Underwater welding process
Underwater welding offers a mode of assembly or repairs the structures underwater. It is a type of technology for repairing marine structures. Unconventional methods such as clamp and grout repairs (which may set up inappropriately high loading on offshore structures), and the use of bolted flanges for the tie-ins, are not necessarily always satisfactory.
There are many applications for underwater welding skills such as:
- Repairing ships,
- Working on oil platforms and
- Maintaining underwater pipelines.
People with skills and experience in this field can find employment all over the world.
Why underwater welding needed?
Principles of underwater welding
Underwater welding is a type of welding which takes place underwater. Among the number of different welding techniques, ‘arc welding’ is most common.
DC 300 to 400 Amps (AC welding is not used due to electrical safety and difficulty in maintaining the arc underwater)
Negative polarity (If positive polarity which causes deterioration due to electrolysis takes place)
Underwater welding Requirements:
- Arc welding torch
- Collet or Grip
- Oxygen valve
- Flash arrester
Water proofing surface electrodes:
- Epoxy 152
- Lee lac
Underwater welding can be divided into two main types that have been in use for many years:
Underwater wet welding:
Manual Metal Arc Welding (MMA) is the most common process. Flux Cored Arc Welding (FCAW) has been widely used. FCAW, which has the advantages of being relatively insensitive to depth and which tends itself to robotic operation has the potential for use in deep water repairs.
- Very fast welding in underwater
- Cheapest welding
- Tensile strength is high
- No habitat required
- No need of construction
- Due to Rapid quenching reduces impact strength and ductility
- Poor visibility in water
- Possible of Hydrogen embrittlement
Hyperbaric welding or Dry welding:
In which a chamber is sealed around the structure to be welded and is filled with a inert gas (commonly Helium containing 0.5 bar of oxygen) at the generally accepted pressure.
This method is carried out in the dry air; where a rigid steel structure to house the welding is sealed against the side of the structures to be welded and is open to the atmosphere.
Dry Habitat welding:
Welding takes place at ambient water pressure in a large chamber were the water is displaced.
Dry chamber welding:
Welding at ambient water pressure in simple open bottom dry chambers that accommodates the head and shoulder of welder.
Dry spot welding:
Welding at ambient water pressure in a small transparent, gas filled enclosure with the welder in the water and arm inside the chamber.
- Good quality welds
- Possible testing methods such as NDT inspection, driver monitoring
- Safety to welder due to risks in welding
- Large, complex construction equipments required to weld
- Higher costs of welding equipment
- Unreachable place cant welded
Underwater Welding Dangers or Risks:
For the humans involved, the risks are of three main types:
- There is a probable risk to the welder / diver due to electric shock. Precautions include, completing enough electrical insulation of the welding equipment, shutting off the electricity supply immediately the arc is extinguished and limiting the open circuit voltage of Manual metal arc welding sets.
- Hydrogen and oxygen are formed by the arc in wet welding and cutting process. Precautions must be taken to avoid the built up of pockets of gas which are potentially explosive.
- The other main area of risks is the life / health of the welder / diver from nitrogen gas introduced into the bloodstream during exposure to air at increased pressure. Precautions include the provision of an emergency air or gas supply, stand by divers and decompression chambers to avoid decompression sickness following saturation diving or too rapid return to the surface from a deep dive. For the structures being welded by wet underwater welding, inspection following welding may be more difficult than for welds deposited in air. Guaranteeing the integrity of these type underwater welds may be more difficult and there is a danger, which defects may stay behind undetected.
- Alternative welding methods such as Friction welding, Stud Welding and Explosive welding can be used
- Development of THOR -1 (“TIG Hyperbaric Orbital Robot) for the automatic welding in underwater