UNDERWATER WELDING

UNDERWATER WELDING

                                          Underwater welding is performed while the welder is submerged, often at elevated barometric pressures. Because of the adverse conditions and inherent dangers associated with underwater welding (also known as wet welding) divers must be trained to an exceptionally rigorous standard with highly specialized instruction.

                                   Underwater 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.

CLASSIFICATION

Under water welding can be classified as

I. Wet welding

II. Dry welding

WET WELDING

     It is the Key technology for repairing marine structure. In this 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. Complete insulation of the cables and hoses are essential in case to prevent the chance for electric shock. MMA (Manual Metal Arc) welding is commonly used process in the repair of offshore platforms.

                                  Wet welding entails the diver to perform the weld directly in the water. It involves using a specially designed welding rod, and employs a similar process used in ordinary welding. Here are advantages to wet welding:

·         Cheap and fast

·         high tensile strength

·         ease of access to weld spot

·         no habitat

·         no construction

Disadvantages

·         Rapid 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.

PRINCIPLE OF OPERATION

The work is connected to the positive side of dc source and electrode to the negative. The two parts of the circuit are brought together and then slightly separated. The two parts of the circuit are brought together and then slightly separated. An 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

Advantages

The versatility and low cost.

Less costly than dry welding.

Speed with which it is carried out

No enclosures so no time is lost for     

    Building

Disadvantages

Rapid 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.

DRY WELDING

 A 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 works

 Gas metal arc welding is the best process for this welding.

CLASSIFICATION OF DRY WELDING

There are two basic types of dry welding:

I. Hyperbaric welding

II. Cavity welding

Hyper baric welding: -

 It is carried out in chamber sealed around the structure

to be welded

 The chamber is filled with a gas at the prevailing

pressure, to push water back

 The welder fitted with breathing mask and other

protective devices on the pipe line

 Mask filled with a breathable mixture of helium and

oxygen in the habitat

 The area under the floor of the habitat is open to water,

so hyper baric welding is termed as “HABITATWELDING”

Limitation: -

 As depth increase pressure also increases, it affects both

for driver and welding process

Cavity welding: -

 Cavity welding is another approach to weld in water free

environment

 Conventional arrangements for feeding wire and shielding

gas

 Introducing 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

Advantages: -

Welder/diver safety

Good quality weld

Surface monitoring

Non-destructive testing

Disadvantages: -

The habitat welding requires large quantities of complex

equipment and much support equipment on the surface

Cost is extremely high