underwater welding

1. Underwater Welding

2. INTRODUCTION

3. • The fact that electric arc could operate was
known for over a 100 years. The first ever
underwater welding was carried out by British
Admiralty - Dockyard for sealing leaking ship
rivets below the water line.
• Underwater welding is an important tool for
underwater fabrication works.
• In 1946, special waterproof electrodes were
developed in Holland by ‘Van der Willingen’.

4. CONTD.
• In recent years the number of offshore
structures including oil drilling rigs, pipelines,
platforms are being installed significantly.
• Some of these structures will experience failures
of its elements during normal usage and during
unpredicted occurrences like storms, collisions.
Any repair method will require the use of
underwater welding.

5. CONTD.
• Underwater welding is the process of welding at
elevated pressures, normally underwater. 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 predominantly referred to as
"hyperbaric welding" when used in a dry environment, and
"underwater welding" when in a wet environment
• The applications of underwater welding are diverse—it is oeen
used to repair ships, offshore oil platforms,
and pipelines. Steel is the most common material welded

6. CONTD.
• Dry hyperbaric welding is used in preference to wet
underwater welding when high quality welds are required
because of the increased control over condiVons which can be
exerted, such as through applicaVon of prior and post
weld heat treatments
• This improved environmental control leads directly to
improved process performance and a generally much higher
quality weld than a comparative wet weld. Thus, when a very
high quality weld is required, dry hyperbaric welding is
normally utilized

7. CONTD.
• Research into using dry hyperbaric welding at depths of up to
1,000 metres (3,300 e) is ongoing. In general, assuring the
integrity of underwater welds can be difficult (but is possible
using various non-destructive testing applications), especially
for wet underwater welds, because defects are difficult to
detect if the defects are beneath the surface of the weld.

8. Classification
1. Dry
2. wet

9. DRY WELDING
• Dry hyperbaric welding involves the weld being
performed at the prevailing pressure in a
chamber filled with a gas mixture sealed around
the structure being welded.
• Most welding processes SMAW, FCAW, GTAW,
GMAW, PAW could be operated at hyperbaric
pressures, but all suffer as the pressure
increases. Gas tungsten arc welding is most
commonly used.

10. CONTD.
• The degradation is associated with physical
changes of the arc behavior as the gas flow
regime around the arc changes and the arc roots
contract and become more mobile.
• Of note is a dramatic increase in arc voltage
which is associated with the increase in
pressure. Overall a degradation in capability and
efficiency results as the pressure increases.

11. • Although, a large number of techniques are
available for welding in atmosphere, many of
these techniques can not be applied in offshore
and marine application where presence of water
is of major concern.
• In this regard, it is relevant to note that, a great
majority of offshore repairing and surfacing work
is carried out at a relatively shallow depth, in the
region intermittently covered by the water
known as the splash zone.

12. CONTD.
• Though, numerically most ship repair and welding jobs
are carried out at a shallow depth, most technologically
challenging task lies in the repairing at a deeper water
level, especially, in pipelines and occurrence/creation of
sudden defects leading to a catastrophic accidental
failure.
• The advantages of underwater welding are of
economical nature, because underwater-welding for
marine maintenance and repair jobs bypasses the need
to pull the structure out of the sea and saves valuable
time and dry docking costs.

13. • Special control techniques have been applied
which have allowed welding down to 2500m
simulated water depth in the laboratory, but dry
hyperbaric welding has thus far been limited
operationally to less than 400m water depth by
the physiological capability of divers to operate
the welding equipment at high pressures and
practical considerations concerning construction
of an automated pressure / welding chamber at
depth

14. ADVANTAGES
1) Welder/Diver Safety - Welding is performed in a chamber,
immune to ocean currents and marine animals. The warm,
dry habitat is well illuminated and has its own
environmental control system (ECS).
2) Good Quality Welds - This method has ability to produce
welds of quality comparable to open air welds because
water is no longer present to quench the weld and H2 level
is much lower than wet welds.
3) Surface Monitoring - Joint preparation, pipe alignment, NDT
inspection, etc. are monitored visually.
4) Non-Destructive Testing (NDT) - NDT is also facilitated by
the dry habitat environment.

15. DISADVANTAGES
1) The habitat welding requires large quantities of complex
equipment and much support equipment on the surface.
The chamber is extremely complex.
2) Cost of habitat welding is extremely high and increases with
depth. Work depth has an effect on habitat welding.
3) At greater depths, the arc constricts and corresponding
higher voltages are required.
4) The process is costly - a $ 80000 charge for a single weld
job. One cannot use the same chamber for another job, if it
is a different one.

16. WET WELDING
• Simply means that job is performed directly in the water
• It involves using special rod and is similar to the process in
ordinary air welding

17. PRINCIPLE OF OPERATION
• The process of underwater wet welding takes in the following
manner:
• 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 top 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 barrel of the electrode.

18. WET WELDING

19. PARAMETERS
• Power supply : DC 300 OR 400 AMP
• Polarity : straight polarity

20. EFFECT OF WET ENVIROMENT
• WATER = HYDROGEN + OXYGEN
• Dissolve in weld pool
• Solubility decreases and then comes out = porosity
• Oxygen as solid , liquid inclusions or gases
• Hydrogen combines with oxygen forming vapor.
V-groove wet weld deposited at 100 m depth (a) and its
radiographic image

21. Formation of Hydrogen
• Once the welding circuit is completed by striking an
arc, the heat of the arc is sufficient to vaporise the
surrounding water. Hence, the arc is surrounded by
a vapor shield. However, reaction with the molten
metal influences the composition of this vapor and
it comprises of about 70% hydrogen, 25% carbon
dioxide and 5% carbon monoxide.
• The risk of hydrogen induced cracking increases as
welding depth increases in water (sea/ocean).

22. • D4301, D4313 and D4327 are electrode
classification in JIS (Japanese Welding Society).
• Actually these electrodes are used in arc welding
• For underwater welding, special type of ilmenite
coating is applied around the electrodes
• Picture Courtesy: Kobelco Welding and Hyundai
Welding Co. Ltd.

23. ADVANTAGES
1) The versatility and low cost of wet welding makes this
method highly desirable.
2) Other benefits include the speed. With which the operation
is carried out.
3) It is less costly compared to dry welding.
4) The welder can reach portions of offshore structures that
could not be welded using other methods.
5) No enclosures are needed and no time is lost in building.
Readily available standard welding machine and equipments
are used. The equipment needed for mobilization of a wet
welded job is minimal.

24. DISADVANTAGES
• Rapid quenching decreases impact strength and ductility.
• Hydrogen embrittlement.
• Poor visibility in water.
• Higher energy density of hydrogen, higher efficiency.

25. REQUIREMENTS
• Power supply requirements - 400 amp or larger. DC
generators, motor generators and rectifiers are acceptable
power supplies
• Power converters.
• Welding Generator, Pre-Setup
• Polarity.
• Diesel Driven Welding Generator Amperage and Voltage
settings.
• Gas Manifolds

26. Figure showing schematic diagram for
underwater welding or cutting

27. DANGERS AND DIFFICULTIES
• Hydrogen and oxygen are dissociated from the
water and will travel separately as bubbles.
• Oxygen cuung is about 60 percent efficient
• Above river beds, especially in mud, because
trapped methane gas in the proper
concentrations can explode.

28. CONTD.
• There is a risk to the welder/diver of electric
shock.
• There is a risk that defects may remain
undetected
• The other main area of 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

29. SAFETY MEASURES
• Start cuung at the highest point and work downward
• By withdrawing the electrode every few seconds to allow
water to enter the cut
• Gases may be vented to the surface with a vent tube
(flexible hose) secured in place from the high point
where gases would collect to a position above the
waterline.
• Precautions include achieving adequate electrical
insulation of the welding equipment
• Areas and voids must be vented or made inert.

30. DEVELOPMENTS
• Wet welding has been used as an underwater welding
technique for a long time and is still being used.
• With recent acceleration in the construction of offshore
structures underwater welding has assumed increased
importance.
• This has led to the development of alternative welding
methods like friction welding, explosive welding, and stud
welding. Sufficient literature is not available of these
processes.

31. SCOPE
• Wet welding 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 pipe fixing, installs the
trace and orbital head on the pipe and the rest process is
automated.
• Developments of driverless Hyperbaric welding system is an even
greater challenge calling for annexed developments like pipe
preparation and aligning, automatic electrode and wire reel
changing functions, using a robot arm installed. This is in testing
stage in deep waters.
• Explosive and friction welding are also to be tested in deep waters.

32. REFERENCES
1) D. J Keats, Manual on Wet Welding.
2) Annon, Recent advances in dry underwater pipeline welding,
Welding Engineer, 1974.
3) Lythall, Gibson, Dry Hyperbaric underwater welding, Welding
InsVtute.
4) W.Lucas, InternaVonal conference on computer technology in
welding.
5) Stepath M. D, Underwater welding and cuung yields slowly to
research, Welding Engineer, April 1973.
6) Silva, Hazlel, Underwater welding with iron - powder electrodes,
Welding Journal, 1971.
7) wikipedia.org
8) Amit Mukund Joshi, Underwater Welding, JRF, IIT-Bombay,