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.