Process and Precautions in Underwater Welding

Underwater welding is carried out to repair pipelines, platforms, and other structures that are constructed in the deep, oceanic waters. The ScienceStruck post outlines the process and precautions in underwater welding.
ScienceStruck Staff
Last Updated: Jun 27, 2018
Welding is a fabrication process used for joining metals or thermoplastics. It helps establish a strong bond between the metal components. Generally, the material parts are melted and mixed with another material that acts as a 'filler'. This forms a molten liquid that is referred to as the 'weld pool'.
As this cools, it forms the finished product, which is a strong component. There are many welding techniques, prominent among them are gas tungsten arc welding, gas metal arc welding, submerged arc welding, etc. When this process is conducted on underwater structures, it is termed as underwater welding.
This process is even tougher than the regular welding and involves plenty of risks. Skilled experts are necessary to conduct this procedure, and many of them are employed in the oil or shipping industry and the military.
Classification
Wet Welding
  • It is carried on under the water, hence the name, 'wet welding'.
  • The process is similar to the regular welding process; here, a special electrode is used for the purpose.
  • The power supply, however, is not exposed to the water, it lies on the surface and is connected to the welder by means of hoses.
  • The AC is not used in wet welding due to the risks of electricity in the underwater scenario.
  • Thus, the DC is used in this case, and this sparks the electrolysis process.
  • The welder makes use of a knife switch to operate the circuit.
  • The electrode holders have special insulation and waterproofed.
  • Special care must be taken to ensure that the seawater does not come in contact with the metals, or else there is a possibility of current leakage.
  • This method is efficient and economical, costs less, and requires less time and planning.
Dry Welding
  • It is also called 'Hyperbaric welding'.
  • The structure to be welded is first sealed within an enclosed chamber.
  • Then, the chamber is filled with a gas at the required pressure.
  • The gas tungsten arc welding process is normally used here.
  • This is a very efficient method too, and produces high-quality results.
  • It is called 'dry welding' because the structure is not directly in contact with a wet source, but is in the natural hydrostatic environment.
  • The pressure within the chamber is set at a slightly higher level than the one at which the process will take place.
  • Important factors concerning the welding, like monitoring joint preparation, can generally be carried on at the surface itself.
Risks and Precautions
  • In case of wet welding, the risks include reduction of the ductility and impact of the weld, making it susceptible to porosity.
  • Since the process takes place in a wet environment, there is great risk of electric shocks.
  • In case of dry welding, the equipment cost is tremendous, since the construction of the chamber itself is a huge, complicated process.
  • Moreover, cost increases with the water depth, and the same chamber can be very rarely used again.
  • Adequate precaution must be taken by the welder. For instance, he needs to wear shock-proof attire and other insulation.
  • Care must be taken to limit the voltage of the welding sets.
  • When exposed to high pressure under the water, nitrogen is generated in the bloodstream, which is highly dangerous. Adequate protection must be taken to prevent this.
  • Worst of all, this atmosphere is conducive to the formation of hydrogen and oxygen by the welding arc, and this may result in a huge explosion, destroying human life and other resources.
Even though the inspection concerned with underwater welding is difficult, it must be compulsorily carried out. The weld must be inspected very carefully to confirm that no defects remain.