Ship hulls are constructed from hundreds of sheets of metal, and good ship welding during the shipbuilding process is crucial to ensure that they have the right shape and strength. In fact, welding accounts for between 3 % and 5 % of the total weight of a ship, which can amount to between 700 and 1150 tonnes on a 270-metre gas tanker, to give an example.
The most commonly used types of welding
It is of great importance to weld ships with the proper technique. A simple excess of heat applied could weaken the mechanical properties of the steel, leading to structural damage later on. Equally relevant is the choice of the correct welding process, based on the material and the desired design of the project. Thus, there are the following types of welding for ships.
Gas shielded arc welding
As the name suggests, this welding is carried out by arc welding. A solid or tubular electrode with a continuous consumable feed is used for this purpose. The molten zone and the arc zone are kept protected from atmospheric contamination, as they are “covered” by a blanket of a flux, which consists of a granular flux composed of calcium oxide, silicon dioxide, manganese oxide, calcium fluoride and other compounds.
In this case, welding does not need to be done manually, but can be done automatically, in a mechanised mode or with a semi-automatic (portable) gun application with pressure or gravity feed flux emission.
This technique allows the use of very high current intensities (200 to 2000 amperes) without sputtering or air entrainment. It is therefore widely used in shipbuilding.
Submerged arc welding
This is done with the bare electrode, since a granulated powder called flux serves as protection. Part of the flux is melted in the process and the rest is reused. This process is fast and can be easily automated. It is also cost-effective when used to weld sheets thicker than 6 mm. This is why this method is so common for medium to thick shipbuilding materials.
Plasma Arc Welding or PAW
This welding is based on TIG welding, but higher temperatures (up to 28000 °C) can be reached and thicker parts can be welded. Two types of gas are used: a central gas and an annular gas. The former acquires a plasma state due to the high temperatures and melts the base metal, while the latter provides additional protection.
This process for welding ship plates achieves a flame of 3500 °C, which makes it possible to carry out a combustion welding, known as autogenous welding. It can be carried out with or without material input. Thus, this type of welding is often used for thin steel plates or complicated pipelines.
Manual welding with coated electrodes
This is the best-known welding process in the world. It consists of joining metals by means of an electric arc, which is an electrical discharge transmitted through an ionised gas. The gas also prevents the metal from oxidising during welding. An electrical discharge is produced between the electrode and the base metal which is heated, and this causes both to melt. It allows very localised melting, which is why almost all small and medium-sized welding jobs are carried out with the coated electrode. Moreover, this technique can weld metal of almost any thickness and type. Manual stick welding requires a great deal of skill and knowledge on the part of the welder in order for the work to be successful. This welding is carried out manually, so it is very important to have qualified personnel for this.
Semi-automatic continuous wire welding (MIG/MAG)
In this case, the shielding gas and the filler material are applied at the same time through the same nozzle. The shielding gas may be inert (known as MIG welding) or it may be an active gas (MAG welding). The electric arc is produced by the filler material, a consumable continuous wire. This type of welding was developed for melting non-ferrous metals and is highly efficient, guaranteeing 80-95 % efficiency. It is often used for the brazing of the ship’s hull, as it has a low carbon content. It works very well in small and medium thicknesses, in steel and aluminium alloy structures, especially where a lot of manual work is required. It is also used for stainless steel and aluminium superstructures.
Shielded Arc Gas or TIG Welding (Tungsten Inert Gas)
This uses a permanent electrode of wolfram or tungsten, since this is the metal with the highest melting point, around 3400 °C. It melts the filler material and the base metal, although this type of welding can be carried out without filler material. Inert gases such as helium, argon or a mixture of both are used. It has a high penetration capacity: this is why it is a high quality weld. This type of welding can be used on various metals, such as stainless steels, nickel alloys, titanium, aluminium and normal iron.
Thanks to the development of all these techniques, it is now even possible to carry out ship welding underwater. If your vessel needs welding, Suisca Group will put you in touch with expert companies in the relevant sector. With over 30 years dedicated to providing a comprehensive service in ports, we will provide professional ship welders with a proven track record to ensure that the results will be totally safe and of the highest quality. Suisca Group offers everything you could possibly need for a vessel in your port of call!
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