Abstract:
The aim of this research is based on the welding consumable related issues at
the pipe line construction sites which were experienced by the author of this
thesis. Weld corrosion describes selective attack of the weld itself. The origin
of this attack is usually a combination of a more active Weld Metal (the Weld
Metal tends to be more susceptible to corrosion than the Base Metal) together
with Galvanic Corrosion coupling to the Base Metal. The influence of
coupling is accentuated by the poor area ratio, i.e. a small anode Weld Metal /
large cathode Base Metal. Preferential Weld Metal corrosion of C-Mn steels
has historically been a major problem. On the basis of various studies, early
researchers concluded that the weldments of silicon killed C-Mn steels are the
most electronegative (i.e. cathodic) and the unkilled steels with a low silicon
content are the most electro positive. Weld Metal Zones of the welds made
with the normal basic-coated electrodes exhibit most electro negative potential
and with the acid types exhibit most electropositive whilst the potentials of the
Weld Metal Zone of the welds made with rutile electrodes are placed in an
intermediate position. The Weld Metals are usually more electronegative than
the Base Metal depending upon relative silicon content. The operating
conditions can change the weld behaviour from anodic to cathodic or vice
versa at any stage during the process.
