Under water welding.smnr

UNDERWATER WELDING

Presented by

Suresh Beera

12ETMM11

M.Tech/Ph.D

Materials Engineering

SEST, UoH• Wednesday, April 12, 202

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Outline• Importance Of Underwater Welding

• Principle Of Operation

• Classification

• Wet/Dry Underwater Welding

• Advantages& Disadvantages

• Risk Involved & Safety

• Applications

• Future Scope

• References

•Wednesday, April 12, 2023

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• Wednesday, April 12, 2023

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what is an Under water welding???Many of us won't have heard of under water welding but it's actually a very important thing in many industries. Underwater welding includes a lot of different processes that join steel on offshore oil platforms, pipelines & ships etc. under water. At present, underwater welding becomes more sophisticated and can be done deeper. GTAW has been used to weld pipes at depths of 200 ft (61 m)


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Principle of Operation

_Power Supply

- +

work

Knife switch

electrode

Waterproof Electrode

Holder

• The welding circuit must include a positive type of switch, usually a knife switch operated on the surface and commanded by the welder and is used for safety reasons.

• 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


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Underwater welding is classified into two categories

1.Welding in-the-wet environment 2.Welding in-the-dry environment

Dry welding Wet welding


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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.

Welding in the wet environment

A special electrode is used and welding is carried out manually

just as one does in open air welding.

The 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


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Advantages

• cheapest and fastest method

• tensile strength is high

• easy of access the weld spot

• no habitat, no construction,

• no waste of time

Disadvantages

• Rapid quenching decreases impact strength, ductility

• Hydrogen embrittlement,cracks

• Poor visibility in water

Hyperbaric(dry) welding Hyperbaric welding is a welding in which a chamber is

sealed around the structure to be welded and is filled with breathable gas(commonly helium containing 0.5 bar of oxygen) at the prevailing pressure. at which the welding is to take place. This method produces high-quality weld joints

The gas tungsten arc welding process is employed for this process. The area under the floor of the Habitat is open to water. Thus the welding is done in the dry but at the hydrostatic pressure of the sea water surrounding the Habitat


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Dry welding


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Advantages of Dry welding

• Welder/diver safety

• Good quality welds

• Surface monitoring

• Non destructive testing

Disadvantages

• Higher cost of process,training,etc.,.

• Large quantity of costly and complex equipments.

• More deep,more energy is required

• Can’t be weld,if weld spot is at unreachable places

Risk Involved & safety


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Electric shock Explosion. 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

Hydrogen and Oxygen are produced during welding. Precautions must be taken to avoid the build-up of pockets

of gas, which are potentially explosive

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

Inspection of welds.


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• Application of Underwater Welding

• Offshore construction for tapping sea resources,

• Temporary repair work caused by ship’s collisions or unexpected

accidents.

• Salvaging vessels sunk in the sea

• Repair and maintenance of ships

• Construction of large ships beyond the capacity of existing docks.


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• Scope for further developments

• 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,.

• Developments of driverless Hyperbaric welding system is an even greater challenge

in developments like pipe preparation and aligning, automatic electrode.

• This is in testing stage in deep waters. Explosive and friction welding are also to be

tested in deep waters.

Friction welding (FRW)


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REFERENCE

Underwater Welding –Present Status And Future Scope.Jyotsna Dutta Majumdar.Department Of Metallurgical And Materials Engineering, Indian Institute Of Technology, Kharagpur, West Bengal, India

Underwater Welding Amit Mukund Joshi (Mechanical Engineer) ,Junior Research Fellow Mechanical Engineering Department ,Indian Institute Of Technology ,I.I.T – Bombay

Annon, Recent Advances In Dry Underwater Pipeline Welding, Welding Engineer, 1974.

Lythall, Gibson, Dry Hyperbaric Underwater Welding, Welding Institute.


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THANK YOU

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