Today, there are five main methods of welding stainless steel tubes and pipes. They are used individually or in combination.

TIG:   Tungsten Inert Gas Welding PAW: Plasma Arc Welding SAW: Submerged Arc Welding LBW:  Laser Beam Welding HF:     High Frequency Welding

The first four belong to the Electric Fusion Welding (EFW) category while HF is classed as Electric Resistance Welding (ERW).

We are using TIG and PAW at all our units and also SAW for Storfors thick wall pipe.
At the units in Torshälla, Fagersta and Jakobstad 4 lines are equipped with LBW.
HF-welding is performed at Jakobstad.

TIG (GTAW; WIG) welding
TIG welding or Gas Tungsten Arc Welding (GTAW) or wolfram inert gas (WIG) welding, refers to the nonconsumable electrode, an alloy of 98% W (tungsten) and 2% Th (thorium), is. Filler material, if required, is added separately to the weld pool.

Welding is usually done in one bead and uses 1-4 electrodes combined in a multiple torch. For thicknesses over approx. 3 mm, TIG welding is sometimes complemented with PAW.

TIG welding is most suitable for material thicknesses up to around 3 mm. Welding speed is about 3m/min for 2 mm thick sheet.

Ar + 7-15% H₂ is used as the shielding gas.

In the longitudinal welding of pipes and tubes, filler wire is not normally used. It is, however, often used when joining pipes/tubes.

Plasma Arc Welding (PAW)
The electric arc burns between a nonconsumable tungsten electrode and the workpiece. Unlike TIG welding, the electrode tip is enclosed in a water-cooled gas nozzle, through which the plasma gas is forced. PAW gives a narrower arc than TIG welding and thus gives a narrower and deeper penetration profile.

Welding is done in one bead and normally in combination with multiple torch TIG equipment.

The high-energy plasma arc has a temperature of 30,000-40,000°C. This makes it suitable for material
thicknesses of 3-10 mm.

For equivalent thicknesses, welding speed is higher than TIG welding. The shielding gas is pure argon or argon + 5-10 % hydrogen.

In the longitudinal welding of pipes and tubes, filler wire is not normally used.

Root gas
A root gas is used in the PAW and TIG welding of root beads. The root gas protects the weld pool from oxidation. Root gas composition is either the same as that of the shielding gas or 90%N₂ + 10% H₂.

Submerged Arc Welding (SAW)
Filler material must be used in this welding method and is supplied by the consumable electrode. The method is highly productive and gives the highest deposition rate (quantity of deposited material as a function of time) of the methods here described.

The method is suitable for material thicknesses over approx. 10 mm.
Welding speed is approx. 0.4-0.7 m/min.

A flux fed to the weld area completely covers the arc and the weld pool. A part of the flux is consumed during welding and forms a slag coating on the weld. This coating acts as a protection against oxidation.
A shielding gas is, therefore, not used in SAW.

Laser Beam Welding, LBW
The laser method uses a highly concentrated beam of light with a power density which can be up to 1,000 times higher than that obtained using a TIG arc. Laser welding gives an extremely narrow weld.With a material thickness of 3 mm, weld width does not exceed 0.3-0.5 mm. Highly stable welding machines, which can accurately follow the joint line, are thus essential.


                  

When welding pipes/tubes, lasers are used for material thicknesses up to about 6 mm.

The high welding speed (up to 18 m/min) for pipes/tubes, is the main advantage of laser welding.

Filler wire is not used; the shielding gas is helium.

High Frequency welding (HF)
HF is the most commonly used method for welding carbon steel and ferritic stainless steel pipes for exhaust systems. Today many manufacturers are also using HF for welding austenitic pipes.
The biggest advantage of HF is that welding speed can be as high as 100 m/min. Stainless steel pipes/tubes with a material thickness of up to 4 mm can be welded. Filler wire is not used.

The method is classed as electric resistance welding (ERW). Coil edges are heated and pressed together in a magnetic field created by inductance coils, and shielding gas is not used. The bead is shaved off inline.