Page 214 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 199

mechanically similar in that both utilize copper dams or shoes that
are applied to either side of a square-edged butt joint. An electrode or
multiple electrodes are fed into the joint. A starting sump is typically
applied for the beginning of the weld. As the electrode is fed into the
joint, a puddle is established that progresses vertically. The copper
dams, which are commonly water-cooled, chill the weld metal and
prevent it from escaping from the joint. The weld is completed in one
pass.
These processes may be used for groove welds in butt, corner, and
tee joints. Typical applications involve heavier plate, usually 1 in or
thicker. Multiple electrodes may be used in a single joint, allowing
very heavy plate up to several inches thick to be joined in a single
pass. Because of the sensitivity of the process to the number of vari-
ables involved, specific operator training is required, and the D1.1-98
code requires welding procedures to be qualified by test.
In building construction, applications for ESW/EGW with traditional
connection designs are somewhat limited. However, they can be high-
ly efficient in the manufacture of tree columns. In the shop, the beam
flange-to-column welds can be made with the column in the horizon-
tal plane. With the proper equipment and tooling, all four flange
welds can be made simultaneously. In addition, continuity plate welds
can be made with ESW/EGW. Future connection designs may utilize
configurations that are more conducive to these processes.
Another common application is for the welding of continuity plates
inside box columns. It is possible to weld three sides of the continuity
plate to the interior of the box prior to closing the box with the fourth
side. However, once this closure is made, access to the final side of the
continuity plate is restricted. This final closure weld can be made by
operating through a hole in the outside of the box column. This
approach is very popular in the Far East where box columns are
widely used.
In electroslag welding, a granular flux is metered into the joint dur-
ing the welding operation. At the beginning, an arc, similar to that of
submerged arc welding, is established between the electrode and the
sump.
After the initial flux is melted into a molten slag, the reaction
changes. The slag, which is carefully designed to be electrically conduc-
tive, will conduct the welding current from the electrode through the
slag into the pieces of steel to be joined. As high currents are passed
through the slag, it becomes very hot. The electrode is fed through the
hot slag and melts. Technically, electroslag welding is not an arc-welding
process, but a resistance-welding process. Once the arc is extinguished
and the resistance-melting process is stabilized, the weld continues
vertically to completion. A small amount of slag is consumed as it chills

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