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Welding and cutting under water sound dramatic, but in practice they are careful, slow and well-planned jobs. Underwater welding and cutting in Nagoya is carried out by trained divers using proven methods, and with a safety plan that is written before anyone enters the water.
The most common method is shielded metal arc welding with waterproofed electrodes, used for wet welding. The electrode is coated so that the arc burns in a small gas bubble that protects the weld. The Diver works with a ground clamp attached to the plate, and the current is switched on only when he calls for it. For higher quality work, dry welding in a habitat or cofferdam is used, and the weld is made in a dry environment.
For cutting steel, a Diver can use an oxy-arc torch, which burns a hollow electrode in a stream of oxygen, or an exothermic cutting rod, which burns at very high temperature in water. Other tools include hydraulic shears, saws and abrasive wheels. The choice depends on the thickness, the shape and the safety conditions. Cutting is often needed to remove damaged plates, bent fittings, ropes or pieces of wreckage.
One of the main risks of hot work in water is trapped gas. Cutting or welding can create hydrogen and oxygen pockets under a plate or inside a hollow structure. If these ignite, the result can be an explosion. We vent any enclosed space, avoid cutting into closed compartments without checking, and follow our written procedure. Tank spaces behind the plate must be gas-freed and certified before hot work is permitted.
Water conducts electricity, so equipment must be designed and maintained for the job. We use insulated cables, switches that cut power at the surface, and a trained supervisor who controls the current. The ship's own cathodic protection and impressed current system may be switched off during welding. The Diver is never in contact with live equipment unless the supervisor has cleared it.
Hot work on a ship's Hull needs a hot work permit from the master and, where the work affects structure, the class society's approval. We provide the welding procedure, the Diver's qualification and the equipment records. The surveyor can attend the dive and watch the work on CCTV.
Tell us the ship's name, the location of the work and the aim. We inspect first, produce a plan and arrange the permit and the surveyor. Welding and cutting can then be done in a short window, and the result is recorded on video.
Welding and cutting divers need training beyond ordinary diving, and their equipment needs regular inspection. Cables, torches, electrodes and switches are checked before each job, and the supervisor keeps a log. We will show the surveyor the records if he asks. This is part of what class societies expect from a contractor doing hot work on a ship's Hull, and it is why we do not offer these services on short notice without proper preparation.
Wet welding quality depends on water conditions. Strong current can disturb the arc, and poor visibility makes it hard to see the joint. We check conditions before starting and wait for better ones if needed.
Q1. Which welding method is used for most wet welding?
Shielded metal arc welding with waterproofed electrodes. The coated electrode creates a small gas bubble that protects the weld.
Q2. What is the main hazard in underwater cutting?
Trapped hydrogen and oxygen gas under plates or in hollow structures, which can ignite. We vent enclosed spaces and follow a written procedure.
Q3. Does the ship’s cathodic protection need to be switched off?
The ship’s impressed current system may be switched off during welding, as agreed with the chief engineer and the supervisor.
Q4. Who issues the hot work permit?
The master issues the hot work permit. For structural repairs, the class society also reviews the plan.
