Page 78 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Welding Processes

rates are required. On thick materials it is commonly used for
the initial root run(s) because the welder has such good
control of the weld pool and can therefore achieve a better
quality weld than with most other manual processes.
Common uses are high quality welds in the aerospace
industry, critical root welds in pipe and general light
fabrications.
Typical defects
Typical defects are tungsten inclusions caused by touching
the electrode into the weld pool during welding, porosity
from the loss of gas shielding or surface contamination,
oxidation from insufficient purging gas, root concavity from
excess purging gas and crater pipes from breaking the arc too
quickly.
Submerged arc welding (SAW)
Process description
Figure 5.11 shows the equipment used for SAW. An electric
arc is struck between a continuously fed consumable solid
electrode wire and the workpiece. The arc is formed and
protected within a blanket of flux, which is partially
consumed within the process. The flux is supplied from a
hopper attached to the weld head and fed through a tube to
form a continuous layer in front of the torch deep enough to
contain the arc (Fig. 5.12). The weld metal is formed from a
combination of the base metal, filler metal and flux
constituents, and will therefore be affected by changes to
currents or voltages. The weld metal can be cleaned of
contaminants by flux additions and then protected by the
slag that forms at the top of the weld. This slag must be
removed after each weld run before the next pass is added to
prevent slag inclusions within the completed weld. Any
unused flux can be collected, mixed with new flux and re-
used, provided it is not contaminated. Because a flux layer is
used, SAW is normally restricted to the flat or horizontal–
vertical positions, although some very specialised equipment

63

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 63 of 66