UNDERWATER WELDING TECHNOLOGY ,ART , COURAGE

1

Study of Various Methods and Parameters Involved in Underwater Welding

Subject Code-ME1637Under the guidance of:Dr. A K DasPresented By:Abhishek Jain1201076Department of Mechanical Engineering National Institute of Technology PatnaContentsIntroductionClassificationWet WeldingDry WeldingAdvantages DisadvantagesSchematic Diagram of Apparatus RequiredRisksApplicationsEffect of Wet environment on weldsPorosity CurveReferences

2INTRODUCTION TO UNDERWATER WELDING3

How can big ships or underwater Rigs be repaired ????We cant lift ships and then repair them.4

INTRODUCTIONUnderwater welding is an important tool for underwater fabrication works.In 1946, special waterproof electrodes were developed in Holland by Vander Willingen'. In recent years the number of offshore structures including oil drilling rigs, pipelines, platforms are being installed significantly. 55CLASSIFICATIONUnder water welding can be classified as :

Dry weldingWet welding

6DRY WELDINGA chamber is created near the area to be welded and the welder does the job by staying inside the chamber.It produces high quality weld joints .The gas-tungsten arc welding process is used mostly for pipe worksGas metal arc welding is the best process for this welding.

78CLASSIFICATION OF DRY WELDINGThere are two basic types of dry welding :

Hyperbaric welding

Cavity weldingHyper baric welding:-It is carried out in chamber sealed around the structure to be welded filled with a gas to push water back.Gas generally used is a breathable mixture of helium and oxygen.The area under the floor of the habitat is open to water, so hyper baric welding is termed as HABITAT-WELDING

9An image for Habitat Welding10

Hyper = High, Baric = PressureHyper Baric welding means high Pressure WeldingCavity welding:-Cavity welding is another approach to weld in water free environment.Conventional arrangements for feeding wire and shielding gasIntroducing cavity gas and the whole is surrounded by a trumpet shaped nozzle through which high velocity conical jet of water passes. It avoids the need for a habitat chamber and it lends itself to automatic and remote control.The process is very suitable for flat structures.

11Advantages:-12Disadvantages:- The habitat welding requires large quantities of complex equipment and much support equipment on the surfaceCost is extremely high hence cannot be afforded by normal or small firms.

13

Large habitat for underwater hyperbaric weldingWET WELDINGKey technology for repairing marine structure

Welding is performed under water directly exposed to the wet environment

Increased freedom movement makes more effective, efficient and economical

Supply is connected to the welder/driver via cables or hoses 14Complete insulation of the cables and hoses are essential in case to prevent the chance for electric shockMMA (Manual Metal Arc) welding is commonly used process in the repair of offshore platforms.

15PRINCIPLE OF OPERATIONThe work-piece is connected to the positive side of dc source (Anode) and electrode to the negative side (Cathode).The two parts of the circuit are brought together and then slightly separated.

16An electric current occurs in the gap and causes a sustained spark which melts the bare metal forming a weld pool.The flux covering the electrode melts to provide a shielding gas.Arc burns in the cavity formed inside the flux covering, which is designed to burn slower than the metal barrel to the electrode.17

AdvantagesThe versatility and low cost.

Less costlier than dry welding.

Speed with which it is carried out.

No enclosures so no time is lost for building.18

DisadvantagesRapid quenching of the weld metal by the surrounding water.

Welders working under water are restricted in manipulating arc.

Hydrogen embrittlement causes cracks.

Poor visibility due to water contaminance.19RISKS V/S PRECAUTIONSRisk of electric shock so precaution is taken for checking the electrical insulation of electrical welding equipments.Hydrogen and oxygen are produced by the arc in wet welding which are potentially explosive so precaution must be taken to avoid the build up of pockets of gasThe life or health of the welder will be in risk from nitrogen introduction into the blood stream, hence precautions include the provision of an emergency air cylinder for the welder.20APPLICATIONSOffshore construction for tapping sea resources.

Temporary repair work caused by ships collisions, or unexpected accidents.Salvaging vessels sunk in the sea.

Construction of large ships beyond the capacity of existing docks.Maintenance of oil rigs.21

22

Figure showing schematic diagram for underwater welding or cuttingEFFECT OF WET ENVIRONMENT

Water dissociates into Oxygen and Hydrogen which dissolves in the molten pool causing:Gas Inclusion DefectsPorosityWater Inclusion as after some times hydrogen combines with oxygen forming water vapor.

V-groove wet weld deposited at 100 m depth (a) and its radiographic image (b)

(a)(b)2323

Graph Between the Porosity and Water Pressure during welding2425

Most Underwater Structures are formed using this method as the method is economical, flexible, versatile, Speedy.

Combined additions of titanium, boron, and manganese increased the tensile strength of the steel wet welds due to microstructural refinement and increased hardenability thus providing new dimensions to underwater structuresCONCLUSIONREFERENCESwww.Wikipedia.orgPaper on Underwater Welding-Jyotsana Dutta Majumdar (IIT KGP 2006)Manual for underwater welding, US Navywww.howstuffworks.com26THANK YOU27