The following summary projects the important aspects of underwater welding from the point of view of a welding engineer:
1 . Underwater welding is carried out where the cost or impracticability of bringing the structures to be welded to the surface prohibit the use of conventional air welding.
2. Shielded metal arc wet-welding is most convenient and economical process among the processes used.
3. Underwater welding electrodes should have softer arc behaviour to eliminate undercuts.
4. The coating should be such that it shields (shrouds) the underwater arc to eliminate current leakage and rapid quenching of the weld pool. This can be achieved by selecting a suitable water-proofing coating.
5. The coating should burn or fry out easily so that the feed rate is uniform and there is no jerky movement of electrode.
6. The coating should contain ingredients which give highly stable arc so that weaving of the weld bead is possible.
7. Water-proofing coating should be non-conducting and non-hygroscopic. This will avoid current leakage from electrode to electrically conducting sea water and the electrodes will not absorb moisture during welding.
8. Iron powder electrodes have been found useful but due to the arc elongation effect they do not give good results. With plain rutile coating this effect is not dominated, but the strength of welds is inferior to the values obtained with iron powder electrodes. A coating in between the two would prove useful.
9. Rutile or iron-oxide flux covering water proofed by cellulosic lacquer gave best arc stability, and good mechanical properties of the wet-welds.
10. A bubble of steam and gases is formed around the arc during wet-welding. This bubble protects the arc and weld pool from water.
11. Salinity of water improves arc stability and penetration.
12. Underwater arc core temperatures are around 11000°K (at 10 m depth), while air — arc temperature is around 6000°K the droplet transfer frequency is 44 for iron-powder and 80-100 for rutile-electrode during underwater welding.
13. Weld microstructure contains ferrite-pearlite structures in the weld metal and a narrow band of bainite-martensite adjacent to the fusion boundary in the heat affected zone.