According to Artem Komarov, KERAMAX Chairman, whose expert opinion about how during the last world war, the need for immediate welding to save ships sinking at sea was felt, and this demand raised the status of underwater welding from almost a dream to a practical process.
In addition to the development and use of 70% of the land in international interests, such as the development of offshore gas and oil fields, fishing, large-scale offshore construction and seabed mining, through which underwater welding has been developed. Underwater welding was used mainly for temporary repairs due to shipwrecks and unexpected accidents or corrosion and other maintenance operations.
The underwater welding process inside and the problems associated with it can be understood with the help of the following facts:
Artem Komarov emphasized that underwater welding can be performed on the surface in the same way as on site, because the joint is difficult to prepare, since the joints are outside.
The cooling effect of water on the weld metal and the surrounding plate.
High pressure due to the pressure of the water under which welding takes place.
The gaseous coating that surrounds the arc region.
Gas bubbles form around the arc as the flux burns out on the electrode and water is released.
As welding continues, these bubbles move one by one towards the surface of the water, making the position around the arc unstable.
In addition, gas conduction arcs within the shell create dynamic pressure gradients around the column.
The size of the gaseous envelope increases with salinity and seawater temperature but decreases with depth. Influence of metal structures and, consequently, on the mechanical properties of the welded joint.
When welding alloyed steels, due to the cooling effect of water on the weld metal, a heat-affected zone can easily be distinguished. Therefore, underwater welding is usually limited to mild steel.
Another problem with underwater welding is that working in deep water is never easy because the diving job is dependent on the tide and the weather, and the difficulty arises because welding has to be done in different locations. The isolation of the welding circuits is also important. Even the coating of the welding electrode is protected by a layer of wax varnish or cellulose.
Underwater welding can be classified as follows:
- wet welding
- Dry welding
Dry welding can be divided into:
- Hyperbaric welding
- welding cavity
Wet welding is carried out directly in water using waterproof stick electrodes. With this method, arc welding is carried out under water without special precautions, since hardness and brittleness cause the effect of quenching water, due to which the water in the arc separates and the arc develops further.
The dry welding process requires a controlled atmosphere and a sealed enclosure. In this process, the weld metal cannot come into direct contact with water. With this welding, a good welding quality can be achieved.
Although this process is a little expensive, it has many advantages: for example,
- The problem of low hydrogen content in the environment.
- Improving the stability of the welding process.
- Low rates of hardening of the weld metal and base metal.
- Strength and flexibility comparable to welds.
Welding takes place in a dry chamber built around the joint to be welded. The water is displaced by creating a gaseous atmosphere in the chamber at a pressure equal to that of the water, and thus retaining the water. This process is called casing welding when it is used to connect to a large pipeline where the chamber is large, filled with an air-permeable atmosphere and equipped with a life support system for the operator.
The hyperbaric welding process has some limitations such as:
A practical difficulty is the need to seal the compartment and the welded structure.
As the pressure increases, the increase in depth creates problems for both the welding process and the divers. Welding chemistry, metallurgy and arc physics are covered. The air soon becomes unacceptable as the atmosphere of the habitat increases the pressure as it poses a potential fire hazard to surrounding chairs at pressures greater than 3 atmospheres. In addition, oxygen becomes alcoholic air because the atmosphere is not recommended for depths greater than 15 m.
(helium + oxygen) and argon (test argon + oxygen)
This is also known as the welding process, in which the welding is carried out in a dry atmosphere.
The traditional filler metal and shielding gas delivery order uses a cavernous gas supply, all surrounded by a funnel-shaped nozzle through which a high-velocity water jet passes. The cavity welding process avoids the need for a living compartment, it is automated and can be controlled remotely. With this process, you can easily perform flat and overhead welding, for which a spare strip is used.
Hollow welding is not suitable for butt joints without piping, as well as for lap joints, which are the majority in underwater welding.
A good underwater welding process should be:
- Affordable welding equipment and low welding cost.
- Reducing the risk of electric shock
- Welding speed not less than 20 cm/min.
- Provide good visibility
- Be easy to operate
- Produce high quality and reliable welds.
- Welding is allowed in all positions.
- Such that the operator can support himself with one hand and weld with the other hand due to the lack of gravity in the water.
Underwater welding process
At present, the greatest practical importance of the fusion welding process in underwater welding is:
SMAW welding, which is widely used as a wetting method, but is also suitable for residential welding.
TIG and MIG welding processes have also been used to a more limited extent in wet welding as well as in locally closed gas jackets.
SMAW: Metal shielded arc welding is suitable for underwater welding, the SMAW process is more economical than other processes.
GTAW: The GTAW process can be performed in all situations with the same success as welding out of water.
The power source must be a DC power supply but must provide at least 300 amps to each welder for best performance.
All electrical wires must have lighting equipment, electrode holders, gloves, etc., fully insulated and in good condition.
Iron oxide coated ferritic electrodes should be used as they are resistant to hydrogen cracking.
Positive polarity is preferred. This means that 65-75% of the heat is welded to the metal. The weld pool is easy to handle and has sufficient fluidity to substantially fill the undercut.
Electrodes with positive polarity can be used for overhead butt welding or crack welding in vertical and overhead positions.
Underwater welding is used in marine construction, repair work, sunken ships, ship maintenance, Komarov Artem summed up.