Underwater Welding & Cutting Companies

Steel below the waterline fails on its own schedule. A crack found at a routine inspection, a sea chest grating torn off in heavy weather, a bilge keel opened up on a quay wall - each one raises the same question, which is not how to repair it but whether the repair can wait for the next docking. Underwater welding and cutting exist to answer that question without hauling the ship out, and the honest version of the answer often is: yes, afloat, as a repair class will accept for a defined period. Not every diving contractor carries the capability, and the ones that do are not always the firms already cleaning the vessel’s hull.

What Gets Welded and Cut Afloat

Underwater ship welding on merchant tonnage is narrower work than the term suggests. The recurring scopes are crack arrest holes drilled and sealed, doubler plates fitted over a wasted or fractured area, sea chest gratings and their frames renewed, rope guards and bilge keel sections re-attached, anode pads welded back on, and shell plate patches over damage from contact or grounding. Cutting accompanies almost all of it: the damaged section comes off before anything new goes on.

Cutting also stands alone as a scope. Wire and net cut away from a shaft, a fouled thruster grid cleared, a dropped object removed from a sea chest, mooring wire freed from a rudder - none of it involves welding, and all of it is booked from the same contractors. Before either job starts the area has to be cleaned back to bare metal, which is why a welding attendance is frequently combined with hull cleaning on the same mobilisation.

Wet Welding, Cofferdam Work and Dry Hyperbaric Welding

Three approaches exist, and the price difference between them is an order of magnitude. Wet welding is carried out directly in the water with waterproofed electrodes on direct current - alternating current is not used, for reasons of diver safety. It is fast, mobilises anywhere, and is the method behind most in-water repairs on merchant ships. Its limitation is metallurgical: the surrounding water quenches the weld almost instantly, which hardens the heat-affected zone and drives hydrogen into it, so underwater wet welding is restricted by the steel's carbon equivalent and produces a weld of lower toughness than the same joint made dry.

A cofferdam or habitat removes the water locally. A sealed box is clamped over the work area and dewatered, and the welder then works dry at ambient pressure on a small patch - slower to set up, far better metallurgy, and available in most ports. Dry hyperbaric welding takes the same principle to a full pressurised chamber with a controlled atmosphere, allowing preheat and post-weld heat treatment; hyperbaric underwater welding produces welds comparable to shop work, and is priced accordingly. On merchant vessels it appears mainly where a permanent, class-accepted repair has to be made without docking.

AWS D3.6M Weld Classes and What Class Will Accept

The reference document for this work is AWS D3.6M, the underwater welding code, which sorts welds into classes by the properties they have to meet. Class A is intended to be comparable to a surface weld of the same specification; Class B accepts lower ductility for less critical applications; Class C is for work where structural strength is not the point; Class O has to satisfy an additional standard as well. Wet welding routinely achieves Class B; Class A wet welds are possible on suitable steels with qualified procedures but are not the default assumption.

This matters because the class society, not the contractor, decides what the weld is worth. The procedure and the welder qualification both have to be approved before work starts, on the specific joint configuration and material. A quotation that does not name the intended AWS class, or does not confirm the procedure is already accepted by the attending society, is quoting a repair whose status nobody has agreed.

Underwater Cutting: Exothermic, Mechanical and Hydraulic

Exothermic cutting is the workhorse. An oxygen-fed rod burns through steel of considerable thickness quickly and works in near-zero visibility, which is why underwater cutting on damaged structure almost always starts here. It is also the method with the most safety constraints: an enclosed space behind the plate can trap gas, and the pre-cut survey exists to establish what is on the other side.

Mechanical cutting - hydraulic saws, grinders, shears - is slower but produces a controlled edge and no heat, which is what a repair joint needs when new steel will be welded to it. Abrasive water jet cutting sits between the two and is used where heat is prohibited outright, as on a gas carrier or alongside a live pipeline. The method is chosen against the hazard and the intended follow-on work, not against speed alone; a fast cut that leaves an edge nobody can weld to has cost the vessel a day.

Temporary Repair or Permanent Repair

Most in-water welding on merchant ships is agreed as a temporary repair with a time limit - valid until the next scheduled docking, or for a stated number of months, recorded as a condition of class. That is not a lesser outcome; it is usually the intended one, because it converts an unplanned docking into a planned one.

Deciding otherwise raises the specification sharply. A permanent repair generally means dry conditions at the joint, an approved procedure to the corresponding AWS class, and post-weld inspection to match. Where the damage is extensive enough that neither option holds, the work goes ashore, and a steel workshop at a repair yard takes it. The diving team's measurement and video file is what lets that decision be made from the office rather than after the ship arrives.

Diver-Welder Qualification and Contractor Approval

Two separate qualifications sit behind a valid weld, and enquiries routinely confuse them. The diver-welder is qualified under AWS D3.6M by welding test coupons in conditions representing the job, and holds commercial diving competence separately under ADCI Consensus Standards, IMCA D014, or OSHA 29 CFR 1910 Subpart T according to region. The contractor is approved by a classification society as a service supplier, for a defined scope. The individual's certificate does not substitute for the firm's approval, and the firm's approval does not cover a welder who has not passed the relevant test.

Verification after welding is a third capability again. Visual inspection by the diver is the minimum; anything load-bearing normally calls for underwater NDT, and a contractor who can deliver both in one attendance saves the vessel a second mobilisation.

Emergency Mobilisation and What to Establish First

Welding is the one scope in this trade most often bought under time pressure, and the enquiry usually arrives with a vessel already alongside. What separates a contractor who can help from one who cannot is rarely equipment - it is whether procedures are pre-approved and a team is within reach.

• Class society approval as a service supplier, named per society, and confirmation that the welding procedure is already accepted for the material and joint in question.
• Diver-welder qualifications to AWS D3.6M with current dates, and the class the procedure is qualified to.
• Intended repair status stated in the quotation - temporary with a stated period, or permanent - rather than left for the surveyor to determine afterwards.
• Pre-cut survey included where cutting is involved, so what sits behind the plate is established before a torch is lit.
• Post-weld inspection scope: visual only, or NDT, and who carries it out.
• Genuine presence in the port, with the diving spread and welding sets local rather than flown in.
• Mobilisation time quoted in hours from instruction, and what triggers standby charges.
• Where the damage may be worse than the photographs show, the extended scope priced as an option in advance.

Damage assessment normally precedes all of it. Where the extent is not yet known, the first attendance is an underwater inspection, and the welding scope is written from what it finds rather than from the master's initial report.

Underwater Welding Companies by Country

This work is bought where the ship is, and almost never worth mobilising across a region. A contractor with a diving spread and welding sets standing in the port can be in the water the same day; the same firm two countries away is a week and a flight, by which time the vessel has often sailed with a temporary fix or gone to a yard.

• Underwater Welding Companies in Oman
• Underwater Welding Companies in Egypt
• Underwater Welding Companies in New Zealand
• Underwater Welding Companies in Bahrain
• Underwater Welding Companies in the Philippines
• Underwater Welding Companies in Mauritius

Frequently Asked Questions

What is the difference between wet welding and hyperbaric welding?

Wet welding is done directly in the water with waterproofed electrodes on direct current. Hyperbaric welding is done dry, inside a chamber or habitat sealed against the structure. Wet is faster and mobilises anywhere; hyperbaric gives weld properties comparable to shop work and costs accordingly.

Is an underwater weld accepted as a permanent repair?

Sometimes, but most in-water welding on merchant ships is agreed as a temporary repair valid until the next docking or for a stated period, recorded as a condition of class. The status has to be agreed with the attending society before work starts, not established afterwards.

What standard applies to underwater welding?

AWS D3.6M, the underwater welding code, which sorts welds into classes by required properties. Class A is intended to be comparable to a surface weld; Class B accepts lower ductility. Both the welding procedure and the individual welder have to be qualified to the class the repair needs.

How quickly can an underwater welding company mobilise?

Within hours if the contractor holds a diving spread and welding sets in the port and its procedures are already class-accepted. Across a region it is days. This is why the practical shortlist is built by port rather than by company size.

What can be cut underwater?

Exothermic cutting handles thick steel quickly and works in near-zero visibility. Mechanical cutting gives a controlled edge for joints that will be welded afterwards. Water jet cutting is used where heat is prohibited, as on gas carriers. A pre-cut survey establishes what sits behind the plate first.