It is probable that similar microstructural
considerations also apply to the preferential
corrosion of weld metal, but in this case, the situation
is further complicated by the presence of
deoxidation products, their type and number
depending largely on the flux system employed.
Consumable type plays a major role in determining
weld metal corrosion rate, and the highest
rates of metal loss are normally associated
with shielded metal arc electrodes using a basic
coating. In seawater, for example, the corrosion
rate for a weld made using a basic-flux-coated
consumable may be three times as high as for
weld metal from a rutile-flux-coated consumable.
Fewer data are available for submerged
arc weld metals, but it would appear that they
are intermediate between basic and rutile flux
shielded metal arc electrodes and that a corrosion
rate above that of the base steel can be
expected. In many cases, the underlying cause
of the problem is the electrochemical potential
difference between the weld metal and the adjacent
parent steel, as discussed subsequently.