Deposition of stringer beads (see Fig. 15.7) has, generally, been recommended in the literature. Necessary strength can be achieved by superimposing additional beads. The advan­tages of stringer-bead technique include:

1. Easy control over travel speed.

2. Uniform bead surface.

3. Good arc stability.

4. Reduced risk of slag inclusions.

5. Reduced chances of undercutting.

6. Consistent and satisfactory penetration.

7. Ease of welding in low visibility conditions.

The following precautions are taken to produce good welds:

1. The joints should be well fitted.

2. Should be free from rust, oil, paint etc.

3. No abrupt changes in weld contours.

4. The ends of the short welds or tacks should be thoroughly cleaned and hammered to give a smooth surface.

5. The bead or layer deposited should be cleaned of slag, spater or globules before super­imposing additional runs. Van der Willingen (1946) described the use of a special wrapped heavy coated iron powder electrode which gave high deposition rate and excellent touch weld­ing characteristics. Fig. 15.7 shows the types of beads made in underwater welding. Table 15.1 shows the effect of the type of underwater welding conditions mentioned above on weldability of steels commonly used.

Stringer

bead