UNDERWATER WELDING

Underwater welding is the ideal solution for restoring repairing damage to vessels with ruptures, cracks, etc. because it provides speediness with low repair costs. Underwater welding is used for ships for temporary or permanent repairs of cracks in the hull of the ship, for the installation of anodic protection, for temporary repair of cracks on rudder and rudder blades. 

 

In DIVING TASK underwater welding is divided into two areas wet welding and dry welding. Wet underwater welding is the direct exposer of the diver and electrode to the wet environment and is widely used for many years for underwater repairs. 

The diver is dressed in a proper diving suit, depending on the method of diving that he carries out and depending on the water temperature that he will dive. He also wears rubber gloves for protection from the electricity and special filters on the diving mask for eye protection from the radiation of the electric arc. The equipment required is the same as those used on the surface. 

 

The only difference is that in the wet welding the electrode must be waterproof. Commonly used method for wet welding is the shielded metal arc welding (SMAW) also known as manual metal arc welding (MMA or MMAW), which is done with fully insulated waterproofed electrode holder designed for water and (waterproofed) stick electrodes’ coated with a flux that releases gases to preserve the integrity of the weld. The welding power supply is connected to the welding equipment through cables and hoses which give direct current around 300 – 400 amps to power the electrode. 

 

The electric arc heats the work-piece and the welding rod, whilst the molten metal is transferred through the gas bubble around the arc. The gas bubble is partly formed from the decomposition of the flux coating on the electrode but it is usually contaminated to some extent by steam. Current flow induces transfer of metal droplets from the electrode to the work-piece and enables positional welding by a diver. 

Welding Procedure 

  • Inspection of damage to determine whether the welding can be performed safely and effectively

  • Cleaning of marine growth and coating or other foreign matter on damaged area and proximity where the welds will be placed

  • Cropping and smoothing out of damaged sections

  • Welding of a double plate with specially treated waterproof electrodes and fully insulated waterproofed electrode holder

  • Welding of flat bars

  • Application of underwater epoxy resin on all the welds for protection in order to reduce metal wastage

Advantage of Wet Welding

  • The flexibility of the diver, who can reach inaccessible parts of the ship, with which other methods is impossible.

  • Faster execution of work.with low expenses.

  • Time-saving, since the equipment required is minimised and does not require a chamber to be structured.

  • The possibility for non-destructive testing (NDT) * of welding and the ability to monitor the entire process from cameras placed underwater (NDT inspections).