Underwater Welding Information
The British Admiralty Dockyard, were the first to use underwater welding. They used it for sealing ship rivets which were below the water. Underwater welding is an important tool for repair of off-shore ships, oil platforms, drilling rigs, pipelines and for fabrication of structures below the water surface. It is mostly performed on steel materials and for welding purpose special waterproof electrodes are used, which were developed by ‘Van der Willingen’ of Holland in 1946.
There are two types of hyperbaric underwater welding:
a. Wet welding.
b. Dry welding.
A brief description of the two methods of welding are given below.
It is done in wet environment and uses manual metal arc welding (MMA). Welding is done as one does in normally open air with the help of special electrode. It is the most effective, economical and efficient method of welding due to more freedom of movement. The power supply used in wet welding is direct current (DC) with negative polarity. The use of DC with positive polarity will cause electrolysis and in turn rapid deterioration of electrode in the electrode holder will take place. Alternate current (AC) supply is not used, as AC cannot sustain the arc underwater and due to electrical safety issues.
Advantages of underwater wet welding:
1. Desirable due to versatility and low cost.
2. Speed with which work is carried out.
3. Less costlier than dry underwater welding.
4. No enclosures are required.
5. Standard welding equipment’s and machine are used.
It is carried out in a dry chamber, completely sealed around the structure to be welded and uses gas tungsten arc welding.
The sealed chamber, at the prevailing pressure is filled with helium gas containing 0.5 bar of oxygen. A habitat is sealed on-to the chamber with a breathable mixture of helium and oxygen and at the desired pressure so as to facilitate welding to take place. This produces high quality welds.
Advantages of underwater dry welding:
a. Welder safety is more as welding in performed in a chamber, with warm,dry habitat and well illuminated – having ECS (environment control system).
b. Welds done are of good quality and also the immediate quenching effect of water and hydrogen level is less as compared to wet welding.
c. Non-destructive testing can be done due to dry habitat.
d. Visual monitoring of alignment and joint preparation is possible.