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UNDERWATER WELDING

A concise presentation about underwater welding. It briefly discusses about the main types, risks involved and practices involved in underwater welding

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UNDERWATER WELDING

  1. 1. UNDERWATER WELDING SUBMITTED BY ALEN JOSE B120007ME RAMGOPAL G B120027ME RIJO JOSE
  2. 2. HOW TO WELD HERE?
  3. 3. NOT A GOOD SOLUTION
  4. 4. WHAT IS UNDERWATER WELDING ?
  5. 5. VERY HIGH PRESSURE VERY LOW TEMPERATURE WET , GAS DISSOLVED IN WATER In these conditions, normal welding is impossible Underwater welding method enables us to weld properly under these conditions.Underwater welding is an important tool for underwater fabrication works
  6. 6. HISTORY • 1930s: Russian metallurgist Konstantin Khrenov made the first underwater weld - in lab tests. • The first ever underwater welding was carried out by British Admiralty – Dockyard for sealing leaking ship rivets below the water line. In 1946, special waterproof electrodes were developed in Holland by Van der Willingen. • 1970s: Whitey Grubbs and Dale Anderson of Chicago Bridge & Iron (CB&I) qualified an underwater wet welding procedure to American Welding Society (AWS) standards.
  7. 7. CLASSIFICATION Underwater welding can be classified as 1) Wet Welding 2) Dry Welding • In wet welding the welding is performed underwater, directly exposed to the wet environment. • 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.
  8. 8. WET WELDING • As the name implies, underwater wet welding is done in an environment where the base metal and the arc are surrounded entirely by water. In wet welding MMA (manual metal arc welding) is used • increased freedom of movement makes wet welding the most effective, efficient and economical method • Welding power supply is located on the surface with connection to the diver/welder via cables and hoses. video
  9. 9. Power Supply used : DC • Polarity : -ve polarity When DC is used with +ve polarity, electrolysis will take place and cause rapid deterioration of any metallic components in the electrode holder. • For wet welding AC is not used on account of electrical safety and difficulty in maintaining an arc underwater. • The power source should be a direct current machine at 300 or 400 amperes
  10. 10. Principle of operation of Wet Welding  Work to be welded is connected to one side of an electric circuit, and a metal electrode to the other side. These two parts of the circuit are brought together, and then separated slightly.  The electric current jumps the gap and causes a sustained spark (arc), which melts the bare metal, forming a weld pool.  At the same time, the tip of electrode melts, and metal droplets are projected into the weld pool.  During this operation, the flux covering the electrode melts to provide a shielding gas, which is used to stabilize the arc column and shield the transfer metal.  The arc burns in a cavity formed inside the flux covering, which is designed to burn slower than the metal barrel of the electrode.
  11. 11. Advantages of Wet Welding  The versatility and low cost of wet welding makes this method highly desirable.  Other benefits include the speed with which the operation is carried out.  It is less costly compared to dry welding.  The welder can reach portions of offshore structures that could not be welded using other methods.  No enclosures are needed and no time is lost building. Readily available standard welding machine and equipments are used. The equipment needed for mobilization of a wet welded job is minimal.
  12. 12. Disadvantages of Wet Welding  There is rapid quenching of the weld metal by the surrounding water. Although quenching increases the tensile strength of the weld, it decreases the ductility and impact strength of the weldment and increases porosity and hardness.  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 퐻2 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.  Another disadvantage is poor visibility. The welder some times is not able to weld properly.
  13. 13. Figure showing schematic diagram for underwater welding.
  14. 14. DRY WELDING  Inside a specially constructed positive pressure enclosure and hence a dry environment.  Use for high quality welds as more control over conditions  Involves the weld being performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded.  Most arc welding processes such as shielded metal arc welding (smaw), flux-cored arc welding (fcaw), gas tungsten arc welding (gtaw), gas metal arc welding (gmaw), plasma arc welding (paw) could be operated at hyperbaric pressures. video
  15. 15. METHODS USED  Pressure Welding: Working in a pressure vessel measuring one atmosphere unit of pressure (same as pressure at sea level).  Habitat Welding: Using a chamber in ambient pressure (same as surrounding pressure at working depth) about the size of a small room to weld. Before entering, the chamber displaces its water the surrounding ocean or lake.  Dry Chamber Welding: It is habitat welding, but with a smaller chamber. The chamber holds the head and shoulders of a diver (dressed in diving gear) and is open at the bottom for the to fit in.  Dry Spot Welding: Here the habitat is even smaller. The habitat shrinks to the size of about the welder-diver’s head, and it’s completely clear. It’s placed on the weld site and the welder-inserts his or her electrode inside the habitat, which seals around
  16. 16. ADVANTAGES  Better diver safety  Better quality welds No build up of hydrogen and oxygen pockets  Allows for heat treatment before and after welding  Non destructive testing  Surface monitoring possible
  17. 17. DISADVANTAGES  Requires large, complex equipment. Chamber has to be fabricated differently for different applications  Cost is very high and increases with depth More energy requirement
  18. 18. Application of underwater welding The important applications of underwater welding are: (a) Offshore construction for tapping sea resources, (b) Temporary repair work caused by ships collisions or unexpected accidents. (c) Salvaging vessels sunk in the sea (d) Repair and maintenance of ships (e) Construction of large ships beyond the capacity of existing docks. (f) Repair and maintenance of underwater pipelines.
  19. 19. DANGERS OF UNDERWATER WELDING 1.Chances of an Electric Shock • This happens when the welding equipment that is used is not adapted to work under the water. • The equipment should be tested properly, well-insulated and a waterproof electrode should be connected to it. 2.Possibility of an Explosion • The chances of such explosions are more in processes, wherein both, hydrogen and oxygen are involved, and may lead to the formation of numerous gas pockets. • during hyperbaric welding, the formation and combination of hydrogen and oxygen pockets is dangerous because they are explosive, when ignited..
  20. 20. 3.Decompression Sickness • Decompression sickness, also known as 'diver's disease • Diver inhales harmful gases such as nitrogen, when he dives quickly from a high pressure zone to a low pressure zone. • If the welder dives too fast to the surface of the water, nitrogen bubbles enters his bloodstream. These bubbles then spread inside the diver's body, and start showing numerous adverse symptoms. • Decompression sickness may lead variably to rashes, joint pain, paralysis or even death of a person. 4.Breakdown of Dental Amalgam • As a result a metallic taste in the mouth • Recent studies have shown that in the process of electric welding and cutting under the water, a magnetic field with alternating current gets created. This magnetic field, in turn, induces a secondary current in the oral tissues of the welders, due to which their dental amalgam breaks down.
  21. 21. Further developments • 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 • Developments of diver less Hyperbaric welding system is an even greater challenge in developments like pipe preparation and aligning, automatic electrode. • Explosive and friction welding are also to be tested in deep waters.
  22. 22. Thank you…

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