication—not improvised diver-held underwater welding. If your marine project includes topside component fabrication, dry workshop repair, fixtures or automated subassemblies, we can review the material, thickness, joint and production target.
Send these project details
- Base material and verified grade
- Thickness, joint type and fit-up tolerance
- Required penetration and appearance
- Daily output and operator workflow
- Photos, drawings and sample-part availability
Related welding engineering guides
Use these resources to understand controlled laser joining, automation and process selection outside the underwater environment.
Underwater welding FAQ
Short answers to the questions that most often appear during process and repair planning.
What are the five main underwater welding techniques?
A practical five-route overview is wet SMAW, dry hyperbaric welding, mechanized FCAW or another wire process, friction stud/stitch welding, and robotic or local-dry subsea welding. The categories overlap because an arc process such as FCAW may operate inside a habitat or a robotic work cell.
Is wet or dry underwater welding better?
Neither is universally better. Wet welding offers direct access and faster deployment, while dry hyperbaric welding provides better control of the joint, shielding, visibility, heat treatment and inspection. Required weld class, consequence and access determine the preferred route.
Can wet underwater welding produce permanent repairs?
It can when the engineering design, qualified procedure, personnel, material, production controls and inspection satisfy the governing code and owner requirements. Wet welding should not automatically be treated as temporary, but it also should not be assumed acceptable for every critical joint.
Why is underwater wet welding prone to cracking?
Water causes rapid heat loss, while arc reactions can introduce hydrogen. Susceptible steel chemistry, high restraint and a hard heat-affected-zone microstructure can combine to raise hydrogen-assisted cracking risk. Qualification is needed to establish a safe window.
Is FCAW used underwater?
Yes, but the environment must be stated. FCAW can be used in dry hyperbaric habitats and specialized wet or local-dry systems. Continuous wire feeding can improve deposition, but it adds feed, torch, pressure and seam-tracking requirements.
What is hyperbaric welding?
Hyperbaric welding is performed at elevated pressure. In common marine usage, “dry hyperbaric welding” means the joint is enclosed in a gas-filled chamber at pressure related to the surrounding water depth. The welder or welding head works in that controlled dry space.
Does underwater welding use AC or DC?
Wet arc welding normally uses a qualified direct-current setup, but polarity and operating parameters come from the approved procedure and applicable rules. Safety also depends on surface-tended current interruption, grounding, insulation and communications—not merely on selecting DC.
How are underwater welds inspected?
The inspection plan may combine visual examination, dimensional checks and appropriate nondestructive examination. The exact methods and acceptance criteria depend on weld class, geometry, access and governing specification. Surface appearance alone is insufficient for high-consequence work.
Can robots replace underwater welders?
Robots can reduce diver exposure and improve repeatability in suitable tasks, but they require reliable positioning, sensing, preparation, water exclusion, welding and inspection. Many systems remain project-specific rather than universal replacements for trained dive teams.
Can laser welding be performed underwater?
Underwater laser and laser-assisted welding are active research and specialized engineering areas. Water, bubbles, plume behavior, optical protection and path stability complicate the process. Most production laser welding equipment, including Oceanplayer systems, is intended for controlled dry industrial environments.
What standard covers underwater welding?
AWS D3.6M covers underwater welding in wet and dry environments and defines weld classes and requirements. Other owner, classification, national and sector standards may also apply. Use the specific edition named by the contract.
How do you become an underwater welder?
The usual route combines recognized commercial diving training, welding competence, specialized underwater welding training and supervised experience. Required certificates vary by jurisdiction, employer and project, so candidates should verify current local and offshore requirements before enrolling.
- American Welding Society — AWS D3.6M:2017 Underwater Welding Code
- OSHA — 29 CFR 1910.422, Procedures During Dive
- OSHA — Commercial Diving Overview and Hazards
- TWI — What Is Underwater Welding and How Does It Work?
- TWI — Wet Welding Repairs
- TWI — Underwater Friction Welding for Electrical Couplings
- Applied Ocean Research — Mechanisms of Rapid Cooling in Underwater Welding
- Materials & Design — Repair of an Arc-Welded DH36 Joint by Underwater Friction Stitch Welding
- TWI — Qualification Standards Including ISO 15618