welding New trends


Published on

its is a simple view on under sea water welding mehods

Published in: Technology, Business
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

welding New trends

  2. 2. Abstract The process of joining together two pieces of metal-Welding is carried out by the use ofheat or pressure or both and with or without added metal-types of welding methods-under wateror under sea welding methods- 1.Dry welding 2.Wet welding. this welting process arise duringthe last world war an urgent need was felt for salvaging vessels sunk into the deep sea and thisneed raised the status of underwater welding from almost a pipe dream to a practical process.Moreover international interests to develop and utilize ocean which covers 70% of the earth andits resources such as development of offshore gas and oil field, fisheries multiplication, largeoffshore construction and mineral resources, mining in sea bottom etc. have led to thedevelopment of underwater welding. The interesting matter is an Underwater welder earns$100,000 to $200,000.
  3. 3. Introduction How under water welding arise Welding is a fabrication process that Russian metallurgist Konstantin Khrenovjoins metals or thermoplastics by using made the first underwater weld in 1930’s hecoalescence. Melting the work pieces and made simple experiments in his lab to bringadding a filler material to form a pool of out the new method in welding process. Themolten material known as the weld puddle first under water welding was carried out bythat cools to become a strong joint describes British Admiralty – Dockyard for sealingthe process of welding. This is in contrast to leaking in ship rivets below the water line.soldering and brazing which involves Underwater welding advanced throughmelting of a material with lower melting World War II, particularly during Pearlpoint material between the work pieces. Harbor salvage ops. Under water welding isWelding process is many types such as Solid an important tool for underwater fabricationstate Welding-Resistance Welding- works. In 1946, special waterproofSoldering-Oxyfuel gas welding-Brazing- electrodes were developed in Holland byother process such as Induction welding; Van der Willingen. In 1970’s Whiteyelectron beam welding, thermit welding, Grubbs and Dale Anderson of Chicagolaser beam welding and electro slag Bridge & Iron (CB&I) qualified anwelding. Other than this now there is an underwater wet welding procedure tointeresting topic that is underwater welding American Welding Society (AWS)or undersea welding. Underwater standards. In recent years the number ofwelding provides a means to assemble or offshore structures including oil drilling rigs,repair underwater. This is a highly useful pipelines and platforms are being installedtechnology available that allows repairs of significantly. Some of these structures willships damaged during hurricanes or wars. experience failures of its elements duringThere are a couple of alternatives available, normal usage and during unpredictedwhich include clamped and grouted repairs occurrences like storms, collisions. Anyand bolted flanges. However, these repair method will require the use ofalternatives do not always provide underwater welding.satisfactory results and also introduces highloading at offshore structures. This is a Under water Weldinghighly specialized trade and most people are Hyperbaric welding is the processemployed in the oil or shipping industry and of welding at elevated pressures,the military. normally underwater Hyperbaric weldingUnderwater welding process can be can either take place wet in the water itselfclassified into the following two categories: or dry inside a specially constructed positive pressure enclosure and hence a dry Wet Welding environment. It is predominantly referred to Dry Welding as "hyperbaric welding" when used in a dry environment, and "underwater welding" when in a wet environment. The
  4. 4. applications of hyperbaric welding are welding procedures and production weldingdivers. It is often used to repair ships, on materials with a relatively high carbonoffshore oil platforms, and pipelines. Steel is equivalent, up to 0.47%. The accepted normal upper limit is 0.40% using ferriticthe most common material welded. electrodes. The welding was carried out by aTypes of Underwater welding selected team of 20 coded wet welder divers, who’s variety of skills and commitment to There are two main categories in the the project was invaluable and who must beunderwater welding process which are; Wet commended. All of the wet welds were subjected to 100% visual inspection andWelding and Dry Welding. Wet Welding is MPI by the client with a 100% pass rate.performed underwater where the welding isbeing done while being exposed to water.Wet Welding is most effective as it provides Wet Welding indicates that welding isthe freedom of movement for the welder, performed underwater, directly exposed tobecause of this wet welding is efficient, the wet environment. A special electrode iseconomical and the most utilized choice for used and welding is carried out manually just as one does in open air welding. Therepair work underwater. increased freedom of movement makes wet welding the most effective, efficient andWet welding economical method. Welding power supplyHydroweld and Underwater Technical is located on the surface with connection to the diver/welder via cables and hoses.Services pooled their technical and Power Supply used: DCadministrative skills to successfully Polarity: -ve polaritycomplete a contract for DML (DevonportManagement Ltd), which carry out work on Principle of Wet Weltingbehalf of the MoD (Ministry of Defence). The process of underwater wet weldingThe project, the first ever of its kind, takes in the following manner:required the wet welding of over 40 The work piece to be welded is connected toblanking plates to the ballast tanks of a one side of an electric circuit, and a metalsubmarine, the largest being 2.6 x 1.2 electrode to the other side. These two partsmeters. The contract was completed on time, of the circuit are brought together, and thenin budget with no lost time accidents and at separated slightly. The electric currenta fraction of the cost of dry docking. jumps the gap and causes a sustained spark (arc), which melts the bare metal, forming aAll of the wet welding was completed weld pool. At the same time, the tip ofusing Hydro weld FS wet weldingelectrodes, which are the only underwater electrode melts, and metal droplets arewelding electrodes have been approved, by projected into the weld pool. During thisthe MoD, for permanent and temporary operation, the flux covering the electroderepairs to war ships. This project further melts to provide a shielding gas, which isproved the electrodes capabilities and used to stabilize the arc column and shieldwelding techniques used by Hydroweld, the transfer metal. The arc burns in a cavitythrough the successfully completion of wet formed inside the flux covering, which is
  5. 5. designed to burn slower than the metal come in contact with the metal parts. If thebarrel of the electrode. 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. We prefer Wet Welting method for When DC is used with +ve polarity, Wet underwater MMA welding has nowelectrolysis will take place and cause rapid been widely used for many years in thedeterioration of any metallic components in repair of offshore platforms. The benefits ofthe electrode holder. For wet welding AC is wet welding are: -not used on account of electrical safety and 1) The versatility and low cost of wetdifficulty in maintaining an arc underwater. welding makes this method highlyThe power source should be a direct current desirable.machine rated at 300 or 400 amperes. Motor 2) Other benefits include the speed. With which the operation is carried out.generator welding machines are most often 3) It is less costly compared to dryused for underwater welding in the wet. The welding.welding machine frame must be grounded to 4) The welder can reach portions ofthe ship. The welding circuit must include a offshore structures that could not bepositive type of switch, usually a knife welded using other methods.switch operated on the surface and 5) No enclosures are needed and no timecommanded by the welder-diver. The knife is lost building. Readily available standard welding machine andswitch in the electrode circuit must be equipments are used. The equipmentcapable of breaking the full welding current needed for mobilization of a wetand is used for safety reasons. The welding welded job is minimal.power should be connected to the electrode We oppose Wet Welting method forholder only during welding. Although wet welding is widely used forDirect current with electrode negative underwater fabrication works, it suffers from(straight polarity) is used. Special welding the following drawbacks: - 1) There is rapid quenching of the weldelectrode holders with extra insulation metal by the surrounding water.against the water are used. The underwater Although quenching increases thewelding electrode holder utilizes a twist type tensile strength of the weld, ithead for gripping the electrode. It decreases the ductility and impactaccommodates two sizes of electrodes. strength of the weldment and increases porosity and hardness.The electrode types used conform to AWS 2) Hydrogen Embrittlement – LargeE6013 classification. The electrodes must be amount of hydrogen is present in thewaterproofed. All connections must be weld region, resulting from thethoroughly insulated so that the water cannot dissociation of the water vapour in
  6. 6. the arc region. The H2 dissolves in X-ray and code requirements. Most welding the Heat Affected Zone (HAZ) and processes can be operated at hyperbaric the weld metal, which causes pressures, but all processes suffer a Embrittlement, cracks and reduction in capability and efficiency results microscopic fissures. Cracks can as the pressure increases. Hyperbaric grow and may result in catastrophic welding, using MMA (SMA), TIG (GTA) or failure of the structure. FCAW, is the preferred process for high 3) Another disadvantage is poor integrity welds, particularly for deep water visibility. The welder sometimes is welds, including tie-ins in pipelines and not able to weld properly. risers in the oil and gas industries; however GTA is the method most commonlyDry welding method employed for hyperbaric welding Hyperbaric Welding is the process operations.in which a chamber is sealed around the Risk of Dry weldingstructure to be welded, and is filled with a There is a risk to the welder/diver of electricgas (commonly helium containing 0.5 bar of shock. Precautions include achievingoxygen) at the prevailing pressure. adequate electrical insulation of the weldingThe hyperbaric welding may be one of two equipment, shutting off the electricity supply immediately the arc is extinguished, andtypes: limiting the open-circuit voltage of MMAA) Mini-Habitat welding - makes use of a (SMA) welding sets. Secondly, hydrogensmall, easily portable, gas-filled, often and oxygen are produced by the arc in wetPlexiglas enclosure, which is placed over the welding.joint by a diver. Water is displaced by an Precautions must be taken to avoid theinert gas or air supplied from the surface. In build-up of pockets of gas, which are potentially explosive. The other main area ofthis instance welding is performed at risk is to the life or health of theelevated ambient pressures. Depending on welder/diver from nitrogen introduced intothe size of the enclosure, the diver is the blood stream during exposure to air atpartially immersed in water (only the divers increased pressure. Precautions include thehands and the welding torch are inside the provision of an emergency air or gas supply,habitat). This method requires adequate stand-by divers, and decompression chambers to avoid nitrogen narcosisvisibility and is limited to areas with clear following rapid surfacing after saturationaccess. The diver/welder welds with each of diving.several MMA electrodes, positioned in For the structures being welded by wetadvance through the flexible port. underwater welding, inspection followingB) Large Habitat welding - a specially welding may be more difficult than fordesigned chamber is built and positioned welds deposited in air. Assuring the integrityaround the intended weld and the of such underwater welds may be morewelder/diver enters the chamber in order to difficult, and there is a risk that defects mayundertake the work. The habitat is sealed remain undetected.and water is excluded by introducing anappropriate gas. Hyperbaric weldingproduces high-quality weld joints that meet
  7. 7. 4) Non-Destructive Testing (NDT) – NDT is also facilitated by the dry habitat environment. We oppose Dry welting forWe prefer Dry welding for 1) The habitat welding requires large quantities of complex equipment and 1) Welder/Diver Safety – Welding is much support equipment on the performed in a chamber, immune to surface. The chamber is extremely ocean currents and marine animals. complex. The warm, dry habitat is well 2) Cost of habitat welding is extremely illuminated and has its own high and increases with depth. Work environmental control system (ECS). depth has an effect on habitat 2) Good Quality Welds – This method welding. At greater depths, the arc has ability to produce welds of constricts and corresponding higher quality comparable to open air welds voltages are required. The process is because water is no longer present to costly – a $ 80000 charge for a single quench the weld and H2 level is weld job. One cannot use the same much lower than wet welds. chamber for another job, if it is a 3) Surface Monitoring – Joint different one. preparation, pipe alignment, NDT inspection, etc. are monitored visually.
  8. 8. Concluded as Even through under water welding is more advantageous, there are more risk factor facedby the workers. Wet welding has been used as an underwater welding technique for a long timeand is still being used. With recent acceleration in the construction of offshore structuresunderwater welding has assumed increased importance. This has led to the development ofalternative welding methods like friction welding, explosive welding, and stud welding.Sufficient literature is not available of these processes.under water welding has it scope; Developments of diver less Hyperbaric welding system is aneven greater challenge calling for annexes developments like pipe preparation and aligning,automatic electrode and wire reel changing functions, using a robot arm installed. This is intesting stage in deep waters. Explosive and friction welding are also to be tested in deep waters.