Abhishek jain underwater welding

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Study of Various Methods and

Parameters Involved in Underwater Welding

Subject Code-ME1637

Under the guidance of:Dr. A K Das

Presented By:

Abhishek Jain

1201076

Department of Mechanical Engineering

National Institute of Technology Patna

2Contents Introduction

Classification

Wet Welding

Dry Welding

Advantages

Disadvantages

Schematic Diagram of Apparatus Required

Risks

Applications

Effect of Wet environment on welds

Porosity Curve

References

3INTRODUCTION TO UNDERWATER WELDING

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How can big ships or underwater Rigs be repaired ????We can’t lift ships and then repair them.

5INTRODUCTION

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.

6CLASSIFICATION

• Under water welding can be classified as :

i. Dry welding

ii. Wet welding

7DRY 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.

8CLASSIFICATION OF

DRY WELDING

There are two basic types of dry welding :

i. Hyperbaric welding

ii. Cavity welding

9Hyper 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”

An image for Habitat Welding

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Hyper = High, Baric = Pressure

Hyper Baric welding means high Pressure Welding

11Cavity 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.

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Advantages:-

Welder/diver is safe.

Good quality

welds are formed.

Surface monitoring of welders condition can

be done.

Non destructive testing of weld is

easy.

13Disadvantages:-

The habitat welding requires large quantities of complex equipment and much support equipment on the surface

Cost is extremely high hence cannot be afforded by normal or small firms.

Large habitat for underwater hyperbaric welding

14WET WELDING

Key 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

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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.

PRINCIPLE OF OPERATION

The 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.

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17 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.

18Advantages

The 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.

19Disadvantages

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.

20RISKS V/S PRECAUTIONS

Risk 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 gas

The 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.

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APPLICATIONS

Offshore construction for tapping sea resources.

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

Salvaging vessels sunk in the sea.

Construction of large ships beyond the capacity of existing docks.

Maintenance of oil rigs.

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Figure showing schematic diagram for underwater welding or cutting

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EFFECT OF WET ENVIRONMENTWater dissociates into Oxygen and Hydrogen which dissolves in the molten pool causing: Gas Inclusion Defects Porosity Water 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)

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Graph Between the Porosity and Water Pressure during welding

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• 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 structures

CONCLUSION

26REFERENCES

www.Wikipedia.org

Paper on Underwater Welding-Jyotsana Dutta

Majumdar (IIT KGP 2006)

Manual for underwater welding, US Navy

www.howstuffworks.com

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THANK YOU