this is a presentation on under water weding,its advantage and future scope.

1. Under Water Welding
By:
Shivani Agarwal
Roll = 001511301043
Metallurgical & Material engg.
JADAVPUR UNIVERSITY
To:
Prof. Subir Paul
&
Dr.Rajib Dey

2. Structure under water (like ships)
 Solution: Under water welding
Introduction
Ø Not a good option

3. History
 In1930s, Russian metallurgist Konstantin Khrenov made the first
underwater weld - in lab tests.
 In 1946, special waterproof electrodes were developed in Holland by
‘Vander Willingen’ Konstantin Khrenov
What is Under water welding?
 Under water welding is the process of welding at
elevated pressures, normally underwater.
 Underwater welding is an important tool for
underwater fabrication works.

4. Under water welding
Wet welding Dry welding
 Underwater welding can either take place wet in the water itself or dry inside a specially
constructed positive pressure enclosure and hence a dry environment.
 It is referred to as “hyperbaric welding” when used in dry environment, and “underwater
welding” when in a wet environment.

5. 1. Offshore construction for tapping sea resources
2. Temporary repair work caused by ship’s collisions, unexpected
accidents
3. Salvaging vessels sunk in the sea
APPLICATIONS
4. Repair and maintenance of ships
5. Construction of large ships beyond the capacity of existing docks

6. 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.
It produces high quality weld joints
Gas metal arc welding is the best process for this welding
The gas-tungsten arc welding process is used mostly for
pipe works
Dry welding

7. Advantages & disadvantages

8. Wet Welding
In wet welding MMA (manual metal arc welding) is used in the repair of
offshore platforms
1 Underwater wet welding is done in an environment where the base
metal and the arc are surrounded entirely by water.
2 Welding power supply is located on the surface with connection to the
diver/welder via cables and hoses
5
Increased freedom of movement makes wet welding the most
effective, efficient and economical method
4
3
A special electrode is used and welding is carried out manually
just as one does in open air welding.

9. Advantages & disadvantages
• 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
Advantages
• 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
Disadvantages

10. .
.
Principle Of Operation
Power Supply used : DC
Polarity : -ve polarity
 The welding circuit must include a positive type of
switch, usually a knife switch operated on the surface
and commanded by the welder
 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
 An electric current occurs in the gap and causes a
sustained spark which melts the bare metal forming a
weld pool

11. There is a risk that
defects may remain
undetected
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
Hydrogen and Oxygen are
produced during welding
Electric shock Explosion
Risk involved
1
2
4
3

12.  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
 Precautions must be taken to avoid the build-up of pockets of gas, which are potentially
explosive
 Precautions include the provision of an emergency air or gas supply, stand-by divers, and
decompression chambers to avoid nitrogen
Safety Measures

13. • 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, installs the tracks and orbital head on the
pipe and rest process is automated.
• Explosive ,friction and stud welding are also to be tested in deep waters.
• Research being carried out for welding at a range of 500 to 1000m deep.
Scope for further developments
Friction welding