Underwater Welding
Welding is an unavoidable process of modern engineering – civil, electrical,
mechanical, automobiles, marine aeronautical – in all branches. It is used in
fabrications and erections in infrastructures and installations. It joins metals
or thermoplastics. Forming a pool of molten mass – the weld puddle – and
allowing it to cool to become a strong joint is the basis of the process of
welding. For repairing to be carried out underwater, there is a separate
process. That is called underwater welding. If damaged ships are to be
repaired, underwater welding is the basic technology to be used. It is a
highly-specialized profession – more employed in the oil or shipping industry
and also in the defense operations.
Underwater welding process is categorized into two divisions.
• Wet welding
• Dry welding
Wet welding:
In the case of wet welding, the operation is completed under water, directly
exposed to the wet environment. For this purpose, a different type of
electrode is used. The function is carried out manually. The welder is
allowed to have freedom of movement. Hence, wet welding is the most
effective, efficient and economical process.
The welding power and supply unit is placed on the surface and is connected
to the welder with the help of cables and hoses.
The Advantages:
* The expenditure is very minimal. Unlike in the case of dry welding.
* The speed of the operation is extremely high.
* As the equipments are very minimum, the welding can be performed in
a shorter time with minimal planning.
The Disadvantages:
* The weld is quenched is very fast under water. It decreases the ductility
and impact strength an also makes the weld very porous.
* The visibility of the welder is not up to the required level.
* The amount of voltage that can b employed is very limited. Care has to
be taken so that the welder is not harmed by probable electrical shocks.
Dry Welding:
In case of dry welding, otherwise known as Hyperbaric welding, the whole
operation is completed in a chamber, sealed around the structure to be

welded. The chamber is filled with gas – normally helium – containing 0.5 bar
oxygen. The chamber is fitted onto the pipeline and is filled with the
breathable mixture of air. The operation is carried out in higher pressure. The
gas tungsten arc welding process is used.
The Advantages:
* Welding can be carried out without getting affected by ocean currents
and marine animals.
* Better quality welds can be used.
* From the surface itself, there is a possibility of visually monitoring joint
preparation and pipe alignment.
The Disadvantages:
* The chamber is very complex. Large support equipment is needed at the
surface to support the chamber.
* The expense will be very high. The cost increases proportionately to the
depth under water.
* The chamber has limited reusability.
Risks & Precautions:
Both the welder and the structure are at risk. The welder has to protect
himself from electric shocks. The welder has to be insulated. The voltage of
the welding sets has to be controlled. Pockets of oxygen and hydrogen built
up by the arc will be potentially explosive. The welder has to take precaution
because nitrogen will be built up in the blood stream of the welder, when
exposed to air at high pressure under the water surface. Inspection, although
very difficult, is a mandatory requirement. No defects should remain. In
addition to all these precautions, safe arc-welding precautions are to be
taken.
Underwater welding is mostly employed in marine engineering products –
in installations of oil and gas rigs. Underwater welding can be classified
depending upon the types of equipments and the types of procedures
involved. The most common underwater welding process, known as manual
metal arc building (MMA), is employed for deep water repairing activities.
Cofferdam welding process and Hyperbaric welding process are normally
carried out for underwater welding operations. They are employed for
welding steel pipelines, other offshore structures, submerged parts of large
ships and underwater structures supporting a harbor. The safety measures
include emergency air or gas supply, stand-by divers and decompression
chambers.
Source:
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