• WeldingWelding is a is a fabrication that joins that joins materials, usually materials, usually metals or or thermoplastics, , by causing coalescence. by causing coalescence.

• This is often done by melting the This is often done by melting the workpieces and adding a filler material to workpieces and adding a filler material to form a pool of molten material (the form a pool of molten material (the weld weld poolpool) that cools to become a strong joint, ) that cools to become a strong joint, with pressure sometimes used in with pressure sometimes used in conjunction with heat, or by itself, to conjunction with heat, or by itself, to produce the weld.produce the weld.

•Underwater welding was invented by the Underwater welding was invented by the Russian metallurgist Konstantin Khrenov in Russian metallurgist Konstantin Khrenov in

1932.1932.

• The first ever underwater welding was The first ever underwater welding was carried out by British Admiralty – Dockyard for carried out by British Admiralty – Dockyard for

sealing leaking ship rivets below the water sealing leaking ship rivets below the water line.line.

•Underwater welding is an important tool for Underwater welding is an important tool for underwater fabrication works.underwater fabrication works.

• underwater welding is also known as Hyperbaric welding.

CLASSIFICATIONUnderwater welding can be classified as-1) Wet Welding2) Dry WeldingIn 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.

Wet underwater welding

•Power Supply used : DC

•Polarity : -ve polarity

For wet welding AC is not used on account of electrical safety and difficulty in maintaining an arc underwater.

WET WELDINGWET WELDING•Wet Welding indicates that welding is performed underwater, directly exposed to 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.

Power supply

work

Electrode holder

electrode

switch

Electric circuit of wet welding

EarthDC

Principle of operation of Wet WeldingPrinciple of operation of Wet Welding The 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 of the electrode.

Electrode used in wet weldingElectrode used in wet welding These copper coated These copper coated

carbon/graphite electrodes carbon/graphite electrodes are especially made for are especially made for the Arcwater process. the Arcwater process. Arcwater electrodes that Arcwater electrodes that are waterproof with a are waterproof with a white coating. Arcwater white coating. Arcwater electrodes require 350 to electrodes require 350 to 450 amperes for proper 450 amperes for proper oxygen free burning.oxygen free burning.

Specifications. Specifications. Diameter Diameter x Length(8 mm x 228.6 x Length(8 mm x 228.6 mm) .mm) .

Dry weldingDry welding Dry welding is carried out in chamber sealed around the Dry welding is carried out in chamber sealed around the

structure to be welded.structure to be welded. The chamber is filled with a gas (commonly helium The chamber is filled with a gas (commonly helium

containing 0.5 bar of oxygen) at the prevailing pressure. containing 0.5 bar of oxygen) at the prevailing pressure. The habitat is sealed onto the pipeline and filled with a The habitat is sealed onto the pipeline and filled with a

breathable mixture of helium and oxygen, at or slightly breathable mixture of helium and oxygen, at or slightly above the ambient pressure at which the welding is to above the ambient pressure at which the welding is to take place.take place.

This method produces high-quality weld joints.This method produces high-quality weld joints. The gas tungsten arc welding process is employed for The gas tungsten arc welding process is employed for

this process.this process.

The Dry welding may be one of two types:

Mini-Habitat welding - Makes use of a small, easily portable, gas-filled, often plexiglas enclosure, which is placed over the joint by a diver. Water is displaced by

an inert gas or air supplied from the surface. Depending on the size of the enclosure, the diver is partially immersed in water (only the diver's hands

and the welding torch are inside the habitat).

Large Habitat welding - A specially designed chamber is built and positioned around the intended

weld and the welder/diver enters the chamber in order to undertake the work. The habitat is sealed and

water is excluded by introducing an appropriate gas.

Advantage and Disadvantage of Advantage and Disadvantage of Wet weldingWet welding

AdvantagesAdvantages

Time consumption is Time consumption is less in case of wet less in case of wet welding as compared to welding as compared to dry welding.dry welding.

It is less costly It is less costly compared to dry compared to dry welding.welding.

DisadvantagesDisadvantages

There is There is rapid quenchingrapid quenching of the weld metal by the of the weld metal by the surrounding water, it surrounding water, it decreases the ductility and decreases the ductility and impact strength of the impact strength of the weldment and increases weldment and increases porosity and hardness.porosity and hardness.

Another disadvantage is Another disadvantage is poor visibility.poor visibility.

Advantage and disadvantage of Advantage and disadvantage of Dry weldingDry welding

AdvantagesAdvantages

Welder/Diver Safety – Welder/Diver Safety – Welding is performed in a Welding is performed in a chamber, immune to chamber, immune to ocean currents and marine ocean currents and marine animals. animals.

Good Quality Welds – This Good Quality Welds – This method has ability to method has ability to produce welds of good produce welds of good quality.quality.

DisadvantagesDisadvantages

The habitat welding The habitat welding requires large quantities of requires large quantities of complex equipment and complex equipment and much support equipment much support equipment on the surface. The on the surface. The chamber is extremely chamber is extremely complex.complex.

Cost of habitat welding is Cost of habitat welding is extremely high and extremely high and increases with depth. increases with depth.

ApplicationsApplications

Temporary repair work caused by ship's collisions Temporary repair work caused by ship's collisions or unexpected accidents.or unexpected accidents.

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

Offshore oil platforms Offshore oil platforms other offshore structures other offshore structures Pipelines. Pipelines. Repair and maintenance of ships.Repair and maintenance of ships.

Future of Underwater weldingFuture of Underwater weldingThe major efforts on research and development should be focused on the following topics:

• Automation of the underwater welding. Present trend Present trend is towards automation to develop a technology, where is towards automation to develop a technology, where diver performs pipefitting, installs the trac and the rest diver performs pipefitting, installs the trac and the rest process is automated. process is automated.

• Developing automated Inspection technique of the welded structures.

• Invention of new welding techniques and explore the possibility of its application in underwater welding.