underwater weldingPresentation water.pptx

underwater

1. A POWER POINT PRESENTATION ON UNDER WATER WELDING

2. SLIDE PLAN ABOUT UNDER WATER WELDING CLASSIFICATION OF UNDER WATER WELDING POWER SUPPLY AND INSTALLATION OF DIFFERENT UNDERWATER WELDING PROCESSES ADVANTAGES AND DISADVANTAGES OF DIFFERENT TYPES OF UNDER WATER WELDING LITERATURE SURVEY ON THE BASIS OF METALLURGICAL PURPOSE RISK INVOLVED DEVELOPMENT AND FUTURE SCOPE FOR UNDER WATER WELDING CONCLUSION

3. INTRODUCTION FIRSTLY USED- In 1946, special water proof electrodes were develop in Holland by “Van der Willengen”. In recent years the number of offshore structures including oil drilling rings, pipelines, and platforms are being installed significantly. Welding is an unavoidable process of modern engineering, like civil, mechanical, electrical, automobile, marine and aeronautical etc. If damaged ships are to be repaired, underwater welding is the basic technology to be used . UNDER WATER WELDING- It is a highly-specialized technique – mostly employed in the oil or shipping industry and also in the defence operations. Most ship repair and welding jobs are carried out at a shallow depth, the most technologically challenging task is repair at greater depths, especially in pipelines and repair of accidental failure. The advantages of underwater welding are largely of an economic nature, because underwater-welding for marine maintenance and repair jobs bypasses the need to pull the structure out of the sea and saves valuable time and dry docking costs.

4. CLASSIFICATION OF UNDER WATER WELDING Basically under water welding process classified in two different ways according to their installation process, they are 1. WET WELDING – In wet welding, Welding process performed under water, directly exposed to the wet environment. Drivers usually use around 300-400 amps of direct to power their electrode, and use varied form of arc welding. 2. DRY WELDING – Another name of Dry welding is Hyperbaric welding , basically carried out in helium gas filled pressurized chamber.

5. POWER SUPPLY AND INSTALLATION FOR WET WELDING PROCESS WET WELDING - Wet welding performed in under water and directly exposed to the wet environment. Here Welding power supply is located on the surface with connection to the driver/welder via cables and hoses. In wet welding MMA( manual metal arc welding) is used.

6. POWER SUPPLY AND INSTALLATION FOR DRY WELDING PROCESS DRY WELDING- In dry welding or Hyperbaric Welding in a pressurized chamber containing helium and 0.5 bar of oxygen. This method produces high-quality weld joints that meet X-ray and code requirements. The gas tungsten arc welding process is employed for this process. Special control techniques have been applied which have allowed welding down to 2,500 m (8,200 ft.) simulated water depth in the laboratory, but dry hyperbaric welding has thus far been limited operationally to less than 400 m (1,300 ft.) water depth by the physiological capability of divers to operate the welding equipment at high pressures and practical considerations concerning construction of an automated pressure/ welding chamber at depth.

7. ADVANTAGES AND DIS ADVANTAGES OF WET WELDING ADVANTAGES OF WET WELDING 1. The versatility and low cost of wet welding makes this method highly desirable. 2. Other benefits include the speed, with which operation carried out. 3. The welder can reach location of offshore structures that could not be welded using other methods. 4. No enclosures are needed and no time is lost building. Readily available standard welding machine and equipment’s are used. The equipment needed for mobilization of a wet welded job is minimal . DISADVANTAGES OF WET WELDING 1. Hydrogen Embrittlement – Large amount of hydrogen is present in the weld region, resulting from the dissociation of the water vapour in the arc region. The H2 dissolves in the Heat Affected Zone (HAZ) and the weld metal, which causes Embrittlement, cracks and microscopic fissures. Cracks can grow and may result in catastrophic failure of the structure . 2. The welder sometimes is not able to view HAZ, for this welding does not do properly.

8. ADVANTAGES AND DISADVANTAGES OF DRY WELDING ADVANTAGES OF DRY WELDING 1. Welding is performed in a chamber, immune to ocean currents and marine animals. The warm, dry habitat is well illuminated and has its own environmental control system ( ECS ). 2. Joint preparation, pipe alignment, NDT inspection, etc. are monitored visually . 3. Non destructive testing(NDT) is also facilitated by the dry habitat environment. DISADVANTAGES OF DRY WELDING 1. Cost of habitat welding is extremely high and increases with depth. Work depth has an effect on habitat welding. At greater depths, the arc constricts and corresponding higher voltages are required. The process is costly – an $ 80000 charge for a single weld job. One cannot use the same chamber for another job, if it is a different one . 2. The habitat welding requires large quantities of complex equipment and much support equipment on the surface. The chamber is extremely complex.

9. LITERATURE SURVEY Xinjei Di et al. Quenched and tempered E550 steel was joined using flux-cored arc welding. The effect of cooling rate on microstructure, inclusions and mechanical properties of the weld metal was investigated by optical microscope, scanning electron microscope, transmission electron microscope and mechanical testing. Results show that weld metal microstructures consist of proeutectoid ferrite, ferrite side plate and acicular ferrite. As the cooling rate increased, the volume fraction of pro-eutectoid ferrite and ferrite side plate decreased, acicular ferrite increased accompanied with refined grain. Furthermore, inclusions of Ti, Mn oxide with diameter below 2.0 μm were found in the weld metal and rapid cooling rate causes distinct Mn-depleted zone between inclusions and matrix .

10. RISKS INVOLVED There is a risk to the welder/diver of electric shock. Precautions include achieving adequate electrical insulation of the welding equipment, shutting off the electricity supply immediately the arc is extinguished, and limiting the open-circuit voltage of MMA (SMA) welding sets . The welder has to take precaution because nitrogen will be built up in the blood stream of the welder, when exposed to air at high-pressure under the water surface. Inspection, although very difficult, is a mandatory requirement. No defects should remain. In addition to all these precautions, safe arc-welding precautions are to be taken . The welder has to protect himself from electric shocks. The welder has to be insulated. The voltage of the welding sets has to be controlled. Pockets of oxygen and hydrogen built up by the arc will be potentially explosive.

11. DEVELOPMENT AND FUTURE SCOPE IN UNDER WATER WELDING Wet MMA is still being used for underwater repairs, but the quality of wet welds is poor and are prone to hydrogen cracking. Dry Hyperbaric welds are better in quality than wet welds. Present trend is towards automation. THOR – 1 (TIG Hyperbaric Orbital Robot) is developed where diver performs pipefitting, installs the track and orbital head on the pipe and the rest process is automated. Mechanized underwater welding for actual usage of a very large floating structures . Investigation of the potential of using a robot manipulator for underwater ultrasonic testing of welds in complex geometry. Application of advanced welding technique, like friction, laser welding should be understand the behaviour of Materials after the welding and process optimization . Invention of new welding techniques and explore the possibility of its application in underwater welding.

12. CONCLUSION Wet welding is still being used for under water repair, but the quality of wet welding is poor than dry welding, the Dry welding is costlier than Wet welding. Underwater welding is mostly employed in marine engineering product in installation of oil and gas rigs. The most common underwater welding process, known as manual metal arc building (MMA), is employed for deep water repairing activities . Precautions must be taken to avoid the build-up of pockets of gas, which are potentially explosive. The other main area of risk is to the life or health of the welder/diver from nitrogen introduced into the blood steam during exposure to air at increased pressure. Precautions include the provision of an emergency air or gas supply, stand-by divers, and decompression chambers to avoid nitrogen narcosis following rapid surfacing after saturation diving.

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