Submerged Arc Welding (SAW)

Flux is mainly used to avoid the oxidation reaction with oxygen present in the atmosphere. If the flux is used along with filler material in the form of coated electrodes, the oxidation reaction may not be completely prevented. In order to avoid the oxidation reaction completely, enough quantity of flux should be supplied with a separate control independently with filler material.

Submerged arc welding is also called sub arc welding or hidden arc welding. In this welding, the complete welding setup is dipped in the flux powder and hence, it is named as submerged arc welding. In this type of welding, an electric arc is produced between consumable bare electrode and workpiece. But, the arc is completely submerged i.e., hidden under the flux powder as shown in Figure 2.15. The arc is not visible outside. The metal electrode is continuously fed from the reel by a moving head. The flux powder is fed in front of the moving head. It is supplied from a hopper. Since the arc is completely covered by flux powder, there will not be any defect in the weld due to atmosphere effects.

The flux powder is made up of silica, metal oxides and other compounds fused together and it is crushed to the proper size. The flux not only protects the weld surface from atmosphere and it also acts as a deoxidiser and scavenger. It may also contain powder metal alloying elements. The flux covers the arc and molten metal. Some of the flux melts and forms the slag on the weld. The unused flux is sucked by a pipe.

Voltage used is 25 V to 40 V. Current used in SAW welding depends on the workpiece thickness. Normally, DC is employed using 600 A to 1000 A and AC is usually 200 A.

Since the flux must cover the joint to be welded, this method is restricted to make straight welds in the flat position. Thus, it is suitable for cylinders, steel pipes etc.

Submerged arc welding is specially used for welding carbon steels and alloy steels. It can be used to weld chromium steels and austenitic chromium-nickel steels. Plates of 12 mm to 50 mm can be welded with one pass.

1. Advantages, Limitations and Applications of SAW

Advantages:

1. Very high quality welds are produced.

2. It is a very fast method.

3. Deep penetration can be obtained.

4. Shielding accessory for eyes is not needed.

5. Long joints can be easily welded.

6. This welding process has high deposit rate. Almost 45 kg/h can be deposited.

7. There is no chance of weld spatter as it is submerged in a flux blanket.

8. This process is applicable indoor as well as outdoor,

9. No edge preparation is needed.

10. Very little welding fume is seen.

11. This method ensures high utilization of electrode wire.

12. Easy automation can be obtained for high-operator factor.

Limitations:

1. It is not suitable for welding works which is inclined and vertical.

2. The welding zone is not seen. So, it is difficult to guide the electrode movement.

3. Operation is limited to some specific metals.

4. The application is limited to straight seams and pipes and vessels.

5. The flux handling can be tough.

6. Health issue can be caused because of the flux.

7. Slag removal is needed after welding.

Applications:

1. The submerged arc process is widely used in heavy steel plate fabrication work. It includes the welding of structural shapes, longitudinal seam of larger diameter pipe, manufacture of machine components for all types of heavy industry and manufacture of vessels and tanks for pressure and storage use.

2. It is also used in pressure vessels, boilers, tanks, nuclear reactors, chemical vessels, etc.

3. Another use is in the fabrication of trusses and beams.

4. It is also used for surfacing and buildup work, maintenance and repair.