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Review Paper on Under Water Welding International Journal of Mechanical and Production Engineering, ISSN(p): 2320-2092, ISSN(e): 2321-2071 Volume- 7, Issue-6, Jun.-2019, http://iraj.in REVIEW PAPER ON UNDER WATER WELDING 1PIYUSH SEHGAL, 2NEERAJ KUMAR 1Student, Rayat Bahra University, Kharar, Punjab, India 2Asstt. Professor, Rayat Bahra University, Kharar, Punjab, Indi E-mail: [email protected] Abstract - Welding in offshore and marine application is an area of research and understanding where, many problems are still unsolved. In the present paper, a brief classification of underwater welding is made, the principals involved and the advantages and disadvantages of the various types of underwater welding are described. Finally, the scope of further research has been recommended. In the present paper, a brief description of the different commercial underwater techniques has been made. The problems in underwater welding have also been discussed in context to the existing welding techniques. Detailed description of a few advanced welding techniques has also been made. Finally, the scope of further research has been recommended. Keywords - Welding Techniques; Marine Application. I. INTRODUCTION are needed. These include lighting, staging and hand tools. The fact that electric arc could operate was known for There are advantages to wet welding. The underwater over a 100 years. The first ever underwater welding welder can work freely on any portion of complex was carried out by British Admiralty – Dockyard for structures or on sections with restricted access, sealing leaking ship rivets below the water line. whereas other underwater techniques may encounter Underwater welding is an important tool for difficulties. Patching can be performed faster and at underwater fabrication works. In 1946, special less cost because no time is lost in construction and waterproof electrodes were used by ‘Vander installation of enclosures. Because standard welding Willingen’ with a substantial amount of iron powder power sources and equipment are used, a wet welding in its flux coating. In recent years the number of job can be easily mobilized at remote job sites. Wet offshore structures including oil drilling rigs, welding also allows more freedom of patch design pipelines and platforms are being installed and size of patch sections. significantly. Some of these structures will experience failures of its elements during normal Fig.1 shows the schematic diagram of wet welding usage and during unpredicted occurrences like process. storms, collisions. Any repair method will require the use of underwater welding. II. UNDERWATER WELDING CLASSIFICATION Underwater welding can be classified in to two types as follows: 1) WET UNDERWATER WELDING 2) DRY UNDERWATER WELDING 1) WET UNDERWATER WELDING Fig. 1 Wet under water welding is considered as the welding at the ambient pressure where there is no mechanical Power supply used: DC barrier between welder and surrounding water. MIG, Polarity: Negative (-ve) polarity TIG and PLASMA arc welding is more promising because of arc stability and high heat content in the When DC is used with positive (+ve) polarity arc. electrolysis takes place and cause rapid deterioration of any metallic components in the electrode holder. The wet welding process used for salvage operations The power source should be a DC machine at 300 or is usually a simple underwater joining technique. 400 amperes. The materials required are commercially For wet welding AC is not used on account of manufactured shielded metal arc equipment and electrical safety and difficult in maintaining of arc in waterproofed electrodes. Minimal ancillary devices water. Review Paper on Under Water Welding 1 International Journal of Mechanical and Production Engineering, ISSN(p): 2320-2092, ISSN(e): 2321-2071 Volume- 7, Issue-6, Jun.-2019, http://iraj.in PRINCIPLE OF OPERATION OF WET 2) DRY UNDERWATER WELDING WELDING Dry water welding is considered as welding in dry Work to be welded is connected to one side of an ambient atmosphere or hyperbaric pressure where electric circuit and a electrode on other side. welder diver is separated from the surrounding water When electrode touches the work piece the current by means of mechanical barrier which could be jumps the gap and causes a arc, which melts the bare designed as several alternatives as follows:- metal, which forms a weld pool. At the same time tip of electrode is melt and metal DRY WELDING IN A HABITAT droplets are projected into weld pool. Welding can be done at ambient pressure in During the operation flux which is covering the melt a large chamber from which water was electrode provides shielding of gas, used to stabilize displaced and where such atmosphere is the arc column and shield the transfer metal. achieved that welder has no need to use Arc burns in the cavity formed inside flux, which is diving equipment. designed to burn slower than the metal barrel of DRY WELDING AT ONE electrode. ATMOSPHERE Welding can be done in pressure vessel in which pressure is reduced to one atmosphere which is independent of water depth DRY SPOT WELDING Welding at ambient pressure in a small transparent, gas willed enclosure withthe welder outside in the water. It uses TIG and MIG welding. TIG is preferred as it gives stable arc and less porous welds. DRY CHAMBER WELDING Welding at ambient pressure in a simple open bottomed dry chamber that at least accommodates the head and shoulder of diver-welder in full diving equipment. Fig.2 Fig.3 shows the schematic diagram of dry welding process. Advantages The versatility and low cost makes this method desirable. The operation is carried out with speed. It is cheaper than dry welding. Readily available standard welding machine and equipment are used. The mobilization of equipments is minimal. Welder can reach portions of offshore Fig.3 structures easily. PRINCIPLE OF OPERATION OF DRY WELDING Disadvantages Underwater welding in a dry environment makes There is rapid quenching of the weld metal possible by encompassing the area to be welded with due to surrounding water. Quenching a weld chamber that excludes water. The weld increases the tensile strength, decreases the chamber is designed and custom built to ductility and impact strength of weldment accommodate braces and other structural members and increase porosity and hardness. whose centerlines may intersect at or near the area Large amount of hydrogen is present in the that is to be welded. The chamber is usually built of weld region resulting from the dissociation steel, rubberized canvas, but plywood etc. or other of the water vapours in the in the arc region. suitable material. Size and configuration of the The H2 dissolves in HAZ (Heat Affected chamber are determined by dimensions and geometry Zone) and the weld metal causes of the area that must be encompassed and the number Embrittlement and cracks. Cracks may result of welders that will be working in the chamber at the in catastrophic failure of the structure. same time. Water is placed from within the chamber Due to poor visibility sometimes welder is by air or a suitable gas mixture, depending upon not able to weld properly. water depth and pressure at the work site. Buoyancy of the chamber is offset by ballast, by mechanical Review Paper on Under Water Welding 2 International Journal of Mechanical and Production Engineering, ISSN(p): 2320-2092, ISSN(e): 2321-2071 Volume- 7, Issue-6, Jun.-2019, http://iraj.in connections and chamber to the structure, or by a Diver inhales harmful gases when he dives quickly combination of both. from high pressure zone to low pressure zone. If dive too fast to surface of water nitrogen bubbles HYPERBARIC WELDING enters in bloodstream and show numerous adverse Hyperbaric welding is the process of welding at symptoms. elevated pressures, normally underwater. It can It may lead variably to rashes, joint pain, paralysis or either take place wet in the water itself or dry inside a even death. specially constructed positive pressure enclosure and Breakdown of Dental Amalgam hence a dry environment. When used in a dry As a result a metallic taste in the mouth. In the environment it is referred as "hyperbaric welding". process of electric under water welding a magnetic This welding is carried out in chamber sealed around field with alternating current is created. This the structure be welded. The chamber is filled with a magnetic field in turn induces a secondary current in gas (commonly helium containing 0.5 bar of oxygen) the oral tissues due to dental amalgam breaks down. at the prevailing pressure. The habitat is sealed onto the pipeline and filled with a breathable mixture of IV. APPLICATIONS helium and oxygen, at or slightly above the ambient pressure at which the welding is take place. This Offshore construction for tapping sea method produces high-quality weld joints. For this resources. process gas tungsten arc welding is employed. The Temporary repair work caused by ships area under the floor of the Habitat is open to water. collisions or unexpected accidents. Thus the welding is done in the dry but at the Repair and maintenance of underwater hydrostatic pressure of the sea water surrounding the pipelines. Habitat. Construction of large ships beyond the In 1932, the Russian metallurgist Konstantin Khrenov capacity of existing docks. was invented underwater hyperbaric welding. Repair and maintenance of ships. Salvaging vessels sunk in the sea. Advantages Better safety. V. CONCLUSION Better quality welds. No build up of hydrogen and oxygen Proper training is necessary for under water pockets. welding. Allows for heat treatment before and after Welding should only be carried out by welding. experienced welders. Non destructive testing. Wet welding is being used for under water Surface monitoring possible. repairs, but the quality of wet welding is Disadvantages poor than dry welding. Requires large and complex equipments. Dry welding is costlier than wet welding.
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