UNDER WATER WELDING

The Welding is an unavoidable process of modern engineering – civil, electrical, mechanical, automobiles, marine aeronautical – in all branches. It is used in fabrications and erections in infrastructures and installations. It joins metals or thermoplastics. The Hyperbaric welding OR UNDER WATER WELDING is the process of welding at elevated pressures, normally in underwater. It is of 2 types DRY & WET Welding. The Hyperbaric welding can either take place wet in the water itself OR dry inside. Here a specially constructed positive pressure enclosure is used and hence it is called dry welding. Similarly Hyperbaric welding term used in dry environment & underwater welding term used as in wet environment. The hyperbaric welding is used to repair damaged ships, under water pipe line & etc.

 

The fact that electric arc could operate was known for over a 100 years. The first ever underwater welding was carried out by British Admiralty – Dockyard for sealing leaking ship rivets below the water line.
Underwater welding is an important tool for underwater fabrication works. In 1946, special waterproof electrodes were developed in Holland by ‘Van der Willingen’. In recent years the number of offshore structures including oil drilling rigs, pipelines, platforms are being installed significantly. Some of these structures will experience failures of its elements during normal usage and during unpredicted occurrences like storms, collisions. Any repair method will require the use of underwater welding.


CLASSIFICATION OF UNDERWATER WELDING

The Underwater welding can be classified as:

1) Wet Welding: In wet welding the welding is performed underwater, directly exposed to the wet environment.
2) Dry Welding: In dry welding, a dry chamber is created near the area to be welded and the welder does the job by staying inside the chamber

 

COMPONENTS OF WATER WELDING
Electrode Holder - This new generation compression type welding stinger is engineered with features that let you know it’s from Broco. Lightweight, durable and designed to hold the electrode at the optimum angle to reduce diver fatigue. The new BR-21... Setting the wet welding standard.

Water Resistant Electrodes - The fundamental process of welding underwater does not differ from welding on land. An electrode carrying a direct current creates an arc of electricity. That arc is then applied to melt the target metal. The difference is that the electrodes used underwater are waterproof. Extra insulation around the connections ensure that the current will be able to generate the arc and not degrade the copper wiring. Doing this underwater presents a new set of risks. Both the risk of electrocution and the technical difficulty of maintaining the electrical arc underwater, is the reason why direct currents are used instead of alternating currents.

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The power source should be a direct current machine rated at 300 or 400 amperes. Motor generator welding machines are most often used for underwater welding in the wet. The welding machine frame must be grounded to the ship. The welding circuit must include a positive type of switch, usually a knife switch operated on the surface and commanded by the welder-diver. The knife switch in the electrode circuit must be capable of breaking the full welding current and is used for safety reasons. The welding power should be connected to the electrode holder only during welding. Direct current with electrode negative (straight polarity) is used. Special welding electrode holders with extra insulation against the water are used. The underwater welding electrode holder utilizes a twist type head for gripping the electrode. It accommodates two sizes of electrodes. The electrode types used conform to AWS E6013 classification. The electrodes must be waterproofed. All connections must be thoroughly insulated so that the water cannot come in contact with the metal parts. If the insulation does leak, seawater will come in contact with the metal conductor and part of the current will leak away and will not be available at the arc. In addition, there will be rapid deterioration of the copper cable at the point of the leak.